Gibberellin, a Primary Determinant in the Expression of Apical Dominance, Apical Control and Geotropic Movement of Conifer Shoots

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

“…Of interest here is the fact that exogenous application of GAs will enhance (1.5-fold) the upward movement of geostimulated Avena shoots during the first 20 h of curvature, relative to control plants, a GA4/7 mixture being more effective than GA3 (Kaufman, Pharis, and Reid, unpublished results). A similar situation occurs with regard to GA3 for conifer shoots and lateral branches, both in intact and decapitated plants (3,(18)(19)(20).…”

“…10), including peanut shoots (10), sunflower buds (21), maize coleoptiles (22), and for conifer shoots (3,18,19), which indicate that increased levels of GAs, present endogenously, or applied exogenously, are associated with, and indeed appear to control, the differential growth that allows plant shoots to respond to geostimulation by growing upright. Auxins are also implicated in many of these systems, including the Avena shoot system (12,13), as is ethylene (3,17,26), the latter perhaps being the first growth regulator involved in sensing the environmental stimulus and/or signaling the receptor tissue [secondary cambial meristem (3) and p-l node-pulvinus/internode (Kaufman, Reid, and Pharis, unpublished)].…”

“…Most of what is known about the possible roles of gibberellins (GAs) in geotropic movements of plant shoots is based on the exogenous application of GAs, or GA antagonists to the plant. Thus, exogenous GA3 can enhance hyponasty, even counteracting positively geotropic growth of lateral branches and the main stem of intact conifers under certain conditions (18)(19)(20), and GAs are implicated in the growth habit of the shoot of peanut (10) and a number of plant species (references cited in 10,18). It has also been reported (21) that the activity of GA-like substances diffusing from the lower halves of geotropically stimulated sunflower buds was almost 10 times that of upper halves, and a similar redistribution was noted for the lower halves of geotropically stimulated maize coleoptiles (22).…”

Apical Control of Branch Movements in White Pine: Biological Aspects

“…Of the few hormonal studies, auxin applied to a severed stem above a branch can replace the control of the terminal (13), and exogenous gibberellins increase apical control in conifers, including pines, but decrease control in Sequoia sempervivens (8). An hypothesis for direct apical control would assume that a correlative, hormonal message moves from the terminal shoot to the lateral branch, where it acts to inhibit branch growth (9,10) or to cause epinastic bending and downward growth (7).…”

Efeito de giberelina, óxido nítrico e etileno no estiolamento de Dendrobium "Second Love" (Orchidaceae)

“…Estudos têm demonstrado que as giberelinas também são sintetizadas em folhas jovens e transportadas preponderantemente, em direção às regiões inferiores das plantas (Jones e Phillips, 1966;Jones e Phillips, 1967), e que as mesmas estão envolvidas diretamente na inibição das gemas laterais (Jacobs e Case, 1965;Pharis et al, 1970;Pharis et al, 1965;Ruddat e Pharis, 1966;Scott et al, 1967). Várias plantas intactas tratadas com giberelinas tiveram sua dominância apical promovida (Martin e Thimann, 1972;Pharis et al, 1970;Pharis et al, 1965;Goldsmith, 1969 Love" crescidas no escuro, de certa forma a presença de paclobutrazol indica a extrema importância da giberelina sobre o alongamento caulinar nesta orquídea, semelhante ao verificado em plantas de Catasetum fimbriatum (Suzuki, et al 2004).…”