Leaf senescence is a complex phenomenon occurring in all plant species, but it is still poorly understood in plants grown in Mediterranean field conditions and well-adapted to harsh climatic conditions. To better unde...Leaf senescence is a complex phenomenon occurring in all plant species, but it is still poorly understood in plants grown in Mediterranean field conditions and well-adapted to harsh climatic conditions. To better understand the physiological processes underlying leaf senescence in mastic trees （Pistacia lentiscus L.）, we evaluated leaf growth, water and N content, photosystem II （PSII） photochemistry, lipid peroxidation and levels of photosynthetic pigments, antioxidants, abscisic acid, and salicylic acid and jasmonic acid during the complete leaf lifespan, from early expansion to late senescence in relation to natural climatic conditions in the field. While mature leaves suffered from water and N deficit during late spring and summer, both young （emerging） and old （senescing） leaves were most sensitive to photo- oxidative stress, as indicated by reductions in the Fv/Fm ratio and enhanced lipid peroxidation during late autumn and winter. Reductions in the FvlFm ratio were associated with low ^-tocopherol （vitamin E） levels, while very old, senescing leaves additionally showed severe anthocyanin losses. We have concluded that both young （emerging） and old （senescing） leaves suffer oxidative stress in mastic trees, which may be linked in part to suboptimal temperatures during late autumn and winter as well as to low vitamin E levels.展开更多
Cold is a seasonal and circadian risk factor for cardioand cerebrovascular morbidity and mortality. Colder temperatures have been associated with higher blood pressure(BP), based on studies which show that BP levels m...Cold is a seasonal and circadian risk factor for cardioand cerebrovascular morbidity and mortality. Colder temperatures have been associated with higher blood pressure(BP), based on studies which show that BP levels measured during the summer months are generally lower than those measured during the winter months. Residents in geographic areas which have greater seasonal temperature differences show greater fluctuation in BP. Surprisingly, atmospheric pressure, rainfall, and humidity were not related to BP levels. The increased sympathetic nervous activity due to cold, as evidenced by elevated BP and by plasma and urinary catecholamines, has been proposed as being the underlying etiology. Patients with heart failure may experience, in cold conditions, endothelial dysfunction and produce fewer endogenous vasodilators(e.g., nitric oxide, prostaglandins) and more endogenous vasoconstrictors(e.g., endothelin), thus increasing afterload. Arterial stiffness is also related to seasonal BP changes. Increased BP, arterial stiffness and endothelial dysfunction could predispose to increased coronary and cerebrovascular events. Improved protection against lower temperatures or increased doses of existing medications or the addition of newer medications could lead to a reduction in increased cardiovascular mortality in winter. Here, we briefly review findings from existing literature and provide an update on seasonal long-term variation in BP along with the related complications.展开更多
基金supported by the Spanish Government (BFU2009-07294)the research was also received through the prize ICREA Academia given to S.M.-B., funded by the Generalitat de Catalunya
文摘Leaf senescence is a complex phenomenon occurring in all plant species, but it is still poorly understood in plants grown in Mediterranean field conditions and well-adapted to harsh climatic conditions. To better understand the physiological processes underlying leaf senescence in mastic trees （Pistacia lentiscus L.）, we evaluated leaf growth, water and N content, photosystem II （PSII） photochemistry, lipid peroxidation and levels of photosynthetic pigments, antioxidants, abscisic acid, and salicylic acid and jasmonic acid during the complete leaf lifespan, from early expansion to late senescence in relation to natural climatic conditions in the field. While mature leaves suffered from water and N deficit during late spring and summer, both young （emerging） and old （senescing） leaves were most sensitive to photo- oxidative stress, as indicated by reductions in the Fv/Fm ratio and enhanced lipid peroxidation during late autumn and winter. Reductions in the FvlFm ratio were associated with low ^-tocopherol （vitamin E） levels, while very old, senescing leaves additionally showed severe anthocyanin losses. We have concluded that both young （emerging） and old （senescing） leaves suffer oxidative stress in mastic trees, which may be linked in part to suboptimal temperatures during late autumn and winter as well as to low vitamin E levels.
文摘Cold is a seasonal and circadian risk factor for cardioand cerebrovascular morbidity and mortality. Colder temperatures have been associated with higher blood pressure(BP), based on studies which show that BP levels measured during the summer months are generally lower than those measured during the winter months. Residents in geographic areas which have greater seasonal temperature differences show greater fluctuation in BP. Surprisingly, atmospheric pressure, rainfall, and humidity were not related to BP levels. The increased sympathetic nervous activity due to cold, as evidenced by elevated BP and by plasma and urinary catecholamines, has been proposed as being the underlying etiology. Patients with heart failure may experience, in cold conditions, endothelial dysfunction and produce fewer endogenous vasodilators(e.g., nitric oxide, prostaglandins) and more endogenous vasoconstrictors(e.g., endothelin), thus increasing afterload. Arterial stiffness is also related to seasonal BP changes. Increased BP, arterial stiffness and endothelial dysfunction could predispose to increased coronary and cerebrovascular events. Improved protection against lower temperatures or increased doses of existing medications or the addition of newer medications could lead to a reduction in increased cardiovascular mortality in winter. Here, we briefly review findings from existing literature and provide an update on seasonal long-term variation in BP along with the related complications.
