CARBON-DIOXIDE EXCHANGE OF DEVELOPING AVOCADO (PERSEA-AMERICANA MILL) FRUIT

Net efflux of CO2 from attached avocado (Persea americana Mill.) fruit was measured periodically from three weeks after anthesis to fruit maturity. Net CO2 exchange was determined in daylight (light respiration, R1) at a photosynthetic photon flux (PPF) greater than 600-mu-mol m-1 s-1, and in the dark (dark respiration, Rd). Dark respiration and R1 were highest during the early cell division stage of fruit growth (about 25 and 22 nmol CO2 g(dw)-1 s-1, respectively) and decreased gradually until fruit maturity to about 1 and 0.5 nmol CO2 nmol CO2 g(dw)-1 s-1, respectively. Fruit photosynthesis, calculated from the difference between Rd and R1, ranged from 0.5 to 3.1 nmol CO2 g(dw)-1 s-1. Net rate of CO2 assimilation on a fruit dry weight basis was highest during the early stages of fruit growth and reached the lowest rate at fruit maturity. Net rate of CO2 assimilation of fruit exposed to light was 0.4 to 2.5% of that for fully expanded leaves. Although the relative amount of carbon assimilated by the fruit was small compared with the total amount of carbon assimilated by the leaves, the data indicate that avocado fruit contribute to their own carbon requirement by means of CO2 assimilated in the light.