Plant regeneration from mesophyll protoplasts of Diplotaxis muralis,a wild crucifer

Mesophyll protoplasts from leaves of aseptically grown shoot tips of Diplotaxis muralis were isolated (6.2–7.1×10⁵ protoplasts/g fresh weight of tissue) using one step enzyme digestion. The protoplasts (71% viability) underwent divisions (4.2+0.1%) on plating in M8PS₂ medium and ultimately formed calli with 0.45+0.03% plating efficiency. Plant regeneration could be achieved both through embryogenesis and organogenesis. The efficiency of plant regeneration through organogenesis was 9 times higher than embryogenesis. Forty eight out of 52 plants regenerated so far from 3 independent experiments were normal with respect to fertility and meiotic chromosomal behavior.Abbreviations BAP 6-benzylaminopurine - GA₃ Gibberellic acid - A Kao and Michayluk, 1981 - KM Kao and Michayluk, 1975 - MK₃ Modified K₃ - M8P Modified 8P - MS Murashige and Skoog, 1962 - NAA 1-naphthalene acetic acid - PE Plating efficiency     

A simple haemolytic method for quantitation of the delta endotoxin of Bacillus thuringiensis subsp. israelensis from crude samples

A simple haemolytic assay method for quantitative estimation of the delta endotoxin of Bacillus thuringiensis subsp. israelensis from a crude preparation has been developed. The method has several advantages over mosquito-larvicidal methods of assay as it is inexpensive, highly sensitive and easier to run and can be used for performing a reasonably large number of assays rapidly with high precision and with a coefficient of variation that does not exceed 1.96%.     

Synconset Waves and Chains: Spiking Onsets in Synchronous Populations Predict and Are Predicted by Network Structure

Synfire waves are propagating spike packets in synfire chains, which are feedforward chains embedded in random networks. Although synfire waves have proved to be effective quantification for network activity with clear relations to network structure, their utilities are largely limited to feedforward networks with low background activity. To overcome these shortcomings, we describe a novel generalisation of synfire waves, and define ‘synconset wave’ as a cascade of first spikes within a synchronisation event. Synconset waves would occur in ‘synconset chains’, which are feedforward chains embedded in possibly heavily recurrent networks with heavy background activity. We probed the utility of synconset waves using simulation of single compartment neuron network models with biophysically realistic conductances, and demonstrated that the spread of synconset waves directly follows from the network connectivity matrix and is modulated by top-down inputs and the resultant oscillations. Such synconset profiles lend intuitive insights into network organisation in terms of connection probabilities between various network regions rather than an adjacency matrix. To test this intuition, we develop a Bayesian likelihood function that quantifies the probability that an observed synfire wave was caused by a given network. Further, we demonstrate it''s utility in the inverse problem of identifying the network that caused a given synfire wave. This method was effective even in highly subsampled networks where only a small subset of neurons were accessible, thus showing it''s utility in experimental estimation of connectomes in real neuronal-networks. Together, we propose synconset chains/waves as an effective framework for understanding the impact of network structure on function, and as a step towards developing physiology-driven network identification methods. Finally, as synconset chains extend the utilities of synfire chains to arbitrary networks, we suggest utilities of our framework to several aspects of network physiology including cell assemblies, population codes, and oscillatory synchrony.     

Sodium channel modulating activity in a delta-conotoxin from an Indian marine snail

A 26 residue peptide (Am 2766) with the sequence CKQAGESCDIFSQNCCVG-TCAFICIE-NH(2) has been isolated and purified from the venom of the molluscivorous snail, Conus amadis, collected off the southeastern coast of India. Chemical modification and mass spectrometric studies establish that Am 2766 has three disulfide bridges. C-terminal amidation has been demonstrated by mass measurements on the C-terminal fragments obtained by proteolysis. Sequence alignments establish that Am 2766 belongs to the delta-conotoxin family. Am 2766 inhibits the decay of the sodium current in brain rNav1.2a voltage-gated Na(+) channel, stably expressed in Chinese hamster ovary cells. Unlike delta-conotoxins have previously been isolated from molluscivorous snails, Am 2766 inhibits inactivation of mammalian sodium channels.     

Plastid transformation in Arabidopsis thaliana

Plastid transformation is reported in Arabidopsis thaliana following biolistic delivery of transforming DNA into leaf cells. Transforming plasmid pGS31A carries a spectinomycin resistance (aadA) gene flanked by plastid DNA sequences to target its insertion between trnV and the rps12/7 operon. Integration of aadA by two homologous recombination events via the flanking ptDNA sequences and selective amplification of the transplastomes on spectinomycin medium yielded resistant cell lines and regenerated plants in which the plastid genome copies have been uniformly altered. The efficiency of plastid transformation was low: 2 in 201 bombarded leaf samples. None of the 98 plants regenerated from the two lines were fertile. Received: 13 February 1998 / Revision received: 24 April 1998 / Accepted: 5 June 1998     

Genetic diversity in important members of Cucurbitaceae using isozyme, RAPD and ISSR markers

Biochemical and molecular markers have been used on eleven species of Cucurbitaceae collected from lower Gangetic plains. Six enzyme systems were selected. Among 40 primers examined, 14 random amplified polymorphic DNA (RAPD) and 10 inter-simple sequence repeat (ISSR) primers were selected for the analysis. Generated RAPD (100) and ISSR (100) fragments showed high variations among the species. Jaccard similarity coefficients were used for the evaluation of pairwise genetic divergence; cluster analysis of the similarity matrices was performed to estimate interspecific diversity. Further, principal coordinate analysis was performed to evaluate the resolving power of the three marker systems to differenciate among the species.     

Socioeconomic covariates and their impact on the opportunity for natural selection in a riparian tribe of Northeast India

The intensity of natural selection correlates with various bio-social variables which influence the genetic structure of a population. In this paper it has been sought to find out the influence of variable environmental setting and economic condition on selection intensity among the Mising tribal population of Assam, Northeast India. Detailed reproductive pattern of 309 post menopausal women is obtained and a comparison has been made between different environmental as well as economic backgrounds. The impact of secular change on selection intensity has been assessed. For this study I have proposed a modified formula of Johnston & Kensinger's (1971) index for selection intensity. Crow's index of selection intensity has also been used for comparative analyses. After considering standard statistical procedure, a clear disparity of selection intensity has been noticed in terms of varying socioeconomic condition as well as habitational background. It can be concluded from the study that environmental factors act more in terms of selection pressure on infants rather than the other post natal stages.     

Modeling Excess Retrieval in Rat Melanotroph Membrane Capacitance Records

We have used the patch-clamp technique to monitor changes in membrane capacitance (C_m) elicited by fast and spatially homogeneous rises in cytosolic calcium concentration ([Ca²⁺]_i) using flash photolysis of NP-EGTA. Average peak [Ca²⁺]_i amplitudes of 20-25 μM triggered three different types of responses in C_m: (i) In 42% of cells, a rise in [Ca²⁺]_i activated a monotonic increase in C_m followed by a slow decline to resting values; (ii) In 30% of cells, the rise in C_m was clearly characterized by two dynamic components, consisting of a rapid and a slow exo-endocytosis cycle; (iii) In 28% of cells, after the initial rapid rise in C_m, endocytosis exhibited excess retrieval that was characterized by a decline in C_m below resting C_m. The aim of this work is to develop a unified mathematical model with a minimum number of parameters that would describe all the observed types of responses. Three models were considered: Model A, a model with a single component of exo-endocytosis cycle; model B, a model consisting of a sum of two independent dynamic components; and model C, a model in which, in addition to the two dynamic components as in model B, excess retrieval due to a lipid flow through the reversal closing of the fusion pore during the rapid component of exo-endocytosis cycle was considered. The results show that the latter model describes all the types of responses in C_m recorded in rat melanotrophs. The association of excess retrieval exclusively with the rapid, but not the slow, exocytosis indicates that some fusing vesicles mediate a lipidic flux during the reversal closing of the fusion pore, whereas those entering the slow phase of exocytosis may fuse with the plasma membrane completely and are retrieved by other endocytic machinery, independent of the lipid flow that might have occurred as the fusion pore opened permanently.