Changes in the photosynthetic activities during several stages of vegetative growth of Spirodela polyrhiza: Effect of chromate

The photosynthetic behavior of fresh green plants, plants carrying turions and the detached turions of Spirodela polyrhiza, was studied by using chlorophyll a (Chl a) fluorescence. The fresh green fronds showed a normal Chl a fluorescence transient, OJIP. However, the mother fronds carrying turions did not show an OJIP transient. Instead, a clear OKJIP with an additional K step, which usually appears due to limitation on the water splitting system, was detected. The K step again disappeared in matured turions. The photosynthetic performance index (PI) of turions was more than 46% lower than the fresh green plants, which has been correlated with a decrease in the probability that an absorbed photon will move an electron into the electron transport chain. Cr2O72- inhibited the plant growth, though it induces the turion formation. Cr2O72- also induces the K step in green fronds. The overall photosynthetic efficiency of PS II and PS I of green fronds was found to be decreased after Cr2O72- treatment.