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 f actors suspected to induce genetic instability in vitro. In our previous wo rk, we have achieved regeneration of a severely endangered cactus Mammillar ia san-angelensis Sanchez-Mejorada from a long-term culture in the presence of auxins. The aim of this work was to investigate the cytogenetic charact eristics of in vitro derived regenerants, analyzing nuclear DNA content: pl oidy level and the extent of endopolyploidy. Plantlets grown for up to 7 ye ars in MS medium alone were used as a source of explants which were culture d 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 contro ls. Adult plants grown in a greenhouse and in vitro young plantlets were bo th found to be diploids (2n = 22) with the same karyotype, and no differenc es 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 exte nt of endopolyploidy (the frequency of cells with 2C; 4C, 8C, and 16C DNA c ontent) in differentiated tissues was basically the same in the control as in plants regenerated in the presence of auxins, and only marginal differen ces were detected in five cases, without any pattern, Meiosis in adult plan ts was a normal behavior with eleven bivalents (n = 11). This study demonst rated karyological stability of tissue cultured M. san-angelensis despite i ts origin from long-term subculture and the presence of auxins. (C) 1999 El sevier Science Ireland Ltd. All rights reserved.