R. Sharma

University of Hyderabad, Bhaganagar, Andhra Pradesh, India

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Publications (4)13.31 Total impact

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    ABSTRACT: Developmental mutants serve as a useful material to unravel the mechanisms necessary for organ development. The polycotyledon (poc) mutant of tomato, with multiple cotyledons in the seedling and varied phenotypic effects in the adult plant is one such mutant. Studies using physiological and anatomical methods in our lab suggest that POC is involved in the negative regulation of polar auxin transport, which is likely the reason for the pleiotropic phenotype in the mutant. Because of the physiological significance of the polycotyledon mutant described in this paper and also being first of its kind in tomato and also other plant species, we are using a map-based cloning approach to map the polycotyledon gene. Molecular mapping of this locus using segregating interspecific F2 mapping population localized polycotyledon gene close to TG424 marker on the long arm of chromosome 9. The closest marker mapped was a PCR marker identified in this study, E8A2 at a distance of 7.4 cM from the poc locus. The absence of tightly linked RAPD markers and the non-availability of more mapped markers in this region led us to initiate chromosome walk to polycotyledon gene. Both the flanking markers TG248 and E8A2 were used to screen the BAC library and a contig was developed for TG248 marker. The BAC-end sequences were analyzed for their use as RFLP markers to enrich this region for markers. Analysis of the BAC-end sequences revealed that poc is localized in the region surrounded by copia-like retrotransposon elements explaining the absence of markers in the euchromatin region on long arm of chromosome 9. Further studies identified two BAC-end sequences which mapped around the poc locus and also indicated very low physical versus genetic distance ratio in this region. The double mutant analyses of poc with the other two known polycotyledon mutants of tomato, pct and dem revealed allelism with pct; therefore, the poc mutant was named as pct1-2, and also the original pct mutant was renamed as pct1-1.
    Theoretical and Applied Genetics 09/2006; 113(4):673-83. DOI:10.1007/s00122-006-0332-0 · 3.79 Impact Factor
  • V. A. MANGA · R. SHARMA ·
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    ABSTRACT: In cotyledons of mustard (Sinapis alba L.) seedlings grown with distilled water (DW) phytochrome controlled increase in β-amylase (E.C. level takes place at about 42 h after sowing (starting point), while the photoresponse escapes from photoreversibility at 30 h after sowing. The temporal onset of starting point is presumed to be determined by innate process of developmental homeostasis, which is not amenable to influence of environmental factors such as light and nutrients. However, the temporal appearance of onset of phytochrome controlled increase in β-amylase level (starting point) in seedlings grown with Hoagland's nutrient solution (HS) is delayed by 9 h as compared to DW-grown seedlings. Concomitantly, the temporal appearance of the loss of photoreversibility of phytochrome mediated increase in β-amylase level (coupling point) is also delayed by 9 h in HS-grown seedlings. HS does not influence the primary action of phytochrome, the lifetime of components involved in signal chain of above photoresponse and the turnover of β-amylase enzyme. These results indicate that HS-induced temporal shift in onset of starting point of above photoresponse is caused by interaction of nutrients with the process of developmental homeostasis.
    Plant Cell and Environment 04/2006; 8(5):339 - 344. DOI:10.1111/j.1365-3040.1985.tb01408.x · 6.96 Impact Factor
  • V.A. Manga · R. Sharma ·
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    ABSTRACT: In the cotyledons of mustard (Sinapis alba L.) seedlings, phytochrome-mediated increase in the rate of de novo synthesis of β-amylase (E.C. under continuous red light involves a stable regulatory element (≪transmitter≫) in the signal transduction chain which has a life time of about 12 h and acts in an allor -none fashion. Therefore continuous red light can be quantitatively substituted by alternate cycles of red light and darkness, each of 12 h duration. However, when phytochrome is reverted to the Pr form before the onset of the daily dark cycle, seedlings require a 17 h light/7 h dark period to sustain uninterrupted β-amylase synthesis as in continuous red light. The same result is obtained with a 6 h red light/6 h dark period. Using inhibitors of transcription and translation it is established that the transmitter is a stable β-amylase mRNA. The uninterrupted increase in β-amylase level in light/dark cycles results from the continued presence of stable β-amylase mRNA in the dark periods and the resumption of β-amylase mRNA synthesis at the onset of the next light period. These results indicate that under natural conditions β-amylase accumulation in mustard cotyledons would proceed normally through the daily night period.
    Journal of Plant Physiology 02/1988; 132(1):116–122. DOI:10.1016/S0176-1617(88)80194-9 · 2.56 Impact Factor
  • V. A. Manga · R. Sharma ·
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    ABSTRACT: In the cotyledons of mustard seedlings light mediates an increase in β-amylase [EC] activity via agency of phytochrome. In order to understand the functional significance of above photoresponse, the relationship between light induced β-amylase increase, chloroplast development and starch content of cotyledon was investigated. The application of SAN 9789 a chlorosis inducing inhibitor to mustard seedlings, though destroyed chloroplast, had no effect on light mediated increase in β-amylase indicating the lack of functional interrelationship between chloroplast development and β-amylase increase. The subcellular localization studies revealed that β-amylase is a cytosolic enzyme. Additionally, the increase in the level of β-amylase had no relationship with in vivo starch level, which was present only in trace amounts. The noncorrelation of the photoregulated β-amylase increase with the starch content and its extra-chloroplastic localization indicates that β-amylase does not participate in the mobilization of plastidic starch in mustard cotyledon.