Li Pengli, Weng Jinyang, Zhang Qing, Yu Liyao, Yao Qi, Chang Liying, Niu Qingliang
School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, China.
Planting Management Station, Ningbo, China.
Front Plant Sci. 2018 Oct 22;9:1525. doi: 10.3389/fpls.2018.01525. eCollection 2018.
Phosphorus (P) is a limiting plant soil nutrient. Long-term low inorganic phosphate (Pi) irreversibly damages plant cells and hinders plant growth. Plants have evolved several adaptive biochemical, physiological, and developmental responses to low-Pi stress. However, little is known about chloroplast responses to low-Pi stress. In this study, we used physiological and biochemical analyses to investigate melon chloroplast responses to low-Pi stress. The results indicated that low-Pi stress impeded melon seedling growth and reduced its dry matter content by inhibiting the photosynthesis. Low-Pi stress reduced the P content in shoots, which inhibited ATP synthase (ATP-ase) activity, and disturbed the proton and electron transport efficiency on chloroplast photosynthetic electron transport chain. In addition, low-Pi stress induced reactive oxygen species (ROS) production in the leaves, which caused membrane peroxidation. Therefore, redox homeostasis was not maintained, and the melon leaves presented with symptoms of photooxidative stress. To mitigate photoinhibition, the melon plants initiated non-photochemical chlorophyll fluorescence quenching (NPQ) initiated by acidification of the thylakoid lumen to dissipate excess excitation energy, significantly improved ROS-scavenging enzyme activity. Based on these experimental results, we concluded that low Pi inhibited photosystem activity and caused photooxidative stress and photoinhibition. To alleviate these negative effects, the plant activated its NPQ mechanism, alternative electron transport pathways, and antioxidant system to protect its chloroplasts.
磷（P）是一种限制植物生长的土壤养分。长期低无机磷（Pi）会对植物细胞造成不可逆的损害，并阻碍植物生长。植物已经进化出几种对低磷胁迫的适应性生化、生理和发育反应。然而，关于叶绿体对低磷胁迫的反应知之甚少。在本研究中，我们使用生理和生化分析方法来研究甜瓜叶绿体对低磷胁迫的反应。结果表明，低磷胁迫通过抑制光合作用阻碍了甜瓜幼苗的生长，并降低了其干物质含量。低磷胁迫降低了地上部的磷含量，抑制了ATP合酶（ATP酶）的活性，并扰乱了叶绿体光合电子传递链上的质子和电子传递效率。此外，低磷胁迫诱导叶片中活性氧（ROS）的产生，导致膜过氧化。因此，氧化还原稳态未得到维持，甜瓜叶片出现光氧化胁迫症状。为了减轻光抑制，甜瓜植株启动了由类囊体腔酸化引发的非光化学叶绿素荧光猝灭（NPQ），以耗散多余的激发能，显著提高了ROS清除酶的活性。基于这些实验结果，我们得出结论，低磷抑制了光系统活性，导致光氧化胁迫和光抑制。为了减轻这些负面影响，植物激活了其NPQ机制、替代电子传递途径和抗氧化系统来保护其叶绿体。
