Nuclear genome stability of Mammillaria san-angelensis (Cactaceae) regenerants induced by auxins in long-term in vitro culture

Prolonged cultivation and the presence of exogenous growth regulators are factors suspected to induce genetic instability in vitro. In our previous work, we have achieved regeneration of a severely endangered cactus Mammillaria san-angelensis Sanchez-Mejorada from a long-term culture in the presence of auxins. The aim of this work was to investigate the cytogenetic characteristics of in vitro derived regenerants, analyzing nuclear DNA content: ploidy level and the extent of endopolyploidy. Plantlets grown for up to 7 years in MS medium alone were used as a source of explants which were cultured on MS in the presence of NAA: IAA, IBA, 2,4-D or Picloram at 2, 4, and 6 mg l(-1). In vitro plantlets regenerated without auxins were used as controls. Adult plants grown in a greenhouse and in vitro young plantlets were both found to be diploids (2n = 22) with the same karyotype, and no differences in DNA content were found between these two groups, both having a 2C DNA content = 3.20 pg. However, differences in the frequency of endopolyploid cells were found between young and adult plants. On the other hand the extent of endopolyploidy (the frequency of cells with 2C; 4C, 8C, and 16C DNA content) in differentiated tissues was basically the same in the control as in plants regenerated in the presence of auxins, and only marginal differences were detected in five cases, without any pattern, Meiosis in adult plants was a normal behavior with eleven bivalents (n = 11). This study demonstrated karyological stability of tissue cultured M. san-angelensis despite its origin from long-term subculture and the presence of auxins. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.