Coleoptile gibberellin

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. 

Abscisic acid is a negative regulator in that it primarily antagonizes the action of cytokinins, auxins, and in particular, gibberellins. Abscisic acid decreased the activity of polymerase in radishes (52), peas (53), maize coleoptiles (54), and pear embryos (55). More detailed studies are needed before the question of ABA-induced "modification" of RNA polymerase (54) or "alterations" in the number of sites for template activity (56) can be answered. In barley aleurone cells, ABA-induced suppression of GA-induced <-amylase formation was presumed to involve the continuous synthesis of a short-lived RNA (57). 

Figure 1. Effects of CaCl2 on bioassays for auxin, gibberellin, and cytokinin. A effects of CaCl2 on elongation of oat coleoptile sections in the presence and absence of indoleactic acid B effects on elongation of lettuce hypocotyls in the presence and absence of gibberellic add and C effects on enlargement of Xanthium cotyledon pieces in the presence and absence of benzyladenine (13).

Heliangin a sesquilactone and plant growth inhibitor first isolated from the leaves of the Jerusalem artichoke (Helianthus tuberosus). It is a gibberellin antagonist and inhibits the growth of oat coleoptiles but it stimulates root growth in beans (Phaseolus spp.). 

On reflection, it is interesting to review the earlier (pre-gibberellin) studies on the physiology of genetic dwarfism in maize. For example, in 1938 van Overbeek [19] reported lower levels of diffusible auxin from dl, d2, dS, and d5 coleoptiles. In 1951, Harris [11] confirmed the lower levels from dl coleoptiles based on ether extractable auxin he also found that addition of lAA to decapitated coleoptiles... 

Atkin RK, Barton GE, Robinson DK (1973) Effect of root-growing temperature on substances in xylem exudate of Zea mays. J Exp Bot 24 475-487 Atsmon D, Lang A, Light EN (1968) Contents and recovery of gibberellins in monoecious and gynoecious cucumber plants. Plant Physiol 43 806-810 Backus GE, Schrank AR (1952) Electrical and curvature responses of the Avena coleoptile to unilateral illumination. Plant Physiol 27 251-262 Bandurski RS (1978) Chemistry and physiology of myo-inositol esters of indole-3-acetic acid. In Wells W, Eisenberg F (eds) Cyclitols and phosphoinositides. Academic Press, London New York, pp 35-54... 

Cleland RE (1975) Auxin-induced hydrogen ion excretion correlation with growth, and control by external pH and water stress. Planta 127 233-242 Cleland RE (1976) Kinetics of hormone-induced H excretion. Plant Physiol 58 210-213 Cleland RE, Prins H, Harper R, Higinbotham N (1977) Rapid hormone-induced hyperpolarization of the oat coleoptile transmembrane potential. Plant Physiol 59 395-397 Clor MA (1967) Translocation of tritium-labelled gibberellic acid in pea stem segments and potato tuber cylinders. Nature 214 1263-1264 Cohen D, Robinson JB, Paleg LG (1966) Decapitated peas and diffusible gibberellins. Aust J Biol Sci 19 535-543... 

Lavender DP, Sweet GB, Zaerr JB, Hermann RK (1973) Spring shoot growth in Douglas-flr may be initiated by gibberellins exported from the roots. Science 182 838-839 Lembi CA, Morre DJ, Thomson KSt, Hertel R (1971) 1-N-naphthylphthalamic-acid (NPA)-binding activity of a plasma membrane-rich fraction from maize coleoptiles. Planta 99 37-45... 

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