Changes in the content and biosynthesis of phytoalexins in banana fruit

Changes in the phytoalexin content in unripe fruit of banana, Musa acuminat a, were analyzed after various treatments. The results show that level of h ydroxyangiorufone started to increase 1-2 day after either wounding or inoc ulation with conidia of Colletotrichum musae. Inoculation followed by wound ing induced the formation of many other phenylphenalenones. The accumulatio n of hydroxyanigorufone decreased, after its transient maximum, on ripening by exposure of the wounded fruit to ethylene. The level of production of h ydroxyanigorufone in ripe fruit treated by wounding and/of by inoculation w as much tower than that in unripe fruit. 2-Aminooxyacetic acid, an inhibito r of phenylalanine ammonia-lyase (PAL), inhibited the accumulation of hydro xyangiorufone in wounded fruit, and the PAL activity increased after woundi ng and ethylene treatment, respectively. Feeding experiments with [1-1(3C)I ] and [2-C-13]cinnamic acids, and [2-C-13]malonate show that two molecules of cinnamic acid and one of malonate were incorporated into each molecule o f hydroxyanigorufone. The phytoalexins isolated from fruit to which deutera ted hydroxyanigorufone and irenolone had been administered revealed that 2- (4'-hydroxyphenyl)-1,8-naphthalic anhydride was biosynthesized from hydroxy anigorufone rather than from irenolone.