natural-products-in-plant-pest-management

Control of Virus Diseases of Plants 155et al., 1992; Barbieri et al., 1993). Type-I RIPs consist of a single polypeptidechain that is enzymatically active. These are scarcely toxic to animals andinhibit protein synthesis in cell-free systems, but have little or no effect onwhole cells. The three well known antiviral proteins PAPs, dianthins andMAP belong to this category. Type-II RIPs contain two types of polypeptidechains. Chain A is linked to chain B through a disulfide bond. Chain B bindsthe toxin to the cell surface and chain A enzymatically inactivates the ribosomes(Olsnes and Pihl, 1982). These are toxic to cells and inhibit proteinsynthesis in intact cells and in cell-free systems. Several similarities existamong the type-I RIPs. They are all basic proteins with a molecular weight inthe range 26–32 kDa. They have an alkaline isoelectric point and are usuallystable, being resistant to denaturing agents and protease. A majority of theRIPs are glycoproteins. Type-I RIPs are strongly immunogenic. Strocchi et al.(1992) established that cross reactivity between RIPs obtained from unrelatedplants was either very weak or absent.Recently cloning and expression of antiviral/ribosome-inactivatingprotein from Bougainvillea xbuttiana was reported by Choudhary et al. (2008).They reported that full-length cDNA encoding ribosome inactivating/ antiviral protein (RIP /AVP) consisted of 1364 nucleotides with an openreading frame (ORF) of 960 nucleotides encoding a 35.49 kDa protein of 319amino acids.The three well known antiviral proteins, namely PAPs (from Phytolaccaamericana), dianthins (from Dianthus caryophyllus) and MAPs (from Mirabilisjalapa) belong to the category of type-I RIPs.Pokeweed antiviral proteins (PAPs)The antiviral protein present in the leaves of Phytolacca americana was purifiedto homogeneity and its molecular weight determined as 29 kDa (Irvin, 1975).This protein, called pokeweed antiviral protein (PAP), had a PI of 8.1 (Irvin,1983). The antiviral effect of PAP was most pronounced when it was coinoculatedwith the virus. PAP also inhibited virus infection when appliedprior to virus challenge. Local lesion formation by TMV on N. tabacum cv.Xanthi-nc was inhibited by nearly 70% even after 48 h of treatment. The virusinhibitory effect of PAP increased with the decrease in the time lapse betweentreatment and challenge inoculation. PAP was less effective in preventingvirus infection when applied a short time after virus inoculation. No inhibitionwas observed when PAP was applied 50 min after virus infection (Chenet al., 1991). PAP reduced infectivity of several mechanically transmitted RNAand DNA viruses when the purified virus or sap from virus-infected plantswas mixed with an equal volume of PAP solution and the mixture rubbed onthe leaves of the local-lesion hosts (N. glutinosa / TMV; Chenopodium quinoa /CMV; C. amaranticolor / TMV, CMV, alfalfa mosaic virus, PVY; Gomphrena globosa/ PVX) or systemic hosts (Brassica campestris / cauliflower mosaic virus;N. benthamiana / African cassava mosaic virus). PAP, thus, appears to be ageneral inhibitor of virus infection (Tomlinson et al., 1974; Stevens et al., 1981;