Hormone-induced caulogenesis in long-term tobacco cell lines and its effect on nuclear DNA content

Abstract

Manipulation of exogenous auxin and cytokinin levels during sequential subculture in vitro has been used to induce caulogenesis in several long-term tobacco cell lines. Concurrently, tissue samples at various stages of caulogenesis have been examined for nuclear DNA content. While a variety of hormone regimes permitted caulogenesis, extremely high (122.95 μM) cytokinin levels and extremely low (0.285 μM) auxin levels generally gave optimal response. For three lines, caulogenesis was accompanied by a progressive decrease in nuclear DNA content beyond that due to the loss of polyploid cells. In one line, however, DNA content remained stable during regeneration, perhaps reflecting the acquisition of a stably adapted aneuploid karyotype. Both caulogenic response and amount of nuclear DNA were affected by changes in the culture medium. The progressive nature of the observed changes in DNA content is inconsistent with a single-step selection for euploid competent cells. Alternative models postulating either progressive selection for euploidy, or the regulation of karyotype are proposed to explain the results.

Patterns of variability in DNA content and nuclear volume in regenerating cultures of Nicotiana tabacum

“…Even in the case where the young shoots showed a restricted range of DNA per nucleus, the older shoots showed wider variability. This contrasts with the progressive decrease in DNA content per nucleus during the course of early shoot formation in three of the four tobacco cell lines examined by Traynor and Flashman (1981). However, the callus stocks that they used had a much higher DNA content per nucleus than our lines and they examined only very early stages of shoot formation in the cultures.…”

Chromosome number and DNA content in callus culture ofCostus speciosus (Koen.) Sm.

“…Chromosomal instability and variation of DNA content of callus cultured in vitro have been reported (Bayliss, 1980;Berlyn, 1983;Cavallini etal., 1986;Karp & Maddock, 1984;Orton, 1980Orton, , 1983Traynor & Flashman, 1981) despite the fact that in several plant species stability has also been recorded (Swedlund & Vasil, 1985). Factors like composition of nutrient media and growth regulators, endoreduplication, non-disjunction and fragmentation of chromosomes and others that may be responsible for such variation have been analysed (Bayliss, 1980;D'Amato etal., 1980;Dolezel & Novak, 1985;Krikorian etaL, 1983;Larkin & Scowcroft, 1981 ;Mukhopadhyay et aL, 1988).…”