Capsular polysaccharides facilitate enhanced iron acquisition by the colonial cyanobacterium Microcystis sp. isolated from a freshwater lake

Microcystis sp., especially in its colonial form, is a common dominant species during cyanobacterial blooms in many iron‐deficient water bodies. It is still not entirely clear, however, how the colonial forms of Microcystis acclimate to iron‐deficient habitats, and the responses of unicellular and colonial forms to iron‐replete and iron‐deficient conditions were examined here. Growth rates and levels of photosynthetic pigments declined to a greater extent in cultures of unicellular Microcystis than in cultures of the colonial form in response to decreasing iron concentrations, resulting in the impaired photosynthetic performance of unicellular Microcystis as compared to colonial forms as measured by variable fluorescence and photosynthetic oxygen evolution. These results indicate that the light‐harvesting ability and photosynthetic capacity of colonial Microcystis was less affected by iron deficiency than the unicellular form. The carotenoid contents and nonphotochemical quenching of colonial Microcystis were less reduced than those of the unicellular form under decreasing iron concentrations, indicating that the colonial morphology enhanced photoprotection and acclimation to iron‐deficient conditions. Furthermore, large amounts of iron were detected in the capsular polysaccharides (CPS) of the colonies, and more iron was found to be attached to the colonial Microcystis CPS under decreasing iron conditions as compared to unicellular cultures. These results demonstrated that colonial Microcystis can acclimate to iron deficiencies better than the unicellular form, and that CPS plays an important role in their acclimation advantage in iron‐deficient waters.     

Growth and photosynthetic response of the cyanobacterium Microcystis aeruginosa in relation to photoperiodicity and irradiance

Growth and photosynthetic characteristics, P _max (maximum light-saturated oxygen production rate) and (photosynthetic affinity), of Microcystis aeruginosa were studied in continuous cultures under a range of photoperiod lengths and growth irradiances. Microcystis showed a low specific maintenance rate constant and a high growth affinity for light (typical cyanobacterial features), but required a dark period to obtain maximum growth rate. P _max and per unit dry weight increased, as did pigment content, when less light became available. By regulation in and P _max (crucial in light-limiting and high-light conditions, respectively) this buoyant species can flourish in low light, but also in high-light environments which may arise when buoyancy is lost.The two different types of light conditions affected growth, and photosynthesis, in different ways. One needs thus to discriminate between photoperiod- and irradiance-limitation, which restricts the utility of simple algal growth models. It was emphasized that photosynthetic adaptation patterns of light-limited species may resemble short-term nutrient uptake kinetics of nutrient-limited organisms.With prior knowledge of the growth limitation, we were able to assess the growth rate of a natural population of Microcystis from its photosynthetic response and from data of laboratory cultures of a known physiological state.     

Differences in growth,pigment composition and photosynthetic rates of two phenotypes Microcystis aeruginosa strains under high and low iron conditions

This paper provided insight into the influence of iron on the growth of Microcystis aeruginosa strains related to different phenotypes of this species. In this research it was intended to compare the growth, pigment composition, photosynthetic efficiency and extracellular polysaccharides production of unicellular and colonial strains of M. aeruginosa. A significantly growth inhibition under iron-limited condition on unicellular M. aeruginosa was noted, whereas the colonial strain could maintain a steady growth along with the culture time. This observation was reconfirmed by the content of chlorophyll a. Compared with unicellular strain; the colonial strain exhibited a higher PSII maximum light energy transformation, photosynthetic oxygen evolution and extracellular polysaccharides (EPS) production in iron-limited condition. Further, in order to gain more information about the accessibility of iron in the two phenotypic Microcystis, we found the two strains could produce hydroxamate-type siderophores, the content of siderophores produced by the colonial strain was more than those in unicellular strain under the iron-limited condition. It was interpreted as an adaptation to the dilute environment. Our results demonstrated that the colonial phenotypes possessed stronger ability to endure iron-limited condition than unicellular strain by higher pigment contents, higher photosynthetic activities, higher EPS production and higher siderophores secretion. It might elucidate that the colonial M. aeruginosa bloom can sustain in eutrophic reservoirs and lakes.     

Different strategies for photoprotection during autumn senescence in maple and oak

During autumn senescence, plants must disassemble the photosynthetic apparatus as nutrients are remobilized from the leaves. The goal of this study was to examine changes in relative abundance of photosynthetic proteins and pigments throughout autumn senescence in order to understand the mechanisms of photoprotection used during this process. We sampled leaves from two deciduous tree species [sugar maple (Acer saccharum Marsh.) and swamp white oak (Quercus bicolor Willd.)] throughout autumn during 2010 and 2013. Chlorophyll fluorescence was measured, thylakoids were isolated for western blotting with antibodies to individual proteins and pigment content was assessed. Both species retained high photochemical efficiency until late autumn and showed earlier onset of degradation of photosystem I relative to photosystem II. The species differed in the timing and pattern of degradation of individual photosynthetic proteins and pigments. In maple, there were increases in anthocyanins, more rapid degradation of light‐harvesting proteins and enrichment of xanthophyll cycle pigments in late autumn. In oak, light‐harvesting proteins were retained in higher abundance throughout autumn, PsbS levels increased during early autumn and lutein was enriched in late autumn samples. The results suggest that the species differ in strategies for photoprotection during autumn senescence.     

Role of Cell Hydrophobicity on Colony Formation in Microcystis (Cyanobacteria)

Colony formation is highly import ant for the competitive advantage of the cyanobacterium Microcystis over other phytoplankton species. The laboratory‐grown colonial Microcystis strains isolated from Lake Taihu (China) maintained colonial forms under the low light condition (10 μE m^–2 s^–1). The cell surface hydrophobicities of the Microcystis colonies were measured by cyanobacterial adherence to xylene in comparison with unicellular Microcystis strains. The cells of the tested colonial strains were all hydrophobic, while the cells of the tested unicellular strains were all hydrophilic. Incubation under the higher light condition (75 μE m^–2 s^–1) leaded to the significant decrease in the cell hydrophobicities of the colonial Microcystis and the transition from colonial forms to unicellular forms. These findings indicated that the cell hydrophobicity of Microcystis may play a role in cell‐cell adherence and colony formation. Phosphate‐limitation, nitrate‐limitation and pH did not affect cell hydrophobicities of colonial Microcystis. Treatment with proteolytic enzymes had no effect on the cell hydrophobicity, indicating that cell surface proteins did not contribute to high cell hydrophobicity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of light and oxygen and adaptation to changing light conditions in a photosynthetic mutant in which the LHII complex of Rhv. sulfidophilum was heterologously expressed in a strain of Rb. capsulatus whose puc operon was deleted

In this paper we show the effect of oxygen and light on the expression of the photosynthetic apparatus of a mutant heterologously expressing the puc operon. This mutant was obtained by introducing in trans an expression plasmid, bearing the puc A, B, and C genes of Rhv. sulfidophilum, as well as its own promoter, in an LHII⁻ mutant of Rb. capsulatus. The results showed that oxygen and light repressed LHII expression. Even low-light intensities lowered the LHII content to undetectable levels by spectrophotometry or by SDS-PAGE. In high-light grown cells, where the relative ratios of LHI and LHII complexes were significantly diminished, we were able to detect LHII complexes. Under the latter condition, the absorption spectrum showed that some pigment accumulated in the membrane even in the absence of cell division. These pigments were used in a later step to assemble LHII complexes, when the high-light grown cells were transferred to semiaerobiosis in the dark. Transition of high-light grown cells to low-light conditions allowed us to study the adaptability of these heterologous mutant cells. We observed that adaptation never occurred, in part probably owing to energy limitation. Received: 20 November 2001 / Accepted: 31 December 2001     

Occurrence and function of the orange carotenoid protein in photoprotective mechanisms in various cyanobacteria

Excess light is harmful for photosynthetic organisms. The cyanobacterium Synechocystis PCC 6803 protects itself by dissipating the excess of energy absorbed by the phycobilisome, the water-soluble antenna of Photosystem II, into heat decreasing the excess energy arriving to the reaction centers. Energy dissipation results in a detectable decrease of fluorescence. The soluble Orange Carotenoid Protein (OCP) is essential for this blue-green light induced mechanism. OCP genes appear to be highly conserved among phycobilisome-containing cyanobacteria with few exceptions. Here, we show that only the strains containing a whole OCP gene can perform a blue-light induced photoprotective mechanism under both iron-replete and iron-starvation conditions. In contrast, strains containing only N-terminal and/or C-terminal OCP-like genes, or no OCP-like genes at all lack this light induced photoprotective mechanism and they were more sensitive to high-light illumination. These strains must adopt a different strategy to longer survive under stress conditions. Under iron starvation, the relative decrease of phycobiliproteins was larger in these strains than in the OCP-containing strains, avoiding the appearance of a population of dangerous, functionally disconnected phycobilisomes. The OCP-containing strains protect themselves from high light, notably under conditions inducing the appearance of disconnected phycobilisomes, using the energy dissipation OCP-phycobilisome mechanism.     

In vivo fluorescence excitation and absorption spectra of marine phytoplankton: I. Taxonomic characteristics and responses to photoadaptation

Absorption and fluorescence excitation spectra were measuredfor batch cultures of five species of marine phytoplankton grownunder high and low light. These spectra were examined for propertiescharacteristic of taxonomic position and of photoadaptive response.While regions of absorption and excitation of chlorophyll afluorescence diagnostic of pigment composition were identifiable,photoadaptive response had greater influence on spectral variability.Although reduced growth irradiance caused changes in both theabsorption and fluorescence excitation spectra, the fluorescenceexcitation spectrum appears to be more sensitive to alterationsin the ambient light field for growth than does the absorptionspectrum. For a single species. the fluorescence excitationspectrum for a sample grown at low irradiance showed greaterstructure than that for the sample grown at a high irradiance.Under low light conditions, the excitation of chlorophyll afluorescence by accessory pigments increased relative to theexcitation by chlorophyll a itself The highest fluorescenceyields occur in the blue-green region of the spectrum, correspondingto bands of peak absorption by the accessory pigments. Changesin absorption spectra are less marked, but two features recur.First. in the blue-green region of the spectrum from -500–560nm. absorption is enhanced in the low-light cells relative tothat of the high-light cells. Second, the ratio of absorptionat 435 nm to that at 676 nm was greater for the high-light cells.Correlating changes in pigment concentrations were observed.The influence of photoadaptation on the properties of fluorescenceexcitation spectra is as great or greater than the influenceof pigment complements characteristic of specific algal taxa.     

Effects of UVB Radiation on competition between the bloom‐forming cyanobacterium Microcystis aeruginosa and the Chlorophyceae Chlamydomonas microsphaera1

The growth, photosynthetic characteristics, and competitive ability of three algal strains were investigated under different doses of ultraviolet‐B (UVB) radiation (0, 0.285, and 0.372 W · m^?2). The organisms were the toxic bloom‐forming cyanobacterium Microcystis aeruginosa FACHB 912, nontoxic M. aeruginosa FACHB 469, and the green microalga Chlamydomonas microsphaera FACHB 52. In monocultures, the growth of all three strains was inhibited by UVB. In mixed cultures, enhanced UVB radiation resulted in decreased percentages of the two M. aeruginosa strains (19%–22% decrease on d 12 of the competition experiment). UVB radiation resulted in increased contents of chlorophyll a, b, and carotenoids (CAR) in C. microsphaera, and decreased contents of allophycocyanin (APC) or phycocyanin in the two Microcystis strains. All three strains showed increased levels of UVabsorbing compounds and intracellular reactive oxygen species under 0.372 W · m^?2 UVB radiation, and decreased light compensation points, dark respiratory rates, and maximal quantum efficiency of PSII. After a 20 h recovery, the photosynthetic oxygen evolution of C. microsphaera was restored to its maximum value, but that of Microcystis strains continued to decrease. Nonphotochemical quenching was increased by UVB radiation in C. microsphaera, but was unaffected in the two M. aeruginosa strains. Our results indicated that C. microsphaera has a competitive advantage relative to Microcystis during exposure to UVB irradiation.     

Different physiological responses of cyanobacteria to ultraviolet‐B radiation under iron‐replete and iron‐deficient conditions: Implications for underestimating the negative effects of UV‐B radiation

Iron deficiency has been considered one of the main limiting factors of phytoplankton productivity in some aquatic systems including oceans and lakes. Concomitantly, solar ultraviolet‐B radiation has been shown to have both deleterious and positive impacts on phytoplankton productivity. However, how iron‐deficient cyanobacteria respond to UV‐B radiation has been largely overlooked in aquatic systems. In this study, physiological responses of four cyanobacterial strains (Microcystis and Synechococcus), which are widely distributed in freshwater or marine systems, were investigated under different UV‐B irradiances and iron conditions. The growth, photosynthetic pigment composition, photosynthetic activity, and nonphotochemical quenching of the different cyanobacterial strains were drastically altered by enhanced UV‐B radiation under iron‐deficient conditions, but were less affected under iron‐replete conditions. Intracellular reactive oxygen species (ROS) and iron content increased and decreased, respectively, with increased UV‐B radiation under iron‐deficient conditions for both Microcystis aeruginosa FACHB 912 and Synechococcus sp. WH8102. On the contrary, intracellular ROS and iron content of these two strains remained constant and increased, respectively, with increased UV‐B radiation under iron‐replete conditions. These results indicate that iron‐deficient cyanobacteria are more susceptible to enhanced UV‐B radiation. Therefore, UV‐B radiation probably plays an important role in influencing primary productivity in iron‐deficient aquatic systems, suggesting that its effects on the phytoplankton productivity may be underestimated in iron‐deficient regions around the world.     

Different tolerances and responses to low temperature and darkness between waterbloom forming cyanobacterium <Emphasis Type="Italic">Microcystis</Emphasis> and a green alga <Emphasis Type="Italic">Scenedesmus</Emphasis>

The dynamics of planktonic cyanobacteria in eutrophicated freshwaters play an important role in formation of annual summer blooms, yet overwintering mechanisms of these water bloom forming cyanobacteria remain unknown. The responses to darkness and low temperature of three strains (unicellular Microcystis aeruginosa FACHB-905, colonial M. aeruginosa FACHB-938, and a green alga Scenedesmus quadricauda FACHB-45) were investigated in the present study. After a 30-day incubation under darkness and low temperature, cell morphology, cell numbers, chlorophyll a, photosynthetic activity (ETR_max and I _k), and malodialdehyde (MDA) content exhibited significant changes in Scenedesmus. In contrast, Microcystis aeruginosa cells did not change markedly in morphology, chlorophyll a, photosynthetic activity, and MDA content. The stress caused by low temperature and darkness resulted in an increase of the antioxidative enzyme-catalase (CAT) in all three strains. When the three strains re-grew under routine cultivated condition subjected to darkness and low temperature, specific growth rate of Scenedesmus was lower than that of Microcystis. Flow cytometry (FCM) examination indicated that two distinct types of metabolic response to darkness and low temperature existed in the three strains. The results from the present study reveal that the cyanobacterium Microcystis, especially colonial Microcystis, has greater endurance and adaptation ability to the stress of darkness and low temperature than the green alga Scenedesmus. Handling editor: D. Hamilton     

THE EFFECT OF IRON LIMITATION ON THE PHOTOPHYSIOLOGY OF PHAEOCYSTIS ANTARCTICA (PRYMNESIOPHYCEAE) AND FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE) UNDER DYNAMIC IRRADIANCE1

The effects of iron limitation on photoacclimation to dynamic irradiance were studied in Phaeocystis antarctica G. Karst. and Fragilariopsis cylindrus (Grunow) W. Krieg. in terms of growth rate, photosynthetic parameters, pigment composition, and fluorescence characteristics. Under dynamic light conditions mimicking vertical mixing below the euphotic zone, P. antarctica displayed higher growth rates than F. cylindrus both under iron (Fe)–replete and Fe‐limiting conditions. Both species showed xanthophyll de‐epoxidation that was accompanied by low levels of nonphotochemical quenching (NPQ) during the irradiance maximum of the light cycle. The potential for NPQ at light levels corresponding to full sunlight was substantial in both species and increased under Fe limitation in F. cylindrus. Although the decline in F_v/F_m under Fe limitation was similar in both species, the accompanying decrease in the maximum rate of photosynthesis and growth rate was much stronger in F. cylindrus. Analysis of the electron transport rates through PSII and on to carbon (C) fixation revealed a large potential for photoprotective cyclic electron transport (CET) in F. cylindrus, particularly under Fe limitation. Probably, CET aided the photoprotection in F. cylindrus, but it also reduced photosynthetic efficiency at higher light intensities. P. antarctica, on the other hand, was able to efficiently use electrons flowing through PSII for C fixation at all light levels, particularly under Fe limitation. Thus, Fe limitation enhanced the photophysiological differences between P. antarctica and diatoms, supporting field observations where P. antarctica is found to dominate deeply mixed water columns, whereas diatoms dominate shallower mixed layers.     

INFLUENCE OF DIFFERENT LIGHT INTENSITIES AND DIFFERENT IRON NUTRITION ON THE PHOTOSYNTHETIC APPARATUS IN THE DIATOM CYCLOTELLA MENEGHINIANA (BACILLARIOPHYCEAE)1

The diatom Cyclotella meneghiniana Kütz. (SAG 1020‐a) was cultured under high‐light (HL) and low‐light (LL) conditions with either high (12 μM) or low (1 μM) iron in the media. Changes in cell morphology, especially cell volume and chloroplast size, were observed in cells grown under low iron. In contrast, HL had a much stronger influence on the photosynthetic apparatus. PSII function was unimpaired under lowered iron supply, but its quantum efficiency and reoxidation rate were reduced under HL conditions. As reported before, HL induced changes in antenna polypeptide composition. Especially the amount of Fcp6, an antenna protein related to LI818 and known to be involved in photoprotection, was increased under HL but was significantly reduced under lowered iron. The diatoxanthin content correlated with the amount of Fcp6 in isolated FCPa antenna complexes and was thus increased under HL and reduced under low iron as well. While the diatoxanthin (Dt) content of whole cells was enhanced under HL, no decrease was observed under lowered iron supply, ruling out the possibility that the decreased amounts in FCPa were due to a hampered diadinoxanthin de‐epoxidase activity under these conditions. Thus, diatoxanthin not bound to FCPa has to be responsible for protection under the slight reduction in iron supply used here.     

不同光照强度下花魔芋（Amorphophallus konjac）与谢君魔芋（Amorphophallus xiei）光合特性及光保护机制研究

为探讨不同耐光性植物光合特性及光保护机制,本研究以耐高光的喜阴植物花魔芋（Amorphophallus konjac K.Coch）和典型的喜阴植物谢君魔芋（Amorphophallus xiei H.Li & Z.L.Dao）为材料,测定与分析在透光率为100%、15%及2%光照条件下两种魔芋的光合能力、抗氧化酶活性及抗氧化物和光合色素组分的含量。结果表明,花魔芋最大光合速率和气孔导度随着生长环境光照强度降低而显著降低（P<0.05）,谢君魔芋在透光率为15%时最大光合速率达最大值。大部分情况下,花魔芋的超氧化物歧化酶、抗坏血酸过氧化物酶、过氧化氢酶、谷胱甘肽还原酶活性比谢君魔芋高（P<0.05）,而谢君魔芋具有较高的过氧化物酶活性（P<0.05）。总的来看,在中高光照环境下两种植物的抗氧化酶活性较高（P<0.05）。在透光率15%时,花魔芋谷胱甘肽和抗坏血酸显著比谢君魔芋高（P<0.05）。谢君魔芋的光合色素含量在透光率为15%时最高（P<0.05）;相应地,花魔芋的光合色素含量在透光率为2%时含量最低（P<0.05）;在不同光照强度下花魔芋光合色素含量基本上显著高于谢君魔芋（P<0.01）。本研究结果暗示,喜阴植物花魔芋耐受高光可能源于相对较高的光合作用能力和有效的光保护机制。     

Improvement of acclimatization of micropropagated grapevine: Photosynthetic competence and carbon allocation

Grapevine plantlets multiplied in vitro were acclimatized at 40 or 90 μmol m⁻² s⁻¹ photon flux density for 12 or 16 h per day, respectively. In the high-light regime a decrease in total chlorophyll and an increase in chlorophyll a/chlorophyll b ratio occurred. However, at high-light intensity lower photosynthetic capacities and higher apparent photosynthesis were measured than at the low-light regime. In leaves expanded during acclimatization, the light compensation point was higher in plantlets under high-light while quantum yield was higher in low-light conditions. High-light also gave rise to an increase in carbohydrate concentration. As a whole, the results suggest that high-light increases carbon assimilation and growth although with a low investment in the photosynthetic apparatus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Analysis of photosynthetic pigments and chlorophyll fluorescence characteristics of different strains of Porphyra yezoensis

The levels of photosynthetic pigments and chlorophyll fluorescence of Porphyra yezoensis strains selected from high-light environments were investigated. Sutong and Sulian strains originated from the same high-light environment but were selected from different sites on the Yellow Sea coast of Jiangsu Province, China. In January (a low temperature period), the Sulian strain and the WT (a widely cultivated strain) had higher levels of chlorophyll a, phycoerythrin, phycocyanin, and allophycocyanin, and higher actual photochemical efficiency of PSII (ΔF/F _m′) than the Sutong strain. This indicated that Sulian and the WT may have better adaptation to low temperature. In March (an optimal temperature period), Sutong had higher levels of photosynthetic pigments and higher ΔF/F _m′ than the WT and Sulian strains. This suggested that Sutong had higher light use efficiency at optimal temperatures and that most energy absorbed by PSII was used for photosynthetic electron transport. The differing areas of origin of these strains may have resulted in these differences in temperature adaptation.     

Cyanobacterial carotenoids: their roles in maintaining optimal photosynthetic production among aquatic bloom forming genera

Summary Photoprotective and photosynthetic roles of carotenoid pigments (xanthophylls and -carotene) were examined in the major bloom forming blue-green algal (cyanobacterial) genera, Anabaena, Aphanizomenon and Microcystis. Since these genera often reside as scums in surface waters, attention was given to the ability of carotenoids to counter potential photooxidation due to maximum near U.V. and visible radiation as well as O₂ supersaturation, characterizing surface waters supporting blooms. In U.V.-transparent quartz incubation flasks it was shown that inhibition of carotenoid synthesis by diphenylamine led to rapid photooxidation among the above genera. When carotenoid synthesis was allowed to proceed, a high degree of resistance to photooxidation resulted. Prolonged exposure to near U.V. irradiation led to enhanced carotenoid synthesis relative to chlorophyll a, which extended viability. Carotenoid enhancement also increased chlorophyll a-specific photosynthetic O₂ production. It is concluded that enhanced carotenoid synthesis observed during blooms serves at least two ecological functions, i) providing photoprotection and ii) increasing photosynthetic performance of surface cyanobacterial populations.     

Photosynthetic acclimation to shade: probing the role of phytochromes using photomorphogenic mutants of tomato

Photomorphogenic mutants of tomato were used to probe the possible involvement of phytochrome A in photosynthetic acclimation to shade. Plants of wild-type Lycopersicon esculentum, the near isogenic mutants aurea (au, deficient in phytochrome A, and also possibly other phytochromes) and high pigment (hp, exhibiting exaggerated photomorphogenic responses), and the au/hp double mutant were grown in a greenhouse under either unfiltered daylight, or daylight attenuated by neutral density filters or green filters that simulated the spectral effects of vegetation shade. Growth and photosynthetic parameters were measured over a growing period of 15 d. Typical effects of simulated vegetation shade on extension growth were observed only in the wild-type and hp strains; the presence of the au lesion resulted in reduced capacity to respond to vegetation shade by increased extension. Photosynthetic light saturation curves obtained using infrared gas analysis at 15 d indicated that neither the au nor the hp mutations caused serious reductions in maximum net photosynthetic rate in plants acclimated to full daylight, although the au/hp double mutant showed a significantly reduced maximum rate. In the wild-type and hp strains grown under both neutral and simulated vegetation shade, the photosynthetic light saturation curves were similar. Plants with the au lesion showed a significantly lower capacity to acclimate to vegetation shade, as seen by their reduced maximum rate of net photosynthesis. However, in situ measurements of photosynthetic rate in the greenhouse were indistinguishable between the four strains. Thylakoid stoichiometry measurements revealed a very large increase in PSII/PSI ratio under simulated vegetation shade as compared with either unfiltered daylight or neutral density shade. These increases were not diminished in the phytochrome-deficient au strains, and were even larger in the hp strains. The results indicate that the au lesion has little effect on the capacity of tomato to exhibit photoadaptation to simulated vegetational shade when measured at the thylakoid level. On the other hand, net leaf photosynthesis under vegetation shade can be significantly affected by the phytochrome deficiency caused by the au mutation, implying a possible role for one or more of the phytochromes in photoadaptation at the leaf level.     

过表达AtchyB基因提高洋桔梗光胁迫耐受性的研究

类胡萝卜素尤其是叶黄素循环类物质在植物抵抗由强光照引起的非生物胁迫中发挥着重要的作用,为了提高洋桔梗对强光照的抗性,从拟南芥中克隆了类胡萝卜素生物合成途径中参与叶黄素循环关键酶——β-胡萝卜素羟化酶基因(AtchyB),利用农杆菌介导法将其转入洋桔梗中,最终得到遗传转化植株2个株系,研究发现,转基因植株中总类胡萝卜素含量高于对照组,且叶黄素循环池被不同程度地放大。在不同光照强度下,转基因洋桔梗植株对光照耐受性明显强于对照组,且转基因植株生物量也明显提高。表明过表达AtchyB基因使洋桔梗光胁迫耐受性有所增强。