| A computer-based video digitizer is described which allows calculation of relative growth rates at points along a plant surface, and determination of the angle and radius of curvature for graviresponding organs. It was used in studies of growth and gravitropism in roots of Zea mays.;The involvement of ethylene in root gravitropism was studied by removal of ethylene with hypobaric conditions, inhibition of ethylene binding by 2,5-norbornadiene, and inhibition of ethylene biosynthesis by L-(alpha)-(2-amino-ethoxyvinyl)-glycine and cobalt. All failed to eliminate gravitropism, however all affected growth. The results indicate that ethylene is not necessary for normal gravitropic curvature, but may be involved in growth.;The role of the epidermis in graviresponse of roots was studied by abrasion. Complete abrasion of the epidermis slowed graviresponse, but also slowed growth. Roots abraded partially exhibited greater graviresponsiveness when the remaining epidermis was on the top and bottom rather than on the two sides. Reattainment of graviresponsiveness correlated with return of epidermal cells into the extending region. The data indicate that the epidermal layer is necessary for normal gravicurvature.;The temporal and spatial distribution of growth during graviresponse was discerned by mapping growth at 1 h intervals. The temporal and spatial distribution of curvature was discerned by determining the radii of curvature at points along the root surface, and mapping these every 30 min. The results indicate that the basipetal shift in the extending zone is transient, and that curvature propagates basipetally during gravitropism.;Relative growth rates were calculated along the surface of roots. The region of extension was found to be from 1 to 6 mm from the root tip, with maximal growth occurring at 3 mm from the tip. Gravitropism was found to occur by a differential inhibition of growth, concomitant with a basipetal shift in the region of surface extension.;The digitizer system provides a highly accurate means of assessing the growth patterns leading to plant forms. However, it provides only a kinematic description of growth, while a complete understanding of growth involves dynamics. |
