Physiological characterization of exaggerated-photoresponse mutants of tomato

Four monogenic mutants in tomato (Lycopersicon esculentum Mill.), i.e. three recessive mutations, high-pigment-1 (hp-l), high-pigment-2 (hp-2), and atroviolacea (atv), and one dominant mutation, Intense pigmentation (Ip), were used in this study. These mutants all show exaggerated photoresponses during deetiolation and seedlings having shorter hypocotyls and higher anthocyanin levels. The hp-1 and hp-2 have higher chlorophyll levels in immature fruit, giving them a dark green colour. Spectrophotometrical and immunological analyses of phytochrome A and phytochrome B revealed no differences between the mutants and the wild types (WTs), suggesting that the mutants are not photoreceptor mutants. Both hp-1 and hp-2 accumulate high levels of anthocyanin in continuous blue (B) and red (R) broad-band light. In contrast, atv has a WT level of anthocyanin in B and an exaggerated response ill R. The It, mutant has the opposite response: a WT level of anthocyanin in R and an exaggerated response in B. In B and R pretreatment studies, all mutants show an enhanced R/far-red light (FR)-reversible response compared with WT, but the Ip mutant shows a preferentially enhanced response in B. The hp-1 mutant exhibits a strong amplification of both the low fluence rate response and high irradiance response components of anthocyanin biosynthesis in red light. The atv mutant shows the strongest amplification of the HIR component. The Ip mutant exhibits an exaggerated anthocyanin response in B. All four mutants exhibit a normal elongation response to supplementary FR during the daily photoperiod.