The dynamics of photosynthetic acclimation to changes in light quanlity and quality in three Australian rainforest tree species

Photosynthetic acclimation was studied in seedlings of three subtropical rainforest species representing early (Omalanthus populifolius), middle (Duboisia myoporoides) and late (Acmena ingens) successional stages in forest development. Changes in the photosynthetic characteristics of pre-existing leaves were observed following the transfer of plants between deep shade (1–5% of photosynthetically active radiation (PAR), selectively filtered to produce a red/far-red (R/FR) ratio of 0.1) and open glasshouse (60% PAR and a R/FR ratio of 1.1–1.2), and vice versa. The extent and rate of response of the photosynthetic characteristics of each species to changes in light environment were recorded in this simulation of gap formation and canopy closure/overtopping. The light regimes to which plants were exposed produced significant levels of acclimation in all the photosynthetic parameters examined. Following transfer from high to low light, the light-saturated rate of photosynthesis was maintained near pre-transfer levels for 7 days, after which it decreased to levels which closely approximated those in leaves which had developed in low light. The decrease in photosynthetic capacity was associated with lower apparent quantum yields and stomatal conductances. Dark respiration was the parameter most sensitive to changes in light environment, and responded significantly during the first 4–7 days after transfer. Acclimation of photosynthetic capacity to increases in irradiance was significant in two of the three species studied, but was clearly limited in comparison with that of new leaves produced in the high light conditions. This limitation was most pronounced in the early-successional-stage species, O. populifolius. It is likely that structural characteristics of the leaves, imposed at the time of leaf expansion, are largely responsible for the limitations in photosynthetic acclimation to increases in irradiance.     

马铃薯AGPase活力反馈调控光合速率定量分析

为了揭示ADP-葡萄糖焦磷酸化酶(AGPase)改变对叶片光合作用的反馈调控,以改变AGPase活力的马铃薯转化株系为材料,测定了其AGPase活力(AA)、块茎淀粉积累量(SC)、叶片光合速率(PR)、叶绿素(CC)和蔗糖含量(SUC)等;测定结果分析显示,各株系的AGPase活力(AA)、块茎淀粉积累量(SC)和叶片光合速率(PR)间存在显著差异,且均显著高于对照;株系间AGPase活力、块茎淀粉含量和叶片光合速率呈显著正相关性;每单位AGPase活力上升可贡献贮藏器官淀粉积累增加2.5%,且是影响叶片光合速率的重要因素;结果表明,AGPase不仅是下游淀粉积累的限速酶,而且可向上游反馈调控光合速率。     

Soluble carbohydrates of Pinus sylvestris L. sapwood and heartwood

Summary The amounts of glucose, fructose, sucrose, arabinose/galactose, raffinose/stachyose and starch were investigated in the outer sapwood, innermost sapwood, transition zone and heartwood of four stems of Pinus sylvestris L. The samples were taken in October and the determination of the compounds was done enzymatically. It was not possible to distinguish arabinose from galactose and raffinose from stachyose. The amounts of glucose, fructose and sucrose were greatest in the outer sapwood and decreased gradually towards the innermost sapwood and the heartwood. In the outermost heartwood glucose, fructose and sucrose were only present in trace amounts. Raffinose/stachyose showed highest concentrations in the outer sapwood and decreased towards the heartwood. In contrast, the concentrations of arabinose/galactose increased towards the heartwood and the greatest amount was found in the inner heartwood. When identified by thin-layer chromatography (TLC), arabinose was found to be present in greater amounts than galactose. The amount of starch decreased markedly towards heartwood. However, the amounts of sugars in all the studied stems was very variable. The changes in the amounts of carbohydrates in the different zones of the stems and the possible relationships of these phenomena with heartwood formation are discussed.     

Diel changes in the CO2 exchange rates of reproductive organs of the tropical tree Durio zibethinus

The daily variations in the in situ CO₂ exchange of the reproductive organs of Durio zibethinus trees, growing in an experimental field at University Putra Malaysia (UPM), were examined at different growth stages. Reproductive organs emerged on the leafless portions of branches inside the crown. The photon flux densities (PFD) in the chambers used for the measurements were less than 100 mol m^–2 s^–1 and were 40% of the PFD outside of the crown. The daytime net respiration rate and the nighttime dark respiration rate were higher at the time of flower initiation and during the mixed stages, when flower buds, flowers, and fruit coexist, than at the flower bud stage. The net respiration rate was lower than the daytime dark respiration rate at given temperatures, especially at the flower bud and fruit stages. Conversely, the net respiration rate was similar to the daytime dark respiration rate at the mixed stage. Photosynthetic CO₂ refixation reduced the daily respiratory loss by 17, 5, 0.3, and 24% at the flower bud, flower initiation, mixed, and fruit stages, respectively.     

12个不同基因型冬小麦的光合能力

 研究了12个不同基因型冬小麦(Triticum aestivum)品种(其中两个为北京本地品种)的光合能力。结果表明：小偃22、陕麦897和8907-11-5三个品种的净光合速率超过20μmolCO2·m-2·s-1,均比其它实验品种高,其PSⅡ总的光化学量子产额(Yield)、光化学荧光猝灭系数(qP)和水分利用效率(WUE)也较高;而其暗呼吸速率和非光化学荧光猝灭系数(qN)较低,表现出具有良好的光合生理功能,而且这些参数具有连锁相关的趋势。因此,北京地区要引种外地具有优良光合生理功能的冬小麦作为栽培品种或育种亲本时,在所实验的10个外地品种中,上述3个品种应为首选品种。     

超高产杂交稻不同生育期的光合色素含量、净光合速率和水分利用效率

 较为系统地研究了两个超高产杂交稻‘两优培九’、‘华安3号’和多年来大面积推广的常规杂交稻‘汕优63’不同生育期的光合色素含量、净光合速率和水分利用效率。结果表明,在苗期,3个杂交稻的单位叶面积的叶绿素（Chl）含量差别不大,类胡萝卜素（Car）的含量以‘汕优63’为最高。然而,随着发育阶段的推进,到分蘖期,尤其是抽穗期剑叶的单位叶面积Chl和Car含量,两个超高产杂交稻高于‘汕优63’。从苗期到抽穗期,超高产杂交稻‘两优培九’和‘华安3号’的净光合速率（Pn）都比‘汕优63’高,而在苗期的午间强光条件下和分蘖期的早晨以及抽穗期的早晚相对弱光条件下其Pn的差别尤为显著。在苗期,‘汕优63’的水分利用效率（WUE）略高于‘两优培九’和‘华安3号’;到分蘖期和抽穗期,在上午10时之前和下午14时以后的时间段,则是两个超高产杂交稻明显高于‘汕优63’。这些结果说明,超高产杂交稻‘两优培九’和‘华安3号’不仅有较高的Pn和较强的抗光抑制能力,而且还能充分利用早晨和傍晚较弱的光强进行光合作用,这些是它们之所以高产的重要生理基础。此外,超高产杂交稻在生长发育的中后期（分蘖期和抽穗期）具有较高的WUE,有利于节约农业用水。     

Herbivore-induced changes in plant carbon allocation: assessment of below-ground C fluxes using carbon-14

Effects of above-ground herbivory on short-term plant carbon allocation were studied using maize (Zea mays) and a generalist lubber grasshopper (Romalea guttata). We hypothesized that above-ground herbivory stimulates current net carbon assimilate allocation to below-ground components, such as roots, root exudation and root and soil respiration. Maize plants 24 days old were grazed (c. 25–50% leaf area removed) by caging grasshoppers around individual plants and 18 h later pulse-labelled with¹⁴CO₂. During the next 8 h,¹⁴C assimilates were traced to shoots, roots, root plus soil respiration, root exudates, rhizosphere soil, and bulk soil using carbon-14 techniques. Significant positive relationships were observed between herbivory and carbon allocated to roots, root exudates, and root and soil respiration, and a significant negative relationship between herbivory and carbon allocated to shoots. No relationship was observed between herbivory and¹⁴C recovered from soil. While herbivory increased root and soil respiration, the peak time for¹⁴CO₂ evolved as respiration was not altered, thereby suggesting that herbivory only increases the magnitude of respiration, not patterns of translocation through time. Although there was a trend for lower photosynthetic rates of grazed plants than photosynthetic rates of ungrazed plants, no significant differences were observed among grazed and ungrazed plants. We conclude that above-ground herbivory can increase plant carbon fluxes below ground (roots, root exudates, and rhizosphere respiration), thus increasing resources (e.g., root exudates) available to soil organisms, especially microbial populations.     

Synthesis and Characterization of Melanins From Dihydroxyindole-2-Carboxylic Acid and Dihydroxyindole

Several studies have confirmed that a melanocyte-specific enzyme, dopachrome tautomerase (EC 5.3.2.3), catalyzes the isomerization of dopachrome to 5,6-dihydroxyindole-2-carboxylic acid (DHICA) (Pawelek, 1991). Here we report that DHICA, produced either enzymatically with dopachrome tautomerase or through chemical synthesis, spontaneously polymerized to form brown melanin that was soluble in aqueous solutions above pH 5. Under the same reaction conditions, solutions of either DOPA, DOPAchrome, or 5,6-dihydroxyindole (DHI) formed black, insoluble melanin precipitates. When DHICA and DHI were mixed together, with DHICA in molar excess, little or no precipitation of DHI-melanin occurred and the rate and extent of soluble melanin formation was markedly enhanced over that achieved with DHICA alone, suggesting co-polymerization of DHICA and DHI. With or without DHI, DHICA-melanins absorbed throughout the ultraviolet and visible spectra (200-600 nm). The DHICA-melanins precipitated below pH 5, at least in part because of protonation of the carboxyl groups. DHICA-melanins could be passed through 0.22 μm filters but could not be dialyzed through semi-permeable membranes with exclusion limits of 12,000-14,000 daltons. HPLC/molecular sieve analyses revealed apparent molecular weights ranging from 20,000 to 200,000 daltons, corresponding to 100-1,000 DHICA monomers per molecule of melanin. DHICA-melanins were stable to boiling, lyophilization, freezing and thawing, and incubation at room temperature for more than 1 year. The natural occurrence of oligomers of DHICA was first reported by Ito and Nichol (1974) in their studies of the brown tapetal pigment in the eye of the sea catfish (Arius felis L.). In experiments reported here, brown, but not black, melanins from mouse hairs, human melanoma cells, and peacock feathers were soluble in aqueous buffers. Since DHICA-melanins are both soluble and brown, the results raise the possibility that they are determinants of brown colors in the animal kingdom.     

Improved growth,productivity and quality of tomato (Solanum lycopersicum L.) plants through application of shikimic acid

A field experiment was conducted to investigate the effect of seed presoaking of shikimic acid (30, 60 and 120 ppm) on growth parameters, fruit productivity and quality, transpiration rate, photosynthetic pigments and some mineral nutrition contents of tomato plants. Shikimic acid at all concentrations significantly increased fresh and dry weights, fruit number, average fresh and dry fruit yield, vitamin C, lycopene, carotenoid contents, total acidity and fruit total soluble sugars of tomato plants when compared to control plants. Seed pretreatment with shikimic acid at various doses induces a significant increase in total leaf conductivity, transpiration rate and photosynthetic pigments (Chl. a, chl. b and carotenoids) of tomato plants. Furthermore, shikimic acid at various doses applied significantly increased the concentration of nitrogen, phosphorus and potassium in tomato leaves as compared to control non-treated tomato plants. Among all doses of shikimic acid treatment, it was found that 60 ppm treatment caused a marked increase in growth, fruit productivity and quality and most studied parameters of tomato plants when compared to other treatments. On the other hand, no significant differences were observed in total photosynthetic pigments, concentrations of nitrogen and potassium in leaves of tomato plants treated with 30 ppm of shikimic acid and control plants. According to these results, it could be suggested that shikimic acid used for seed soaking could be used for increasing growth, fruit productivity and quality of tomato plants growing under field conditions.     

不同还田方式对Bt玉米秸秆中Bt蛋白田间降解的影响

采用网袋法在田间研究了Bt（Bacillus thuringiensis）玉米(Zea may)1246×1482和H9235Bt/RR秸秆中Bt蛋白的降解动态,并应用移动对数模型进行拟合及估算DT₅₀和DT₉₀,探讨不同还田方式对降解的影响。结果表明:1246×1482和H9235Bt/RR秸秆中Bt蛋白在埋入土壤和地表覆盖2种还田方式下均能在7 d内降解90%以上,但还田180 d时仍能检测到占初始含量0.004%～0.069%的Bt蛋白;不同还田方式并没有显著影响到1246×1482秸秆中Bt蛋白的降解过程,其埋入土壤和地表覆盖处理的DT₅₀分别为0.90 d和0.79 d,DT₉₀则分别为3.45 d和5.03 d;但不同还田方式影响了另一Bt玉米H9235Bt/RR秸秆中Bt蛋白的降解过程,在秸秆还田前期,埋入土壤处理下Bt蛋白的降解比地表覆盖处理慢,其埋入土壤和地表覆盖处理下Bt蛋白降解的DT₅₀分别为6.80 d和0.54 d,DT₉₀则分别为21.76 d和7.12 d。由此可见,2个Bt玉米品种秸秆中Bt蛋白在2种还田方式下均能快速降解,不同还田方式只影响到H9235Bt/RR秸秆中Bt蛋白的田间降解,使得地表覆盖处理下Bt蛋白的降解比埋入土壤处理快。     

模拟酸雨及其酸化土壤对小麦幼苗体内可溶性糖和含氮量的影响

以小麦为试材,采用盆栽方法研究了模拟酸雨及其酸化土壤对小麦幼苗体内可溶性糖和含N量的影响.结果表明,pH值为5.6、4.5、3.5、3.0和2.5的系列模拟酸雨引起了土壤酸化和盐基流失.当模拟酸雨的pH值由5.6下降到2.5时,被淋溶土壤的pH值由.0下降到3.41,土壤中交换性盐基总量从56.5下降到41.1mmol·kg^-1.将小麦幼苗栽培在该系列酸化土壤上,并分别用5种不同pH值的模拟酸雨喷淋地上器官,导致小麦幼苗体内的可溶性糖含量、含N量迅速下降,某些生理活动降低.其中,模拟酸雨喷淋对小麦幼苗茎叶可溶性糖含量、含N量、叶绿素含量以及光合速率的影响大于酸化土壤对其产生的影响.而酸化土壤对小麦幼苗根系中可溶性糖含量、含N量、硝酸还原酶(NR)和谷氨酸合成酶(GOGAT)活性的影响大于模拟酸雨喷淋的影响.pH≤3.0的高强度酸雨以及由其产生的酸化土壤(T₄、T₅土壤)对小麦幼苗的碳素代谢和氮素代谢具有明显的抑制作用.     

Effects of nitrogen addition on photosynthetic characteristics of Leymus chinensis in the temperate grassland of Nei Mongol,China北大核心CSCD

Aims The increased atmospheric nitrogen (N) deposition due to human activity and climate change greatly causes grassland ecosystems shifting from being naturally N-limited to N-eutrophic or N-saturated, and further affecting the growth of grass species. The aims of this study are: 1) to evaluate the effects of different N addition levels on morphology and photosynthetic characteristics of Leymus chinensis; 2) to determine the critical N level to facilitate L. chinensis growth. Methods We conducted a different N addition levels experiment in dominant species in the temperate steppe of Nei Mongol. The aboveground biomass, morphological and leaf physiological traits, pigment contents, chlorophyll a fluorescence parameters and biochemical parameters of L. chinensis were investigated. Important findings Our results showed that aboveground biomass first increased and then decreased with the increased N, having the highest values at the 10 g N·m-2·a?1 treatment, but the 25 g N·m-2·a?1 still significantly increased the aboveground biomass relative to 0 g N·m-2·a?1. Leymus chinensis accommodate low N situation through allocating less N to carboxylation system and decreasing leaf mass per area (LMA) in order to get more light energy. Moderate N addition captured more light energy through increasing total chlorophyll (Chl) contents and decreasing the ratio of Chl a/b. Moderate N addition increased LMA, carboxylation efficiency, maximum car boxylation rate (Vcmax), maximum electron transport rate (Jmax) and decreased Jmax/Vcmax, thus allocating more N to carboxylation system to enhance carboxylation capability. Moreover, the photochemical activity of PSII was increased through higher effective quantum yield of PSII photochemistry, electron transport rate and photochemical quenching coefficient. Excessive N addition had negative effects on physiological variables of L. chinensis due to lower carboxylation capability and photochemical activity of PSII, further leading to decreased net photosynthetic rate, whereas increased non-photochemical quenching coefficient and carotenoids played the role in the dissipation of excess excitation energy. Overall, moderate N addition facilitated the photosynthetic characteristics of dominant species, but excessive N addition inhibited photosynthetic characteristics. The most appropriate N addition for the growth of L. chinensis was 5-10 g N·m-2·a?1 in the temperate steppe of Nei Mongol, China.     

Analysis of chlorophylls and their derivatives by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry

The analysis of chlorophylls and their derivatives by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry is described. Four matrices—sinapinic acid, a-cyano-4-hydroxycinnnamic acid, terthiophene, and 3-aminoquinoline—were examined to determine optimal conditions for analysis of the molecular mass and structure of chlorophyll a as a representative chlorophyll. Among them, terthiophene was the most efficient without releasing metal ions, although it caused fragmentation of the phytol-ester linkage. Terthiophene was useful for the analyses of chlorophyll derivatives as well as porphyrin products such as 8-deethyl-8-vinyl-chlorophyll a, pheophorbide a, pyropheophorbide a, bacteriochlorophyll a esterified phytol, and protoporphyrin IX. The current method is suitable for rapid and accurate determination of the molecular mass and structure of chlorophylls and porphyrins.     

Nitrate uptake and nitrite release by tomato roots in response to anoxia

Excised root systems of tomato plants (early fruiting stage, 2nd flush) were subjected to a gradual transition from normoxia to anoxia by seating the hydroponic root medium while aeration was stopped. Oxygen level in the medium and respiration rate decreased and reached very low values after 12 h of treatment, indicating that the tissues were anoxic thereafter. Nitrate loss from the nutrient solution was strongly stimulated by anoxia (after 26 h) concomitantly with a release of nitrite starting only after 16 h of treatment. This effect was not observed in the absence of roots or in the presence of tungstate, but occurred with whole plants or with sterile in vitro cultured root tissues. These results indicate that biochemical processes in the root involve nitrate reductase. NR activity assayed in tomato roots increased during anoxia. This phenomenon appeared in intact plants and in root tissues of detopped plants. The stimulating effect of oxygen deprivation on nitrate uptake was specific; anoxia simultaneously entailed a release of orthophosphate, sulfate, and potassium by the roots. Anoxia enhanced nitrate reduction by root tissues, and nitrite ions were released into xylem sap and into medium culture. In terms of the overall balance, the amount of nitrite recovered represented only half of the amount of nitrate utilized. Nitrite reduction into nitric oxide and perhaps into nitrogen gas could account for this discrepancy. These results appear to be the first report of an increase in nitrate uptake by plant roots under anoxia of tomato at the early fruiting stage, and the rates of nitrite release in nutrient medium by the asphyxiated roots are the fastest yet reported.     

羊草呼吸作用与温度、光照和土壤水分的关系

本文报道了两种土壤水分条件下羊草明呼吸速率与光照和温度的关系,以及暗呼吸速率与温度的关系。结果表明,羊草的明呼吸速率与光强呈非线性函数关系。在低光强下,明呼吸速率随光强升高而有较快的增加;随着光强的增高,其增加速度减慢。在温度低于羊草光合的高温补偿点的条件下,明呼吸速率在一定温度范围内随温度升高而增大;当温度达到一定限度时,有一个下降阶段,而后又回升。羊草的暗呼吸速率随温度增加而升高,且在一定限度内,其升高速度随温度增高而加快。当土壤干旱时,明呼吸速率显著降低,而暗呼吸速率仅略有减小。     

δ13C of CO2 respired in the dark in relation to δ13C of leaf metabolites: comparison between Nicotiana sylvestris and Helianthus annuus under drought

The variations of δ¹³C in leaf metabolites (lipids, organic acids, starch and soluble sugars), leaf organic matter and CO₂ respired in the dark from leaves of Nicotiana sylvestris and Helianthus annuus were investigated during a progressive drought. Under well‐watered conditions, CO₂ respired in the dark was ¹³C‐enriched compared to sucrose by about 4‰ in N. sylvestris and by about 3‰ and 6‰ in two different sets of experiments in H. annuus plants. In a previous work on cotyledonary leaves of Phaseolus vulgaris, we observed a constant ¹³C‐enrichment by about 6‰ in respired CO₂ compared to sucrose, suggesting a constant fractionation during dark respiration, whatever the leaf age and relative water content. In contrast, the ¹³C‐enrichment in respired CO₂ increased in dehydrated N. sylvestris and decreased in dehydrated H. annuus in comparison with control plants. We conclude that (i) carbon isotope fractionation during dark respiration is a widespread phenomenon occurring in C₃ plants, but that (ii) this fractionation is not constant and varies among species and (iii) it also varies with environmental conditions (water deficit in the present work) but differently among species. We also conclude that (iv) a discrimination during dark respiration processes occurred, releasing CO₂ enriched in ¹³C compared to several major leaf reserves (carbohydrates, lipids and organic acids) and whole leaf organic matter.     

Metal tolerance of an indigenous cyanobacterial strain, Lyngbya putealis

Response of an indigenous cyanobacterial strain (Lyngbya putealis) isolated from contaminated site to increasing levels of copper and cobalt was investigated in single metal systems. This cyanobacterial strain showed better response when the medium was spiked with metal. As compared to cobalt treatment, copper had more favorable effect. In single metal systems (copper or cobalt), metal treatments positively effected the cyanobacterial growth as indicated by higher concentration of the primary and accessory photosynthetic pigment (chlorophyll and phycobiliproteins), and biomass production at 0.5 mg/L (M_0.5) as compared to that at control (M₀). Exopolymer production (exopolysaccharides and extracellular proteins) too tended to increase significantly in response to both copper and cobalt in L. putealis and found to be maximum at metal concentration M_2.0. This species also showed increased accumulation of starch and carbohydrates in presence of metal (copper or cobalt) at M_0.1. But the overall response was better for copper as compared to cobalt in single metal systems for almost all the studied parameters which show that the strain offered good protection against copper but was sensitive to cobalt.