Department of Botany, University of Delhi, Delhi - 110 007, India.
Z Naturforsch C J Biosci. 2012 Jul-Aug;67(7-8):418-28. doi: 10.1515/znc-2012-7-810.
Leaf detachment is a common signal that triggers both the differentiation of dormant epiphyllous buds as well as the onset of foliar senescence in Kalanchoe pinnata Lam. (Pers.). The present study looked for any probable correlations among selected attributes of foliar senescence, e.g. soluble proteins, chlorophylls a and b (Chl(a+b)), and membrane stability index (MSI), and the antioxidative status, e.g. phenolics, ferric reducing ability in plasma equivalence (FRAP(eq)), and membrane protection index (MPI), during epiphyllous bud differentiation. The experimental system comprised 0.75-cm leaf discs, with or without a dormant epiphyllous bud, cultured in vitro and exposed for ten days to continuous light or dark. A steady depletion of soluble proteins and Chl(a+b), and lowering of MSI in the leaf discs were observed, the decline being relatively faster and of higher magnitude in discs exposed to dark rather than to light. The pigment loss in discs with differentiating epiphyllous buds was greater and faster than in those lacking buds, a somewhat reverse situation was observed in case of soluble proteins. Simultaneously, a time-dependent decrease in the level of phenolics was also observed. Their content was found to be lower in discs exposed to dark as compared to light, pointing to a relationship with a higher rate of senescence-related degradative processes in the dark. The change in the content of Chl(a+b) was found to be significantly correlated with the variation in the level of phenolics. The average FRAP(eq) after ten days was one half that of the initial level, which could be correlated with the decreasing levels of phenolics (intra-correlation) and maximally correlated with variations in Chl(a+b) and protein contents (inter-correlation). Aqueous alcohol foliar extracts significantly (p < 0.05) protected membranes against peroxidative stress, although the pattern was not found to be in line with that of the phenolics content or FRAP(eq). The diminishing Chl(a+b) content was found to be maximally correlated with alterations in the membrane protection.
叶片脱落是触发景天科伽蓝菜属植物（Pers.）休眠附生芽分化以及叶片衰老的常见信号。本研究探讨了叶片衰老过程中某些特征，如可溶性蛋白、叶绿素 a 和 b（Chl(a+b)）以及膜稳定性指数（MSI），与抗氧化状态，如酚类、血浆等效还原力（FRAP(eq)）和膜保护指数（MPI）之间的可能相关性。实验系统包括带有或不带有休眠附生芽的 0.75cm 叶片圆盘，在体外培养并连续暴露于光照或黑暗中 10 天。观察到叶片圆盘的可溶性蛋白和 Chl(a+b)含量逐渐减少，MSI 降低，与光照相比，黑暗条件下叶片圆盘的下降速度更快，幅度更大。具有分化附生芽的叶片圆盘的色素损失比缺乏芽的叶片圆盘更大且更快，而可溶性蛋白则呈现出相反的情况。同时，还观察到酚类物质的水平随时间呈下降趋势。与光照相比，黑暗条件下叶片圆盘的酚类物质含量较低，这表明与黑暗条件下衰老相关降解过程的更高速率有关。Chl(a+b)含量的变化与酚类物质水平的变化显著相关。经过 10 天后，FRAP(eq)的平均值为初始值的一半，这与酚类物质（内相关）和最大程度上与 Chl(a+b)和蛋白质含量变化（互相关）的降低水平相关。10 天后，叶片水醇提取物显著（p < 0.05）保护了膜免受过氧化应激的影响，尽管其模式与酚类物质含量或 FRAP(eq)并不一致。Chl(a+b)含量的减少与膜保护的变化呈最大相关性。
