BETA-1,3-GLUCANASES IN WHEAT AND RESISTANCE TO THE RUSSIAN WHEAT APHID

The Russian wheat aphid (RWA); Diuraphis noxia (Mordvilko) is one of t he most destructive insect pests of cereals world-wide. Although resis tant cultivars have been bred, the biochemical mechanism of resistance is unknown. The aim of this work was to gain information on the mecha nism of resistance which could contribute to more directed breeding of resistant cultivars in the future. The effect of RWA infestation on t he inter- and intracellular beta-1,3-glucanase activities was studied in different resistant wheat (Triticum aestivum L.) cultivars containi ng the Dn-1 gene for RWA resistance and corresponding near-isogenic su sceptible cultivars. The activity was determined spectrophotometricall y by measuring the release of glucose from laminarin. infestation diff erentially induced the intra- and intercellular activities to much hig her levels in resistant than susceptible cultivars within 48 h. Accord ing to immunological studies induced enzyme activities were due to inc reased protein levels. The intracellular beta-1,3-glucanase contained about 8% exo-activity. The exo-activity made an insignificant contribu tion to the intercellular activity. The genetic back ground into which the resistance gene was bred did affect the level of activity that co rresponded to the resistance performance. Seven apoplastic isoforms of beta-1,3-glucanase, varying from acidic to basic, were resolved by is oelectric focusing. All isoenzymes were equally induced and no specifi c one could be linked to resistance or susceptibility. The RWA induced beta-1,3-glucanase activity in resistant cultivars closely resembles defence responses during pathogenesis and seems to be part of a genera l defence response like the hypersensitive reaction (HR), which confer s resistance to the RWA. This knowledge might be helpful in future to identify genes for RWA resistance. The increased beta-1,3-glucanase ac tivity after RWA infestation might serve as an additional measure to b iochemically trace resistance in crosses during breeding.