Accumulation and metabolic profile of phenolic compounds (PheCs; serving as UV-screening pigments and antioxidants) as well as carbon fixation rate (An) and plant growth are sensitive to irradiance and temperature. Since these factors are naturally co-acting in the environment, it is worthy to study the combined effects of these environmental factors to assess their possible physiological consequences. We investigated how low and high irradiance in combination with different temperatures modify the metabolic profile of PheCs and expression of genes involved in the antioxidative enzyme and PheCs biosynthesis, in relation to photosynthetic activity and availability of non-structural carbohydrates (NSC) in spring barley seedlings. High irradiance positively affected An, NSC, PheCs content, and antioxidant activity (AOX). High temperature led to decreased An, NSC, and increased dark respiration, whilst low temperature was accompanied by reduction of UV-A shielding but increase of PheCs content and AOX. Besides that, irradiance and temperature caused changes in the metabolic profile of PheCs, particularly alteration in homoorientin/isovitexin derivatives ratio, possibly related to demands on AOX-based protection. Moreover, we also observed changes in the ratio of sinapoyl-/feruloyl- acylated flavonoids, the function of which is not yet known. The data also strongly suggested that the NSC content may support the PheCs production.

• Keywords
• CO2 assimilation, HPLC, antioxidants, carotenoids, flavonoids, gene expression, non-structural carbohydrates, photosynthetically active radiation (PAR), secondary metabolism, spring barley (Hordeum vulgare), temperature,
• MeSH
• Antioxidants pharmacology   MeSH
• Phenols pharmacology   MeSH
• Photosynthesis MeSH
• Hordeum * metabolism   MeSH
• Temperature MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antioxidants MeSH
• Phenols MeSH

Light quality significantly influences plant metabolism, growth and development. Recently, we have demonstrated that leaves of barley and other plant species grown under monochromatic green light (500-590 nm) accumulated a large pool of chlorophyll a (Chl a) intermediates with incomplete hydrogenation of their phytyl chains. In this work, we studied accumulation of these geranylgeranylated Chls a and b in pigment-protein complexes (PPCs) of Arabidopsis plants acclimated to green light and their structural-functional consequences on the photosynthetic apparatus. We found that geranylgeranylated Chls are present in all major PPCs, although their presence was more pronounced in light-harvesting complex II (LHCII) and less prominent in supercomplexes of photosystem II (PSII). Accumulation of geranylgeranylated Chls hampered the formation of PSII and PSI super- and megacomplexes in the thylakoid membranes as well as their assembly into chiral macrodomains; it also lowered the temperature stability of the PPCs, especially that of LHCII trimers, which led to their monomerization and an anomaly in the photoprotective mechanism of non-photochemical quenching. Role of geranylgeranylated Chls in adverse effects on photosynthetic apparatus of plants acclimated to green light is discussed.

• Keywords
• Arabidopsis thaliana, Chlorophylls, Green light, Structure and function of photosystem II, Thermal stability, Thylakoid membrane,
• MeSH
• Adaptation, Ocular physiology   MeSH
• Arabidopsis metabolism   MeSH
• Chlorophyll metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Prenylation MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll MeSH
• Photosystem II Protein Complex MeSH
• Light-Harvesting Protein Complexes MeSH

The role of non-bilayer lipids and non-lamellar lipid phases in biological membranes is an enigmatic problem of membrane biology. Non-bilayer lipids are present in large amounts in all membranes; in energy-converting membranes they constitute about half of their total lipid content-yet their functional state is a bilayer. In vitro experiments revealed that the functioning of the water-soluble violaxanthin de-epoxidase (VDE) enzyme of plant thylakoids requires the presence of a non-bilayer lipid phase. 31P-NMR spectroscopy has provided evidence on lipid polymorphism in functional thylakoid membranes. Here we reveal reversible pH- and temperature-dependent changes of the lipid-phase behaviour, particularly the flexibility of isotropic non-lamellar phases, of isolated spinach thylakoids. These reorganizations are accompanied by changes in the permeability and thermodynamic parameters of the membranes and appear to control the activity of VDE and the photoprotective mechanism of non-photochemical quenching of chlorophyll-a fluorescence. The data demonstrate, for the first time in native membranes, the modulation of the activity of a water-soluble enzyme by a non-bilayer lipid phase.

• MeSH
• Calorimetry, Differential Scanning MeSH
• Epoxy Compounds metabolism   MeSH
• Kinetics MeSH
• Hydrogen-Ion Concentration MeSH
• Lipid Bilayers chemistry   MeSH
• Lipids chemistry   MeSH
• Magnetic Resonance Spectroscopy MeSH
• Oxidoreductases metabolism   MeSH
• Solubility MeSH
• Spinacia oleracea metabolism   MeSH
• Light MeSH
• Temperature MeSH
• Thylakoids chemistry   MeSH
• Water chemistry   MeSH
• Xanthophylls metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Epoxy Compounds MeSH
• Lipid Bilayers MeSH
• Lipids MeSH
• Oxidoreductases MeSH
• violaxanthin de-epoxidase MeSH Browser
• violaxanthin MeSH Browser
• Water MeSH
• Xanthophylls MeSH