Gas exchanges and leaf water potential (Ψw) of six-years-old trees of fourteen Prunus amygdalus cultivars, grafted on GF-677, were studied in May, when fruits were in active growing period, and in October, after harvesting. The trees were grown in the field under rain fed conditions. Predawn Ψw showed lower water availability in October compared with May. The lowest Ψw values at midday in May increased gradually afterwards, while in October they decreased progressively until night, suggesting a higher difficulty to compensate the water lost by transpiration. However, relative water content (RWC) measured in the morning was similar in both periods, most likely due to some rainfall that occurred in September and first days of October that could be enough to re-hydrate canopy without significantly increasing soil water availability. The highest net photosynthetic rate (PN) was found in both periods early in the morning (08:00-11:00). Reductions in PN from May to October occurred in most cultivars except in José Dias and Ferrastar. In all cultivars a decrease in stomatal conductance (gs) was observed. Photosynthetic capacity (Pmax) did not significantly change from spring to autumn in nine cultivars, revealing a high resistance of photosynthetic machinery of this species to environmental stresses, namely high temperature and drought. Osmotic adjustment was observed in some cultivars, which showed reductions of ca. 23 % (Duro d' Estrada, José Dias) and 15 % (Tuono) in leaf osmotic potential (Ψπ). Such decreases were accompanied by soluble sugars accumulation. The Portuguese cultivar José Dias had a higher photosynthetic performance than the remaining genotypes. and M. C. Matos ... [et al.].
Impact of UV-A and UV-B radiation on pattern of pigments of the Antarctic macroalga Leptosomia simplex L. was studied during the Polarstern cruise (ANT XII/2) 1994/95 under controlled laboratory conditions. An 8 h exposure to UV-A of 17.6 W m-2 led usually to an increase of carotenoid contents, but to a decrease in contents of chlorophyllide (Chlide) a and chlorophyll (Chl) a. UV-B irradiation (300-320 nm) caused a decrease in contents of Chlide a, lutein, and zeaxanthin, but an increase in contents of Chl a and carotenes. Enhancement of carotenoid contents was attributed to a protection of the photosynthetic apparatus. UV effects on the 15N-ammonium uptake were correlated with the changes in pigment contents.
Spearmint cultivars MSS-5, Arka, and Neera grown in nutrient culture in controlled conditions differed in plant height, number of tillers, internodal position, fresh mass, dry mass, leaf stem ratio, and chlorophyll contents. Initial transpiration rate, stomatal conductivity, and CO2 exchange rate showed better increase in MSS-5 genotype. Mn stress decreased oil content whereas the content of oil constituent carvone increased in MSS-5 and Arka. and P. Singh, A. Misra, N. K. Srivastava.
Cross stress of heat and high irradiance (HI) resulted in the accumulation of active oxygen species and photo-oxidative damage to photosynthetic apparatus of wheat leaves during grain development. Pre-treatment with calcium ion protected the photosynthetic system from oxidative damage by reducing O-2 production, inhibiting lipid peroxidation, and retarding electrolyte leakage from cell. Therefore, high Fv/Fm [maximal photochemical efficiency of photosystem 2 (PS2) while all PS2 reaction centres are open], Fm/F0 (another expression for the maximal photochemical efficiency of PS2), ΦPS2 (actual quantum yield of PS2 under actinic irradiation), qP (photochemical quenching coefficient), and PN (net photosynthetic rate) were maintained, and lower qNP (non-photochemical quenching coefficient) of the leaves was kept under heat and HI stress. EGTA (a chelant of calcium ion) and LaCl3 (a blocker of Ca2+ channel in cytoplasmic membrane) had the opposite effect. Thus Ca ion may help protect the photosynthetic system of wheat leaves from oxidative damage induced by the cross stress of heat and HI. and Hui-Jie Zhao, Ji-Fang Tan.
At various intervals after inoculation of the roots of groundnut plants with the fungus Macrophomina phaseoli, 14CO2 was administered to branch 2 (from the base) of the plants in the light. The effects of the disease on the translocation of 14C-photosynthates out of the source branch to the rest of the plant were studied 24 h after labelling. As the plant aged and the disease symptom development became more evident, an increasing percentage of the fixed 14C-photosynthates was exported from branch 2 of the inoculated plants (IP) compared to the non-inoculated plants (NIP). The apex, main stem, and branch 1 of NIP imported more of the total fixed 14C throughout the developmental stages of the plant except for day 10 after inoculation when branch 1 of IP imported almost 76 % of the total fixed 14C. The roots of IP were the major sink and imported higher percent of the total fixed 14C than the roots of NIP.