Leaf gas exchange, photochemical responses and oxidative damages in assai (Euterpe oleracea Mart.) seedlings subjected to high temperature stress

•Assai palms tolerate constant temperature of 36 °C, but are sensitive to 40 °C.•Net CO2 assimilation and chlorophyll fluorescence were down-regulated under 40 °C.•Photo-oxidative damages and lipid peroxidation were induced by incubation at 40 °C.•The increased antioxidant enzymes activities did not attenuate cell damages.•Leaf chlorosis were only evident under 40 °C and first affected the younger leaves.