PHOTOCONTROL OF ANTHOCYANIN BIOSYNTHESIS IN TOMATO

Juvenile anthocyanin biosynthesis has been studied in dark-grown seedl ings of tomato (Lycopersicon esculentum Mill.) wild types (WTs) and ph otomorphogenic mutants. During a subsequent 24-hr period of monochroma tic irradiation at different fluence rates of red light (R) the fluenc e-rate response relationships for induction of anthocyanin in all the WTs are similar, yet complex, showing a response at low fluence rates (LFRR) followed by a fluence rate-dependent high irradiance response ( HIR). In the hypocotyl this response is restricted to the sub-epiderma l layer of cells. The high-pigment-1 (hp-1) mutant exhibits st strong amplification of both response components. The atroviolacea (atv) muta nt shows strongest amplification of the HIR component. In contrast, a transgenic line overexpressing an oat phytochrome A gene (PHYA3(+)) sh ows a most dramatic amplification of the LFRR component. The far-red l ight (FR)-insensitive (fri) mutant, deficient in phytochrome A (phyA), lacks the LFRR component whilst retaining a normal HIR. The temporari ly R-insensitive (fri) mutant, deficient in phytochrome B1 (phyB1) ret ains the LFRR, but lacks the HIR. The hp-1,fri and hp-1,tri double mut ants exhibit amplified, yet qualitatively similar responses to the mon ogenic fri and tri mutants. The fri,tri double mutant lacks both respo nse components in R, but a residual response to blue light (B) remains . Similarly, the aurea (au) mutant deficient in phytochrome chromophor e biosynthesis and presumably all phytochromes, lacks both response co mponents in the R and FR regions of the spectrum. Experiments at other wavelengths demonstrate that while there is only a small response in the FR spectral region (729 nm) in tomato, there is an appreciable HIR response in the near FR at 704 nm, which is retained in the tri mutan t. This suggests that the labile phyA pool participates in the HIR at this wavelength. The intense pigmentation (Ip) mutant appears to be sp ecifically deficient in the B1 induced anthocyanin biosynthesis. Adult plants, grown under fluorescent light/dark cycles, show a reduction o f anthocyanin content of young developing leaves upon application of s upplementary or end-of-day FR. The involvement of different phytochrom e species in anthocyanin biosynthesis based on micro-injection studies into the au mutant and studies using type specific phytochrome mutant s is discussed.