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.].
In leaves of four tomato (Lycopersicon esculentum Mill.) cultivars (Red Cloud, Floradade, Peto 95, and Scorpio) the contents of chlorophyll (Chl) (a+b), Chl a, and β-carotene decreased due to 100 mM NaCl treatment as compared with those of controls. The contents of soluble sugars and total saccharides were significantly increased in leaves of NaCl-treated plants, but the starch content was not significantly affected. Transmission electron microscopy indicated that in leaves of NaCl-treated plants, the chloroplasts were aggregated, the cell membranes were distorted and wrinkled, and there was no sign of grana and thylakoid structures in chloroplasts. and R. A. Khavari-Nejad, Y. Mostofi.
In view of predicted climatic changes for the Mediterranean region, study of high temperature and drought impacts on physiological responses of endangered species regains relevance. In this context, micropropagated plants of Tuberaria major, a critically endangered species, endemic of Algarve, were transferred to a controlled-environment cabinet with day/night temperatures set at 25/18°C (Reference) or 32/21°C (HT). After 15 days of HT acclimation, some plants were subjected to progressive drought followed by rewatering. The enhancement of temperature alone did not affect water relations and photosynthetic rates (PN) but the stomatal conductance (gs) exhibited a 3-fold increase in comparison with reference plants. The maximum quantum yield of photosystem (PS) II (Fv/Fm), the effective quantum yield of PSII photochemistry (ΦPSII), carotenoid (Car) and anthocyanin content enhanced, whereas the quantum yields of regulated (ΦNPQ) and nonregulated (ΦNO) energy dissipation decreased. Drought combined with HT reduced predawn leaf water potential to values of about -1.3 MPa, which had adverse effects on gas exchange and PSII activity. Values of PN and gs were 71 and 79% lower than those of HT plants. An impairment of photochemical activity was also observed: the decrease in ΦPSII and the increase of ΦNPQ. However, an irreversible photoinhibitory damage had not occurred. Carotenoid and anthocyanin content remained elevated and soluble sugars (SS) increased twice, whereas proline and MDA accumulation was not detected. On the first 24 h after water-stress relief, gs, PN, ΦPSII, and ΦNPQ did not recover, but SS returned to the reference level. Overall, T. major acquired an adequate capacity for a protection against the development of oxidative stress during drought and water recovery under HT. These findings suggest that T. major is prepared to deal with predicted climate changes., M. L. Osório, J. Osório, A. Romano., and Obsahuje bibliografii
The source-sink relationship is one of major determinants of plant performance. The influence of reproductive sink demand on light-saturated photosynthesis (Pmax), dark respiration (RD), stomatal conductance (gs), intrinsic water-use efficiency (WUEi), contents of soluble sugar (SSC), nitrogen, carbon, and photosynthetic pigments was examined in blueberry (Vaccinium corymbosum L. cv. ‘Brigitta’) during the final stage of rapid fruit growth. Measurements were performed three times per day on developed, sun-exposed leaves of girdled shoots with 0.1, 1, and 10 fruit per leaf (0.1F:L, 1F:L, and 10F:L, respectively) and nongirdled shoots bearing one fruit per leaf (NG). Girdling and lower fruit amount induced lower Pmax, gs, N, and total chlorophyll (Chl) and higher WUEi, SSC, RD, Chl a/b ratio and carotenoids-to-chlorophylls ratio (Car/Chl) for the 1F:L and 0.1F:L treatments. The impact of girdling was counterbalanced by 10F:L, with NG and 10F:L having similar values. Variables other than Pmax, RD, gs, WUEi, and SSC were unaffected throughout the course of the day. Pmax and gs decreased during the course of the day, but gs decreased more than Pmax in the afternoon, while WUEi was increasing in almost all treatments. SSC increased from the morning until afternoon, whereas RD peaked at noon regardless of the treatment. Generally, Pmax was closely and negatively correlated to SSC, indicating that sugar-sensing mechanisms played an important role in regulation of blueberry leaf photosynthesis. With respect to treatments, Pmax and N content were positively related, while RD was not associated to substrate availability. The enhanced Car/Chl ratio showed a higher photoprotection under the lower sink demand. Changes in the source-sink relationship in 'Brigitta' blueberry led to a rearrangement of physiological and structural leaf traits which allowed adjusting the daily balance between carbon assimilation and absorbed light energy., E. Jorquera-Fontena, M. Alberdi, M. Reyes-Díaz, N. Franck., and Obsahuje bibliografii
Dark respiration rate in the night (R D) was measured in five-year-old Scots pine (Pinus sylvestris L.) trees grown for two years under ambient (AC) and elevated (AC + 400 µmol mol-1 = EC) CO2 concentrations in open top chambers. Two needle age classes (i.e., current-year and one-year-old) were measured at AC and EC in both AC- and EC-grown pines. Additionally different chemical characteristics were determined on the needles, such as nitrogen (N), carbon (C), starch, and soluble sugar concentrations as well as specific leaf area. The direct, short-term and indirect, long-term effects of EC on R D for the two needle age classes were examined. R D was expressed on a per needle area, needle mass, N, C, and C/N bases. Direct effects were only pronounced in the AC treatment where inhibition of R D was found at EC in both current- and one-year-old needles. Indirect effects were only significant in one-year-old needles where a decrease was found in the EC grown trees as compared with AC ones when R D was expressed per unit needle mass, C, or C/N. R D per unit needle area and needle N were not sensitive to long-term EC, in any needle age class. Long-term EC treatment also influenced the response of the two needle age classes. One-year-old needles from the EC treatment had significantly lower R D than current-year needles, but no such response was observed in the AC treatment. Our experiment re-emphasised the importance of expressing R D on different bases for a correct interpretation of the responses to EC. Moreover, we showed that different needle age classes can respond differently to a CO2 enrichment. and M. E. Jach, R. Ceulemans.
We studied the seasonal changes in water relations, chlorophyll a fluorescence, and leaf saccharide contents of the tropical flood-tolerant trees Acosmium nitens, Campsiandra laurifolia, Eschweilera tenuifolia, Symmeria paniculata, and Psidium ovatifolium. Xylem water potential increased with flooding to a larger extent than leaf sap osmotic potential in all the species, and soluble sugars contributed up to 66 % of osmotic potential at maximum flooding. Starch was accumulated in leaves. Maximum quantum yield of photosystem 2 decreased in emerged leaves, values being always higher than 0.76. Daily maximum net photosynthetic rate and leaf conductance decreased in all the species. This reduction was associated in all the species but S. paniculata with the absence of a compensatory increase in non-photochemical quenching. and E. Rengifo, W. Tezara, A. Herrera.