Effect of 2,4-Dichlorophenoxyacetic Acid and Other Growth-Regulators on the Formation of a Red Pigment in Jerusalem Artichoke Tuber Tissue.

In the course of investigations concerning cellular growth in Helianthus tuberosus (Jerusalem artichoke) tuber discs, it was noted that 2,4-dichlorophenoxyacetic acid (2,4-D) induced the formation of a red pigment which was clearly evident only when the discs and the ambient culture solution were brought into prolonged contact with a cellulose substrate such as filter paper or cheese cloth. The 2,4-D acid used was triply recrystallized to minimize contamination by 2,4-dichlorophenol. Attempts to produce the pigment in greater quantity resulted in finding that tuber slices approximately 250 microns thick, incubated on filter paper impregnated with 2,4-D for 24 to 48 hours, gave a maximum pigmentation. Although the pigment was visible directly in the tissue, most of the red color appeared on the filter paper, which acted as a reservoir on which the pigment was strongly adsorbed. Localization of pigment formation was evident when slices cut normal to the tuber axis were incubated with 10 mg/l 2,4-D on filter paper. Maximum pigment production was coincident with the occurrence of the vascular bundles. Microscopic examination of the sections showed strong red pigment coloration in the phloem and xylem elements suggesting a relationship with the phenolphenolase system which is localized in the peripheral and vascular tissue of Jerusalem artichoke according to Belval and Legrand (1). Pigment formation is obligately aerobic as indicated by the complete lack of red color when tuber slices were incubated with 2,4-D in an atmosphere of purified nitrogen. Experiments with dark-prepared 2,4-D-treated tuber slices exposed to red, far-red, and unfiltered radiation as well as continuous darkness showed equal pigment formation with all treatments, indicating no photoperiodic response. The pigment was only very slightly water-soluble and rapidly turned brown when so removed from the stabilizing influence of the filter paper. Moderate solubility was obtained with methanol, and greatest solubility was attained with pyridine and dioxane. Reflectance measurements of the red impregnated filter paper using the G. E. Hardy spectrophotometer showed absorption maxima at 540, 510, and 460 m,u. Optical density data from methanol and pyridine extracts of the pigment were obtained with a Beckman DU quartz spectrophotometer. In methanol, absorption maxima were at 518, 485, 455 (weak) and 340 m,u, and in pyridine the maxima were 526, 490, 455 (weak), and 340 m,u. Browning of the extracts oc-