干旱胁迫下紫花苜蓿幼苗非结构性碳水化合物代谢对NO的响应

以紫花苜蓿（Medicago sativa）为材料，采用盆栽试验方法，用聚乙二醇（PEG-6000）作为渗透介质模拟干旱胁迫，外源喷施NO供体硝普钠，NO清除剂（carboxy-PTIO，cPTIO），对紫花苜蓿幼苗叶片、根系中非结构性碳水化合物含量及相关酶活性的变化进行研究，探讨NO对紫花苜蓿耐旱机制的作用。结果表明：外源NO促进了紫花苜蓿叶片中淀粉的分解、根系中淀粉的积累，提高叶片及根系中可溶性糖（蔗糖、果糖和葡萄糖）含量，降低了渗透势，促进细胞吸水，缓解干旱造成的损伤。此外，外源NO能提高干旱胁迫下紫花苜蓿叶片中蔗糖合成酶（SS）、酸性转化酶（AI）和中性转化酶（NI）活性，降低了蔗糖磷酸合成酶（SPS）的活性，提高根系中SS、SPS和转化酶活性，使蔗糖的合成与分解处于高水平的动态平衡，增强了紫花苜蓿的抗旱性。而NO清除剂cPTIO则会不同程度的抑制紫花苜蓿幼苗中非结构性碳水化合物（NSC）及其相关酶活性。因此，NO可以通过调控NSC的代谢响应干旱胁迫，缓解干旱胁迫造成的不利影响，在紫花苜蓿的抗旱中扮演着重要的角色。

Responses of non-structural carbohydrate metabolism of Medicago sativa seedlings to nitric oxide under drought stress

The effects of nitric oxide on non-structural carbohydrate metabolism of Medicago sativa seedlings leaves and roots under drought stress by 10% PEG were investigated. Solutions with:(i) osmotic potentials obtained using polyethylene-glycol-6000 (PEG-6000); (ii) a nitric oxide donor sodium nirorpusside (SNP); (iii) an NO scavenger (carboxy-PTIO, cPTIO); were sprayed onto the leaves of alfalfa seedlings in pot experiment at different combinations. The results showed that exogenous nitric oxide promoted the starch decomposition of leaves, the accumulation of starch in roots and increased the content of soluble sugar (sucrose, fructose and glucose) in leaves and roots in Medicago sativa seedlings under drought stress, which decreased the osmotic potential, promoted cell water absorption and alleviated damage caused by drought. Furthermore, under drought stress exogenous nitric oxide can increase the activity of sucrose synthetase (SS), acid invertase (AI), neatral invertase (NI), reduce the activity of Sucrose phosphate synthase(SPS) in leaves and can increase the activity of SS, SPS, invertase in roots, so that make the synthesis and decomposition of sucrose at a high level of dynamic balance. It enhances the drought resistance of alfalfa. The metabolism of NSC and related enzymes were inhibited by NO scavenger cPTIO. Therefore, nitric oxide played an important role in the drought resistance of Medicago sativa. It can regulate the metabolic of NSC response to drought stress and alleviate the adverse effects caused by drought stress.