De la Haba, P., De la Mata, L., Molina, E. and Agu¨era, E. 2014. High temperature promotes early senescence in primary leaves of sunflower (Helianthus annuus L.) plants. Can. J. Plant Sci. 94: 659Á669. High temperature affects numerous biochemical and physiological traits in plants. Primary leaves of sunflower (Helianthus annuus L.) were collected from plants grown under a control temperature (day/night regime of 23/198C) or a high temperature (day/night regime of 33/ 298C) for 16, 22, 28, 32 or 42 d. Leaves of sunflower plants exposed to high temperature exhibited decreased growth, as reflected by lower specific leaf mass and reduced leaf area as compared with controls. A superior decrease in soluble protein content during leaf life span in plants grown at high temperature relative to control plants (70% vs. 45%, respectively) suggests that high temperature promotes soluble protein degradation in leaves. High temperature also reduces net photosynthetic rate (P N ) possibly by decreasing the content in photosynthetic pigments and the stomatal conductance (g s ). The activity of nitrate reductase and glutamine synthetase decreased while deaminating activity in glutamate dehydrogenase increased in leaves exposed to high temperature. Our results suggest that high temperature induced early senescence in sunflower leaves, probably as a result of an accumulation of soluble sugars and the associated decrease in starch levels. Oxidative damage resulting from increased H 2 O 2 accumulation and a decline in antioxidant activity may have also contributed to accelerated senescence of primary leaves at high temperature. De la Haba, P., De la Mata, L., Molina, E. et Agu¨era, E. 2014. High temperature promotes early senescence in primary leaves of sunflower (Helianthus annuus L.) plants. Can. J. Plant Sci. 94: 659Á669. Les tempe´ratures e´leve´es affectent plusieurs processus biochimiques et physiologiques chez les plantes. Les premie`res feuilles ont e´te´preleve´es de plants de tournesol (Helianthus annuus L.) cultive´s a`une tempe´rature te´moin (re´gime jour/ nuit de 23/19 8C) et de plants cultive´s aù ne tempe´rature e´leve´e (re´gime jour/nuit de 33/29 8C) 16, 22, 28, 32 et 42 jours apre`s l'e´mergence. Les plants de tournesol cultive´s a`une tempe´rature e´leve´e ont montre´une croissance re´duite qui s'est traduite par une masse foliaire spe´cifique (SLM) et une surface foliaire infe´rieures comparativement aux plantes te´moins.Une diminution plus marque´e au cours de la pe´riode d'e´chantillonnage du contenu en prote´ines solubles chez les plantes cultive´s à tempe´rature e´leve´e comparativement aux plantes te´moins (70% et 45% respectivement) sugge`re que les tempe´ratures e´leve´es favorisent la de´gradation des prote´ines foliaires. L'exposition a`une tempe´rature e´leve´e a e´galement re´duit le taux de photosynthe`se nette (P N ), probablement a`cause de la diminution du contenu des pigments photosynthe´tiques et de la conductance stomatique (g s ). Au cours du de´veloppment foliaire, la tempe´rature e´leve´e a d...
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