Influence of the developmental stage on the (proto)-hypericin and (proto)pseudohypericin levels of Hypericum plants from Crete.

The contents of (pseudo)hypericin and their immediate precursors were studied in wild populations of various Hypericum species on the island of Crete, Greece. Therefore, the aerial parts of wild grown H. perforatum, H. triquentrifolium, H. empetrifolium and H. perfoliatum shoots were collected throughout the island and the quantitative variations in (proto)hypericin and (proto)pseudohypericin examined. The plant material was harvested at different stages of the life cycle of the species and the contents in the above-mentioned compounds analyzed discriminating between flowers/fruits and leaves/petioles. HPLC analysis of hypericin, pseudohypericin and their immediate precursors, protohypericin and protopseudohypericin, revealed great differences in the contents of the compounds in dependence on the developmental stage of the plants. In all examined species the highest concentrations of hypericin were found during blossoming whereas the lowest concentrations were present during ripening of the fruits. H. perforatum and H. triquentrifolium show much higher hypericin levels in flowers/fruits compared to leaves/petioles, whereas the species H. empetrifolium and H. perfoliatum show similar concentrations of total hypericins in both flowers/fruits and leaves/petioles. In the different species the levels of (proto)hypericin and (proto)pseudohypericin varied, but in almost all samples from flowers/fruits and leaves/petioles the ratio of (proto)hypericin to (proto)pseudohypericin was higher than one. When the total amount of hypericins per entire aerial part of a plant was calculated for all developmental stages, we found that H. perforatum contained the highest amount of hypericin. This in combination with the comparatively high concentration of hypericins in flowers/fruits and in leaves/petioles in this species, as well as the high ratio of (proto)hypericin to (proto)pseudohypericin, especially during the developmental stage of blossoming, encourages us to think about the possibility of cultivating Hypericum perforatum in Crete as a medicinal plant in the future.

Changes in the LHCII-mediated energy utilization and dissipation adjust the methanol-induced biomass increase.

Considerably low methanol concentrations of 0.5% (v/v), induce an immense increase in biomass production in cultures of the unicellular green alga Scenedesmus obliquus compared to controls without additional methanol. The effect is light-regulated and it mimics high-CO2 induced changes of the molecular structure and function of the photosynthetic apparatus. There is evidence that methanol enhances under high light conditions by molecular changes in the LHCII--a decrease of the functional antenna-size per active reaction center--the photochemical effectiveness of the absorbed energy. This means that the non-photochemical quenching (NPQ) is minimized and thereby the overall dissipation energy. Experiments with mutants of Scenedesmus Wt produced evidence that the LHCII is the locus of the mechanism which regulates the methanol effect. The employed mutants were Wt-LHC, lacking a functioning LHCII, the light-dependent greening mutant C-2A', and the double mutant C-2A'-LHC, combining both mutations.

Simulated solar irradiation with enhanced UV-B adjust plastid- and thylakoid-associated polyamine changes for UV-B protection.

Polyamines have been described to protect against numerous oxidative stresses in plants. Increasing UV-B radiation (280-315 nm) in the biosphere may also induce an increase in radical formation in tissues. This study employed the tobacco cultivars Bel B and Bel W3 to describe possible protective functions of polyamines against UV-B radiation in sun light simulators (GSF/Munich) with natural diurnal fluctuations of simulated UV-B. Polyamine measurements on a whole leaf basis in isolated chloroplasts and thylakoids were paralleled to photosynthetic and respiration rates, photosynthetic efficiency, leaf thickness and photosynthetic pigment compositions. The study revealed that an increase of polyamines, and especially of putrescine level in thylakoid membranes upon elevated UV-B exposure comprises one of the primary protective mechanisms in the photosynthetic apparatus of the tobacco variety Bel B against UV-B radiation. The tobacco cultivar Bel W3, sensitive to ozone, was also proved to be sensitive to UV-B. This sensitivity is attributed to its incapability to enhance putrescine level in thylakoid membranes. After prolongation of UV-B exposure, when endogenous plant balances are being gradually restored, due to secondary responses, (e.g., biosynthesis of carotenoids and of additional flavonoids) and the plant is adapting to the altered environmental conditions, then the polyamine level is being reduced. Thus, we can discriminate the UV-B induced stress period from a UV-B acclimation period.

Ozone impact on the photosynthetic apparatus and the protective role of polyamines.

One of the primary plant mechanisms protecting leaf cells against enhanced atmospheric ozone is the accumulation of polyamines, generally observed as an increase in putrescine level, and in particular its bound form to thylakoid membranes. Ozone-sensitive plants of tobacco (cultivar Bel W3) in contrast to ozone-tolerant Bel B, are not able to increase their endogenous thylakoid membrane-bound putrescine when they are exposed to an atmosphere with enhanced ozone concentration, resulting in reduction of their photosynthetic rates and consequently reduction in plant biomass formation. In comparison to the tolerant cultivar Bel B, a prolongation of ozone exposure thus can lead to typical visible symptoms (necrotic spots) in leaves of the sensitive plant. Exogenously manipulated increase of the cellular putrescine levels of the ozone-sensitive Bel W3 is sufficient to revert these effects, whereas a reduction in endogenous putrescine levels of the tolerant cultivar Bel B renders them sensitive to ozone treatment. The results of this work reveal a regulator role for polyamines in adaptation of the photosynthetic apparatus and consequently to its protection in an environment polluted by ozone.