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In young systemically infected leaves of Datura stramonium L., a severe strain of Potato virus X (PVX) accumulated to a lower degree than a mild strain. Infected leaves had increased protease and RNase activities in comparison with those of healthy controls. The highest hydrolase activities were found in leaves infected with the severe strain. Negative-staining electron microscopy of dips from the infected leaves indicated that PVX virions underwent destructive changes, which resulted in the appearance of abnormal (swollen and ‘thin’) particles. Immuno-electron microscopic assays showed that thin PVX particles, in contrast to those of normal diameter, lost the ability to bind with specific antiserum. The relative number of thin virions in leaves infected with the severe PVX strain was considerably higher than in leaves infected with the mild strain. This shows that a correlation exists between increased protease activity and intracellular destruction of virions. In abnormal virions, the viral RNA appears to be available for RNase attack. Therefore, it seems that high RNase activity together with increased generation of abnormal virions in the leaves infected with the severe strain promote inactivation of the viral RNA with RNase. We suppose that the enhanced hydrolase activities in the leaves infected with severe PVX strain, on the one hand, limit viral accumulation and thus play a defensive role and, on the other hand, cause considerable intracellular pathological changes resulting in severe symptoms.

Glucan preparations were obtained by transformation of laminaran from the alga Laminaria cichorioides with endo-β-1,3-glucanase from marine mollusks. These preparations, like those of other sources, have an inhibitory effect on tobacco mosaic virus (TMV) infection of detached leaves of local and systemic host tobacco plants.

In mixed infection by Tobacco Mosaic Virus (TMV) and Potato Virus X (PVX) of leaves of Datura stramonium L., PVX particles were observed in the developing local lesions in both the central part and on the periphery, in addition to TMV. PVX virions were found either separately or together with TMV. Sometimes in local lesions mainly in their periphery, PVX-specific laminar inclusion components were observed and, in certain cases, cylindrical bodies about 120—140 nm in diameter. In 2 mm surrounding zones from the edge of the lesions, TMV particles were not observed. However, in the majority of cells of these zones, PVX intensively accumulated, often forming large masses. In some cases, we observed parts of cells with relatively small amounts of dispersed PVX particles, associated with laminar inclusion bodies. In cell areas with large accumulations of PVX, laminar inclusions were not found. Zusammenfassung Beobachtung von Kartoffel Virus X in von Tabakmosaikvirus (TMV)-induzierten Lokallasionen und umgebenden Zonen in Blattern von Datura stramonium L. bei Mischinfektion In Blattern von Datura stramonium L., die mit einer Mischung von Tabakmosaikvirus (TMV) und Kartoffelvirus X (PVX) infiziert worden waren, wurde in den sich entwickelnden lokalen Lasionen sowohl im Zentrum als auch in der Randzone auser TMV auch PVX-Partikel beobachtet. PVX-Partikel wurden entweder einzeln oder zusammen mit TMV gefunden. Manchmal wurden, besonders an den Randern der Lasionen, besondere laminare Einschlusse, in bestimmten Fallen zylindrische Korper mit einem Durchmesser von 120—140mm beobachtet. In einer vom Rand der Lasion 2 mm entfernten Zone wurden keine TMV-Panikel festgestellt. Indessen war PVX in der Mehrzahl der Zellen dieser Zonen stark angereichert und bildete oft grose Massen. In einigen Fallen beobachteten wir Teile von Zellen mit verhaltnismasig geringen Mengen von PVX-Partikeln, gemeinsam mit laminaren Einschluskorpern. In Zellen mit grosen Mengen PVX wurden diese jedoch nicht gefunden.