过量强度光照引发的“记忆性”系统抗病和强光适应反应中线粒体交替氧化酶生理学功能的研究

In natural environment, sometimes only partial leaves of a plant are exposed to excess light intensity. Recent studies have shown that such an “experience” can be physiologically “memorized” by both the partial leaves that experienced excess light intensity and the other (systemic) leaves of the same plant, and this “memory” is used for enhancement or optimization of the defense responses to future pathogen attack and the acclimatory responses to future high light stress. This phenomenon reflects a distinctive and important acclimation strategy of plants to natural environment, which was also formed in changing natural environment. As center of plant metabolism, mitochondrial respiration should play important but unknown roles in this acclimation strategy to natural environment. More importantly, many physiological features of the alternative oxidase of plant mitochondria appear to fit well the characteristics of this excess-light-triggered “memristive” systemic defense responses to pathogen infection and systemic acclimatory responses to high light. Thus, the alternative oxidase could play important role in this process. The investigation on this possible role of the alternative oxidase would deeply reveal the mechanism for this distinctive and important acclimation strategy of plants to natural environment from the perspective of respiratory metabolism. And, this investigation would also greatly develop new understandings about the behaviors and functions of plant mitochondrial respiration from the perspectives of the characteristic of changing natural environment and the physiological timeliness and systematization of plants. In addition, this investigation would be helpful to the researches on the acclimation mechanism of the plants growing in the intensive radiation region and the researches on how to improve crop resistance to environmental stresses by utilizing light illumination.

在自然环境中，往往植株的部分叶片会经历过量强度的光照。近期研究表明，这一“经历”能被过量强度光照射过的叶片和同株其它叶片（系统叶片）所“记忆”，并由此提升或优化了植株叶片对未来出现的病原菌和强光的抗性反应。该现象表征了植物在自然环境中形成的一种独特且重要的环境适应策略。作为代谢的中心环节，线粒体呼吸在这种环境适应策略中的作用不应被忽视却尚未被了解；而更重要的是，植物线粒体交替氧化酶的诸多生理学特性和过量强度光照引发的这种“记忆性”系统抗病和强光适应反应的特点相吻合。因此，交替氧化酶很可能在其中扮演着重要角色。对这一尚未被探索的科学问题的研究不仅能深层次地从呼吸代谢的角度来阐释植物这种独特环境适应策略的内在生理机制，也将从环境变化的自然特点、植物生理的时效性和系统性等新角度来认识线粒体呼吸的行为及功能。同时，这对于强辐射地区植物的环境适应机制和农业中利用光照提高作物抗性等研究也具有重要意义。

本项目研究了在过量强度光照引发的植株“记忆性”系统抗病和强光适应反应中交替呼吸途径的变化、其所扮演的生理学角色及相关的信号调控和作用机制。研究发现，短期过量强度光照能引起植物的“记忆性”抗病反应，且其和光合电子传递链密切相关；而短期过量强度光照和光合电子传递链的干扰均能够增加病程中叶片交替呼吸途径的水平。通过使用AOX1a基因反义突变体，揭示了交替氧化酶参与了过量强度光照引发的植株“记忆性”抗病反应。此外，AOX1a基因在系统叶片中并未明显影响短期过量强度光照诱导的植株系统叶片的抗病反应；但尚无法排除其它的交替氧化酶基因家族成员在其中的生理学功能。进一步实验显示，病菌侵染所造成的植物光系统Ⅱ光化学活性的下降与活性氧水平上升有关；而在病程中，交替呼吸途径的上升可能通过影响活性氧代谢保护了叶片光系统Ⅱ的光化学活性。此外，我们也揭示了交替呼吸途径在重金属和渗透胁迫下也具有保护植物光化学活性、降低氧化压力的生理学角色。同时，我们研究了植物对强光的适应性反应中交替呼吸途径的生理学意义及可能的信号机制。结果表明，短期过量强度光照提升了交替呼吸途径的水平，且交替氧化酶参与了植株对强光的适应性反应。进一步实验表明，在短期过量强度光照前，过氧化氢的增加能激活植株对强光的适应性反应，也提升了交替呼吸途径的水平和水杨酸含量；利用AOX1a基因反义突变体和salicylate hydroxylase gene转基因植株发现，交替氧化酶和水杨酸参与了过氧化氢所引发的强光适应性反应。上述结果较深层次地从呼吸代谢的角度来阐释植物环境适应策略的内在生理机制，也从新的角度来认识线粒体呼吸的行为及功能。同时，这对于强辐射地区植物的环境适应机制和利用光照和呼吸作用提高作物抗性等研究工作也具有一定的参考价值和意义。