Powdery mildew infection of wheat leaves changes host solute transport and invertase activity

The effect of powdery mildew (Blumeria graminis) infection of wheat leaves on solute transport and invertase activity of the host tissue has been examined. Sugars (glucose, sucrose, maltose) and amino acids (glutamine, histidine) were taken up by leaf pieces, and radioactivity was transferred to the fungal mycelium. Infection had a marked effect on sugar uptake, particularly for glucose which was taken up into infected tissue at considerably higher rates than into uninfected tissues. In contrast, amino acid uptake rates into infected tissues were lower when compared with those into uninfected tissue. The increase in glucose uptake could be correlated with a change in sugar transporter gene expression as a wheat homologue of the monosaccharide carrier AtSTP4 was shown to increase in infected tissue. Efflux analysis showed a higher leakage of preloaded glucose from infected leaves in comparison with uninfected tissue and transfer to the mycelium was greater for glucose than for the other solutes measured. All types of invertase, measured enzymatically, showed an increase in infected tissue, with the highest proportional increase observed for cell-wall invertase. A partial-length complementary DNA, TaINV2, was isolated for a putative cell-wall invertase; expression studies indicated that levels for this or related sequences increased substantially 3 days after infection.