Peroxisomal metabolism alterations associated to Z. aethiopica spathe senescence and regreening

Abstract

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 results have suggested that during the spathe whitening the peroxisomes differentiate into glyoxysomes and that the regreening process is followed by their conversion back into peroxisomes, resulting in the re-acquisition of photorespiratory capacity. In this work, changes in peroxisomal metabolism were studied in what concerns key-enzymes of glyoxylate and glycolate pathways. An increase in isocitrate lyase (ICL) activity during the late stages of spathe whitening suggests that there is an induction of glyoxysomal metabolism. The increase of hydroxypyruvate reductase (HPR) activity during spathe regreening, accompanied with the decrease of the glyoxylate key-enzyme ICL, points to an induction of leaf-type peroxisome metabolism thus suggesting the conversion of glyoxysomes back into peroxisomes. This hypothesis is further supported by the expression analysis of genes encoding enzymes from glycolate and glyoxylate pathways. The results will be discussed taking into account hydrogen peroxide levels evaluated during the time course of Z. aethiopica spathe development.