Localized infections produced by tobacco necrosis virus (TNV) or tomato mosaic virus (ToMV) in White Burley tobacco induced a systemic acquired resistance in upper, uninoculated leaves. This resistance was effective against challenge infection by TNV or ToMV but not by potato virus Y, necrotic strain (PVYn), tobacco mosaic virus (TMV) or tobacco rattle virus (TRV), viruses giving systemic infections.
Systemic acquired resistance against TNV or ToMV was expressed as a reduction in lesion size but not in viral antigen content of the resulting necrotic local lesions. The acquisition of resistance was concurrent with an increased capacity of the resistant leaves to convert 1‐aminocyclopropane‐1‐carboxylic acid into ethylene.
Systemic acquired resistance was ineffective to contrast or minimize in whatever way the systemic challenge infection produced by PVYN, TMV or TRV. Severity of symptoms and virus multiplication did not differ in resistant leaves from controls. This result does not allow any optimistic promise on possible application of the systemic acquired resistance against severe viral diseases of crops.
Salicylate, acetylsalicylate, benzoate and 3,5‐diiodosalicylate were examined for their effects on pea (Pisum sativum L. cv. Alaska) stem mitochondria and on a tonoplast‐enriched fraction. Salicylate collapsed the transmembrane electrochemical potential of mitochondria and the ATP‐dependent proton gradient of the tonoplast‐enriched vesicle preparation. Benzoate and acetylsalicylate did not show any effect, while 3,5‐diiodosalicylate inhibited both basal O2 consumption and ATPase activity of pea mitochondria. Salicylate seems to act as a protonophore. However, its effect is evident only at concentrations higher than those required by classical protonophores and, in addition, can be abolished after removing salicylate from the incubation medium. The activity of salicylate appears linked to the presence of the free phenolic hydroxyl on the benzene ring.
Exogenously supplied cadmium and nickel considerably affected the ethylene biosynthesis in soybean cuttings. Cadmium stimulated ethylene production by increasing production of free ACC and stimulating EFE activity. Nickel inhibited ethylene production by depressing EFE activity, but stimulated the production of free ACC. Both heavy metals did not apparently affect cell membrane integrity.
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