Barley yellow dwarf virus: effects on carbohydrate metabolism in oat (Avena sativa) during cold hardening

Barley yellow dwarf virus (BYDV) causes significant losses in yield and in overwintering ability of winter cereals. Mechanisms by which the physiology of plants is affected by the virus are not clear. To see how carbohydrates in the crown of winter cereals were affected by BYDV, fructan isomers of d egree of polymerization (DP) 3-5, fructan DP > 6 and the simple sugars, glu cose, fructose and sucrose, were measured before and during cold hardening in three oat (Avena sativa L.) cultivars,'Wintok', 'Coast Black' and 'Fulgh um'. On a fresh weight basis fructan DP > 6 decreased by 50 %, in infected 'Wintok' and 'Coast Black' and by 25 %, in 'Fulghum'. Two DP3, one DP4 and one DP5 isomer were significantly higher than non-infected controls. The pe rcentages of simple sugars in infected crowns were significantly higher tha n controls in all three cultivars in every week except the first week of ha rdening. Crude enzyme extracts from BYDV infected plants incubated with suc rose suggested higher invertase and lower sucrose-sucrosyl transferase acti vity. When incubated with 1-kestose and neokestin, no significant differenc e was found in fructose fructosyl transferase or in hydrolase activity. The activity of unidentified enzymes catalysing the synthesis of larger (DP > 5) fructan was altered by BYDV. The decrease of carbohydrates in the crown induced indirectly by BYDV may alter the plant's capacity to regenerate til lers in the spring. The ability of plants to prevent or tolerate carbohydra te fluctuations induced by BYDV infection may be an important genetically r egulated characteristic for developing virus-resistant cultivars.