MAIN CONCLUSION This study highlights the potential link between high light-induced canopy-level photosynthesis and mesophyll cell K+, Cl-, Ca2+, and H+ homeostasis in tomato. Light is a primary energy source for photosynthesis and a vital regulator of mineral nutrient uptake and distribution in plants. Plants need to optimize photosynthesis and nutrient balance in leaves for performance in fluctuating light conditions that are partially regulated by light-induced ion homeostatsis in the mesophyll cells. It is still elusive whether high light-induced leaf mesophyll ion fluxes affect leaf photosynthesis at different canopy levels in Solanum lycopersicum L. Leaf gas exchange and microelectrode ion flux (MIFE) measurements were employed to study the effects of prolonged light-induced canopy-level leaf physiological responses of tomato plants. High light resulted in a significant lowering in photosynthesis in the fully-exposed top canopy leaves of tomato, but not to mid- or low-canopy leaves. Leaf mesophyll K+ effluxes of all canopies were significantly decreased after three weeks of high light treatment. However, high light-induced leaf mesophyll Ca2+ effluxes were significantly enhanced only in the top and mid canopies. Moreover, we found that photosynthetic parameters were significantly correlated with leaf mesophyll ion fluxes. We thus propose that canopy-level significant Ca2+ efflux and K+ efflux of leaf mesophyll may serve as early indicators for light-induced regulation on photosynthesis. We conclude that light-induced differential photosynthetic performance and ion fluxes in leaves may implicate a requirement of more uniform light irradiance and spectra at different canopy levels of tall greenhouse tomato plants. This can be achieved through new innovative greenhouse lighting technologies and covering materials towards the enhancement of crop photosynthesis and yield.

中文翻译：

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强光对番茄冠层光合作用和叶肉离子通量的影响

主要结论 本研究强调了番茄中强光诱导的冠层光合作用与叶肉细胞 K+、Cl-、Ca2+ 和 H+ 稳态之间的潜在联系。光是光合作用的主要能源，也是植物吸收和分配矿物质养分的重要调节剂。植物需要优化叶片中的光合作用和养分平衡，以在波动的光照条件下发挥性能，这些光照条件部分由叶肉细胞中光诱导的离子稳态调节。高光诱导叶片叶肉离子通量是否会影响 Solanum lycopersicum L. 不同冠层水平的叶片光合作用仍然难以捉摸。叶片气体交换和微电极离子通量 (MIFE) 测量用于研究延长光诱导冠层水平的影响番茄植株叶片生理反应。高光导致完全暴露的番茄顶部冠层叶片的光合作用显着降低，但对中冠层或低冠层叶子没有影响。在强光处理三周后，所有冠层的叶肉素K+流出量均显着降低。然而，高光诱导的叶肉Ca2+ 外流仅在顶部和中部冠层显着增强。此外，我们发现光合参数与叶肉离子通量显着相关。因此，我们提出叶叶肉的冠层水平显着 Ca2+ 外流和 K+ 外流可作为光诱导光合作用调节的早期指标。我们得出结论，叶片中光诱导的差异光合性能和离子通量可能意味着在高大温室番茄植物的不同冠层水平上需要更均匀的光辐照度和光谱。这可以通过新的创新温室照明技术和覆盖材料来实现，以增强作物的光合作用和产量。