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Abstract
Changes in the level of 1-aminocyclopropane-1-carboxylic acid (ACC) were compared to ethylene production during fruit ripening of avocado (Persea americana Mill.) banana (Musa sapientum L.) and tomato (Lycopersicon esculentum Mill.). Preclimacteric tissues contained less than 0.1 nmol/g of ACC in all tissues. In avocado, the level of ACC increased to 45 nmol/g in the later stage of the climacteric rise, then decreased to 5 nmol/g, and later increased to over 100 nmol/g in overripe fruit. In banana ACC increased to 5 nmol/g during the climacteric, decreased to 2 nmol/g several days after the climacteric peak, and increased up to 5 nmol/g in overripe fruit. Levels of ACC in tomato ranged from 0.1 to 10 nmol/g and were significantly correlated with ethylene production rates in all but overripe fruits. The correlation between the ACC content and the production of ethylene is discussed.
Abstract
Overall plant resistance to environmental stresses is conferred by characters expressed at four levels of organization: developmental, structural, physiological, and metabolic or biochemical (Fig. 1). Characters expressed at the upper levels are usually controlled by many genes. The potential for using recombinant DNA (rDNA) technology to understand and alter stress resistance is presently limited to single-gene traits, especially those expressed at the biochemical level. Such traits may be rare, and the effects on overall crop performance of modifying them cannot be foretold (Fig. 1), but they remain invaluable for basic research. The ability to construct specific mutations in vitro with cloned genes, and then to reintroduce them into the plant via some mechanism of transformation, would provide the power of genetic analysis to test models of molecular function in stress (2, 22). The ability to suppress expression of individual genes by the use of anti-sense messages would serve similar ends (4, 25). Thus, there is much interest in identifying and isolating single genes related to stress resistance or susceptibility. We discuss and criticize three ways of going about this task and show how helpful an understanding of stress physiology and biochemistry can be.