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.
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.].
Chloroplast proteins of the Alb3/YidC/Oxa1p family are necessary for assembly of photosynthetic complexes in the thylakoid membranes. Alb3p in Arabidopsis thaliana is essential for posttranslational LHCII-integration into thylakoid membranes and participates in cotranslational assembly of D1. However, the pleiotropic defects of an Alb3p mutant, albino3, suggest additional functions for Alb3p. To obtain an impression of such potential further Alb3p activities from phenotypic manifestations, properties of mutants disturbed in thylakoid membrane protein transport or carotenoid biosynthesis were compared with the albino3 mutant. Specific defects observed in albino3 were similar to those in a carotenoid synthesis mutant. While this correlation did not provide tangible evidence for Alb3p being involved in the integration of carotenoids in photosynthetic complexes, it suggests a possible avenue for future investigations., M. Kugelmann, A. Fausser, F. Ossenbühl, A. Brennicke, and Obsahuje bibliografii
Two light treatments [ambient sunlight (L1) during the entire growth period and 40% shade (L2) from 40 d after sowing until 24 d after flowering] and two phosphate fertilizer treatments [no phosphate fertilizer application (P0) and a conventional phosphate fertilizer application (P1)] were used to determine how phosphate fertilizer regulates soybean [Glycine max (L.) Merr.] photosynthesis under shading. We showed that phosphorus significantly increased chlorophyll content and grain yield under shading. The light-saturated net photosynthetic rate, apparent quantum yield, maximum electron transport rate, and maximum Rubisco carboxylation rate in P1 under L2 significantly increased. Moreover, phosphate fertilizer significantly improved the electron transfer and PSII reaction center performance under shading. Therefore, phosphate fertilizer increases low light-utilization efficiency by improving PSII performance, promoting ribulose-1,5-bisphosphate regeneration, ensuring a source of carboxylate substrates, and coordinating the balance between photochemical reaction and Calvin cycle under shading.
Phosphoenolpyruvate carboxylase (PEPC) was purified from leaves of four species of Alternanthera differing in their photosynthetic carbon metabolism: Alternanthera sessilis (C3), A. pungens (C4), A. ficoides and A. tenella (C3-C4 intermediates or C3-C4). The activity and properties of PEPC were examined at limiting (0.05 mM) or saturating (10 mM) bicarbonate concentrations. The Vmax as well as Km values (for Mg2+ or PEP) of PEPC from A. ficoides and A. tenella (C3-C4 intermediates) were in between those of C3 (A. sessilis) and C4 species (A. pungens). Similarly, the sensitivity of PEPC to malate (an inhibitor) or G-6-P (an activator) of A. ficoides and A. tenella (C3-C4) was also of intermediate status between those of C3 and C4 species of A. sessilis and A. pungens, respectively. In all the four species, the maximal activity (Vmax), affinity for PEP (Km), and the sensitivity to malate (KI) or G-6-P (KA) of PEPC were higher at 10 mM bicarbonate than at 0.05 mM bicarbonate. Again, the sensitivity to bicarbonate of PEPC from C3-C4 intermediates was in between those of C3- and C4-species. Thus the characteristics of PEPC of C3-C4 intermediate species of Alternanthera are intermediate between C3- and C4-type, in both their kinetic and regulatory properties. Bicarbonate could be an important modulator of PEPC, particularly in C4 plants. and Bhaskarrao Chinthapalli ... [et al.].
Phosphotylatíon of some polypeptides of photosystem 2 (PS2) core was observed for chloroplasts phosphoiylated under anaerobic conditions. These polypeptides appeared in the photosystem 1 (PSI) paiticles isolated from phosphorylated chloroplasts. Phosphorylated PS2 was transferred onto PSI as an integrál complex, which retained photochemical activity and originated variable fluorescence.