Graviresponsiveness and cap dimensions of primary and secondary roots of Ricinus communis (Euphorbiaceae).
After branching from the primary root, secondary roots of castor bean (Ricinus communis) grow laterally for 15-20 mm, after which they bend downward (i.e., become positively gravitropic).  During the first 10 mm of growth, the lengths of caps of secondary roots increase from 120 +/- 26 to 220 +/- 28 micrometers.  Although this increase is statistically significant (P < 0.1%), the resulting secondary roots are only minimally graviresponsive.  A subsequent doubling of the lengths and widths of the root caps (i.e., to 420 +/- 34 and 450 +/- 41 micrometers, respectively) is positively correlated with the onset of gravicurvature.  The graviresponsiveness and dimensions of caps of positively gravitropic secondary roots are not significantly different from those of positively gravitropic primary roots.  These results indicate that (i) a statistically significant increase in the length and length : width ratio of a root cap does not necessarily result in the root becoming positively gravitropic, (ii) there may be a minimum cap length and (or) width necessary for graviresponsiveness, and (iii) the degree of graviresponsiveness exhibited by a particular root may be related to the size of its root cap.
Moore
R
R
Department of Biology, Baylor University, Waco, TX 76798, USA.
Pasieniuk
J
J
D002367:Ricinus communis / Q000033:anatomy & histology / Q000254:growth & development* / Q000648:ultrastructure; D018522:Gravitropism / Q000502:physiology*; D018466:Gravity Sensing / Q000502:physiology; D018518:Plant Root Cap / Q000033:anatomy & histology* / Q000254:growth & development / Q000648:ultrastructure; D018517:Plant Roots / Q000033:anatomy & histology / Q000254:growth & development* / Q000648:ultrastructure; D010947:Plants, Toxic