The photosynthetic response of three Arachis hypogaea L. cultivars (57-422, 73-30, and GC 8-35) grown for two months was measured under water available conditions, severe water stress, and 24, 72, and 93 h following re-watering. At the end of the drying cycle, all the cultivars reached dehydration, relative water content (RWC) ranging between 40 and 50 %. During dehydration, leaf stomatal conductance (gs), transpiration rate (E), and net photosynthetic rate (PN) decreased more in cvs. 57-422 and GC 8-35 than in 73-30. Instantaneous water use efficiency (WUEi) and photosynthetic capacity (Pmax) decreased mostly in cv. GC 8-35. Except in cv. GC 8-35, the activity of photosystem 1 (PS1) was only slightly affected. PS2 and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were the main targets of water stress. After re-watering, cvs. 73-30 and GC 8-35 rapidly regained gs, E, and PN activities. Twenty-four hours after re-watering, the electron transport rates and RuBPCO activity strongly increased. PN and Pmax fully recovered later. Considering the different photosynthetic responses of the studied genotype, a general characterisation of the interaction between water stress and this metabolism is presented. and J. A. Lauriano ... [et al.].
Coral reef bleaching is a global phenomenon poorly understood today. We investigated during 7 d the photosynthetic behaviour of symbionts of coral reef and temperate foraminifers in hospite, by means of the JIP-test. By this screening test the fast fluorescence rise O-J-I-P, measured by a Plant Efficiency Analyser (PEA) with 10 µs time resolution and 12 bit signal resolution, was analysed. It informs about the structure and function of photosystem 2 being at different physiological states established by adaptation to different irradiance and temperature. The test needs a measuring time in vivo of only 1 to 5 s, and thus many samples can be analysed. The measurements can be done continuously even on a single cell in a test tube or on the reef. The reef foraminifers tested here were Amphistegina and Amphisorus, freshly collected in Mauritius. As a temperate foraminifer, Sorites from the Mediterranean Sea was tested. The cells are very sensitive to slight temperature changes (25 to 32 °C). The comparison showed that the more the foraminifers live in an environment with constant temperature the less they are able to respond to temperature changes and, thus, the less they can adapt. Rising the temperature increases in general the sensitivity to different stress factors, such as high irradiance, pH, CO2, etc. After the test series, the cells recovered fully and were kept in an aquarium for long time observation. and R. J. Strasser, M. Tsimilli-Michael, M. Pêcheux.
We investigated the effects of long-term acclimation of Eucalyptus nitens seedlings to ultraviolet-A (UV-A) irradiation (320-400 nm) on phenolic compounds (gallotannins, stilbenes, and flavonols), photochemical efficiency, and chlorophyll and carotenoid contents. Seedlings were raised under four nutrient regimes, ranging from low to high application rates, in an environment that included or excluded UV-A irradiance. Our aims were: to classify phenolic compounds that absorb in the UV-A and their relative contribution to total UV-A absorption; to identify how phenolic compounds respond to UV-A exposure and exclusion, and to determine how plant nutrient status affects acclimation of photo-and pigment-chemistry to UV-A exposure and exclusion. Gallotannins contributed to only a minor fraction of total absorption within the lower range (320-360 nm) of the UV-A spectrum. Stilbene and flavonol compounds dominated absorption within the 320-360 and 360-400 nm ranges, respectively. Contents of gallotannin were generally high in UV-A-exposed seedlings. Although there was a significant effect of UV-A on contents of stilbenes, a general response (across nutrient treatment comparisons) was not evident. Contents of flavonols were not affected by UV-A exposure. Contents of gallotannin, stilbene, and flavonols decreased from low to high nutrient-application treatments. There were no effects of UV-A on photochemical efficiency or pigment-chemistry. and D. C. Close ... [et al.].