Elongation of Stem Internodes in the Japanese Morning Glory (Pharbitis nil) in Relation to Auxin Destruction

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.

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

“…They confirm the gradient of auxin protection reported previously (6) Extracts of old stem, whose total inhibitor activity always proved to be very weak, contain protector I (major peak) and protector II (the second peak), but no protector A. Comparable results were obtained with leaf extracts.…”

“…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).…”

“…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). The bulk of the inhibitory activity found in young, elongatng internodes could be associated with a substance designated as protector I (mo!ecular weight 5000-10.000 gin/ mole).…”

Studies on Auxin Protectors. VII. Association of Auxin Protectors With Crown Gall Development in Sunflower Stems

“…There is a correlation between interference with auxin destruction and rate of internode elongation in young vines. Thus auxin protection is greatest in leaves and interriodes elongating most rapidly, and diminishes as the tissue matures (29,30). Similar substances have been identified in other plants such as tobacco (15,16), cocklebur, Kalanchoe, Nicotiana affinis, N. glauca, N. ri'stica, sunflower, and tomato (24, and (25).…”

Studies on Auxin Protectors

“…Our results indicate that auxin protectors are highly effective in blocking both of these peroxidase oxidations, and the greatest concentrations of auxin protectors are found associated with juvenile tissue. There exists, in fact, a gradient of Prs along the shoot axis of Japanese morning glories (33,34), Helianthus, Kalanchoe, Nicotiana, and Xantliiimin (26).…”