Maxwell K, Borland AM, Haslam RP, Helliker BR, Roberts A, Griffiths H
Environmental and Molecular Plant Physiology Laboratory, King George VI Building, Department of Agricultural and Environmental Science, The University, Newcastle upon Tyne NE1 7RU, United Kingdom.
Plant Physiol. 1999 Nov;121(3):849-856. doi: 10.1104/pp.121.3.849.
The regulation of Rubisco activity was investigated under high, constant photosynthetic photon flux density during the diurnal phases of Crassulacean acid metabolism in Kalanchoë daigremontiana Hamet et Perr. During phase I, a significant period of nocturnal, C(4)-mediated CO(2) fixation was observed, with the generated malic acid being decarboxylated the following day (phase III). Two periods of daytime atmospheric CO(2) fixation occurred at the beginning (phase II, C(4)-C(3) carboxylation) and end (phase IV, C(3)-C(4) carboxylation) of the day. During the 1st h of the photoperiod, when phosphoenolpyruvate carboxylase was still active, the highest rates of atmospheric CO(2) uptake were observed, coincident with the lowest rates of electron transport and minimal Rubisco activity. Over the next 1 to 2 h of phase II, carbamylation increased rapidly during an initial period of decarboxylation. Maximal carbamylation (70%-80%) was reached 2 h into phase III and was maintained under conditions of elevated CO(2) resulting from malic acid decarboxylation. Initial and total Rubisco activity increased throughout phase III, with maximal activity achieved 9 h into the photoperiod at the beginning of phase IV, as atmospheric CO(2) uptake recommenced. We suggest that the increased enzyme activity supports assimilation under CO(2)-limited conditions at the start of phase IV. The data indicate that Rubisco activity is modulated in-line with intracellular CO(2) supply during the daytime phases of Crassulacean acid metabolism.
在高且恒定的光合光子通量密度下，对落地生根景天酸代谢昼夜阶段的核酮糖-1,5-二磷酸羧化酶（Rubisco）活性调节进行了研究。在第一阶段，观察到显著的夜间C4介导的CO2固定期，生成的苹果酸在第二天（第三阶段）脱羧。白天大气CO2固定发生在一天的开始（第二阶段，C4-C3羧化）和结束（第四阶段，C3-C4羧化）。在光周期的第1小时，当磷酸烯醇式丙酮酸羧化酶仍有活性时，观察到大气CO2吸收速率最高，同时电子传递速率最低且Rubisco活性最小。在第二阶段接下来的1至2小时内，在最初的脱羧期氨甲酰化迅速增加。在第三阶段开始2小时后达到最大氨甲酰化（70%-80%），并在苹果酸脱羧导致的CO2浓度升高条件下维持。在整个第三阶段，初始和总Rubisco活性增加，在第四阶段开始时，光周期9小时达到最大活性，此时大气CO2吸收重新开始。我们认为，酶活性增加支持了第四阶段开始时CO2受限条件下的同化作用。数据表明，在景天酸代谢的白天阶段，Rubisco活性与细胞内CO2供应呈线性调节。
