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" Structural and hydraulic properties of Sorghum bicolor (L.) roots following exposure to water deficit "
R. T. Cruz
W. R. D. Jordan, Malcolm C.
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Latin Dissertation
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English
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| Record Number
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1112397
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TLpq303939958
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| Main Entry
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R. T. Cruz
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W. R. D. Jordan, Malcolm C.
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| Title & Author
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Structural and hydraulic properties of Sorghum bicolor (L.) roots following exposure to water deficit\ R. T. CruzW. R. D. Jordan, Malcolm C.
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| College
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Texas A&M University
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| Date
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1991
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| student score
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1991
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| Degree
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Ph.D.
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| Page No
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103
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| Abstract
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The effects of water deficit on total root (Lp) and axial (Lx) hydraulic conductivities and on the development of the hypodermis, endodermis and xylem were studied for Sorghum bicolor L. Water deficit was imposed in the upper rooting zone while the lower zones were kept moist. Lp and Lx were based on water flow rates obtained by applying suction to proximal xylem ends of excised roots. The development of the hypodermis, endodermis and other tissues were examined by staining with fluorescent berberine hemisulfate, Sudan Black B and phloroglucinol-HCl. The Lp value (usd\timesusd 10 m s MPa) was 22.9 for control roots, 4.2 in roots exposed to an 8-day stress (stress level 1) and 4.4 in roots exposed to a 15-day stress (stress level 2). The low Lp in stressed roots was attributed to accelerated deposition of lignin and suberin in the hypodermis and endodermis. Calcofluor, an apoplastic tracer which binds to cellulose, was blocked at the lignified and suberized outer tangential walls of the hypodermis in stressed roots but readily penetrated the control cortical walls of similar root regions where the Casparian band was not developed. PTS, a more mobile apoplastic tracer with lower molecular weight, penetrated root regions not traversed by Calcofluor. However, there was a decrease in root conductivity to PTS, suggesting the presence of a high resistance to apoplastic flow in the suberized and lignified root regions. The ratio of Lx to Lp was higher in the controls than in stressed roots, suggesting the increasing influence of axial resistance to overall root hydraulic conductivity in stressed roots. Internal diameters and conductivity of the protoxylem and early metaxylem vessels decreased in stressed roots. When stressed roots were rewetted, apical extension growth occurred following stress level 1 but not following stress level 2. After stress level 2, new lateral roots formed in the proximal root regions. Such formation of new roots after stress levels 1 and 2 was associated with increases in both Lp and Lx.
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Agronomy
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Biological sciences
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