Variation of invertase activities in four wheat cultivars as influenced by thiourea and high temperature

The effects of metal ions and thiourea on the activities of invertases in relation to the accumulation of free sugars and soluble protein were studied in four germinating wheat (Triticum aestivum) cultivars PBW 343, PBW 534 (heat susceptible), C 306 and C 273 (heat tolerant) under normal (25 degrees C) and high temperature (HT, 32 degrees C) conditions. High temperature significantly increased the activities of soluble acid, neutral and cell wall-bound invertases in correspondence with an increase in reducing sugar and soluble protein whereas the content of non reducing sugar was decreased in both root and shoot. Thiourea application under HT stress further elevated invertase activities and soluble protein content in all the four cultivars studied. Invertase activities of C 306 and C 273 cultivars were more sensitive to sulfhydryl group modifiers whereas the inhibitory effect of Ca2+, Hg2+, Mg2+ and Zn2+ was much more pronounced in PBW 343 and PBW 534. Apparently, inhibitory effect of iodine and Hg2+ on invertase activities in root and shoot of wheat confirmed the presence of sulfhydryl group at the active site of the enzyme. The results indicate that differential response of wheat cultivars may be anticipated to in vitro modulation of invertases to metal ions and TU that leads to selective modification of carbon metabolism under the influence of HT.