Thylakoid-associated Polyamines Adjust the UV-B Sensitivity of the Photosynthetic Apparatus by Means of Light-harvesting Complex II Changes¶

Bioenergetic changes in the microalgal photosynthetic apparatus by extremely high CO2 concentrations induce an intense biomass production

Unicellular green alga Chlorella minutissima, grown under extreme carbon dioxide concentrations (0.036-100%), natural temperature and light intensities (Mediterranean conditions), strongly increase the microalgal biomass through photochemical and non-photochemical changes in the photosynthetic apparatus. Especially, CO(2) concentrations up to 10% enhance the density of active reaction centers (RC/CS(o)), decrease the antenna size per active reaction center (ABS/RC), decrease the dissipation energy (DI(o)/RC) and enhance the quantum yield of primary photochemistry (F(v)/F(m)). Higher CO(2) concentrations (20-25%) combine the above-mentioned photochemical changes with enhanced non-photochemical quenching of surplus energy, which leads to an enhanced steady-state fraction of 'open' (oxidized) PSII reaction centers (q(p)), and minimize the excitation pressure of PSII (1 - q(p)) under very high light intensities (approximately 1700 micromol m(-2) s(-1) maximal value), avoiding the photoinhibition and leading to an enormous biomass production (approximately 2500%). In conclusion, these extreme CO(2) concentrations - about 1000 times higher than the ambient one - can be easily metabolized from the unicellular green alga to biomass and can be used, on a local scale at least, for the future development of microalgal photobioreactors for the mitigation of the factory-produced carbon dioxide.

Response of transglutaminase activity and bound putrescine to changes in light intensity under natural or controlled conditions in Quercus ilex leaves

In order to further study a previously observed relationship between polyamine (PA) content and changes in irradiation, we examined the level of free and bound PAs, the activity of transglutaminase (TGase, EC 2.3.2.13) and chlorophyll fluorescence in holm oak (Quercus ilex L.) leaves in response to different levels of light intensity and amount. A diurnal trend of free and bound putrescine (F-Put and B-Put, respectively) and TGase activity was observed in plants under natural conditions in the forest, with the highest value corresponding to the maximum light intensity and amount of light received by the leaves. In another set of experiments, potted Q. ilex plants in experimental fields were subjected to a range of periods of natural photosynthetic photon flux density (PPFD) by covering or not covering the whole trees. Under a natural photoperiod (uncovered leaves), B-Put content and TGase activity paralleled the diurnal PPFD pattern, reaching a maximum at the highest PPFD; prior to this maximum, free PAs showed a significant rise. Plants that were in darkness until midday and suddenly exposed to high light intensity showed enhanced TGase activity, resulting in the maximum accumulation of B-Put. The involvement of the accumulation of B-Put reflected in the changes of the B-Put/bound spermidine ratio during the photoprotective responses to high light stress in forest plants is discussed in relation to the chlorophyll fluorescence parameters observed.