Ethylene production by tissue slices from preclimacteric, dimacteric, and postdimactenc apples was significantly reduced by isopentenyl adenosine (IPA), and by mixtures of IPA and indoleacetic acid, and of EPA, indoleacetic acid, and gibberellic acid after 4 hours of incubation.Ethylene production by apple (Pyrus malus L.) slices in abscisic acid was increased in preclimacteric tissues, decreased in climacteric peak tissues, and little affected in postclimacteric tissues. Indoleacetic acid suppressed ethylene production in tissues from predcimactedc apples but stimulated ethylene production in late climacteric rise, dimacteric, and postclimacteric tissue slces. Gibberellic acid had less influence in suppressing ethylene production in preclimacteric peak tissue, and little influenced the production in late climacteric rise, dimacteric peak, and postclimacteric tissues. IPA also suppressed ethylene production in pre-and postdimacteric tissue of tomatoes (Lycopersicon esculentum) and avocados (Persea gratissima). If ethylene production in tissue slices of ripening fruits is an index of aging, then IPA would appear to retard aging in ripening fruit, just as other cytokinins appear to retard aging in senescent leaf tissue.Ripening and aging of fruits are associated with their production of ethylene. Ethylene is also assumed to be the hormone which initiates the ripening process (1). Since some fruits ripen without apparent involvement of ethylene, its role as the major fruit ripening agent has been questioned (2, 9). Other plant hormones have been suggested as being involved, with ethylene, in the ripening and senescence of fruit (2). Interaction between ethylene and other plant hormones was observed in seedlings, wherein auxins induced ethylene production and cytokinins and gibberellins influenced either ethylene production or action (5, 6). The interrelationships among hormones in ripening and senescing fruits are less clear and may be more subtle (2), but fruit ripening most likely involves interactions between ethylene and other plant hormones.We report herein the influence of various hormones on ethylene production in slices from preclimacteric, climacteric, and postclimacteric apples, tomatoes, and avocados. This information should help clarify the possible interrelationships between ethylene and other plant hormones in ripening and in aging fruit tissues. MATERIALS AND METHODSGolden Delicious apples (Pyrus malus L. cv. Golden Delicious) grown at Beltsville were selected from a single tree. ' To whom reprint requests should be sent.Experiments with preclimacteric fruit were carried out with fruit picked from the tree in early morning before each experiment. Fruit harvested in late September were stored at 0 C and withdrawn periodically for experiments through January. Upon removal from cold storage, a sample of five fruit was brought to room temperature and then sampled at 20 C for ethylene production. Another five fruit were cut into slices 0.5-cm thick from which discs of 1 cm diameter were cut with ...
Mutant Selection. Most of the ethionine-resistant mutants were selected from wild type cells treated with a mutagen. Specifically, 1 ml (10' cells) of a stationary culture was centrifuged, and the cells were resuspended in 1 ml of minimal medium containing 100 ,ug of N-methyl-N'-nitro-N-nitrosoguanidine (filter-sterilized). After being shaken in the dark for 45 min at 25 C (0.1 % survival), the cells were centrifuged, washed twice, and 0.1-volume aliquots were used to inoculate 10 ml of minimal glucose medium. The cells were then allowed to grow to stationary phase in the light. Aliquots (0.1 ml) containing about 10' cells were then streaked on ethionine gradient agar, placed in a humid atmosphere at 25 C in the light (150 ft-c) and allowed to grow 7 to 9 days. Discrete colonies were picked from the high ethionine portion of the gradient and tested and purified as described below.The gradient plates were prepared by placing a solution of ethionine in a glass cylinder (10 mm x 10 mm) set in the center of a 9-cm Petri dish containing 10 ml of minimal glucose 2% agar medium. The cylinder was sealed to the solidified agar by dipping the end of the cylinder in melted agar before placing it on the solidified agar. One milliliter of minimal glucose medium containing 25 mg of DL-ethionine (0.15 M) was pipetted into the cylinder, and the plate was allowed to "dry" until most of the solution had passed into the agar (1-2 days). Cell
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