Insect-resistant Bt-maize response to the short-term non-target mite-pest infestation and soil drought

Abstract

Transgenic lepidopteran insect-resistant maize expressing the cry1Ab gene (Bt) and its non-transgenic counterpart at the 12-leaf-stage (V12) were infested by the two-spotted spider mite or dehydrated by cessation of soil watering to check Bt-maize capacity to respond to other stresses than those assured by the presence of Cry protein. Since the antioxidant enzymes are key components of plant defence against biotic and abiotic stresses, the engagement of leaf superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) in response to 6-day mite feeding and soil drought has been investigated. The reduction of leaf hydration and soluble protein content in the fully expanded 8th leaf was independent of genotype and more pronounced in response to water cessation than mite infestation. Similarly, the changes in enzyme activities depended more on the kind of stress than the presence of the transgene. Water shortage in the soil enhanced the activity of all enzymes, whereas mite feeding decreased the activity of SOD and CAT, and markedly increased POX in the 8th leaf of both cultivars. In mite-infested leaves of the non-transgenic plant, the CAT activity remained unaffected, whereas decreased in leaves of Bt maize due to the hampered activity of CAT-2. In comparison to the control, all enzyme activity in the 10th non-infested leaf of mite-infested non-transgenic maize decreased, whereas it changed in the 10th leaf of Bt maize in the same way as in the 8th mite-infested leaf. The results suggest that SOD, CAT and POX can strongly confer short-term drought-stress response in both maize cultivars, whereas POX is the only responsive enzyme in mite-infested Bt maize.