Auxin: a master regulator in plant root development

The demand for increased crop productivity and the predicted challenges related to plant survival under adverse environmental conditions have renewed the interest in research in root biology. Various physiological and genetic studies have provided ample evidence in support of the role of plant growth regulators in root development. The biosynthesis and transport of auxin and its signaling play a crucial role in controlling root growth and development. The univocal role of auxin in root development has established it as a master regulator. Other plant hormones, such as cytokinins, brassinosteroids, ethylene, abscisic acid, gibberellins, jasmonic acid, polyamines and strigolactones interact either synergistically or antagonistically with auxin to trigger cascades of events leading to root morphogenesis and development. In recent years, the availability of biological resources, development of modern tools and experimental approaches have led to the advancement of knowledge in root development. Research in the areas of hormone signal perception, understanding network of events involved in hormone action and the transport of plant hormones has added a new dimension to root biology. The present review highlights some of the important conceptual developments in the interplay of auxin and other plant hormones and associated downstream events affecting root development.     

Isolation and Characterization of Brassinosteroids from Leaves of Camellia sinensis (L.) O. Kuntze

Brassinosteroids are of ubiquitous occurrence in plants and elicit a wide spectrum of physiological responses. In our study, brassinosteroids were isolated and identified in topmost dormant leaves of tea plants. Six brassinosteriods, i.e. 6-deoxocastasterone, 24-epibrassinolide,3-dehydroteasterone, typhasterol, 3-deoxotyphasterol and 28-homodolicholide, were isolated and identified by GC–MS. All the brassinosteroids identified belong to important components of early and late C6 oxidation pathways proposed for brassinosteroids biosynthesis in plants. It suggests that both pathways are operating in tea to produce brassinolide, the most active brassinosteroid biologically.     

Diverse Host Responses and Outcomes following Simian Immunodeficiency Virus SIVmac239 Infection in Sooty Mangabeys and Rhesus Macaques

Sooty mangabeys naturally infected with simian immunodeficiency virus (SIV) do not develop immunodeficiency despite the presence of viral loads of 10⁵ to 10⁷ RNA copies/ml. To investigate the basis of apathogenic SIV infection in sooty mangabeys, three sooty mangabeys and three rhesus macaques were inoculated intravenously with SIVmac239 and evaluated longitudinally for 1 year. SIVmac239 infection of sooty mangabeys resulted in 2- to 4-log-lower viral loads than in macaques and did not reproduce the high viral loads observed in natural SIVsmm infection. During acute SIV infection, polyclonal cytotoxic T-lymphocyte (CTL) activity coincident with decline in peak plasma viremia was observed in both macaques and mangabeys; 8 to 20 weeks later, CTL activity declined in the macaques but was sustained and broadly directed in the mangabeys. Neutralizing antibodies to SIVmac239 were detected in the macaques but not the mangabeys. Differences in expression of CD38 on CD8⁺ T lymphocytes or in the percentage of naive phenotype T cells expressing CD45RA and CD62L-selection did not correlate with development of AIDS in rhesus macaques. In macaques, the proportion of CD4⁺ T lymphocytes expressing CD25 declined during SIV infection, while in mangabeys, CD25-expressing CD4⁺ T lymphocytes increased. Longitudinal evaluation of cytokine secretion by flow cytometric analysis of unstimulated lymphocytes revealed elevation of interleukin-2 and gamma interferon in a macaque and only interleukin-10 in a concurrently infected mangabey during acute SIV infection. Differences in host responses following experimental SIVmac239 infection may be associated with the divergent outcome in sooty mangabeys and rhesus macaques.     

Labelling of amoeboid microglial cells in rats of various ages following an intravenous injection of horseradish peroxidase

The macrophagic amoeboid microglial cells in the corpus callosum of postnatal rats were labelled following an intravenous injection of horseradish peroxidase (HRP). The earliest time when these cells were labelled was 3 h after the injection of HRP in postnatal (1-10 days) rats. Similar cells around the mesencephalic aqueduct and the fourth ventricle were also labelled. These cells, however, were weakly labelled in developing (11-20 days) and unlabelled in weaning (21-30 days) rats. The results suggest that in the postnatal rats, the HRP passed through the endothelial lining of the blood vessels and was then ingested by the amoeboid microglial cells. In the developing and older rats, the wall of blood vessels had developed fully thereby preventing the free passage of HRP into the brain tissues.     

Targeted ablation of alpha-crystallin-synthesizing cells produces lens-deficient eyes in transgenic mice

Genetic ablation techniques were used to study the role of the lens in mammalian eye development. Ablation was accomplished by microinjecting murine eggs with chimeric DNA constructs in which the alpha A-crystallin gene regulatory sequence (-366 to +46) was fused to the highly cytotoxic diphtheria toxin gene coding sequence. For genetic ablation to be successful the promoter regulating expression should be specific and completely silent in cells necessary for normal mouse development. In this report, we describe the generation and analysis of transgenic mice with this readily discernible phenotype: aphakia or eyes without lens. Of the 109 live-born pups, eight carried the transgene and could be grouped according to the apparent severity of eye malformations. Lines 4, 5 and 6 founder (F0) mice had the most severe phenotype. Histological analysis revealed: marked reduction in eye size, total absence of lens, increased retinal cell density and extensive whorling of the retinal fibre layers. The line 1 F0 mouse displayed a distinct lens opacity and lines 2, 3 and 8 F0 mice were mosaics with a relatively mild, but most unusual phenotype. Their eyes contained a small, highly vacuolated lens. The progeny of these mosaics that inherited the transgene, however, again exhibited the severe phenotype. The aberrant structures of the eyes in which complete genetic ablation of the lens has been achieved suggest that the lens plays a pivotal role in the development of multiple components of the murine eye.     

Bacillus megaterium mediated mineralization of calcium carbonate as biogenic surface treatment of green building materials

Microbially induced calcium carbonate precipitation is a biomineralization process that has various applications in remediation and restoration of range of building materials. In the present study, calcifying bacteria, Bacillus megaterium SS3 isolated from calcareous soil was applied as biosealant to enhance the durability of low energy, green building materials (soil–cement blocks). This bacterial isolate produced high amounts of urease, carbonic anhydrase, extra polymeric substances and biofilm. The calcium carbonate polymorphs produced by B. megaterium SS3 were analyzed by scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction and Fourier transmission infra red spectroscopy. These results suggested that calcite is the most predominant carbonate formed by this bacteria followed by vaterite. Application of B. megaterium SS3 as biogenic surface treatment led to 40 % decrease in water absorption, 31 % decrease in porosity and 18 % increase in compressive strength of low energy building materials. From the present investigation, it is clear that surface treatment of building materials by B. megaterium SS3 is very effective and eco friendly way of biodeposition of coherent carbonates that enhances the durability of building materials.