The impacts of drought on plant growth and development limit cereal crop production worldwide. Rice (Oryza sativa) productivity and production is severely affected due to recurrent droughts in almost all agroecological zones. With the advent of molecular and genomic technologies, emphasis is now placed on understanding the mechanisms of genetic control of the drought-stress response. In order to identify genes associated with water-stress response in rice, ESTs generated from a normalized cDNA library, constructed from drought-stressed leaf tissue of an indica cultivar, Nagina 22 were used. Analysis of 7794 cDNA sequences led to the identification of 5815 rice ESTs. Of these, 334 exhibited no significant sequence homology with any rice ESTs or full-length cDNAs in public databases, indicating that these transcripts are enriched during drought stress. Analysis of these 5815 ESTs led to the identification of 1677 unique sequences. To characterize this drought transcriptome further and to identify candidate genes associated with the drought-stress response, the rice data were compared with those for abiotic stress-induced sequences obtained from expression profiling studies in Arabidopsis, barley, maize, and rice. This comparative analysis identified 589 putative stress-responsive genes (SRGs) that are shared by these diverse plant species. Further, the identified leaf SRGs were compared to expression profiles for a drought-stressed rice panicle library to identify common sequences. Significantly, 125 genes were found to be expressed under drought stress in both tissues. The functional classification of these 125 genes showed that a majority of them are associated with cellular metabolism, signal transduction, and transcriptional regulation.
In this communication, we report the preparation and properties of nano-CoFe2O4 by gel combustion in presence of KCl and subsequent heat treatments. The products were characterized by X-ray diffraction, Infrared spectroscopy, and Mössbauer Spectroscopy. Spinel type structure with all Fe in 3+ oxidation states was confirmed from the XRD and Mossbauer spectroscopy. The average crystallite sizes of the studied samples were about 6 and 50 nm. Low temperature magnetic and dielectric properties of the samples were studied by superconducting quantum interference device magnetometry and ac-impedance spectroscopy. The field and temperature dependent magnetization studies indicated superparamagnetic nature for 6 nm sample and ferromagnetic nature for 50 nm sample. The temperature-dependent dielectric properties measured over a wide range of frequencies indicated an increasing trend of dielectric permittivity with the decrease in crystallite size. Variable range polaron hopping conduction was observed in both samples.
Asymptotic critical exponents and amplitudes as well as the leading 'correctionto-scaling' (CTS) amplitudes have been accurately determined through an elaborate analysis of magnetization data taken on amorphous Fe 90−x Co x Zr 10 (0 x 6) and Fe 90+y Zr 10−y (y = 0, 1) alloys in the critical region. Consistent with the Harris criterion, asymptotic critical exponents and the universal amplitude ratio Dm δ 0 /h 0 do not depend on composition and possess values the same as those predicted by theory for an ordered spin system with n = d = 3. The leading amplitude ratio a − M1 /a + χ 1 , which is characteristic of ferromagnets with quenched random disorder and for which no theoretical estimate is presently available, is composition independent and probably universal. The fraction of spins actually participating in the ferromagnetic (FM)paramagnetic (PM) transition occurring at T = T C is small and increases with Co substitution. While the magnetic equation of state (MES) in linear scaling variables and its counterpart in nonlinear scaling variables, valid for a second-order phase transition, form equivalent descriptions of magnetization, M(T , H ), data in the asymptotic critical region (ACR), the latter version of MES alone reproduces closely the observed M(T , H ) behaviour in a temperature range as wide as 0.45T C T 1.5T C . Nonanalytic CTS terms dominate over analytic ones in the ACR but the reverse is true for temperatures outside the ACR. Initial susceptibility follows the generalized Curie-Weiss law from T C to 1.5T C and thereby permits an accurate determination of atomic moment in the PM state. The results of the present investigation provide strong experimental evidence for weak itinerant ferromagnetism in the glassy alloys in question.
We have utilized an efficient method to enrich cDNA libraries for novel genes and genes responsive to drought stress in rice (Oryza sativa L. subsp. indica). We separately constructed standard and normalized cDNA libraries from leaf tissue of rice seedlings grown under controlled drought stress. Sequencing from the 3' end was performed on 1000 clones from the normalized leaf cDNA library and 200 clones from the standard leaf cDNA library. For the first 200 clones, the clone redundancy in the non-normalized library was about 10%, compared with 3.5% in the normalized cDNA library. Comparison of these cDNAs with the sequences in public databases revealed that 28.2% of the expressed sequence tags (ESTs) from the normalized library were novel. Clones from the standard and normalized leaf libraries and a root library uncovered numerous cDNAs that are highly homologous to known drought-responsive genes including those that encode metallothioneins, late embroyonic abundant (LEA) proteins, heat-shock proteins, cytochrome P450 enzymes, catalases, peroxidases, kinases, phosphatases, and transcription factors.
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