Vigor difference during storage and germination in Indian mustard explained by reactive oxygen species and antioxidant enzymes

Abstract

Canola-type genotypes in Indian mustard (Brassica juncea) are a new kind of quality resource developed for their low levels of erucic acid (<2%) and glucosinolate (<30 μmole/g defatted meal) contents. Single-zero (low erucic acid) and double-zero (low erucic acid and glucosinolate content) genotypes of Indian mustard have less vigor. Conventional genotypes (high erucic acid and glucosinolate contents) havea significantly higher seedling vigor index-II (SVI-II) and single-zero genotypes have a significantly higher SVI-I, whereas double-zero genotypes have been observed to have a significantly lower SVI-I and SVI-II. To know the possible reasons for the differences in vigor, the seed quality parameters, reactive oxygen species (ROS) contents (superoxide radicals (O2−·) and hydrogen peroxide), lipid peroxidation, and antioxidant enzyme activity were examined. In the dry seeds, the conventional genotypes revealed lower ROS contents and higher catalase and peroxidase enzyme activity. This trend was reversed in the double-zero genotypes, which could be the reason why they were more susceptible to oxidative damage. During seed germination, an increase in the ROS contents, and corresponding increase in antioxidant enzyme activity, was noticed, which was highest in the conventional genotypes, followed by the single-zero genotypes. Double-zero genotypes showed the lowest increase in ROS contents and antioxidant enzyme activity during this period. This meant that the required attributes were met for maintaining oxidative balance within the cells and triggering physiological activities to reach high vigor. This study proposed 2 causes for the poor vigor of the double-zero genotypes; first, in the dry seeds, the ROS remained high due to low antioxidant activity (ROS scavengers) and the second was less generation of O2−· during germination.