How photosynthetic light phase of spiny cocklebur (Xanthium spinosum L.) changes during times after herbicide application

Abstract

The photosynthetic light phase of spiny cocklebur (Xanthium spinosum L.) plant was studied by JIP-test at different times (12, 36, 60 and 84 hours) after nicosulfuron and bentazon herbicides application. Results indicated that application of nicosulfuron had no effect on the most of chlorophyll a fluorescence parameters. But, application of bentazon significantly decreased photosystem II (PSII) activity via increasing minimum fluorescence and decreasing maximum fluorescence, variable fluorescence, the activity of the water-splitting complex on the donor side of PSII and especially maximum quantum yield of PSII photochemistry. Application of bentazon had a greater effect on the donor site than on the acceptor site of PSII by increasing absorption flux per reaction center and decreasing the values of efficiency through which the trapped electrons from RCs continue beyond QA and also by reduction of quantum yield for electron transport from QA- to PQ. Reduction in photosynthesis relative vitality (PI) by application of bentazon negatively affected reaction centers per PSII antenna chlorophyll, maximum quantum yield for primary photochemistry and the quantum yield for electron transport. In most case, the inhibitory effects of bentazon on PSII activity were recorded at 36 hours after herbicide application. Bentazon treatment decreased the rate of the electron transport chain and this was supported by increasing the photochemical de-excitation rate constant in the excited antennae of energy fluxes for photochemistry.