Identification and characterization of a locus (RTM1) that restricts long‐distance movement of tobacco etch virus in Arabidopsis thaliana

The chloroplast homolog of the 54 kDa subunit of signal recognition particle is required for the in vitro targeting of chlorophyll a/b binding proteins (LHCP) to the thylakoid membrane. To explore the function of cpSRP54 in vivo, plants that are mutated in cpSRP54 function were generated. Dominant negative forms of cpSRP54 altered in single amino acids within the conserved guanine nucleotide binding domain were expressed in Arabidopsis. Transformed plants contained less than 30% of the wild-type level of cpSRP54 protein. As a consequence of the reduced cpSRP54 protein content, the first emerging leaves were yellow and contained immature chloroplasts. Although the chlorophyll (chl) content of the leaves was reduced by 75%, the chl a/b ratio was unaffected, indicating a role of cpSRP54 in the biogenesis of proteins besides LHCP. Many chloroplast proteins were less abundant in the first emerging leaves, including non-pigmented proteins, thylakoid proteins known to be targeted by alternative pathways, and soluble proteins. These observations indicate that the cpSRP54 mutation also has a pleiotropic effect on chloroplast biogenesis. Whereas the level of cpSRP54 remained low as the plants aged, leaves emerging subsequently had a wild-type appearance, suggesting that the adult plants compensated for the reduction in cpSRP54 protein.     

SOMATIC EMBRYOGENESIS AND PLANT REGENERATION FROM TISSUE CULTURES OF PENNISETUM AMERICANUM,AND P. AMERICANUM x P. PURPUREUM HYBRID

Immature embryos as well as explants obtained from young inflorescences of Pennisetum americanum (pearl millet) give rise to callus tissues on nutrient media containing 2,4-dichlorophenoxyacetic acid (2,4-D). A compact and pale-yellow callus that arises from the peripheral cells of the scutellum, and from the young inflorescences, undergoes further organized growth. When transferred to a 2,4-D-free medium, supplemented with indole-acetic acid or kinetin, or both, embryoids are formed in the organized areas of the callus. Embryoids show a bipolar organization with a shoot-coleorhiza (root) axis and have a coleoptile-like structure surrounded at the base by a cup-shaped structure that resembles the scutellum in texture and morphology. Embryoids show bilateral or radial symmetry and “germinate” in vitro to form plants that have been grown to maturity in soil. Similar embryogenic callus cultures have been produced from young inflorescence tissues of hybrid Pennisetum, a triploid sexually sterile hybrid of P. americanum x P. purpureum. Plants derived from these have also been transferred to soil. The regenerated plants showed normal chromosome numbers.     

The Power of Two-Dimensional Dwell-Time Analysis for Model Discrimination, Temporal Resolution, Multichannel Analysis and Level Detection

Two-dimensional (2D) dwell-time analysis of time series of single-channel patch-clamp current was improved by employing a Hinkley detector for jump detection, introducing a genetic fit algorithm, replacing maximum likelihood by a least square criterion, averaging over a field of 9 or 25 bins in the 2D plane and normalizing per measuring time, not per events. Using simulated time series for the generation of the “theoretical” 2D histograms from assumed Markov models enabled the incorporation of the measured filter response and noise. The effects of these improvements were tested with respect to the temporal resolution, accuracy of the determination of the rate constants of the Markov model, sensitivity to noise and requirement of open time and length of the time series. The 2D fit was better than the classical hidden Markov model (HMM) fit in all tested fields. The temporal resolution of the two most efficient algorithms, the 2D fit and the subsequent HMM/beta fit, enabled the determination of rate constants 10 times faster than the corner frequency of the low-pass filter. The 2D fit was much less sensitive to noise. The requirement of computing time is a problem of the 2D fit (100 times that of the HMM fit) but can now be handled by personal computers. The studies revealed a fringe benefit of 2D analysis: it can reveal the “true” single-channel current when the filter has reduced the apparent current level by averaging over undetected fast gating.     

Effect of dimethyl sulfoxide (DMSO) on radiation-induced heteroallelic reversion in diploid yeast

Dimethyl sulfoxide has cryoprotective and radioprotective properties. It is also an efficient scavenger of radicals produced by radiolysis of water. Gamma-induced reversions of diploid yeast in the presence of this chemical during irradiation have been studied. The dose-modifying factor was in the same range as for survival. When the yeast was irradiated in the frozen state the observed protection by DMSO disappeared. The results are discussed in terms of direct and indirect actions of radiations and the radical-scavenging ability of this chemical.     

On Use of Transformed Auxiliary Information in Probability Proportional to Size Method of Sample Selection

A probability proportional to size (PPS) method of sample selection, based on the transformed auxiliary information as the measure of size, has been suggested. It has been observed that the PPS estimator under the suggested method is always better than the simple random sampling with replacement (SRSWR) and the usual PPSWR estimator. The efficiency of the proposed estimator with respect to the estimators under reference has also been empirically compared.     

The physiological response of fishes to a deficiency of cyanocobalamin and folic acid

Environmental adaptive response of fishes to the nutritional deficiencies of two important vitamins of the B-group viz . cyanocobalamin and folacin has been investigated using growth, haematology and haemopoiesis as physiological indices. Extended studies lasting 105 days revealed a consistent decrease in growth or even loss of weight when cyanocobalamin and folacin were absent from the diet. The combined deficiency of these two vitamins had an additive rather than synergistic effect on growth. The feed conversion values of all the deficient groups were significantly low as compared to the control. Haematologically the occurrence of anaemia and leucocytosis were recorded in all the deficient groups, the former mainly of megaloblastic type. Differential WBC counts revealed that leucocytosis was mainly due to an increase in thrombocyte population and cosinophils. On the other hand, there was an relative decrease of other nongranulocytes and granulocytes. Erythro-poietic investigations revealed a decreased proliferation rate of the reticuloendothelial cells and an increased number of young and mature reticulocytes and immature erythrocytes into the peripheral blood.