This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Web of Science (17) Citing Articles via Google Scholar Google Scholar Articles by Keith, B. Articles by Srivastava, L. M. Search for Related Content PubMed PubMed Citation Articles by Keith, B. Articles by Srivastava, L. M. Agricola Articles by Keith, B. Articles by Srivastava, L. M.

Articles

In vivo Binding of Gibberellin A₁ in Dwarf Pea Epicotyls ¹

Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada, V5A 1S6

Binding of [³H]gibberellin A₁ (GA₁) to extracts of dwarf pea epicotyls was investigated using sliced pea epicotyls (0.5-1.0 millimeter thick) that had been incubated in a solution containing [³H]GA₁ at 0 C for 3 days. Gel filtration of a 100,000g supernatant indicated binding to a high (HMW) and an intermediate molecular weight (IMW) fraction with estimated molecular weights of 6 x 10⁵ daltons and 4 to 7 x 10⁴ daltons, respectively. The bound ³H-activity was [³H]GA₁ and not a metabolite as deduced by thin layer chromatography. The bound label did not sediment during centrifugation at 100,000g for 2 hours; also, binding was not disrupted after treatment of a combined HMW and IMW fraction with DNase, RNase, or phospholipase A or C, but it was disrupted by protease or heat treatment. These facts suggest that binding of [³H]GA₁ was occurring to a soluble protein(s). [³H]GA₁ bound to a combined HMW and IMW fraction was not susceptible to changes in pH, nor could it be exchanged with a variety of GAs tested under in vitro conditions. Under in vivo equilibrium conditions, biologically active GAs, such as GA₁, GA₃, GA₄, GA₅, GA₇, and keto GA₁, could reduce the level of [³H]GA₁ binding, whereas inactive GAs, such as iodo GA₁ methyl ester, GA₈, GA₁₃, GA₂₆, and non-GAs, such as (±)abscisic acid, had no effect. By varying the concentration of [³H]GA₁ in the incubation medium, the specific binding of [³H]GA₁ appeared to be due to two classes of binding sites having estimated K_d of 6 x 10^–8 molar and 1.4 x 10^–6 molar. The concentrations of the two sites were estimated to be 0.45 picomole per gram and 4.04 picomoles per gram on a fresh weight and 0.1 picomole per milligram and 0.9 picomole per milligram on a soluble protein basis, respectively.