Investigations of the mechanism of the necrotic response of Nicotiana tabacum L. Var. Samsun NN to infection with tobacco mosaic virus

A number of studies have been conducted in the last two decades trying to determine the principle or principles involved in the mechanism of the necrotic local lesion induced by tobacco mosaic virus (TMV) on certain Nicotiana spp. Physiological-biochemical processes have been investigated during necrotic local lesion formation. Respiratory rates of plants infected locally with TMV were reported to increase compared with noninoculated plants. Similarly, metabolic products have been found to accumulate at the site of infection. Some of these substances have been suggested as the cause of the necrotic local lesion. No definite criteria have been established to elucidate the cause or causes of cell death in a virus induced local lesion. Investigations were carried out to reproduce the necrotic effect with virus-free leaf extracts from local lesions produced on 'Samsun NN' plants. Biologically active substances were sought in the virus-free extracts. Extracts from 'Samsun NN' leaves were studied after the following treatments: leaves inoculated with distilled-sterile water, heat-inactived TMV, infectious TMV, and noninoculated control. The extracts represented the supernatants from ultracentrifuged and ultrafiltered sap obtained from each treatment. Respiration rates of healthy Samsun NN leaf tissue were similar when treated with crude extracts from inoculated treatments. They were higher than those recorded for tissue in noninoculated leaf extracts and in distilled water. The respiration of tissue in autoclaved crude extracts was not appreciably different. Dialysis and decoloration of the extracts with activated charcoal apparently removed the agent responsible for the previously observed respiratory increases. The effect of application of the extracts to 'Samsun NN' tissue was checked. ..