The aim of this research was to develop a new harvest maturity index for highly coloured stone fruit that is not affected by seasonal or climatic factors. The judgement of commercial maturity is difficult with some cultivars of stone fruit because they develop intense skin pigmentation several days before they are ripe. Studies of the changes of the physiochemical and physiological parameters associated with ripening confirmed that no single measurement is suitable for the assessment of harvest maturity in the Japanese type plum cultivars(Prunus salicina Lindl). Two distinct patterns of ripening behaviour were identified. The cool storage (0 degrees Centigrade) responses of fruit harvested at three stages of maturity were examined. Total soluble proteins were extracted and separated from fruit during maturation and ripening using 2-dimensional gel electrophoresis. At least three proteins were first detected in fruit at optimum commercial harvest maturity. Since Gulfruby, Beauty and Rubyred (Japanese type plum cultivars) accumulated similar concentrations of aminocyclopropane-1-carboxylic acid(ACC), it was suggested that the suppressed-climacteric phenotype is the result of an impaired ability of the fruit to convert this compound to ethylene / Doctor of Philosophy (PhD) (Ph.D.)