The involvement of indole-3-acetic acid in the control of stem elongation in dark- and lightgrown pea (Pisum sativum) seedlings

We investigated the role of auxin on stem elongation in pea (Pisum sativum L.) grown for 10 d in continuous darkness or under low-irradiance blue, red, far red and white light. The third internode of treated seedlings was peeled and the tissues (epidermis and cortex+central cylinder) were separately analyzed for the concentration of free and conjugated indole-3-acetic acid (IAA). Under red, far red and white light internode elongation was linearly related with the free IAA content of all internode tissues, suggesting that phytochrome-dependent inhibition of stem growth may be mediated by a decrease of free IAA levels in pea seedlings. The correlation between IAA and internode elongation, however, did not hold for blue light-grown seedlings. The hypothesis that the growth response under low-irradiance blue light might be correlated with the lack of phytochrome B signalling and changes in gibberellin metabolism is discussed in view of current knowledge on hormonal control of stem growth

An analysis of UV-A effects on phytochrome-mediatged induction of phenylalanine ammonia-lyase in the cotyledons of Lycopersicon esculentum Mill.

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/m2 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/m2 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 plant

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-2 s-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

DIPLOIDY AND CHROMOSOME ENDO-REDUPLICATION IN THE DEVELOPMENT OF EPIDERMAL-CELL LINES IN THE 1ST FOLIAGE LEAF OF DURUM-WHEAT (TRITICUM-DURUM DESF)

The development of epidermal cell lines in the first foliage leaf of Triticum durum was studied with a combined cytological and DNA cytophotometric analysis. It was shown that: (1) At emergence, the distal portion of the leaf is made of the cells pre-existing in the embryonic leaf and the mitotic activity is localized at the base of the leaf lamina (basal meristem). (2) The proliferating protoderm (outermost cell layer of the basal meristem) contains a meristematic cell population and a differentiating cell population. The cells produced by the protoderm differentiate with 2C, 4C, 8C, and 16 C nuclear DNA contents. (3) The endoreduplicated cells (EC) together with 4C cells form prominent cell rows in the leaf epidermis. The interstomatal cells (ISC) are all 2 C and the inter-hairs cells (IHC) are mostly 2 C (rare 4 C cells lie adjacent to the EC). (4) In the fully developed leaf, the frequency distribution of EC (8 C and 16 C) and 4C cells in a given epidermal segment (Fig. 1) corresponds to the frequency established in the epidermis differentiation zone (zone b, segment 1) at the time of development of that segment:e.g., segment 6 developed at 1-2 days after seed germination, segment 5 at 3 days after germination and so on. (5) Epidermal cell elongation starts in segment 1 and reachs its maximum in the older leaf segments, 5 and 6. The rate of cell elongation is independent of nuclear DNA content; chromosome endoreduplication precedes elongation. (6) The possibility of using epidermal cell parameters in studies on first leaf growth in T. durum is discussed

Changes in carotenoid and ascorbic acid contents in fruits of different tomato genotypes related to the depletion of UVB radiation

The aim of the present study was to investigate if the depletion of UV-B radiation affected the most representative carotenoids as well as the ascorbic acid content in tomato fruits, harvested at both breaker and firm red stages. To do this, three tomato genotypes, DRW 5981, HP 1, and Esperanza, were grown inside a greenhouse either covered with polyethylene transparent to UV-B or depleted of UV-B by a special covering film. The antioxidant properties of the fruits were evaluated on the water-insoluble fractions according to the ABTS method. UV-B effect on antioxidant activity was negligible in DRW and HP 1 genotypes, whereas it was detrimental in Esperanza at both ripening stages. This genotype seems to have a negligible capability of accumulating carotenoids and a great susceptibility to detrimental effects of UV-B; conversely, the DRW genotype shows high carotenoid levels under sunlight conditions and a further promotion by UV-B. On the other hand, the HP 1 mutant displays an intermediate behavior and represents the only genotype favored by UV-B with respect to ascorbic acid accumulation