Diversity and distribution of entomopathogenic nematodes (Steinernematidae, Heterorhabditidae) in South Africa

A total of 1506 soil samples from different habitats in seven geographic regions of South Africa were evaluated for the presence of entomopathogenic nematodes (EPN). Nematodes were isolated from 5% of the samples. Among the steinernematids, four Steinernema sp. were recovered including Steinernema khoisanae and three new undescribed species. Although steinernematids were recovered from both humid subtropical and semiarid regions, this family accounted for 80% of EPN recovered from the semiarid climate zones characterised by sandy, acidic soils. Eight isolates of S. khoisanae were recovered from the Western Cape province. One of the new undescribed steinernematids (Steinernema sp. 1) was recovered only from the Free State and KwaZulu-Natal provinces where humid subtropical conditions prevail and soils are generally less acidic with higher clay content. A high level of adaptation, however, was noted with Steinernema sp. 2, which was recovered from a wide range of soil conditions and habitats ranging from semiarid (Western Cape province) to humid subtropical (KwaZulu-Natal province). A third undescribed steinernematid, Steinernema sp. 3, seemed better adapted to heavier soils with more than 80% of isolates recovered from fruit orchards in the Free State province. Heterorhabditis bacteriophora was the only heterorhabditid recovered during this survey. This species was particularly prevalent in four provinces ranging from humid subtropical to semiarid regions. Isolation of EPN directly from insect cadavers included Steinernema sp. 2 and one H. bacteriophora from an unidentified white grub (Scarabaeidae) cadaver (i.e., dual infection) and H. bacteriophora from the black vine weevil, Otiorhynchus sulcatus.     

Is direct spectrophotometric determination of chlorophyll in pigment extracts of tissues under different physiological conditions valid?

Direct spectrophotometric determination of chlorophyll content from methanol extracts of young and senescent leaves of $\text{Thunbergia}\text{grandiflora}$ showed 29 and 16%, respectively, of mature leaves. Spectrophotometric estimation in the same extracts after separation of chlorophyll by thin layer chromatography or by direct fluorometric determination showed only 15 and 0.5% of mature leaves, indicating an error of 4 to 40 fold. In the above wide range of absorbance (0.5 to 100%) the lack of linearity between absorption and concentration resulted in additional error. Bound chlorophyll remaining in the pellet, not extractable by any solvent system, was also reported to vary depending on the physiological conditions of the tissue (Plant Physiol. 51, 660–666). Therefore, it is pointed out that the aforementioned errors observed in direct spectrophotometric determinations could be checked by monitoring simultaneously the cell or plastid suspensions $\text{in}\text{vivo}$ by fluorometry without any extraction.     

Arbuscular mycorrhizal morphology in crops and associated weeds in tropical agro-ecosystems

Morphological types of arbuscular mycorrhizae (AM) in crops and associated weeds were examined in agro-ecosystems. In total, 48 plant species (8 crops and 40 weeds) belonging to 43 genera in 18 families were examined. The number of plant species with Arum-type AM was higher than those with Paris-type AM in the examined plants. AM association was absent in 6 weeds, and the average colonization rate was 62.64% in crops and 52.92% in weeds. AM morphology has been reported in 2 crops and 21 weeds for the first time. The influence of plant identity on AM morphology was also analyzed by arranging the examined plants in a current plant phylogenetic scheme. This analysis showed there was a lack of relationship between plant classification and AM morphological type. Actually, the colonization types were not distinguished at the plant family level, but were mostly distinguished at the species level.     

Unraveling gene function in agricultural species using gene co-expression networks

Co-expression networks have been shown to be a powerful tool for inferring a gene's function when little is known about it. With the advent of next generation sequencing technologies, the construction and analysis of co-expression networks is now possible in non-model species, including those with agricultural importance. Here, we review fundamental concepts in the construction and application of co-expression networks with a focus on agricultural crops. We survey past and current applications of co-expression network analysis in several agricultural species and provide perspective on important considerations that arise when analyzing network relationships. We conclude with a perspective on future directions and potential challenges of utilizing this powerful approach in crops. This article is part of a Special Issue entitled: Plant Gene Regulatory Mechanisms and Networks, edited by Dr. Erich Grotewold and Dr. Nathan Springer.     

Discrimination between the binding sites of modulators of the H+-translocating ATPase activity in rat liver mitochondrial membranes

The properties of the components of the mitochondrial ATPase which interact with modulators of energy transduction have been examined. The chromatographic behavior and the size of the components which bind trialkyl tins, carbodiimides and uncouplers, have been shown to be different. However, they all appear to be proteolipids with apparent molecular weights around 10,000. On this basis it is proposed that these inhibitors act at different sites in the membrane sector of the ATP synthase of rat liver mitochondria.