WATERING CONVERTS A CAM PLANT TO DAYTIME CO2 UPTAKE
WATERING CONVERTS A CAM PLANT TO DAYTIME CO2 UPTAKE
复制标题
DOI：
10.1038/262574b0
复制
发表时间：
1976-01-01
期刊：
影响因子：
64.8
通讯作者：
NOBEL, PS
中科院分区：
文献类型：
--
作者：
HARTSOCK, TL;NOBEL, PS
植物已经确定了三种不同的光合作用方式1,2:(1)大多数植物有还原性戊糖磷酸或c3途径，其中co2与核酮糖-1,5-二磷酸（RuDP）结合产生两分子3-磷酸甘油酸，这是一种三碳化合物；(2) c4模式，其中第一个光合产物是四碳二羧酸，如草酰乙酸和苹果酸，在二氧化碳与磷酸烯醇丙酮酸（PEP）结合后形成；(3)在干旱地区许多多肉植物中发现的天冬酸代谢（CAM）。最后，气孔开启和二氧化碳净吸收发生在夜间，二氧化碳通过PEP羧化酶转化为有机酸。在白天，当内部释放的二氧化碳被关闭的气孔阻止离开时，有机酸被脱羧，组织酸度下降。在夜间，组织与周围空气之间的水汽浓度差较小，因此，CAM植物的夜间气孔开放导致了整体的水分保持。例如，在自然条件下，c4植物每固定二氧化碳损失的水分平均比CAM植物高6倍，c31植物高10倍。CAM植物的日净co2吸收量低于c3或c4植物，因此CAM植物生长相对较慢。
THREE different photosynthetic options have been identified in plants1,2: (1) most plants have the reductive pentose phosphate or C3pathway, where CO2is incorporated into ribulose-1,5-diphosphate (RuDP) to yield two molecules of 3-phosphoglyceric acid, a three-carbon compound; (2) the C4mode, where the first photosynthetic products are four-carbon dicarboxylic acids like oxaloacetate and malate formed following CO2incorporation into phosphoenolpyruvate (PEP); and (3) crassulacean acid metabolism (CAM), found in many succulent plants growing in arid regions. In the last, stomatal opening and net CO2uptake occur at night, CO2being incorporated by way of PEP carboxylase into organic acids. The tissue acidity decreases as the organic acids are decarboxylated during the day, when the internally released CO2is prevented from leaving by the closed stomata. The water vapour concentration difference between the tissue and ambient air is less at night, and thus the night-time stomatal opening of CAM plants leads to overall water conservation. For example, the water lost per CO2fixed averages about sixfold higher for C4plants and tenfold higher for C3ones than for CAM plants in natural conditions2. The net daily CO2uptake by CAM plants is less than for C3or C4plants, so CAM plants tend to be relatively slow growing.