Seed dormancy is a dynamic state: variable responses to pre- and post-shedding environmental signals in seeds of contrastingArabidopsisecotypes

Abstract

Seeds have evolved to be highly efficient environmental sensors that respond not only to their prevailing environment, but also their environmental history, to regulate dormancy and the initiation of germination. In the present work we investigate the combined impact of a number of environmental signals (temperature, nitrate, light) during seed development on the mother plant, during post-shedding imbibition and during prolonged post-shedding exposure in both dry and imbibed states, simulating time in the soil seed bank. The differing response to these environments was observed in contrasting winter (Cvi, Ler) and summer (Bur) annual Arabidopsis ecotypes. Results presented show that environmental signals both pre-and post-shedding determine the depth of physiological dormancy and therefore the germination response to the ambient environment. The ecotype differences in seed response to ambient germination conditions are greatly enhanced by seed maturation in different environments. Further variation in response develops following shedding when seeds do not receive the full complement of environmental signals required for germination and enter the soil seed bank in either dry or imbibed states. Species seed dormancy characteristics cannot therefore be easily defined, as seed dormancy is a dynamic state subject to within-species adaptation to local environments.

A laboratory simulation of Arabidopsis seed dormancy cycling provides new insight into its regulation by clock genes and the dormancy‐related genes DOG1, MFT, CIPK23 and PHYA

“…). In the experiments presented, ecotypic differences in the relief and induction of dormancy by the temperatures used in the simulation were consistent with those previously shown for Bur, Col‐0, Ler and Cvi (Cone and Spruit ; Huang et al , Springthorpe and Penfield ; Penfield & Springthorpe ). These differences presumably arose during adaptation to their specific climates from a common underlying species response.…”

“…; Huang et al . ). This is apparently in direct contrast to the results with the summer annual ecotypes Bur, Col‐0 and Ler in which increasing temperature accelerated the induction of secondary dormancy (Fig.…”

“…Seeds first sense the maternal environment to set the depth of primary dormancy at maturity (e.g. temperature) (Kendall et al ; Penfield and Springthorpe ; He et al ; Huang et al , ; Chen et al . ).…”

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

“…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 ., ).…”

Multiple paths to similar germination behavior in Arabidopsis thaliana

“…Decreasing the temperature during seed development results in increased levels of dormancy (i.e. decreased probability of germinating; Donohue et al ., ; Kendall et al ., ; Penfield & Springthorpe, ; Huang et al ., ). The changes in dormancy are mediated by altered gene expression (Kendall et al ., ), seed provisioning, (Finch‐Savage & Leubner‐Metzger, ), and seed coat properties (MacGregor et al ., ).…”