Auxin and gibberellin

Phytohormone-induced action, especially by auxins and gibberellins ... 

Even with gibberellin and auxin the growth of the defoliated or decapitated plants is significantly less than that of the intact ones, suggesting that, as with Gerbera, still other growth factors must be accounted for. In two other cases dual roles of auxin and gibberellin in mitosis are clearly indicated. 

Although in the latter case gibberellin appears to be primarily responsible for the increased mitotic activity and auxin for differentiation of the newly formed cells, auxin may also be involved in the primary cambial activation mechanism (25). After the discovery of the gibberellins several studies showed conclusively that auxin and gibberellin have separate, sometimes additive and sometimes syner-... 

In the belief that the failure of the stem section to grow meant that some essential cofactor must normally be supplied to the stem section by the rest of the plant, we began investigating the effect of plant extracts. A mixture of glycerides isolated from the pea nearly doubled the growth response of the section to auxin and gibberellin, even when applied at the extremely low concentration of 10 mg. per liter (3). Even so, the growth attained by the section is still less than that of the intact plant, and a cofactor other than those discussed in this paper may be involved. 

Further studies have extended this promotion of auxin and gibberellin action to other fat-soluble substances, in particular some isoprenoid vitamins and related compounds (I). For instance, vitamin E, vitamin Kl9 and phytol are quite comparable in their growth-promoting ability to the fatty acid ester, methyl linoleate. But some fat-soluble vitamins are not active—for instance, vitamin A, -carotene, and vitamin D2. 

Peas are a low-fat plant, and it is likely, therefore, that our results should not be freely extended to all other auxin- and gibberellin-induced systems. In fact, the equally classic oat coleoptile section hormone assay does not seem to respond to the fatty substances. Even the pea section fails to respond, unless the seedling has received some red light during the early part of its development. 

Such questions have been raised for the catabolic products of auxins, abscisic acid, conjugates of auxins, and gibberellin, and for the hormonal role of cytokinins and auxins in tRNA molecules, but are not reviewed in this article (17). A satisfactory answer to this question requires elucidation of the cellular mechanisms (discussed in this paper) that are believed to be primarily under hormonal regulation. 

The cytokinins (previously phytokinins) principally stimulate cell division and, together with auxins and gibberellins regulate the developmental and differentiation processes of fruit formation and ripening, bud formation, etc.. ... 

Thus, phenolic compounds and morphactin - which inhibit cell elongation and cell division in higher plants -have no effect on biosynthesis of auxins and gibberellins in cultures of certain fungi. Their action seems to specific for higher plants. 

In contrast to the auxins and gibberellins, abscisic acid (ABA) and ethylene usually retard cell elongation. With some exceptions (Takahashi 1972, Gaither et al. 1975, Malik and Mehan 1975 a, Van Staden and Bornman 1970) ABA is inhibitory to growth (Addicott and Lyon 1969, Milborrow 1974). ABA inhibits stem and root elongation and counteracts the promotive effects of other substances on these organs (Rehm and Cline 1973, Kaufman and Jones 1974,... 

Acton GJ, Murray PB (1974) The roles of auxin and gibberellin in reversing radiation inhibition of hypocotyl lengthening. Planta 117 219-226 Adams DO, Yang SF (1979) Ethylene biosynthesis identification of 1-amino-cyclopropane-1-carboxylic acid as an intermediate in the conversion of methionine to ethylene. Proc Natl Acad Sci USA 76 170-174... 

Katsumi M, Kazama H (1974) Interrelationship between auxin and gibberellin in the elongation of cucumber hypocotyl sections. In Plant growth substances 1973. Hiro-kawa, Tokyo, pp 845-852... 

Well before the discovery of auxins and gibberellins during the 1920 s hormone movement had been suggested as occurring in plants. As early as in 1879 Julius Sachs, considering observations on correlations between main axes and side shoots, proposed substances other than nutrients as involved in these phenom-... 

Aloni R (1979) The role of auxin and gibberellin in differentiation of primary phloem fibers. Plant Physiol 63 609-614... 

Shininger TL (1971) The regulation of cambial division and secondary xylem differentiation in Xanthium by auxins and gibberellin. Plant Physiol 47 417-422 Shininger TL (1979) The control of vascular development. Annu Rev Plant Physiol 30 313-337... 

Evans LT (1964) Inflorescence initiation in Lolium temulentum L. V. The role of auxins and gibberellins. Aust J Biol Sci 17 10-23... 

Majumder, K. and Mazumdar, B. C. (2001). Effects of auxin and gibberellin on pectic substances and their degrading enzymes in developing fruits of cape-gooseberry (Physalis peruviana L.). Journal of Horticultural Science and Biotechnology 76, 276-279. 

Auxins and gibberellins are hormones foimd in Aloe vera and confer anti- inflammatory effects which help in woimd healing (Suijushe et al., 2008). 

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