Abstract
Hydration at low temperatures, commonly referred to as cold stratification, is widely used for releasing dormancy and triggering germination in a wide range of species including wheat. However, the molecular mechanism that underlies its effect on germination has largely remained unknown. Our previous studies showed that methyl-jasmonate, a derivative of jasmonic acid (JA), promotes dormancy release in wheat. In this study, we found that cold-stimulated germination of dormant grains correlated with a transient increase in JA content and expression of JA biosynthesis genes in the dormant embryos after transfer to 20 (o)C. The induction of JA production was dependent on the extent of cold imbibition and precedes germination. Blocking JA biosynthesis with acetylsalicylic acid (ASA) inhibited the cold-stimulated germination in a dose-dependent manner. In addition, we have explored the relationship between JA and abscisic acid (ABA), a well-known dormancy promoter, in cold regulation of dormancy. We found an inverse relationship between JA and ABA content in dormant wheat embryos following stratification. ABA content decreased rapidly in response to stratification, and the decrease was reversed by addition of ASA. Our results indicate that the action of JA on cold-stratified grains is mediated by suppression of two key ABA biosynthesis genes, TaNCED1 and TaNCED2.
Highlights
Timing of germination is one of the most critical adaptation strategies used by plants to ensure reproductive success
We have identified several lines of evidence that point to a new role for jasmonic acid (JA) in dormancy release by cold stratification
We have found that JA biosynthesis in wheat embryos is induced following cold stratification of dormant grains and that the increase in JA content correlates with the effect on germination
Summary
Timing of germination is one of the most critical adaptation strategies used by plants to ensure reproductive success. Dormancy has a key role in ensuring survival of a population by blocking seed germination until conditions become favourable for germination and seedling establishment (Bewley, 1997). In addition to genetic determinants, environmental signals experienced during seed maturation and following dispersal strongly influence the timing of dormancy loss. Unlike many wild plant species, cultivated crops such as wheat (Triticum aestivum L.) display weak grain dormancy at maturity due to selective breeding against dormancy for uniform and vigorous germination. Modern wheat varieties exhibit increased susceptibility to pre-harvest sprouting (PHS) following cool and moist conditions in the field, which result in serious loss of grain yield and quality (Gubler et al, 2005; Rodríguez et al, 2015). Research aimed at understanding environmental and genetic control of dormancy will assist in developing new strategies for the elimination of PHS worldwide in domesticated crops
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