Temperature response of mesophyll conductance. Implications for the determination of Rubisco enzyme kinetics and for limitations to photosynthesis in vivo
Temperature response of mesophyll conductance. Implications for the determination of Rubisco enzyme kinetics and for limitations to photosynthesis in vivo
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DOI：
10.1104/pp.008250
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发表时间：
2002-12-01
期刊：
影响因子：
7.4
通讯作者：
Long, SP
中科院分区：
文献类型：
--
作者：
Bernacchi, CJ;Portis, AR;Long, SP
CO2从叶细胞间隙到叶绿体的传递传导率，定义为叶肉传导率（g（m））是有限的。因此，当CO2不饱和时，它将限制光合作用，就像现在大气中的C3叶子一样。我们对决定g（m）大小的过程知之甚少。虽然碳酸酐酶、水通道蛋白和CO2在水中的扩散率都被提出，但支配g（m）的过程是不确定的。本文研究了烟草成熟叶片g（m）对温度（10 ℃ ~ 40 ℃）的响应。cv W38）的叶片二氧化碳和水蒸气交换的测定，结合调制叶绿素荧光。这些测量揭示了对于g（m）的约2.2的温度系数（Q（10）），这表明通过蛋白质促进的过程进行控制，因为CO2在水中扩散的Q（10）约为1.25。此外，g（m），值在35 ℃至37.5 ℃最大，再次表明蛋白质促进的过程，但具有比Rubisco更低的失活能量。用g（m）的温度响应计算Rubisco的CO_2浓度，计算了10 ℃ ~ 40 ℃温度范围内Rubisco的动力学参数。利用这些参数，我们确定了g（m）对光合作用的限制。尽管随着温度的指数上升，g（m）并没有跟上增加的CO2吸收能力在Rubisco的网站。叶内CO2吸收的总限制的分数可归因于g（m）从10 ℃时的0.10上升到40 ℃时的0.22。这表明，CO2从细胞间空气空间到Rubisco的转移是光合作用的一个非常重要的限制，特别是在高温下。
CO2 transfer conductance from the intercellular airspaces of the leaf into the chloroplast, defined as mesophyll conductance (g(m)) is finite. Therefore, it will limit photosynthesis when CO2 is not saturating, as in C3 leaves in the present atmosphere. Little is known about the processes that determine the magnitude of g(m). The process dominating g(m) is uncertain, though carbonic anhydrase, aquaporins, and the diffusivity of CO2 in water have all been suggested. The response of g(m) to temperature (10degreesC-40degreesC) in mature leaves of tobacco (Nicotiana tabacum L. cv W38) was determined using measurements of leaf carbon dioxide and water vapor exchange, coupled with modulated chlorophyll fluorescence. These measurements revealed a temperature coefficient (Q(10)) of approximately 2.2 for g(m), suggesting control by a protein-facilitated process because the Q(10) for diffusion of CO2 in water is about 1.25. Further, g(m), values are maximal at 35degreesC to 37.5degreesC, again suggesting a protein-facilitated process, but with a lower energy of deactivation than Rubisco. Using the temperature response of g(m) to calculate CO2 at Rubisco, the kinetic parameters of Rubisco were calculated in vivo from 10degreesC to 40degreesC. Using these parameters, we determined the limitation imposed on photosynthesis by g(m). Despite an exponential rise with temperature, g(m) does not keep pace with increased capacity for CO2 uptake at the site of Rubisco. The fraction of the total limitations to CO2 uptake within the leaf attributable to g(m) rose from 0.10 at 10degreesC to 0.22 at 40degreesC. This shows that transfer of CO2 from the intercellular air space to Rubisco is a very substantial limitation on photosynthesis, especially at high temperature.