Allelopathy Journal

Effect of exogenous cinnamic acid at different concentrations using substrate culture approach, was studied on the structure and function of plasmalemma in cucumber seedlings. Cinnamic acid at 25µM promoted the growth of cucumber seedlings, but inhibition occurred at 50–150µM. Five days after treating the cucumber seedlings with cinnamic acid, the ratio of unsaturated fatty acids to saturated fatty acids (∑U/∑S), the index of unsaturated fatty acids (IUFA) and the double-bond index (DBI) increased. At 6-days after the treatment, these parameters decreased with the increase in concentration of cinnamic acid. Cinnamic acid inhibited the H⁺-ATPase activity at concentration of 100µM (p<0.05), the inhibition ameliorated with increase in cinnamic acid concentrations. However, 25µM cinnamic acid promoted the H⁺-ATPase activity. Cinnamic acid lead to electrolyte exosmosis from the leaves of cucumber seedlings, whose rate under 50µM of cinnamic acid significantly differed from control and related to its concentration positively (p<0.05). The exosmic amounts of K⁺ and NO₃-were significantly higher till 100µM of cinnamic acid compared to control (p<0.01). At cinnamic acid concentration of 150µM, the exosmic amounts of HPO₄²-were significantly higher than control (p<0.01).

This suggested that cucumber seedlings got adapted to the compositions and contents of fatty acids under the autotoxicity stress from cinnamic acid. The cinnamic acid at high concentrations, may damage the structure and function of plasmalemma in cucumber seedlings.