Differential expression of putative floral genes in Pharbitis nil shoot apices cultured on glucose compared with...

If, following an inductive treatment of 2 d of continuous darkness, shoot apices of Pharbitis nil are cultured 1 d later on White's medium supplemented with 2% sucrose, they cannot form carpels, but they can if they are cultured on 2% glucose. It was hypothesized that the differential effect of these sugars was because of differential expression of carpel-specific genes. Partial cDNA homologues to the Arabidopsis genes, LEAFY (PnLFY), AGAMOUS (PnAG1/2), and CRABS CLAWS (PnCRC1/2) were cloned. PnLFY was expressed in the shoot apex 1 d following the start of induction and remained higher than in non-induced apices for a further 6 d before exhibiting a major peak of expression on day 7. Peaks of expression of PnAG1 and PnAG2 spanned days 7-11, coinciding with the appearance of stamens and then carpels. The Pharbitis 'PnCRC2' showed greatest homology to Arabidopsis YABBY2 (PnYABBY). Its expression peaked on day 8 when the carpels first appeared. 'PnCRC1' showed greatest homology to Arabidopsis FILAMENTOUS (PnFIL). Its expression was approximately the same in inductive and non-inductive treatments. Apart from PnFIL these partial cDNAs could be used as markers to test the hypothesis concerning differential effects of sucrose and glucose. Cultured shoot apices from induced plants were sampled at weekly intervals. All four genes were expressed more strongly in the glucose compared with the sucrose treatment, most notably at day 17. A more intensive sampling (days 15-19) indicated that PnLFY and PnYABBY exhibited much higher expression on glucose compared with sucrose, most notably on days 15-16 and days 18-19.