Biochemical characterization of digestive carbohydrases of the tomato leaf miner, Tuta absoluta (Lepidoptera: Gelechiidae) larvae in response to feeding on six tomato cultivars

The tomato leaf miner, Tuta absoluta (Meyrick) is an imported pest and serious threat to tomato production in farms and greenhouses of Iran. Use of genetically engineered plants expressingcarbohydrase inhibitors is one of the non-chemical methods for controlling insect pests, and knowledge about enzymatic properties of carbohydrases will help us to achieve this goal. Therefore, in present study we characterized biochemical properties of digestive carbohydrases in the midgut of last larval instar of T. absoluta fed on different tomato cultivars (Kingston, Riogrande, Super Luna, Super Chief, Super strain B and Calj). While the highest amylolytic activity was on Super strain B, the lowest was on Super Chief. The optimal pH and temperature for α-amylase were found to be at pH 9.0 and 45 °C, respectively. As calculated from Lineweaver-Burk plots, the highest Km and Vmax values for α-amylase obtained in Super Chief and Super Luna cultivars were 0.565 ± 0.11mM and 2.287 ± 0.4mM/min, respectively. The effects of different compounds on amylolytic activity indicated that CaCl2, MgCl2, NaCl and KCl increased amylase activity, whereas EDTA, ZnCl2 and BaCl2 decreased the enzyme activity in Super Luna cultivar. The highest activity of α-/ß-glucosidases was observed at pH 6.0 and 7.0, respectively, whereas the optimal pH for α/ß-galactosidases was at 5.0. The highest specific activity of α-/ß-glucosidases was determined in Riogrande-fed larvae, whereas the highest α/ß-galactosidases activity was in the larvae fed on Riogrande and Calj cultivars, respectively. By the native- PAGE, two bands were clearly detected for α-amylase. Since the larvae reared on Kingston showed lowest carbohydrase activities, this cultivar could possibly be suggested as the least suitable host for feeding of T. absoluta.