Phytochrome Control of Anthocyanin Biosynthesis in Tomato Seedlings: Analysis Using Photomorphogenic Mutants

Abstract

Abstract Anthocyanin biosynthesis has been studied in hypocotyls and whole seedlings of tomato ( Lycoperskon esculentum Mill.) wild types (WTs) and photomorphogenic mutants. In white light (WL)/dark (D) cycles the fri 1 mutant, deficient in phytochrome A (phyA), shows an enhancement of anthocyanin accumulation, whereas the tri 1 mutant, deficient in phytochrome Bl (phyBl) has a WT level of anthocyanin. Under pulses of red light (R) or R followed by far‐red light (FR) given every 4 h, phyA is responsible for the non‐R/FR reversible response, whereas phyBl is partially responsible for the R/FR reversible response. From R and blue light (B) pretreatment studies, B is most effective in increasing phytochrome responsiveness, whereas under R itself it appears to be dependent on the presence of phyBl. Anthocyanin biosynthesis during a 24 h period of monochromatic irradiation at different flu‐ence rates of 4 day‐old D‐grown seedlings has been studied. At 660 nm the fluence rate‐response relationships for induction of anthocyanin in the WT are similar, yet complex, showing a low fluence rate response (LFRR) and a fluence rate‐dependent high irradiance response (HIR). The high‐pigment‐1 ( hp‐1 ) mutant exhibits a strong amplification of both the LFRR and HIR. The fri 1 mutant lacks the LFRR while retaining a normal HIR. In contrast, a transgenic tomato line overexpressing the oat PHYA3 gene shows a dramatic amplification of the LFRR. The tri 1 mutant, retains the LFRR but lacks the HIR, whereas the fri 1 , tri 1 double mutant lacks both components. Only an LFRR is seen at 729 nm in WT; however, an appreciable HIR is observed at 704 nm, which is retained in the tri 1 mutant and is absent in the fri 1 mutant, indicating the labile phyA pool regulates this response component.