Restoration of Photosynthesis in Dried Tobacco Leaf Tissue

A comparison of ¹⁴CO₂ fixation rates in dehydrating tobacco leaf tissue, either intact or epidermis-free, shows that stomatal closure is the primary cause for photosynthetic reduction due to dehydration. Rehydration of the dried, epidermis-free tissue was accompanied by restoration of photosynthetic activity. The restoration was not only affected by hydration level but was notably time-dependent, apparently for reorganization of the photosynthetic apparatus.     

Photosynthesis in Salt-Adapted Heterotrophic Tobacco Cells and Regenerated Plants

Tobacco (Nicotiana tabacum L.) cells growing heterotrophically in the light on supplied sucrose (S0) have previously been adapted to grow in 428 mM NaCl (S25). Among the changes occurring in salinity-adapted cell cultures are (a) elevated levels of chlorophyll compared to unadapted cells; (b) decreased levels of starch; (c) alterations in chloroplast ultrastructure, including loss of starch grains, increased thylakoid membrane structure, and the presence of plastoglobules; and (d) increased rates of O2 evolution, CO2 fixation, and photophosphorylation relative to S0 cells. These latter changes apparently derive from the fact that thylakoid membranes in S25 cells contain higher levels of photosystem I- and II-associated proteins as well as thylakoid ATPase components. S25 chloroplasts contain immunologically detectable levels of ribulose-1,5-bisphosphate carboxylase/oxygenase, whereas S0 completely lack the enzyme. These changes taken together suggest that even in the presence of sucrose, S25 cells have acquired a significant degree of salt-tolerant photosynthetic competence. This salt-tolerant photoysynthetic capability manifests itself in plants backcrossed with normal plants for three generations. These plants contain chloroplasts that demonstrate in vitro more salt-tolerant CO2 fixation, O2 evolution, and photophosphorylation than do backcross progeny of plants regenerated from S0 cultures.     

Manipulation of Catalase Levels Produces Altered Photosynthesis in Transgenic Tobacco Plants

Constructs containing the cDNAs encoding the primary leaf catalase in Nicotiana or subunit 1 of cottonseed (Gossypium hirsutum) catalase were introduced in the sense and antisense orientation into the Nicotiana tabacum genome. The N. tabacum leaf cDNA specifically overexpressed CAT-1, the high catalytic form, activity. Antisense constructs reduced leaf catalase specific activities from 0.20 to 0.75 times those of wild type (WT), and overexpression constructs increased catalase specific activities from 1.25 to more than 2.0 times those of WT. The NADH-hydroxypyruvate reductase specific activity in transgenic plants was similar to that in WT. The effect of antisense constructs on photorespiration was studied in transgenic plants by measuring the CO₂ compensation point (Γ) at a leaf temperature of 38°C. A significant linear increase was observed in Γ with decreasing catalase (at 50% lower catalase activity Γ increased 39%). There was a significant temperature-dependent linear decrease in Γ in transgenic leaves with elevated catalase compared with WT leaves (at 50% higher catalase Γ decreased 17%). At 29°C, Γ also decreased with increasing catalase in transgenic leaves compared with WT leaves, but the trend was not statistically significant. Rates of dark respiration were the same in WT and transgenic leaves. Thus, photorespiratory losses of CO₂ were significantly reduced with increasing catalase activities at 38°C, indicating that the stoichiometry of photorespiratory CO₂ formation per glycolate oxidized normally increases at higher temperatures because of enhanced peroxidation.     

Photosynthesis and Carbon Partitioning in Transgenic Tobacco Plants Deficient in Leaf Cytosolic Pyruvate Kinase

Whole-plant diurnal C exchange analysis provided a noninvasive estimation of daily net C gain in transgenic tobacco (Nicotiana tabacum L.) plants deficient in leaf cytosolic pyruvate kinase (PK_c−). PK_c− plants cultivated under a low light intensity (100 μmol m⁻² s⁻¹) were previously shown to exhibit markedly reduced root growth, as well as delayed shoot and flower development when compared with plants having wild-type levels of PK_c (PK_c+). PK_c− and PK_c+ source leaves showed a similar net C gain, photosynthesis over a range of light intensities, and a capacity to export newly fixed ¹⁴CO₂ during photosynthesis. However, during growth under low light the nighttime, export of previously fixed ¹⁴CO₂ by fully expanded PK_c− leaves was 40% lower, whereas concurrent respiratory ¹⁴CO₂ evolution was 40% higher than that of PK_c+ leaves. This provides a rationale for the reduced root growth of the PK_c− plants grown at low irradiance. Leaf photosynthetic and export characteristics in PK_c− and PK_c+ plants raised in a greenhouse during winter months resembled those of plants grown in chambers at low irradiance. The data suggest that PK_c in source leaves has a critical role in regulating nighttime respiration particularly when the available pool of photoassimilates for export and leaf respiratory processes are low.     

叶绿素b缺失与植物的光合作用

文章介绍叶绿素b的结构性质、生物合成和功能以及叶绿素b缺失与植物光合作用的关系的研究进展。     

Photosynthesis and Photoprotection in Overwintering Plants

Abstract: Seasonal differences in the capacity of photosynthetic electron transport, leaf pigment composition, xanthophyll cycle characteristics and chlorophyll fluorescence emission were investigated in two biennial mesophytes ( Malva neglecta and Verbascum thapsus ) that grow in full sunlight, and in leaves/needles of sun and shade populations of several broad-leafed evergreens and conifers (Vinca minor, Euonymus kiautschovicus, Mahonia repens, Pseudotsuga menziesii [Douglas fir], and Pinus ponderosa). Both mesophytic species maintained or upregulated photosynthetic capacity in the winter and exhibited no upregulation of photoprotection. In contrast, photosynthetic capacity was downregulated in sun leaves/needles of V. minor, Douglas fir, and Ponderosa pine, and even in shade needles of Douglas fir. Interestingly, photosynthetic capacity was upregulated during the winter in shade leaves/needles of V. minor, Ponderosa pine and Euonymus kiautschovicus. Nocturnal retention of zeaxanthin and antheraxanthin, and their sustained engagement in a state primed for energy dissipation, were observed largely in the leaves/needles of sun-exposed evergreen species during winter. Factors that may contribute to these differing responses to winter stress, including chloroplast redox state, the relative levels of source and sink activity at the whole plant level, and apoplastic versus symplastic phloem loading, are discussed.     

植物光合作用的三维特性研究进展

光合作用是地球上最重要的化学反应。虽然针对植物光合作用已经进行了广泛深入的研究,但从三维层面探讨植物叶片光合功能及其调节作用的工作较少。叶片结构、光合机构组分、叶片内光能吸收和传递均具有明显的三维特性,极大影响叶片内CO₂转运、叶肉细胞的电子传递和碳同化,进而使叶片光合功能及其调控表现出复杂的三维特征。因此,从三维角度分析叶片光合特性有助于理解光合作用机理,也能够为提高植物光合作用效率提供理论支持。     

Peroxidase-Induced Wilting in Transgenic Tobacco Plants

Peroxidases are a family of isoenzymes found in all higher plants. However, little is known concerning their role in growth, development, or response to stress. Plant peroxidases are heme-containing monomeric glycoproteins that utilize either H2O2 or O2 to oxidize a wide variety of molecules. To obtain more information on possible in planta functions of peroxidases, we have used a cDNA clone for the primary isoenzyme form of peroxidase to synthesize high levels of this enzyme in transgenic plants. We were able to obtain Nicotiana tabacum and N. sylvestris transformed plants with peroxidase activity that is 10-fold higher than in wild-type plants by introducing a chimeric gene composed of the cauliflower mosaic virus 35S promoter and the tobacco anionic peroxidase cDNA. The elevated peroxidase activity was a result of increased levels of two anionic peroxidases in N. tabacum, which apparently differ in post-translational modification. Transformed plants of both species have the unique phenotype of chronic severe wilting through loss of turgor in leaves, which was initiated at the time of flowering. The peroxidase-induced wilting was shown not to be an effect of diminished water uptake through the roots, decreased conductance of water through the xylem, or increased water loss through the leaf surface or stomata. Possible explanations for the loss of turgor, and the significance of these types of experiments in studying isoenzyme families, are discussed.     

高等植物光合作用的光抑制研究进展

光抑制是目前高等植物光合作用研究中的热点,近此年来无论是对其本质的认识,还是机理研究都已取得很进展。本文首先简要回顾了光抑制研究发展的历程,阐明现代光抑制理论包括耗散过剩光能的光保持机制运转和过剩光能对光合机构的破坏两个方面。然后,应叶黄素循环、Ｍｅｈｌｅｒ反应、光呼吸、ＬＨＣⅡ磷酸化、ＰＳⅡ光化学活性下降以及由类胡罗卜素、Ｃｙｔｂ－５５９参与的一些主要光保护机制作了综述,着重论述了其作用机理及研     

不同温度对烟草生长发育及光合作用的影响

该试验通过人工气候室模拟相对低温(日均温16.5℃)、常温(日均温23.5℃)和相对高温(日均温30.5℃)3种日动态温度,研究了不同温度对烟草生长发育及光合作用的影响。结果表明:(1)与常温下生长的烟草相比,相对低温和高温处理均降低了烟株的株高、叶长和叶宽,在一定程度上抑制了烟草的生长。(2)相对低温和高温处理比常温处理下有较低的烟叶净光合速率(Pn)、胞间CO_2浓度(Ci)、气孔导度(Gs)、蒸腾速率(Tr)、PSⅡ最大光化学量子效率(F_v/F_m)、PSⅡ实际光化学量子效率(ΦPSⅡ)、光化学猝灭系数(qp)、Rubisco羧化酶活性和相对较高的初始荧光强度(F0)。长期较高或较低的温度均会对烟草的生长发育产生抑制,这可能因其在一定程度上抑制了烟叶的光合机构活性并对反应中心造成了损伤,从而降低了烟草的光合作用,抑制了烟株的生长,长期日均温23.5℃有利于烟草的生长和光合作用。     

高等植物光合作用的光抑制研究进展

光抑制是目前高等植物光合作用研究中的热点,近些年来无论是对其本质的认识,还是机理研究都已取得很大进展。本文首先简要回顾了光抑制研究发展的历程,阐明现代光抑制理论包括耗散过剩光能的光保持机制运转和过剩光能对光合机构的破坏两个方面。然后,就叶黄素循环、Mehler反应、光呼吸、LHCII磷酸化、PSII光化学活性下降以及由类胡罗卜素、Cytb 559参与的一些主要光保护机制作了综述,着重论述了其作用机理及研究进展。最后,就现阶段光破坏原初作用位点的认识及光破坏机理的最新研究成果作了总结。     

烟草花叶病毒对烟草叶片光合特征和POD表达的影响

以烤烟(Nicotiana tabacum L.)品种'中烟5号'为实验材料,对烟草健康株与感染烟草花叶病毒(TMV)株的叶绿素、光合速率、光合速率对光强的响应曲线、光暗反应荧光特征、POD活性及其表达等进行研究,以探讨TMV感染对烟草植株生理生态特征的影响.结果显示:病株的叶绿素a(Chl a)和叶绿素b(Chl b)含量显著低于健康株,但Chl a/Chl b值基本相同;病株暗中初始荧光(F0)、暗中最大荧光(Fm)、暗中可变荧光(Fv)、光下初始荧光(F0′)、光下最大荧光(Fm′)、光下可变荧光(Fv′)、非光化学猝灭系数(NPQ)、PSⅡ捕光效率(Fv′/Fm′)、PSⅡ实际光化学效率(ФPSⅡ)及光饱和点显著低于健康株;净光合速率在光强较大(＞1 500 μmol·m-2·s-1)时病株比健康株低,光强适中(1 500 μmol·m-2·s-1左右)时两者相差不大,光强较弱(＜1 500 μmol·m-2·s-1左右)时病株比健康株高;病株叶片的过氧化物酶(POD)活性显著升高,POD同工酶中一些大分子量蛋白分子表达量加大.研究表明,感染TMV使烟草植株对光抑制更为敏感,叶片的荧光激发能力和热耗散能力下降,PSⅡ反应中心捕光效率和光化学反应效率降低,光合电子传递能力和碳同化能力受到抑制;POD活性提高和表达量增加可能是诱导烟草抗病性的一个关键生理过程.     

Studies on Nitrogen Metabolism in Tobacco Plants

Δ¹-Pyrroline-5-carboxylate reductase has been considerably purified from tobacco leaves. This enzyme uses NADPH or NADH for the formation of proline, although the former is better used. This enzyme was found in washed chloroplast extract as well as in cytoplasmic fluid and utilized NADPH, formed by the photosynthetic NADP reduction, for the sythesis of proline in the light.     

The Effect of Oxygen Concentration on Photosynthesis in Higher Plants

The influence of oxygen concentration in the range 0–21% on photosynthesis in intact leaves of a number of higher plants has been investigated. Photosynthetic Co₂ fixation of higher plants is markedly inhibited by oxygen in concentrations down to less than 2%. The inhibition increases with oxygen concentration and is about 30% in an atmosphere of 21% O₂ and 0.03% Co.₂. Undoubtedly, therefore, oxygen in normal air exerts a strong inhibitory effect on photosynthetic Co₂ fixation of land plants under natural conditions. The inhibitory effect of oxygen is rapidly produced and fully reversible. The degree of inhibition is independent of light intensity. The quantum yield for Co₂ fixation, i.e. the slope of the linear part of the curve for Co₂ uptake versus absorbed quanta, is inhibited to the same degree as the light saturated rate at all oxygen concentrations studied. Diverse species of higher plants, varying greatly in photosynthetic response to light intensity and Co₂ concentration, and with light saturated roles of Co₂ fixation differing by a factor of more than 10 times, show a remarkable similarity in their response to oxygen concentration. By contrast, when studied under the same conditions as the higher plants, the green algae Chlorella and Ulva did not show-any measurable inhibition of photosynthetic Co₂ fixation. Similarity, the increase in fluorescence intensity with increasing oxygen concentrations found in higher plants also was not seen in Chlorella. The present results, together with previous data on the photosynthetic response of algae to oxygen concentration, indicate that the photosynthetic apparatus of higher plants differs considerably from that of algae in its sensitivity to oxygen. The inhibitory effect of oxygen on photosynthetic Co₂ fixation in higher plants is somewhat higher at wavelengths which excite preferentially photosystem I. Also, the Emerson enhancement of Co₂ fixation measured when a far red beam of low intensity is imposed on a background of red light is greater under low oxygen concontrution than under air. Measurements of reversible light-induced absorbance changes reveal that the change at 591 nm, probably caused by pla.stocyanin, is affected by oxygen concentration only if photosystem II is excited. the reducing effect on plastocyanin, caused by excitation of this system, decreases with increasing oxygen concentration. From these results it is suggested that a possible site of the inhibition by oxygen is in the electron carrier chain between the two photosystems. Oxygen might act as an electron acceptor at this site, causing reducing power to react back with molecular oxygen. However, this hypothesis does not account for equal inhibitions of the quantum yield and the light saturated rate of photosynthetic CO₂ uptake. Through the photosynthetic process plants take up carbon dioxide and evolve oxygen. The present high concentration of molecular oxygen in the atmosphere is generally considered to have arisen from the activity of photo-synthetic organisms. The effect of oxygen concentration would seem, therefore, to he a problem of great interest, not only in the field of the biophysics and biochemistry of photosynthesis, but in ecology and other branches of biology as well. It was discovered by Warburg (1920) that high concentrations of oxygen inhibit the rate of photosynthetic oxygen evolution in the unicellular alga Chlorella. Since then, it has been confirmed by various authors that oxygen cconcentrations in the range 21–100 per cent have a marked inhibitory effect on photosynthesis, particularly at saturating light intensities. There is some evidence that under conditions when carbon dioxide concentration limits photosynthesis, the inhibition may become obvious even in 21 per cent oxygen. The inhibition has not been considered to operate at low light intensities. A review on the subject has been given by Turner and Brittain (1962). Various hypotheses have been put forward to explain the inhibitory effect of oxygen, commonly referred to as the Warhurg effect. Some authors favor the idea of enzyme inhibition; Turner et al. (1958) that one or more enzymes of the carbon reduction cycle are inactivated by oxygen: lirianlals (1962) that enzymes of the oxygen-evolving complex are inhihited. Other hypotheses concern back-reactions in which molecular oxygen is taken up, thus reversing the photosynthetic process. These reactions include photo-oxidation, photorespiration, and the Mehler reaction (Tamiya et al., 1957). At present, there is no generally accepted hypothesis explaining the effect. The often conflicting results on which these hypotheses were based have been obtained mostly on algae. The first observation of an inhibitory effect on photosynthesis in a higher plant was made hy McAlister and Myers (1940) in wheat leaves. They found that the photosyntlietic CO₂ uptake was markedly lower in air than in an atmosphere of about 0.5 per cent oxygen. At the CO₂ concentration used (0.03%) the inhibition was present both at high and moderate light intensities. No data were obtained at low light intensities. Although the study of the effect of oxygen concentration on photosynthesis in higher plants would seem to be of great interest, particularily since the natural environment of most land plants is an atmosphere with an oxygen content of 21 per cent, it has attracted very little attention. To the author's knowledge no thorough investigation on the subject has been published. The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO₂ fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that of green algae. The present investigalion is directed toward elucidatirng the photosynthetic response of higher plants to oxygen concentrations up to that of normal air. Data are presented showing that the photosynthetic CO₂ fixation in intact leaves of higher plants, regardless of light intensity, is strongly inhibited by oxygen in normal air, and that the pholosynthetic response to oxygen differs considerably from that of green algae.     

Effects of Nitrogen Nutrition on Photosynthesis in Cd-treated Sunflower Plants

Increased nitrogen supply stimulates plant growth and photosynthesis.Since it was shown that heavy metals may cause deficienciesof essential nutrients in plants the potential reversal of cadmiumtoxicity by increased N nutrition was investigated. The effectson photosynthesis of low Cd (0, 0.5, 2 or 5 mmol m^-3) combinedwith three N treatments (2, 7.5 or 10 mol m^-3) were examinedin young sunflower plants. Chlorophyll fluorescence quenchingparameters were determined at ambient CO₂and at 100 or 800 µmolquanta m^-2 s^-1. The vitality index (R_fd) decreased approx. three-timesin response to 5 mmol m^-3Cd, at 2 and 10 mol m^-3N. The maximumphotochemical efficiency of PSII reaction centres (F_v/ F_m) wasnot influenced by Cd or N treatment. The highest Cd concentrationdecreased quantum efficiency of PSII electron transport (_II)by 30%, at 2 and 10 mol m^-3N, mostly due to increased closureof PSII reaction centres (q_P). Photosynthetic oxygen evolutionrates at saturating CO₂were decreased in plants treated with5 mmol m^-3Cd, at all N concentrations. The results indicatethat Cd treatment affected the ribulose-1,5-bisphosphate (RuBP)regeneration capacity of the Calvin cycle more than other processes.At the same time, the amounts of soluble and ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco) protein increased with Cd treatment.Decreased photosynthesis, but substantially increased Rubiscocontent, in sunflower leaves under Cd stress indicate that asignificant amount of Rubisco protein is not active in photosynthesisand could have another function. It is shown that optimal nitrogennutrition decreases the inhibitory effects of Cd in young sunflowerplants. Copyright 2000 Annals of Botany Company Helianthus annuus L., cadmium, nitrogen, photosynthesis, Rubisco, sunflower