The effect of variable temperatures (10–50 ºC) on photosynthesis and chlorophyll fluorescence in Conocarpus lancifolius was evaluated. Additionally, the ability of the species to synthesize heat-shock proteins (HSPs) to protect against high temperatures, and malondialdehyde (MDA) as a by-product of lipid peroxidation was investigated. Plants at 10 ºC showed virtually no measurable growth, leaf discoloration and a few brown lesions, while high temperatures (40 and 50 ºC) promoted growth and lateral branch development. Chlorophyll content index, photochemical efficiency (Fv/Fm) of PS II, electron transport rate and photosynthetic rate declined with decreasing temperature but increased significantly at higher temperatures. Heat-shock protein (HSP 70 kDa) was produced at temperatures 30–50 ºC and an additional 90 kDa protein was also produced at 50 ºC. Increase in the efficiency of excitation energy captured by the open PS II reaction centers (Fv/Fm) increased linearly (P B 0.05) with the accumulation of HSP 70 at higher temperatures. However, at low temperatures the concentration of MDA increased significantly, indicating lipid peroxidation due to oxidative stress. The production and accumulation of HSP 70 and 90 kDa coupled with increased electron transport rate and photochemical efficiency can be used to assess survival, growth capacity and to some extent the tolerance of C. lancifolius to elevated temperatures.
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