G. Palomino et al., Nuclear genome stability of Mammillaria san-angelensis (Cactaceae) regenerants induced by auxins in long-term in vitro culture, PLANT SCI, 141(2), 1999, pp. 191-200
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.