Molecular Mechanisms in Understanding Anoxia Tolerance in Rice Seeds under Submergence and Their Implication in Rice Biotechnology

Abstract

Submergence in rice fields creating inundation stress and realizing anoxia or hypoxia is a problem in agriculture. Seeds under this oxygen deficit are faced with fermentative respiration, where the end product would be poisoning the tissue viability. This is more aggravated in direct seeded rice cultivation with the accumulation of lactate as a poison. This review is concerned with the basic insights into anoxia tolerance in seeds and possible strategies to reduce anoxic shock through the modification of metabolism preceded by gene expression. The major concern of anoxic germination is starch metabolism and downstream physiological realization to facilitate escape or quiescence strategy, overcoming submergence stress. The coleoptiles facing hypoxic stress mated with transcripts for oxidative traits, energy metabolism, and proteins for membrane peroxidation in support of energy metabolism are the most important. Hypoxic genes are recovered from traditional indica and japonica land races of rice, and show changes in glycolytic flux and sugar sensing. Anoxic germination and seedling vigor are based on a combinational regulation of oxidative stress and fermentative catabolism. De novo antioxidant and antioxidative enzyme production can support improved seed germination in this condition. Pre-harvest spouting with seed-coat-induced dormancy, hormonal ratios, and hydrolyses would be of concern. Therefore, comprehensive analysis aimed to understand rice seed priming for better gas exchange, diffusion, temperature sensitivity, ion uptake, redox balance, and others. Still, in-depth insights are being awaited for better understanding the physiological and molecular basis using a multi-omics approach for better seed priming to overcome the anoxic/hypoxic revelation mostly acquainted with submergence stress.