Camp P J, Huber S C, Burke J J, Moreland D E
United States Department of Agriculture, Agricultural Research Service, North Carolina State University, Raleigh, North Carolina 27650.
Plant Physiol. 1982 Dec;70(6):1641-6. doi: 10.1104/pp.70.6.1641.
Changes in activities of photosynthetic enzymes and photochemical processes were followed with aging of vegetative and flag leaves of wheat (Triticum aestivum L. cv Roy). Activities of stromal enzymes began to decline prior to photochemical activities. In general, total soluble protein and the activities of ribulose-1,5-bisphosphate carboxylase and NADP-triose-phosphate dehydrogenase declined in parallel and at an earlier age than leaf chlorophyll (Chl), leaf photosynthesis, and photosynthetic electron transport activity. Leaves appeared to lose whole chloroplasts as opposed to a general degradation of all chloroplasts based on three lines of evidence: (a) electron transport activity calculated on an area basis declined much earlier than the same data expressed on a Chl basis; (b) Chl content per chloroplast was similar for mature and senescent tissue; and (c) the absorbance at 550 nanometers (light scattering) per unit of Chl remained essentially constant until the end of senescence. Chloroplasts did, however, undergo some modifications before they were lost (e.g. loss of stromal enzyme activities), but the reduction in leaf photosynthesis was apparently caused by a loss of whole chloroplasts.
随着小麦（Triticum aestivum L. cv Roy）营养叶和旗叶的衰老，对光合酶活性和光化学过程的变化进行了跟踪研究。基质酶的活性在光化学活性之前就开始下降。一般来说，总可溶性蛋白以及1,5-二磷酸核酮糖羧化酶和NADP-磷酸丙糖脱氢酶的活性平行下降，且比叶片叶绿素（Chl）、叶片光合作用和光合电子传递活性下降的时间更早。基于三条证据，叶片似乎是失去了完整的叶绿体，而不是所有叶绿体的普遍降解：（a）以面积为基础计算的电子传递活性比以Chl为基础表示的相同数据下降得早得多；（b）成熟组织和衰老组织中每个叶绿体的Chl含量相似；（c）直到衰老结束，每单位Chl在550纳米处的吸光度（光散射）基本保持恒定。然而，叶绿体在丢失之前确实经历了一些变化（例如基质酶活性的丧失），但叶片光合作用的降低显然是由完整叶绿体的丢失引起的。
