Regreening in spathes of Zantedeschia after anthesis: its physiology and control by fructification and hormones.

The mature pigmented spathe of Zantedeschia is characterized by a developmental process, wherein the spathe regreens after anthesis and prior to senescence of the inflorescence. Previous research has shown that spathe regreening involves redifferentiation of chloroplasts and re-accumulation of chlorophyll, but the detailed physiological changes associated with regreening are still largely unknown. Using Zantedeschia aethiopica and the Zantedeschia pentlandii variety 'Best Gold' as models, this study explores the physiological mechanism and possible roles of fructification, 6-benzylaminopurine (BAP) and gibberellin (GA3 ) in induction or progression of spathe regreening. Application of BAP stimulated regreening in spathe tissue of 'Best Gold' by enhancing accumulation of carotenoid and chlorophyll, and also increasing stacking of grana. In contrast, GA3 retarded formation of double-membrane lamella during chloroplast redifferentiation, thus delaying the onset of regreening. We suggest that these actions of BAP and GA3 have a synergistic effect in delaying the onset of regreening in 'Best Gold' so that when applied together retardation of chlorophyll accumulation, chloroplast redifferentiation and accumulation of carotenoids were enhanced. The elimination of fructification did not prevent the occurrence of regreening in either Zantedeschia model plants, indicating that fructification was not a prerequisite for the induction of regreening. It is still unclear how regreening in Zantedeschia is triggered. We propose that the onset of regreening in Zantedeschia is likely to be a genetically programmed event.