A DNA cytophotometric study of salt adaptation in Allium cepa and Nicotiana bigelovii

Abstract

Nuclear DNA was measured by Feulgen cytophotometry in NaCl-exposed Allium cepa roots and Nico-tiana bigelovii calli cultured in vitro. Analysis of the differentiation zone of A. cepa roots grown in water showed that only 2.8% of the nuclei had DNA contents higher than 4 C, where 2 C nuclei were predominant. In roots grown in salt water, 2 C nuclei were less numerous than 4 C nuclei and the DNA content was greater than 4 C in 19.2% of the cells, with 1.4% of the cells having a DNA content of 16 C. Two C, 4 C, 8 C, and a few 16 C nuclei, together with many nuclei with intermediate DNA content values, occurred in both the control and salt-treated calli of N. bigelovii. About 49.1% of the nuclei had DNA values around 2 C in the controls, while the percentage of cells with nuclei with higher DNA content values increased in calli as the NaCl concentration in the medium increased. Fifteen per cent of the nuclei had DNA values around 16 C in calli grown on media with 10 gr l⁻¹ NaCl added, compared to 2.8% in the controls. In calli exposed to 15 gr l⁻¹ NaCl, 18.4% of the nuclei had DNA contents around 16 C, and 3.1% of the nuclei had a DNA value of 32 C. These results are added evidence that chromosome endoreduplication occurs in plants as a widespread adaptive response to salt.

Key words:

• Allium cepa
• endopolyploidy
• Feulgen cytophotometry
• Nicotiana bigelovii
• salt adaptation