Root-shoot interaction in the greening of wheat seedlings grown under red light

Wheat seedlings grown with roots exposed to constant red light (300-500 micromoles m-2 s-1) did not accumulate chlorophyll in the leaves. In contrast, seedlings grown with their roots shielded from light accumulated chlorophylls. Chlorophyll biosynthesis could be induced in red-light-grown chlorophyll-deficient yellow plants by either reducing the red-light intensity at the root surface to 100 micromoles m-1 s-1 or supplementing with 6% blue light. The inhibition of chlorophyll biosynthesis was due to impairment of the Mg-chelatase enzyme working at the origin of the Mg-tetrapyrrole pathway. The root-perceived photomorphogenic inhibition of shoot greening demonstrates root-shoot interaction in the greening process.     

Desensitization and recovery of phototropic responsiveness in Arabidopsis thaliana.

Phototropism is induced by blue light, which also induces desensitization, a partial or total loss of phototropic responsiveness. The fluence and fluence-rate dependence of desensitization and recovery from desensitization have been measured for etiolated and red light (669-nm) preirradiated Arabidopsis thaliana seedlings. The extent of desensitization increased as the fluence of the desensitizing 450-nm light was increased from 0.3 to 60 micromoles m-2 s-1. At equal fluences, blue light caused more desensitization when given at a fluence rate of 1.0 micromole m-2 s-1 than at 0.3 micromole m-2 s-1. In addition, seedlings irradiated with blue light at the higher fluence rate required a longer recovery time than seedlings irradiated at the lower fluence rate. A red light preirradiation, probably mediated via phytochrome, decreased the time required for recovery from desensitization. The minimum time for detectable recovery was about 65 s, and the maximum time observed was about 10 min. It is proposed that the descending arm of the fluence-response relationship for first positive phototropism is a consequence of desensitization, and that the time threshold for second positive phototropism establishes a period during which recovery from desensitization occurs.     

亚热带季雨林植物罗伞气体交换对光质的反应

亚热带季雨林林下阴生植物罗伞(Ardisia quinquegona)叶片的气体交换速率(PN.μmol.m~(-2),s~(-1))随光强(PFD,μmol,m~(-2),s~(-1))增高而增大。在光强低于80μmol,m~(-2),s~(-1),PN=29.21PFD×10~(-3)+0.36。在光强150μmol,m~(-2),s~(-1)对出现气体交换的光饱和现象。在低光强下,气孔传导率(G,m mol,m~(-2),s~(-1)与光强(m mol,m~(-2),s~(-1)的关系为G=265.6 PFD+4.6。在低光强下。开阔地的阳生灌木桃金娘(Rhodmyrtus tomentosa)的气体交换速率和气孔传导率与光强关系曲线的直线部分斜率皆较罗伞的低,在红光上,罗伞叶片气体交换速率(μmol,m~(-2),s~(-1)与光强(μmol,m~(-2),s~(-1)的关系为PN=32.4 PFD×10~(-3)-0.04。气孔传导率(m mol,m~(-2),s~(-1)与光强(m mol,m~(-2),s~(-1)的关系为G=339.08 PFD+7.37。同时气体交换速率的饱和红光光强亦较白光的高。在蓝光光强低时,气体交换速率(μmol,m~(-2),s~(-1))与光强(μmol,m~(-2),s~(-1))的关系为PN=13.54 PFD×10~(-3)—0.17,而气孔传导率(m mol,m~(-2),s~(-1))与光强(mμmol,m~(-2),s~(-1))的关系为G=80.5 PFD+4.35。在低的蓝光下,体交换速率和气孔传导率与光强关系曲线的直线部分斜率显著较在白光和红光下的低。罗伞叶片气体交换对红光的反应敏感。     

Blue light and phytochrome-mediated stomatal opening in the npq1 and phot1 phot2 mutants of Arabidopsis

Recent studies have shown that blue light-specific stomatal opening is reversed by green light and that far-red light can be used to probe phytochrome-dependent stomatal movements. Here, blue-green reversibility and far-red light were used to probe the stomatal responses of the npq1 mutant and the phot1 phot2 double mutant of Arabidopsis. In plants grown at 50 micromol m-2 s-1, red light (photosynthetic)-mediated opening in isolated stomata from wild type (WT) and both mutants saturated at 100 micromol m-2 s-1. Higher fluence rates caused stomatal closing, most likely due to photo-inhibition. Blue light-specific opening, probed by adding blue light (10 micromol m-2 s-1) to a 100 micromol m-2 s-1 red background, was found in WT, but not in npq1 or phot1 phot2 double mutant stomata. Under 50 micromol m-2 s-1 red light, 10 micromol m-2 s-1 blue light opened stomata in both WT and npq1 mutant stomata but not in the phot1 phot2 double mutant. In npq1, blue light-stimulated opening was reversed by far-red but not green light, indicating that npq1 has a phytochrome-mediated response and lacks a blue light-specific response. Stomata of the phot1 phot2 double mutant opened in response to 20 to 50 micromol m-2 s-1 blue light. This opening was green light reversible and far-red light insensitive, indicating that stomata of the phot1 phot2 double mutant have a detectable blue light-specific response.     

Light-stimulated cell expansion in bean (Phaseolus vulgaris L.) leaves

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.     

Properties of Proton Pumping in Response to Blue Light and Fusicoccin in Guard Cell Protoplasts Isolated from Adaxial Epidermis of Vicia Leaves

Guard cell protoplasts (GCPs) were isolated from the adaxial epidermis of Vicia leaves. The properties of isolated adaxial GCPs (ad GCPs) were compared with those of abaxial GCPs (ab GCPs) with respect to H+-pumping activity. A saturating pulse of blue light (200 [mu]mol m-2 s-1, 30 s) induced H+ pumping in both ad GCPs and ab GCPs under red light. The maximum rate of blue-light-dependent H+ pumping was slightly higher in ad GCPs than in ab GCPs, but the magnitude of H+ pumping in ad GCPs was 68% of that in ab GCPs. H+ pumping was responsive to the second pulse, and the rate and magnitude of the pumping increased with the time between two pulses. The periods required to achieve 50% of the maximum rate were 12 and 22 min for ad GCPs and ab GCPs, respectively. The rates of blue-light-dependent H+ pumping were saturable, with half-saturation at 630 [mu]mol m-2 (21 [mu]mol m-2 s-1, 30 s) for ad GCPs and 105 [mu]mol m-2 (3.5 [mu]mol m-2 s-1, 30s) for ab GCPs. In contrast, fusicoccin, an activator of the plasma membrane H+- ATPase, induced H+ pumping with a slightly higher rate in ad GCPs than in ab GCPs. Both types of protoplast swelled similarly in response to fusicoccin. These results suggest that ad GCPs have almost the same activity for H+ pumping as ab GCPs, whereas ad GCPs require a larger number of photons to activate the H+ pump than ab GCPs.     

Specificity and Photomorphogenic Nature of Ultraviolet-B-Induced Cotyledon Curling in Brassica napus L

Three general classes of photomorphogenic photoreceptors have been characterized in higher plants: phytochrome, a blue light/ultraviolet (UV)-A photoreceptor(s), and a UV-B sensory system(s). Although a great deal is known about phytochrome and the blue light/UV-A photoreceptor(s), little is known about UV-B detection processes. One reason for this is the lack of readily quantifiable morphogenic responses that are specifically induced by UV-B radiation. We have discovered a response to UV-B, upward curling of Brassica napus L. cotyledons, that may be useful for probing the mechanism of UV-B photoreception. The process was initially observed when B. napus seeds were germinated under visible light plus UV-B radiation, but did not occur under visible light alone or visible light plus UV-A. When 5-d-old seedlings grown in visible light were given relatively short exposures of UV-B (100 min of 5.5 [mu]mol m-2 s-1), the curling response was also observed. Development of curling was separated from the application of this UV-B pulse by a 14-h latent period. Pulses of red light, blue light, farred light, and UV-A (100 min of 5.5 [mu]mol m-2 s-1) did not induce curling, indicating UV-B specificity Additionally, these other spectral regions did not reverse or enhance the UV-B-triggered response. The degree of curling showed a log-linear dependence on UV-B fluence (6-40 mmol m-2) and reciprocity with respect to length of exposure and fluence rate. The data indicate that curling is photomorphogenic in nature and may be triggered by a single photoreceptor species.     

Blue-Light-Induced Shrinking of Protoplasts from Maize Coleoptiles and Its Relationship to Coleoptile Growth

Protoplasts isolated from red-light-grown maize (Zea mays L.) coleoptiles shrank transiently upon brief exposure (e.g. 30 s) to blue light under background irradiation with red light. The maximal volume reduction (about 4% at a saturating fluence) occurred about 5 min after blue-light stimulation. The response was prevented by the anion-channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid. Red light and far-red light did not induce any comparable response. Protoplasts of different sizes and those isolated from different coleoptile positions showed similar responses. After treatment with a saturating blue-light pulse, the protoplasts became responsive to a second pulse and gained full responsiveness within 5 min, suggesting that the photoreceptor system involves a dark-reversible component. The response to continuous blue light was also found to be transient. The protoplast volume was reduced during about 6 to 9 min of irradiation and returned within the next 30 min to the control level. The response to continuous blue light was saturated at 30 [mu]mol m-2 s-1. However, when the fluence rate was enhanced 10-fold after a period of irradiation at 30 [mu]mol m-2 s-1, the protoplasts showed another shrinking response. These and other kinetic results indicate that the photoreceptor system undergoes a photosensory adaptation. Growth in different zones of the coleoptile was inhibited by blue light transiently after pulse stimulation, as well as during continuous stimulation. It was concluded that the observed protoplast shrinking is related to the blue-light-induced inhibition of coleoptile growth.     

Anatomical features of pepper plants (Capsicum annuum L.) grown under red light-emitting diodes supplemented with blue or far-red light

Pepper plants (Capsicum annuum L. cv., Hungarian Wax) were grown under metal halide (MH) lamps or light-emitting diode (LED) arrays with different spectra to determine the effects of light quality on plant anatomy of leaves and stems. One LED (660) array supplied 90% red light at 660 nm (25nm band-width at half-peak height) and 1% far-red light between 700-800nm. A second LED (660/735) array supplied 83% red light at 660nm and 17% far-red light at 735nm (25nm band-width at half-peak height). A third LED (660/blue) array supplied 98% red light at 660nm, 1% blue light between 350-550nm, and 1% far-red light between 700-800nm. Control plants were grown under broad spectrum metal halide lamps. Plants were gron at a mean photon flux (300-800nm) of 330 micromol m-2 s-1 under a 12 h day-night photoperiod. Significant anatomical changes in stem and leaf morphologies were observed in plants grown under the LED arrays compared to plants grown under the broad-spectrum MH lamp. Cross-sectional areas of pepper stems, thickness of secondary xylem, numbers of intraxylary phloem bundles in the periphery of stem pith tissues, leaf thickness, numbers of choloplasts per palisade mesophyll cell, and thickness of palisade and spongy mesophyll tissues were greatest in peppers grown under MH lamps, intermediate in plants grown under the 660/blue LED array, and lowest in peppers grown under the 660 or 660/735 LED arrays. Most anatomical features of pepper stems and leaves were similar among plants grown under 660 or 660/735 LED arrays. The effects of spectral quality on anatomical changes in stem and leaf tissues of peppers generally correlate to the amount of blue light present in the primary light source.     

Photosynthetic characteristics of rice leaves grown under red light with or without supplemental blue light

In rice plants grown under red light supplemented with blue light (red/blue-light PPFD ratio was 4/1), photosynthetic rates per unit leaf area measured under white light at 1,600 and 250 micromol m-2) s-1 were higher than those in the plants grown under red light alone. The higher photosynthetic rates were associated with higher total N content of leaves, which was accompanied by larger amounts of key components of photosynthesis-limiting processes, including Rubisco, Cyt f, Chl and LHCII. These results suggested that the increase in total N content of leaves induced by supplemental blue light enhanced both light-saturated and light-limited photosynthesis.     

Effect of Different Light Quality on Photosynthetic Characteristics of Cucumber Leaves

Cucumber (Cucumis sativus L. cultivar "Changchun Mici") seedlings were cultured in Hoagland solution under irradiation with different light spectra (8 h per day) for 20 days. The red light (λmax 658 nm, λ1/2 25 nm), blue light (λmax 450 nm, λ1/2 43 nm) and white fluorescent light possessed the same fluent rate (20 μmol· m-2·s-1 ). The experimental results showed that chlorophyll content of the leaves grown under white light was 7 % and 22.4% higher than those in red and blue light, respectively. Compared with white and blue light, red light induced a lower Chl a/b ratio and a higher level of Chl b in the cucumber leaves. Measurements of the low temperature (77 K) fluorescence emission spectra and kinetics of Chl a fluorescence induction of the leaves proved that the leaves grown under red light expressed the highest PSⅡ and the lowest PSⅠactivities while the leaves under blue light had the lowest PSⅡand the highest PSⅠ activities. The O2 evolution rate of red light-grown leaves was 44.9% higher than that of the white light-grown leaves, while blue light effect was similar to that of white in respect of O2 evolution. It is concluded that light quality is an important factor in regulating the development and activities of PSⅡ and PSⅡand the O2 evolution of photosynthesis in cucumber leaves.     

Sugar and Organic Acid Accumulation in Guard Cells of Vicia faba in Response to Red and Blue Light

Changes in neutral sugar and organic acid content of guard cells were quantitated by high-performance liquid chromatography during stomatal opening in different light qualities. Sonicated Vicia faba epidermal peels were irradiated with 10 [mu]mol m-2 s-1 of blue light, a fluence rate insufficient for the activation of guard cell photosynthesis, or 125 [mu]mol m-2 s-1 of red light, in the presence of 1 mM KCl, 0.1 mM CaCl2. The low-fluence-rate blue light stimulated an average net stomatal opening of 4.7 [mu]m in 2 h, whereas the saturating fluence rate of red light stimulated an average net opening of 3.8 [mu]m in 2 h. Under blue light, the malate content of guard cells increased to 173% of the initial level during the first 30 min of opening and declined as opening continued. Sucrose levels continuously rose throughout the blue light-stimulated opening, reaching 215% of the initial level after 2 h. The starch hydrolysis products maltose and maltotriose remained elevated at all times. Under red light, guard cells showed very little increase in organic acid or maltose levels, whereas sucrose levels increased to 208% of the initial level after 2 h. Total measured organic metabolite concentrations were correlated with stomatal apertures in all cases except where substantial malate increases occurred. These results support the hypothesis that light quality modulates alternative mechanisms of osmotic accumulation in guard cells, including potassium uptake, photosynthetic sugar production, and starch breakdown.     

Heat Emission as a Protective Mechanism against High-irradiance Stress in Sugar Maple Leaves

High-irradiance (HI) induced changes in heat emission, fluorescence, and photosynthetic energy storage (EST) of shade grown sugar maple (Acer saccharum Marsh.) saplings were followed using modulated photoacoustic and fluorescence spectroscopic techniques. HI-treatment at 900-4400 µmol m-2 s-1 for 15 min caused an increase in heat emission and a decrease in EST. In some leaves, HI-treatment of 900 µmol m-2 s-1 for 1 min induced a rapid increase in heat emission with a marginal decrease in EST. Parallel to the increase in heat emission, there was a decrease in fluorescence, and this phenomenon was reversible in darkness. Quenching of thermal energy dissipation and a recovery in EST were observed during the first 15 min after the HI-treatment. This down-regulation of photochemical activity and its recovery may be one of the photoprotective mechanisms in shade grown sugar maple plants. The increase in thermal energy dissipation was greater in the red absorbing long wavelength (640-700 nm) region than in the blue absorbing short wavelength region of photosynthetically active excitation radiation. The photochemical activity was affected more in short wavelengths (400-520 nm) than in the long wavelength region of the spectrum. This can be due to the migration of light-harvesting chlorophyll (Chl) a/b protein complex from photosystem (PS) 2 to PS1 and/or to the disconnection of carotenoid pool from Chls in the pigment bed of photosynthetic apparatus.     

Effects of CO2 and photosynthetic photon flux on yield, gas exchange and growth rate of Lactuca sativa L. 'Waldmann's Green.'

Enrichment of CO2 to 46 mmol m-3 (1000 mm3 dm-3) at a moderate photosynthetic photon flux (PPF) of 450 micromoles m-2 s-1 stimulated fresh and dry weight gain of lettuce leaves 39% to 75% relative to plants at 16 mmol m-3 CO2 (350 mm3 dm-3). Relative growth rate (RGR) was stimulated only during the first several days of exponential growth. Elevating CO2 above 46 mmol m-3 at moderate PPF had no further benefit. However, high PPF of 880-900 micromoles m-2 s-1 gave further, substantial increases in growth, RGR, net assimilation rate (NAR) and photosynthetic rate (Pn), but a decrease in leaf area ratio (LAR), at 46 or 69 mmol m-3 (1000 or 1500 mm3 dm-3) CO2, the differences being greater at the higher CO2 level. Enrichment of CO2 to a supraoptimal level of 92 mmol m-3 (2000 mm3 dm-3) at high PPF increased leaf area and LAR, decreased specific leaf weight, NAR and Pn and had no effect on leaf, stem and root dry weight or RGR relative to plants grown at 69 mmol m-3 CO2 after 8 d of treatment. The results of the study indicate that leaf lettuce growth is most responsive to a combination of high PPF and CO2 enrichment to 69 mmol m-3 for several days at the onset of exponential growth, after which optimizing resources might be conserved.     

转GFP::cDNA基因拟南芥筛选及相关基因的功能分析

本研究以随机GFP::cDNA融合基因转基因拟南芥为材料,筛选到在细胞核或在细胞核和细胞质中均表达GFP信号的转基因株系58个。对这些转基因株系中的cDNA插入片段进行克隆,获得4株插入片段能按原初编码框进行编码的转基因株系。对插入片段为编码富含甘氨酸蛋白AtGRP8 C-末端(富含甘氨酸的结构域)的转基因株系R2的表型分析发现,连续白光、红光或蓝光下其幼苗的下胚轴比野生型的要短,且较低光照强度白光(低于100μmol m-2s-1)、蓝光(低于75μmol m-2s-1)下的差异更加明显,但是黑暗中其幼苗的下胚轴与野生型相比无明显差异,表明AtGRP8蛋白可能通过其C-末端功能域参与调控拟南芥的光形态建成反应。     

Action spectra for changes in the “high irradiance reaction” in hypocotyls of Sinapis alba L.

Detailed action spectra are presented for the inhibition of hypocotyl extension in dark-grown Sinapis alba L. seedlings by continuous (24 h) narrow waveband monochromatic light between 336 nm and 783 nm. The results show four distinct wavebands of major inhibitory action; these are centred in the ultra-violet (_max=367 nm), blue (_max=446 nm), red (_max=653 nm) and far-red (_max=712 nm) wavebands. Previous irradiation of the plants with red light (which also decreases Ptot) causes decreased inhibitory action by all wavelengths except those responsible for the red light inhibitory response. Pre-irradiation did not alter the wavelength of the action maxima. It is concluded that ultra-violet and blue light act mainly on a photoreceptor which is different from phytochrome.Abbreviations B blue - D dark - FR far-red - HIR high irradiance reaction - HW half power bandwith - Pr R absorbing form of phytochrome - Pfr FR absorbing form of phytochrome - Ptot total phytochrome=Pr+Pfr - R red - UV ultra violet     

不同波长蓝光LED对两个品种水稻秧苗生长的影响

传统的大田育秧方式容易受到自然条件的影响,如在连续的阴雨天容易导致烂秧,而采用人工可控的工厂化育秧则有助于解决此类问题。LED光源具有光质纯、光效高以及低能耗等优势,是一种有望在工厂化育秧中应用的人工光源。该研究以生长特性差异明显的水稻天优998(籼稻)和圣稻14(粳稻)为材料,在光强为(60±5)μmol·m~-2·s~-1、光周期为12 h·d~-1的条件下,以450、470和490 nm 3个波长的蓝光LED照射天优998和圣稻14秧苗,考察了不同波长蓝光对两个品种的三叶期和五叶期水稻秧苗生长的影响。结果表明:蓝光处理下两个品种、不同秧龄幼苗的壮苗指数、根系活力和根数增加,体内碳、氮代谢活性增强,抗氧化物酶活性也会增加。3个波长的蓝光对两个品种、不同秧龄水稻秧苗生长的影响存在差异,450 nm照射下水稻秧苗的各项生长指标较优,生产上育秧可根据秧龄选择450 nm或490 nm作为独立和组合光源。     

Light-activated heterotrophic growth of the cyanobacterium Synechocystis sp. strain PCC 6803: a blue-light-requiring process.

A glucose-tolerant strain of Synechocystis sp. strain 6803 will not grow on glucose under complete darkness unless given a daily pulse of white light, typically 5 min of 40 mumol m-2 s-1 (light-pulsed conditions). The light pulse is insufficient for photoautotrophy, as glucose is required and growth yield is dependent on glucose concentration. Growth rate is independent of fluence, but growth yield is dependent on fluence, saturating at 40 to 75 mumol m-2 s-1. A Synechocystis strain 6803 psbA mutant strain grows under light-pulsed conditions at rates similar to those for the glucose-tolerant strain, indicating that photosystem II is not required for growth. The relative spectral sensitivity of the growth of light-pulsed cultures (growth only in blue light, 400 to 500 nm, maximum at 450 nm) precludes energetic contribution from cyclic electron transport around photosystem I. Pulses of long-wavelength light (i.e., 550 and 650 nm) did not support the growth of Synechocystis strain 6803 and, when supplied before or after a blue-light pulse, did not inhibit blue-light-stimulated growth of Synechocystis strain 6803. We conclude that the required blue-light pulse does not support growth via photosynthetic electron transport but appears instead to function as an environmental signal regulating heterotrophic metabolism, cell division, or other photomorphogenic processes. We have termed the growth of Synechocystis strain 6803 pulsed with light and kept otherwise in complete darkness light-activated heterotrophic growth. This observation of a blue-light requirement for the growth of Synechocystis strain 6803 represents a novel blue light effect on the growth of a cyanobacterium.     

柚树(Citrus grandis)叶片光合作用对补增UV-B辐射的响应

生长在人工光照 4 0 0μmol m- 2 s- 1 下的柚树幼树光合速率的最大值为 1 0 .2± 0 .5μmol m- 2 s- 1 ;而补增UV-B辐射 ( 3.8-4 .2μW cm- 2 ,2 4 5～ 2 97nm,4 5d)的叶片则为 6.4± 0 .8μmol m- 2 s- 1 ,较对照植株降低37.2 %。对照植物的表观量子产率 (固定 mol CO2 mol- 1量子 )为 0 .0 75± 0 .0 1 2 ,而经 UV-B辐射处理植株则为0 .0 4 1± 0 .0 0 8,明显较对照植株低。UV-B辐射处理使植株叶片的光呼吸和不包括光呼吸的 CO2 补偿点增高。对照植株叶片的最大值的 CO2 羧化速率 (μmol m- 2 s- 1 )为 57.1± 1 .5μmol m- 2 s- 1 ,较 UV-B辐射处理的高30 .9% ,而 UV-B辐射处理的植株的光合电子传递速率较对照低 30 %。同时 UV-B辐射植株叶片有较低的光能转化效率 ,其较对照低 39.1 % ,叶片亦含有较低的叶绿素含量。结果表明 ,UV-B辐射明显抑制叶片光合羧化速率和光合电子传递速率 ,UV-B辐射可能抑制包括 Rubisco羧化作用在内的多个光合生理过程 ,降低叶片光合速率。柚树叶片对 UV-B辐射敏感 ,选育抗 UV-B辐射的柚树品种势在必行。