Determination of the rate of photoreduction of O2 in the water-water cycle in watermelon leaves and enhancement of the rate by limitation of photosynthesis
Determination of the rate of photoreduction of O2 in the water-water cycle in watermelon leaves and enhancement of the rate by limitation of photosynthesis
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DOI：
10.1093/pcp/41.3.335
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发表时间：
2000-03-01
影响因子：
4.9
通讯作者：
Yokota, A
中科院分区：
文献类型：
--
作者：
Miyake, C;Yokota, A
研究了光合碳还原（PCR）和光呼吸碳氧化（PCO）循环的电子通量如何影响水-水循环中限制步骤PSP的O-2光还原。同时测量CO2气体交换，蒸腾作用和PSII [Phi（PSII）]的量子产率使用西瓜叶片（西瓜）。在不同的CO2和O-2分压和1，100 μ mol光子m（-2）s（-1）条件下，由Phi（PSII）估算的PSII中的总电子通量[Je（PSII）]总是大于PCR和PCO循环所需的总电子通量。这一观察结果表明存在替代电子通量（Ja）。Ja分为O-2依赖性[Ja（O-2-depend）]和O-2非依赖性[Ja（O-2-independ）]组分。半Ja（O-2-dependent）的大小为7.5 - 9.5 μ mol e（-）m（-2）s（-1），其对O-2的表观K-m约为8.0 kPa，这可以通过PSI下O-2的光还原来解释，无论是由铁氧还蛋白介导的还是由单脱氢抗坏血酸还原酶催化的。结果表明，Ja（O-2-depend）是由水-水循环驱动的。在21千帕O-2增强Ja（O-2-依赖）的系数为1.3的CO2从23到5.0帕的细胞间分压的下降。通过增加光子通量密度诱导Ja的PCR和PCO循环的活动饱和。这些结果表明，PSII中的电子通量，超过所需的PCR和PCO循环的通量诱导光还原的O-2在水-水循环。
A study was performed to determine how the electron fluxes for the photosynthetic carbon reduction (PCR) and the photorespiratory carbon oxidation (PCO) cycles affect the photoreduction of O-2 at PSP, which is the limiting step in the water-water cycle. Simultaneous measurements were made of CO2-gas exchange, transpiration and quantum yield of PSII [Phi(PSII)] using leaves of watermelon (Citrullus lanatus). The total electron flux in PSII [Je(PSII)], as estimated from Phi(PSII), was always larger than the total electron flux required for the PCR and PCO cycles at various partial pressures of CO2 and O-2 and 1,100 mu mol photons m(-2) s(-1). This observation suggested the existence of an alternative electron flux (Ja). Ja was divided into O-2-dependent [Ja(O-2-depend)] and O-2-independent [Ja(O-2-independ)] components. The magnitude of half Ja(O-2-depend), 7.5 to 9.5 mu mol e(-) m(-2) s(-1), and its apparent K-m for O-2, about 8.0 kPa, could be accounted for by the photoreduction of O-2 at PSI either mediated by ferredoxin or catalyzed by monodehydroascorbate reductase. The results indicated that Ja(O-2-depend) was driven by the water-water cycle. A decrease in the intercellular partial pressure of CO2 from 23 to 5.0 Pa at 21 kPa O-2 enhanced Ja(O-2-depend) by a factor of 1.3. Saturation of the activities of both the PCR and PCO cycles by increasing the photon flux density induced Ja. These results indicate the electron flux in PSII that exceeds the flux required for the PCR and PCO cycles induces the photoreduction of O-2 in the water-water cycle.