Alam Badre creator Jacob J text xx National Seminar on Plant Physiological Paradigm for Fostering Agro and Biotechnology & Augmenting Environmental Productivity in Millennium 2000 7th - 9th November 2000 : Abstract & Souvenir 9999 monographic und

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Four months old Hevea plants growing as large polybag containers were kept from September 1999 to January 2000 at two agro-climatically distinct locations, namely, Mattupetty, a hill station in the Western Ghats and Kottayam, situated on the plains in the state of Kerala. While both these locations receive abundant sunlight throughout the year except during the brief south-west monsoon spell(June-July), the winter temperatures can be quite cool in Mattupetty and not in Kottayam in December/January when the present studies were made. Low temperature severely inhibited leaf photosynthetic rate (A) in the plants grown at Mattupetty. High light inhibited A in the cold stressed plants, but not in the control plants grown at Kottayam indicating that high light is injurious when the plants are experiencing a low temperature stress. The maximum potential quantum yield of PSII photochemistry as studied from the ratio of the maximum to variable chlorophyll fluorescence (Fv/Fm) in the dark adapted state was also significantly reduced in the low temperature grown plants of Mattupetty. PSII quantum yield was smaller at Mattupetty than at Kottayam at any given light intensity. The above results indicate the occurrence of severe photoinhibition in the low temperature grown Hevea plants, which are naturally acclimated to warm humid conditions. Inspite of the down regulation in the PSII activity, there was relatively more electron transport through PSII for every mole of carbon assimilated and it is suggested that these excess electrons would have produced large amounts of active oxygen species (AOS) which caused photooxidative damage as evidenced from the decreased leaf chlorophyll and increased malondialdehyde (MDA) contents in the leaves of the low temperature grown plants. All these effects were reflected in the extremely poor growth of the plants at Mattupetty. Hevea brasiliensis Photoinhibition Retarded growth PPrnt PPrnt 220216