Role of xanthophyll and water-water cycles in the protection of photosynthetic apparatus in Arbutus unedo and Arabidopsis thaliana

Photosynthetic organisms have sought out the delicate balance between efficient light harvesting under limited irradiance and regulated energy dissipation under excess irradiance. One of the protective mechanisms is the thermal energy dissipation through the xanthophyll cycle that may transform harmlessly the excitation energy into heat and thereby prevent the formation of damaging active oxygen species (AOS). Violaxanthin deepoxidase (VDE) converts violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z) defending the photosynthetic apparatus from excess of light. Another important biological pathway is the chloroplast water-water cycle, which is referred to the electrons from water generated in PSII reducing atmospheric O2 to water in PSI. This mechanism is active in the scavenging of AOS, when electron transport is slowed down by the over-reduction of NADPH pool. The control of the VDE gene and the variations of a set of physiological parameters, such as chlorophyll florescence and AOS content, have been investigated in response to excess of light and drought condition using Arabidopsis thaliana and Arbutus unedo.. Pigment analysis showed an unambiguous relationship between xanthophyll de-epoxidation state ((A+Z)/(V+A+Z)) and VDE mRNA amount in not-irrigated plants. Unexpectedly, gene expression is higher during the night when xanthophylls are mostly epoxidated and VDE activity is supposed to be very low than during the day. The importance of the water-water cycle in protecting the chloroplasts from light stress has been examined through Arabidopsis plant with a suppressed expression of the key enzyme of the cycle: the thylakoid-attached copper/zinc superoxide dismutase. The analysis revealed changes in transcript expression during leaf development consistent with a signalling role of AOS in plant defence responses but no difference was found any in photosynthesis efficiency or in AOS concentration after short-term exposure to excess of light. Environmental stresses such as drought may render previously optimal light levels excessive. In these circumstances the intrinsic regulations of photosynthetic electron transport like xanthophyll and water-water cycles might modify metabolism and gene expression in order to deal with increasing AOS.

Nuove acquisizioni in termini di insufficienza mitralica: complicanze tromboemboliche dopo chirurgia della valvola mitrale: incidenza, predittori e implicazioni cliniche

Objectives: to define in patients undergoing surgery for mitral regurgitation (MR) the risk of thrombo-embolic complications, particularly ischemic stroke (IS) compared to that in the general population. Background: MR is frequent, occurs mostly in the elderly and guidelines recommend surgery in asymptomatic patients but IS risks are unknown. Methods: in 1344 patients (65±12 years) consecutively operated for MR (procedures: 897 valve repair, MRep; 447 valve replacement, 231 mechanical, MVRm; 216 biological, MVRb), thrombo-embolic complications particularly IS (diagnosed by a neurologist) during follow-up were assessed early (<30 days), mid-term (30-180 days) and long-term (180 days). Results: IS occurred in 130 patients and IS or transient ischemic attack in 201. IS rates were 1.9±0.4% and 2.7±0.5%, at 30 and 180 days and 8.1±0.8% at 5 years. IS rates were lowest after MRep vs. MVRb and MVRm (6.1±0.9, 8±2.1 and 16.1±2.7% at 5 years, p<0.001). Comparison to IS expected rates in the population showed high risk within 30 days of surgery (Risk-ratio 41[26-60], p<0.001 but p>0.10 between procedures) and moderate risk after 30 days (risk-ratio 1.7 overall, p<0.001; 1.3 for MRep, p=0.07; 0.98 for MVRb, p=0.95; 4.8 for MVRm, p<0.001). Beyond 180 days, IS risk declined further and was not different from the general population for MRep (1.2, p=0.30) and for MVRb (0.9, p=0.72). Risk of IS or transient ischemic attack was higher than the general population in all groups up to 180 days. The risk of bleeding beyond 30 days was lowest in MRep vs. MVRb and MVRm (7±1, 14±4 and 16±3% at 10 years, p<0.001). Conclusion: thrombo-embolic complications after MR surgery are both reason for concern and encouragement. IS risk is notable early, irrespective of the procedure performed, but long-term is not higher than in the general population after MRep and MVRb. Preference for MRep should be emphasized and trials aimed at preventing IS should be conducted to reduce the thrombo-embolic and hemorrhagic risk in patients undergoing surgery for MR.