Capsaicin biosynthesis in water-stressed hot pepper fruits

“Hungariana,” “Beauty Zest,” and “Home Flavor” hot pepper plants (Capsicum annuum L. var. annuum) were grown with an ample or a limited water supply. The fruits of plants in the water deficit treatment were small, had a proportionally heavier placenta and had a higher concentration of capsaicin. The concentration of capsaicin in the placenta of “Beauty Zest” fruits in the water deficit treatment began to increase rapidly 10 days after flowering (DAF). It reached a maximum 30 days DAF and was 3.84-fold higher than in the placenta of control treatment plants. In the pericarp, the concentration of capsaicin reached a maximum 50 days DAF and was 4.52-fold higher than in the control treatment. In “Hungariana” fruits, the concentration of capsaicin in the placenta was not significantly different among treatments. Phenylalanine ammonia-lyase (PAL) activity was higher in the placenta of “Beauty Zest” fruits in the water deficit treatment than in the fruits of control plants 50 DAF. In 40 or 50 DAF, cinnamic acid-4hydroxylase (C4H) activity was higher in plants subjected to the water deficit treatment than in control plants. In both treatments, C4H activity in placenta was 1.4 to 1.5-fold greater than in the pericarp 40 DAF. Capsaicinoid synthetase (CS) activity 40 DAF was 1.45 to 1.58-fold higher in fruits in the water deficit treatment than in fruits in the control treatment. Although peroxidase activity was lower in plants in the water deficit treatment than in the control treatment, the difference was not significant.