A Study on Aphids and Plant Viruses

Abstract

1. Turnip Yellow Mosaic Virus (TYMV) is precipitated in the presence of extracts of Myzus persicae (Sulz). 2. The precipitation reaction occurs only in the region of pH 4.8 and appears to be due to the formation of a complex between the virus and a substance present in extracts of the aphid. 3. The substance responsible for virus precipitation is probably a protein or contains protein. It has a molecular weight of about 80,000 and is iso-electric at about pH 5.3 4. Both the virus and the precipitating factor may be recovered from precipitated mixtures. The precipitating factor has its original activity. The virus is again soluble. It reacts with specific antiserum but is not able to be re-precipitated by aphid extracts. 5. Weights of Tobacco Mosaic Virus (TMV) equal to those of TYMV are also precipitated by the aphid factor. However, in mixtures of TMV and TYMV, the latter is precipitated selectively. 6. Extracts of two species of aphids other than M. persicae also precipitate TYMV. One has a higher precipitating ability per unit weight than M. persicae; the other has a lower precipitating ability. Extracts of the common housefly also precipitate TYMV but extracts of a common ant have no precipitating ability at pH 4.8. 7. TYMV precipitated by aphid extracts is less infectious than TYMV exposed to aphid extracts but not precipitated. 8. Three methods adequate to demonstrate TYMV in the amounts likely to be present in aphids fed on infected plants failed to reveal TYMV in ingested sap. 9. Detached leaves of Chinese cabbage, brassica pekinesis (Rupr), take up TYMV but a proportion of the virus is denatured within the leaves. Thus the virus uptake of aphids fed on these leaves cannot be determined easily. 10. Aphids fed by attaching them to glass capillaries containing labelled solutions were shown to ingest these solutions 11. A description is given of an apparatus which continuously records the uptake of radio-active solutions by single aphids. 12. Radioautographs of sections of aphids which had fed on suspensions of labelled TYMV, demonstrated unequivocally that the virus had been ingested and was confined to the gut. 13. TYMV recovered from aphids was found to have the nucleic acid dissociated from the protein component.