Leaf gas exchange of terrestrial and epiphytic orchids from the Atlantic Rainforest in northeast Brazil was investigated under artificial growth conditions. The terrestrial orchids showed higher values of all photosynthetic parameters in comparison to epiphytic ones. There was a close relationship between PN and gs for both terrestrial and epiphytic orchids. Taken together, our results demonstrated that the photosynthetic parameters were related to the specific growth habits of the orchids under study., M. V. Pires ... [et al.]., and Obsahuje bibliografii
The aim of the current work was to determine whether grafting could improve salinity tolerance of melon and cucumber, and whether possible induction of tolerance to salt stress was associated with the protection of the photosynthetic apparatus. Two greenhouse experiments were carried out to determine gas exchange, mineral composition, growth and yield of melon (Cucumis melo L. cv. Cyrano) and cucumber (Cucumis sativus L. cv. Akito) plants, either ungrafted or grafted onto the Cucurbita hybrid rootstocks (Cucurbita maxima Duch. × Cucurbita moschata Duch.), ‘P360’, and ‘PS1313’, respectively. Plants were grown hydroponically and supplied with two nutrient solutions - a nonsalinized control and a salinized solution which contained 40 mmol L-1 of NaCl. Salinity induced a smaller decrease in leaf area index (LAI), in grafted-compared to ungrafted plants. Similarly, the
PN and gs reduction in NaCl treatment compared to control were significantly lower in grafted plants (34% and 34%, respectively, for melon and 14% and 15.5%, respectively, for cucumber) compared to ungrafted plants (42% and 40%, respectively, for melon and 30% and 21%, respectively, for cucumber). In all grafting combinations, negative correlations were recorded between Na+ and Cl- in the leaf tissue and PN. Grafting reduced concentrations of sodium, but not chloride, in leaves. Under saline conditions a smaller reduction in melon and cucumber shoot biomass dry mass and fruit yield were recorded, with positive correlations between shoot biomass, yield and PN. These results suggest that the use of salt tolerant Cucurbita rootstock can improve melon and cucumber photosynthetic capacity under salt stress and consequently crop performance., Y. Rouphael ... [et al.]., and Obsahuje bibliografii
Changes of photosynthesis under blue light were examined in the ABA-overproducing 7B-1 mutant in tomato. Net photosynthetic rate (PN), stomatal conductance (gs), intrinsic water-use efficiency (WUEi) and chlorophyll (a+b) [Chl (a+b)] content in leaves of different insertion (1st, 4th and 9th ones) were measured in 5-, 7- and 9-week-old plants. PN, gs, and Chl (a+b) content were mostly similar in young leaves of 7B-1 and wild type (WT) plants. With the aging of leaves, a blue-light-induced increase in PN and gs to steady-state was delayed and steady-state values of PN and gs were lower in 7B-1 plants compared with WT. Steady-state values of WUEi were increased in 4th and 9th leaves of 7B-1 plants compared with WT. The results can be explained by the higher endogenous level of ABA in 7B-1 plants and their lower sensitivity to ABA in earlier growth stage., E. Ježilová ... [et al.]., and Obsahuje bibliografii
The Amur Grape (Vitis amurensis Rupr.) cultivars ’shuangFeng’ and ‘ZuoShanyi’ were grown in shelter greenhouse under natural sunlight and subjected to drought. Sap flow rate, net photosynthetic rate (PN), and chlorophyll (Chl) fluorescence were measured on Amur Grape leaves subjected to different drought treatments. Significant decreases in P N were associated with increasing intercellular CO2 concentration (Ci), suggesting that the reduction in PN was caused by nonstomatal limitation. Analysis of OJIP transients according to the JIP-test protocol revealed that specific (per PSII reaction center) energy fluxes for light absorption, excitation energy trapping and electron transport have significantly changed. The appearance of a pronounced K-step and J-step in polyphasic rise of fluorescence transient suggested the oxygen-evolving complex and electron transport were inhibited. Drought stress has relatively little effect on the parameter maximal quantum yield of PSII photochemistry (Fv/Fm), but the performance index (PIABS) is more sensitive in different drought treatment. There are cultivar differences in the response of PSII activity to drought, the photosynthetic apparatus of ‘ZuoShanyi’ cultivar is more resistant to drought than that of ‘ShuangFeng’, and JIP-test could be a useful indicator for evaluation and selection to drought tolerance., Z. X. Wang ... [et al.]., and Obsahuje bibliografii
Giant rosettes are ones of the most striking features of the vegetation in the high tropical Andes, with Coespeletia moritziana reaching the highest altitudes up to 4,600 m a.s.l. Different from other giant rosettes, this species grows on rock outcrops with poorly developed soils and where water availability may be limited. Two questions are addressed in this study: How does this species respond in terms of water relations to maintain favorable gas-exchange conditions? Considering that adult plants rely on a water-reserving central pith, how do early stages respond to this environment’s extreme conditions? Water relations and gas-exchange studies were carried out on juveniles, intermediate and adult C. moritziana plants during wet and dry seasons in Páramo de Piedras Blancas at 4,200 m a.s.l. Adult plants maintained higher leaf water potentials (ΨL) during the wet season, however, no differences between stages were found for the dry season. Minimum dry season ΨL were never near the turgor loss point in any of the stages. Juveniles show a more strict stomatal control during the dry season to maintain a favorable water status. Net photosynthesis significantly decreased in intermediate and juvenile stages from wet to dry seasons. Our results suggest that
C. moritziana resists more extreme conditions compared to other Andean giant rosettes., F. Rada, A. Azócar, A. Rojas-Altuve., and Obsahuje bibliografii