Translocation of C¹⁴ in Sugarcane

Abstract

Since sugarcane plants in Hawaii translocate sucrose at the rate of over one million tons per year, translocation studies have an immense economic potential. Studies with the infrared analyzer indicate that the accumulation of sucrose in leaves during the day may inhibit photosynthesis (unpublished data), so that translocation may form a bottleneck in production. Of more importance to the general plant physiologist, sugarcane studies may contribute to the theory of translocation. In 1947 investigations on translocation of C14 were begun at the Experiment Station of the Hawaiian Sugar Planters' Association (7, 12, 27), and the results of the ensuing 15 years of research are summarized here. The sugarcane plant possesses many advantages for studying translocation. The long symmetrical blade, with parallel venation and with no lobes or dissections, can be readily cut into uniform parts for studying velocities of movement. The large size of the plant makes it possible to take samples from uniform tissues for several types of analysis. Samples can be taken at specific positions because of the regular subdivision of the stalk into nodes and internodes. Thus, sugarcane is well constructed for determination of components moved and of rates and direction of movement. Sugarcane has a disadvantage for translocation tests because it is a monocotyledon with typical monocotyledonous structure of the stem. It is therefore difficult to separate xylem and phloem for studying tissues involved in transport; moreover, on sugarcane there is no stem-infesting aphis which could be used for sampling the phloem. Studies of translocation of radioactive photosynthate have been summarized recently (17, 48, 57). Even so, Crafts (17) has called attention to the need for collecting more data on this important subject. Translocation in sugarcane was studied by Hartt (23) who analyzed the sugars in sheaths during the day and the night and concluded that a temporary storage of polysaccharides in the sheath during the night facilitated trianslocation. Burr et al. (8) reviewed studies of translocation of C14 in sugarcane through October 1956, and also presented evidence of a circulatory system in the sugarcane plant (9). Yang (55) reported on studies in Taiwan on translocation of C14 in sugarcane. Brief presentations of some of the results reported herein are in press (24, 27). This paper describes the normal course of translocation in plants grown with adequate fertilization. Effects of varying climatic conditions, deficiencies of N, P, or K, and other factors will be presented in subsequent papers.