DEVELOPMENT OF RESIN CANAL EPITHELIA IN PARTHENIUM ARGENTATUM GRAY AND THE MODULATION OF RUBBER DEPOSITION BY 2-(3,4-DICHLOROPHENOXY)-TRIETHYLAMINE (GUAYULE, MORPHOMETRY, BIOREGULATORS)

Parthenium argentatum Gray, Guayule, bears large quantities of cis-polyisoprene rubber, which is deposited as globules in parenchyma cells. A limiting factor for rubber yield is the amount of parenchymatous tissue available for rubber storage. Resin canal epithelia are the first site of rubber deposition; thus, it may be possible to use them as a model system of rubber deposition in the plant.; It is known that 2-(3,4-dichlorophenoxy)-triethylamine (DCPTA) increases biomass and rubber yield in P. argentatum. For this study, plants were sprayed with DCPTA and stem resin canals were observed using light microscopy.; Five primary cortical resin canals are associated with each leaf in the stem. The pattern of organization is similar regardless of season and treatment. Epithelial cells of DCPTA treated plants are longer than those of controls. Rubber volume, per cell, is increased 37% during winter by DCPTA.; On pith canal differentiates centrad and parallel to each median leaf trace. A greater number of pith canals are in the most distal one centimeter of stem during winter. Pith canal density in summer decreases following DCPTA treatment, indicating an increased growth rate. The size of pith canal epithelial cells is stable in both winter and summer, regardless of treatment. DCPTA increases rubber volume, per cell, 6% during the winter.; Secondary cortical resin canals arise from derivatives of the vascular cambium, differentiating when three to five cells distant from the vascular cambium. These canals appear in circumferential layers alternating with growth increments of phloem. Since secondary cortical resin canals anastomose only with other canals in the same growth increment, each layer of canals constitutes an independent system. Cell size is similar in both primary and secondary cortical resin canal epithelia. New resin canals differentiate primarily during late summer. Unlike the primary canal systems, rubber is deposited early in secondary cortical canal development, even before the schizogenously formed lumen has appeared. Rubber content of secondary cortical resin canal cells increases with the age of the cell.; DCPTA increases both growth and rubber deposition in P. argentatum.