Analysis of Native Gibberellins in the Internode, Nodes, Leaves, and Inflorescence of Developing Avena Plants

ABSTRACIPotential sites of gibberellin biosynthesis in 10-day-old 'Alaska' pea (Pisum sativum L.) seedlings were investigated using a cell-free ezyme system capable of incorporating Cl4C-mevalonic acid into ent-kaurene. In peas, ent-kaurene is assumed to be a committed intermediate in the gibberellin biosynthetic pathway. Comparative results from enzyme assays using extracts from shoot tips, leaf blades, internodes, and root tips indicate that the highest capacity for ent-kaurene (and presumably gibberellin) synthesis is in those tissues with the greatest potential for growth. The highest rates were obtained with extracts prepared from the fifth (youngest) internode, the fourth (youngest) expanded leaf, and the shoot tip itself. This report represents the first direct evidence that the enzymes responsible for early stages in gibberellin biosynthesis occur in internode tissues with potential for rapid elongation.All of these results, however, are based upon relatively indirect measurements of GAs extracted or diffused from tissues or the growth response of plants to applied GAs or growth regulators. The use of a cell-free enzyme system from pea seedling shoot tips which is capable of catalyzing certain key reactions in the GA biosynthetic pathway (Fig. 1

Section: Resultsmentioning

confidence: 99%

Sites of Gibberellin Biosynthesis in Pea Seedlings

Coolbaugh

1985

“…1) could include GA1 and/or GA3, and GA19. GA1, GA3, GA4, GA7, and GA19 have all been characterized from various members of the Graminae, and GA19 is native to corn (4,10,11,14,20). Thus, large increases in GA-like activity, particularly of a nonpolar nature, were observed in apical meristems undergoing a sex reversal.…”

Section: Methodsmentioning

confidence: 99%

Changes of Endogenous Gibberellin-like Substances with Sex Reversal of the Apical Inflorescence of Corn

Rood¹,

Pharis²,

Major³

1980

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In developing apical meristems of corn, the level of acidic, ethyl acetate-soluble gibbereilin (GA)-ike substances increased to a maximum of 108 micrograms GA3requivalents per kilogram dry weight of tissue at inflorescence initiation, and then fel rapidly. At anthesis, only a trace (0.2 microgram per kilogram) of GA-like activity remained in the apical (male) inflorescences, whereas moderate activity (32 micrograms per kilogram), mostly of a nonpolar nature, was present in lateral, female, inflorescences.A sex reversal of the apical inflorescence, from male to female, was elicited by reducing the ambient light intensity. Higher levels of GA-lke substances, particularly those eluting from a SiOe partition column in the nonpolar region, were observed at all harvests in the reverdng mer{stems; levels increased to 180 micrograms per kilogram at inflorescence initiation, then dropped to 122 micrograms per kilogram in the apical (female), reverted meristems. This increase in endogenous GA-ike activity with reversion to the female inflorescence is consistent with observations that (a) reversion can be obtained with exogenous application of GA3 and (b) maleness is enhanced in GA-deficient mutants of maize. Endogenous GAs may thus play a key role in the control of sexuaHty of corn.Along with an increase in plant height, one of the major morphological changes in corn following exogenous application of GA3 is an alteration of sexuality. Male florets become sterile, and functional female florets develop in the apical inflorescence, or tassel, where normally only male flowers would have developed (7,15,17). The quantity of exogenous GA3 required to produce a sex reversal is dependent on genotype (17, 18) and is only effective in altering sexuality if applied prior to microspore meiosis (7). Results from a number of studies are consistent, however, and suggest that exogenous GA3 reduces maleness and promotes femaleness in the apical inflorescence of corn (7,15,17,18).A relationship between endogenous GAs and sexuality is also suggested by the behavior of certain single gene corn mutants. In anther ear (an,) and certain dwarf mutants (dl, d2, d3, dQ), male florets are observed in the lateral inflorescence, or ear, whlch is normally entirely female (16). The mutants d3, d5 and an, appear to be GA-deficient, whereas the levels of endogenous GA-like substances in di and d2 are less than half the normal level (19).

“…This growth in the nodepulvinus which results in negative geotropic curvative can be enhanced by, and is very sensitive to, auxin application in A vena (13), and in Poa pratensis to Ethephon, and especially Ethephon plus GA3, but not to GA3 alone (25). In A vena, a festucoid grass, the leaf sheath pulvinus (termed node-pulvinus hereafter) is a significant source of GAs, as are elongating internodes and inflorescences (15). During transition from lag to log phases of internodal extension there is a significant increase in more polar GAs (15).…”

mentioning

confidence: 99%

Changes in Endogenous Gibberellins and the Metabolism of [³H]GA₄ after Geostimulation in Shoots of the Oat Plant (Avena sativa)

Pharis¹,

Legge²,

Noma³

et al. 1981

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The recovery from "lodging," or bending over, by shoots of 42-day-old Avena sativa plants is controlled primarily by a negatively geotropic differential growth of the lower halves of the p-I node-pulvinus and the base of the p-I internode, relative to the upper halves. Although geostimulation causes a significant reduction in p-1 internode length, dry matter accumulation in the p-i node-pulvinus is increased, apparently at the expense of the sheath. Recovery to an angle of 300 is associated with changes in endogenous gibberellin-like substances (GAs), and in differential metabolism of applied I3HIGA4 (1.4 Curie per millimole). Although geostimulation depressed total GAs (relative to upright plant parts) to 0.40 and 0.13 for node-pulvini and sheaths, respectively, it increased them 2-fold for internodes. Within the plant part geostimulation increased GAs (relative to upper halves) 29-and 7-fold in lower halves of node-pulvini and internodes, respectively, but reduced GAs to 0.3 in lower halves of sheaths. At age 42 days a GA4/7-like (nonpolar) substance predominates, with lesser amounts of a GA3-llke (polar) substance. Native GAs of Avena include GA3, GA4, and GA7. Geostimulation enhanced the ratio of nonpolar to polar GAs for both halves of internodes, but tended to depress it for sheaths and nodepulvini.The disposition and metabolism of applied 13HIGA4 confirmed the above trends for endogenous GAs regarding localization (e.g. up to 2-fold increases in 13HIGA4 and acidic 3H-metabolites in the lower halves, relative to upper halves). Also, metabolism into highly water-soluble 3H-metabolites (biologically jnactive conjugates?) was greater (up to 1.8-fold) in upper than in lower halves. The end result of such metabolic trends would be to reduce acidic (biologically active?) GAs in the upper half, while retaining them for a longer time in the lower half.Geotropically stimulated Avena shoots thus increase, within 24 hours, the levels of acidic GAs in the lower halves of the p-1 node-pulvinus and p-I internode, the two plant parts responsible for the geostimulated growth.