Relationship between ethylene and leaf-yellowing induced by darkness in cut small-flowered chrysanthemum

Abstract

Chrysanthemums (Chrysanthemum × morifolium) are the most widely produced cut flowers in Japan. During transportation, the leaves of cut small-flowered chrysanthemums grown in the summer season sometimes turn yellow. The previous study used detached chrysanthemum leaves to clarify the acceleration of leaf yellowing due to warm temperatures and dark conditions. In this study, to clarify the relationship between ethylene and leaf-yellowing senescence induced in cut small-flowered ‘Kosuzu’ chrysanthemums, ethylene production and sensitivity to ethylene were investigated. Under 24 h of continuous darkness (DD conditions), leaves turned yellow during the experimental period (days 0 to 9), with lightness (L*) and chroma (C*) values of leaves increasing from 35.8 to 53.6 and from 19.1 to 42.8, respectively, and hue values decreasing from 128.0 to 112.9. The concentrations of chlorophyll a and b decreased more under DD conditions than under storage under 12 h light/12 h dark (LD) conditions. Ethylene production by leaves decreased under both light regimes. At days 3 and 4, the leaves of LD flowers produced more ethylene than those of DD flowers. Under both light regimes, treatment with ethylene (10 µL/L for 24 h) did not accelerate leaf-yellowing compared to the control (no ethylene treatment). Hue values of leaves decreased immediately in DD flowers, regardless of ethylene treatment, but there was almost no change in LD flowers during the experimental period. The results suggest that dark conditions induce chlorophyll degradation and leaf-yellowing senescence, chlorophyll degradation under dark conditions is not associated with an increase in endogenous ethylene, and dark conditions may accelerate leaf yellowing markedly compared to exogenous ethylene application in cut small-flowered chrysanthemums.