Photomorphogenic responses to UV radiation: Involvement of phytochrome and UV photoreceptors in the control of hypocotyl elongation in <i>Lycopersicon esculentum</i>

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.

Section: Hypocotyl Growthcontrasting

confidence: 81%

Physiological Characterization of a High‐pigment Mutant of Tomato

Peters

Schreuder

Verduin

et al. 1992

“…According to the classical photobiological techniques the action spectra and the kinetics of the responses must be established in order to identify the causal factors involved in UV-mediated responses (8,9). Ultraviolet-induced inhibition of elongation growth has been shown in different species, so it appears to be a general phenomenon (5,7,(12)(13)(14)(15)(16)(17). In this work we have measured the short-and long-term stem elongation responses to UV radiation of S. splendens plants by using linear voltage transducers interfaced with data loggers.…”

Section: Introductionmentioning

confidence: 99%

The Use of UV Radiation to Control the Architecture of Salvia splendens Plants. II. Relationships between PAR Levels and UV Radiation in the Photoregulation of Stem Elongation

Bertram

Lercari

1996

Self Cite

The effects of UV irradiation on stem elongation of Sulvia splendens plants preadapted to two and grown under four different irradiances of visible light, were studied using linear voltage differential transducers. The levels of radiant energy during the experimental phase showed a temporary and opposite effect during the day-time and the night-time: increasing levels of photosynthetically active radiation (PAR)? reduced stem growth during the day and enhanced elongation growth during the night. It appears, therefore, that similar final stem elongation in plants grown under very different PAR levels is the result of the algebraic sum of different and sometimes opposite effects of PAR on stem growth. Except for the controls, the plants received one UV treatment from Philips TL 12 40 W fluorescent tubes either in the middle of the light period or at the beginning of the dark period. The results show that the preadapting PAR conditions changed the sensitivity of the plants to both UV and to the following PAR conditions. The sensitivity of S. splendens to UV radiation is inversely correlated to the PAR levels before and during the UV treatments. Furthermore the presence of active photosynthetic and photomorphogenic systems, i.e. the presence of visible light during the UV treatment, decreases the sensitivity of the plants to UV radiation. Depending on PAR levels, the UV treatments given during the night induced a temporary inhibition of growth followed by a promotion of stem elongation.

“…Previous studies on the effects of UV radiation, between 300 and 400 nm, on tomato and cabbage stem elongation (Lercari et al, 1989(Lercari et al, , 1990 have shown that the inhibitory effect of UV radiation, at high photon thence rates, can be completely ascribed in some cases to the action of phytochrome; in other cases to the action of both phytochrome and a specific UV photoreceptor; and in yet other cases to the action of only a UV photoreceptor. Studies on conifer species (Sullivan and Teramura, 1988) showed a fluence-dependent, UV-induced reduction of seedling height in Pinus contorta, Pinus *To whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 97%

“…Since UV radiation induces phytochrome photoconversion (Butler et al, 1964;Lercari et al, 1989Lercari et al, , 1990 it is not possible with a single experimental approach to establish if the phytochrome system is involved or not in a UV-mediated response. In the present paper the involvement of phytochrome in the UV-mediated inhibition of hypocotyl elongation was studied using different experimental approaches: (a) by giving exposures of increasing duration to 692 nm and UV radiation, that are equivalent with respect to the phytochrome system (Lercari et al, 1989(Lercari et al, , 1990), (b) by giving various UV irradiations in which the UV spectral range was modified with specific cut-off filters.…”

Section: Introductionmentioning

confidence: 99%

“…The aurea mutant has reduced or absent photoregulation of chl albbinding (cab) proteins, chloroplast development and anthocyanin accumulation (Adamse et al, 1988, Oelmiiller andKendrick, 1991). Furthermore, hypocotyl elongation appears to be photoregulated very differently in the aurea mutant than in the isogenic wild type (Lercari et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

PHOTOMORPHOGENIC RESPONSES TO UV RADIATION. II: A COMPARATIVE STUDY OF UV EFFECTS ON HYPOCOTYL ELONGATION IN A WILD‐TYPE AND AN aurea MUTANT OF TOMATO (Lycopersicon esculentum Mill.)

Lercari

Sodi

1992

Self Cite

Abstract— Hypocotyl growth in etiolated seedlings of wild‐type and an aurea mutant of tomato (Lycopersicon esculenturn Mill.), that appears to be deficient in labile phytochrome, is strongly inhibited by UV radiation in the region of 300–400 nm. The role of phytochrome in the UV‐mediated inhibition of hypocotyl growth was studied using different experimental approaches: (1) by comparing the effectiveness of treatments of increasing duration of exposure to 692 nm and UV radiation; (2) by modifying the UV spectral range with specific cut‐off filters. The experimental results suggest that the UV‐induced inhibition of growth in wild‐type tomato is mediated to a large extent by the longer wavelengths of the UV‐A region and is mediated mainly by phytochrome. In contrast, at wavelengths < 305 nm a strong UV‐B effect was found in the aurea mutant, suggesting a preeminent action of a specific UV‐B absorbing photoreceptor that displays less action in the wild‐type.