Stem Internode Elongation in the Japanese Morning Glory (Pharbitis nil Choisy) in Relation to an Inhibitor System of Auxin Destruction

Abstract

Further investigations on a vk^ild-type strain of the Japanese morning glorj' (Pharbitis nil Choisy) to ascertain the relationship between stem internode maturation, decreasing rate of internode elongation, and increasing auxin destruction, have established the following: There exists in young, elongating, internode tissue, svibstances which prevent the destruction of indoleacetic acid by enzymes normally found in stem tissue. Almost all of the protecting activity can be attributed to two substances, one of them possessing an apparent molecular weight in the 5000 to 10,000 g/mol range, the other, in the 1500-5000 g/mol range. Both are water soluble, and heat labile, at least in vitro. It is further suggested that associated with Japanese morning glory stem maturation, is the loss of these auxin-protecting substances, and as a consequence of this loss, the loss of further endogenous auxin-induced elongation.

Distribution of Three Auxin Protector Substances in Seeds and Shoots of the Japanese Morning Glory (Pharbitis nil)

“…The results amplify our earlier observations that along the shoot axis of mature Japanese morning glory vines there exists a gradient of relativelv large molecular weight substances which interfere with the enzymatic destruction of auxin (5,6). Such a gradient of inhibitors of auxin destruction has also been reported by other workers, e.g., again recently in cotton by Morgan (1,2).…”

“…1500-5000 gm/mole) accounted for a smaller, but significant fraction of the inhibitory activity. A third component with molecular weights exceeding 10,000 gnm/mole was also found, but in the elongating internodal tissue studied, this component appeared to account for only a very small part of the inhibition (5 Seed, 17 hours: seeds were incubated at 220 on moist paper towels in a petri dish for 17 hours. The seed coat and associated mucilaginous substance were then removed and the remaining tissue analyzed.…”

“…A previous report described the occurrence of substances with re!atively high molecular weights, which inhibit the destruction of IAA both bv commercial horseradish peroxidase and by enzymes present in Japanese morning glory stems (5). In young morning glory plants the inhibition of enzymatic destruction of IAA varied inversely with the age of the internode tissue, i.e., inhibition decreased as one descended along the stem, and the interference with destruction correlated with the rate of internode elongation in young vines (6).…”

Studies on Auxin Protectors

“…All operations were carried out in the cold. Auxin protector activity of these preparations was assayed as usual (25).…”

“…Auxin protectors appear to be cellular poisers whose antioxidant properties inhibit peroxidase-catalyzed oxidations (21): Prs' are known to inhibit the peroxidase-catalyzed oxidation of indoleacetic acid (25) and probably inhibit peroxidasecatalyzed oxidations, leading to lignin formation (24). It In both plants and animals, embryonic tissue is in a reduced state.…”