Fruit auxin

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

Various plant species produce both the shorter and the longer transcripts for the same ACS isozyme. For example, organ-speciftc production of different length transcripts was observed in carnation flowers, winter squash, and in tomato leaves, fruits, or elicitor-treated tomato cell suspension. An auxin-induced... 

Increase in fruit size is due mainly to cell enlargement. It is, therefore, not surprising that because auxins (indole-3-acetic acid and its derivatives) control cell extension,400-404 they have also been presumed to play... 

However, the general lack of correlation between endogenous-auxin levels and fruit growth397-409-411 suggests that, for some species at least, auxins are not the sole controlling factors. The conclusion follows that other classes of plant-growth regulators must play a part. 

Ethylene is now considered to be one of the main plant-hormones involved in fruit development. Many responses formerly believed to result from the presence of auxins are now ascribed to induced ethylene production.425 The biosynthetic pathway for formation of ethylene from methionine, in a wide variety of plant tissues, including shoots of mung bean,426 tomato,427 and pea427 carrot427 and tomato428 roots and the fruits of apple,429,430 tomato,427 and avocado,427 has been elucidated, and is as follows. 

Application of ethylene-,4C to plants resulted in only a 2.4% conversion into soluble carbohydrates, 11% into ether-soluble materials, 6.9% into phytol, 31.7% into cellulose and lignin, and 9.6% into soluble protein and non-protein material, mainly phosphates. 9 Treatment of detached fruit (such as apples, bananas, peaches, figs, and pears) with synthetic auxins, especially (2,4,5-trichlorophenoxy) acetic acid, speeded up ripening, as indicated by color, taste, softness, and starch breakdown. 7 Other fruits have been similarly ripened, 8 and the treatments are effective both on climacteric and non-climacteric fruit. 

The results show that the role of gibberellin in fruit set and development must be thoroughly investigated. It has long been the viewpoint that auxins produced in the seeds control fruit set and development. 

Auxins have set several many-seeded fruits such as tomato, but have failed to set single-seeded fruit. Gibberellin has set many-seeded fruits, and Crane, Primer, and Campbell (14) showed that it can also set single-seeded fruits such as peach, almond, and plum. 

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