Measurement of the chlorophyll (Chl) a fluorescence rise (FR) under higher exciting irradiance (EI), the O-J-I-P transient, or under lower irradiance, the O-I-P transient, is a routinely used method to access photosystem 2 function in thylakoid membranes of chloroplasts. Our measurements with a suspension of pea thylakoid membranes showed that the relative heights of the J and I steps in the FR depended not only on EI but also on the concentration and thickness of the sample. We explain this effect as a consequence of the gradient of EI within the sample. We tested this suggestion by theoretical simulations of the FR based on the model that was previously used for simulation of the FR considering in addition the gradient of EI within the sample. Our theoretical results correspond well with the experiments. The irradiance gradient effect may influence measured FR significantly and this fact should be taken into consideration in the interpretation of measured FRs. and P. Sušila ... [et al.].
Differences in ultrastructural parameters of mesophyll cell (MC) chloroplasts, contents of photosynthetic pigments, and photochemical activities of isolated MC chloroplasts were studied in the basal, middle, and apical part of mature or senescing leaf blade of two maize genotypes. A distinct heterogeneity of leaf blade was observed both for structural and functional characteristics of chloroplasts. In both mature and senescing leaves the shape of MC chloroplasts changed from flat one in basal part of leaf to nearly spherical one in leaf apex. The volume density of granal thylakoids decreased from leaf base to apex in both types of leaves examined, while the amount of intergranal thylakoids increased in mature leaves but decreased in senescing leaves. The most striking heterogeneity was found for the quantity of plastoglobuli, which strongly increased with the increasing distance from leaf base. The differences in chloroplast ultrastructure were accompanied by differences in other photosynthetic characteristics. The Hill reaction activity and activity of photosystem 1 of isolated MC chloroplasts decreased from leaf base to apex in mature leaves. Apical part of senescing leaf blade was characterised by low contents of chlorophyll (Chl) a and Chl b, whereas in mature leaves, the content of Chls as well as the content of total carotenoids (Car) slightly increased from basal to apical leaf part. This was reflected also in the ratio Chl (a+b)/total Car; the ratio of Chl a/b did not significantly differ between individual parts of leaf blade. Both genotypes examined differed in the character of developmental gradient observed along whole length of leaf blade. and J. Kutík ... [et al.].
Responses of two sides of Rumex K-1 leaves to chilling stress (5 °C, photon flux density of 100 µmol m-2 s-1) were studied by using gas exchange, chlorophyll (Chl) fluorescence, and spectrum reflectance techniques. The Chl and carotenoid contents in the two sides were not affected by chilling treatment, and both were higher in the adaxial side. The maximum quantum yield of photosystem (PS) 2 and fraction of functional PS1 in the abaxial side decreased more markedly than those in the adaxial side during the chilling treatment, indicating that the abaxial side was damaged more significantly than the adaxial side. Before chilling, there were no obvious differences in actual photochemical efficiency of PS2, photosynthesis, and photorespiration between two sides of the leaves. Under chilling stress, the actual photochemical efficiency of PS2, photosynthesis, and photorespiration all declined more significantly in the abaxial side, which was partly attributed to lower carboxylation efficiency in the abaxial side than that in the adaxial side. Non-photochemical quenching was higher in the adaxial side, though the de-epoxidation of xanthophyll cycle pigments' pool on basis of Chl was higher in the abaxial side. Both the slower decrease in the photochemical quenching and the higher non-photochemical quenching may account for the higher resistance to chilling stress in the adaxial side of Rumex K-1 leaves. and P.-M. Li ... [et al.].
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
Overexpression of chloroplastic glycerol-3-phosphate acyltransferase gene (LeGPAT) in tomato increased
cis-unsaturated fatty acid content in phosphatidylglycerol (PG) of thylakoid membrane. By contrast, suppressing the expression of LeGPAT decreased the content of cis-unsaturated fatty acid in PG. Under salt stress, sense transgenic plants exhibited higher activities of chloroplastic antioxidant enzymes, lower content of reactive oxygen species (ROS) and less ion leakage compared with the wild type (WT) plants. The net photosynthetic rate (PN) and the maximal photochemical efficiency (Fv/Fm) of photosystem II (PSII) decreased more slightly in sense lines but more markedly in the antisense ones, compared to WT. D1 protein, located in the reactive center of the PSII, is the primary target of photodamage and has the highest turnover rate in the chloroplast. Under salt stress, compared with WT, the content of D1 protein decreased slightly in sense lines and significantly in the antisense ones. In the presence of streptomycin (SM), the net degradation of the damaged D1 protein was faster in sense lines than in other plants. These results suggested that, under salt-stress conditions, increasing
cis-unsaturated fatty acids in PG by overexpression of LeGPAT can alleviate PSII photoinhibition by accelerating the repair of D1 protein and improving the activity of antioxidant enzymes in chloroplasts. and Y. L. Sun ... [et al.].
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
The influence of increased solar UV-B radiation on the photosynthetic characteristics in cowpea seedlings (Vigna unguiculata) grown at optimal (Mgs) and low (Mgd) Mg levels were studied. Both higher UV-B and Mgd treatments caused significant drops of photochemical activities and net CO2 uptake rates (PN). Yet the UV-B-induced decrease in the photosynthetic efficiency was lesser in Mgd seedlings. The leaf Chl a fluorescence measurements proved that after receiving an enhanced UV-B radiation these seedlings showed a significant enhancement in their variable parts. The PSM oscillation of slow fluorescence kinetics was remarkably altered by both treatments. The PN also followed a typical inhibitory pattern as seen in photochemical activities. Concentrations of several chloroplast proteins in trifoliate leaves were significantly reduced by Mgd treatment and unaffected by the other two treatments. Whereas the contents of 43-47 kDa polypeptides in primary leaves were markedly reduced with a maximal effect in Mgd seedlings, no major difference was noted for combined stress. and A. Premkumar, G. Kulandaivelu.
Net CO2 exchange rate (PN) of shoots and diel fluctuations in titratable acidity of leaves of Senecio rowleyanus were measured to determine whether penetration of radiant energy through leaf "windows" (narrow, translucent strips on the leaf epidermis) resulted in increased CAM. Nocturnal PN and nighttime increases in acidity were compared among plants with windows covered with reflective adhesive tape, transparent adhesive tape (to control for potential effects of the adhesive), and no tape. The windows did not significantly enhance the degree of CAM in S. rowleyanus. and K. J. Egbert, C. E. Martin.
Four fluorescence parameters [Fv/Fm = the intrinsic efficiency of energy conversion via photosystem 2 (PS2); Fv'/Fm'= the efficiency of energy conversion via PS2 in the light; P = fraction of absorbed radiant energy utilized for photosynthesis; and D = fraction of absorbed radiant energy dissipated as heat] were measured on leaves of seven species of succulents having epidermal windows. While the function of leaf windows has reportedly been to increase absorption of radiant energy and, hence, the rate of photosynthesis in these species, recent evidence indicates that this translucent portion of epidermal tissue, lacking chlorophyll, may also result in photoinhibition in these species, especially for those with growth habits aboveground. Species with aboveground and belowground growth habits were compared with their leaf windows covered with reflective tape and with windows unobstructed. Results showed no increase in photoinhibition for these species resulting from the radiant energy penetrating the window tissue. Although the efficiency of the photosynthetic mechanism was not significantly influenced by the additional radiant energy provided by the window for individual species, there were significant differences in the efficiencies of radiant energy capture (Fv'/Fm') and utilization (P) between the two growth habits. Species with an aboveground growth habit were less efficient in radiant energy utilization compared with the species having a belowground growth habit. and K. J. Egbert, C. E. Martin.