Seed

Depending on which tissue serves as the main storage depot in the mature seed, three main seed types are distinguished (North et al., 2010; Radchuk & Borisjuk, 2014).

Endospermic (albuminous) seeds. In such seeds, most reserves are concentrated in the endosperm — a specialized tissue that in angiosperms arises from double fertilization and is usually triploid (Beck, 2010). The embryo in these seeds is relatively small, and its cotyledons function to absorb and transfer nutrients from the endosperm to the growing axes. Typical examples are grass caryopses (wheat, maize, rice), castor bean seeds (Ricinus communis), onion (Allium cepa), and coffee (Coffea arabica) (Raven et al., 2013; Serebryakova et al., 2006). In gymnosperms, the haploid female gametophyte serves as the endosperm analog (e.g., in pine seeds — Pinus sylvestris), also performing a storage function (Beck, 2010; Raven et al., 2013).

Non‑endospermic seeds. In these seeds, the endosperm is completely or almost completely consumed by the developing embryo during maturation, and the storage function shifts to the cotyledons. The cotyledons become fleshy, thickened, and accumulate starch, proteins, and oils. Classic examples are legume seeds: bean (Phaseolus vulgaris), pea (Pisum sativum), soybean (Glycine max), as well as pumpkin, sunflower (although the fruit is an achene, the seed itself is non‑endospermic), and oak (Raven et al., 2013; Stern et al., 2021). In many Brassicaceae (e.g., rapeseed, Brassica napus), the embryo also occupies almost the entire seed volume, with remnants of endosperm possibly remaining as a thin film (North et al., 2010; Choudhary et al., 2023).

Seeds with perisperm (and sometimes endosperm). Perisperm is a storage tissue formed from the nucellus (megasporangium), i.e., of maternal sporophytic origin. In most angiosperms, the nucellus is used up during seed development, but in some groups it persists and accumulates starch or other substances. Pure perisperm is characteristic of the families Caryophyllaceae, Piperaceae, and Chenopodiaceae (Serebryakova et al., 2006; Radchuk & Borisjuk, 2014). In some species (e.g., in water lilies — Nyphaeaceae), both endosperm and perisperm can be present simultaneously — a rare but interesting phenomenon (Bell, 1991).

From a botanical perspective, this division is important because the type of storage tissue determines the pattern of reserve mobilization during germination and influences the seedling’s survival strategy (Das & Majee, 2026).

Cotyledons are the first leaves of the embryo. Their number is one of the main characteristics by which flowering plants are divided into two major classes (although modern systematics uses the terms Magnoliopsida and Liliopsida, the traditional names “dicotyledons” and “monocotyledons” persist in morphological descriptions) (Stern et al., 2021; Raven et al., 2013).

Dicotyledonous seeds contain an embryo with two cotyledons. In non‑endospermic forms (legumes, cucurbits), the cotyledons are massive, fleshy, and serve a storage function. In endospermic dicots (castor bean, tomato), the cotyledons are thin, flat and primarily absorb nutrients from the endosperm (Serebryakova et al., 2006). The two cotyledons are opposite, with the plumule (apical bud) located between them (Bell, 1991).

Monocotyledonous seeds contain an embryo with one cotyledon, which is usually shield‑shaped and called the scutellum in grasses, or may be cylindrical in lilies. In monocots, endosperm is generally well‑developed (e.g., in wheat, maize, onion), and the single cotyledon lies adjacent to the endosperm, absorbing nutrients from it (Raven et al., 2013; Beck, 2010). In some monocots (e.g., water plantain — Alisma plantago-aquatica), the embryo may be non‑endospermic, and then the single cotyledon becomes fleshy (Serebryakova et al., 2006).

The number of cotyledons is closely related to germination characteristics: dicots with epigeal germination lift their cotyledons to the surface, where they start photosynthesizing; in monocots, the scutellum usually remains in the soil or seed, providing transport of reserves (Stern et al., 2021; Tsan et al., 2025).

The embryo can occupy different positions within the seed relative to the endosperm (or perisperm) and the seed coat. This position is determined by the shape of the embryo and its degree of differentiation (Bell, 1991; Serebryakova et al., 2006). Several types are distinguished:

The embryo position has important agronomic significance: it affects the sowing depth and seedling tolerance to adverse conditions. For example, in crops with a curved embryo and large endosperm (castor bean, maize), deep sowing is permissible because reserves enable hypocotyl or coleoptile elongation until light is reached. In non‑endospermic legumes with straight, massive cotyledons, seeds should be sown shallowly; otherwise, the cotyledons cannot lift the plumule to the surface or may rot (Stern et al., 2021; Choudhary et al., 2023).

The seed coat, or testa, forms from the ovule integuments — usually one (in most gymnosperms) or two (in most angiosperms) (Raven et al., 2013). In the mature seed, it is a multilayered structure in which several functional zones can be distinguished (Radchuk & Borisjuk, 2014; North et al., 2010).

In some groups (grasses, sedges), the seed coat is highly reduced and fuses with the fruit wall (pericarp), forming a single covering structure — the caryopsis (Raven et al., 2013; Serebryakova et al., 2006). In legumes, on the other hand, the seed coat is well developed and often has a cuticular layer, leading to so‑called “hard‑seededness” (physical dormancy).

Endosperm is the storage tissue that in angiosperms is formed by the fusion of one sperm with two polar nuclei of the central cell of the embryo sac, thus being triploid (3n). In gymnosperms, the haploid female gametophyte fulfills an analogous function, though the botanical literature often also calls it primary endosperm (Beck, 2010; Raven et al., 2013). In the mature seed, the endosperm may persist in large volume (endospermic seeds) or be almost entirely consumed for embryo nutrition during maturation (non‑endospermic seeds) (North et al., 2010).

Two main components are distinguished in the tissue structure of the endosperm.

Aleurone layer (peripheral layer). In grasses and many other monocots (as well as some dicots), the outermost layer of endosperm cells differentiates into the aleurone layer. Aleurone cells have thick primary walls, dense cytoplasm rich in protein granules (aleurone grains), and contain almost no starch. During germination, it is the aleurone cells that synthesize and secrete hydrolytic enzymes (α‑amylase, proteases) that break down endosperm reserves, making them available to the embryo (North et al., 2010; Das & Majee, 2026). In dicots, the aleurone layer may consist of one or two rows of cells, but in legumes it is usually absent because the storage function has shifted to the cotyledons (Raven et al., 2013).

Storage parenchyma (endosperm parenchyma). The bulk of the endosperm in endospermic seeds consists of large parenchyma cells filled with storage substances: in grasses and buckwheat — starch grains; in oilseed crops (castor bean, rapeseed, sunflower) — oil droplets and proteins as aleurone grains; in legumes that remain endospermic (e.g., lupine) — hemicelluloses (mannans, galactans) (North et al., 2010; Choudhary et al., 2023). Endosperm cells are usually dead in the mature seed, lacking nuclei and active cytoplasm, functioning as a passive reservoir. However, in some groups (e.g., date palm), endosperm cells remain alive and contain oil and protein, enhancing nutritional value (Raven et al., 2013; Radchuk & Borisjuk, 2014).

In gymnosperms (pine, spruce, ginkgo), the endosperm is haploid and is by nature the vegetative body of the female gametophyte. Its cells are living, rich in oils and proteins, and serve as a reserve for the embryo throughout seed development and germination (Beck, 2010; Raven et al., 2013).

Embryo is a small but already differentiated plant in a state of enforced dormancy. It possesses all the main axes of the future sporophyte and several types of meristems. Anatomically, the following parts are distinguished in the embryo (Raven et al., 2013; Serebryakova et al., 2006).

It is important to note that seed anatomy can vary greatly among different groups: for example, in orchids, the embryo is not differentiated into tissues and consists of only a few dozen cells; in parasitic plants (dodder, broomrape), the embryo lacks cotyledons and is represented only by an undifferentiated cell cluster (Bell, 1991; Serebryakova et al., 2006). However, the basic structural principles outlined above apply to the vast majority of angiosperms and gymnosperms.

After double fertilization in angiosperms, the zygote gives rise to the diploid embryo, and the central cell of the embryo sac, fusing with the second sperm, forms the triploid endosperm (Raven et al., 2013). Fertilization serves as a signal to trigger proliferation of nucellus and integument cells, which develop into the seed coat. In gymnosperms, fertilization also initiates embryo development from the zygote, while the female gametophyte (haploid) begins to accumulate storage substances, functioning as endosperm (Beck, 2010; Serebryakova et al., 2006).

The first divisions of the zygote usually occur without a noticeable increase in ovule volume. In most flowering plants, a characteristic suspensor forms — a multicellular structure that pushes the embryo into the endosperm and likely participates in nutrient absorption from maternal tissues (Bewley et al., 2013; Serebryakova et al., 2006).

Embryogenesis in angiosperms is traditionally divided into several successive stages (North et al., 2010; Beck, 2010).

In some dicots (castor bean, legumes), embryo cells become highly vacuolated at later stages and accumulate storage products in the cotyledons. In grasses, the bulk of reserves is concentrated in the endosperm, while the embryo remains relatively small (North et al., 2010).

Concurrently with embryogenesis, active accumulation of storage substances occurs in the endosperm (in endospermic seeds) or in the embryo cotyledons (in non‑endospermic seeds). This process is called seed filling. The main reserve compounds — starch, oils (triacylglycerols), and proteins (globulins, prolamins, glutelins) — are synthesized from products delivered from the mother plant via the phloem through the funiculus and chalaza (Radchuk & Borisjuk, 2014; Bewley et al., 2013).

In grasses, starch accumulation in the endosperm proceeds very intensively, and endosperm cells become filled with large starch grains. In oilseeds (rapeseed, sunflower, castor bean), triacylglycerols are synthesized in the endosperm or cotyledons and stored as oil droplets (oleosomes). Proteins are stored as aleurone grains — vacuoles filled with protein matrices and often containing phytin globoids (North et al., 2010; Choudhary et al., 2023).

Concurrently with reserve accumulation, chaperone proteins are synthesized in the seed: heat shock proteins (HSP) and late embryogenesis abundant (LEA) proteins. They play a critical role in protecting cellular structures from desiccation and oxidative stress during the final stages of maturation (Das & Majee, 2026; North et al., 2010).

In the final stage of development, the seed loses 80–95% of its water. Moisture content can drop to 5–15% depending on the species (orthodox seeds). This process is not passive drying but is genetically and hormonally regulated — primarily by abscisic acid (ABA), which inhibits water uptake and activates desiccation genes (He et al., 2026; Xu et al., 2025). Water loss leads to the transition of the cytoplasm to a vitrified (glassy) state, in which molecular mobility is sharply reduced, virtually halting metabolism and slowing aging (Das & Majee, 2026).

Physiological maturity occurs at the point of maximum dry matter accumulation, when the seed reaches its greatest mass and maximum germinability. However, seed moisture at this phase is still high (often 30–50%), and seeds cannot be stored for long periods. Only after additional desiccation (on the plant or by artificial drying) do they acquire the ability for long‑term storage (Bewley et al., 2013; Choudhary et al., 2023).

After desiccation is complete, the seed enters a state of dormancy — a temporary arrest of growth even under favorable conditions. Dormancy may be due to properties of the seed coat (physical dormancy) or the state of the embryo and the action of inhibitors (physiological dormancy) (He et al., 2026; Xu et al., 2025). This phase is not obligatory for all species, but for most wild and many cultivated plants, dormancy ensures germination in the most favorable season.

Polyembryony. In some plants (citrus, mango, many orchids), multiple embryos may develop within a single seed. This phenomenon is called polyembryony. It arises either by splitting of a single zygotic embryo (true polyembryony) or by the development of additional embryos from nucellus or integument cells (false polyembryony). In citrus, nucellar embryos are genetically identical to the mother plant and are used to produce clonal seedlings (Raven et al., 2013; Stern et al., 2021).

Thus, seed ontogeny is a complex, multi‑stage process in which the zygote transforms into a miniature but fully formed sporophyte, supplied with a store of nutrients and protected by coverings. Understanding the stages of seed formation is essential for managing harvest timing, storage conditions, and pre‑sowing seed treatment.

Dormancy is a state of a mature viable seed in which it does not germinate for a certain period even under favorable external conditions (moisture, temperature, oxygen) (He et al., 2026; North et al., 2010). Dormancy is an evolutionarily developed adaptation that allows the seed to survive an unfavorable season (winter, drought) and germinate when the chance of seedling survival is highest. Furthermore, dormancy prevents premature germination of seeds still on the mother plant (pre‑harvest sprouting), which is especially important for cereal crops (Xu et al., 2025; Baskin & Baskin, 2004).

Why does a seed not germinate immediately after maturation? The reasons can be various: a water‑impermeable seed coat, deficiency or excess of hormones (primarily the balance between abscisic acid — ABA and gibberellins — GA), incomplete embryo development, or the presence of inhibitors in the pericarp (He et al., 2026; Baskin & Baskin, 2004). In many wild species, dormancy is obligatory, while in cultivated plants it has often been weakened or lost through breeding, which can lead to pre‑harvest sprouting in wet weather (Xu et al., 2025).

The most widely used classification of dormancy types was proposed by J. M. Baskin and C. C. Baskin (Baskin & Baskin, 2004) and includes five main classes: physical dormancy (PY), morphological dormancy (MD), physiological dormancy (PD), morphophysiological dormancy (MPD), and combined dormancy (PY+PD) (He et al., 2026). We will discuss the key categories relevant to seeds.

Exogenous dormancy (physical dormancy, PY). This type of dormancy is due to properties of the seed coat or pericarp that prevent the penetration of water and/or gases. A classic example is hard‑seededness in legumes (seeds of alfalfa, clover, acacia). The water‑impermeable seed coat prevents the seed from imbibing, and it can remain in the soil for years without germinating. In nature, physical dormancy is broken by scarification — disruption of the coat integrity by temperature fluctuations, abrasion against soil particles, passage through the digestive tract of animals, or fire (in fire‑adapted species) (He et al., 2026; Baskin & Baskin, 2014). For many agricultural crops (alfalfa, sweet clover), artificial scarification — mechanical damage to the coat or treatment with concentrated sulfuric acid — is used (Choudhary et al., 2023).

Endogenous dormancy. This is due to properties of the embryo itself or surrounding tissues and is divided into two main types (He et al., 2026; North et al., 2010).

Combined dormancy (PY+PD). In this case, the seed has both physical (impermeable coat) and physiological dormancy (e.g., in some legumes and chenopods). To germinate, scarification (coat disruption) is first required, followed by stratification or gibberellin treatment (Baskin & Baskin, 2014; He et al., 2026).

In addition, there is the concept of secondary dormancy. It arises in seeds that have exited primary dormancy but then encounter unfavorable conditions (high temperature, drought, darkness). The seed re‑enters a dormant state (secondary dormancy), allowing it to await better conditions (He et al., 2026; Donohue et al., 2005).

Seed viability is the ability of a seed to maintain a living embryo capable of producing a normal seedling after dormancy release under optimal germination conditions (Bewley et al., 2013; Choudhary et al., 2023). Viability should not be confused with germinability. Germinability is a quantitative measure, expressed as a percentage, that characterizes the ability of a seed lot to produce normal seedlings under standard conditions within a specified time (usually 7–14 days). A viable seed may have low germinability if it is in deep dormancy or damaged, but after dormancy release it is able to germinate (Serebryakova et al., 2006; ISTA, 2020).

Viability gradually decreases during storage — a process of seed aging (deterioration). The main causes of viability loss are oxidative membrane damage, accumulation of mutations in DNA, denaturation and aggregation of proteins, and depletion of reserves (Das & Majee, 2026; Choudhary et al., 2023). Increased moisture and temperature, as well as the presence of oxygen, accelerate aging. Therefore, for long‑term storage, orthodox seeds are dried to 5–7% moisture and stored at low temperatures (-18 °C or below) in airtight packaging (Bewley et al., 2013).

Different species have different potential longevity of seeds. Seeds of many agricultural crops (wheat, maize, sunflower) under proper storage maintain germinability for 5–10 years (Choudhary et al., 2023). Some wild species can remain viable for decades or even centuries. The most famous examples:

Seed longevity depends on the composition of storage substances, the strength of the seed coat, the effectiveness of antioxidant defense, and the ability to repair damage upon imbibition (Das & Majee, 2026; Choudhary et al., 2023). Chaperone proteins (LEA proteins, heat shock proteins) and DNA repair systems (PIMT, MSR) play key roles in maintaining viability in the dry state.

Germinability is determined in laboratory conditions over a set number of days (usually 7–14) at optimal temperature and moisture. For agricultural crops, there are state standards for germinability (not lower than 80–95% depending on the crop). Low germinability leads to sparse stands and yield losses. Germinability can be improved by dormancy‑breaking treatments: scarification, stratification, treatment with gibberellin or nitrates, as well as priming (Choudhary et al., 2023; Xu et al., 2025).

Thus, dormancy and viability are two interrelated but distinct properties of seeds. Dormancy prevents premature germination, while viability ensures the potential to germinate after dormancy release. Understanding the types of dormancy and factors affecting viability is essential for developing effective methods of seed storage, pre‑sowing treatment, and breeding of varieties resistant to pre‑harvest sprouting.

Seed germination proceeds through three successive, partially overlapping phases (Bewley & Black, 1994; He et al., 2026).

1. Imbibition. The dry seed rapidly absorbs water — a process driven by the high osmotic potential of cells and the hydrophilic nature of cell walls and storage substances (starch, proteins) (Das & Majee, 2026). Seed volume increases, the coat softens and often cracks near the micropyle. Imbibition is a physical process that does not require metabolic energy; it also occurs in dead seeds (Bewley et al., 2013). However, imbibition itself activates metabolism: mitochondrial activity is restored, ATP synthesis increases, and transcription and translation are initiated (North et al., 2010).

2. Enzyme activation and metabolism. After reaching a critical moisture level (usually 15–20% water), hydrolytic enzymes are activated in the cells of the embryo and endosperm (or cotyledons). In the aleurone layer of grasses, under the influence of gibberellins (GA), α‑amylases, proteases, and other hydrolases are synthesized and secreted, breaking down starch to sugars, proteins to amino acids, and oils to glycerol and fatty acids (North et al., 2010; Xu et al., 2025). In dicots, similar processes occur in the storage tissues of cotyledons or endosperm. The resulting soluble substances are transported to the growing axes of the embryo, providing energy and building materials (Raven et al., 2013). At the same time, respiration intensity sharply increases (first anaerobic, then aerobic), supplying ATP for synthetic processes (Serebryakova et al., 2006).

3. Embryo growth and radicle emergence. Under hydrostatic pressure and enzymatic softening of cell walls, radicle and hypocotyl cells begin to expand and divide. The radicle is usually the first to start growing, breaking through the seed coat, most often at the micropyle — the weakest point (Raven et al., 2013). The appearance of a visible root is considered the completion of germination. Following the root, the hypocotyl (in dicots) or coleoptile (in grasses) begins to grow, lifting the plumule to the surface or toward light (Stern et al., 2021).

It is important to note that germination can proceed without light (in darkness) if reserves are sufficient for hypocotyl or coleoptile elongation until they reach the surface. However, light, temperature, and other factors regulate the rate and completeness of germination by interacting with the hormonal system (ABA/GA) (Schmid et al., 2026; He et al., 2026).

The balance between abscisic acid (ABA) — a germination inhibitor that maintains dormancy — and gibberellins (GA) — promoters that activate hydrolytic enzymes and cell expansion — plays a key role in triggering germination (North et al., 2010; He et al., 2026). Upon imbibition in viable seeds, ABA levels decrease while GA levels increase. This shift can be triggered by temperature signals (stratification), light (through the phytochrome system), nitrates, or treatment with exogenous GA (Xu et al., 2025; Choudhary et al., 2023). In some species, light is obligatory for germination (photoblastic positive seeds — e.g., lettuce, tobacco); in others, light inhibits germination (e.g., onion, some Allium species); in still others, germination is light‑independent (neutral seeds) (Schmid et al., 2026; Borthwick et al., 1952, cited in He et al., 2026).

Temperature affects germination through enzyme activity and the rates of biochemical reactions. For each species, there are minimum, optimum, and maximum germination temperatures. For most agricultural crops, the optimum lies within 20–30 °C (Stern et al., 2021). Low temperatures (stratification) are necessary to break physiological dormancy in many woody and perennial species (Baskin & Baskin, 2004). Oxygen is required for aerobic respiration, although some species (e.g., rice) can germinate under hypoxia thanks to activation of enzymatic hydrolysis and anaerobic respiration (Xu et al., 2025).

Reactive oxygen species (ROS) also play an important role in regulating germination. A small increase in ROS levels at the onset of imbibition acts as a signal promoting dormancy release and activation of protective mechanisms; however, excessive ROS accumulation during seed aging or stress leads to oxidative damage and loss of germinability (Das & Majee, 2026; Bailly, 2019, cited in Choudhary et al., 2023).

Based on the behavior of the cotyledons during germination, two main types are distinguished: epigeal (above‑ground) germination and hypogeal (below‑ground) germination (Raven et al., 2013; Stern et al., 2021).

Practical implication: sowing depth. The germination type directly determines the agronomic practice — the depth of seed sowing. Seeds with epigeal germination (bean, pumpkin, cucumber) lift their cotyledons to the surface, so they cannot be sown too deep — otherwise the cotyledons cannot overcome a thick soil layer, the energy of reserves will be exhausted, and the seedling will die. They are sown at a depth of 2–5 cm (depending on seed size). Seeds with hypogeal germination (pea, maize, wheat, oak) can be sown deeper (5–10 cm or more) because the cotyledons remain in the soil, while the coleoptile or epicotyl elongates, which are specifically adapted to push through a soil layer (Stern et al., 2021; Serebryakova et al., 2006). This distinction is important when cultivating crops in arid regions, where deep sowing allows access to moisture from deeper soil horizons.

After the radicle emerges and the first green leaves unfold, the seedling transitions to autotrophic nutrition. However, until the photosynthetic apparatus becomes functional, it lives off the seed’s reserves. The period of heterotrophic nutrition is especially important for crops with hypogeal germination, as their cotyledons are in the soil and cannot photosynthesize. Timely emergence of true leaves and the start of photosynthesis are critical moments determining seedling survival (Bewley et al., 2013).

Thus, germination is a complex, multifactorial process combining physical (imbibition), biochemical (enzyme activation), and morphogenetic (embryo growth) events. Understanding the stages of germination and its types is essential for developing optimal sowing regimes, pre‑sowing seed treatments, and breeding varieties with uniform emergence.

Water is the first and absolutely necessary factor for the initiation of germination. The dry seed must absorb a certain amount of water to activate metabolism. The process of imbibition depends on the water potential of the seed and the environment: the lower the soil water potential (drought, salinity), the slower the imbibition (Stern et al., 2021; Bewley et al., 2013).

Critical water potential thresholds. For each species, there is a minimum soil water potential (Ψ_b₀) below which germination is impossible. For mesophytes (most agricultural crops), Ψ₀ is about -1.0 to -1.5 MPa; for xerophytes (desert grasses, some legumes), the threshold may be lower (-2.0 to -3.0 MPa) (Schmid et al., 2026; Finch‑Savage & Bassel, 2016, cited in Choudhary et al., 2023). With water deficiency, seeds either do not germinate at all or germinate partially, and the emerging seedlings quickly die.

Water stress and secondary dormancy. If conditions become unfavorable after imbibition (drying of the topsoil), the seed may re‑enter dormancy (secondary dormancy). However, repeated wetting‑drying cycles deplete reserves and reduce viability (He et al., 2026).

Waterlogging (hypoxia). Excess water in the soil leads to oxygen deficiency (see Section 8.4). In some species (rice, millet), seeds can germinate under hypoxia by activating anaerobic respiration and mobilizing sugars (Xu et al., 2025).

Temperature affects the rate of all biochemical reactions and the ABA/GA balance. For each species, three cardinal temperatures are characteristic: minimum (T_min), optimum (T_opt), and maximum (T_max). At T_min, processes are just initiated but proceed slowly; at T_opt, germination is fastest and most uniform; at T_max, germination is still possible, but above it heat stress causes seed death (Stern et al., 2021; Choudhary et al., 2023).

Stratification (cold treatment). To break physiological dormancy, many seeds (apple, cherry, pine) require exposure to low positive temperatures (0–10 °C) for several weeks in a moist environment. This leads to a decrease in ABA and an increase in GA, which then triggers germination upon subsequent warming (North et al., 2010; He et al., 2026). Artificial stratification is widely used in nursery management and forest restoration.

Thermoinhibition (high‑temperature suppression). In some species (lettuce, celery, parsley), germination is suppressed at temperatures above 25–30 °C. This is an adaptation to prevent germination during hot, dry periods. Thermoinhibition is often linked to ABA accumulation in the embryo and can be relieved by GA or nitrate treatment (He et al., 2026; Xu et al., 2025).

Alternating temperatures. Many wild species (especially from arid regions) germinate better under daily temperature fluctuations (e.g., 25 °C day / 10 °C night) than at constant temperature. This signals that the soil is in the upper, warm layer and that the risk of frost has passed (Schmid et al., 2026; Baskin & Baskin, 2004).

Light affects germination through photoreceptors — phytochromes and cryptochromes. Based on their response to light, seeds are divided into three groups (He et al., 2026; Schmid et al., 2026).

Intensity and spectral composition. Low light intensity or shading (high far‑red to red ratio) can suppress germination in positively photoblastic species, which is important for seeds that have fallen under a plant canopy (Schmid et al., 2026). Blue light through cryptochromes can also inhibit germination in some grasses (barley, wheat) (Xu et al., 2025; He et al., 2026).

Seeds respire, consuming oxygen and releasing carbon dioxide. For most species, germination requires aerobic conditions. Soil oxygen content can decrease due to waterlogging, compaction, or ice crust formation (Radchuk & Borisjuk, 2014; Xu et al., 2025).

Critical oxygen threshold. For wheat, maize, sunflower, germination slows sharply when O₂ concentration falls below 10–15% (by volume). Complete cessation occurs at 5% (Bewley et al., 2013). Many weeds and some cultivated species (rice) are more tolerant to hypoxia and can even germinate underwater via anaerobic respiration (alcoholic fermentation). In rice, breeding for anaerobic germination (AG) ability is an important direction for developing direct‑seeded rice (DSR) (Xu et al., 2025).

Carbon dioxide. Increased CO₂ concentration (e.g., in sealed storage) slows respiration, which can extend seed preservation, but very high concentrations can damage the embryo (Choudhary et al., 2023).

Mechanical resistance of soil. Although not a gas, this is related to gas exchange: compacted soil hinders oxygen penetration and impedes radicle growth. However, some seeds are capable of mechanical soil fracture (e.g., in grasses, the coleoptile has high breakthrough capacity) (Radchuk & Borisjuk, 2014).

For seeds with physical dormancy (hard‑seededness), disruption of the seed coat integrity is a necessary germination factor. This can occur through:

Artificial scarification in agriculture: mechanical damage (sandpaper, filing), treatment with concentrated sulfuric acid (5 to 30 min), or hot water (80–90 °C) followed by rapid cooling. Used for seeds of alfalfa, clover, sweet clover, acacia (Choudhary et al., 2023).

Nitrates (NO₃⁻) — not only a nitrogen source but also a signal promoting dormancy release. Nitrates increase expression of the gene CYP707A2, encoding an ABA catabolism enzyme, and reduce ABA levels in seeds (He et al., 2026; North et al., 2010). Nitrate treatment (e.g., KNO₃) is often used in laboratory practice to test germinability of seeds with physiological dormancy (especially in wild species).

Nitric oxide (NO) — another signaling gas that breaks dormancy. NO suppresses ABA action through S‑nitrosylation of proteins (SnRK2, ABI5) and activates ABA catabolism (He et al., 2026; Das & Majee, 2026).

Karrikins — compounds formed during combustion of plant material (smoke). They stimulate germination of seeds of many species from fire‑prone ecosystems (Australia, South Africa, Mediterranean). Karrikins act through the KAI2 receptor and a signaling pathway independent of GA but interacting with ABA (He et al., 2026; Schmid et al., 2026).

Salinity (NaCl, other salts). High salt concentration creates a low water potential (osmotic stress), suppressing imbibition and germination. In addition, Na⁺ ions can be toxic to the embryo. Salinity tolerance varies: salt‑tolerant species (halophytes) can germinate at 200–300 mM NaCl, while most agricultural crops are inhibited already at 50–100 mM (Stern et al., 2021; Choudhary et al., 2023). Salt stress is often alleviated by potassium (K⁺) or calcium (Ca²⁺), which compete with Na⁺.

Soil acidity (pH). Extreme pH values (strongly acidic or strongly alkaline) can inhibit germination by affecting enzyme activity and ion uptake. Most crops prefer neutral or slightly acidic conditions (pH 6.0–7.5) (Stern et al., 2021).

In field conditions, environmental factors act simultaneously and often synergistically. For example, high temperature exacerbates the effect of drought; the combination of salinity and hypoxia is especially detrimental. Hydrothermal time models allow prediction of germination as a function of temperature and water potential, which is important for forecasting field emergence and modeling weed growth (Schmid et al., 2026; Bewley et al., 2013).

Practical implications for agronomy:

To assess the suitability of a seed lot for sowing, a system of parameters regulated by national and international standards (in Russia — GOST, internationally — ISTA rules — International Seed Testing Association) is used. The main parameters are:

Viability is a broader concept than germinability. A viable seed may be in deep dormancy and not germinate under standard conditions, but after dormancy release (stratification, scarification, GA treatment) can produce a normal seedling. Viability is determined using the tetrazolium test (staining the embryo) or germination after artificial dormancy release (Stern et al., 2021; Bewley et al., 2013).

Seed quality is controlled by state seed inspection services and by agricultural producers themselves when purchasing seeds. In the Russian Federation, GOST R 52325-2021 on seed quality of agricultural crops applies. Internationally, standards are developed by the OECD (Organisation for Economic Co‑operation and Development) under its seed certification schemes. These standards ensure the free movement of seeds between countries and guarantee their quality.

To improve germinability, germination energy, and disease resistance, seeds undergo various pre‑sowing treatments. The choice of method depends on the type of dormancy (physical, physiological, combined) and the crop’s characteristics.

Scarification — disruption of the hard, water‑impermeable seed coat (physical dormancy). Methods:

Stratification — keeping seeds in a moist environment at low positive temperatures (0–10 °C) to break physiological dormancy. Duration — from several weeks to several months (depending on species). Mimics the winter period. Used for seeds of apple, pear, cherry, plum, many conifers (pine, spruce), and ornamental woody species (North et al., 2010; He et al., 2026). In production conditions, stratification is carried out in refrigerators, mixing seeds with moist sand, peat, or vermiculite.

Soaking (priming) — partial imbibition of seeds in water or solutions of physiologically active substances, followed by drying back to original moisture. Priming activates repair processes, shortens germination time, and increases stress tolerance (cold, drought). Types of priming:

Bubbling — soaking seeds in water with simultaneous aeration (supplying compressed air or oxygen). Accelerates germination, especially in crops with slow imbibition (carrot, onion, tomato). Used in hydroponic and vegetable‑growing operations (Stern et al., 2021).

Pelleting (coating) — covering seeds with a protective‑nutrient shell made of a mixture of peat, clay, glue, micronutrients, fungicides, and growth stimulants. Facilitates mechanized sowing (especially for small‑seeded crops — carrot, lettuce, parsley), ensures uniform emergence, and protects against diseases at the initial stage. Pelleted seeds have a standard spherical or oval shape and size (3–6 mm), allowing the use of pneumatic seed drills with high precision (Stern et al., 2021).

Encrusting — applying a thin layer of polymer with pesticides and micronutrients onto the seed surface. The coating does not significantly increase seed size but protects against diseases and pests in the early growth stages. Often used for maize, sunflower, and rapeseed seeds (Choudhary et al., 2023).

Maintaining seed quality during the period from harvest to sowing is a critical task. The main factors affecting longevity are: seed moisture, temperature, oxygen content, and cleanliness (absence of pathogens) (Choudhary et al., 2023; Das & Majee, 2026).

Gene banks (seed vaults). The world’s largest seed storage facility is the Svalbard Global Seed Vault on the island of Spitsbergen (Norway). It is built into permafrost at a depth of 120 m and maintains a temperature of -18 °C. It stores duplicate seeds from collections around the world to preserve biodiversity (Choudhary et al., 2023). In Russia, the largest seed collections are held at the Vavilov Institute (VIR) in St. Petersburg and its branches.

Seed aging (deterioration). Even under optimal storage conditions, seeds gradually age: mutations accumulate in DNA, proteins are damaged (isomerization, carbonylation, methionine oxidation), membranes are disrupted, and antioxidants are depleted (Das & Majee, 2026). The rate of aging depends on the genotype: breeding for seed longevity is an active direction (see genes DOG1, PIMT, MSR, LOX). Biochemical tests (dehydrogenase activity, peroxide content, leachate conductivity) are used to assess the degree of aging (Choudhary et al., 2023).

Seeds are not only sowing material but also the main food product for humans and animals (cereals, pulses, oilseeds). Seed quality affects:

Thus, managing seed quality, pre‑sowing treatments, and proper storage are integral parts of modern agronomic production, ensuring food security and economic efficiency of agriculture.