Seed germination variability: Why do genetically identical seeds not germinate at the same moment?

Abstract

For survival in the wild environment, plants prefer a bet-hedging strategy where individual variation is high and also produce a range of phenotypes. When faced with unpredictable environmental conditions, fluctuation in seed behaviour is a beneficial trait that allows the survival of plants, particularly if seedlings from early germinated seeds don't survive. However, this is not a desired trait when agriculture is concerned, where a set of uniformly grown seedlings are required. Even though variability in seed behaviour is unavoidable, over the centuries, humans might have selected seeds with minimum variability for agricultural use. In the model plant Arabidopsis, non-stratified seeds even in the same silique germinate variably. How this variability is manifested from genes to a physiological outcome and what molecular mechanism of bet-hedging facilitates this diversity remains elusive. Will the reintroduction of valuable wild alleles in domesticated crops contribute to this variability between individual seeds by promotion of bet-hedging? Recent advances have shed light on possible molecular pathways of germination that are impacted at the level of single seeds and single cells. Here, we review the hormonal, molecular and cellular mechanisms that may impact the germination outcome of individual genetically identical seeds.