Responses of meristematic callus cells of two Cynodon dactylon genotypes to aluminium

Abstract

Responses to Al 3+ of embryogenic callus cells of an Al-sensitive (Al-S) and Al-resistant (Al-R) Cynodon dactylon genotype were evaluated with regard to Al 3+ toxicity and resistance. A chemical equilibrium speciation model (MINTEQA2) was used to ensure the availability of the Al 3+ ion in culture media, which was supplied as 0.08–2.3 mM Al 3+ for 2–8 weeks. Increasing Al 3+ concentration and exposure time had a greater negative impact on the Al-S than on the Al-R genotype, in terms of callus growth rate and frequency of non-embryogenic cells. Exposure to 0.8 mM Al 3+ for 2 weeks resulted in an 88% reduction in the Al-S meristematic cell number, whereas that of the Al-R genotype remained unaffected. In addition, the Al-S cells accumulated three times more Al in the nucleus than did the Al-R cells, suggesting that Al interfered with mitosis. The Al-R cells appeared to exclude Al 3+ from its cells through an increase in extracellular pH (4.34 in Al-R and 4.08 in Al-S) and by the immobilisation of Al in the cell wall (33% more in Al-R). The results showed that by studying the cellular responses to Al 3+ it is possible to discriminate between the Al-S and Al-R C. dactylon genotypes.