James R. Dunlap
Agricultural Research Service
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Featured researches published by James R. Dunlap.
Plant Physiology | 1996
James R. Dunlap; Maria L. Binzel
Indole-3-acetic acid (IAA) was measured in leaves and roots of tomato (Lycopersicon esculentum) genotypes subjected to salt stress. An abscisic acid (ABA)-deficient mutant of tomato (sitiens), the genetic parent (Rheinlands Ruhm, RR), and a commercial variety (Large Cherry Red, LCR) of tomato were treated with 50 to 300 mM NaCl in nutrient culture. Both LCR and RR had significantly higher levels of IAA in the roots compared with that in sitiens prior to treatment. The initial levels of IAA in the roots of LCR and RR declined by nearly 75% after exposure to NaCl, whereas those in roots from the sitiens mutant remained unchanged. IAA levels in the leaves of all genotypes remained unchanged or increased slightly in response to NaCl. ABA was highest in leaves from the normal genotypes after exposure to NaCl. ABA levels in the roots of sitiens were similar to the levels in the normal genotypes, whereas levels in the leaves were only 10% of the levels found in normal genotypes regardless of the salt treatment. Treatment of LCR and sitiens with exogenous ABA increased the ABA levels in leaves and roots, but there were no measurable changes in endogenous IAA. Therefore, the reduction in IAA appears to result from an ABA-independent effect of NaCl on IAA metabolism in the roots of stressed plants.
Journal of Plant Growth Regulation | 1991
Sarah E. Lingle; James R. Dunlap
Changes induced by the pollination of ovaries may be mediated by phytohormones and involve sudar-mediated by phytohormones and involve sugar-metabolizing enzymes. In order to further explore these relationships, soluble sugars, sucrose-phosphate synthase (EC 2.4.1.14), sucrose synthase (EC 2.4.1.13), acid and neutral invertases (EC 3.2.1.26), indole-3-acetic acid (IAA), and ethylene were investigated in muskmelon (Cucumis melo L.) ovaries sampled before, during, and after anthesis. The fresh weight of ovaries increased 100% within 48 h after pollination, but did not change significantly in the absence of pollination. While sugar content per ovary increased after pollination, sugar content per mg protein was unaffected. Sucrose was not detected in nonpollinated ovaries 48 h after anthesis. Free IAA content was highest in ovaries sampled 48h before anthesis. Pollination had no immediate effect on IAA content per mg protein in postanthesis ovaries. Although detected in all ovaries sampled, ethylene production increased significantly only in nonpollinated ovaries. Activity of sucrose-phosphate synthase was the same at all stages. The specific activities of sucrose synthase and the invertases were highest in nonpollinated ovaries. The increase in rate of sugar import into ovaries following pollination was not accompanied by an increase in the specific activity of any enzyme assayed, but was coincident with an increase in the total activity per ovary of surcose synthase and acid invertase. There appears to be no direct relationship between sucrose-metabolizing enzymes, IAA or ethylene in developing pollinated ovaries but the increase in sucrose cleavage activity in nonpollinated ovaries may be related to the increase in ethylene production.
Plant Physiology | 1987
Sarah E. Lingle; James R. Dunlap
Plant Physiology | 1988
James R. Dunlap; Karen M. Robacker
Plant Physiology | 1989
James R. Dunlap; Gene Guinn
Hortscience | 1990
James R. Dunlap; Sarah E. Lingle; Gene E. Lester
Plant Physiology | 1990
James R. Dunlap; Karen M. Robacker
Plant Physiology | 1990
Gene Guinn; James R. Dunlap; Donald L. Brummett
Hortscience | 1987
Sarah E. Lingle; Gene E. Lester; James R. Dunlap
Hortscience | 1991
James R. Dunlap; Yin-Tung Wang; Anneamma Skaria