Anthocyanin accumulation in the hypocotyl of an ABA-over producing male-sterile tomato (Lycopersicon esculentum) mutant

Anthocyanin accumulation is known to be regulated by light and plant hormones but its occurrence varies with plant species and/or organ and tissue, and it has been negatively correlated with male sterility. In this study, we have examined the light responsive changes in anthocyanin in an abscisic acid (ABA) over-producer, male-sterile 7B-1 mutant and wild-type (WT) tomato hypocotyls. The results show that light-induced anthocyanin accumulation in the hypocotyl was more in WT compared with the 7B-1 mutant and more so under white light (W) compared with blue light (B) or red light (R). In contrast, the chlorophyll content was greater in the mutant than in WT. Exogenous ABA caused a transitory increase in anthocyanin content in WT but a reduction in 7B-1 , both in W and B. The high level of anthocyanin in WT under light conditions was not correlated with increased mRNA levels of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and dihydroflavonol 4-reductase (DFR), some of the anthocyanin biosynthetic genes. However, the activity of PAL (EC 4.3.1.5) was higher in the WT than in 7B-1 hypocotyls, and exogenous ABA caused an increase in PAL activity in the WT but a reduction in the mutant. The results presented show that high ABA negatively affects anthocyanin accumulation and that in the 7B-1 mutant it is related, in part, to reduced PAL activity. The results also support the view that the 7B-1 mutant has a defect in light perception and ABA sensitivity.