Abstract

Photosynthetic characteristics of the rotund or orbicular leaves of a monocarpic aquatic plant lotus (Nelumbo nucifera Gaertn.) leaves growing under direct sun light of tropics is studied and the developmental pattern of chloroplast along the foliage during vegetative, bud and flowering stages are studied by the measurement of the quantum efficiency of PS II photochemistry or photosynthetic quantum yield (F_V/F_M) through fast Chl a fluorescence measurement. The quantum efficiency of PS II photochemistry (F_V/F_M) increased in the middle portions of leaf compared to that of base but decreased in the apex (margins) of lotus leaf during vegetative stage. The plant growth (development), maturation and aging (senescence) stages are accomplished with vegetative, bud and flowering stages. The efficiency of PS II quantum yield (F_V/F_M) increased from base to apex during bud stage, but that decreased gradually during flowering stage. The changes in the F_V/F_M ratio with an increase in the ratio during bud (maturation stage) and a subsequent decrease at he aging (senescence stage) clearly demonstrates that the lotus leaf development takes place by the activity of the basal meristems leading to a well defined chloroplast developmental gradient along the leaf lamina. Also, this suggests the use of Chl a fluorescence kinetics for the developmental studies of chloroplast in aquatic plants.

Key words: Chl a fluorescence, Nelumbo nucifera, photosynthetic electron transport, primary photochemistry, photosystem II, photosynthetic quantum yield, F_V/F_M.