We analyzed the response of potted strawberry tree (Arbutus unedo L.) seedlings exposed to water stress by withholding water for 10 d (WS). Leaf water potential, net CO2 assimilation, and stomatal conductance decreased with increasing water deficit. A 30 % reduction of chlorophyll (Chl) content in the antenna complexes was observed in WS-plants. Simultaneously, a decline of photochemical efficiency (Fv/Fm) occurred as a result of an excess of solar radiation energy when carbon assimilation was limited by stomata closure due to soil water deficit. The non-photochemical quenching of Chl fluorescence (ΦNPQ) significantly increased, as well as the leaf contents of zeaxanthin (Z) and antheraxanthin (A) at the expense of violaxanthin during the WS-period. Elevated predawn contents of de-epoxidized xanthophyll cycle components were associated with a sustained lowering of predawn photosystem 2 efficiency; this suggested an engagement of Z+A in a state primed for energy dissipation. Thus, the ability of strawberry trees to maintain the functionality of the xanthophyll cycle during the Mediterranean summer is an efficient mechanism to prevent irreversible damages to the photosynthetic machinery through thermal energy dissipation in the antenna and the reduction in photochemical efficiency. and R. Baraldi ... [et al.].
The oligomeric state of photosystem 2 (PS2) complex in soybean leaves treated with saturating irradiance was studied by non-denaturing polyacrylamide gel electrophoresis (PAGE) and gel filtration chromatography. PS2 dimers resolved by non-denaturing PAGE accounted for about 75 % of total PS2 complex and there was no significant difference in the ratio of PS2 dimer to monomer between samples from saturating irradiance-treated and fully dark-adapted leaves. Furthermore, BBY particles were resolved into four chlorophyll-enriched fractions by gel filtration chromatography. From their molecular masses and protein components, these fractions were deduced to be PS2 dimer, PS2 monomer, oligomeric light-harvesting complex 2 (LHC2), and monomeric LHC2. Also, no change in the proportion of PS2 dimer in total PS2 was observed in the granal region of thylakoid membranes from soybean leaves after saturating irradiation. Hence the dimer is the predominant natural form of PS2 in vivo and no monomerisation of PS2 dimer occurs during saturating irradiance-induced photoinhibition in soybean leaves. and Shi-Qing Cai ... [et al.].
The relationship between soil water availability, physiological responses [leaf chlorophyll (Chl) fluorescence, leaf water potential (Ψ), and stomatal conductance (gs)] and plant stress was studied in Halimium halimifolium (L.) Willk, Cistaceae, in three sites with contrasted water regimes (Monte Blanco - MB, Monte Intermedio - MI, and Monte Negro - MN) of Doñana National Park (SW of Spain) along the day, in September (summer period) and December (winter period) 1994. In winter, differences among the areas were not significant, with Ψ, gs, and photochemical efficiency values of -1.5 MPa, 0.200 cm s-1, and 0.70, respectively. In summer, however, high declines of gs (0.014 cm s-1 in MI and 0.021 cm s-1 in MB), photochemical efficiency (0.65 Fv/Fp in MB and MI sites) and Ψ (-3.76 in MI and -3.04 MPa in MB) were recorded. Winter-summer differences were minimum in well-watered sites (MN) and maximum in MI. The Ψ and photosystem 2 (PS2) fluorescence were correlated and showed similar seasonal patterns in all three areas. and M. Zunzunegui ... [et al.].
The effects of summer and winter stress on the chlorophyll and carotenoid contents and photosystem 2 efficiency were examined in six Mediterranean scrub species. These six species belong to two different plant functional types: drought semi-deciduous (Halimium halimifolium L., Rosmarinus officinalis L., Erica scoparia L.) and evergreen sclerophylls (Juniperus phoenicea L., Pistacia lentiscus L., Myrtus communis L.). Two sites with different water availability were chosen. In the xerophytic site, despite they belong to two different functional types, R. officinalis and J. phoenicea showed a similar response. These were the most affected species in summer. H. halimifolium showed optimal values of Fv/Fm and non-significant seasonal changes in xanthophyll content. In the mesic site, E. scoparia and M. communis were apparently the most affected species by winter climatic conditions. P. lentiscus presented a pattern similar to H. halimifolium, except for elevated F0 values. In all the studied species, lutein plus zeaxanthin content was negatively correlated with Fv/Fm in summer and with leaf water potential, thus indicating that the thermal dissipation of energy was a general pattern for all species. Under stress, plant response is more species-specific than dependent on its functional type. and F. Ain-Lhout ... [et al.].
In the bark of Populus tremula L. photochemical efficiency of photosystem 2 (PS2) determined as Fv/Fm decreased during winter. The strongest reduction was found after cold periods. The degree of reduction depended on irradiance since the lowest levels of Fv/Fm were found on the sun-exposed side of the stem and below thin phellem. Therefore, photoinhibition was partly responsible for the reduction in Fv/Fm. The photochemical efficiency of PS2 recovered in late April about a month before the trees got leaves. In the laboratory, Fv/Fm recovered within about a week under low irradiance at 20 °C. Rapid recovery of photochemical efficiency of PS2 in the bark may be important to reduce respiratory loss of CO2 from the stem before the trees get leaves. and K. A. Solhaug, J. Haugen.
Twelve randomly chosen Stipa tenacissima L. individuals were grouped into three tussock size classes, small (ST), medium (MT), and large (LT) with 5.6±0.8, 34.1±4.2, and 631.9±85.8 g of dry green foliar matter, respectively, in three plots with different S. tenacissima cover. Instantaneous (WUEi) and long-term (WUEl) water-use efficiencies were measured in two seasons of contrasting volumetric soil water content (early winter 21.0±0.8 % and summer 5.8±0.3 %). Maximum photochemical efficiency of photosystem 2 and stomatal conductance in summer assessed the extent of water and irradiance stress in tussocks of different size. WUEi was lower in MT and ST “water spender” strategies than in LT during the high water-availability season. In summer net photosynthetic rate and WUEi were higher and photoinhibition was lower in LT than in MT and ST. Significant spatial variability was found in WUEi. Water uptake was competitive in stands with denser alpha grass and more water availability in summer, reducing their WUEi. However, WUEl showed a rising tendency when water became scarce. Thus it is important to explicitly account for plant size in ecophysiological studies, which must be combined with demographic information when estimating functional processes at stand level in sequential scaling procedures. and D. A. Ramírez ... [et al.].
The PsbH protein of cyanobacterium Synechocystis sp. PCC 6803 was expressed as a fusion protein with glutathione-S transferase (GST) in E. coli grown on a mineral medium enriched in 15N isotope. After enzymatic cleavage of the fusion protein, the 1H-15N-HSQC spectrum of PsbH protein in presence of the detergent β-D-octyl-glucopyranoside (OG) was recorded on a Bruker DRX 500 MHz NMR spectrometer equipped with a 5 mm TXI cryoprobe to enhance the sensitivity and resolution. Non-labelled protein was used for secondary structure estimation by deconvolution from circular dichroism (CD) spectra. Experimental results were compared with our results from a structural model of PsbH using a restraint-based comparative modelling approach combined with molecular dynamics and energetic modelling. We found that PsbH shows 34-38% α-helical structure (Thr36-Ser60), a maximum of around 15% of β-sheet, and 12-19% of β-turn. and D. Štys ... [et al.].
The objective of this study was to assess genotypic variation in soybean chlorophyll (Chl) content and composition, and to test if these data could be used as a rapid screening method to predict genotypic variation in leaf tissue N content. Chl contents and composition were examined among 833 soybean (Glycine max L. Merr.) accessions and related to SPAD meter readings and leaf N content. In the initial year of the study (2002), the relationship between leaf Chl and leaf N contents (r 2 = 0.043) was not sufficiently close for Chl to be useful as a predictive tool for leaf N content. Therefore, leaf N content was not determined in 2004 but samples were again collected for determination of Chl content and composition. In 2002, the soybean accessions separated into two distinct groups according to leaf Chl a/b ratios, with the majority of a mean ratio of 3.79. However, approximately 7 % (60) of the genotypes could be readily assigned to a group with a mean Chl a/b ratio of 2.67. Chl a/b analyses in 2004 confirmed the results obtained in 2002 and of 202 genotypes, all but 6 fell into the same group as in 2002. and F. B. Fritschi, J. D. Ray.
Boron deficiency induced a dramatic inhibition in sunflower plant growth, shown by a reduction in dry mass of roots and shoots of plants grown for 10 d in nutrient solution supplied with 0.02 µM B. This low B supply facilitated the appearance of brown purple pigmentation on the plant leaves over the entire growth period. Compared to B-sufficient (BS) leaves, leakage from B-deficient (BD) leaves was 20 fold higher for potassium, 38 fold for sucrose, and 6 fold for phenolic compounds. High level of membrane peroxidation was detected by measuring peroxidase activities as well as peroxidative products in BD sunflower plants. Soluble and bound peroxidase activities measured in BD thylakoid membranes were accelerated two fold compared to those detected in BS-membranes. No detectable change in soluble peroxidase activity in roots whereas a 4 fold stimulation in bound peroxidase activity was detected. Thylakoid membranes subjected to low B supply showed enhancement in lipoxygenase activity and malondialdehyde (MDA) content in parallel with 40 and 30 % decrease of linoleic and linolenic acid contents (related to total unsaturated fatty acids). A slower rate of Hill reaction activity (40 %) and a suppressed flow of electron transfer of the whole chain (30 %) were detected in BD thylakoid membranes. This reduction was accompanied with a decline in the activity of photosystem 2 shown by a diminished rate of oxygen evolution (42 %) coupled with a quenching (27.5 %) in chlorophyll a fluorescence emission spectra at 685 nm (F685). Thus B is an important element for membrane maintenance, protection, and function by minimizing or limiting production of free oxygen radicals in thylakoid membranes of sunflower leaves.
The review summarizes basic information about slow and fast chlorophyll (Chl) a fluorescence induction kinetics (FIK) recorded using fluorimeters working on a principle of the pulse amplitude modulation (PAM) of a Chl fluorescence signal. It explains fundamental principles of the measuring technique, evaluates the terminology, symbols, and parameters used. Analysis of Chl FIK resulting in a set of Chl fluorescence parameters (FPs) provides qualitative and quantitative information about photosynthetic processes in chloroplasts. Using FPs, one can describe the functioning of the photosynthetic apparatus under different internal and external conditions. Brief comments on proper application of the fluorimetric method in photosynthesis research and some actual examples are also given. and K, Roháček, M. Barták.