Stomatal Movement and Sucrose Uptake by Guard Cell Protoplasts of Commelina benghalensis L.

Sucrose concentration in guard cells of epidermal strips ofCommelina benghalensis increased with stomatal opening. Sucroseuptake patterns were investigated using guard cell protoplastsof C. benghalensis. Sucrose (0.5 mM) uptake into these protoplastswas sensitive to pH, with an optimum at pH 6. Uptake of sucroseinto guard cell protoplasts was inhibited by 2,4-dinitrophenol(DNP), diethylstilbestrol (DES) and (ptrifluoromethoxy)carbonylcyanide phenylhydrozone (FCCP), while DCMU and o-phenanthrolinehad no effect on the uptake of sucrose. Fusicoccin (FC) stimulatedsucrose influx. The influence of pH and the effect of the metabolicinhibitors on the sucrose uptake into the guard cell protoplastsare consistent with an energy dependent membrane-function. (Received July 7, 1986; Accepted September 26, 1986)     

Identification and sequence characterization of a 1.3 Kb EcoRI repeat fragment that harbors a DNA repair site of rat pachytene spermatocytes

Introduction of well-programmed nicks and gaps and the associated DNA repair activity in the genome at the pachytene interval is a characteristic feature of the meiotic prophase in organisms as varied as lilium and mouse. In the present study we have shown that the DNA synthetic activity in rat pachytene spermatocytes is insensitive to aphidicolin, a specific inhibitor of DNA polymerase , and , suggesting DNA -polymerase-mediated repair synthesis in these cells. We have developed a novel approach for the isolation of the DNA repair sites by combining two independent techniques. Following incorporation of BrdUrd into pachytene spermatocytes in the presence of aphidicolin, the repair sites were released as ssDNA fragments by treatment of nuclei with 30 mM NaOH. Subsequently, the BrdUrd containing ssDNA fragments were specifically isolated using polyclonal anti-BrdUrd antibodies. The DNA fragments released were of two size classes, namely 4–7S (major) and 9–12S (minor) and constituted approximately 1.75% of the pachytene genomic DNA. These DNA repair fragments were distinct from Okazaki fragments and other replicative intermediates isolated from rat bone marrow cells as evidenced by (a) their different size distribution and (b) little cross-hybridization. Southern hybridization of restriction enzyme digests of rat genomic DNA with probes made against BrdUrd-ssDNA fragments revealed that although the repair sites were distributed throughout the genome, strong hybridization signals were observed in EcoRI, (1.3 kb and 2.4 kb), BamH1 (9 kb) and HindIII (5 kb) repetetive DNA fragments. The EcoRI 1.3 kb family were cloned into M13 mp19, and a repair positive (1.3 A) and a repair negative (1.3 B) were identified and sequenced. The repair positive clone contained (a) (CA)₂₂ repeat, (b) a (CAGA)₆ repeat and (c) 4 sequences sharing high homology with various hypervariable minisatellite (HVMS) sequences. One of the HVMS sequence contained a GGCAGG motif known to be responsible for germline instability. The repair negative clone had (a) (CA)₆ repeat and (b) a HVMS like sequence without GGCAGG. The significance of these motifs and their relevance to the events of DNA metabolism at pachytene interval have been discussed.     

Hybridization and introgression of the genomes of Drosophila nasuta and Drosophila albomicans: evolution of new karyotypes.

Drosophila nasuta (2n = 8) and Drosophila albomicans (2n = 6) are cross-fertile allopatric sibling chromosomal races of the nasuta subgroup of Drosophila. Hybrids of these races can be maintained for any number of generations. Some of the introgressed hybrid lineages of D. nasuta and D. albomicans, after passing through a transient phase of karyotypic polymorphism, ended up with a stable karyotype whose composition is different from those of the parental races. Such hybrid populations were called cytoraces, in which the chromosomes of D. nasuta and D. albomicans are represented in different combinations. The karyotypic composition of 16 such cytoraces have been presented and discussed with reference to evolutionary strategies such as balancing selection, directional selection, and sex-specific effect on different components of the evolving karyotypes.     

Drought-induced responses of photosynthesis and antioxidant metabolism in higher plants

Environmental stresses trigger a wide variety of plant responses, ranging from altered gene expression and cellular metabolism to changes in growth rates and crop yields. A plethora of plant reactions exist to circumvent the potentially harmful effects caused by a wide range of both abiotic and biotic stresses, including light, drought, salinity, high temperatures, and pathogen infections. Among the environmental stresses, drought stress is one of the most adverse factors of plant growth and productivity. Understanding the biochemical and molecular responses to drought is essential for a holistic perception of plant resistance mechanisms to water-limited conditions. Drought stress progressively decreases CO2 assimilation rates due to reduced stomatal conductance. Drought stress also induces reduction in the contents and activities of photosynthetic carbon reduction cycle enzymes, including the key enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase. The critical roles of proline and glycine-betaine, as well as the role of abscisic acid (ABA), under drought stress conditions have been actively researched to understand the tolerance of plants to dehydration. In addition, drought stress-induced generation of active oxygen species is well recognized at the cellular level and is tightly controlled at both the production and consumption levels in vivo, through increased antioxidative systems. Knowledge of sensing and signaling pathways, including ABA-mediated changes in response to drought stress, is essential to improve crop management. This review focuses on the ability and strategies of higher plants to respond and adapt to drought stress.     

Structural characterization of a flavonoid glycosyltransferase from Withania somnifera

Medicinal plants are extensively utilized in traditional and herbal medicines, both in India and around the world due to the presence of diverse low molecular weight natural products such as flavonoids, alkaloids, terpenoids and sterols. Flavonoids which have health benefits for humans are the large class of phenylpropanoid-derived secondary metabolites and are mostly glycosylated by UDP-glycosyltransferases (UGTs). Although large numbers of different UGTs are known from higher plants, very few protein structures have been reported till now. In the present study, the three-dimensional model of flavonoid specific glycosyltransferases (WsFGT) from Withania somnifera was constructed based on the crystal structure of plant UGTs. The resulted model was assessed by various tools and the final refined model revealed GT-B type fold. Further, to understand the sugar donors and acceptors interactions with the active site of WsFGT, docking studies were performed. The amino acids from conserved PSPG box were interacted with sugar donor while His18, Asp110, Trp352 and Asn353 were important for catalytic function. This structural and docking information will be useful to understand the glycosylation mechanism of flavonoid glucosides.

Abbreviations

DOPE - Discrete Optimized Potential Energy, PDB - Protein Data Bank, PSPG - Plant Secondary Product Glycosyltransferase, RMSD - Root Mean Squared Deviation, UDP - Uridine diphosphate, UGT - UDP-glycosyltransferases.     

Efficiency of RAPD,ISSR and ITS markers in detecting genetic variability among Salacia species sampled from the Western Ghats of Karnataka

Diversity and phylogenetic relationship between four closely related Salacia species, i.e., Salacia chinensis, Salacia macrosperma, Salacia fruticosa and Salacia oblonga, collected from the Western Ghats of Karnataka, India, was assessed. Ten each of RAPD and ISSR primers generated a total of 76 and 68 loci, generating polymorphisms of 92.21 and 89.71%, respectively. Maximum likelihood analysis of the ITS sequences revealed three clades. Dendrogram analyses of RAPD and ISSR revealed two and four clusters, respectively. Overall polymorphism revealed by RAPD was 41.45?±?10%, ISSR was 33.58?±?6.52%, and ITS was 25.50?±?17.25%. Molecular variance revealed significant variance within and among the Salacia species. Tajima’s D neutrality test and Fu’s Fs were negative for all four species, implying presences of rare alleles and population expansion. Comparative study of RAPD, ISSR and ITS for Salacia species has given an insight into the efficiency of each technique in detecting diversity within and among the population sampled in the Western Ghats of Karnataka.

     

Copy number variation-based polymorphism in a new pseudoautosomal region 3 (PAR3) of a human X-chromosome-transposed region (XTR) in the Y chromosome

A 3.5-Mb region of the X chromosome underwent duplication and transposition to the Y chromosome ~5–6 Mya. This X-transposed-region (XTR) originated at Xq21.3 and was inserted at Yp11.2. The two locations have 98.78 % homology and a high concentration of tandem repeats. In whole-genome scans of ten large families with dyslexic members, we identified transposed blocks comprising >102 kb of the Yp11.2 region in its homologous region at Xq21.3 in three females from three different families. Although recombination is known to be limited only to the pseudoautosomal regions (PARs) of the X and Y chromosomes, we report allelic unequal recombination between the XTR region Yp11.2 and Xq21.3, indicating the presence of a new PAR, which we named PAR3. This PAR3 region was also found in 2 % of the general population. An additional layer of justification could be provided from six other dyslexic cases which harbored duplications and deletions in the same Xq21.3 and Yp11.2 regions through allelic unequal recombination.     

A Novel Imidazole Nucleoside Containing a Diaminodihydro-S-triazine as a Substituent: Inhibitory Activity Against the West Nile Virus NTPase/Helicase

The attempted synthesis of a ring-expanded guanosine (1) containing the imidazo[4,5-e][1,3]diazepine ring system by condensation of 1-(2′-deoxy-β-D-erythropentofuranosyl)-4-ethoxycarbonylimidazole-5-carbaldehyde (2) with guanidine resulted in the formation of an unexpected product, 1-(2′-deoxy-β-D-erythropentofuranosyl)-5-(2,4-diamino-3,6-dihydro-1,3,5-triazin-6-yl)imidazole-4-carboxamide (7). The structure as well as the pathway of formation of 7 was corroborated by isolation of the intermediate, followed by its conversion to the product. Nucleoside 7 showed promising in vitro anti-helicase activity against the West Nile virus NTPase/ helicase with an IC ₅₀ of 3-10 μg/mL.