Abstract

Upon a sudden transition from high to low light, the rate of CO₂ assimilation (A_N) in some plants first decreases to a low level before gradually becoming stable. However, the underlying mechanisms remain controversial. The activity of chloroplast ATP synthase (g_H⁺) is usually depressed under high light when compared with low light. Therefore, we hypothesize that upon a sudden transfer from high to low light, the relatively low g_H⁺ restricts ATP synthesis and thus causes a reduction in A_N. To test this hypothesis, we measured gas exchange, chlorophyll fluorescence, P700 redox state, and electrochromic shift signals in Bletilla striata (Orchidaceae). After the transition from saturating to lower irradiance, A_N and ETRII decreased first to a low level and then gradually increased to a stable value. Within the first seconds after transfer from high to low light, g_H⁺ was maintained at low levels. During further exposure to low light, g_H⁺ gradually increased to a stable value. Interestingly, a tight positive relationship was found between g_H⁺ and ETRII. These results suggested that upon a sudden transition from high to low light, A_N was restricted by g_H⁺ at the step of ATP synthesis. Taken together, we propose that the decline in A_N upon sudden transfer from high to low light is linked to the slow kinetics of chloroplast ATP synthase.

中文翻译：

---

从高光向低光转移时光合速率的下降与白B中叶绿体ATP合酶的慢动力学有关

摘要

在从高光突然转变为低光时，一些植物中的CO ₂同化率（A _N）首先降低到低水平，然后逐渐变得稳定。但是，其基本机制仍存在争议。与弱光相比，强光下叶绿体ATP合酶（g _H ⁺）的活性通常降低。因此，我们假设当从高光突然转移到低光时，相对较低的g _H ^+会限制ATP的合成，从而导致A _N的降低。为了检验该假设，我们测量了气体交换，叶绿素荧光，P700氧化还原状态和白let（兰科）。从饱和到较低的辐照度过渡后，A _N和ETRII首先下降到较低水平，然后逐渐增加到稳定值。从高光转移到低光后的最初几秒钟内，g _H ⁺维持在低水平。在进一步暴露于弱光下期间，g _H ⁺逐渐增加至稳定值。有趣的是，在g _H ⁺和ETRII之间发现了紧密的正相关。这些结果表明，当从高光突然过渡到低光时，A _N被g _H ⁺限制。在ATP合成步骤中。两者合计，我们建议从高光到低光突然转移后，A _N的下降与叶绿体ATP合酶的缓慢动力学有关。