A TEMPORARILY RED LIGHT-INSENSITIVE MUTANT OF TOMATO LACKS A LIGHT-STABLE, B-LIKE PHYTOCHROME

We have selected four recessive mutants in tomato (Lycopersicon escule ntum Mill.) that, under continuous red light (R), have long hypocotyls and small cotyledons compared to wild type (WT), a phenotype typical of phytochrome B (phyB) mutants of other species. These mutants, which are allelic, are only insensitive to R during the first 2 days upon t ransition from darkness to R, and therefore we propose the gene symbol tri (temporarily red light insensitive). White light-grown mutant pla nts have a more elongated growth habit than that of the WT. An immunoc hemically and spectrophotometrically detectable phyB-like polypeptide detectable in the WT is absent or below detection limits in the tri(1) mutant. In contrast to the absence of an elongation growth response t o far-red light (FR) given at the end of the daily photoperiod (EODFR) in all phyB-deficient mutants so far characterized, the tri(1) mutant responds to EODFR treatment. The tri(1) mutant also shows a strong re sponse to supplementary daytime far-red light. We propose that the phy B-like phytochrome deficient in the tri mutants plays a major role dur ing de-etiolation and that other light-stable phytochromes can regulat e the EODFR and shade-avoidance responses in tomato.