COMPARATIVE NET BIOSYNTHESIS OF INDOLEACETIC ACID FROM TRYPTOPHAN IN CELL-FREE EXTRACTS OF DIFFERENT PARTS OF PISUM SATIVUM PLANTS

Some optimum conditions for assaying the enzymic conversion of tryptophan to indoleacetic acid (IAA) in crude cell-free extracts of pea (Pisum sativum L.) seedlings are described. The assay is based upon the use of tryptophan-14C and the isolation of IAA-14C by TLC. Degradation of the enzymic product, measured by the rate of decarboxylation of IAA-1-14C which was added to enzyme extracts, accounted for the absence of absolute direct proportionality between yield of IAA and either enzyme concentration or reaction time. A comparison was made of the capacities for net biosynthesis of IAA from tryptophan in extracts of various parts of light-grown pea seedlings and immature pea seeds. The greatest net auxin production occurred in extracts of terminal buds, young stems and young leaves of seedlings. Lesser amounts of net auxin production occurred in extracts from older stems and leaves and from root tips. Extracts from developing pea seeds exhibited an auxin-synthesizing capacity comparable to that of terminal buds of seedlings. Several experiments employing various antibiotics, sterile filtration and aseptic culture of seedlings in vitro indicated that microbial contamination was not a significant problem in the assay procedure. © 1970.