The stereoselectivity of metconazole in wheat seedling growth:
implication for growth and defense balance
Triazole fungicides have a broad fungicidal activity spectrum through
inhibiting the sterol biosynthesis, which damages the cell membrane
function. In addition, triazoles also regulate phytohormone synthesis.
Chiral pesticides have different fungicidal activities, environmental
fate, and toxicities. In this study, four optical isomers and racemates
of metconazole (a chiral triazole fungicide) were used to seed-coat
wheat seeds (2.5 g/100 kg seed) before germination. The results showed
that cis-1S,5R-metconazole treatment inhibited seedling emergence, which
could be impeded by adding exogenous gibberellin3(GA3). Seedling
morphology identified the stereoselectivity of metconazole isomers.
Plants exposed to cis-1S,5R-metconazole had shorter and thicker
appearance, while plants treated with trans-1S,5S-metconazole were
taller and thinner, compared with the control plants. Furthermore, the
effects of metconazole on plant hormones, gibberellins (GAs), and
Jasmonic acid (JA) were investigated. Related enzyme activity and gene
RT-qPCR results showed that trans-1S,5S-metconazole treatment
upregulated the activity of related enzyme and gene expression in GAs
biosynthesis. cis-1S,5R-metconazole caused down-regulation of GAs
biosynthesis, and upregulation of JA synthetase activity. Moreover, all
metconazole treatments increased antioxidant enzyme activity, especially
trans-1S,5S-metconazole, trans-1R,5R-metconazole, and rac-metconazole.
Generally, cis-1R,5S-metconazole treatment showed minimum interference
of the growth of wheat seedlings, thus cis-1R,5S-metconazole may be a
safer metconazole seed-coating application.