Department of Botany, National University of Singapore, Lower Kent Ridge Road, 0511, Singapore, Republic of Singapore.
Planta. 1989 Aug;179(1):115-22. doi: 10.1007/BF00395778.
The regulation of Crassulacean acid metabolism (CAM) in the fern Pyrrosia piloselloides (L.) Price was investigated in Singapore on two epiphytic populations acclimated to sun and shade conditions. The shade fronds were less succulent and had a higher chlorophyll content although the chlorophyll a:b ratio was lower and light compensation points and dark-respiration rates were reduced. Dawn-dusk variations in titratable acidity and carbohydrate pools were two to three times greater in fronds acclimated to high photosynthetically active radiation (PAR), although water deficits were also higher than in shade fronds. External and internal CO2 supply to attached fronds of the fern was varied so as to regulate the magnitude of CAM activity. A significant proportion of titratable acidity was derived from the refixation of respiratory CO2 (27% and 35% recycling for sun and shade populations, respectively), as measured directly under CO2-free conditions. Starch was shown to be the storage carbodydrate for CAM in Pyrrosia, with a stoichiometric reduction of "C3-skeleton" units in proportion to malic-acid accumulation. Measurements of photosynthetic O2 evolution under saturating CO2 were used to compare the light responses of sun and shade fronds for each CO2 supply regime, and also following the imposition of a photoinhibitory PAR treatment (1600 μmol·m(-2)·s(-1) for 3 h). Apparent quantum yield declined following the high-PAR treatment for sun- and shade-adapted plants, although for sun fronds CAM activity derived from respiratory CO2 prevented any further reduction in photosynthetic efficiency. Recycling of respiratory CO2 by shade plants could only partly prevent photoinhibitory damage. These observations provide experimental evidence that respiratory CO2 recycling, ubiquitous in CAM plants, may have developed so as to alleviate photoinhibition.
在新加坡,对适应阳光和遮荫条件的两种附生种群的蕨类植物 Pyrrosia piloselloides (L.) Price 进行了肉质化景天酸代谢(CAM)的调控研究。遮荫叶片的肉质化程度较低,叶绿素含量较高,尽管叶绿素 a:b 比值较低,光补偿点和暗呼吸速率降低。适应高光能有效辐射(PAR)的叶片,其可滴定酸度和碳水化合物库的早晚变化幅度是遮荫叶片的两到三倍,尽管水分亏缺也高于遮荫叶片。通过改变外部和内部 CO2 对附着叶片的供应,调节 CAM 活性的幅度。可滴定酸度中有相当大的比例是由呼吸 CO2 的再固定(分别为 27%和 35%用于阳光和遮荫种群的循环)直接在无 CO2 条件下测定。淀粉被证明是 Pyrrosia 中 CAM 的储存碳水化合物,与苹果酸积累成比例地减少“C3 骨架”单位。在饱和 CO2 下测量光合作用 O2 演化,用于比较每种 CO2 供应条件下阳光和遮荫叶片的光响应,以及在施加光抑制 PAR 处理(1600 μmol·m(-2)·s(-1) 3 h)之后。高光能处理后,阳光和遮荫适应植物的表观量子产量下降,尽管对于阳光叶片,CAM 活性源自呼吸 CO2,防止了光合作用效率的进一步降低。遮荫植物的呼吸 CO2 循环只能部分防止光抑制损伤。这些观察结果提供了实验证据,表明呼吸 CO2 循环在 CAM 植物中普遍存在,可能是为了缓解光抑制而发展起来的。