Inhibition by White Light of 86Rb+ Absorption in the Root Apex of Corn

Measurements of cell lengths made at 0.5 millimeter intervals in median longitudinal sections of the primary roots of corn (Zea mays) were used to construct a growth curve. The region 1.5 to 4.0 millimeters from the apex contained the largest number of elongating cells. Absorption of (86)Rb(+) was measured using intact, dark-grown corn seedlings. Following uptake and exchange, the terminal 8.0 millimeters of each root was cut into four 2.0 millimeter segments. Maximum (86)Rb(+) uptake occurred in the region from 0.0 to 4.0 millimeter from the root tip. Washing the intact primary root in fresh 2.0 millimolar CaSO(4) for 2 hours prior to uptake augmented the rate of (86)Rb(+) uptake in all regions. Illumination with white light during washing caused a reduction of (86)Rb(+) uptake as compared with controls washed in darkness, and the region of greatest light response was the region of elongation. Removal of the coleoptile prior to washing did not prevent the light inhibition of subsequent (86)Rb(+) uptake. Removal of the root cap prior to washing in light partially reversed the light-induced inhibition of the washing response.