Winter K, Awender G
Lehrstuhl für Botanik II der Universität, Mittlerer Dallenbergweg 64, 8700 Würzburg, Federal Republic of Germany.
Plant Physiol. 1989 Jul;90(3):948-54. doi: 10.1104/pp.90.3.948.
Kalanchoë daigremontiana, a species possessing crassulacean acid metabolism, was grown at four photon flux densities (1300, 400, 60, and 25 micromole photons per square meter per second). In leaves which had developed at 1300 and 400 micromole photons per square meter per second, CO(2) was mainly incorporated through the lower, shaded leaf surfaces, and the chlorenchyma adjacent to the lower surfaces showed a higher degree of nocturnal acid synthesis than the chlorenchyma adjacent to the upper surfaces. In leaves acclimated to 60 and 25 micromole photons per square meter per second, the gradient in CAM activity was reversed, i.e. more CO(2) was taken up through the upper than through the lower surfaces and nocturnal acidification was higher in the tissue next to the upper surfaces. Total net carbon gain and total nocturnal acid synthesis were highest in leaves which had developed at 400 micromole photons per square meter per second. Chlorophyll content was markedly reduced in leaves which had developed at 1300 micromole photons per square meter per second, especially in the exposed adaxial parts. There was also a sustained reduction in photosystem II photochemical efficiency as indicated by measurements of the ratio of variable over maximum chlorophyll a fluorescence. These findings suggest that, at high growth photon flux densities, the reduced activity of the exposed portions of these succulent leaves is caused by (a) the adverse effects of excess light, (b) together with a genotypic component which favors CO(2) uptake and acid synthesis in the abaxial (lower) leaf parts even when light is not or only marginally excessive. This latter component is predominant at medium photon flux densities, e.g. at 400 micromole photons per square meter per second. It becomes overridden, however, under conditions of deep shade when strongly reduced light levels in the abaxial parts of the leaf chlorenchyma severely limit photosynthesis.
落地生根,一种具有景天酸代谢的植物,在四种光量子通量密度(分别为每秒每平方米1300、400、60和25微摩尔光量子)下生长。在以每秒每平方米1300和400微摩尔光量子生长的叶片中,二氧化碳主要通过叶片下部的背阴面被固定,与下表面相邻的叶肉组织比与上表面相邻的叶肉组织表现出更高程度的夜间酸合成。在适应每秒每平方米60和25微摩尔光量子的叶片中,景天酸代谢活性的梯度发生了反转,即通过上表面吸收的二氧化碳比通过下表面吸收的更多,并且上表面附近组织的夜间酸化程度更高。在以每秒每平方米400微摩尔光量子生长的叶片中,总净碳增益和总夜间酸合成最高。在以每秒每平方米1300微摩尔光量子生长的叶片中,叶绿素含量显著降低,尤其是在暴露的近轴部分。通过测量可变叶绿素a荧光与最大叶绿素a荧光的比率表明,光系统II的光化学效率也持续降低。这些发现表明,在高生长光量子通量密度下,这些肉质叶片暴露部分活性降低是由以下原因导致的:(a)过量光照的不利影响,(b)以及一种基因型成分,即使光照不过量或仅略微过量,这种成分也有利于叶片背面(下部)部分吸收二氧化碳和酸合成。后一种成分在中等光量子通量密度下占主导,例如在每秒每平方米400微摩尔光量子时。然而,在深度遮荫条件下,当叶片叶肉组织背面部分光照强度大幅降低严重限制光合作用时,这种成分就会被掩盖。