Differential Expression of Putative Floral Genes in Pharbitis nil Shoot Apices Cultured on Glucose Compared with Sucrose

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 with2%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 expressionon 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.