Our study examined the relationship between photosynthetic performance and activities of key photosynthetic enzymes to understand the photosynthetic variation and reasons for the variation during dormancy induction under different photoperiods in peach (Prunus persica L. cv. Chunjie). Furthermore, the study explained the changes in the key enzymes from the viewpoint of differential proteomics. The results showed that the leaf net photosynthetic rate (PN) and stomatal conductance tended to decrease, while the intercellular CO2 concentration rose, which indicated that the reduced PN resulted from nonstomatal limitation. During the dormancy induction period, the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) declined, which was the main reason for the reduced PN. Two-dimensional electrophoresis maps and differential protein identification demonstrated that the decrease in activity of the photosynthetic enzymes was mainly due to enzymatic degradation. The enzyme degradation by a long-day treatment occurred later and to a lesser degree than that of the short-day treatment. In the long-day treatment, the carboxylation activity of Rubisco was higher than that of the control treatment, and the PEPC activity and the ratio of the PEPC/Rubisco activity were lower than the corresponding activities during the control treatment. These differences under long-day conditions were significant but did not occur in the short-day treatment, suggesting that the C4 pathway might be more active under short-day conditions., H.-S. Zhang, D.-M. Li, Q.-P. Tan, H.-Y. Gao, D.-S. Gao., and Obsahuje bibliografii
Pachyrhizus ahipa (Wedd.) Parodi, originally from Latin America, is an agronomy interesting legume crop due to high seed protein content and saccharides-rich tuber root. Its capacity of adaptation to Mediterranean climate, where heat and water stress are frequently associated, is being tested. Two accessions of P. ahipa (AC 102 and AC 524) differing in field production were compared as concerns the effects of water stress and high temperature on photosynthetic performance. Membrane integrity was also evaluated through electrolyte leakage (injury index, I%), lipid composition, and ultrastructure observations. Short-term heat stress (40 °C) did not affect net photosynthetic rate (PN), stomatal conductance (gs), and most of fluorescence parameters in both accessions, what was consistent with low electrolyte leakage. However, photosynthetic capacity (Pmax) showed a significant reduction, AC 524 being more affected than AC 102. Relative water content (RWC) below 70 % caused a drastic decrease in PN and gs. Fluorescence parameters, Pmax, and I% were affected in the two accessions, which also presented a strong reduction (42 %) in total fatty acids (TFA). Contents of galactolipids were drastically reduced, and changes in their saturation also occurred, namely a decrease in linolenic acid (C18:3) percentage of monogalactosyl-diacylglycerol (MGDG) in both accessions. Thylakoid ultrastructure in AC 524 submitted to drought showed disorganisation of grana stacking. Mitochondria presented signs of injured cristae. When water-stressed plants were subjected to high temperature, photosynthesis and fluorescence parameters did not show significant additional changes in both accessions. The exposure of drought stressed plants to 40 °C further increased electrolyte leakage in AC 524, but not in AC 102. Chloroplasts, mitochondria, and plasmalemma showed an increased disorganisation. Vesicles appeared in the cytoplasm, which became electron-transparent, reflecting a strong reduction in the number of ribosomes. Hence AC 102 was less affected than AC 524 as regards some components of photosynthetic process, namely Pmax and membrane integrity. This could account for its better yield production previously observed in field grown plants. and M. C. Matos ... [et al.].
Differences in leaf traits among the dune species developing along the Latium coast were analysed. Cakile maritima Scop. subsp. maritima, Elymus farctus (Viv.) Runemark ex Melderis subsp. farctus, Ammophila arenaria (L.) Link subsp. australis (Mabille) Lainz, Ononis variegata L., Pancratium maritimum L., Eryngium maritimum L., and Anthemis maritima L. were considered. The considered species showed a similar net photosynthetic rate (PN) and chlorophyll content (Chl) during the year, with a peak from the end of April to the middle of May [13.0±3.6 μmol (CO2) m-2 s-1 and 0.63±0.21 mg g-1, respectively, mean values of the considered species], favoured by air temperature in the range 13.3-17.5°C, and 6% of soil water availability. In June-July, the increase of air temperature (Tmax = 28.4°C), associated with a lower water availability (42 mm, total rainfall of the period) and a 1% of soil water availability determined a significant decrease of P N (59%, mean of the considered species) and Chl (38%), and an increase of the carotenoid (Car)/Chl ratio (59%). The significant correlation between PN and stomatal conductance (gs) (p<0.05) explained 67% of P N variations. Moreover, the correlation between P N and leaf temperature (Tl) underlined that the favourable Tl enabling 90-100% of the highest PN for the considered species was within the range 23.4 to 26.6°C. P N decreased below half of its maximum value when Tl was over 35.8 and 37.4°C for E. farctus subsp. farctus and A. arenaria subsp. australis, respectively and over 32.2°C for the other considered species (mean value). Leaf mass area (LMA) varied from 6.8 ± 0.7 mg cm-2 (O. variegata) to 30.6 ± 1.6 mg cm-2 (A. arenaria). PCA (principal component analysis) carried out using the considered morphological and physiological leaf traits underlined that the co-occurring species were characterised by different adaptive strategies: E. farctus and A. arenaria photosynthesized for a long period also when air temperature was over 35.8 and 37.4°C, respectively, because of their lower transpiration rates [E, 1.4 ± 0.1 mmol (H2O) m-2 s-1], which seemed to be controlled by the highest LMA. On the contrary, A. maritima and C. maritima subsp. maritima had a higher PN (on an average 52% higher than the others) in the favourable period, allowed by the highest succulence index (SI, 85.7 ± 9 mg cm-2) and the lower LMA. The results allowed us to hypothesize that A. arenaria and E. farctus might be at a competitive advantage relative to the other considered species with respect to the increase of air temperature, by their ability to photosynthesize at sufficient rates also during summer. and L. Gratani, L. Varone, M. F. Crescente.
The photosynthetic rate of seed wings developed from sepals was compared with the leaf photosynthetic rate in nine dipterocarp tree species (Dipterocarpus pachyphyllus, Dryobalanops aromatica, Dryobalanops lanceolata, Shorea beccariana, Shorea ferruginea, Shorea macroptera ssp. bailonii, Shorea macroptera ssp. macropterifolia, Shorea pilosa, and Vatica spp.). The wings showed positive photosynthetic activity, but at much lower rates than in the leaves. The daily CO2 uptake of wings showed slightly negative values in diurnal gas exchange measurements, even in D. aromatica that showed the highest photosynthetic capacity of all nine species. This low photosynthetic rate in the wings may be the result of low nitrogen and chlorophyll contents in the wing compared with leaves. However, the wings had a higher C/N ratio than leaves, and were thicker. Hence, dipterocarp wings have physical strength and defence against herbivores as higher priorities than photosynthetic activity. and T. Kenzo ... [et al.].
Diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem 2 (PS2) as well as Chl content were analyzed in Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub during dehydration and rehydration. The net photosynthetic rate (PN), maximum photochemical efficiency of PS2 (variable to maximum fluorescence ratio, Fv/Fm), quantum efficiency of non-cyclic electron transport of PS2, and Chl content decreased, but non-photochemical quenching of fluorescence and carotenoid content increased in stems with the increasing of drought stress. 6 d after re-hydration, new leaves budded from stems. In the re-watered plants, the chloroplast function was restored and Chl a fluorescence returned to a similar level as in the control plants. This improved hydraulic adjustment in plant triggered a positive effect on ion flow in the tissues and increased shoot electrical admittance. Thus R. soongorica plants are able to sustain drought stress through leaf abscission and keep part of Chl content in stems. and D. H. Xu ... [et al.].
Gas exchanges, chlorophyll (Chl) a fluorescence and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) were determined in tomato (Lycopersicon esculentum Mill.) fruits picked at different developmental stages (immature, red-turning, mature, and over-ripe). The fruits did not show signs of CO2 fixation. However, photochemical activity was detectable and an effective electron transport was observed, the values of Chl fluorescence parameters in green fruits being similar to those determined in the leaves. The RuBPCO activity, which was similar to those recorded in the leaves at the immature stage of the fruit, decreased as the fruit ripened. PEPC activity was always higher than RuBPCO activity. and S. Carrara ... [et al.].
Different pigments often occur together and affect photosynthetic characteristics of the respective leaf portions. In this study, photosynthetic activity in variegated leaves of five cultivars of the ornamental and medicinal plant, Coleus × hybridus hort., was estimated by image analysis and point data measurements of major chlorophyll (Chl) fluorescence parameters and related to the amount of photosynthetic pigments measured with a Chl meter or spectrophotometrically in leaf extracts. Significant differences in Chl and carotenoid (Car) contents were noticed among differentially pigmented sectors of a leaf and among the cultivars. Although the higher Chl concentration was noticed in purple parts compared to green parts of the leaves, the values of minimal and maximal fluorescence yield at the dark- and light-adapted state (F0, Fm, F0', Fm', respectively) were a little lower than those in the green sectors, indicating photoprotective effects provided by anthocyanins and Car, more abundant in the red parts. The lowest Chl and Car content was detected in creamy-yellow and pink sectors and this contributed to low F0, Fm, and Fm', maximal quantum yield of PSII photochemistry, and nonphotochemical and photochemical quenching but high PSII maximum efficiency and effective quantum yield of PSII photochemistry. Both methods of Chl fluorescence analysis revealed heterogeneity in capture, transfer, and dissipation of excitation energy but Chl fluorescence imaging was more suitable in examining very narrow pigmented leaf areas., M. Borek, R. Bączek-Kwinta, M. Rapacz., and Seznam literatury
Leafless Duvalia velutina Lavranos (Apocynaceae) is an
arido-active stem succulent common in the arid region southwest of the Arabian Peninsula. This region is characterized by a short wet season with erratic rainfall and a long dry season with high temperature and high irradiance. We investigated the survival strategy of D. velutina by studying nurse association, gas exchange, and chlorophyll fluorescence. Results showed that D. velutina exhibited the strict nurse association with shade for protection against heat and high irradiance. Results also showed that D. velutina is an obligate CAM plant with ample physiotypic plasticity involving a shift to CAM-idling under prolonged drought. Chlorophyll fluorescence measurements revealed water stress-induced reduction of PSII activity occurring in concomitance with a marked rise of nonphotochemical quenching and chlorenchyma anthocyanin content. These results reflected photoprotective capacity involving nonradiative excess energy dissipation and antioxidative attributes. We concluded that the complex survival strategy of D. velutina in its natural arid habitat includes a multifaceted interplay of nurse association, physiotypic plasticity, and photoprotective mechanisms., Y. S. Masrahi, T. A. Al-Turki, O. H. Sayed., and Obsahuje seznam literatury
Cadmium (Cd) treatments caused an inhibition in the net photosynthetic rate (PN) of peanut (Arachis hypogaea) plants, due to the reduction of stomatal conductance (gs) and photosynthetic pigment contents, as well as the alteration in leaf structure. The decrease of the transpiration rate and gs might result from the Cd-induced xerophyte anatomic features of leaves (i.e. thick lamina, upper epidermis, palisade mesophyll, high palisade to spongy thickness ratio, as well as abundant and small stomata). The decline of PN was independent of the impairment in photosystem 2. and G. R. Shi, Q. S. Cai.
Water deficit is an important exogenous factor that enhances the influx of sucrose into sugarcane (Saccharum spp.) stem internodes during ripening, when photosynthetic ability in supplying sinks is essential. The aim of this study was to test the hypothesis that drought tolerance in sugarcane is associated with an effective antioxidant protection during the ripening phase that might maintain a favorable redox balance in chloroplasts and protect photosynthesis under drought conditions. Two commercial sugarcane varieties, IACSP94-2094 (tolerant) and IACSP96-2042 (sensitive), with contrasting behavior under water deficit, were subjected to water withholding during the ripening stage. Our results revealed that the tolerant variety was less affected by water deficit, maintaining photosynthesis for a longer period and showing a faster recovery after rehydration as compared to the sensitive one. As consequence, the tolerant variety faced lesser excess of light energy at PSII. The maintenance of photosynthesis under water deficit and its fast recovery after rehydration resulted in the lower leaf H2O2 concentration and favorable redox status in the drought-tolerant genotype, which was associated with stimulation of superoxide dismutase during ripening. Our results also revealed that ferric superoxide dismutase isoforms were strongly enhanced under drought conditions, playing an important role in chloroplast redox homeostasis., C. R. G. Sales, P. E. R. Marchiori, R. S. Machado, A. V. Fontenele, E. C. Machado, J. A. G. Silveira, R. V. Ribeiro., and Obsahuje seznam literatury