The tropic response of plant roots to oxygen: oxytropism in Pisum sativum L. |
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Authors: | D Marshall Porterfield Mary E Musgrave |
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Institution: | (1) Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA, US |
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Abstract: | Plant roots are known to orient growth through the soil by gravitropism, hydrotropism, and thigmotropism. Recent observations
of plant roots that developed in a microgravity environment in space suggested that plant roots may also orient their growth
toward oxygen (oxytropism). Using garden pea (Pisum sativum L. cv. Weibul's Apollo) and an agravitropic mutant (cv. Ageotropum), root oxytropism was studied in the controlled environment
of a microrhizotron. A series of channels in the microrhizotron allowed establishment of an oxygen gradient of 0.8 mmol · mol−1 · mm−1. Curvature of seedling roots was determined prior to freezing the roots for subsequent spectrophotometric determinations
of alcohol dehydrogenase activity. Oxytropic curvature was observed all along the gradient in both cultivars of pea. The normal
gravitropic cultivar showed a maximal curvature of 45° after 48 h, while the agravitropic mutant curved to 90°. In each cultivar,
the amount of curvature declined as the oxygen concentration decreased, and was linearly related to the root elongation rate.
Since oxytropic curvature occurred in roots exposed to oxygen concentrations that were not low enough to induce the hypoxically
responsive protein alcohol dehydrogenase, we suspect that the oxygen sensor associated with oxytropism does not control the
induction of hypoxic metabolism. Our results indicate that oxygen can play a critical role in determining root orientation
as well as impacting root metabolic status. Oxytropism allows roots to avoid oxygen-deprived soil strata and may also be the
basis of an auto-avoidance mechanism, decreasing the competition between roots for water and nutrients as well as oxygen.
Received: 14 January 1998 / Accepted: 10 February 1998 |
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Keywords: | : Alcohol dehydrogenase Diagravitropism Oxygen Oxytropism Pisum (oxytropism) Tropism |
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