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.

No abstract

The relationship between auxin destruction and stem internode elongation was investigated in the vines of the Japanese morning glory (Pharbitis nil Choisy). In young plants an age‐dependent gradient was demonstrated in which the decreasing rate of elongation of older internodes correlated with an increasing ability of such tissue to destroy indoleacetic acid. Fragments of tissue from old internodes when incubated with indoleacetic acid (IAA), destroyed the hormone immediately and rapidly; in contrast, young, rapidly elongating internode tissue destroyed IAA only after a lag of several hours. In older plants the gradient was more erratic towards the middle of the plant but old and young tissue behaved as in young plants, i.e., old internodes destroyed IAA rapidly whereas young internodes did not. It appears reasonable to conclude that cessation of elongation in maturing internodes is brought about by developing an internal environment in which auxin is rapidly destroyed.

No abstract