Atmospheric CO2 concentration continues to rise and is predicted to reach approximately 700 ppm by 2100. Some predictions suggest that the dry season in West Africa could be extended with climate change. This study examined the effects of elevated CO2 concentration and water deficit on growth and photosynthesis of juvenile cacao. Light-saturated photosynthesis (Pmax), quantum efficiency, and intrinsic water-use efficiency increased significantly in response to elevated CO2, as did a range of growth and development responses (e.g. leaf area and leaf number), but the magnitude of the increase was dependent on the water treatment. Stomatal index was significantly greater in the elevated CO2 treatment; an atypical response which may be a reflection of the environment in which cacao evolved. This study shows a positive effect of elevated CO2 on juvenile cacao which may help to alleviate some of the negative impacts of water deficit stress., F. Lahive, P. Hadley, A. J. Daymond., and Obsahuje bibliografii
The objective of this study was to evaluate the significance of blue light (B) in the growth and photosynthetic capacity of cucumber. Gas exchange, chlorophyll (Chl) fluorescence kinetics, chloroplast ultrastructure, and leaf growth were investigated to explore the influence of three different light qualities of light emitting diodes (LEDs) on plant morphogenesis and the development of photosynthetic apparatus in cucumber (Cucumis sativus) leaves from emergence to full expansion under weak light [50 μmol(photon) m-2 s-1]. We found that B could significantly increase the leaf area (LA), shoot elongation, Chl a/b, net photosynthetic rate, and stomatal conductance (g s). In addition, the comparisons of maximal quantum yield of PSII photochemistry and the photosynthetic performance index between B-, W (white light)-, and R (red light)-grown leaves suggested that B was essential for the development of photosynthetic apparatus under weak light. B-grown leaves had the lowest Chl content under weak light, however, they had well-developed chloroplasts with the highest degree of stacked lamellae and the lowest starch accumulation. This could explain to a considerable extent the highest net photosynthetic rate per Chl unit. The results demonstrated that B optimized photosynthetic performance by improving the photosynthetic rate, increasing LA, and prolonging active photosynthesis duration under low irradiance. Therefore B is necessary to ensure healthy development of chloroplasts and highly efficient photosynthetic functions in cucumbers under a weak light environment. More importantly, our study also provided theoretical and technical support for the development of light environmental control technology., X. Y. Wang, X. M. Xu, J. Cui., and Obsahuje bibliografii
The purpose of the current investigation was to evaluate the influence of antimycin A (AA) as an activator of the alternative respiratory pathway (AP) on photosynthetic pigment composition and functional activity of the photosynthetic apparatus of wheat seedlings (Triticum aestivum L.) under exposure to high temperature as well as their acclimation. Our results indicated that a significant decrease (44-74%) of photosynthetic pigment contents was caused by a long-term exposure to high temperature (42°C), while the short-term exposure resulted in 20-46% decline. However, a combined effect of AA and long-term high temperature reduced the total pigment contents by 28-41%. Our results demonstrated that the reduction of the chlorophyll a/b ratio was less significant under the combined effect of AA and high temperature than that under the stressful condition without AA. We observed that short-term and long-term high temperature modified PSII functionality of the first leaves in wheat seedlings, which was manifested by the low maximal quantum yield of PSII photochemistry, maximum fluorescence yield in the dark-adapted state, and by high minimum fluorescence yield in the dark-adapted state. The quantum yield of PSII photochemistry decreased rapidly by 16-24% under the combination of AA and high temperature. Overall, these results suggest that the activation of the alternative pathway, induced by AA, contributed to the stabilization of the photosynthetic apparatus in wheat seedlings under high temperature., A. Batjuka, N. Škute, A. Petjukevičs., and Obsahuje bibliografii
We studied the effect of herbicide and nitrogen supply on photosynthesis in Perilla frutescens L. Britt. Plants were exposed to combined treatment of urea and herbicide, fenoxaprop-P-ethyl (FPE), in various concentrations. FPE reduced significantly chlorophyll (Chl) content, photosynthetic rate, and stomatal conductance, but increased significantly intercellular CO2 concentration; thus, FPE inhibited significantly the photosynthetic capacity. In addition, FPE also decreased significantly the PSII photochemical efficiency, effective quantum yield of photochemical energy conversion in PSII, PSII potential activity, and photochemical quenching of variable Chl fluorescence. It also decreased nonphotochemical quenching. It indicated that FPE impaired PSII and blocked the electron transport in light reaction. The urea treatment at moderate concentration (1-4 g L-1) could antagonize the negative effect of FPE, while the high urea concentration (8 g L-1) aggravated this effect. The treatment with urea (4 g L-1) and then with FPE (1.33 mL L-1) enhanced Chl content index, photosynthetic rate, and stomatal conductance by 12.5, 36.1, and 28.5% compared to FPE treatment alone. Thus, we suggested to treat plants first with urea (4 g L-1) and then by FPE (1.33 mL L-1) as the best and the safest method to balance the fertilization and weeding., J. H. Zhang, S. J. Guo, P. Y. Guo, X. Wang., and Obsahuje bibliografii
Chlorophyll a (Chl a) has an asymmetrical molecular organization, which dictates its orientation and the location of the pigment in the mature photosynthetic apparatus. Although Chl a fluorescence (ChlF) is widely accepted as a proxy for plant photosynthetic performance under countless stress conditions and across species, a mechanistic understanding of this causality is missing. Since water plays a much greater role than solvent for the photosynthetic machinery, elucidating its influence on Chl a may explain the reliable reflection of plant stress response in the ChlF signal. We examine the effect of hydration from well-watered to lethal drought on ChlF imagery results across morphologically diverse species to begin testing the impact of molecular scale hydration of Chl a on ChlF. Our results support a conceptual model where water is an integral part of the photosystems' structure and directly influences Chl a behavior leading to changes in the energy partitioning and ultimately in ChlF., C. R. Guadagno, D. P. Beverly, B. E. Ewers., and Obsahuje bibliografické odkazy
Arthrospira maxima is unique among cyanobacteria, growing at alkaline pH (<11) in concentrated (bi)carbonate (1.2 M saturated) and lacking carbonic anhydrases. We investigated dissolved inorganic carbon (DIC) roles within PSII of A. maxima cells oximetrically and fluorometrically, monitoring the light reactions on the donor and acceptor sides of PSII. We developed new methods for removing DIC based on a (bi)carbonate chelator and magnesium for (bi)carbonate ionpairing. We established relative affinities of three sites: the water-oxidizing complex (WOC), non-heme iron/QA-, and solvent-accessible arginines throughout PSII. Full reversibility is achieved but (bi)carbonate uptake requires light. DIC depletion at the non-heme iron site and solvent-accessible arginines greatly reduces the yield of O2 due to O2 uptake, but accelerates the PSII-WOC cycle, specifically the S2-S3 and S3-S0 transitions. DIC removal from the WOC site abolishes water oxidation and appears to influence free energy stabilization of the WOC from a site between CP43-R357 and Ca2+., G. Ananyev, C. Gates, G. C. Dismukes., and Obsahuje bibliografické odkazy
Ultrafast time resolved emission spectra were measured in whole cells of a PSI-deficient mutant of Synechocystis sp. PCC 6803 at room temperature and at 77K to study excitation energy transfer and trapping. By means of a target analysis it was estimated that the terminal emitter of the phycobilisome, termed allophycocyanin 680, transfers its energy with a rate of (20 ps)-1 to PSII. This is faster than the intraphycobilisome energy transfer rates between a rod and a core cylinder, or between the core cylinders., A. M. Acuña, P. Van Alphen, R. Van Grondelle, I. H. M. Van Stokkum., and Obsahuje bibliografické odkazy
Tropical savanna ecosystems are extremely diverse and important for global carbon storage. In the state of Mato Grosso, tropical savanna (locally known as the Cerrado), turns from well-drained, upland areas into seasonally flooded areas within the Pantanal; however, the Cerrado and the Pantanal share many common tree species, such as Vochysia divergens, a flood-adapted tree native to the Amazon Basin, and Curatella americana, a tree, adapted native to the welldrained the Cerrado. We measured the photosynthetic light response of these species in the the Cerrado and the Pantanal over a 1-year period to determine how these species physiologically adjust to these hydrologically distinct habitats. We hypothesized that neither species would experience a significant decline in maximum, light-saturated photosynthetic rate (Pmax) in their naturalized habitat. Physiological performance of each species was generally higher in the habitat that they were adapted to; however, our data indicated that both species have broad tolerance for seasonal variations in hydrology, allowing them to tolerate seasonal drought during the dry season in the Cerrado, and seasonal flooding during the wet season in the Pantanal. In V. divergens, flexible water-use efficiency, higher specific leaf area (SLA), and a greater ability to adjust mass-based Pmax (Pmax,m) to variations in leaf N and P concentration appeared to be key traits for withstanding prolonged drought in the Cerrado. In C. americana, increases in SLA and higher nutrient-use efficiency appeared to be important in maintaining high rates of Pmax,m in the seasonally flooded Pantanal. Flexibility in physiology and resource-use efficiency may allow these species to survive and persist in habitats with broadly differing hydrology., H. J. Dalmagro, F. de A. Lobo, G. L. Vourlitis, Â. C. Dalmolin, M. Z. Antunes Jr., C. E. R. Ortíz, J. de S. Nogueira., and Obsahuje bibliografii
The effects of foliar spray of putrescine (Put; 8 mM) on chlorophyll (Chl) metabolism and xanthophyll cycle in cucumber seedlings were investigated under saline conditions of 75 mM NaCl. Exogenous Put promoted the conversion of uroporhyrinogen III to protoporphyrin IX and alleviated decreases in Chl contents and in a size of the xanthophyll cycle pool under salt stress. Moreover, the Put treatment reduced the activities of uroporphyrinogen III synthase, chlorophyllase, and Mg-dechelatase and downregulated the transcriptional levels of glutamyl-tRNA reductase, 5-aminolevulinate dehydratase, uroporphyrinogen III synthase, uroporphyrinogen III decarboxylase, and chlorophyllide a oxygenase, but significantly increased the expression levels of non-yellow coloring 1-like, pheide a oxygenase, red chlorophyll catabolite reductase, and violaxanthin de-epoxidase. Taken together, these results suggest that Put might improve Chl metabolism and xanthophyll cycle by regulating enzyme activities and mRNA transcription levels in a way that improved the salt tolerance of cucumber plants., R. N. Yuan, S. Shu, S. R. Guo, J. Sun, J. Q. Wu., and Obsahuje bibliografii
Physiological traits, which are positively associated with yield under salt-stress conditions, can be useful selection criteria in screening for salt tolerance. We examined whether chlorophyll (Chl) content can be used as screening criterion in wheat. Our study involved 5 wheat genotypes under both saline and nonsaline field conditions as well as in a sand-culture experiment. Salt stress reduced significantly biomass, grain yield, total Chl and both Chl a and b in all genotypes. In the sand-culture experiment, Chl accumulation was higher in PF70354/BOW, Ghods, and H499.71A/JUP genotypes at nonsaline control, moderate, and high salt concentrations, respectively. In the field experiment, genotype H499.71A/JUP belonged to those with the highest Chl density. The SPAD (Soil Plant Analysis Development) meter readings were linearly related to Chl content both in the sand-culture and in the field experiment. However, salt stress affected the calibration of SPAD meter. Therefore, separate Chl-SPAD equations were suggested for saline and nonsaline conditions. The correlation coefficients between the grain yield and SPAD were positive and significant both in the sand culture and in the field experiment. These findings suggested that SPAD readings could be used as a tool for rapid assessment of relative Chl content in wheat genotypes. It could be used for the indirect selection of high-yielding genotypes of wheat under saline condition in sand-culture and field experiments., A. Kiani-Pouya, F. Rasouli., and Obsahuje bibliografii