Action of the Non-ripening (nor) Mutant on Fruit Ripening of Tomato1

Changes in respiration, ethylene production, firmness, pectolytic enzyme activity and carotenoid accumulation during ripening were monitored in fruit of a segregating population of the non-ripening ( nor ) mutant of tomato ( Lycopersicon esculentum Mill.). In fruit from mutant ( nor/nor ) plants, no respiratory or ethylene climacteric was observed, firmness declined very slowly with only trace levels of polygalacturonase present in mature fruit and phytoene, β-carotene and neurosporene were the major carotenes. In very old fruit (120 days’ post-anthesis), lycopene and β-carotene were the predominant carotenoids, however lycopene content was less than 10% of normal. Ripening of fruit from heterozygous ( nor + /nor ) plants was delayed and occurred more slowly than for normal ( nor + /nor + ) fruit. The respiratory climacteric was partially suppressed, peak ethylene production was one-sixth of normal, fruit softening was retarded, and polygalacturonase activity was lower at comparable maturity stages. Fruit from heterozygous ( nor + nor ) plants accumulated lycopene, gamma-carotene, phytofluene, and phytoene at a slower rate, but β-carotene accumulation was similar to normal. A mechanism for action of nor in control of ripening is proposed.