Influence of host plant (Terminalia arjuna)defences on the evolution of feeding behaviourin the tasar silkworm

Both under indoor and outdoor rearing conditions, early instars of Antheraea mylitta showed differential preference for eating towards developmentally different leaves of host plant, Terminalia arjuna. Semi-mature leaves were preferred by first, second and third instar of A. mylitta. Nutritional-value study of leaves of different age groups with respect to soluble protein and electrophoretic profile showed that young leaves are nutritionally rich compared to semi-mature and mature leaves. However, growth response and survival of larvae were better on semi-mature leaves compared to young and mature leaves. When analysed, semi-mature leaves showed protease inhibitor activity intermediate between young and mature leaves. This observation suggests optimal defence theory, where young and semi-mature leaves having high fitness and high probability of attack tend to have higher concentration of defence metabolites. Differential inhibition of midgut and bovine proteases by host plant protease inhibitor indicates that the tasar silkworm might have detoxified or evolved proteases that are insensitive to the leaf protease inhibitor of the host plant. Thus the differential feeding behaviour of larvae of tasar silkworm is an adaptation for coexistence of the insect and its host plant

Variability in foliar essential oils among different morphotypes of Lantana species complexes, and its taxonomic and ecological significance

The genus Lantana has many species complexes, and L. camara is one of the aggressive alien weedy species complexes; species delimitation in these complexes is a nightmare for taxonomists. We examined the diversity in the chemical composition of foliar essential oils among morphotypes of Lantana species complexes inhabiting the same ecological gradient, and its taxonomic and ecological significance. The yields of essential oils varied from 0.1 to 0.79% in foliar hydrodistillates of eleven morphotypes, and a total of 39 chemical constituents were detected by GC/MS. The quantitative and qualitative variability in the composition of essential oils among morphotypes was very high, and hence they represent chemotypes. The diversity observed in the composition of essential oils appears to be of genetic origin and thus of taxonomic value. The formation of distinct clusters and sub-clusters at high distance cluster combine values also substantiates that the patterns of distribution of chemical constituents among morphotypes can be used in delimiting species and infraspecific taxa within the species complexes. The presence of β-caryophyllene and other such compounds, which are known to prevent herbivory, in morphotypes of Lantana species complexes suggest that these compounds may provide selective advantage to Lantana over native species in the invasion of new and disturbed habitats

Nutritional potential of Vigna minima (Roxb.) Ohwi and Ohashi: I. Seed protein content and amino acid composition

The seed protein content and amino acid composition of 14 natural populations and their three-generation progenies (grown in different locations) belonging to Vigna minima (Roxb.) Ohwi & Ohashi and of V. umbellata cv IC 1568 have been investigated. The populations of V. minima were sampled from different ecozones of Western Ghats of Kerala and Tamil Nadu (India). The range of variation in protein levels is narrow, but the protein content of the coastal population is higher than the rice bean suggesting its breeding potential for high protein and salt tolerant lines of rice bean. Although the seed protein content shows genotype × environment interaction, there is a substantial genetic variability among the populations. The tenuous relationship between protein content and yield conponents suggest the presence of correlation breakers which can be utilized in breeding programmes of rice bean. There is a broad genetic base in the levels of essential amino acids, and the range of variation observed is higher than that recorded for different species of Vigna and Phaseolus. The wild relative is nutritionally as good as or superior to the cultigen

Isolation and characterization of a lectin from peanut roots

A glucose-specific lectin has been purified to apparent homogeneity from 7-day-old peanut (Arachis hypogaea) roots by affinity chromatography on a Sephades G-50. The lectin has a 66 kDa native molecular mass and a 33 kDa subunit molecular mass as revealed by native and denaturing sodium dedecyl sulphate-polycrylamide gel electrophoresis, respectively. The purified lectin, gives a single precipitin line with the antiserum produced against 7-day-old root extract and shows 5 bands in the pH range of 4.4–5.4 in the isoelectric focusing gel. The glucose-specific lectin activity in the peanut roots appears from the fourth day onwards. Lipopolysaccharides isolated from the host specific Rhizobium strain are a 68-fold more potent inhibitor of the lectin as compared to glucose

A Kunitz proteinase inhibitor from Archidendron ellipticum seeds: Purification, characterization, and kinetic properties

Leguminous plants in the tropical rainforests are a rich source of proteinase inhibitors and this work illustrates isolation of a serine proteinase inhibitor from the seeds of Archidendron ellipticum (AeTI), inhabiting Great Nicobar Island, India. AeTI was purified to homogeneity by acetone and ammonium sulfate fractionation, and ion exchange, size exclusion and reverse phase chromatography (HPLC). SDS–PAGE of AeTI revealed that it is constituted by two polypeptide chains (α-chain, Mr 15,000 and β-chain, Mr 5000), the molecular weight being ∼20 kDa. N-terminal sequence showed high homology with other serine proteinase inhibitors belonging to the Mimosoideae subfamily. Both Native-PAGE as well as isoelectric focussing showed four isoinhibitors (pI values of 4.1, 4.55, 5.27 and 5.65). Inhibitory activity of AeTI remained unchanged over a wide range of temperatures (0–60 °C) and pH (1–10). The protein inhibited trypsin in the stoichiometric ratio of 1:1, but lacked similar stoichiometry against chymotrypsin. Also, AeTI-trypsin complex was stable to SDS unlike the SDS unstable AeTI-chymotrypsin complex. AeTI, which possessed inhibition constants (Ki) of 2.46 × 10-10 and 0.5 × 10-10 M against trypsin and chymotrypsin activity, respectively, retained over 70% of inhibitory activity after being stored at −20 °C for more than a year. Initial studies on the insecticidal properties of AeTI indicate it to be a very potent insect antifeedant

Crystal structure of Himalayan mistletoe ribosome-inactivating protein reveals the presence of a natural inhibitor and a new functionally active sugar-binding site

Ribosome-inactivating proteins (RIPs) are toxins involved in plant defense. How the plant prevents autotoxicity is not yet fully understood. The present study is the first structural evidence of a naturally inhibited form of RIP from a plant. Himalayan mistletoe RIP (HmRIP) was purified from Viscum album leaves and crystallized with lactose. The structure was determined by the molecular replacement method and refined at 2.8-Å resolution. The crystal structure revealed the presence of high quality non-protein electron density at the active site, into which a pteridine derivative (2-amino 4-isopropyl 6-carboxyl pteridine) was modeled. The carboxyl group of the ligand binds strongly with the key active site residue Arg162, nullifies the positive charge required for catalysis, and thereby acts as a natural inhibitor. Lectin subunits of RIPs have two active sugar-binding sites present in 1α- and 2γ-subdomains. A third functionally active site has been identified in the 1β-subdomain of HmRIP. The 1β-site is active despite the absence of conserved polar sugar-binding residues. Loss of these residues is compensated by the following: (i) the presence of an extended site where the penultimate sugar also interacts with the protein; (ii) the interactions of galactose with the protein main chain carbonyl and amide nitrogen atoms; (iii) the presence of a well defined pocket encircled by four walls; and (iv) a favorable stacking of the galactose ring with Tyr66 besides the conserved Phe75. The mode of sugar binding is also distinct at the 1α and 2γ sugar-binding sites