Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
National Local Joint Engineering Research Center on Germplasm Utilization and Innovation of Chinese Medicinal Materials in Southwest China, Yunnan Agricultural University, Kunming, 650201, China.
Plant Sci. 2020 Mar;292:110371. doi: 10.1016/j.plantsci.2019.110371. Epub 2019 Dec 12.
Moderate heat stress is usually accompanied with fluctuating light in summer. Although either heat stress or fluctuating light can cause photoinhibition of photosystems I and II (PSI and PSII), it is unclear whether moderate heat stress accelerate photoinhibition under fluctuating light. Here, we measured chlorophyll fluorescence, P700 redox state and the electrochromic shift signal under fluctuating light at 25 °C and 42 °C for tobacco leaves. We found that (1) the thylakoid proton conductance was significantly enhanced at 42 °C, leading to a decline in trans-thylakoid proton gradient (ΔpH); (2) this low ΔpH at 42 °C did not decrease donor-side limitation of PSI and thermal energy dissipation in PSII; (3) the activation of cyclic electron flow (CEF) around PSI was elevated at 42 °C; and (4) the moderate heat stress did not accelerate photoinhibition of PSI and PSII under fluctuating light. These results strongly indicate that under moderate heat stress the stimulation of CEF protects PSI under fluctuating light in tobacco leaves.
中度热胁迫通常伴随着夏季光照的波动。尽管热胁迫或光照波动都可能导致光系统 I 和 II（PSI 和 PSII）的光抑制，但中度热胁迫是否会加速光照波动下的光抑制尚不清楚。在这里，我们测量了在 25°C 和 42°C 下波动光照下的叶绿素荧光、P700 氧化还原状态和电致变色位移信号。我们发现：（1）在 42°C 时，类囊体质子电导显著增强，导致跨类囊体质子梯度（ΔpH）下降；（2）42°C 时的低 ΔpH 并未降低 PSI 的供体侧限制和 PSII 中的热能耗散；（3）PSI 周围的循环电子流（CEF）的激活在 42°C 时升高；（4）中度热胁迫并没有加速波动光照下 PSI 和 PSII 的光抑制。这些结果强烈表明，在中度热胁迫下，CEF 的刺激在烟草叶片的波动光照下保护 PSI。
