The 5'-upstream region of the class I patatin gene B33 directs strong expression of the beta-glucuronidase (GUS) reporter gene in potato tubers and in leaves treated with sucrose. Cis-acting elements affecting specificity and level of expression were identified by deletion analysis in transgenic potato plants. A putative tuber-specific element is located downstream from position -195. Nuclear proteins present in leaf and tuber extracts bind specifically to a conserved AT rich motif within this region. A DNA fragment between -183 and -143, including the binding site is, however, not able to enhance the expression of a truncated 35S promoter from cauliflower mosaic virus. Independent positive elements contributing to a 100-fold increase relative to the basic tuber-specific element are located between -228 and -195; -736 and -509, -930 and -736 and -1512 and -951. Sucrose inducibility is controlled by sequences downstream of position -228, indicating that the tuber-specific and sucrose-inducible elements are in close proximity.

We found that cadmium promoted flowering in Arabidopsis and suppressed nitric oxide accumulation in leaves. Supplementation with NO donor SNP delayed flowering, whereas application of NO scavenger cPTIO further promoted the transition from vegetative to reproductive stage under Cd stress. Semi-quantitative RT-PCR showed that Cd treatment up-regulated the expression of CONSTANS and FLOWERING LOCUS T, whereas down-regulated the expression of FLOWERING LOCUS C.Additional key words: nitric oxide, CONSTANS, FLOWERING LOCUS C, FLOWERING LOCUS T.