Bartolomeo Lercari

PHOTOMORPHOGENIC RESPONSES TO UV RADIATION III: A COMPARATIVE STUDY OF UVB EFFECTS ON ANTHOCYANIN and FLAVONOID ACCUMULATION IN WILD-TYPE and aurea MUTANT OF TOMATO (Lycopersicon esculentum MILL.)

The UV‐mediated induction of anthocyanin and UV‐absorbing compounds was characterized in etiolated hypocotyls of wild‐type and aurea (au) mutant tomato seedlings. Ultraviolet radiation induced significant increases of anthocyanin and UV‐absorbing compounds in hypocotyls of die au mutant and of its isogenic wild‐type, but the differences in the time courses of UV‐induced pigment accumulation indicate mat different photoregulatory mechanisms are involved for each of these two groups of pigments. It appears mat prolonged presence of adequate levels of UVB (290–320nm) energy and consequently the action of a specific UVB photoreceptor are indispensable for the photoinduction of anthocyanin accumulation in UV‐irradiated hypocotyl of the au mutant that is missing the labile phytochrome pool. The large difference found between the wild‐type and the au mutant strongly indicate the involvement of labile phytochrome as the primary functional photoreceptor for the photoinduction of anthocyanin accumulation in wild‐type tomato hypocotyls. The UVB photoreceptor could at least partly replace the action of labile phytochrome (as far as anthocyanin accumulation is concerned) when the functional phytochrome pool is missing as in the au mutant. The general picture of UV‐mediated induction of total UV‐absorbing compounds shows only a macroscopic difference between wild‐type and die au mutant of tomato: the higher initial level (in darkness) of these compounds in die wild‐type in contrast to the au mutant. Although there is UV‐induced accumulation of UV‐absorbing compounds in bom genotypes, the levels in the au mutant never reach mat of the wild‐type under the same UV exposure. A UVB photosensor may play a more important role in the photoinduction of UV‐absorbing compounds. Indeed, in the absence of labile phytochrome, i.e. in the au mutant, a UVB‐absorbing photoreceptor alone is able to establish high responsiveness for the UV‐induced flavonoid accumulation.

Photomorphogenic responses to UV radiation : involvement of phytochrome and UV photoreceptors in the control of hypocotyl elongation in Lycopersicon esculentum

The photo-inhibition of Lycopersicon esculentum Mill, hypocotyl growth induced by UV radiation may be mediated by both phytochrome and UV-absorbing receptors. The inhibition of growth induced by continuous irradiation with high fluence rate UV radiation is similar in the au mutant, which is severely deficient in spectrophoto metrically and immunochemically detectable phytochrome, and in the isogenic wild type. Parallel irradiation with 692 nm light, which is equivalent to UV radiation for the phytochrome system in our experimental conditions, induced at high photon fluence rates a significant increase in hypocotyl growth in the au mutant. The same light treatments inhibited the hypocotyl growth of the wild type. The responses of water-grown seedlings and chlorophyll-free seedlings (streptomycin and norflurazon treated seedlings) were compared. Water-grown and chlorophyll-free seedlings responded similarly to UV radiation. The presence of chlorophyll correlates with a significant increase in hypocotyl growth of au mutants irradiated with 692 nm light. These results support the conclusion that UV-induced inhibition of growth in the au mutant is independent of phytochrome.

ANALYSIS OF LASER-INDUCED FLUORESCENCE LINE SHAPE OF INTACT LEAVES : APPLICATION TO UV STRESS DETECTION

Abstract— In vivo laser‐induced fluorescence spectra of intact leaves of healthy and UV‐irradiated Salvia splendens plants excited at 337 nm by a nitrogen laser were recorded using an optical multichannel analyzer system. The spectra showed the typical fluorescence bands centered around 450, 530, 685 and 730 nm. Exposure to UV radiation changed the relative intensity values of these bands and their peak positions. The analysis of the acquired spectra in terms of a linear combination of Gaussian bands was carried out to determine accurately the peak positions and the relative intensity contribution of the various bands to the laser‐induced fluorescence spectra on healthy and UV‐treated plants of different age.

Photomorphogenic control of shoot regeneration from etiolated and light-grown hypocotyls of tomato

We have investigated the role of phytochrome in the photocontrol of shoot regeneration from hypocotyls of tomato (Lycopersicon esculentum Mill.) by comparing the regenerative capability of explants obtained from etiolated and light grown seedlings of an aurea (au) mutant and its isogenic wild type. No shoot regeneration was displayed by etiolated aurea hypocotyls. While significant regeneration was shown by etiolated wild type explants. De-etiolated explants of both genotypes were able to regenerate shoots if cultured in presence of 16 h light/8 h dark cycles. When cultured in darkness on a medium devoid of hormones no one explant regenerated shoots. Out of more than 500 aurea explants, only one differentiated a shoot under continuous red and far red light, while significant shoot regeneration from wild type hypocotyl explants was induced by both the wavebands. Hypocotyl cultures under constant red, far red and blue light showed a position-dependent capability of regenerate shoots. We propose that the phytochrome play a crucial role in shoot regeneration from hypocotyl explants of tomato. Furthermore we provide evidence that a gradient in phytochrome content between the different segments of the hypocotyl is involved in the position-dependent capability of hypocotyl cells of regenerate shoots.

The Use of UV Radiation to Control the Architecture of Salvia splendens Plants. I. Effects on Plant Growth, Water Relations and Gas Exchange

In experiments with Salvia splendens plants grown in the greenhouse we evaluated the possible use of irradiation with unfiltered UV (UVA + UVB + UVC) lamps for the control of plant growth. The effect of UV Irradiation on the growth of S. splendens plants in the grcenhouse was closely dependent on the growing season and the level of available photosynthetically active radiation. In summer UV treatments were ineffective, but in the low light conditions of winter UV irradiation inhibited the growth via both photomorphogenic and photosynthetic effects. The reduction of stomatal conductance and expansion growth, which in turn depressed photosynthesis and dry matter accumulation, were not a consequence of an impairment of plant water status but appeared to be a direct UV effect on stomata and cell wall rheological propertles. Our findings suggest that the use of unfiltered UV irradiation could become an effective tool for the regulation of growth in greenhouse crops, particularly during the poor light conditions of the winter season.

Identification of retinal in higher plants: Is a rhodopsinlike protein the blue light receptor?

Abstract We here report the purification and identification of all- trans -retinal by column chromatography, HPLC and GC-MS in a tomato mutant ( Lycopersion esculentum Mill. aurea mutant). Since retinal, wherever present, is almost exclusively associated to an opsin to form a light-sensitive complex (rhodopsin-like proteins), this finding suggests that a rhodopsin-like protein could function as a blue light photoreceptor in higher plants.

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.)

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.

Light Quality Influences Indigo Precursors Production and Seed Germination in Isatis tinctoria L. and Isatis indigotica Fort.

Isatis tinctoria L. and Isatis indigotica Fort. are biennial herbaceous plants belonging to the family of Cruciferae that are used as a source of natural indigo and show several morphological and genetic differences. Production of indigo (indigotin) precursors, indican (indoxyl β‐D glucoside) and isatan B (indoxyl ketogluconate), together with seed germination ability were compared in Isatis tinctoria and Isatis indigotica grown under six different light conditions (darkness, white, red, far red, blue, yellow light) at 25°C. Light quality influenced both germination and production of indigo precursors in the two Isatis species. Different responsiveness to far red and blue light was observed. Indeed, a detrimental effect on germination by blue and far red light was found in I. tinctoria only. Different amounts of isatan B were produced under red and far red light in the two Isatis species. In I. tinctoria, the level of main indigo precursor isatan B was maximal under red light and minimal under far red light. Whereas in I. indigotica far red light promoted a large accumulation of isatan B. The photon fluence rate dependency for white and yellow light responses showed that the accumulation of indigo precursors was differently influenced in the two Isatis species. In particular, both white and yellow light enhanced above 40 μmol m−2s−1 the production of isatan B in I. indigotica while only white light showed a photon fluence dependency in I. tinctoria. These results suggest a different role played by the labile and stable phytochrome species (phyA and phyB) in the isatan B production in I. tinctoria and I. indigotica. I. indigotica, whose germination percentage was not influenced by light quality, demonstrated higher germination capability compared with I. tinctoria. In fact, I. tinctoria showed high frequency of germination in darkness and under light sources that establish high phytochrome photoequilibrium (red, white and yellow light). Germination in I. tinctoria was negatively affected by far red and blue light. I. indigotica seeds appear to be indifferent to canopy‐like light (far red). Our results provide further insights on the distinct behaviour of I. tinctoria and I. indigotica that belong to two different genetic clusters and different original environments.

Use of UV radiation for control of height and conditioning of tomato transplants (Lycopersicon esculentum Mill.)

Abstract Treatments in greenhouse of plug transplants of tomato ( Lycopersicon esculentum Mill. CV. Marmande) with supplemental UV radiation from fluorescent lamps were performed to control plant height and to condition them to outdoor conditions. Our investigation examined how tomato transplants responded to varying doses of UV radiation at different time of year (winter-spring). UV treatments, depending on the dose, significantly lowered plant height (up to 47%), leaf area (up to 65%) and shoot dry weight (up to 56%). The effects of UV treatments depended on both the daily applied dose and the environmental conditions. UV treatments were effective on tomato plants in winter, i.e., in the presence of low PAR, as well as in spring, i.e., in presence of high PAR. The main effect of the presence of high PAR was the enhancement of the threshold dose of UV energy required for induction of evident morphological damage to tomato plants. Blooming time and early production was similar in untreated and UV-treated plants, irrespective of the presence of the severe reduction of growth produced by UV radiation.

An analysis of UV-A effects of phytochrome-mediated induction of phenylalanine ammonia-lyase in the cotyledons of Lycopersicon esculentum mill

Abstract A 15-min exposure with UV-A light (320–400 nm) significantly increased the extractable activity of phenylalanine ammonia-lyase (PAL) 4 hr after the onset of the light treatment. The effect produced by a 15-min UV-A exposure was completelt reversed by a consecutive brief exposure to far red light. The UV-A- and red-mediated increases in PAL activity appear to be very similar with continuous exposure. Seedlings grown under 5 W/m 2 UV-A supplemented with blue, far red, and white light showed less PAL activity than control seedlings (i.e. exposed to blue, far red, and white light alone). Seedlings grown under 5W/m 2 UV-A supplemented with red light showed the same PAL activity as control seedlings exposed to UV-A and red light alone. It appears that prolonged UV-A exposure does not affect the response to continuous red light, but it is able to decrease significantly PAL activity in the blue and far red part of the spectrum. Furthermore, the positive and the inhibitory effects of prolonged UV-A irradiation demonstrate a different fluence rate requirement. The data indicated that phytochrome and a separate UV-A photoreceptor are involved in the photoregulation of PAL activity in cotyledons of tomato plants.