Sugar accumulation in tobacco plants systemically protected against blue mold (Peronospora tabacina)

A two- to threefold increase in total soluble sugar content was detected in the leaves of tobacco plants (Nicotiana tabacum L.) 24 days after stem inoculation with conidia of Peronospora tabacina (=Peronospora hyoscyami f. sp. tabacina), relative to leaves of non-inoculated control plants. Glucose and fructose accounted for most of this increase. The leaves of the inoculated plants were also protected against blue mold incited by P. tabacina. The increased sugar content may be due to the three- to fourfold increase in activity of (β-1,3 glucanase in the leaves and/or to the threefold increase in activities of β-1,3 glucanase, invertase and amylase in the inoculated sems. Tobacco leaf discs floated on glucose or other mono- and disaccharides at 55.5 mM, but not on polyethyleneglycol at a similar osmotic potential, reacted hypersensitively upon challenge with P. tabacina.