Two calcium dependent protein kinases are differently regulated by light and have different activity patterns during seedling growth in Pharbitis nil

Abstract

In this study using biochemical approaches we identified two calcium-dependent protein kinases (CDPKs) named PnCDPK52 and PnCDPK56 in soluble protein extracts from seedlings of Pharbitis nil. Both enzymes phosphorylated the specific substrate histone III-S in the presence of Ca2+ and cross-reacted with antibodies against the CDPK. PnCDPKs exhibited quite different activity and protein levels during germination and successive stages of seedling growth. PnCDPK52 protein level was high in seeds and during germination, whereas PnCDPK56 increased in the next stages of seedling growth, being the dominant enzymes in mature seedlings, of the light- and dark-grown plant. In all cases both activity and accumulation of protein PnCDPK56 was higher in dark grown plants whereas exposure to light reduced both factors. When etiolated cotyledons were exposed to light, the activity of PnCDPK56 was reduced to the basal level within 5 h. Conversely, increasing activity of PnCDPK56 in cotyledons of green plants shifted to darkness was extremely rapid, reaching the maximum level after just 1 h of darkness and then gradually decreased. Further lengthening of the darkness to 16 h resulted in a strong increase in activity at 12 h. These data indicate that at least two isoforms of CDPK are involved in germination and seedling growth of P. nil. The differences in PnCDPKs strongly argue for the pleiotropic role of these isoforms. It seems that PnCDPK52 is associated with the germination process and PnCDPK56 with seedling growth. Moreover it suggests that activity of PnCDPK56 is controlled by light via the photoreceptor-dependent pathway. © 2011 The Author(s).