Effects of light quality on the chloroplastic ultrastructure and photosynthetic characteristics of cucumber seedlings

To understand how light quality influences plant photosynthesis, we investigated chloroplastic ultrastructure, chlorophyll fluorescence and photosynthetic parameters, Rubisco and chlorophyll content and photosynthesis-related genes expression in cucumber seedlings exposed to different light qualities: white, red, blue, yellow and green lights with the same photosynthetic photon flux density of 100 μmol m^?2 s^?1. The results revealed that plant growth, CO₂ assimilation rate and chlorophyll content were significantly reduced in the seedlings grown under red, blue, yellow and green lights as compared with those grown under white light, but each monochromatic light played its special role in regulating plant morphogenesis and photosynthesis. Seedling leaves were thickened and slightly curled; Rubisco biosynthesis, expression of the rca, rbcS and rbcL, the maximal photochemical efficiency of PSII (Fv/Fm) and quantum yield of PSII electron transport (Ф_PSII) were all increased in seedlings grown under blue light as compared with those grown under white light. Furthermore, the photosynthetic rate of seedlings grown under blue light was significantly increased, and leaf number and chlorophyll content of seedlings grown under red light were increased as compared with those exposed to other monochromatic lights. On the contrary, the seedlings grown under yellow and green lights were dwarf with the new leaves etiolated. Moreover, photosynthesis, Rubisco biosynthesis and relative gene expression were greatly decreased in seedlings grown under yellow and green light, but chloroplast structural features were less influenced. Interestingly, the Fv/Fm, Ф_PSII value and chlorophyll content of the seedlings grown under green light were much higher than those grown under yellow light.     

Light Quality Regulates Lateral Root Development in Tobacco Seedlings by Shifting Auxin Distributions

Light is an important environmental regulator of diverse growth and developmental processes in plants. However, the mechanisms by which light quality regulates root growth are poorly understood. We analyzed lateral root (LR) growth of tobacco seedlings in response to three kinds of light qualities (red, white, and blue). Primary (1°) LR number and secondary (2°) LR density were elevated under red light (on days 9 and 12 of treatment) in comparison with white and blue lights. Higher IAA concentrations measured in roots and lower in leaves of plants treated with red light suggest that red light accelerated auxin transport from the leaves to roots (in comparison with other light qualities). Corroborative evidence for this suggestion was provided by elevated DR5::GUS expression levels at the shoot/root junction and in the 2° LR region. Applications of N-1-naphthylphthalamic acid (NPA) to red light-treated seedlings reduced both 1° LR number and 2° LR density to levels similar to those measured under white light; DR5::GUS expression levels were also similar between these light qualities after NPA application. Results were similar following exogenous auxin (NAA) application to blue light-treated seedlings. Direct [³H]IAA transport measurement indicated that the polar auxin transport from shoot to root was increased by red light. Red light promoted PIN3 expression levels and blue light reduced PIN1, 3–4 expression levels in the shoot/root junction and in the root, indicating that these genes play key roles in auxin transport regulation by red and blue lights. Overall, our findings suggest that three kinds of light qualities regulate LR formation in tobacco seedlings through modification of auxin polar transport.     

Gene expression profile of zeitlupe/lov kelch protein1 T-DNA insertion mutants in Arabidopsis thaliana: Downregulation of auxin-inducible genes in hypocotyls

Elongation of hypocotyl cells has been studied as a model for elucidating the contribution of cellular expansion to plant organ growth. ZEITLUPE (ZTL) or LOV KELCH PROTEIN1 (LKP1) is a positive regulator of warmth-induced hypocotyl elongation under white light in Arabidopsis, although the molecular mechanisms by which it promotes hypocotyl cell elongation remain unknown. Microarray analysis showed that 134 genes were upregulated and 204 genes including 15 auxin-inducible genes were downregulated in the seedlings of 2 ztl T-DNA insertion mutants grown under warm conditions with continuous white light. Application of a polar auxin transport inhibitor, an auxin antagonist or an auxin biosynthesis inhibitor inhibited hypocotyl elongation of control seedlings to the level observed with the ztl mutant. Our data suggest the involvement of auxin and auxin-inducible genes in ZTL-mediated hypocotyl elongation.     

Effects of red, far-red and blue light in maintaining growth in latitudinal populations of Norway spruce (Picea abies)

Seedlings of trees with a free growth pattern cease growth when night-lengths become shorter than a critical value, and this critical night-length (CNL) decreases with increasing latitude of origin. In northern populations, the light quality also appears to play an important role and a clinal variation in requirement for far-red (FR) light has been documented. In this study we dissected the light quality requirements for maintaining growth in different latitudinal populations of Norway spruce (Picea abies (L.) H. Karst.) using light emitting diodes for red (R), FR and blue (B) light, as 12 h day extension to provide 24 h photoperiod. At equal spectral photon flux, FR light was more effective than R light in maintaining growth, and the requirement of both R and FR increased with northern latitude of origin. One-to-one mixtures of R and FR light were more effective in maintaining growth than either FR or R light alone, indicating a possible interaction between R and FR light maintaining growth. Using the blue light as day extension could not prevent growth cessation in any of the populations, but delayed the bud set slightly in all populations. Our results suggest that phytochrome(s) are the primary photoreceptors in high irradiance responses maintaining growth in Norway spruce seedlings.     

The Effect of Monochromatic Light on α-Linolenic and Trans-3-Hexadecenoic Acids Biosynthesis, and Its Correlation to the Development of the Plastid Lamellar System

Seven day old etiolated Zea mays L. (cv. Wisconsin 355) seedlings were illuminated for 20 h under monochromatic radiations (100 Á pass band) produced by a spectral illuminator of high energy. Four regions of the visible spectrum were observed to stimulate chlorophyll synthesis. With poorly developed leaves (grown for 7 days at 22°C: experiment A). the most efficient wavelengths were found to be in the blue and green (between 445 and 505 nm). yellow (between 580 and 605 nm) and red (maximum 650 nm) parts of the spectrum. With well developed leaves (grown for 7 clays al 27°C: experiment B), a slight displacement of the maxima towards shorter wavelengths was observed. ¹⁴C-acetate was furnished to illuminated maize seedlings to follow lipid synthesis during greening. In the leaves of experiment A, the biosynthesis of α-linolenic acid and monogalactosyldiacylglycerol followed chlorophyll accumulation. In the more developed leaves of experiment B. containing higher amounts of galactolipids, the biosynthesis of α-linolenic acid and monogalactosyldiacylglycerol followed chlorophyll accumulation only in blue and yellow light. The biosynthesis of trans-3-hexadecenoic acid was strictly dependent on the wavelength of the irradiating light in the leaves of experiment A; it was optimal under blue (420 nm) and still very high under yellow (580 nm) and red (650 nm). In the more developed leaves of experiment B, it was optima in blue (445 nm) and in yellow (580 nm), and the red maximum was shifted to 630 nm. All C-trans-3-hexadecenoic acid was incorporated into phosphatidylglycerol. A marked relationship was observed between the intensity of galactolipid synthesis and the development of the lamellar system of maize plastids during greening. A positive correlation could be established between the biosynthesis of trans-3-hcxadeccnoie acid and the development of well constituted grana stacks in the plastids.     

Effect of partial drying and desiccation on somatic seedling quality in Norway and Serbian spruce

Somatic embryo quality is still a problem for many researchers. To improve the efficiency of germination, special procedures are used, such as partial drying of somatic embryos at high relative humidity or desiccation in the presence of supersaturated solutions of salt. In this work, cotyledonary somatic embryos of Norway spruce (Picea abies) and Serbian spruce (P. omorika) were placed on culture media (ME or BM-5) to germinate. We found that after 4 weeks of incubation on these media, hypocotyl and radicle growth of control (non-dried) somatic embryos of both species was not adequate to yield seedlings able to acclimatize to greenhouse conditions. Therefore, somatic embryos were partly dried at relative humidity of 97 % or desiccated at relative humidity of 79 %, for 2 or 3 weeks, and then placed on the Margara (ME) medium. Partial drying of somatic embryos at the higher relative humidity (97 %) enabled an improvement of radicle growth of germinating somatic embryos in both species. The highest conversion rate (45 %) was obtained for embryos of Norway spruce maintained for 2 weeks at relative humidity of 97 %. This treatment contributed to the improvement of germination and conversion efficiency of somatic embryos of Norway spruce, regardless of the drying period. Improved radicle growth facilitated development of better quality seedlings of this spruce species. In Serbian spruce, we did not obtain seedlings of sufficient quality, due to poor hypocotyl growth. Desiccation at humidity of 79 % for 3 weeks proved to be lethal to somatic embryos of both species.     

Blue Light Inhibition of Tuberization in a Day-Neutral Potato

In tests on the effects of light quality on potato tuberization, continuous blue light was found to consistently inhibit tuberization of tissue-cultured plantlets of Solanum tuberosum ssp. tuberosum cv. ??Norland??. Other tested cultivars, including sports of ??Norland??, formed tubers under continuous blue light. Microarrays identified BL, GA7ox, and Nudix genes as exhibiting altered expression in response to blue light treatment. Quantitative RT-PCR (qRT-PCR) showed that GA7ox RNA increased in ??Norland?? but not in ??Sangre?? plantlets in blue light compared to darkness. RNA levels of genes identified in the literature as having roles in potato tuberization were also measured using qRT-PCR. Levels of GA20o1x, but not GA2ox, RNA increased in response to blue light in ??Norland?? plantlets. BEL5 RNA content was greater under blue light compared to darkness for both ??Norland?? and ??Sangre?? plants. Levels of FT were not significantly different in blue light compared to dark-treated ??Norland?? plants, but were low in blue light-treated compared to dark-treated ??Sangre?? plants. Addition of ancymidol to ??Norland?? plants exposed to blue light overcame blue light inhibition of tuberization. Ancymidol prevents the oxidation of ent-kaurene to ent-kaurenoic acid, thus inhibiting gibberellin biosynthesis. These data suggest that blue light may increase GA accumulation in ??Norland?? plants, as has been shown to occur in Arabidopsis plants. The novel effect of blue light in inhibiting tuberization of ??Norland?? plants suggests that this system could be a useful tool in further elucidating the mechanisms of day-neutral potato tuberization.     

Effects of Quality, Intensity, and Duration of Light Breaks during a Long Night on Dormancy in Blue Spruce (Picea pungens Engelm.) Seedlings

Blue spruce (Picea pungens Engelm.) seedlings grow continuously when exposed to photoperiods exceeding 16 hours and enter dormancy within 4 weeks under photoperiods of 12 hours or less. Dormancy was prevented under 12-hour photoperiods by 2-hour light breaks of red light (1.70 μw/cm² at 650 nm) or high intensity white light (2,164.29 μw/cm² at 400 to 800 nm) given in the middle of the 12-hour night, and by continuous low intensity white light (204.76 μw/cm² at 400 to 800 nm). Two-hour light breaks of far red light (1.80 μw/cm² at 730 nm), red light followed by far red light, or low intensity white light were not effective in delaying dormancy. The results imply that the phytochrome system mediates the photoperiodic control of dormancy in blue spruce seedlings. The similarity of results obtained using the low intensity, long duration as against the high intensity, short duration light treatments suggests that the law of reciprocity applies in this response.     

Blue-light irradiation up-regulates the ent-kaurene synthase gene and affects the avoidance response of protonemal growth in Physcomitrella patens

Main conclusion

We report a novel physiological response to blue light in the moss Physcomitrella patens . Blue light regulates ent -kaurene biosynthesis and avoidance response to protonemal growth.

Abstract

Gibberellins (GAs) are a group of diterpene-type plant hormones biosynthesized from ent-kaurenoic acid via ent-kaurene. While the moss Physcomitrella patens has part of the GA biosynthetic pathway, from geranylgeranyl diphosphate to ent-kaurenoic acid, no GA is found in this species. Caulonemal differentiation in a P. patens mutant with a disrupted bifunctional ent-copalyl diphosphate synthase/ent-kaurene synthase (PpCPS/KS) gene is suppressed under red light, and is recovered by application of ent-kaurene and ent-kaurenoic acid. This indicates that derivatives of ent-kaurenoic acid, not GAs, might act as endogenous developmental regulators. Here, we found unique responses in the protonemal growth of P. patens under unilateral blue light, and these regulators were involved in the responses. When protonemata of the wild type were incubated under blue light, the chloronemal filaments grew in the opposite direction to the light source. Although this avoidance was not observed in the ent-kaurene deficient mutant, chloronemal growth toward a blue-light source in the mutant was suppressed by application of ent-kaurenoic acid, and the growth was rescued to that in the wild type. Expression analysis of the PpCPS/KS gene showed that the mRNA level under blue light was rapidly increased and was five times higher than under red light. These results suggest that regulators derived from ent-kaurenoic acid are strongly involved not only in the growth regulation of caulonemal differentiation under red light, but also in the light avoidance response of chloronemal growth under blue light. In particular, growth under blue light is regulated via the PpCPS/KS gene.     

Ethylene is not involved in the blue light-induced growth inhibition of red light-grown peas

Although the growth of intact plants is inhibited by irradiation with blue light, the growth rate of isolated stem segments is largely unaffected by blue light. We hypothesized that this loss of responsiveness was a result of ethylene production as part of the wounding response. However, we found no interaction between ethylene- and blue light-induced growth inhibition in dark- or red light-grown seedlings of pea (Pisum sativum L.). Inhibition of growth begins in dark-grown seedlings exposed to blue light within 3 min of the onset of blue light, as was known for red light-grown seedlings. By contrast, ethylene-induced inhibition of growth occurs only after a lag of 20 to 30 min or more (dark-grown seedlings) or 60 min (red light-grown seedlings). Also, the inhibition response of red light-grown seedlings is the same whether ethylene is present from the onset of continuous blue-light treatment or not. Finally the spatial distribution of inhibition following blue light was different from that following ethylene treatment.     

Analyzing photosynthetic activity and growth of Solanum lycopersicum seedlings exposed to different light qualities

To investigate how light quality influences tomato (Solanum lycopersicum L) seedlings, we examined changes in plant growth, chloroplast ultrastructure, photosynthetic parameters and some photosynthesis-related genes expression levels. For this, tomato plants were grown under different light qualities with the same photosynthetic photon flux density: red (R), blue (B), yellow (Y), green (G) and white (W) lights. Our results revealed that, compared with plants grown under W light, the growth of plants grown under monochromatic lights was inhibited with the growth reduction being more significant in the plants grown under Y and G lights. However, the monochromatic lights had their own effects on the growth and photosynthetic function of tomato seedlings. The plant height was reduced under blue light, but expression of rbcS, rbcL, psbA, psbB genes was up-regulated, and the ΦPSII and electron transport rate (ETR) values were enhanced. More starch grains were accumulated in chloroplasts. The root elongation, net photosynthetic rate (Pn), NPQ and rbcS and psbA genes expression were promoted under red light. Yellow light- and green light-illuminated plants grew badly with their lower Rubisco content and Pn value observed, and less starch grains accumulated in chloroplast. However, less influence was noted of light quality on chloroplast structure. Compared with yellow light, the values of ΦPSII, ETR, qP and NPQ of plants exposed to green light were significantly increased, suggesting that green light was beneficial to both the development of photosynthetic apparatus to some extent.     

Profiles of photosynthetic pigment accumulation and expression of photosynthesis-related genes in the marine cyanobacteria Synechococcus sp.: Effects of LED wavelengths

Light quality is a significant environmental factor that influences photosynthetic pigments in cyanobacteria. In the present study, we illuminated the marine cyanobacteria Synechococcus sp. with white (350 ～ 700 nm), red (630 nm), green (530 nm), and blue (450 nm) light emitting diodes (LEDs) and measured pigment levels (chlorophyll, carotenoid, and phycobiliprotein) and expression of photosynthesis-related genes (pebA, psbB, and psaE). The amount of photosynthetic pigments (total pigments, chlorophyll, and phycobiliproteins) was higher in the green and blue LED groups than in the white and red LED groups after 8 days of culture. The cells were prepared in a 1.5 mL solution for the analysis of the total pigments, chlorophyll, and carotenoid, and in a 2 mL for analysis of phycobiliproteins. The mRNA expression levels of pebA and psbB significantly increased after 8 days of cultivation under green and blue light, while the mRNA expression levels of psaE decreased. These results indicate that green and blue light increase the accumulation of photosynthetic pigments. In contrast red light induced mRNA expression of psaE and stimulated cell growth in Synechococcus sp.     

Photosynthetic action spectra of trees: I. Comparative photosynthetic action spectra of one deciduous and four coniferous tree species as related to photorespiration and pigment complements

Comparative isoenergetic action spectra of net photosynthesis for intact, current year foliage of five tree species were determined from 400 to 710 nm by CO₂ exchange analysis. The blue (400 to 500 nm) peak of net photosynthetic activity for the green broadleaves of red alder (Alnus rubra Bong.) was reduced to a plateau for the green needle-leaves of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) and Sitka spruce (Picea sitchensis [Bong.] Carr.), a shoulder for the blue-green needles of Colorado spruce (Picea pungens Engelm.), and a reduced shoulder for the blue-white needles of Blue spruce (Picea pungens var. hoospii). These differences were attributable neither to a differential blue light stimulation of photorespiration nor to a differential presence of a nonplastid screening pigment. The conifers all had similar carotenoid-chlorophyll ratios, with approximately 50% more carotenoid relative to chlorophyll as compared to red alder. Blue light absorption and low efficiency of energy transfer by the carotenoids probably accounts for the low net photosynthetic activity of the green conifers in blue light as compared to red alder. Leaf form per se (broad versus needle) had no distinguishable influence on these results.     

光质对白芨组培苗生理特性及酶基因表达的影响

为探讨光质对白芨(Bletilla striata)组培苗生长发育的影响,对不同光质下白芨组培苗的生长特征、抗氧化酶活性以及酶基因表达进行了研究。结果表明,蓝光和红光对白芨生长有显著促进作用,绿光的作用不明显。除了CAT外,不同光质处理白芨的APX、POD、SOD活性均呈上升趋势,且黄光处理的白芨SOD和APX活性最高,红光处理的POD活性最高,绿光处理的抗氧化酶活性比其他光质的低,蓝光处理35~45 d对抗氧化酶基因表达具有促进作用。因此,红光和黄光促进白芨生根组培苗的长高和生根;不同光质处理总体上提高了白芨氧化酶活性;白芨抗氧化酶基因的表达在蓝光处理下最大。