Under water stress, plants accumulate various organic and inorganic substances to increase the concentration of cell sap and reduce its osmotic potential, so that plants can keep water and adapt to water stress environment. Usually the accumulated metabolites are proline, betaine, mannitol, sorbitol, trehalose, fructan and so on. Through transgenic technology, crops can produce more osmotic adjustment protective substances under drought conditions, which can greatly improve the drought resistance of crops. At present, people have transferred the osmotic substance regulating enzyme gene into plants to improve their drought resistance. Such as proline synthase gene, fructan synthase gene, betaine synthesis related enzyme gene, trehalose and mannitol synthesis related gene, etc.
Through a lot of research on plant antioxidant defense system under drought stress, people think that the system is composed of some enzymes and antioxidant substances that can scavenge active oxygen. Such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbic acid (AsA). They cooperate to resist oxidative damage induced by drought stress. In the whole defense system, SOD is an antioxidant enzyme and plays an important role in the oxidation of all plants. According to different metal ions, SOD can be divided into three types: Cu/Zn-SOD, Mn-SOD and Fe-SOD3.
SOD is the first key antioxidant enzyme to scavenge active oxygen in plants. In recent years, the drought tolerance of plants has been improved through SOD genetic engineering. For example, after tobacco Mn-SODcDNA was introduced into alfalfa, the drought resistance of transgenic alfalfa was improved and its viability remained unchanged.
Because some transcription factors related to stress can regulate the expression of functional genes and signal transduction under stress conditions, their over-expression in transgenic plants will activate the simultaneous expression of many stress-resistant functional genes. Therefore, the drought tolerance of plants can be improved by transforming regulatory genes. DREB transcription factor is a transcription factor that has been widely studied to resist abiotic stress. For example, many drought-induced genes were cloned from drought-treated Arabidopsis thaliana by differential display method, and these genes were defined as RD (Response to Drought) genes. The promoter of rd29A gene was analyzed, and a DRE cis-acting element related to drought, high salt and low temperature stress response gene was revealed, and three transcription factors, DREB2A and DREB2B, were cloned. Within 10min of drought or high salt (250mmol/LNaCl) treatment, DREB2A and DREB2B were induced rapidly and strongly, without being induced by exogenous ABA.