The effect of the arginine analogue, canavanine on growth and heterocyst differentiation in the nitrogen-fixing algaAnabaena doliolum has been studied. The analogue inhibited growth and heterocyst differentiation at a concentration as low as 1 μM. The treated
algal cells lacked conspicuous granular inclusions, whereas treatment with chloramphenicol led to increased synthesis of granules
(probably cyanophycin granules). Exogenously added arginine completely reversed the effect of the analogue but lysine could
only partially relieve the effect. A time course study with canavanine indicated inhibition of fresh protein(s) synthesis
at all steps where a new class of proteins is synthesized so that the action of the analogue does not seem to be specific
for a particular kind of protein. A mutant resistant to this analogue has been successfully isolated indicating that this
alga does not show mutational immunity at least to the amino acid analogues unlike in the observation with different antibiotics.
Our observations indicate that canavanine either directly inhibits protein synthesis or forms defective protein(s) which produces
all the observed effects. 相似文献
The involvement of alternative respiration in thermogenesisduring the ripening of banana {Musa paradisiaca var. MysoreKadali) fruits, attached to a bunch, has been examined. Thetemperature of the youngest (unripened) banana fruit increasedfrom 27·0 ± 0·2°C to 30·8±0·1°C and the total respiration (in nmo1 oxygen min1 g1 drywt.) increased from 1·39·6 ± 5·5to 167·3 ± 7·0 at the fully ripened stage.Although the capacity for alternative respiration showed littlechange, the actual operation of this pathway increased from38 to 73% (p= 0·38 to 0·73) during ripening. Similarresults were obtained in fruits along the central axis at differentstages of ripening. It is suggested that alternative respirationmay contribute to the temperature rise observed in ripeningbanana fruit. Key words: Alternative respiration, tehrmogenesis, fruit ripening 相似文献
THE molecular mechanism for initiating DNA replication can be studied using a subcellular system. Rao and Johnson1 found that HeLa cells in the pre-DNA-synthetic (G-1) period of the cell cycle initiate DNA synthesis after fusion with cells that are in the DNA synthetic (S) period. A previous subcellular system of DNA replication from HeLa cells2–4 consisted of intact nuclei, supplemented with the four deoxy-nucleoside triphosphates, salt, ATP and a cytosol factor. The nuclei in this system appeared to be permeable to proteins and DNA synthesis was very similar to that within intact cells. We report here the initiation of DNA synthesis in nuclei isolated from HeLa cells. Our results suggest that, with the synchronization method used, a small percentage of dormant G-1 nuclei can be stimulated by S-phase cytoplasm; this would be the case if the cells were receptive to stimulation for only 30–60 min during the cell cycle. illustration
Gibberellic acid (GA3) increases the height of Impatiens balsamina under both 8- and 24-h photoperiods. The height also increases with all guanosine monophosphates (GMPs) under 8-h photoperiods but only with 5′-GMP under 24-h photoperiods. GA3 as well as GMPs increase the number of leaves under 8-h but not under 24-h photoperiods. GA3 as well as GMPs induce floral buds under strictly non-inductive photoperiods and increase the number of floral buds under 8-h photoperiods. The floral bud initiation occurs earlier when cGMP is used in combination with 100 mg/l GA3. 相似文献
Abstract: A new fossil osteoglossid fish, Taverneichthys bikanericus gen. et sp. nov. and an unnamed but probable new species of ?Lepisosteus (Lepisosteidae) are described from the subsurface beds of the Palana (lignite) Formation near Bikaner, western Rajasthan, India. T. bikanericus is founded on a skull, which is the first osteoglossid skull from the Indian subcontinent, whereas ?Lepisosteus sp. is represented by a part of its trunk covered with ganoid scales. The taxonomic assignment of the latter specimen to gars is based on the micro‐ and ultrastructure of its scales. Taverneichthys is included in the Osteoglossinae because it shares at least three of the seven diagnostic characters of the subfamily: (1) jaw articulation behind the vertical midline of orbit, (2) palatine and ectopterygoid fused to form palato‐ectopterygoid, and (3) horizontal arm of preopercle short, ending anteriorly behind orbit (inferred). It is characterized by a considerably larger dermethmoid bone and the two nasals that are in contact with each other behind it separating this bone from the frontals. In this respect it is more evolved than Cretophareodus and Phareodus, and closer to Brychaetus, Musperia, Opsithrissops and modern osteoglossids. The fossils documented herein are the first vertebrate remains from the Palana Formation. They were recovered from a highly indurated greyish‐black calcareous shale approximately 90 m below ground level from a dug‐well section. The occurrence of fossil remains of osteoglossid and lepisosteid fish in the Palana Formation, both of which are among the major predators of a terrestrial aquatic community, and their association with the crocodilian remains, are indicative of the mature and diverse nature of the Palana vertebrate community. It postulates the recovery of a varied assemblage of vertebrates, especially fish and crocodilians and possibly also mammals. The association of osteoglossid and lepisosteid fish characterizes a dominantly freshwater deposit and is consistent with a Paleocene age for the Palana Formation. The known distribution of fossil and living osteoglossid and lepisosteid fish suggests a marked shift in their climatic adaptability in time and space. Their close association in the fossil record, especially in the Indian subcontinent, is well documented, but today they thrive in different climatic zones. 相似文献
Sterility mosaic disease (SMD), an important biotic constraint on pigeonpea (Cajanus cajan) in the Indian subcontinent, is caused by Pigeonpea sterility mosaic virus (PPSMV) transmitted by the eriophyid mite, Aceria cajani. Distinct PPSMV isolates occur in different geographical regions and broad‐based resistance to all these isolates is scarce in cultivated pigeonpea germplasm. Wild relatives of pigeonpea, which are known to possess resistance to several pests and diseases, were evaluated for broad‐based SMD resistance. One hundred and fifteen wild Cajanus accessions from six species (C. albicans, C. platycarpus, C. cajanifolius, C. lineatus, C. scarabaeoides and C. sericeus) were evaluated against three PPSMV isolates prevailing in peninsular India. Evaluations were done under greenhouse conditions in endemic locations of each isolate through mite‐mediated virus inoculation. Fifteen accessions showed resistance to all three isolates: ICP 15614, 15615, 15626, 15684, 15688, 15700, 15701, 15725, 15734, 15736, 15737, 15740, 15924, 15925 and 15926. Most of the wild accessions did not support mite multiplication. The majority of the accessions resistant to PPSMV following inoculations with viruliferous mites were susceptible by graft inoculation, suggesting that vector resistance is conferring resistance to infection with PPSMV. The 15 accessions identified as being resistant to infection to all three virus isolates tested are cross compatible with pigeonpea by traditional breeding. They are therefore useful for exploitation in breeding programmes to increase both the level of SMD resistance and to diversify its genetic base in the cultivated pigeonpea gene pool. 相似文献
The donorrecipient fusion method was usedto investigate the intraspecific transfer of organelles andorganelle-encoded traits from donor to recipient Nicotiana speciesunder conditions which were selective for chloroplast transfer.An alloplasmic male sterile line of N. tabacum carrying thecytoplasm of N. bigelovii as the recipient and N. tabacum SR-1,a mutant with maternallyinherited streptomycin resistance, asthe cytoplasm donor were used. Organelle composition of 13 cybridplants was investigated by analysis of tentoxin and streptomycinsensitivities, chloroplast and mitochondrial DNA restrictionpatterns, and alloplasmic male sterility Chloroplast DNA analysisand the tentoxin test both showed that all 13 cybrid plantspossessed chloroplasts from the N. tabacum, SR-1 parent only.Analysis of mitochondrial DNA from second generation plantsderived from 11 of the original cybrid plants indicated verylittle heterogeneity with nine of the plants expressing pureparental-type mtDNAs. Although conditions were selective fordonor-type chloroplast transfer, the results indicate the generationof novel cytoplasmic combinations; pure donor chloroplasts incombination with either pure or recombinant-type recipient mitochondria.Our results support previous findings that the donor-recipientfusion method can be used to restore fertility of CMS linesof Nicotiana Key words: Nicotiana, cytoplasmic male sterility, chloroplast DNA, mitochondrial DNA, somatic hybridization 相似文献
One hundred and sixteen accessions representing 28 species in the genus Arachis were evaluated for resistance to groundnut rosette disease using an infector row technique during the 1996/97, 1997/98, 1998/99 and 1999/2000 growing seasons at Chitedze, Malawi. Of these, a total of 25 accessions belonging to Arachis diogoi (1 accession), A. hoehnei (2), A. kretschmeri (2), A. cardenasii (2), A. villosa (1), A. pintoi (5), A. kuhlmannii (2), A. appressipila (3), A. stenosperma (5), A. decora (1), and A. triseminata (1) showed resistance to the groundnut rosette disease. No visible disease symptoms were observed in several accessions belonging to A. appressipila, A. cardenasii, A. hoehnei, A. kretschmeri, A. villosa, A. pintoi, A. kuhlmannii, and A. stenosperma. Some accessions in A. appressipila, A. diogoi, A. stenosperma, A. decora, A. triseminata, A. kretschmeri, A. kuhlmannii, and A. pintoi were resistant to all three components of rosette, Groundnut rosette ass is tor virus (GRAV), Groundnut rosette virus (GRV) and its satellite RNA (sat. RNA). Two accessions in A. stenosperma and one accession in A. kuhlmannii showed the presence of all three components of the rosette disease. Several wild Arachis accessions were resistant to GRAV. All the accessions of A. batizocoi (4), A. benensis (2), A. duranensis (46), A. dardani (1), A. ipaensis (1), A. magna (1), A. monticola (3), A. oteroi (1), A. pusilla (4), and A. valida (2) were susceptible to rosette disease. In all these accessions, infected plants were chlorotic and severely stunted. The value of exploitation of the resistance in wild Arachis species in rosette resistance breeding programmes is discussed. 相似文献
The present study was undertaken to investigate the pattern of optimal codon usage in Archaea. Comparative analysis was executed to understand the pattern of codon usage bias between the high expression genes (HEG) and the whole genomes in two Archaeal phyla, Crenarchaea and Euryarchaea. The G + C% of the HEG was found to be less in comparison to the genome G + C% in Crenarchaea, whereas reverse was the case in Euryarchaea. The preponderance of U/A ending codons that code for HEG in Crenarchaea was in sharp contrast to the C/G ended ones in Euryarchaea. The analysis revealed prevalence of U-ending codons even within the WWY (nucleotide ambiguity code) families in Crenarchaea vis-à-vis Euryarchaea, bacteria and Eukarya. No plausible interpretation of the observed disparity could be made either in the context of tRNA gene composition or genome G + C%. The results in this study attested that the preferential biasness for codons in HEG of Crenarchaea might be different from Euryarchaea. The main highlights are (i) varied CUB in the HEG and in the whole genomes in Euryarchaea and Crenarchaea. (ii) Crenarchaea was found to have some unusual optimal codons (OCs) compared to other organisms. (iii) G + C% (and GC3) of the HEG were different from the genome G + C% in the two phyla. (iv) Genome G + C% and tRNA gene number failed to explain CUB in Crenarchaea. (v) Translational selection is possibly responsible for A + T rich OCs in Crenarchaea. 相似文献