In crowns of chestnut trees the absorption of radiant energy is not homogeneous; leaves from the south (S) side are the most irradiated, but leaves from the east (E) and west (W) sides receive around 70 % and those from north (N) face less than 20 % of the S irradiation. Compared to the S leaves, those from the N side were 10 % smaller, their stomata density was 14 % smaller, and their laminae were 21 % thinner. N leaves had 0.63 g(Chl) m-2, corresponding to 93 % of total chlorophyll (Chl) amount in leaves of S side. The ratios of Chl a/b were 2.9 and 3.1 and of Chl/carotenoids (Car) 5.2 and 4.8, respectively, in N and S leaves. Net photosynthetic rate (PN) was 3.9 µmol(CO2) m-2 s-1 in S leaves, in the E, W, and N leaves 81, 77, and 38 % of that value, respectively. Morning time (10:00 h) was the period of highest PN in the whole crown, followed by 13:00 h (85 % of S) and 16:00 h with 59 %. Below 500 µmol m-2 s-1 of photosynthetic photon flux density (PPFD), N leaves produced the highest PN, while at higher PPFD, the S leaves were most active. In addition, the fruits from S side were 10 % larger than those from the N side. and J. Gomes-Laranjo ... [et al.].
The microstructure of leaves and ultrastructure of chloroplasts were examined in tomato (Lycopersicon esculentum L.) plants treated with elevated temperature. Plants were exposed to 35°C for 30 d after florescence. The plants grown continuously under 25°C served as controls. Compared with the controls, the net photosynthetic rate (PN) in stressed plants decreased significantly. Stomatal conductance, intercellular CO2 concentrations, the rate of transpiration, and the limitation of stomatal conductance showed that the decrease in PN was caused mainly by nonstomatal restrictions. Meanwhile, stomata density increased significantly in the stressed plants. The stomata status of opening and closing became disorganized with a prolonged 35°C exposure. The damage of chloroplast membrane occurred earlier and was more serious in the plants under elevated temperature. At the same time, the thylakoids were loosely distributed with lesser grana, but the number of lipid droplets increased in chloroplasts. The number of starch grains in chloroplasts increased first and then decreased. In addition, the length of the main nerve in leaves increased and the main vein showed distortion in the plants stressed by 35°C. An increase was observed in the number of cells on the abaxial side of the main vein and these cells were overly congregated. The thickness of a vertical section became thinner in the stressed leaves. The cells of the upper epidermis thinned, and the ratio of palisade tissue to spongy tissue decreased. Generally, the photosynthetic apparatus of tomato changed significantly and the changed chloroplast ultrastructure might be one of the important reasons that caused the decrease of PN under 35°C., J. Zhang, X. D. Jiang, T. L. Li, X. J. Cao., and Obsahuje bibliografii
Water stress is a major abiotic constraint leading to serious crop losses. Recently, in the Mediterranean region, water stress has become markedly sensed, especially in Citrus orchards. This study investigated the physiological responses of local sour orange (Citrus aurantium L.) clones to severe water stress. Water stress was applied by withholding irrigation during weeks, followed by a rewatering phase during three months. Under water stress, sour orange clones decreased their stomatal conductance, net photosynthetic rate, and transpiration rate. On the contrary, biomass was stable, especially in the Kliaa clone. In addition, reduced leaf water potentials (-3 MPa) and water contents were measured in most of the clones, except Kliaa which kept the highest water potential (-2.5 MPa). After rewatering, all clones recovered except of the Ghars Mrad (GM) clone. Ultrastructural observations of leaf sections by transmission electron microscopy did not reveal marked alterations in the mesophyll cells and chloroplast structure of Kliaa in comparison to the sensitive clone GM, in which palisade parenchyma cells and chloroplasts were disorganized. This contrasting behavior was mainly attributed to genetic differences as attested by molecular analysis. This study highlighted GM as the drought-sensitive clone and Kliaa as the tolerant clone able to develop an avoidance strategy based on an efficient stomatal regulation. Although a high percentage of polyembryony characterizes C. aurantium and justifies its multiplication by seeds, heterogeneous water-stress responses could be observed within sour orange plants in young orchards., A. Ben Salem-Fnayou, I. Belghith, M. Lamine, A. Mliki, A. Ghorbel., and Obsahuje bibliografii