Williams W E, Grivet C, Zeiger E
Department of Biological Sciences, Stanford University, Stanford, California, 94305.
Plant Physiol. 1983 Jul;72(3):906-8. doi: 10.1104/pp.72.3.906.
Net photosynthesis and stomatal conductance were measured in attached leaves of Paphiopedilum insigne. At 20 degrees C and a vapor-pressure deficit of 0.5 kilopascal, both net photosynthesis and stomatal conductance were light-saturated below 0.2 millimole per square meter per second, a response typical of shade plants. The absolute values of photosynthetic rate and conductance however were remarkably low, presumably reflecting an adaptation to the low-light, limited-nutrient habitat characteristic of these orchids. The leaves also showed a vapor-pressure deficit response, with net photosynthesis and conductance varying over a 2-fold range between 0.3 and 1.6 kilopascals.These results confirm that Paphiopedilum stomata are functional. The correlation between achlorophyllous guard cells and low conductance rates, however, singles them out as an exceptional biological system, exhibiting basic differences from typical stomata in higher plants. Available evidence showing that guard-cell chloroplasts are needed to sustain high conductance rates at moderate to high irradiances indicates that the genetic changes leading to the loss of chloroplast differentiation in Paphiopedilum guard cells were not deleterious because of the low conductance rates characteristic of this genus.
对带叶兜兰的附着叶片进行了净光合速率和气孔导度的测定。在20摄氏度、蒸汽压亏缺为0.5千帕的条件下，净光合速率和气孔导度在光照强度低于0.2微摩尔每平方米每秒时达到光饱和，这是阴生植物的典型反应。然而，光合速率和导度的绝对值非常低，这可能反映了这些兰花对低光照、有限养分生境的适应性。叶片还表现出对蒸汽压亏缺的响应，净光合速率和导度在0.3至1.6千帕之间变化了2倍。这些结果证实了带叶兜兰的气孔是有功能的。然而，无叶绿素保卫细胞与低导度率之间的相关性将它们作为一个特殊的生物系统区分出来，显示出与高等植物典型气孔的基本差异。现有证据表明，在中等至高光照强度下维持高导度率需要保卫细胞叶绿体，这表明导致带叶兜兰保卫细胞叶绿体分化丧失的基因变化并非有害，因为该属植物具有低导度率的特征。
