Does oxidative stress metabolism play a role in Zantedeschia aethiopica spathe senescence?

Abstract

Plant senescence is a natural regulated and programmed process that leads ultimately to cell death. Numerous studies in different plant species have suggested a role for reactive oxygen species (ROS) in the progress of senescence programs, which is frequently associated with the degradative aspects of senescence physiology. The general increase of ROS during leaf aging as well as their damage products are probably due to the induction of the generating systems of these oxidative species and/or to a decrease in the protective mechanisms against activated oxygen forms. In this work the development of the C3 monocot Zantedeschia aethiopica floral spathe has been used as a natural model for studying the physiological and biochemical features of senescence. This photosynthetic leaf-like organ undergoes senescence displaying the common features of leaf senescence, such as loss of protein, chlorophyll and a decline on photosynthetic ability. Fruiting inhibits the ongoing spathe senescence and the regreening of its abaxial parenchyma cells is observed. Previous studies have shown that during the time course of spathe development some dramatic changes occurs, namely in the ultraestructure of chloroplasts and peroxisomes. Some evidences suggest that during the spathe whitening peroxissomes differentiate into glyoxysomes and chloroplasts into amyloplasts. The regreening process is followed by the restructuration of chloroplasts and peroxisomes, resulting in the re-acquisition of photosynthetic and photorespiratory capacities. In order to clarify the role of oxidative stress metabolism in spathe senescence two cytosolic ascorbate-glutathione cycle enzymes (cytCuZn-SOD and csAPX), directly involved in the antioxidant cellular mechanism were studied. The corresponding expression analysis was correlated with H2O2 content and lipid peroxidation level during the time course of Z. aethiopica spathe development suggesting an initial burst of H2O2 in the cytosol that could serve as a signal for the progression of the senescence program during spathe whitening. An integrated approach involving EST analysis and multiparallel expression profiling by macroarray analysis of senescence associated genes and oxidative stress related genes was also undertaken. Expression profile of oxidative stress related genes seems to parallel the expression profile of senescence associated genes suggesting an involvement of ROS in signalling and in degradative processes during Z. aethiopica spathe senescence.