Seasonal changes in leaf gas exchange, assimilation response to light and leaf area were monitored in bearing and nonbearing pistachio shoots. Shoot bearing status did not directly affect leaf photosynthetic rate. However, photosynthetic light-response curves strongly varied during the season demonstrating the dominant effect of the tree’s seasonal phenology on assimilation. Early in the season low photosynthetic rates were associated with high rates of dark respiration indicating limited photosynthesis in the young leaves. As leaves matured, dark respiration decreased and assimilation reached maximum values. Photosynthetic efficiency was strongly reduced late in the season due to leaf age and senescence. Fruit load precipitated an early leaf senescence and drop that resulted in a 53% decrease in leaf area in bearing vs. nonbearing shoots, strongly decreasing the seasonal photosynthetic performance of bearing shoots. Bearing shoots produced a 26% lower seasonal carbon gain compared to nonbearing shoots., G. Marino, M. La Mantia, T. Caruso, F. P. Marra., and Obsahuje bibliografii
Photochemical efficiency of photosystem 2 (PS2), assessed from in situ chlorophyll (Chl) fluorescence measurements, was seasonally monitored in five evergreen sclerophyll and five malacophyllous drought semi-deciduous species, co-occurring in the same Mediterranean field site. In evergreen sclerophylls, a considerable drop in the variable (Fv) to maximum (Fm) Chl fluorescence ratio coincided with the lowest winter temperatures, indicating low PS2 efficiency during this period. Summer drought caused a comparatively slight decrease in Fv/Fm and only in three of the five evergreen sclerophyll species tested. In drought semi-deciduous shrubs, the winter drop in Fv/Fm was much less conspicuous. During the summer, and in spite of the severe and prolonged desiccation of their malacophyllous leaves, Fv/Fm was maintained high and only in one species the PS2 efficiency was transiently suppressed, when the leaf relative water content became lower than 30 %. Thus evergreen sclerophylls are more prone to photoinhibition by low winter temperatures, while the sensitivity of drought semi-deciduals depends on the extent and duration of summer drought. and S. Karavatas, Y. Manetas.
Some photosynthetic attributes of leaves and stems were seasonally followed in the small-leaved, summer-deciduous, green-stemmed Mediterranean shrub Calicotome villosa. Both leaves and stems displayed similar photon energy-saturated photosystem 2 (PS2) efficiencies with a minimum during winter. A second minimum in stems during the leafless summer period could be ascribed to sustained photoinhibition. Yet, stems were slightly inferior in photon capture, resulting partly from lower chlorophyll (Chl) contents and partly from higher reflectance due to pubescence. As a result, photon energy-saturated linear electron transport rates were slightly higher in leaves. However, when the total leaf and stem areas were taken into account, this superiority was abolished during autumn and winter and more than overturned during spring. Given that during summer the stems were the only photosynthetic organs, the yearly photosynthetic contribution of stems was much higher. Chl contents in stems displayed a transient and considerable summer drop, accompanied by an increase in the carotenoid to Chl ratio, indicating a photo-protective adaptation to summer drought through a decrease of photo-selective capacity, typical for leaves of many Mediterranean plants. and C. Yiotis, G. K. Psaras, Y. Manetas.
Leaf chlorophyll (Chl) content, net photosynthetic rate (P^) and biomass production were estimated at monthly intervals in Chukrasia tabularis, Dolichandrone atrovirem, Eugenia Jambolana, Gmelina arborea, Lannea coromandelica, Terminalia arjuna and Terminalia bellerica from September 1990 to August 1991. The leaves of all the seven tree species showed significantly higher Chl content during summer than in winter, when it was expressed on area and/or fresh mass basis. Chl concentration showed marked variations from month to month and these differed from one plant species to the other. Clear positive correlations were found between Chl content and and/or biomass production in all the seven deciduous forest tree species studied. The scope for screening and selecting the right type of tree species prospective for energy plantations can be based on a simple technique such as estimation of leaf Chl content and PN.
Seasonal variations in photosynthesis of cassava cv. Rayong 9 (RY9) under irrigated and rain-fed conditions were evaluated at the age of three and six months after planting (MAP). Photosynthetic light-response (PN/I) curves revealed that cassava leaves attained the highest maximum net photosynthetic rates (PNmax) in the rainy season, followed by the hot one, while the lowest PNmax was found in the cool season. Photosynthetic potential of the 3-month-old plants was mostly higher than that of the 6-month-old plants, and the seasonal variation in photosynthetic capacity was also more apparent in the younger plants. PN/I curves were used to predict daily net photosynthetic rate (PN) for each season based on daily average solar radiation data. The predicted PN were considerably lower than the PNmax values. This indicated that solar radiation is a limiting factor for photosynthesis, particularly in the rainy season. The data provided basic information for breeding cassava genotypes with enhanced photosynthesis during the period of unfavorable environment. Furthermore, the data are potentially useful in modeling photosynthesis and crop growth as affected by environmental factors., K. Vongcharoen, S. Santanoo, P. Banterng, S. Jogloy, N. Vorasoot, P. Theerakulpisut., and Obsahuje bibliografii
The ribulose 1,5-bisphosphate carboxylase (RuBPC) activity, protein content and net photosynthetic rate (P^) were estimated at monthly intervals from September 1990 to August 1991 in Chukrasia íabularis, Dolichandrom atrovirens, Eugenia jambolana, Gmelina arborea, Lamea coromandelica, Terminalia arjuna and Terminalia bellehca. The leaves of all these tree species showed significantly higher RuBPC activity during summer than in winter, when it was expressed on the basis of chlorophyll (Chl) content. RuBPC exhibited seasonal variations in its activity and these differed from one tree species to the other. When expressed on the basis of leaf area, the activity of RuBPC correlated with protein content, but not with P^.
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.
Nowadays, a quest for efficient greenhouse heating strategies, and their related effects on the plant's performance, exists. In this study, the effects of a combination of warm days and cool nights in autumn and spring on the photosynthetic activity and efficiency of Phalaenopsis were evaluated; the latter, being poorly characterised in plants with crassulacean acid metabolism (CAM) and, to our knowledge, not reported before in Phalaenopsis. 24-h CO2 flux measurements and chlorophyll (Chl) fluorescence analyses were performed in both seasons on Phalaenopsis 'Hercules' exposed to relatively constant temperature regimes, 25.5/24.0°C (autumn) and 30/27°C (spring) respectively, and distinctive warm day/cool night temperature regimes, 27/20°C (autumn) and 36/24°C (spring), respectively. Cumulated leaf net CO2 uptake of the distinctive warm day/cool night temperature regimes declined with 10-16% as compared to the more constant temperature regimes, while the efficiency of carbon fixation revealed no substantial differences in both seasons. Nevertheless, a distinctive warm day/cool night temperature regime seemed to induce photorespiration. Although photorespiration is expected not to occur in CAM, the suppression of the leaf net CO2 exchange during Phase II and Phase IV as well as the slightly lower efficiency of carbon fixation for the distinctive warm day/cool night temperature regimes confirms the involvement of photorespiration in CAM. A seasonal effect was reflected in the leaf net CO2 exchange rate with considerably higher rates in spring. In addition, sufficiently high levels of photosynthetically active radiation (PAR) in spring led to an efficiency of carbon fixation of 1.06-1.27% which is about twice as high than in autumn. As a result, only in the case where a net energy reduction between the temperature regimes compensates for the reduction in net CO2 uptake, warm day/cool night temperature regimes may be recommended as a practical sustainable alternative. and B. Pollet ... [et al.].
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.].