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.
The chloroplast development in maize (Zea mays L.) is retarded at low growth temperatures. The composition of thylakoid membranes isolated from fiiliy-expanded leaves of plants grown at 17/14 or 14/12 “C (day/night) differed markedly from that of 25/22 "C-grown plants dne to a deficiency of chloroplast-encoded gene products. Appreciable net synthesis of thylakoid proteins in vivo was observed in a 3-h labelling period with p^SJ-methionine at 14/12 “C, but the ratio of accumuiated chloroplast- to nuclear-encoded products was lesser than at 25/22 °C. The protein synthesis by chloroplasts in vitro demonstrated that the accumulation of thylakoid membrane proteins was markedly temperature-dependent. Both the protein assembly into thylakoids and its subsequent breakdown took plače more rapidly at higher temperatures. Extensive differences in nuclear protein composition were observed between maize leaves grown at 14/12 and 25/22 "C, suggesting a possible role for nuclear factors in suppressing the expression of genes for chloroplast proteins at temperatures which inhibit thylakoid assembly.