Zeiger E, Field C
Department of Biological Sciences, Stanford University, Stanford, California 94305.
Plant Physiol. 1982 Aug;70(2):370-5. doi: 10.1104/pp.70.2.370.
The photocontrol of the functional coupling between photosynthesis and stomatal conductance in the leaf was investigated in gas exchange experiments using monochromatic light provided by lasers. Net photosynthesis and stomatal conductance were measured in attached leaves of Malva parviflora L. as a function of photon irradiance at 457.9 and 640.0 nanometers.Photosynthetic rates and quantum yields of photosynthesis were higher under red light than under blue, on an absorbed or incident basis.Stomatal conductance was higher under blue than under red light at all intensities. Based on a calculated apparent photon efficiency of conductance, blue and red light had similar effects on conductance at intensities higher than 0.02 millimoles per square meter per second, but blue light was several-fold more efficient at very low photon irradiances. Red light had no effect on conductance at photon irradiances below 0.02 millimoles per square meter per second. These observations support the hypothesis that stomatal conductance is modulated by two photosystems: a blue light-dependent one, driving stomatal opening at low light intensities and a photosynthetically active radiation (PAR)-dependent one operating at higher irradiances.When low intensity blue light was used to illuminate a leaf already irradiated with high intensity, 640 nanometers light, the leaf exhibited substantial increases in stomatal conductance. Net photosynthesis changed only slightly. Additional far-red light increased net photosynthesis without affecting stomatal conductance. These observations indicate that under conditions where the PAR-dependent system is driven by high intensity red light, the blue light-dependent system has an additive effect on stomatal conductance.The wavelength dependence of photosynthesis and stomatal conductance demonstrates that these processes are not obligatorily coupled and can be controlled by light, independent of prevailing levels of intercellular CO(2). The blue light-dependent system in the guard cells may function as a specific light sensor while the PAR-dependent system supplies a CO(2)-modulated energy source providing functional coupling between the guard cells and the photosynthesizing mesophyll.
在气体交换实验中，利用激光提供的单色光，对叶片中光合作用与气孔导度之间功能耦合的光控作用进行了研究。在457.9纳米和640.0纳米波长下，测定了小锦葵（Malva parviflora L.）离体叶片的净光合作用和气孔导度随光子辐照度的变化。基于吸收或入射的光子量，红光下的光合速率和光合量子产率高于蓝光。在所有光强下，蓝光下的气孔导度高于红光。根据计算得出的气孔导度表观光子效率，在高于0.02毫摩尔每平方米每秒的光强下，蓝光和红光对气孔导度的影响相似，但在极低光子辐照度下，蓝光的效率要高出数倍。在光子辐照度低于0.02毫摩尔每平方米每秒时，红光对气孔导度没有影响。这些观察结果支持了以下假设：气孔导度受两个光系统调节：一个是蓝光依赖型光系统，在低光强下驱动气孔开放；另一个是光合有效辐射（PAR）依赖型光系统，在较高辐照度下起作用。当用低强度蓝光照射已经被高强度640纳米光照射的叶片时，叶片的气孔导度显著增加。净光合作用仅略有变化。额外的远红光增加了净光合作用，而不影响气孔导度。这些观察结果表明，在PAR依赖型系统由高强度红光驱动的条件下，蓝光依赖型系统对气孔导度具有累加效应。光合作用和气孔导度的波长依赖性表明，这些过程并非必然耦合，并且可以由光独立于细胞间CO₂的现有水平进行控制。保卫细胞中的蓝光依赖型系统可能作为一种特定的光传感器，而PAR依赖型系统提供一个受CO₂调节的能量源，实现保卫细胞与光合叶肉之间的功能耦合。
