Abstract

Chemical mutagens such as sodium azide (NaN3) have been widely used to increase genetic variability in crops, but the undirected mutations induced can have undesirable effects, which need to be characterized. This study investigated the effects of in vitro NaN3 (0-0.45 mM) exposure (30 days) on the micropropagation of sugarcane within temporary immersion bioreactors (TIB). Shoot multiplication rate and cluster fresh weight, and aldehyde, phenolic, carotenoid, and chlorophyll levels were measured on in vitro produced shoots. The soluble phenolic content of the culture medium was also assessed. NaN3 concentration was negatively correlated with sugarcane shoot multiplication rate and fresh weight; at 0.45 mM NaN3, these parameters were only 20% and 39% that of the untreated control, respectively. Shoot multiplication rate and fresh weight, and chlorophyll a and b levels were negatively correlated with NaN3 concentration. In contrast, malondialdehyde, other aldehyde, carotenoid, and exuded phenol levels were positively correlated with NaN3 concentration. Statistical comparisons suggest that shoot multiplication rate and the biochemical parameters that were positively correlated with NaN3 concentration may be the most suitable indicators of stress when optimizing the concentration of NaN3 for sugarcane explants. An interpolated 50% reduction of multiplication rates at 0.23 mM NaN3 suggests that this concentration to be suitable for TIB-based induction of mutagenesis in shoots and eventual production of agriculturally useful mutants.