Roles of Jasmonates in Fruit Ripening and Environmental Stress

Jasmonates [jasmonic acid (JA) and methyl jasmonate (MeJA)] are linolenic acid-derived compounds. n-Propyl dihydrojasmonate (PDJ), a JA derivative, has been used to improve fruit quality in Japan. In apples (Malus sylvestris L.), PDJ application increased fruit coloration in the field by stimulating the anthocyanin biosynthetic gene MdUFGluT. Jasmonates were also able to regulate ethylene biosynthesis. The expression of the ACC synthase (ACS) 1 and ACC oxidase (ACO) 1 genes increased in the skin of apples and pears (Pyrus communis L.) treated by PDJ at the preclimacteric stage. In contrast, the ACS1 mRNA accumulations decreased in the skin of fruit treated by PDJ at the climacteric stage. These results suggest that jasmonates may influence system 2 ethylene synthesis. Jasmonate application also influenced aroma volatiles as well as ethylene in apples and pears. Jasmonate application to pre-climacteric fruit increased ester and alcohol productions while treatment of climacteric fruit decreased them. Jasmonates have a role in plant defense against environmental stress. The application of PDJ decreased low-temperature injuries such as splitting and spotting in apple fruit. The EC50 values of superoxide anion radial-scavenging activity in PDJ-treated fruit after a low-temperature treatment were lower than in the untreated control. Under low-temperature conditions, the accumulation of the MdCHS gene increased in PDJ-treated fruit, resulting in epi-catechin accumulation. Ultraviolet radiation or water stress induced endogenous jasmonate synthesis in apple seedlings and one-year-old citrus trees, respectively. PDJ application induced stomatal closure in citrus leaves. These results suggest that jasmonates have properties that can be put to practical use in commercial fruit growing.