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This article in AJ

  1. Vol. 70 No. 5, p. 751-755
     
    Received: Aug 31, 1977


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doi:10.2134/agronj1978.00021962007000050014x

Comparison of Root Activity in Vegetative and Reproductive Soybean Plants1

  1. C. Allan Jones,
  2. Alvin Reeves,
  3. John D. Scott and
  4. D. A. Brown2

Abstract

Abstract

Attempts to delineate the factor(s) which limit soybean (Glycine max (L.) Merrill) yields suggest that one of the reasons may be the decline in new root growth, longevity, and/or metabolic activity of the root system as the plant changes from the vegetative to the reproductive stage of growth. The objective of this research was to investigate the absorption and desorption characteristics of intact soybean roots of plants in the vegetative and reproductive stages of growth. Compartmental analysis was used to determine whether the movement of 45Ca and 32P within the roots of intact soybean plants is different in the vegetative and reproductive stages. Soybeans were grown under greenhouse conditions in nutrient solution. Half the plants were induced to flower at 7 weeks of age, by reducing the day length from 16 to 12 hours. At 12, 14, 15, and 16 weeks of age both vegetative and reproductive plants were transferred to a controlled environment chamber, and 45Ca and 32P were used to characterize nutrient translocation to the tops and nutrient efflux from the root tissue to the nutrient solution. At 16 weeks of age the cation exchange capacity, mitotic activity, and oxygen consumption of the roots of the greenhouse-grown plants were determined. The initial rate of 45Ca and 32P efflux from the cytoplasmic compartment and the initial 45Ca and 32P content of the cytoplasmic compartment of the roots of reproductive plants were twice those of vegetative plants. Oxygen consumption and mitotic activity were greater in the roots of vegetative plants. Cation exchange capacity was greater in the roots of reproductive than in vegetative plants. There was little evidence that the accumulation of 32P and 45Ca in the tops, the rate constants of 32P and 45Ca from the cytoplasmic or vacuolar compartments, or the initial rate of efflux of 32P or 45Ca from the vacuolar compartments differed significantly in vegetative and reproductive plants. The implications of the results are discussed with regard to nutrition of reproductive soybeans.

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