Physiological Characterization of a High‐pigment Mutant of Tomato

Abstract

Abstract— A high‐pigment (hp) mutant, which shows exaggerated phytochrome responses and three other genotypes of Lycopersicon esculenrum Mill. cv. Ailsa Craig: the aurea (au) mutant deficient in the bulk light‐labile phytochrome (PI) pool, the au, hp double mutant, and their isogenic wild type, were used in this study. Measurements of phytochrome destruction in red light (R) revealed that the exaggerated responses of the hp mutant are not caused by a higher absolute phytochrome level or a reduced rate of phytochrome destruction. Fluence‐response relationships for anthocyanin synthesis after a blue‐light pretreatment were studied to test if the hp mutant conveys hypersensitivity to the far‐red light (FR)‐absorbing form of phytochrome (Pfr), i.e. the threshold of Pfr required to initiate the response is lower. The response range for the hp mutant and wild type was identical, although the former exhibited a 6‐fold larger response. Moreover, the kinetics of anthocyanin accumulation in continuous R were similar in the wild‐type and hp‐mutant seedlings, despite the latter accumulating 9‐fold more anthocyanin. Since the properties of phytochrome are the same, the hp mutation appears to affect the state of responsiveness amplification, i.e. the same amount of Pfr leads to a higher response in the hp mutant. We therefore propose that the hp mutation is associated with an amplification step in the phytochrome transduction chain. Escape experiments showed that the anthocyanin synthesis after different light pretreatments terminated with a R pulse was still 50% FR reversible after 4–6 h darkness, indicating that the Pfr pool regulating this response must be relatively stable. However, fluence‐rate response relationships for anthocyanin synthesis and hypocotyl growth induced by a 24‐h irradiation with 451, 539, 649, 693, 704 and 729 nm light showed no or a severely reduced response in the au and au, hp mutants, suggesting the importance of PI in these responses. We therefore propose that the capacity for anthocyanin synthesis (state of responsiveness amplification) could be established by PI, while the anthocyanin synthesis is actually photoregulated via a stable Pfr pool. The Hp gene product is proposed to be an inhibitor of the state of responsiveness amplification for responses controlled by this relatively stable Pfr species.

Phenotype of the Tomato high pigment-2 Mutant Is Caused by a Mutation in the Tomato Homolog of DEETIOLATED1

“…The small but significant reduction in hypocotyl length and the small increase in anthocyanin found in the au hp-2 double mutant compared with au ( Figure 8) are likely, therefore, to be a result of hypersensitivity caused by the hp-2 mutation toward the low amounts of functional phytochrome present in the au mutant, which is estimated to be ‫%3ف‬ of wild-type levels (Parks et al, 1987;Adamse et al, 1989). Similar results have been found in the au hp-1 double mutant (Peters et al, 1992;Kerckhoffs et al, 1997b). …”

An Arabidopsis Mutant Hypersensitive to Red and Far-Red Light Signals

“…Thus, hp is likely a response amplification or an amplitude mutant rather than a light-hypersensitive mutant. Moreover, hp accumulates anthocyanin in leaves, stems, and fruits and also overaccumulates chlorophyll in fruits (Peters et al, 1992). These features were not seen in psi2.…”

“…In contrast, the psi2 phenotype is strictly dependent on red or far-red light. This observation emphasizes the specific involvement of PSI2 in the negative regulation of phytochrome pathways.Whereas the hypocotyl response of psi2 to light is reminiscent of the hp mutant of tomato (Peters et al, 1989(Peters et al, , 1992, there are differences between the two mutants. hp shows an increased reduction of hypocotyl length at all light intensities tested; by contrast, the reduction of hypocotyl elongation in psi2 is proportionately more at low light intensity rather than high light intensity, as compared with the wild type (Table 3).…”

The light‐hyperresponsive high pigment‐2dg mutation of tomato: alterations in the fruit metabolome

“…lycopene and carotenes), flavonoids and ascorbic acid have also been found in fruits of hp-1 mutant tomato plants (Baker & Tomes, 1964;Konsler, 1973;Soressi, 1975;Peters et al, 1992;Kerckhoffs et al, 1997;Levin et al, 2003). hp-1 is the tomato homologue of the human and A. thaliana gene encoding DDB1 (Lieberman et al, 2004;Liu et al, 2004).…”