光质对植物光合作用的调控及其机理

光合作用是植物生长发育的基础.光质对植物光合作用的调控主要包括可见光对植物气孔器运动、叶片生长、叶绿体结构、光合色素、D1蛋白及其编码基因和光合碳同化等的调节,以及紫外光对植物光系统Ⅱ的影响.蓝光和红光能促进气孔的开张,而绿光能够逆转这种作用.蓝光有利于叶绿体的发育,红、蓝、绿复合光有利于叶面积的扩展,而红光更有利于光合产物的积累;不同光质对不同植物、不同组织器官叶绿素积累的影响不同.蓝光和远红光可以促进psbA基因转录物质的积累.大多数高等植物和绿藻在橙、红光下光合速率最高,蓝紫光其次,绿光最低.紫外光可以导致光系统Ⅱ的电子传递活性下降.此外,针对光质与光合作用研究领域中存在的问题,对今后的研究方向进行了讨论.     

Reversal of blue light-stimulated stomatal opening by green light

Blue light-stimulated stomatal opening in detached epidermis of Vicia faba is reversed by green light. A 30 s green light pulse eliminated the transient opening stimulated by an immediately preceding blue light pulse. Opening was restored by a subsequent blue light pulse. An initial green light pulse did not alter the response to a subsequent blue light pulse. Reversal also occurred under continuous illumination, with or without a saturating red light background. The magnitude of the green light reversal depended on fluence rate, with full reversal observed at a green light fluence rate twice that of the blue light. Continuous green light given alone stimulated a slight stomatal opening, and had no effect on red light-stimulated opening. An action spectrum for the green light effect showed a maximum at 540 nm and minor peaks at 490 and 580 nm. This spectrum is similar to the action spectrum for blue light-stimulated stomatal opening, red-shifted by about 90 nm. The carotenoid zeaxanthin has been implicated as a photoreceptor for the stomatal blue light response. Blue/green reversibility might be explained by a pair of interconvertible zeaxanthin isomers, one absorbing in the blue and the other in the green, with the green absorbing form being the physiologically active one.     

The phototropin family as photoreceptors for blue light-induced chloroplast relocation

Blue light-induced chloroplast accumulation and avoidance relocation movements are controlled by the blue light photoreceptor phototropin. The Arabidopsis thaliana genome has two phototropin genes encoding phot1 and phot2. Each of these photoreceptors contains two LOV (light oxygen and voltage) domains and a kinase domain. The LOV domains absorb blue light though an associated flavin mononucleotide chromophore, while the kinase domain is thought to be associated with signal transduction. The phototropins control not only chloroplast relocation movement, but also blue light-induced phototropic responses, leaf expansion and stomatal opening. Here I review the role of phototropin as a photoreceptor for chloroplast photorelocation movement. Electronic Publication     

The inhibition of mitosis in tissue culture cells by blue light

Blue light (wavelength 350-480 nm) irradiation of the early mitotic (prophase and prometaphase) tissue culture cells at the dose of 50-3000 J/cm2 delay mitosis or completely block it at the metaphase. Cell sensitivity to the near UV light (wavelength 360 nm) was few times more as compared with the sensitivity to the visible light (wavelength 400-480 nm). Mitotic cells irradiated with the green light (wavelength more than 500 nm; dose up to 7500 J/cm2) completed division normally. The effect of the blue light did not depend on the presence of phenol red in tissue culture medium. Rhodamin 123 staining did not show any changes in the mitochondrial system in the irradiated mitotic cells. Blue light irradiation with the dose enough for the induction of mitotic delay appears to be insufficient to affect the proliferation of interphase cells.     

Interactions of green or red light with blue light on the dark closure of Albizzia pinnules

The interactions of green or red light with blue light on the dark closing of Albizzia julibrissin Durazz. pinnules have been investigated. Irradiations at 430, 450 and 470 nm progressively delay dark closing with increasing photon fluence rates. Red or green light alone has no effect. However, when the blue fluence rate is low, both red and green light interact with it and increase the delaying effect of the blue light. When the blue fluence rate is high, green light interacts with it to negate some of the effectiveness of the blue light, while red light has no effect. This is similar to results obtained previously with far-red light. It is suggested that the same unidentified photoreceptor is operating in both the far-red and blue regions. The results also indicate the presence of a blue-only absorbing photoreceptor whose action is increased by phytochrome.     

Purification and characterization of the mitochondrial translocase from Euglena gracilis

The Euglena gracilis mitochondrial protein biosynthetic elongation factor G (EF-Gmt) has been purified in four steps to greater than 50% homogeneity by use of a fusidic acid affinity procedure and conventional chromatographic techniques. The purification scheme results in 1100-fold purification with about 3% recovery of the total EF-G activity present in the postribosomal supernatant prepared from whole cell extracts. E. gracilis EF-Gmt has an approximate molecular weight of 76,000, comparable to that observed for procaryotic translocases. As is the case for other translocases which have been examined, pretreatment of E. gracilis EF-Gmt with N-ethylmaleimide results in a loss of polymerization activity, indicating a role for an essential cysteine residue in catalytic activity. GDP partially protects EF-Gmt from N-ethylmaleimide inactivation. E. gracilis EF-Gmt functions well on both Escherichia coli and E. gracilis chloroplast ribosomes, but has negligible activity on wheat germ cytoplasmic ribosomes. In this respect, it differs significantly from the mitochondrial translocase of yeast which has very little activity on chloroplast ribosomes. When assayed on E. coli ribosomes, E. gracilis EF-Gmt is sensitive to the steroid antibiotic, fusidic acid, at levels similar to that required for inactivation of E. coli EF-G. It is less sensitive than E. gracilis chloroplast EF-G, and is more sensitive than Bacillus subtilis EF-G. When assayed on E. gracilis chloroplast ribosomes, the same trends in sensitivities are observed, although the exact level of fusidic acid required for inactivation is slightly altered.     

Red-light and blue-light photoreceptors controlling chlorophyll a synthesis in the red alga Porphyra umbilicalis and in the green alga Ulva rigida

Chlorophyll synthesis is stimulated by red light in the green alga Ulva rigida C. Ag. and in the red alga Porphyra umbilicalis (L.) Kützing. Because the effect of red light showed some far-red reversibility in successive red and far-red light treatments, the involvement of phytochrome or a phytochrome-like photoreceptor is suggested. The extent of the response is dependent on exposure and photon fluence rate of red-light pulses. In addition to the effect of red light, a strong stimulation of chlorophyll synthesis by blue light was only observed in Ulva rigida. The effect of blue light shows also some far-red reversibility. In the green alga the accumulated chlorophyll is higher after blue light pulses than after red light pulses. In Porphyra umbilicalis , however, the contrary is observed. In Ulva rigida the involvement of a blue light photoreceptor in addition to phytochrome or a phytochrome-like photoreceptor is proposed. The different responses to red and blue light in both algae are explained in terms of their adaptation to the natural light environment.     

Photo and Nutritional Regulation of the Light-Harvesting Chlorophyll a/b-Binding Protein of Photosystem II mRNA Levels in Euglena

In Euglena gracillis var bacillaris, light exposure increases the level of mRNA encoding the light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCPII) approximately twofold. LHCPII mRNA levels increased in the dark upon either malate or ethanol addition. LHCPII mRNA is present but LHCPII is not synthesized in the bleached mutants W₃BUL and W₁₀BSmL, which lack protochlorophyll(ide) and most if not all of the chloroplast genome. Light exposure increased LHCPII mRNA levels in W₃BUL but not in W₁₀BSmL. Carbon availability and light acting through a nonchloroplast photoreceptor appear to regulate LHCPII mRNA levels. A chloroplast photoreceptor and/or a product produced by the chloroplast appear to regulate LHCPII mRNA translation.     

Phytochrome and blue light-mediated stomatal opening in the orchid,paphiopedilum

Guard cells of the orchid genus, Paphiopedilum have been reported to lack developed chloroplasts and detectable chlorophyll a autofluorescence. Paphiopedilum stomata lack a photosynthesis-dependent opening response but have a blue light-specific opening. The present study found that low fluence rate green and red light elicited stomatal opening in Paphiopedilum and this opening was reversed by far red light, indicating the presence of a phytochrome-mediated opening response. Phytochrome-dependent, red light-stimulated opening was largest under low fluence rates and decreased to near zero as fluence rate increased. A recently discovered green light reversibility of blue light-specific stomatal opening was used to probe the properties of the blue light response in Paphiopedilum stomata. Blue light-stimulated opening was completely reversed by green light in the presence of far red light. Red light enhanced the blue light response of Paphiopedilum guard cells when given as a pretreatment or together with blue light. Analysis of guard cell pigments showed that guard cells have small amounts of chlorophyll a and b, zeaxanthin, violaxanthin, antheraxanthin and lutein. Zeaxanthin content increased in response to blue light or ascorbate and declined in the dark or under illumination in the presence of dithiothreitol, indicating the presence of an active xanthophyll cycle. Thus Paphiopedilum stomata possess both a blue light-mediated opening response with characteristics similar to species with normal chloroplast development and a novel phytochrome-mediated opening response.     

Photoperiod and light quality effects on rate of dark respiration and on photosynthetic capacity in developing seedlings of Chenopodium rubrum

Development and acclimation of energy transduction were studied in seedlings of Chenopodium rubrum L. ecotype selection 184 (50° 10' N; 105° 35' W) in response to photomorphogenic and photoperiodic treatments. Dark respiration and photosynthetic capacity [nmol O₂ (pair of cotyledons)⁻¹ h⁻¹] were measured with an oxygen electrode. Changes in chloroplast ultrastructure were analyzed concomitantly. After germination, seedlings were grown at constant temperature either in darkness or in continuous light (white, red, far-red and blue) or were subjected to diurnal cycles of light/dark or changes in light quality. Dark respiration was low in far-red light treated seedlings. In red light treated seedlings dark respiration was high and the mean value did not depend on fluence rate or photoperiod. Blue light stimulated transitorily and modulated dark respiration in photoperiodic cycles. Photosynthetic capacity was reduced by far-red light and increased by red light. In response to blue light photosynthetic capacity increased, with indications of a requirement for continuous energy input. Phytochrome and a separate blue light receptor seemed to be involved. In continuous red light a clear cut circadian rhythm of dark respiration was observed. Blue light had a specific effect on chloroplast structure.     

Phytochrome-mediated branch formation in protonemata of the mossCeratodon purpureus

We have analyzed light induction of side-branch formation and chloroplast re-arrangement in protonemata of the mossCeratodon purpureus. After 12 hr of dark adaptation, the rate of branch formation was as low as 5%. A red light treatment induced formation of side branches up to 75% of the dark-adapted protonema. The frequency of light induced branch formation differed between cells of different ages, the highest frequency being found in the 5th cell, the most distal cell studied from the apex. We examined the effect of polarized light given parallel to the direction of filament growth. The position of branching within the cell depended on the vibration plane of polarized red light. Branch formation was highest when the electric vector of polarized light vibrates parallel to the cell surface and is fluence rate dependent. The positional effect of polarized red light could be nullified to some extent by simultaneous irradiation with polarized far-red light. An aphototropic mutant,ptr116, shows characteristics of deficiency in biosynthesis of the phytochrome chromophore and exhibits no red-light induced branch formation. Biliverdin, a precursor of the phytochrome chromophore, rescued the red-light induced branching when added to the medium, supporting the conclusion that phytochrome acts as photoreceptor for red light induced branch formation. The light effect on chloroplast re-arrangement was also analyzed in this study. We found that polarized blue light induced chloroplast re-arrangement in wild-type cells, whereas polarized red light was inactive. This result suggests that chloroplast re-arrangement is only controlled by a blue light photoreceptor, not by phytochrome inCeratodon.     

The germination characteristics of phytochrome-deficient aurea mutant tomato seeds

The role of light reactions in anthocyanin synthesis was studied in both attached and detached corollas of Petunia hybrida (cv. Hit Parade Rosa), the latter grown in vitro in media containing 150 m M sucrose and 50 μ M gibberellic acid (GA). Light was essential for the synthesis of anthocyanin in detached corollas, whereas in intact corollas its effect was only to enhance anthocyanin synthesis. Continuous white light at a fluence rate of at least 20 μmol m⁻² s⁻¹ was needed for anthocyanin synthesis in detached corollas. Blue light was more effective than red or green, and far-red was ineffective. Pigmentation of detached corollas exposed to light was inhibited by the photosynthetic inhibitor 3-(4-dichlorophenyl)-1,1-dimethylurea (DCMU). The chloroplast uncoupler NH₄Cl did not affect anthocyanin synthesis, which was, however, inhibited by the blocking of ATP synthesis in both the chloroplast and the mitochondria by dicyclohexylcarbodiimide (DCCD). Sucrose uptake in vitro was inhibited by DCMU and by darkness, and was promoted equally by blue and red light. The activity of phenylalanine ammonialyase (EC 4.3.1.5) was inhibited in detached corollas grown in the dark or in the light in the presence of DCMU. The activity of chalcone isomerase (EC 5.5.1.6) was not affected by light. These findings suggest that at least two different light reactions are involved in the regulation of anthocyanin synthesis in petunia corollas, namely the high irradiance reaction (HIR) and photosynthesis.     

The Light Requirement for Different Steps in the Development of Chloroplasts in Excised Wheat Roots

For the formation of chloroplasts in excised wheat roots blue light is necessary, but red light enhances the blue light effect. Intensity-response relationships and action spectra have been determined for the specific blue light effect as well as for the effect of red light when given before or after blue light. The longest wave length giving a blue light effect is about 500 nm. The spectrum shows a peak at about 450 nm, and a considerable effect extends down to 368 nm, the shortest wave length tested. The photoreceptor mechanism for the “blue reaction” is thought to be related to that of certain phototropisms and chloroplast movements, and to that involved in carotenoid synthesis in certain fungi. The active pigment is thought to be either a carotenoid or a flavoprotein, probably the latter. The effect of red light shows similar action spectra whether the red light is given before or after the blue, and they are consistent with protochlorophyll absorption. However, much less light is needed to produce a detectable response when the red light is given before the blue light than after. Because of the similarity of the spectra phytochrome may also be involved in the response to red light when given before blue. Far-red reversal has not been tested. The results are discussed in relation to the development of chloroplasts in leaves.     

Changes in Plastidic and Cytoplasmic Pyruvate Kinase Activity during Chloroplast Development of Pea in Blue and Red Light

Pyruvate kinase (PK) activity was demonstrated in the cytosolas well as in the plastids of pea leaves. Etioplasts and chloroplastscontained about 12% of the total activity. The presence of PKactivity in different cellular compartments and the pronounceddifferences in kinetic and regulatory properties indicate thatthese activities are due to isoenzymes. When etiolated pea leaves were illuminated with weak blue light,the plastidic PK activity increased immediately, reaching amaximum (about 21% of the total activity) after 24 h of illumination.Under red light, there was a lag period of about 4 h beforethe increase in isoenzyme activity. After 24 h of illumination,however, it reached the maximum found with blue light. In contrast,light quality had no appreciable effect on cytoplasmic PK andphosphoenolpyruvate carboxylase. Increases in NADP-dependent glyceraldehyde 3-phosphate dehydrogenaseactivity and in the soluble protein in the plastids were somewhathigher, whereas the increase in chlorophyll content was slightlylower under blue light than under red light. Blue light specificallyincreased the chlorophyll alb-ratio. These different responsesto the light quality during chloroplast development indicatethat more than one photoreceptor is involved in these processes. The results obtained for pea PK also are discussed in comparisonwith similar findings for the chlorophyll-free Chlorella mutantno. 20. (Received January 19, 1982; Accepted April 21, 1983)     

Light perception and the role of the xanthophyll cycle in blue-light-dependent chloroplast movements in lemna trisulca L

In most higher plants, chloroplasts move towards the periclinal cell walls in weak blue light (WBL) to increase light harvesting for photosynthesis, and towards the anticlinal walls as an escape reaction, thus avoiding photo-damage in strong blue light (SBL). The photo- receptor(s) triggering these responses have not yet been identified. In this study, the role of zeaxanthin as a blue-light photoreceptor in chloroplast movements was investigated. Time-lapse 3D confocal imaging in Lemna trisulca showed that individual chloroplasts responded to local illumination when one half of the cell was treated with light of different intensity or spectral quality to that received by the other half, or was maintained in darkness. Thus the complete signal perception, transduction and effector system has a high degree of spatial resolution and is consistent with localization of part of the transduction chain in the chloroplasts. Turnover of xanthophylls was determined using HPLC, and a parallel increase was observed between zeaxanthin and chloroplast movements in SBL. Ascorbate stimulated both a transient increase in zeaxanthin levels and chloroplast movement to profile in physiological darkness. Conversely, dithiothreitol blocked zeaxanthin production and responses to SBL and, to a lesser extent, WBL. Norflurazon preferentially inhibited SBL-dependent chloroplast movements. Increases in zeaxanthin were also observed in strong red light (SRL) when no directional chloroplast movements occurred. Thus it appears that a combination of zeaxanthin and blue light is required to trigger responses. Blue light can cause cis-trans isomerization of xanthophylls, thus photo-isomerization may be a critical link in the signal transduction pathway.     

Photocontrol of Growth, and of Anthocyanin and Chlorogenic Acid Production in Cultured Callus Tissues of Haplopappus gracilis

Cultures of dark-grown Haplopappus callus (strain AI) were exposedto continuous blue, green, red, far-red, and white light for33 days at energy levels of approximately 10 J m^-2s^-1. Growthwas suppressed in all but far-red. Blue had the greatest suppressiveeffect, green the least; red and white were about equally effective.Mean cell generation times were increased from 8–8 days(dark control) to 12.5 days in red light and 20.5 days in blue.There was a slight increase in mean wet weight per cell in bluelight but a slight decrease in red, whereas there was almosta twofold increase in mean dry weight per cell in blue and littlechange in red. In contrast, far-red stimulated growth; the meancell generation time was reduced to 6–5 days and therewas little change in wet or dry weight per cell. Anthocyanin synthesis was promoted by all wavebands except far-red.Blue had the greatest effect, then white, red, and green inthat order. In blue light the pigments accumulated rapidly,but only during the early stages of culture. The maximum amountper cell was attained after 7 days and thereafter the valuesdeclined. In red, however, the pigments accumulated relativelyslowly, and the maximum cell content was not attained until22 days; the amount attained was less than half that attainedin blue light. Initially, the ratio of cyanidine-3-glucosideto cyanidine-3-rutinoside exceeded 5.0 in blue light, but theratio fell to almost unity with time. This probably reflecteda rapid initial synthesis of the glucoside accompanied by asteady conversion to the rutinoside. Blue light was also more effective than red in acceleratingchlorogenic acid production. The response to blue light occurredafter the initial rise in anthocyanins and continued for therest of the culture period. The data are discussed in relation to similar high-energy photoresponsesreported for intact systems.