Abstract
Seed dormancy is an adaptive trait that does not allow the germination of an intact viable seed under favorable environmental conditions. Non-dormant seeds or seeds with low level of dormancy can germinate readily under optimal environmental conditions, and such a trait leads to preharvest sprouting, germination of seeds on the mother plant prior to harvest, which significantly reduces the yield and quality of cereal crops. High level of dormancy, on the other hand, may lead to non-uniform germination and seedling establishment. Therefore, intermediate dormancy is considered to be a desirable trait as it prevents the problems of sprouting and allows uniformity of postharvest germination of seeds. Induction, maintenance, and release of seed dormancy are complex physiological processes that are influenced by a wide range of endogenous and environmental factors. Plant hormones, mainly abscisic acid (ABA) and gibberellin (GA), are the major endogenous factors that act antagonistically in the control of seed dormancy and germination; ABA positively regulates the induction and maintenance of dormancy, while GA enhances germination. Significant progress has been made in recent years in the elucidation of molecular mechanisms regulating ABA/GA balance and thereby dormancy and germination in cereal seeds, and this review summarizes the current state of knowledge on the topic.
Highlights
Cereals are among the most economically important crops worldwide with annual production of over 2500 million tons (Food and Agriculture Organization of the United Nations, 2017)
Preharvest sprouting of cereal grains is closely associated with the degree of dormancy, an adaptive trait that inhibits the germination of seeds under optimal environmental conditions (Gao and Ayele, 2014)
Similar to that observed in the seeds of other cereal crops, after-ripening of dormant wheat seeds leads to imbibitionmediated reduction of abscisic acid (ABA) level, while maintenance of elevated ABA level was evident in the corresponding dormant seeds, and these differences in ABA level are mediated by changes in the expression patterns of TaNCED1 and TaABA8 OH1 genes (Jacobsen et al, 2013), implying the contribution of both ABA biosynthesis and catabolism in the regulation of seed ABA level and dormancy in wheat
Summary
Cereals are among the most economically important crops worldwide with annual production of over 2500 million tons (Food and Agriculture Organization of the United Nations, 2017) Their production is challenged by a wide range of biotic and abiotic stress factors including the occurrence of high humidity and wet conditions prior to harvest that causes germination of the grain on the spike, which is referred to as preharvest sprouting. Previous studies have provided important insights into the significance of the metabolic and signaling aspects of different plant hormones and their potential interaction in the maintenance and release of dormancy in cereal seeds (Liu et al, 2013; Chitnis et al, 2014; Shu et al, 2016b). This review highlights the recent advances made in this regard
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