Spectrophotometric Estimation of Nucleic Acid of Plant Leaves

Abstract

In the course of studies on leaf growth, we have frequently been faced with the problem of estimating the nucleic acid content of very young leaves where the amounts, particularly of DNA, were so small as to make phosphorus or pentose analysis unreliable. The sensitivity of a spectrophotometric procedure makes it the method of choice for such small samples, if sufficiently pure nucleic acid can be isolated. Isolation procedures successfully employed with ani- mal tissue or even plant root tips were not directly applicable to leaves, chiefly because of the large amounts of interfering substances present and be- cause of difficulties in achieving complete extraction of nucleic acid. Of several procedures that we have tried, the most satisfactory one was based on the Schmidt and Thannhauser procedure (12). The preliminary extraction of the leaf was patterned after the procedures of Ogur and Rosen (10) and Mark- ham (8). The extraction of nucleic acid by alkali followed the suggestions of Davidson and Smellie (2). Spectrophotometric estimates of nucleic acid were compared with phosphate analysis and with the diphenylamine procedure for DNA. Materials