Effect of low temperature storage and ethylene removal on ripening and gene expression changes in avocado fruit

Abstract

Changes in physiological parameters and in the RNA population from avocado (Persea americana, Mill.) fruit stored under different conditions were analyzed. Storage at low temperatures drastically reduced the respiration and ethylene production rates. Fruit softening was delayed at 7°C, while fruits at 3"C did not soften during long-term storage. Carbon dioxide levels in the atmosphere surrounding fruit treated with a commercial ethylene absorbent, were slightly depressed at 7"C and slightly higher at 3°C, as compared to storage without the absorbent. Ethylene production rates were drastically reduced by low temperatures and appeared not to be affected by ethylene absorption. Changes in the expression of several mRNAs, detected by in vitro translation of RNA during ripening at 20"C (increases in Mr 95, 72, 65, 55, 50, 41, and 40 kD and decreases in 54 and 42 kD polypeptides) were delayed or blocked at low temperatures. Under these conditions, changes in mRNAs encoding two polypeptides (Mr 80 and 42 kD) were found to be opposite those observed during normal ripening, mRNAs for other polypeptides (Mr 90, 69, 47 and 45 kD) showed variations in level depending on storage conditions. A few mRNAs were observed only during cold storage (Mr 62, 60, 58, 57, 56, and 47 kD) and could be related to cold stress or acclimation of the fruits. The results obtained suggest that the main effect of low temperatures in avocado is a delay or blockage in the expression of specific genes related to ripening. The effect of the ethylene absorbent was mainly noted in the polypeptide pattern for translated mRNAs, in which most of the changes observed for non-treated fruit were delayed.