Oxidative stress in leaves of two olive cultivars under freezing conditions.

Olive is one of the most important cultivated Mediterranean plants. In order to determine the differences in frost resistance of two, two-year-old olive cultivars (Olea europaea cv. Leccino and cv. Oblica) growing on different types of nutrient substrates (soil and coconut fibres), the trees were exposed to low temperature (-5 °C) in the dark. It was shown that low temperature caused an increase in H2O2 concentration, level of lipid peroxidation and carbonyl protein content in both cultivars and on both nutrient substrates, respectively. The CAT and APX activities significantly varied depending on the cultivar, the nutrient substrate type and the time of exposure to low temperature. Cv. Oblica and cv. Leccino growing on coconut fibres showed a better antioxidative response to low temperature probably due to the higher nitrogen and phosphorus concentration established in this type of nutrient substrate. That positive antioxidative response determined on coconut fibres was more pronounced in leaves of cv. Leccino.

PSII photochemistry in vegetative buds and needles of Norway spruce (Picea abies L. Karst.) probed by OJIP chlorophyll a fluorescence measurement.

Vegetative buds represent developmental stage of Norway spruce (Picea abies L. Karst.) needles where chloroplast biogenesis and photosynthetic activity begin. We used the analyses of polyphasic chlorophyll a fluorescence rise (OJIP) to compare photosystem II (PSII) functioning in vegetative buds and fully photosynthetically active mature current-year needles. Considerably decreased performance index (PIABS) in vegetative buds compared to needles pointed to their low photosynthetic efficiency. Maximum quantum yield of PSII (Fv/Fm) in buds was slightly decreased but above limited value for functionality indicating that primary photochemistry of PSII is not holdback of vegetative buds photosynthetic activity. The most significant difference observed between investigated developmental stages was accumulation of reduced primary quinine acceptor of PSII (QA-) in vegetative buds, as a result of its limited re-oxidation by passing electrons to secondary quinone acceptor, QB. We suggest that reduced electron transfer from QA- to QB could be the major limiting factor of photosynthesis in vegetative buds.

Biochemical and epigenetic changes in phytoplasma-recovered periwinkle after indole-3-butyric acid treatment.

AIM: To elucidate the possible mechanism of phytoplasma elimination from periwinkle shoots caused by indole-3-butyric acid (IBA) treatment. METHODS AND RESULTS: It has been shown that a transfer of in vitro-grown phytoplasma-infected Catharanthus roseus (periwinkle) plantlets from medium supplemented with 6-benzylaminopurine (BA) to one supplemented with IBA can induce remission of symptoms and even permanent elimination of 'Candidatus Phytoplasma asteris' reference strain HYDB. Endogenous auxin levels and general methylation levels in noninfected periwinkles, periwinkles infected with two 'Candidatus Phytoplasma' species and phytoplasma-recovered periwinkles were measured and compared. After the transfer from cytokinin- to auxin-containing media, healthy shoots maintained their phenotype, methylation levels and hormone concentrations. Phytoplasma infection caused a change in the endogenous indole-3-acetic acid to IBA ratio in periwinkle shoots infected with two 'Candidatus Phytoplasma' species, but general methylation was significantly changed only in shoots infected with 'Ca. P. asteris', which resulted in the only phytoplasma species eliminated from shoots after transfer to IBA-containing medium. Both phytoplasma infection and treatment with plant growth regulators influenced callose deposition in phloem tissue, concentrations of photosynthetic pigments and soluble proteins, H(2) O(2) levels and activities of catalase (CAT) and ascorbate peroxidase (APX). CONCLUSION: Lower level of host genome methylation in 'Ca. P. asteris'-infected periwinkles on medium supplemented with BA was significantly elevated after IBA treatment, while IBA treatment had no effect on cytosine methylation in periwinkles infected with 'Candidatus Phytoplasma ulmi' strain EY-C. SIGNIFICANCE AND IMPACT OF THE STUDY: Hormone-dependent recovery is a distinct phenomenon from natural recovery. As opposed to spontaneously recovered plants in which elevated peroxide levels and differential expression of peroxide-related enzymes were observed, in hormone-dependent recovery changes in global host genome, methylation coincide with the presence/absence of phytoplasma.

Efficiency of the photosynthetic apparatus in developing needles of Norway spruce (Picea abies L. Karst.).

The photosynthetic performance of developing spruce (Picea abies L. Karst.) needles was investigated. As revealed by previous reports, the biosynthesis of chlorophylls and carotenoids was not following the characteristic chloroplast ultrastructure building up during needle elongation process. The aim of our study was to investigate photosynthetic capability (evaluated by oxygen evolution and chlorophyll a fluorescence kinetics measurements), the dynamics of chloroplast pigments biosynthesis and the expression of major photosynthetic proteins as well as to find out possible correlation between components of issue. Low amounts of chlorophylls and carotenoids, LHC II and Rubisco LSU were detected in the embryonic shoot of vegetative buds. Although PS II was functional, oxygen production was not sufficient to compensate for respiration in the same developmental stage. The light compensation point of respiration was successively lowered during the needle elongation. Nevertheless the significant increase in photosynthetic pigments as well as the high level of expression of LHC II and Rubisco LSU proteins was observed in the later stages of needle development. Our results suggest that, besides light, some other environmental factors could be critical for producing fully functional chloroplasts in rapidly growing young needles.