Effect of elevated CO2 concentration on seedling growth rate and photosynthesis inHevea brasiliensis

To study the effect of elevated CO₂ concentration on plant growth and photosynthesis, two clones ofHevea brasiliensis were grown in polybags and exposed to elevated concentration (700±25ppm) for 60 days. There was higher biomass accumulation, leaf area and better growth when compared to ambient air grown plantso From A/Ci curves it is clear that photosynthetic rates increases with increase in CO₂ concentrations. After 60 days of exposure to higher CO₂ concentration, a decrease in the carbon assimilation rate was noticed.     

Response of stem explants to screening and explant source as a basis for methodical advancing of regeneration protocols for chrysanthemum

The effects of 2,4-dichlorophenoxyacetic acid (2,4-D) concentration, length of induction period and light quality on leaf regeneration of quince clone BA 29 were investigated. After 2, 4 or 6 days of induction with 2.5 mg l⁻¹ or 5.0 mg l⁻¹ 2,4-D, leaves were cultured under red, blue, red+blue, far-red+blue, white, far-red light or darkness conditions. Leaves thereby treated showed different responses, with respect to somatic embryogenesis, callus, red-nodular structures or roots. Callus production increased with increasing 2,4-D concentration and induction period, although it was not influenced by light quality; the only exception was far-red+blue light, which reduced callusing response. This result suggested involvement of the blue-absorbing photoreceptor system in the callus formation processes. A high regeneration of red-nodular structures with a meristematic appearance was also observed; from some histological characterizations, we presumed they were adventitious buds that were arrested at an early developmental stage. Red-nodular structures increased with decreasing 2,4-D concentration and induction period. In the regeneration of such structures, the blue-absorbing photoreceptor system appeared to have a negative effect but only at a low photoequilibrium value. In contrast, light quality which activated phytochrome induced an increment in regeneration, but the response did not vary for photoequilibrium values ranging from 0.43 to 0.86. For root regeneration, phytochrome seemed to be the only photoreceptor involved. This revised version was published online in June 2006 with corrections to the Cover Date.     

Distinct pathways of nonhomologous end joining that are differentially regulated by DNA-dependent protein kinase-mediated phosphorylation

Nonhomologous end joining is the most common mechanism of DNA double-strand break repair in human cells. Here we show that nonhomologous end joining can occur by two biochemically distinct pathways. One requires a fraction containing the Mre11-Rad50-NBS1 complex. The other requires a fraction containing a novel, approximately 200-kDa factor that does not correspond to any of the previously described double-strand break repair proteins. The two pathways converge, sharing a common requirement for the DNA ligase IV-XRCC4 complex to catalyze the final step of phosphodiester bond formation. Whereas the Mre11-Rad50-NBS1-dependent pathway does not require, and may be inhibited by, DNA-dependent protein kinase-mediated phosphorylation, the new pathway depends on this phosphorylation for release from a DNA-dependent protein kinase-mediated reaction checkpoint. The existence of two distinct pathways, which are differentially regulated by the DNA-dependent protein kinase, provides a possible explanation for the selective repair defects seen in DNA-dependent protein kinase-deficient mutants.     

PDB@: An offline toolkit for exploration and analysis of PDB files

Protein Data Bank (PDB) is a freely accessible archive of the 3-D structural data of biological molecules. Structure based studies offers a unique vantage point in inferring the properties of a protein molecule from structural data. This is too big a task to be done manually. Moreover, there is no single tool, software or server that comprehensively analyses all structure-based properties. The objective of the present work is to develop an offline computational toolkit, PDB@ containing in-built algorithms that help categorizing the structural properties of a protein molecule. The user has the facility to view and edit the PDB file to his need. Some features of the present work are unique in itself and others are an improvement over existing tools. Also, the representation of protein properties in both graphical and textual formats helps in predicting all the necessary details of a protein molecule on a single platform.     

Assessment of variability in acquired thermotolerance: potential option to study genotypic response and the relevance of stress genes

High-temperature stress affects all growth stages of crops and ultimately yields. This is further aggravated by other environmental stresses like intermittent drought and high light. Management options are few and hence developing intrinsically tolerant plants is essential to combat the situation. As thermotolerance is a multigenic trait, emphasis needs to be on relevant approaches to assess genetic variability in basal and acquired tolerance. This is in fact the major aspect in crop improvement programmes. The relevance of temperature induction (acclimation) response (TIR), a high throughput approach to identify thermotolerant individuals and its utility as potential screening method is described here. This is based on the concept that stress-responsive genes are expressed only during initial stages of stress (acclimation stress) and bring about requisite changes in cell metabolism for adaptation. The fact that acclimation response is ubiquitous has been demonstrated in different crop plants in our studies and by others. Significance of acclimation in acquired tolerance and thus in assessing genetic variability in thermotolerance is discussed. The limitations of present approaches to validate the relevance of specific stress genes either in transgenics or in mutants or knock downs have been analyzed and the need to characterize transformants under conditions that trigger acquired tolerance is also highlighted. This review also focuses on the potential of exploiting acclimation response approach to improve the thermotolerance of crop plants by suitable breeding strategies.     

Agrobacterium-mediated genetic transformation of Withania somnifera using nodal explants

Withania somnifera is an important medicinal plant and used to cure many diseases. Direct regeneration method was standardized for the nodal explants of W. somnifera. In this method, the maximum of 42.4 ± 2.68 shoots produced per explant was achieved at 1.5 mg l^?1 BAP with 0.3 mg l^?1 IAA in the second subculture. Transformation was performed in the nodal explants of W. somnifera via direct regeneration using Agrobacterium tumefaciens strain EHA105 that harbored a binary vector pGA492, which carrying kanamycin resistant (nptII), phosphinothricin resistant (bar) and an intron containing β-glucuronidase (gus-intron) genes. The sensitivity of nodal explants to kanamycin (300 mg l^?1) was determined for the selection of transformed plants. Transformation was confirmed by histochemical β-glucuronidase (GUS) assay and amplification of the nptII gene by polymerase chain reaction (PCR). PCR and southern blot analyses confirmed the integration of nptII gene in the genome of W. somnifera and the transformation frequency of 3.16 % has been achieved. This is the first report on the genetic transformation of W. somnifera using nodal explants, which may aid in the transformation of any other character gene for improving therapeutic value.     

Aldo‐keto reductase enzymes detoxify glyphosate and improve herbicide resistance in plants

In recent years, concerns about the use of glyphosate‐resistant crops have increased because of glyphosate residual levels in plants and development of herbicide‐resistant weeds. In spite of identifying glyphosate‐detoxifying genes from microorganisms, the plant mechanism to detoxify glyphosate has not been studied. We characterized an aldo‐keto reductase gene from Pseudomonas (PsAKR1) and rice (OsAKR1) and showed, by docking studies, both PsAKR1 and OsAKR1 can efficiently bind to glyphosate. Silencing AKR1 homologues in rice and Nicotiana benthamiana or mutation of AKR1 in yeast and Arabidopsis showed increased sensitivity to glyphosate. External application of AKR proteins rescued glyphosate‐mediated cucumber seedling growth inhibition. Regeneration of tobacco transgenic lines expressing PsAKR1 or OsAKRI on glyphosate suggests that AKR can be used as selectable marker to develop transgenic crops. PsAKR1‐ or OsAKRI‐expressing tobacco and rice transgenic plants showed improved tolerance to glyphosate with reduced accumulation of shikimic acid without affecting the normal photosynthetic rates. These results suggested that AKR1 when overexpressed detoxifies glyphosate in planta.