Biosystèmes membranaires, CNRS (UPR 39), Gif-sur-Yvette, France.
Photosynth Res. 1993 Jul;37(1):49-60. doi: 10.1007/BF02185438.
Two genotypes ofLupinus albus L., resistant and susceptible to drought, were subjected to water deficiency for up to two weeks. Such treatment progressively lowered the leaf water content from about 85% to about 60% (water potential from -0.8 to -4.3 MPa). Light-saturation curves of the uncoupled electron transport were analyzed according to a simple kinetic model of separated or connected reversible photoreactions. It gives an extrapolated maximum rate (Vmax) and the efficiency for capturing light (Im, which is the light intensity at Vmax/2). For Photosystem 2, Vmax and, less markedly, Im, declined with increasing severity of drought treatment; the artificial donor, diphenylcarbazide, could not restore the activity. One cause of this Photosystem 2 inhibition could be the loss of active Photosystem 2 centers. Indeed, their concentration relative to chlorophyll, estimated by flash-induced reduction of dimethylquinone, was halved by a medium stress. To the extent that it was still not restored by diphenylcarbazide, the site of Photosystem 2 inactivation must have been close to the photochemical trap, after water oxidation and before or at plastoquinone pool. By relating electron transport rate to active centers instead of chlorophyll, no inhibition by drought was detected. Therefore, water stress inactivates specifically Photosystem 2, without impairing a downhill thermal step of electron transport. On the other hand, the decrease of Im suggests that antennae connected to inactive centers may transfer their excitation energy to active neighbors, which implies that antenna network remains essentially intact. Gel electrophoresis confirmed that the apoproteins of the pigment complexes were well conserved. In conclusion, the inactivation of Photosystem 2 may not be a physical loss of its centers and core antennae but probably reflects protein alterations or conformational changes. These may result from the massive decrease of lipids induced by drought (Meyer et al. 1992, Photosynth. Res. 32: 95-107). Both lupin genotypes behaved similarly but, for a same deficiency, the resistant seemed unexpectedly more sensitive to drought.
两种基因型的白 Lupinus albus L.，耐旱和易感，受到缺水处理长达两周。这种处理逐渐将叶片含水量从约 85%降低至约 60%（水势从-0.8 至-4.3 MPa）。非耦合电子传递的光饱和曲线根据分离或连接可逆光反应的简单动力学模型进行分析。它给出了外推的最大速率（Vmax）和光捕获效率（Im，即 Vmax/2 时的光强度）。对于光系统 2，Vmax 和 Im（受干旱处理严重程度影响较小）随干旱处理严重程度的增加而降低；人工供体二苯卡巴腙不能恢复其活性。光系统 2 抑制的一个原因可能是活性光系统 2 中心的损失。事实上，它们相对于叶绿素的浓度，通过二甲基醌的闪光诱导还原来估计，在中等胁迫下减半。在仍然不能被二苯卡巴腙恢复的情况下，光系统 2 失活的部位必须靠近光化学陷阱，在水氧化之后或在质体醌库之前或之中。通过将电子传递速率与活性中心而不是叶绿素相关联，没有检测到干旱的抑制作用。因此，水分胁迫特异性地使光系统 2失活，而不会损害电子传递的向下热步骤。另一方面，Im 的降低表明与失活中心相连的天线可能将其激发能量转移到活性相邻体，这意味着天线网络基本保持完整。凝胶电泳证实，色素复合物的脱辅基蛋白得到很好的保存。总之，光系统 2 的失活可能不是其中心和核心天线的物理损失，而是可能反映了蛋白质的改变或构象变化。这些可能是由干旱引起的大量脂质减少引起的（Meyer 等人，1992 年，光合作用研究。32：95-107）。两种羽扇豆基因型表现相似，但对于相同的缺乏，耐旱的似乎出乎意料地对干旱更为敏感。
