Modification of Logarithmic Growth Rates of Tobacco Callus Tissue by Gibberellic Acid

Abstract

Logarithmic growth rates (either fresh or dry weight basis) of tobacco callus tissues grown on 10-to 10-1 AM cytokinin are increased if gibberellic acid (10-4-2 AM) is incorporated into the medium. At higher (1-10 jM) cytokinin concentrations gibberellic acid has little effect on growth rate but extends the duration of logarithmic growth. The gibberellic acid effect is noticeable only after one weight doubling, is dependent on concentration, and occurs when either glucose or sucrose is used as carbon source. The gibberellic acid response includes a decrease in percentage of dry weight relative to control tissues. The maximum dry weight yield, although achieved sooner than controls, does not differ appreciably from yields of tissue not treated with gibberellic acid.

Limitation of Tobacco Callus Tissue Growth by Carbohydrate Availability

“…Murashige and Skoog (5) had shown earlier that dry weight yields of tobacco callus on their medium with or without GA3 were not significantly different on the 28th day. Even though the tissues increased in dry weight during logarithmic growth at very different rates (2), our data on maximal dry weight yields in the preceding paper are in agreement with the results of Murashige and Skoog. Thus some factor, other than the growth substances present, may limit the total yield of tissue.…”

“…Logarithmic growth rates were the same for tissues grow either glucose or sucrose (2). As shown for sucrose in Figure wide range of concentrations of a given carbohydrate did alter the logarithmic growth rate.…”

“…The growth rates of these tissues on a defined medium can be controlled by the cytokinin concentration supplied (1) and modified by exogenously supplied GA3 (2). The present work shows that the maximal obtainable dry weight (at growth rates of 0.16 doubling per day or greater) depends on the amount of available carbohydrate in the medium and not on the growth substance regime.…”

“…The concentration of cytokinin in the medium determines the logarithmic growth rate of this tissue (1). The preceding paper (2) shows that under certain conditions logarithmic growth rates may be increased by exogenously supplied GA3 (2). Murashige and Skoog (5) had shown earlier that dry weight yields of tobacco callus on their medium with or without GA3 were not significantly different on the 28th day.…”

“…Measurements of growth kinetics were made as previously described (1,2). Components other than GA3 were autoclaved in the medium.…”