Seed dormancy and germination

Abstract

Reproduction is a critical time in plant life history. Therefore, genes affecting seed dormancy and germination are among those under strongest selection in natural plant populations. Germination terminates seed dispersal and thus influences the location and timing of plant growth. After seed shedding, germination can be prevented by a property known as seed dormancy. In practise, seeds are rarely either dormant or non-dormant, but seeds whose dormancy-inducing pathways are activated to higher levels will germinate in an ever-narrower range of environments. Thus, measurements of dormancy must always be accompanied by analysis of environmental contexts in which phenotypes or behaviours are described. At its simplest, dormancy can be imposed by the formation of a simple physical barrier around the seed through which gas exchange and the passage of water are prevented. Seeds featuring this so-called 'physical dormancy' often require either scarification or passage through an animal gut (replete with its associated digestive enzymes) to disrupt the barrier and permit germination. In other types of seeds with 'morphological dormancy' the embryo remains under-developed at maturity and a dormant phase exists as the embryo continues its growth post-shedding, eventually breaking through the surrounding tissues. By far, the majority of seeds exhibit 'physiological dormancy' - a quiescence program initiated by either the embryo or the surrounding endosperm tissues. Physiological dormancy uses germination-inhibiting hormones to prevent germination in the absence of the specific environmental triggers that promote germination. During and after germination, early seedling growth is supported by catabolism of stored reserves of protein, oil or starch accumulated during seed maturation. These reserves support cell expansion, chloroplast development and root growth until photoauxotrophic growth can be resumed.

Karrikin‐KAI2 signalling provides Arabidopsis seeds with tolerance to abiotic stress and inhibits germination under conditions unfavourable to seedling establishment

“…Environmental signals perceived before and after seed dispersal determine the depth of physiological dormancy and therefore the germination response to the ambient conditions (Penfield, ). Furthermore, seed dormancy is a dynamic state, subject to changes in the local environment, and can undergo cycles of dormancy breaking and re‐imposition as conditions change, especially water availability and temperature (Finch‐Savage & Footitt, ).…”

“…Seeds commonly exhibit one of several types of dormancy, such that germination is controlled by endogenous and environmental factors which break dormancy when conditions are favourable (Finch‐Savage & Leubner‐Metzger, ; Bentsink & Koornneef, ; Footitt et al ., ; Willis et al ., ). Physiological dormancy is established during seed development and can be lost and re‐imposed after dispersal from the mother plant in response to combinations of environmental factors, including water, light, temperature, nutrients and biotic signals (Huang et al ., ; Penfield, ). Such control of dormancy is achieved by complex interactions between the environmental factors and endogenous hormone signalling systems, which determine when a seed will germinate (Footitt et al ., ).…”

A matter of life and death: Molecular, physiological, and environmental regulation of seed longevity

“…For instance, the mutant abi3 seed is known to exhibit shorter dormancy and shorter seed longevity (Mao & Sun, ), suggesting that the degree of seed dormancy level may be positively associated with seed longevity. Cell metabolism is largely inactive during seed dormancy so that much of the energy stored in the seed is maintained (Penfield, ), and this may be one of the most important factors to explain the relationship between seed dormancy and longevity, but the underlying regulatory mechanism and relationship between seed dormancy and longevity are still largely unknown. Whether or not seed dormancy and longevity are directly and causally associated is an interesting and important question.…”

Abscisic acid‐dependent histone demethylation during postgermination growth arrest in Arabidopsis

“…Before germination, seeds contain carbohydrates, proteins, lipids, and phosphates as energy sources and remain in a metabolically quiescent and desiccation‐tolerant state (Bentsink & Koornneef, ). Once the seed senses environmental signals favourable for the release of dormancy, such as water imbibition or stratification, the radicle emerges through the seed coat in the process known as germination (Penfield, ). During a postgermination phase lasting 2–3 days, activation of metabolism results in the gradual hydrolysis and release of storage materials.…”

“…. Once the seed senses environmental signals favourable for the release of dormancy, such as water imbibition or stratification, the radicle emerges through the seed coat in the process known as germination (Penfield, 2017). During a postgermination phase lasting 2-3 days, activation of metabolism results in the gradual hydrolysis and release of storage materials.…”