Transient increase in the level of mRNA for a germin-like protein in leaves of the short-day plant Pharbitis nil during the photoperiodic induction of flowering.

A cDNA corresponding to an in vivo labeled protein whose level increased during flower-inductive darkness in the cotyledon of the short-day plant Pharbitis nil Choisy cv. Violet was isolated and characterized. The deduced amino-acid sequence of the protein (designated PnGLP; P.nil germin-like protein) showed homology to that of a GLP of Sinapis alba, a leaf protein, the mRNA accumulation of which showing circadian oscillations. PnGLP mRNA was detected specifically in the cotyledon and leaf, in particular, in the young expanded cotyledon and leaf. Accumulation of PnGLP mRNA increased transiently during flower-inductive darkness and peaked at a time that corresponded approximately to the critical night length. This mRNA peak was reduced by a brief exposure to red light at the 8th hour of darkness. The level of PnGLP mRNA peaked about 10 h from the beginning of the dark period, whereas it was reported that the level of mRNA for GLP of a long-day plant S. alba increased about 14 h from the beginning of the light period. Thus, the different time courses of accumulation of the mRNAs for leaf-specific GLPs appear to reflect the differences in photoperiodic responses of each plant.