Date of Award

2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Paul F. Bell

Abstract

There are very few studies on B deficiency in rice (Oryza sativa L.). Reported critical values of B deficiency in rice are contradictory and mechanisms of B uptake by plant are not understood. Objectives of this study were to determine B effects on rice grown in hydroponics and soil; to determine critical values of B deficiency in rice tissues, hydroponic solution and soil; and to explore B-uptake mechanisms in both monocots (rice) and dicots (soybean (Glycine max L.)). Rice was grown to maturity in an acid Caddo silt loam at 0 and 1 kg B ha--1 in a greenhouse study, which provided the first report of B deficiency in rice grown on a soil from the USA. Boron increased B concentrations in new leaves, pollen vitality, and grain yields by 11%. Critical value of B deficiency in new rice leaves at tillering or booting is likely 6.0 +/- 1.0 mg B kg--1. A Ca/B ratio above 550 in rice leaves at booting would also indicate B deficiency. Retarded panicle development and delayed heading were observed at tillering and booting. Hydroponic studies indicated that B deficiency occurred when there was <7.3 mg B kg --1 in new leaves and <0.2 muM in solutions. Whitish and twisted new leaf tips occurred at ≤0.05 muM B, and pale bands 2--3 mm wide exhibited on leaves of moderately B-deficient plants. The membrane permeability coefficient of H3BO3 was determined to be 0.488 x 10--6 cm s--1 for rice roots and 1.81 x 10--1 cm s--1 for soybean roots. Estimating boron diffusion during the six-hour assay is a novel and accurate technique for determining the importance of diffusion, transpirational flow, and active uptake mechanisms. It was estimated that 59% of total B uptake for rice and 39% for soybean were due to active uptake for B-deficient plants. Significant effects were found from respiration inhibitors (0.05 mM DNP) on B uptake by B-deficient rice grown in solutions at four levels of B (0.2, 0.5, 2.5 and 10 muM) during a six-hour assay.

ISBN

9780599906365

Pages

147

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