Abstract:

The purpose was to determine the effect of high temperature stress on the photosynthetic apparatus, the change of chlorophyll fluorescence parameters in leaves of Phalaenopsis seedlings were measured when subjected to high temperature stress at 38℃ for 4 d, or 25℃ as a control. The results indicated that the contents of total chlorophyll, the maximal quantum yield of photosystem II (Fv/Fm), actual efficiency of PSⅡ electron transport (ΦPSⅡ), apparent photosynthetic electron transport rates (ETR), the photochemical quenching coefficient (qP) were continuously decreased with the increasing days of high temperature stress, while the content of malondialdehyde (MDA), the initial fluorescence (Fo) and the complete non-photochemical quenching coefficient (qN) showed a constant increase. At the late stage of high temperature stress, there are significant differences in the above indexes as compared to those before high temperature stressing. It was concluded that PSⅡ reaction centre in leaves of Phalaenopsis seedlings were inactivated temporarily or destroyed under high temperature stress so that primary reaction of photosynthesis was be blocked, decreased significantly the efficiency of primary light energy conversion of photosystem Ⅱ, and therefore caused acute photo-inhibition, reduced dramatically photosynthetic electron transport activity, resulted in accumulation of excess energy in PSⅡ reaction centre to cause photo-oxidation damage of the photosynthetic apparatus and chlorophyll. However, Phalaenopsis seedlings could alleviate the photochemical damage through radiationless energy dissipation.