Chlorophyll Fluorescence and Photosystem II Activity of Tomato Leaves as Affected by Irradiance and Prohexadione-Calcium

Abstract: The objective of this research was to investigate the effects of irradiances and growth retardant Prohexadione-Calcium on the growth and physiological parameters of tomatoes (Lycopersicon esculentum Mill, cvs ‘Karla ’ and ‘Hari Moran’) grown under a glass greenhouse environment. Main stem length of tomatoes plants decreased in a quadratic pattern as the concentration of Prohexadione-Ca increased. High concentration (300mgl-1) resulted in shorter plants than control plants. The application of 300mgl-1 of Prohexadione-Ca resulted in diminution of the leaf chlorophyll concentration in both cultivars. In addition high concentration significantly affected variable fluorescence Fv, maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), and the others chlorophyll fluorescence parameters (Fo, Fm, Fv/Fo). Since chlorophyll content and variable fluorescence decreased significantly but Fo did not change significantly the decrease of t1/2 indicates negative changes on the acceptor side of PSII, which also may related to the diminution of the Calvin cycle. Furthermore, electron transport rate (ETR), real photochemical efficiency of PSII (ΦPSII), photochemical quenching (qP) and non-photochemical quenching (qN), were recorded for cvs. ‘Karla ’ and ‘Hari Moran ’ under