Virus Resistance Induced in Plants by Polyacrylic Acid

Polyacrylic acid (PA) injected into tobacco cv. Xanthi-nc induced complete resistance to infection with TMV or tobacco necrosis virus but only partial resistance to potato virus X. The effect was maximal when the injection was made 2 to 3 days before inoculation. The lesion size was limited when the injection was made after inoculation. Using PA of 35oo, 27ooo, 76ooo, 23oooo and ~ × IO ~ tool. wt. the resistance decreased with increasing size of the polymer. In plants younger than 7 weeks, only the smallest polymer was active and evidence suggested that cell permeability to the larger polymers might increase with age of plant. The PAinduced resistance disappeared when plants were kept at 32 °C, but the effect of temperature was reversible. Polyacrylamide failed to induce resistance suggesting that the polyanionic structure of the acid polymers is responsible for the phenomenon. Disc-electrophoresis in Io ~ polyacrylamide gels showed that three additional soluble proteins appeared in PA-injected leaves, but only in conditions in which resistance to infection was induced. These new proteins co-electrophoresed with three out of four proteins produced in TMV-infected leaves of cv. Xanthi plants that also are resistant to infection and may be the cause of resistance.