Stimulation of root elongation and curvature by calcium.
Ca2+ has been proposed to mediate inhibition of root elongation.  However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings.  Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots.  Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent.  Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots.  Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well.  The Ca(2+)-stimulated curvature was substantially enhanced by light.  A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark.  Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+.  Thus, Ca2+ action on root elongation differs depending on its site of application.  The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms.
Takahashi
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H
Institute of Genetic Ecology, Tohoku University, Sendai, Japan.
Scott
T K
TK
Suge
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D000040:Abscisic Acid / Q000502:physiology; D002118:Calcium / Q000502:physiology*; D003624:Darkness; D018522:Gravitropism / Q000502:physiology*; D007476:Ionophores / Q000378:metabolism; D008027:Light; D018532:Pisum sativum / Q000254:growth & development; D010834:Phytochrome / Q000378:metabolism; D018518:Plant Root Cap / Q000254:growth & development / Q000502:physiology*; D018517:Plant Roots / Q000254:growth & development*; D013997:Time Factors; D003313:Zea mays / Q000254:growth & development
D007476:Ionophores; D010834:Phytochrome; D000040:Abscisic Acid; D002118:Calcium