Ammonium nutrition has been suggested to be associated with alterations in the oxidation-reduction state of leaf cells. Herein, we show that ammonium nutrition in Arabidopsis thaliana increases leaf NAD(P)H/NAD(P)+ ratio, reactive oxygen species content and accumulation of biomolecules oxidized by free radicals. We used the method of rapid fractionation of protoplasts to analyse which cellular compartments were over-reduced under ammonium supply and revealed that observed changes in NAD(P)H/NAD(P) + ratio involved only the extrachloroplastic fraction. We also showed that ammonium nutrition changes mitochondrial electron transport chain activity, increasing mitochondrial reactive oxygen species production. Our results indicate that the functional impairment associated with ammonium nutrition is mainly associated with redox reactions outside the chloroplast.
Raman scattering spectra of light-harvesting complex LHCII isolated from spinach were recorded with an argon laser, tuned to excite the most red-absorbing LHCII-bound xanthophylls (514.5 nm). The intensity of the nu(4) band (at ca. 950 cm-1) corresponding to the out-of-plane wagging modes of the C-H groups in the resonance Raman spectra of carotenoids appears to be inversely dependent on the probing laser power density. This observation can be interpreted in terms of excitation-induced change of configuration of the protein-bound xanthophyll owing to the fact that the intensity of this particular band is diagnostic of a chromophore twisting resulting from its binding to the protein environment. The comparison of the shape of the nu(4) band of a xanthophyll involved in the light-induced spectral changes with the shape of the nu(4) band of the xanthophylls present in LHCII, reported in the literature, lets us conclude that, most probably, violaxanthin is a pigment that undergoes light-driven changes of molecular configuration but also the involvement of lutein may not be excluded. Possible physical mechanisms responsible for the configuration changes and physiological importance of the effect observed are discussed.
Chloroplast biogenesis is a multistage process leading to fully differentiated and functionally mature plastids. Complex analysis of chloroplast biogenesis was performed on the structural and functional level of its organization during the photoperiodic plant growth after initial growth of seedlings in the darkness. We correlated, at the same time intervals, the structure of etioplasts transforming into mature chloroplasts with the changes in the photosynthetic protein levels (selected core and antenna proteins of PSI and PSII) and with the function of the photosynthetic apparatus in two plant species: bean (Phaseolus vulgaris L.) and pea (Pisum sativum L). We selected these plant species since we demonstrated previously that the mature chloroplasts differ in the thylakoid organization. We showed that the protein biosynthesis as well as photosynthetic complexes formation proceeds gradually in both plants in spite of periods of darkness. We found that both steady structural differentiation of the bean chloroplast and reformation of prolamellar bodies in pea were accompanied by a gradual increase of the photochemical activity in both species. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.