Ethylene auxin-induced

In this context, we recently discovered close correlations between auxin-induced ethylene synthesis, massive accumulations of ABA in root md even more in shoot tissue and inhibition of their growth. This phenomenon, which has been reported for the first time, was demonstrated for auxin herbicides from different chemical classes (Figure 1), such as quinmerac, quinclorac, MCPA, naphthalene acetic acid, dicamba and picloram, and lAA at high concentration, in a variety of dicot species, including members of the Sola-naceae, Umbelliferae, Fabaceae, Scrophulariaceae and Brassicaceae [35, 39, 40]. ABA accumulation and concomitant epinastic effects and reduced shoot growth were also... 

Brassinosteroids are reported to stimulate overall plant growth and development, especially under stress conditions, to enhance auxin-induced growth as well as auxin-induced ethylene production (5, 6). Brassinosteroids interact with most of the phytohormones, such as cytokinins and gibberellins, and in particular with auxin. 

Brassinosteroids (BRs) interact strongly with auxins. In some test systems, the response is synergistic. BRs, alone and in combination with auxins, induce the synthesis of ethylene. 

A second effect of ethylene is to alter the direction of cell enlargement in stems and roots [81]. By causing a change in orientation of cellulose microfibrils from transverse to random or longitudinal, it causes cells to swell up rather than elongate. As a result, stems and roots become shorter and thicker. The inhibition of stem and root growth induced by excess auxin is due in part to auxin-induced ethylene [82]. In a few tissues, such as... 

In 1971, using the auxin-induced ethylene-producing system of mung bean hypocotyls, Sakai and Imaseki [70] proposed that auxin induces a protein essential to ethylene formation and that the protein is rapidly inactivated with an apparent half-life of 35 min. A similar result was obtained with pea epicotyls [71]. The short-lived essential protein was later identified as ACC synthase [32,72,73]. Wound-induced ACC synthase of tomato fmits is also inactivated but with a slightly longer half-life (30-100 min) [74]. 

In most cases, a detectable induction of mRNA levels is observed within 15-30 min following auxin exposure. The levels of three soybean mRNAs (detected by the cDNA clones 6, lOA and 15) are induced by 2.5 min of treatment of excised elongating soybean hypocotyl sections with the synthetic auxin 2,4-D [8]. These mRNAs and others identified in soybean [5, 16], pea [13] and tobacco [14] are specifically induced by auxins such as lAA and NAA, and not induced by nonauxin analogs. With some exceptions, these auxin-induced sequences do not accumulate in response to other plant growth regulators such as GA, ABA, cytokinins and ethylene, or to environmental stresses such as heat shock or cold... 

Previously we showed that the increase in auxin-induced ACC synthase activity could be partially suppressed by ethylene. If ethylene synthesis in auxin-treated tissue is inhibited by AVG, the endogenous activity of ACC synthase greatly increases [15]. A similar effect of ethylene was also found in wound-induced ACC... 

In any event this behaviour, whichever explanation is favored, can only be a modifying factor, for the three types of results inhibition by applied ethylene, release of auxin-induced inhibition by reduced pressure, and similar release by ethylene antagonists — leave little doubt as to the major influence. The totality of inhibition by the intact growing apex evidently includes some secondary component, and this may explain some of the inconclusiveness of the earlier work. 

Hag L, Curtis RW (1968) Production of ethylene by fungi. Science 159 1357-1358 Imaseki H, Pjon C-J (1970) The effect of ethylene on auxin-induced growth of excised rice coleoptile segments. Plant Cell Physiol 11 827-829 Imaseki H, Pjon C-J, Furuya M (1971) Phytochrome action in Oryza sativa L. IV. Red and far-red reversible effect on the production of ethylene in excised coleoptiles. Plant Physiol 49 631-633... 

Imaseki H, Kondo K, Watanabe A (1975) Mechanism of cytokinin action on auxin-induced ethylene production. Plant Cell Physiol 16 777-787 Itai C, Vaadia Y (1965) Kinetin-like activity in root exudate of water-stressed sunflower plants. Physiol Plant 18 941-944... 

Kang BG, Newcomb W, Burg SP (1971) Mechanism of auxin-induced ethylene production. Plant Physiol 47 504-509... 

Sakai S, Imaseki H (1971) Auxin-induced ethylene production by mung bean hypocotyl segments. Plant Cell Physiol 12 349-359... 

Yang SF (1980) Regulation of ethylene biosynthesis. Hortscience 15 238-243 Yeoman MM, Brown R (1971) Effects of mechanical stress on the plane of cell division in developing callus cultures. Ann Bot 35 1101-1112 Yu Y-B, Adams DO, Yang SF (1979) Regulation of auxin-induced ethylene production in mung bean hypocotyls role of 1-aminocyclopropane-l-carboxylic acid. Plant Physiol 63 589-590... 

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