Zinc nutrition of Nicotiana tabacum L. in relation to multiplication of tobacco mosaic virus

Abstract

Multiplication of tobacco mosaic virus was studied in Nicotiana tabacum L. grown in water culture vessels containing a complete nutrient solution except for zinc which was supplied at various concentrations. Development of virus symptoms was more pronounced in plants grown at zinc levels optimal for growth than in plants grown at zinc levels that were deficient. Optical density and local lesion assays for virus concentration of sap extracts from whole plants and from tip leaves showed that the concentration of virus nucleoprotein and of infective virus increased with increasing levels of zinc up to the level which was optimal for growth, and then decreased at levels which were toxic. Symptoms of zinc deficiency of plants increased after inoculation with tobacco mosaic virus, indicating that virus multiplication was associated directly or indirectly with utilization of zinc. When young inoculated plants were grown under zinc-deficient conditions for approximately 5 days and were then provided with zinc so that the total amount of zinc supplied was equivalent to that required for optimal host growth, the virus concentration remained less (during a period of 14 days) than that in plants grown continuously under optimal conditions. This suggested that virus multiplication was indirectly rather than directly associated with utilization of zinc. Virus concentration in floating leaf discs obtained from plants grown at different concentrations of zinc was found to be similar to that in whole plants. When virus-infected leaf discs were incubated on solutions of indole-3-acetic acid at concentrations of 5 × 10 −5, 1 × 10 −3, and 1 mg/l, there were no significant effects on virus concentration. A decrease in virus concentration, virus symptom expression, and plant growth resulted when indole-3-acetic acid at concentrations of 5 × 10 −5, 1 × 10 −3, 1, and 10 mg/l was added to the nutrient solution in which plants were growing at different concentrations of zinc. The decrease was greater at the higher concentrations of indole acetic acid than at the lower.