Effects of Cytokinins on Growth and Auxin in Coleoptiles of Derooted Avena Seedlings

Abstract

It is known that removal of the endosperm (deseeding) reduces subsequent auxin production in the oat coleoptile tip and the "regeneration of the physiological tip" (auxin production) in the decapitated coleoptile as determined by the For experiments on the effect of cytokinins on auxin secretion from coleoptile tips, the ethanol-carbowax solutions were applied to the tips either after 56 to 60 hr of growth or just 5 min before excision of the tips. For each treatment 36 2-mm tips were excised with a scalpel after 72 to 74 hr of growth and arranged basal end down on 0.1 5-ml agar platelets. Every hour for 5 hr each set of tips was transferred to a fresh platelet. Each platelet was then divided into 12 blocks for auxin assays by the A vena curvature test.The assay was performed in the standard way (15) with uniform plants selected from the same batch of seedlings from which the experimental plants had been selected. During the assay the relative humidity in the Avena room was maintained near 88%. For quantitation of the response each assay included a standard series of IAA concentrations. RESULTSAs illustrated by a typical experiment (Fig. 1), increase in length of the measured apical portion of the coleoptiles was about 50% less in derooted plants in the 20 hr following derooting than in intact controls. In coleoptiles of derooted plants supplied with 2iP immediately upon derooting the increase was about the same as in intact controls. The increase in intact plants treated with 2iP was only slightly greater than in intact controls. Thus treatment with cytokinin overcomes the effect of * Abbreviations: 2iP: 6-(3-methyl-2-butenylamino)purine; BAP: 6-benzylaminopurine. 97www.plantphysiol.org on May 9, 2018 -Published by Downloaded from

Cytokinin-to-Auxin Ratios and Morphology of Shoots and Tissues Transformed by a Chimeric Isopentenyl Transferase Gene

“…Free IAA levels in these plants were reduced to an even greater extent than total IAA. These findings are contrary to numerous reports ofenhanced IAA levels resulting from exogenous applications of cytokinins (6,8,10,19) or from transformation of tobacco and carrot with the native ipt gene carried on a mutated Ti plasmid (7). We only observed a significant increase in free IAA in N. plumbaginifolia tissues transformed with the 35S-ipt gene or, to a lesser degree, with the native gene.…”

The Nature of Spontaneous Changes in Growth Rate in Isolated Coleoptile Segments

“…1). This "regeneration of a physiological tip" is thought not to occur in isolated coleoptile segments, since the process seems to depend upon a supply of cytokinins from the roots or seed (20,32). We considered the possibility that the SGR in Avena segments might represent only a transient regeneration of a physiological tip and therefore may have gone undetected without high resolution measuring techniques.…”

Functions of Hormones at the Cellular Level of Organization

“…Kinetin enhancement of auxin levels may also explain the ability of kinetin to enhance growth promotion by low levels of auxin LARSSON 1972, ANKER 1977). Kinetin may also induce localized increases in auxin by enhancement of auxin movement toward the treated area (LAGERSTEDT and LANGSTON 1967), while cytokinins appear to enhance auxin production in coleoptile tips (JORDAN and SKOOG 1971) and in tobacco callus (DRAVNIEKS et al 1969). It is suspected that cytokinins alter rates of auxin degradation in some tissues through a concentration-dependent promotion XHAUFFLAIRE 1967, LEE 1971) or inhibition (LEE 1971) of IAA-oxidase activity.…”