Volume 25, Issue 4
December 2000, pages 315-416
pp 323-330 Perspectives
I draw attention to the perceptions of and interactions between molecular biologists and scientists engaged in plant breeding in India, who have been attempting to employ molecular biology tools to understand and intervene to improve the rice crop. The present essay suggests that the concept of cognitive empathy is crucial for enabling basic scientists and applied scientists to begin to understand phenomena from the point of view of the other and from the point of view of society at large, and in arriving at solutions that are scientifically feasible and socially acceptable. Socialization into disciplinary cultures, organizational factors and individual anxieties seem to inhibit inter-disciplinary collaboration. The majority of rice breeders and a small group of molecular biologists emphasize the relative merits of marker-assisted selection (MAS) in the near term vis-à-vis the currently controversial transgenic approach for rice crop improvement in India.
pp 331-338 Articles
Among the downstream targets of calcium in plants, calcium-dependent protein kinases (CDPKs) form an interesting class of kinases which are activated by calcium binding. They have been implicated in a diverse array of responses to hormonal and environmental stimuli. In order to dissect the role of CDPKs in the moss Funaria hygrometrica, a polymerase chain reaction (PCR)-based approach was adopted to clone the gene. Using degenerate PCR primers against conserved regions of CDPKs, a 900 bp amplicon was obtained from the genomic DNA of Funaria. Southern hybridization under low stringency conditions indicated the presence of several CDPK related sequences in the Funaria genome. This observation is consistent with reports of multigene families of CDPKs in other plants. The 900 bp fragment was subsequently used to isolate a 2.2 kb partial genomic clone of the CDPK gene from Funaria. The genomic clone encodes an open reading frame (ORF) of 518 amino acids. Interestingly, unlike other CDPK genes from plants, the entire 1.5 kb ORF is not interrupted by introns. The deduced amino acid sequence of the Funaria gene shows extensive homology with CDPKs from higher plants, 73% identity with the Fragaria CDPK and 71% identity with CDPK isoform 7 of Arabidopsis. Phylogenetic analysis revealed that the Funaria CDPK is closer to the CDPKs from higher plants like strawberry and Arabidopsis as compared to those from lower plants such as the liverwort Marchantia, the green alga Chlamydomonas or another moss Tortula. Northern analysis shows enhanced expression of the CDPK transcript within 24–48 h of starvation for nitrogen, phosphorus or sulphur. So far the only other kinase which is known to be induced by nutrient starvation in plants is the wpk 4 which is a snf-1 related kinase (SnRKs). To our knowledge this is the first report that implicates a CDPK in the starvation response.
pp 339-346 Articles
Tyrosine phosphorylation events are key components of several cellular signal transduction pathways. This study describes a novel method for identification of substrates for tyrosine kinases. Co-expression of the tyrosine kinase EphB1 with the intracellular domain of guanylyl cyclase C (GCC) in Escherichia coli cells resulted in tyrosine phosphorylation of GCC, indicating that GCC is a potential substrate for tyrosine kinases. Indeed, GCC expressed in mammalian cells is tyrosine phosphorylated, suggesting that tyrosine phosphorylation may play a role in regulation of GCC signalling. This is the first demonstration of tyrosine phosphorylation of any member of the family of membrane-associated guanylyl cyclases.
pp 347-360 Articles
Assembly of the functional tetrameric form of Mu transposase (MuA protein) at the two att ends of Mu depends on interaction of MuA with multiple att and enhancer sites on supercoiled DNA, and is stimulated by MuB protein. The N-terminal domain I of MuA harbours distinct regions for interaction with the att ends and enhancer; the C-terminal domain III contains separate regions essential for tetramer assembly and interaction with MuB protein (III𝛼 and III𝛽, respectively). Although the central domain II (the ‘DDE’ domain) of MuA harbours the known catalytic DDE residues, a 26 amino acid peptide within III𝛼 also has a non-specific DNA binding and nuclease activity which has been implicated in catalysis. One model proposes that active sites for Mu transposition are assembled by sharing structural/catalytic residues between domains II and III present on separate MuA monomers within the MuA tetramer. We have used substrates with altered att sites and mixtures of MuA proteins with either wild-type or altered att DNA binding specificities, to create tetrameric arrangements wherein specific MuA subunits are nonfunctional in II, III𝛼 or III𝛽 domains. From the ability of these oriented tetramers to carry out DNA cleavage and strand transfer we conclude that domain III𝛼 or III𝛽 function is not unique to a specific subunit within the tetramer, indicative of a structural rather than a catalytic function for domain III in Mu transposition.
pp 361-366 Articles
Mosquitoes are vectors for the transmission of many human pathogens that include viruses, nematodes and protozoa. For the understanding of their vectorial capacity, identification of disease carrying and refractory strains is essential. Recently, molecular taxonomic techniques have been utilized for this purpose. Sequence analysis of the mitochondrial 16S rRNA gene has been used for molecular taxonomy in many insects. In this paper, we have analysed a 450 bp hypervariable region of the mitochondrial 16S rRNA gene in three major genera of mosquitoes, Aedes, Anopheles and Culex. The sequence was found to be unusually A + T rich and in substitutions the rate of transversions was higher than the transition rate. A phylogenetic tree was constructed with these sequences. An interesting feature of the sequences was a stretch of Ts that distinguished between Aedes and Culex on the one hand, and Anopheles on the other. This is the first report of mitochondrial rRNA sequences from these medically important genera of mosquitoes.
pp 367-378 Articles
A total of 3211 colonies of macrolichens, from twelve 50 m × 10 m plots distributed across four macrohabitat (vegetation) types between 1500 m–3700 m in the Chopta-Tunganath landscape of the Garhwal Himalaya, yielded 13 families with 15 genera and 85 species. Lobaria retigera stood out as a broad-niched generalist species with moderate levels of abundance in all the three major microhabitats, viz. rock, soil and wood across 83% of all the plots sampled, whereas Umbilicaria indica emerged as an abundantly occurring specialist confined to rock substrates. Heterodermia incana and Leptogium javanicum appeared to be rare members of the community as they were encountered only once during the field survey. Woody microhabitats turned out to be richer than rock and soil substrates for macrolichens. Amongst the macrohabitats, middle altitude (2500–2800 m) Quercus forest was richest in species and genera followed by high altitude (2900–3200 m) Rhododendron forest, higher altitude grasslands (3300–3700 m) and then the lower elevation (1500 m) Quercus forest. Species, genus and family level alpha- as well as beta-diversities were significantly correlated with each other, implying that higher taxonomic ranks such as genera may be used as surrogates for species thus facilitating cost- and time-effective periodic monitoring of the biodiversity of macrolichens. Dynamics of the diversity of lichen communities in relation to various forms of environmental disturbance including livestock grazing and tourism as dominant land use activities in the higher Himalaya need further research.
pp 379-386 Articles
A study on the microarthropod community with special reference to species diversity of Oribatid and Collembola communities (Microarthropoda: Oribatei and Collembola) in Tam Dao National Park of Vietnam, a subtropical evergreen broad leaf alpine forest, was undertaken with the aim to explain how they are related to forest decline, and whether they can be used as bioindicators of forest plant succession.
The results have shown that microarthropod community structures, particularly species diversity of oribatid and collembolan communities, are related to forest decline. Therefore they can be used as bioindicators of forest plant succession. In Tam Dao National Park, there was an inverse relation between species diversity of the oribatid and collembola communities. The species diversity of the oribatid community gradually decreased with forest decline whereas the species diversity of the collembola community gradually increased.
pp 387-396 Articles
Acoustic signals play an important role in the lives of birds. Almost all avian species produce vocal signals in a variety of contexts either in the form of calls or songs or both. In the present study different types of vocal signals of the tropical avian species Pycnonotus cafer were characterized on the basis of their physical characteristics and context of production. This species used six types of vocal signals: contact signals, roosting signals, alarm signals, twittering signals, distress signals and begging signals. Two types of alarm signals are produced based on predation pressure. These signals are dissimilar in all physical characteristics except for dominant frequency. Although alarm signal type I and roosting signals are phonetically similar, they have completely different sonogram characteristics.
pp 397-404 Mini Review
Activation of receptors coupled to the phospholipase C/IP3 signalling pathway results in a rapid release of calcium from its intracellular stores, eventually leading to depletion of these stores. Calcium store depletion triggers an influx of extracellular calcium across the plasma membrane, a mechanism known as the store-operated calcium entry or capacitative calcium entry. Capacitative calcium current plays a key role in replenishing calcium stores and activating various physiological processes. Despite considerable efforts, very little is known about the molecular nature of the capacitative channel and the signalling pathway that activates it. This review summarizes our current knowledge about store operated calcium entry and suggests possible hypotheses for its mode of activation.
Volume 42 | Issue 4