Two Effects of Cytokinin on the Auxin Requirement of Tobacco Callus Cultures

Abstract

Cytokinin affects the requirement for auxin of a strain of tobacco callus (Nicotiana tabacum) which is cytokinin-autotrophic when grown on Murashige and Skoog medium with 11.4 jAM of indole-3-acetic acid but requires cytokinin 6-(3-methyl-2-butenylamino)purine (PAde) when grown on the same medium with <3 iLM indole-3-acetic acid. As the exogenous concentration of cytokinin (irAde) is increased, the concentration of indole-3-acetic acid required for growth is decreased. A second effect of cytokinin, observed sporadically in cultures with 2.5 jaM or 5 FlM PEAde, is the transformation of some of the callus pieces to auxinautotrophic growth. Stains, both calus-forming and bud-forming tissues, that arise in this manner are not permanently altered in their auxin requirement because subcultures on medium without cytokinin still require exogenous auxin.In vitro reponses of tobacco callus tissue (Nicotiana tabacum cv. Wisconsin No. 38) to cytokinin can be divided into those caused by low concentrations, i.e. the minimum requirement for growth (10), and those dependent on much higher cytokinin levels, i.e. induction of organ formation (11) and the requirement for growth on medium lacking thiamine (1, 2, 7). This paper describes two distinct effects of cytokinin (6-13-methyl-2-butenylamino]purine, i6Ade)2 on the auxin requirement of a cytokinin-autotrophic tobacco callus strain. One of these effects is a decreased requirement for exogenous auxin by callus grown on medium with c 1 MM i6Ade. The other effect is a transformation of callus pieces to auxin-autotrophic tissue when grown on medium with > 1 ,M i6Ade. This transformation occurs sporadically among replicates and results in morphologically different strains. MATERIALS AND METHODSThe origin and maintenance of stock cultures of cytokininautotrophic tobacco callus on RM 1965 medium containing 11.4 Mm IAA have been described (3, 6). The IAA, obtained from Sigma Chemical Company, and the i6Ade, synthesized by N. J. Leonard and S. M. Hecht, were added prior to autoclaving. Fresh weight yields were determined after specified growth periods. RESULTSRequirement for Exogenous IAA.

Effects of IAA and four IAA conjugates on morphogenesis and callus growth from tomato leaf discs

“…The addition of auxin to 0.89/aM BAP appeared to substitute for the missing cytokinin in promoting callus growth. A similar effect has been reported with tobacco callus in which cytokinins have been shown to decrease the auxin requirements of the tissue and to increase endogenous auxins [6,23].…”

Dose responses of auxins

“…10), in agreement with more extensive data for the effect of cytokinins on callus growth (P. Nissen, tinpubiished results). In contrast to lAA-stimulated growth of tobacco callus (Einset 1977), where the Sj^-value was relatively high and supraoptimal concentratioos were not reached, growth in the other esperitnents in Tab. 10 decreased sharply at supraoptimal auxin concentrations.…”

T-DNA Controlled and Plant Specific Metabolism inAgrobacterium tumefaciensTransformed Tobacco and Soybean Tissues

“…Jordan and Skoog (1971) mcntioned that application of cytokinins at high lcvcls rcsultcd in endogcnous production of lAA in tobacco calli. Similar cffccts have bcen rcportcd for cytokinin habitualed tissues (Syono and Furuya, 1972 ;Einset et al, 1977). Furthcrmorc, Montague et al (1981) dcmonstratcd the inhibition by cytokinins of the conjugation of 2,4-D to amino acids in cultured soybean cclls.…”