Effects Of Autotoxins On Watermelon (Citrullus Lanatus Thunb.) Seeding Root Morphology And Structures And Cell Protective Enzymes

Autotoxicity is one of the important factors that result to monoculture. Benzole acid and cinnamic acid are two main autotoxins. This research work concerns on the effect of benzole acid and cinnamic acid on watermelon radicle ultrastructure and seeding root cell protective enzymes. The results are as follows:Benzoic acid and cinnamic acid significantly inhibited watermelon radicles elongation, and with the increasing of benzoic acid and cinnamic acid concentration, the growth speed decreased. The radicles were short, more side root, and root tip tissue became brownish. Through the observation to the radicle's ultrastructure it was found that benzoic acid and cinnamic acid can result to root tip nuclei irregular, nucleolus abnormal, and cytoplasm sparse. Vacuoles became more and bigger.Benzoic acid and cinnamic acid significantly influenced cell protective enzymes of watermelon seeding root, and the effects are distinct to different enzymes and concentrations. Benzoic acid and cinnamic acid reduced peroxidase (POD) activity, and with the treated concentration increasing, peroxidase (POD) activity continuously reduced. Effects on superoxide dismutase (SOD) activity expressed double functions of promotion and control: Superoxide dismutase (SOD) activity increased at low phenolic acids concentration, but decreased when the concentration was higher. To nitrate reductase (NR) activity, only cinnamic acid expressed double functions of promotion and control. NR activity could be increased at low cinnamic acid, but be decreased under higher concentration. Benzoic acid couldn't promote NR activity even under low concentration. Effects of benzoic acid and cinnamic acid on plasma membrane H+-ATPase activity was complicate: reduced at first under low concentration (<0.250mmol/L) and then increased (0.250~-0.500mmol/L), but decreased another once when concentration was more higher (>0.500mmol/L). Effects on POD, SOD, NR activity, benzoic acid treated was more significant than cinnamic acid treated, but to plasma membrane H+-ATPase activity, the effects of cinnamic acid treated was more significant than benzoic acid treated.Benzoic acid and cinnamic acid increased membrane permeability of watermelon seeding root. With the concentration increasing, the relative conductance rate continuously be raised, and the increasing degree of benzoic acid treated was more than cinnamic acid treated.