Wittmann Christiane, Pfanz Hardy, Loreto Francesco, Centritto Mauro, Pietrini Fabrizio, Alessio Giorgio
Institute ofApplied Botany, University of Duisburg-Essen, 45117 Essen, Germany.
Plant Cell Environ. 2006 Jun;29(6):1149-58. doi: 10.1111/j.1365-3040.2006.01495.x.
In illuminated stems and branches, CO2 release is often reduced. Many light-triggered processes are thought to contribute to this reduction, namely photorespiration, corticular photosynthesis or even an inhibition of mitochondrial respiration. In this study, we investigated these processes with the objective to discriminate their influence to the overall reduction of branch CO2 release in the light. CO2 gas-exchange measurements of young birch (Betula pendula Roth.) branches (< 1.5 cm) performed under photorespiratory (20% O2) and non-photorespiratory (< 2%) conditions revealed that photorespiration does not play a pre-dominant role in carbon exchange. This suppression of photorespiration was attributed to the high CO2 concentrations (C(i)) within the bark tissues (1544 +/- 227 and 618 +/- 43 micromol CO2 mol(-1) in the dark and in the light, respectively). Changes in xylem CO2 were not likely to explain the observed decrease in stem CO2 release as gas-exchange measurements before and after cutting of the branches did not effect CO2 efflux to the atmosphere. Combined fluorescence and gas-exchange measurements provided evidence that the light-dependent reduction in CO2 release can pre-dominantly be attributed to corticular refixation, whereas an inhibition of mitochondrial respiration in the light is unlikely to occur. Corticular photosynthesis was able to refix up to 97% of the CO2 produced by branch respiration, although it rarely led to a positive net photosynthetic rate.
在有光照的茎和枝中，二氧化碳释放量通常会降低。许多由光触发的过程被认为导致了这种降低，即光呼吸、皮层光合作用，甚至是对线粒体呼吸的抑制。在本研究中，我们对这些过程进行了调查，目的是区分它们对光照下枝条二氧化碳释放总量降低的影响。在光呼吸（20%氧气）和非光呼吸（<2%）条件下，对年轻白桦（Betula pendula Roth.）枝条（<1.5厘米）进行的二氧化碳气体交换测量表明，光呼吸在碳交换中并不起主要作用。这种对光呼吸的抑制归因于树皮组织内的高二氧化碳浓度（C(i)）（黑暗和光照条件下分别为1544±227和618±43微摩尔二氧化碳摩尔(-1)）。木质部二氧化碳的变化不太可能解释观察到的茎二氧化碳释放量的下降，因为在枝条切断前后进行的气体交换测量并未影响向大气中的二氧化碳排放。荧光和气体交换联合测量提供了证据，表明光照下二氧化碳释放量的降低主要可归因于皮层再固定，而光照下线粒体呼吸不太可能受到抑制。皮层光合作用能够再固定高达97%的枝条呼吸产生的二氧化碳，尽管它很少导致正的净光合速率。
