Douthe Cyril, Dreyer Erwin, Brendel Oliver, Warren Charles R
INRA, Unité Mixte de Recherches 1147 'Ecologie et Ecophysiologie Forestières', F 54280 Champenoux, France.
University of Sydney, School of Biological Sciences, Heydon-Laurence Building, A08, The University of Sydney, NSW 2006, Australia.
Funct Plant Biol. 2012 Jun;39(5):435-448. doi: 10.1071/FP11190.
Mesophyll conductance to CO2 (g m) limits the diffusion of CO2 to the sites of carboxylation, and may respond rapidly (within minutes) to abiotic factors. Using three Eucalyptus species, we tested the rapid response of g m to irradiance under 21% and 1% O2. We used simultaneous measurements of leaf gas exchange and discrimination against 13CO2 with a tuneable diode laser absorption spectrometer. Measurements under 1% O2 were used to limit uncertainties due to 13C-12C fractionation occurring during photorespiration. Switching irradiance from 600 to 200µmolm-2s-1 led to a ≈60% decrease of g m within minutes in all species under both 21% O2 and 1% O2. The g m response to irradiance is unlikely to be a computation artefact since using different values for the parameters of the discrimination model changed the absolute values of g m but did not affect the relative response to irradiance. Simulations showed that possible rapid changes of any parameter were unable to explain the observed variations of g m with irradiance, except for13C-12C fractionation during carboxylation (b), which, in turn, is dependent on the fraction of leaf C assimilated by phospho-enol pyruvate carboxylase (PEPc) (β). g m apparently increased by ≈30% when O2 was switched from 21% to 1% O2. Again, possible changes of β with O2 could explain this apparent g m response to O2. Nevertheless, large irradiance or O2-induced changes in β would be required to fully explain the observed changes in g m, reinforcing the hypothesis that g m is responsive to irradiance and possibly also to O2.
叶肉细胞对二氧化碳的传导率（gm）限制了二氧化碳向羧化位点的扩散，并且可能在数分钟内对非生物因素做出快速响应。我们使用三种桉树物种，测试了在21%和1%氧气浓度下gm对光照强度的快速响应。我们同时使用可调谐二极管激光吸收光谱仪测量叶片气体交换和对13CO2的甄别。在1%氧气浓度下进行测量，以限制由于光呼吸过程中发生的13C-12C分馏所导致的不确定性。在21%氧气浓度和1%氧气浓度条件下，将光照强度从600微摩尔每平方米每秒切换到200微摩尔每平方米每秒，所有物种的gm在数分钟内均下降了约60%。gm对光照强度的响应不太可能是计算假象，因为使用不同的甄别模型参数值会改变gm的绝对值，但不会影响对光照强度的相对响应。模拟结果表明，除了羧化过程中的13C-12C分馏（b）之外，任何参数的可能快速变化都无法解释观察到的gm随光照强度的变化，而13C-12C分馏又取决于磷酸烯醇式丙酮酸羧化酶（PEPc）同化的叶片碳的比例（β）。当氧气从21%切换到1%时，gm明显增加了约30%。同样，β随氧气的可能变化可以解释这种明显的gm对氧气的响应。然而，需要光照强度或氧气诱导的β发生较大变化才能完全解释观察到的gm变化，这强化了gm对光照强度有响应并且可能也对氧气有响应的假设。
