Seed Dormancy

Introduction

In terms of the higher plant’s survival as a species, the seed is a crucial step in its life cycle. It is the plant’s dispersion unit that may survive the time between seed maturation and seedling establishment as a seedling once it has germinated. The seed is well adapted to survive extended periods of unfavourable environments since it is mostly dry. The seed enters a latent state to maximise germination over time. Pre-harvest germination is also prevented by dormancy. Research has been carried out to better understand how environmental conditions and applied chemicals influence germination. The method through which the embryo emerges from the seed, on the other hand, is still a mystery. However, little is known about how the embryo emerges from the seed and completes germination, as well as how embryo emergence is inhibited in latent seeds.

Emerging Mechanisms of Seed Dormancy

Ongoing research is revealing seed dormancy-related elements, some of which increase seed dormancy while others have a negative impact. Table 1 summarises the positive and negative seed dormancy regulators that will be explored in this section. Because there are complex seed dormancy regulatory mechanisms in which a single gene product can exert both positive and negative effects, including negative feedback from a positive regulator, categorising gene function into positive and negative regulators runs the risk of oversimplifying gene function. This category will be used for the discussion in this part to highlight the discoveries of gene function in the original research.

Classification System for Seed Dormancy

Marianna G. Nikolaeva developed a dormancy classification system that takes into account both the seed’s morphological and physiological features (Nikolaeva, 1967, 2004). Baskin & Baskin (1998, 2004) established a complete classification system for seed dormancy based on this framework, which includes five classes: physiological (PD), morphological (MD), morphophysiological (MPD), physical (PY), and combinational (PY + PD). The structure Is hierarchical, with these five classifications further divided into levels and types, as shown below.

1) Physiological dormancy (PD)

PD is the most common kind, present in gymnosperm seeds and all major angiosperm clades. It’s the most common dormancy form in temperate seed banks, as well as the most common dormancy class in the field. In the laboratory, PD is the most common form of dormancy in A. thaliana, Helianthus annuus, Lactuca sativa, Lycopersicon esculentum, Nicotiana spp., Avena fatua, and a variety of cereals. As a result, the focus of this review is on PD. Deep, moderate, and nondeep PD are the three types of PD.

2) Morphological dormancy (MD)

 Dormancy in morphology (MD) MD is seen in seeds with undeveloped (in terms of size) yet differentiated embryos. These embryos are not latent (physiologically), but merely require time to develop and germinate.

3) Dormancy morphophysiology (MDP)

Dormancy in morphophysiology (MPD) MPD is also seen in seeds with undeveloped embryos, although their dormancy also has a physiological component. As a result, these seeds require a dormancy-breaking treatment, such as a specific combination of warm and/or cold stratification, which can be replaced in some circumstances by GA administration. MPD is classified into eight tiers.

4) Physical Dormancy

Physical dormancy (PY) is caused by water-impermeable layers of palisade cells that limit water transport in the seed or fruit coat. PY dormancy can be broken by mechanical or chemical scarification.

5) Combinational Dormancy

PY + PD (combinational dormancy) Seeds with water-impermeable coatings (as in PY) paired with physiological embryo dormancy show PY + PD. 

Germination: Seed Dormancy

To cultivate wildflower seeds properly, they must germinate at the right moment. Seed dormancy is a major contributor to poor or inconsistent germination. Even under perfect growing conditions, seed dormancy occurs when seeds are unable to germinate (Merriam-Webster). Because most favourable growing conditions (different and specific for each species) can break dormancy, seeds germinate when they are most likely to thrive.

Dormancy has evolved in dormant seed species because it is beneficial to their survival. Dormancy is used by plants so that seeds can withstand adverse conditions and not all germinate at the same time and be killed by bad weather (Seed Dormancy). While dormancy might help plants survive in the wild, it can also make it difficult for seeds to germinate evenly and thrive in wildflower seed production sites.

Exogenous and endogenous seed dormancy are the two types of seed dormancy (Scarification). Conditions outside of the seed’s embryo cause exogenous dormancy. Exogenous dormancy occurs when the seed coat is too tough to allow moisture in, effectively blocking germination. Chemical changes within the seed’s embryo cause endogenous dormancy. Because the embryo is not fully grown or specific seasonal cues have not occurred, a plant cannot germinate due to endogenous dormancy (Endogenous Dormancy). Endogenous chemical inhibitors may also prevent seed germination.

Advantages of Seed Dormancy

• Seed dormancy helps plants survive the severe cold in temperate zones, which can be harmful to their vegetative and reproductive growth
• The dormancy of seeds in tropical regions is due to their impenetrable seed coverings, which ensure high survival despite water stress
• Seed dormancy in several grains is critical to human survival. If these seeds germinate in the field just after being harvested, they will be unfit for human consumption. Rain at the time of harvest or maturity has the potential to destroy the entire crop by causing germination

Disadvantages of Seed Dormancy

• To overcome dormancy, it took a long time (for uniform germination)
• Contributes to the weed seed’s long-term viability
• Maintaining the population on the field while growing a crop is extremely difficult with a dormant seed lot

Conclusion

Seed dormancy permits seeds to survive periods where seedling development is difficult, which is important for plant ecology and agriculture. The induction of dormancy and the transition from the dormant to the germination stage are known to entail several mechanisms. Introduction In terms of the higher plant’s survival as a species, the seed is a crucial step in its life cycle. Emerging Mechanisms of Seed Dormancy Ongoing research is revealing seed dormancy-related elements, some of which increase seed dormancy while others have a negative impact. It’s the most common dormancy form in temperate seed banks, as well as the most common dormancy class in the field. Exogenous and endogenous seed dormancy are the two types of seed dormancy. Conditions outside of the seed’s embryo cause exogenous dormancy. Exogenous dormancy occurs when the seed coat is too tough to allow moisture in, effectively blocking germination. The dormancy of seeds in tropical regions is due to their impenetrable seed coverings, which ensure high survival despite water stress. Seed dormancy in several grains is critical to human survival.