Peroxidase and polyphenol oxidase activity in malformed mango inflorescence caused byFusarium moniliforme var.subglutinans

Peroxidase and polyphenol oxidase activities in malformed mango inflorescences of ‘Himsagar’ and ‘Bombay green’ oultivars wore found to be increased considerably following infection byFusarium moniliforme var.subglutinans. Whether such increased activities were due to their synthesis by the pathogen or the host, or both, was not studied although it was found that the pathogen was incapable of producing the enzymesin vitro. The activities of both the enzymes in infected tissues were found to increase considerably during the experimental period. It was found that activities of polyphenol oxidase were inhibited in the presence of sodium diethyldithiocarbamate and phenylthiourea; the former acted as chelating agent of Cu of the enzymes and the latter as a competitive inhibitor. Similarly, peroxidase activity was found to be inhibited by cycloheximide which acted as inhibitor of enzyme protein synthesis. The fact that the ‘Himsagar’ cultivar showed greater enzyme activity than the ‘Bombay green’ cultivar possibly suggests its higher resistance to the pathogen.     

A human glioma cell line secretes three structurally and functionally different dimeric forms of platelet-derived growth factor

A human malignant glioma cell line, U-343 MGa Cl2:6, has previously been shown to secrete platelet-derived-growth-factor(PDGF)-like activity [Nistér, M., Heldin, C.-H., Wasteson, A. and Westermark, B. (1984) Proc. Natl Acad. Sci. USA 81, 926-930]. We report here that this activity consists of three different molecules separable by reversed-phase chromatography and immobilized-metal-ion affinity chromatography. HPLC reversed-phase chromatography resolved two peaks of activity, which were denoted glioma-derived growth factor-I (GDGF-I) and GDGF-II. GDGF-I was purified to greater than 90% purity; in SDS gel electrophoresis, it appeared as a 31-kDa component which by reduction was converted to 17 kDa. Immunoprecipitation of radiolabeled, reduced and alkylated GDGF-I with antisera made against peptides from the A and B chains of PDGF, gave a specific signal only with antiserum against the A chain. Furthermore, when reduced and alkylated GDGF-I was analyzed by reversed-phase HPLC, it eluted at the position of PDGF A chains. We conclude that GDGF-I is a homodimer of a polypeptide similar to the A chain of PGDF. GDGF-II was found to have higher mitogenic activity than GDGF-I. Analysis by immunoprecipitation with PDGF-chain-specific antisera revealed that GDGF-II contained a polypeptide similar to the B chain of PDGF. Immobilized-metal-ion affinity chromatography revealed that 95% of the mitogenic activity of GDGF-II consisted of a heterodimer of one A and one B chain, whereas 5% consisted of a B-chain homodimer. Thus, U-343 MGa Cl 2:6 cells secrete all three possible dimeric forms of PDGF.     

Constant rate allocation in nymphal development in species of Hemiptera

Abstract. This study investigated the existence of rate isomorphy (the constant allocation of relative times to different stages of development under different abiotic conditions) in Macrolophus pygmaeus (Hemiptera: Miridae; a phytophagous and predatory insect). Replicated data were used from a range of temperatures regarding (i) the developmental period of each nymphal stage in relation to the total duration of nymph development, when feeding on three host plants either with different prey species or without prey, and (ii) its egg, total nymphal and preoviposition period, on two host plants, with different prey species. The proportion of time required for the development of each nymphal stage of M. pygmaeus is not different among the temperatures or the kind of food available. These proportions ranged among the different host plants, temperatures and prey presence/absence from 17.3–21.8% in the first, 14.5–18.8% in the second, 14.2–18.3% in the third, 16.5–21.0% in the fourth and from 25.4–30.6% in the fifth nymphal stage. Thus, temperature does not significantly affect the proportion of time spent in each nymphal stage and rate isomorphy exists in nymphal development. This phenomenon was also investigated using data from the literature, and it also occurs in several other Hemiptera species. Therefore, there appears to be a constant time allocation in the nymphal development of the higher taxonomic groups of insects. However, for M. pygmaeus, rate isomorphy does not hold when considering egg‐to‐egg development and the relative duration of times to egg hatch, total nymphal development and preoviposition period. The ecophysiological implications of this rate isomorphy phenomenon are discussed in relation to endocrinological mechanisms. Apart from its theoretical interest, the existence of rate isomorphy simplifies studies on the rate of development and the estimation of thermal constants of an insect, which are essential for the prediction of insect population dynamics. It is also proposed that the term ‘rate isomorphy’ does not strictly describe the phenomenon, and it is suggested that ‘constant rate allocation’ would be a more suitable term.