Kaiser Elias, Morales Alejandro, Harbinson Jeremy, Heuvelink Ep, Marcelis Leo F M
Horticulture and Product Physiology, Department of Plant Sciences, Wageningen University, Wageningen, Netherlands.
Centre for Crop Systems Analysis, Department of Plant Sciences, Wageningen University, Wageningen, Netherlands.
Front Plant Sci. 2020 Aug 25;11:1317. doi: 10.3389/fpls.2020.01317. eCollection 2020.
Due to their slow movement and closure upon shade, partially closed stomata can be a substantial limitation to photosynthesis in variable light intensities. The abscisic acid deficient mutant in tomato () displays very high stomatal conductance ( ). We aimed to determine to what extent this substantially increased affects the rate of photosynthetic induction. Steady-state and dynamic photosynthesis characteristics were measured in and wildtype leaves, by the use of simultaneous gas exchange and chlorophyll fluorometry. The steady-state response of photosynthesis to CO, maximum quantum efficiency of photosystem II photochemistry ( ), as well as mesophyll conductance to CO diffusion were not significantly different between genotypes, suggesting similar photosynthetic biochemistry, photoprotective capacity, and internal CO permeability. When leaves adapted to shade (50 µmol m s) at 400 µbar CO partial pressure and high humidity (7 mbar leaf-to-air vapour pressure deficit, VPD) were exposed to high irradiance (1500 µmol m s), photosynthetic induction was faster in compared to wildtype leaves, and this was attributable to high initial in (~0.6 mol m s): in , the times to reach 50 ( ) and 90% ( ) of full photosynthetic induction were 91 and 46% of wildtype values, respectively. Low humidity (15 mbar VPD) reduced and slowed down photosynthetic induction in the wildtype, while no change was observed in ; under low humidity, was 63% and was 36% of wildtype levels in . Photosynthetic induction in low CO partial pressure (200 µbar) increased in the wildtype (but not in ), and revealed no differences in the rate of photosynthetic induction between genotypes. Effects of higher in were also visible in transients of photosystem II operating efficiency and non-photochemical quenching. Our results show that at ambient CO partial pressure, wildtype is a substantial limitation to the rate of photosynthetic induction, which overcomes by keeping its stomata open at all times, and it does so at the cost of reduced water use efficiency.
由于气孔在遮荫时移动缓慢且关闭，部分关闭的气孔在光照强度变化时可能会对光合作用造成显著限制。番茄脱落酸缺陷型突变体（）具有非常高的气孔导度（）。我们旨在确定这种显著增加的气孔导度在多大程度上影响光合诱导速率。通过同时使用气体交换和叶绿素荧光测定法，测量了突变体和野生型叶片的稳态和动态光合作用特征。光合作用对二氧化碳的稳态响应、光系统II光化学的最大量子效率（）以及叶肉对二氧化碳扩散的导度在不同基因型之间没有显著差异，这表明它们具有相似的光合生物化学、光保护能力和内部二氧化碳渗透性。当叶片在400微巴二氧化碳分压和高湿度（7毫巴叶-气蒸汽压亏缺，VPD）条件下适应遮荫（50微摩尔光子·平方米·秒）后，暴露于高辐照度（1500微摩尔光子·平方米·秒）时，突变体叶片的光合诱导比野生型叶片更快，这归因于突变体中较高的初始气孔导度（~0.6摩尔二氧化碳·平方米·秒）：在突变体中，达到完全光合诱导的50%（）和90%（）所需的时间分别为野生型值的91%和46%。低湿度（15毫巴VPD）降低了野生型的气孔导度并减缓了光合诱导，而突变体中未观察到变化；在低湿度条件下，突变体中的气孔导度为野生型水平的63%，光合诱导速率为野生型的36%。在低二氧化碳分压（200微巴）下的光合诱导增加了野生型的气孔导度（但突变体中未增加），并且揭示了不同基因型之间光合诱导速率没有差异。突变体中较高气孔导度的影响在光系统II运行效率和非光化学猝灭的瞬变中也很明显。我们的结果表明，在环境二氧化碳分压下，野生型的气孔导度对光合诱导速率是一个显著限制，突变体通过始终保持气孔开放克服了这一限制，而这样做是以降低水分利用效率为代价的。
