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The effects of different growth regimes on gluconasturtiin concentration in watercress (Nasturtium officinale R. Br.) were investigated. Watercress plantlets at the 5th mature leaf stage (ca. 2 weeks old) were exposed to different day and night temperatures, to long (16 h) or short (8 h) days, to red (R) or far-red (FR) light given during the main long day photoperiod, and finally to R or FR light given at the end of the main photoperiod. Watercress plants grown under long days contained a 30-40% higher gluconasturtiin concentration and had a higher fresh weight than watercress plants grown under short days. Watercress plants grown under long days and temperatures of 15 or 10 degrees C had at least a 50% higher gluconasturtiin concentration, but a lower fresh weight, than that of plants grown at 20 or 25 degrees C. Watercress plants grown under metal halide light enriched with R light had approximately a 25-40% higher concentration of gluconasturtiin as compared to the FR-enriched plants. Likewise, a brief R light exposure at the end of the main photoperiod resulted in approximately a 25% or higher concentration of gluconasturtiin as compared to a FR end-of-day exposure. These data indicate that the concentration of gluconasturtiin in watercress can be significantly increased by growing plants at lower temperatures, under long days, and by exposure to R light.
Osmoregulation in opening stomata of epidermal peels from Vicia faba L. leaves was investigated under a variety of experimental conditions. The K(+) content of stomatal guard cells and the starch content of guard cell chloroplasts were examined with cobaltinitrite and iodine-potassium iodide stains, respectively; stomatal apertures were measured microscopically. Red light (50 micromoles per square meter per second) irradiation caused a net increase of 3.1 micrometers in aperture and a decrease of -0.4 megapascals in guard cell osmotic potential over a 5 hour incubation, but histochemical observations showed no increase in guard cell K(+) content or starch degradation in guard cell chloroplasts. At 10 micromoles per square meter per second, blue light caused a net 6.8 micrometer increase in aperture over 5 hours and there was a substantial decrease in starch content of chloroplasts but no increase in guard cell K(+) content. At 25 micromoles per square meter per second of blue light, apertures increased faster (net gain of 5.7 micrometers after 1 hour) and starch content decreased. About 80% of guard cells had a higher K(+) content after 1 hour of incubation but that fraction decreased to 10% after 5 hours. In the absence of KCl in the incubation medium, stomata opened slowly in response to 25 micomoles per square meter per second of blue light, without any K(+) gain or starch loss. In dual beam experiments, stomata irradiated with 50 micomoles per square meter per second of red light for 3 hours opened without detectable starch loss or K(+) gain; addition of 25 micomoles per square meter per second of blue light caused a further net gain of 4.4 micometers in aperture accompanied by substantial K(+) uptake and starch loss. Comparison of K(+) content in guard cells of opened stomata in epidermal peels with those induced to open in leaf discs showed a substantially higher K(+) content in the intact tissue than in isolated peels. These results are not consistent with K(+) (and its counterions) as the universal osmoticum in guard cells of open stomata under all conditions; rather, the data point to sugars arising from photosynthesis and from starch degradation as additional osmotica. Biochemical confirmation of these findings would indicate that osmoregulation during stomatal opening is the result of three key metabolic processes: ion transport, photosynthesis, and sugar metabolism.
The action spectrum of photoinduction of carotenoid biosynthesis in Verticillium agaricinum has a high peak in the near-UV region with very small peaks in the blue, yellow and red regions. This suggests that neither a flavoprotein nor a carotenoid could be the photoreceptor, but a new unknown pigment system. Sporulation however is not photoregulated and is unaffected by light in the near-UV region. So, mycochrome cannot be implicated in the sporulation of this fungus. Further, sporulation and carotenogenesis must be under separate regulatory control in this organism, but not necessarily so in other organisms.
Tobacco plants (Nicotiana tabacum L.) were grown on long or short photoperiods followed by 5 minutes of red or far red radiation each day. Plants that received 16-hour photoperiods had a significantly higher concentration of total alkaloids and total phenolics than those that received 8-hour photoperiods. Significantly higher total alkaloid content was found in plants that received red rather than far red radiation last each day. Within each photoperiod, plants that received far red had higher concentrations of soluble phenols, particularly of chlorogenic acid. The interactions among these variables upon alkaloid and phenolic contents are discussed.
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Variations in phytochrome status in grasses were provoked by end of day red and far-red treatments and above canopy irradiations. Lolium perenne L. and Lolium multiflorum Lam. plants developed more tillers when illuminated with higher red/far-red ratios. These results show that branching of grasses is controlled by phytochrome activity in a way similar to that in dicotyledon plants.
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Thin cell-layer explants (TCLs) have been proposed as favorable tissues for the study of root, vegetative shoot and flower formation. We tested the effects of pH, light quality, light quantity, and IBA and kinetin concentrations on the morphogenesis of TCLs cultured individually on a liquid medium. Alterations of the amounts of exogenously supplied IBA and kinetin were sufficient to induce the formation of roots, vegetative shoots and flowers on TCLs cultured on otherwise identical media. The type and number of organs formed were sensitive to the intensity of light (55, 75, 100 and 120 muEinsteins m-2 sec-1) under which TCLs were grown. Evidence was obtained that the effects of light on TCL morphogenesis were associated with photochemical degradation of IBA in the medium. Evaluation of the organogenesis that occurred in TCLs cultured on a medium containing a range of IBA and kinetin concentrations showed that the number and type of organs formed, and overall growth, were dependent upon the initial concentrations of auxin and cytokinin. We have developed the TCL culture system into a sensitive and reproducible bioassay for the study of morphogenesis. The advantages of using the TCL morphogenesis bioassay for the identification and study of molecules (e.g. cell wall oligosaccharides) that may regulate morphogenesis are discussed.
The Arabidopsis photoreceptors cry1, cry2 and phyB are known to play roles in the regulation of flowering time, for which the molecular mechanisms remain unclear. We have previously hypothesized that phyB mediates a red-light inhibition of floral initiation and cry2 mediates a blue-light inhibition of the phyB function. Studies of the cry2/phyB double mutant provide direct evidence in support of this hypothesis. The function of cryptochromes in floral induction was further investigated using the cry2/cry1 double mutants. The cry2/cry1 double mutants showed delayed flowering in monochromatic blue light, whereas neither monogenic cry1 nor cry2 mutant exhibited late flowering in blue light. This result suggests that, in addition to the phyB-dependent function, cry2 also acts redundantly with cry1 to promote floral initiation in a phyB-independent manner. To understand how photoreceptors regulate the transition from vegetative growth to reproductive development, we examined the effect of sequential illumination by blue light and red light on the flowering time of plants. We found that there was a light-quality-sensitive phase of plant development, during which the quality of light exerts a profound influence on flowering time. After this developmental stage, which is between approximately day-1 to day-7 post germination, plants are committed to floral initiation and the quality of light has little effect on the flowering time. Mutations in either the PHYB gene or both the CRY1 and CRY2 genes resulted in the loss of the light-quality-sensitive phase manifested during floral development. The commitment time of floral transition, defined by a plant's sensitivity to light quality, coincides with the commitment time of inflorescence development revealed previously by a plant's sensitivity to light quantity - the photoperiod. Therefore, the developmental mechanism resulting in the commitment to flowering appears to be the direct target of the antagonistic actions of the photoreceptors.
The quantity and quality of light required for light-stimulated cell expansion in leaves of Phaseolus vulgaris L. have been determined. Seedlings were grown in dim red light (RL; 4 micromoles photons m-2 s-1) until cell division in the primary leaves was completed, then excised discs were incubated in 10 mM sucrose plus 10 mM KCl in a variety of light treatments. The growth response of discs exposed to continuous white light (WL) for 16 h was saturated at 100 micromoles m-2 s-1, and did not show reciprocity. Extensive, but not continuous, illumination was needed for maximal growth. The wavelength dependence of disc expansion was determined from fluence-response curves obtained from 380 to 730 nm provided by the Okazaki Large Spectrograph. Blue (BL; 460 nm) and red light (RL; 660 nm) were most effective in promoting leaf cell growth, both in photosynthetically active and inhibited leaf discs. Far-red light (FR; 730 nm) reduced the effectiveness of RL, but not BL, indicating that phytochrome and a separate blue-light receptor mediate expansion of leaf cells.
Larvae of Pieris rapae (L.), the imported cabbage worm, were reared to the adult stage under controlled light conditions. Spectral quality affected their development. The effect of the long wave ultraviolet light was to significantly decrease developmental time. The light source used also appeared to exert an effect on pupal colouration.
The expression of the gene coding for the carotenogenic enzyme phytoene synthase is highly regulated. To study this, its promoter and truncated versions thereof were translationally fused to the luciferase gene as a reporter and these constructs were used to transform Arabidopsis thaliana. The full-length promoter was shown to be active in the dark, but mediated positive responses towards different light qualities (far-red, red, blue and white light). Among the herbicides tested, norflurazon and gabaculine showed no notable effects, while CPTA abolished light induction completely. Response towards different light qualities was mediated by a TATA box-proximal promoter region up to position -300, containing G-box-like elements involved in the distinction of different monochromatic light qualities applied. This is detected in electrophoretic mobility shift assays (EMSAs), which reveal differential complex formation. A TATA box distal region of the promoter was shown to be responsible for a high basal promoter activity that was not modulated by different light qualities. Using EMSAs, a novel cis-acting element ATCTA occurring in tandem between positions -854 and -841 proved to be decisive in this respect. The motif was found in several other promoter regions involved in carotenoid and tocopherol biosynthesis, as well as in the promoter regions mediating the expression of photosynthesis-related genes. The functional equivalence of the motifs was shown by successfully using the respective regions in EMSAs. We conclude that the ATCTA motif represents an element capable of mediating a coordinated regulation of these pathways at the transcriptional level.
In a detailed sterol analysis of the marine diatom Phaeodactylum tricornutum, free sterols as well as esterified and glycosylated conjugates were found. When the alga was grown under standard conditions (i.e., at 13 degrees C under white light), 64% of total sterols were steryl glycosides. In all sterol classes, except steryl esters, (24S)-24-methylcholesta-5,22E-dien-3 beta-ol (epibrassicasterol) was the major (80 to 99%) sterol component. Eight other sterols were identified. Growth under different light spectral quality (red, blue, yellow, and green) at 13 and 23 degrees C was examined. At 23 degrees C, a dramatic decrease in total sterol content was observed, especially under blue light. The distribution of sterols between free and conjugated forms as well as sterol profile inside each class was found to be strongly dependent on the light spectral quality at both temperatures.
The effect of light spectral quality on the growth of in vitro nodal cuttings of potato (Solanum tuberosum L.) cultivars Norland, Superior, Kennebec, and Denali were examined. The different light spectra were provided by Vita-Lite fluorescent (VF) (a white light control), blue fluorescent (BF), red fluorescent (RF), low-pressure sodium (LPS), and a combination of low-pressure sodium plus cool-white fluorescent lamps (LPS/CWF). For all cultivars, stem lengths after 4 wk were longest under LPS, followed by RF, LPS/CWF, VF, and BF (in descending order). Microscopic studies revealed that cells were shortest when cultured in BF or VF environments, and were longest in RF or LPS lamp environments. The highest number of axillary branches occurred on plantlets grown with LPS or LPS/CWF, whereas the lowest number occurred with BF. No leaf or stem edema (callus or gall-like growths) occurred with LPS or LPS/CWF lighting, and no edema occurred on cv. Norland plantlets, regardless of lighting. Results suggest that shoot morphologic development of in vitro grown potato plants can be controlled by controlling irradiant spectral quality.