In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO2 concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the Fv/Fm in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants. and I. Cechin ... [et al.].
Net photosynthetic rate, radiation use efficiency, chlorophyll (Chl) fluorescence, photochemical reflectance index (PRI), and leaf water potential were measured during a 25-d period of progressive water deficit in quinoa plants grown in a glasshouse in order to examine effects of water stress and ontogeny. All physiological parameters except Fv/Fm were sensitive to water stress. Ontogenic variations did not exist in Fv/Fm and leaf water potential, and were moderate to high in the other parameters. The complete recovery of photosynthetic parameters after re-irrigation was related with the stability in Fv/Fm. PRI showed significant correlation with predawn leaf water potential, Fm', and midday Fv/Fm. Thus PRI and Chl fluorescence may help in assessing physiological changes in quinoa plants across different developmental stages and water status. and T. Winkel, M. Méthy, F. Thénot.
The relationship between soil water availability, physiological responses [leaf chlorophyll (Chl) fluorescence, leaf water potential (Ψ), and stomatal conductance (gs)] and plant stress was studied in Halimium halimifolium (L.) Willk, Cistaceae, in three sites with contrasted water regimes (Monte Blanco - MB, Monte Intermedio - MI, and Monte Negro - MN) of Doñana National Park (SW of Spain) along the day, in September (summer period) and December (winter period) 1994. In winter, differences among the areas were not significant, with Ψ, gs, and photochemical efficiency values of -1.5 MPa, 0.200 cm s-1, and 0.70, respectively. In summer, however, high declines of gs (0.014 cm s-1 in MI and 0.021 cm s-1 in MB), photochemical efficiency (0.65 Fv/Fp in MB and MI sites) and Ψ (-3.76 in MI and -3.04 MPa in MB) were recorded. Winter-summer differences were minimum in well-watered sites (MN) and maximum in MI. The Ψ and photosystem 2 (PS2) fluorescence were correlated and showed similar seasonal patterns in all three areas. and M. Zunzunegui ... [et al.].
In the evergreen Quercus rotundifolia and the co-existing deciduous Q. faginea we studied the diurnal variations in photosynthetic capacity (Pmax), measured as the rate of O2 evolution at photon and CO2 saturation, and in the rate of net CO2 assimilation (PN) in the field during the period of maximum photosynthetic activity. Our aim was to check the contribution of stomatal and non-stomatal limitations to the diurnal variation in photosynthesis, and to study the differences between both species. Q. faginea leaves displayed lower mass per unit area and higher nitrogen content than Q. rotundifolia leaves. The maximum stomatal conductance and PN in the field were higher in Q. faginea than in Q rotundifolia. Also Pmax of Q. faginea was higher than that of Q. rotundifolia. Both species attained in the field a high percentage of the Pmax (around 82 % for Q. faginea and 73 % for Q. rotundifolia). This indicates reduced stomatal limitation of photosynthesis under favourable conditions, especially in Q. faginea. PN underwent a sharp decrease towards mid-day in association with increase in the atmospheric vapour pressure deficit and decrease in the leaf water potential. Pmax was also reduced during mid-day. This demonstrated the contribution of mesophyll limitations to the PN in the two species under stress. The mesophyll limitation of photosynthesis seemed to be similar for both species, independently from the differences in leaf traits between them. and S. Mediavilla, H. Santiago, A. Escudero.