Susceptibility to Fungi of Cotton Boll Worms Before and After a Natural Epizootic of the Entomopathogenic Fungus Nomuraea rileyi (Hyphomycetes)

Epizootics caused by Beauveria bassiana and Nomuraea rileyi have been observed on boll worms and Spodoptera litura in south Indian fields during winter since the last 15 years. During the N. rileyi-induced natural epizootics, some boll worms were found surviving without infection. Whether they represent pathogen-resistant genotypes was investigated. Two insect populations, collected 3 months prior to and during the epizootic were established. Their sensitivity to both the fungi was compared in laboratory bioassays. No significant difference in sensitivity was observed between the two populations. It was concluded that the boll worm population surviving the epizootic was not genotypically resistant.     

Markedly low requirement of added CO2 for photosynthesis by mesophyll protoplasts of pea (Pisum sativum): possible roles of photorespiratory CO2 and carbonic anhydrase

Mesophyll protoplasts of pea required only 74.1 μM CO₂ for maximal photosynthesis, unlike chloroplasts, which required up to 588 μM CO₂. Such a markedly low requirement for CO₂ could be because of an internal carbon source and/or a CO₂ concentrating mechanism in mesophyll protoplasts. Ethoxyzolamide (EZA), an inhibitor of internal carbonic anhydrase (CA) suppressed photosynthesis by mesophyll protoplasts at low CO₂ (7.41 μM) but had no significant effect at high CO₂ (741 μM). However, acetazolamide, another inhibitor of CA, did not exert as much dramatic effect as EZA. Three photorespiratory inhibitors, aminoacetonitrile or glycine hydroxamate (GHA) or aminooxyacetate inhibited markedly photosynthesis at low CO₂ but not at high CO₂. Inhibitors of glycolysis or tricarboxylic acid cycle (NaF, sodium malonate) or phosphoenolpyruvate carboxylase (3,3‐dichloro‐2‐dihydroxy phosphinoyl‐methyl‐2‐propenoate) had no significant effect on photosynthesis. The CO₂ requirement of protoplast photosynthesis and the sensitivity of photosynthesis to EZA were much higher at low oxygen (65 nmol ml^?1) than that at normal oxygen (212 nmol ml^?1). In contrast, the inhibitory effect of photorespiratory inhibitors on protoplast photosynthesis was similar in both normal and low oxygen medium. The marked elevation of glycine/serine ratio at low O₂ or in presence of GHA confirmed the suppression of photorespiratory decarboxylation by GHA. While demonstrating interesting difference between the response of protoplasts and chloroplasts to CO₂, we suggest that photorespiration could be a significant source of CO₂ for photosynthesis in mesophyll protoplasts at limiting CO₂ and at atmospheric levels of oxygen. Obviously, carbonic anhydrase is essential to concentrate or retain CO₂ in mesophyll cells.     

Impediment to growth and yeast-to-hyphae transition in Candida albicans by copper oxide nanoparticles

Abstract

The effects of two prominent copper oxide nanoparticles (CuO-NP and Cu₂O-NP), with the oxidation state of Cu⁺⁺ (cupric) and Cu⁺ (cuprous), on Candida albicans were evaluated. CuO-NP and Cu₂O-NP were synthesized and characterized by XRD, FESEM, HR-TEM and Zeta potential. At sub-MIC (50?µg ml^?1), both cupric and cuprous oxide NPs prevented yeast-to-hyphae switching and wrinkling behaviour in C. albicans. The mechanism for the antifungal action of the two NPs differed; CuO-NP significantly elicited reactive oxygen species, whereas membrane damage was more pronounced with Cu₂O-NP. Real time PCR analysis revealed that CuO-NP suppressed the morphological switching of yeast-to-hyphae by down-regulating cph1, hst7 and ras1 and by up-regulation of the negative regulator tup1. In comparison, Cu₂O-NP resulted in down-regulation of ras1 and up-regulation of the negative regulators nrg1 and tup1. Between the two NPs, CuO exhibited increased antifungal activity due to its stable oxidation state (Cu⁺⁺) and its smaller dimensions compared with Cu₂O-NP.