CO 2 Fixation and Rubber Deposition in the Bark and Leaves of Guayule during Winter

Abstract

Summary The chloroplasts found in the stem tissue of Parthenium argentatum (guayule) which had passed through one winter fixed a considerable amount of CO 2 and a relatively large proportion was incorporated into rubber. In this region of the stem the cells were not completely filled with rubber and new cells were still generated by the vascular and cork cambia. While the cells in the oldest part of the two-year-old plants appeared to be filled to capacity with rubber, 14 C was still incorporated into cis -polyisoprene. This indicated that despite the presence of copious amounts of rubber some of these cells still had the ability to synthesize rubber. In the parts of the stem produced by the current season's growth most of the 14 C was incorporated into the aqueous extract and not into rubber which suggests that it was used for general metabolism. At present it is not known which precursors, if any, are obtained directly from the chloroplasts and are used as substrate for rubber production. This aspect is currently receiving attention.