Uptake of Benzyladenine by Tuber Slices of Jerusalem Artichoke (Helianthus tuberosus L.) over a Wide Concentration Range

Abstract

Uptake of the cytokinin benzyladenine by tuber slices of Jerusalem artichoke (HeImtks Obero L) Increased with the concentration of benzylademnle In the wndium in the range 10-' to 10-molar. The kinetics of uptake could be precisely represented by four phases of a single, multipbasic isotherm. K. and V.. increased in a regular manner upon transition to higher phases. The fit to multiphasic kinetics was significantly better than the fit to cooperative kinetics or to the sum of four Independent Michaels-Menten terms.Synthetic plant hormones have been used in a variety of plant tissues to elicit various responses. It is well known that dose response curves of plant hormones are unusually wide, covering four or even six orders of magnitude (12). Under experimental conditions, the external concentrations of hormones have been varied at will (generally within the range l0-9-l0-3 M) in order to obtain an optimal response. Little attention has, however, been given to detailed studies of hormone uptake by the tissue in response to various external concentrations. The few papers that have appeared during the past several years on the kinetics of uptake of plant hormones are limited in scope both with regard to the kinds of tissues used and the type and particularly the concentrations of hormones (2,5,14,26,28). In many cases, only one or two concentrations per decade have been used. Recent studies of hormone binding proteins and their possible dual function in the transport of hormones across the plasmalemma and as sites of hormone action (6,8,18,27) make studies of the concentration dependence of hormone uptake by plant tissues of particular interest. Such studies may thus provide important information concerning the binding of hormones to plant tissues and receptors.The results reported in this article show that the uptake of BA by tuber slices of Jerusalem artichoke increases with increasing concentrations of this hormone in the medium. Furthermore, the kinetics of uptake correspond well to the multiphasic model described previously for uptake of inorganic and organic solutes ( 15,23,24). The implications of a multiphasic carrier for hormone uptake in relation to a possible mode of action of hormones are discussed briefly. A preliminary report of these findings has appeared (17). ' After appropriate periods of incubation, tissue slices were washed in running water for 15 min. Each slice was solubilized separately in 0.5 ml of BTS solubilizer (Beckman) for 3 h at 500C. Radioactivity was assayed by liquid scintillation counting.Details of the statistical analysis of uptake data have been described previously (11,22,24). RESULTSTime Course of BA Uptake. Accumulation of BA in tissue slices with time was studied at four different concentrations. In each case, 32 slices were incubated in 40 ml medium containing 0.4 ,ICi 114C]BA (0.082 /uCi for the lowest concentration). At indicated times, four slices were removed from each flask and processed as described in "Materials and Methods." The results presented in Figure...

Change in shoot proliferation with repeated in vitro subculture of shoots of woody species of Rosaceae

“…Disappearance of carbohydrate from the medium occurs rapidly -in suspension cultures of Rosa, the total carbohydrate of the medium (2% sucrose) disappeared by day 8-10 depending on the density of the inoculum [11]. The rate of BA uptake by Helianthus tuberosus cultures is very rapid and depends on BA concentration in the external medium [8], high concentrations promoting more rapid uptake than low concentrations. Thus, there would be considerable fluctuations in the level of these substances.…”

Effect of applied and internal hormones on vitrification and apical necrosis of different plants cultured in vitro

“…It has been shown that BA is readily taken up by shoots from the medium (Minocha & Nissen, 1982;Nordstr6m & Eliasson 1986;Marino 1988). Agar influences the availability of cytokinins (Debergh 1983) and there exists an inverse correlation between uptake of 14C-labelled BA and agar concentration in the medium (Bornman & Vogelman 1984).…”

Dose responses of auxins

“…insets in Figs 1 and 3 in Shinkle and Briggs 1984), subsensitive dose responses of auxin can usually be represented by multiphasic isotherms with 2 or 3 phases, whenever sufficiently detailed and precise data are available.. These isotherms are, in principle at least, similar to those found for uptake of inorganic and organic solutes in plants (Nissen 1971, Minocha and Nissen 1982. Recently, evidence was obtained for uptake of 2,4-D and IAA into tuber slices of storage tissue via facilitated diffusion (Minocha and Nissen 1985).…”

“…In the case of wide dose response curves, improbably large chatiges in the concentration of PGS would be required for significant changes in their binding to the receptor (Trewavas 1981(Trewavas ,1982. In another development, uptake of benzyladenine by tuber slices of Jenisaletn artichokes was found to be precisely represented by a single, multiphasic isotherm (Minocha and Nissen 1982). As reported in a preliminary communication (Nissen 1983),, reanalysis of published dose response curves for PGS also yielded examples of multiphasic isotherms.…”