AUTORADIOGRAPHY AS AN AID IN DETERMINING THE GROSS ABSORPTION AND UTILIZATION OF FOLIAR APPLIED NUTRIENTS

Abstract

Favorable growth responses have recently been obtained with some phosphorus compounds applied as foliar sprays to vegetable crops, the objective being to supplement the usual supply of phosphorus absorbed by the roots (3). Preliminary studies utilizing a 25 millimolar solution of phos-phoric acid enriched with small quantities of radioactive phosphorus indicated that the nutrient was absorbed by the leaves of a wide variety of crops and within a few hours translocated to-all plant parts, particularly to meristematic regions. A technique for making autoradiograms relating to root absorption and subsequent distribution of phosphorus in tomato fruit and leaves at various stages of development has been outlined (1). Suggestions for improving the quality of autoradiograms of biological materials have been described by BOYD (2). As a means of demonstrating the rapidity of absorption, translocation, and selective utilization of foliar applied nutrients, autoradi-ography offers a unique approach. The effects of chemical agents and variations in the external environment on nutrient absorption can readily be demonstrated. Autoradiograms provide one of the best means of obtaining indications of relative metabolic activities of various plant tissues since their accumulative capacities for many of the foliar applied nutrients is clearly revealed and located. Herein is presented a method of simultaneously preparing a large number of autoradiograms of entire plants, such that the intensity of the images is within limits proportional to the concentration of the radioactive material in the tissues derived from various applications of radio-phosphorus. Autoradiograms are included which illustrate some results obtained. Preparation of autoradiograms Bean, corn, and transplanted tomato seedlings were grown in four-inch clay pots of sand and supplied with a minus phosphorus nutrient solution. Reserves of phosphorus in the seeds of bean and corn and in the transplanted tomato plants were in most instances sufficient for seedling growth. When of the appropriate size to occupy an area of contact film having dimensions of 8 x 10 inches, the foliage or selected parts thereof were treated by momentarily dipping into a 25 millimolar solution of o-phosphoric acid 'Journal Article no. 1233 of the Michigan Agricultural Experiment Station. 792