低氮胁迫下外源色氨酸对高粱幼苗根系伸长的调控作用

Effects of exogenous tryptophan on root elongation of sorghum seedlings under low nitrogen stress

低氮胁迫促进高粱根系伸长,但其具体的生理机制仍不清晰。为解析高粱根系在低氮胁迫下伸长的生理机制,本试验选用高粱耐低氮自交系(398B)和氮敏感自交系(CS-3541)为材料,研究低氮胁迫下高粱根系伸长的物质和能量代谢基础。结果表明,与正常氮相比,低氮胁迫显著促进了398B和CS-3541根长及根尖细胞长度,398B表现出更长的根长;低氮胁迫后1、5和10 d,398B和CS-3541根系中内源色氨酸含量显著增加;应用RNA-seq技术对2个高粱自交系低氮胁迫后根系样品进行差异表达基因鉴定,结果发现色氨酸代谢途径的有关基因参与了低氮下高粱根系的伸长。进一步利用外源色氨酸处理发现,外源色氨酸通过增加生长素含量,激活了质膜H^(+)-ATPase的活性,促进质膜酸化,提高了能量代谢相关酶活性及ATP含量,从而诱导了根系的能量代谢,促进了低氮胁迫下高粱根系的伸长。而且,外源色氨酸对低氮胁迫下398B的作用效果更好。综上所述,低氮胁迫处理激活了内源色氨酸在高粱根系伸长中的关键作用,依赖色氨酸途径合成的生长素及协同提高的能量代谢是促进低氮下高粱根系伸长的生理机制。

The physiological mechanism of root elongation in sorghum under low nitrogen stress remains unclear.Here,two sorghum inbred lines,398B(low nitrogen tolerance)and CS-3541(low nitrogen sensitivity),were used as experimental materials,to clarify the physiological mechanism of root elongation of sorghum seedlings under low nitrogen stress.The results showed that,compared with normal nitrogen stress,low nitrogen stress significantly increased root length and root tip cell length of 398B and CS-3541,and 398B had longer root length.The endogenous tryptophan content in roots of 398B and CS-3541 increased significantly at 1,5,and 10 days after low nitrogen stress.Tryptophan was involved in root elongation of sorghum under low nitrogen conditions through the auxin synthesis pathway by RNA-seq,and the relative expression level of genes in the auxin synthesis pathway of root in 398B was significantly higher than that in CS-3541.Furthermore,the root lengths of 398B and CS-3541 were significantly increased by 50 mg L–1exogenous tryptophan treatment under low nitrogen conditions.Exogenous tryptophan activated the activity of H^(+)-ATPase in plasma membrane by increasing the content of auxin,promoted the acidification of plasma membrane,and improved the activity of enzymes related to energy metabolism and ATP content,and thus inducing energy metabolism of root system.Exogenous tryptophan had a better effect on 398B under low nitrogen stress.In conclusion,low nitrogen stress activated the key role of endogenous tryptophan in sorghum root elongation,and auxin depended on tryptophan pathway and synergistic enhancement of energy metabolism were the physiological mechanism promoting root elongation of sorghum seedlings under low nitrogen stress.