Hormonal Regulation of Cell Elongation in the Hypocotyl of Rootless Soybean: An Evaluation of the Role of DNA Synthesis

Abstract

Abstract. A method was developed where soybean seedlings were grown without roots to study the influence of hormones of root origin on shoot growth. Excision of the root resulted in inhibition of apical section growth and DNA synthesis and inhibited elongating section growth. A synthetic cytokinin restored DNA synthesis in the apical seotion, but did not influence growth in either the apical or elongating sections. Low concentrations of gibberellin with the cytokinin restored growth in the apical section. Gibberellin alone was sufficient to restore grow-th in the elongating section.An inhibitor of DNA synthesis, 5-fluorodeoxyuridine, inhibited the increase in apical section DNA without inhibiting control or gibberellin-induced growth in the elongating section. Experiments with 14C-thymidine resulted in no DNA labeling differences in the elongating section under conditions where gibberellin-induced elongation varied from 50 % to 73 % above controls. It was concluded that gibberellin-induced elongation in soybean hypocotyl occurred in the absence of DNA synthesis. Gibberellin does stimulate DNA synthesis in the apical tissue apart from its effect on cell elongation.Excised soybean hypocotyl elongated maximally at 10-8 M auxin. At higher auxin concentrations, fresh weight and ethylene production increased, but elongation was reduced. Addition of GA to the higher auxin concentations resulted in a 50 % inhibition in auxin-induced ethylene production and resumption in maximal elongation. Added ethylene inhibited elongation 30% at 2 A/l. Addition of up to 100 ll/ ethylene did not inhibit elongation with GA present in the incubation medium. Thus GA may counteract ethylene inhibition of cell elongation in addition to inhibiting othylene production in auxin-treated tissues.Thirty years ago Went (31) proposed the existence of-hormones produced by the roots that were necessary for stem growth. Chibnall (2), studying protein loss in detached leaves, suggested that the root system exerted an influence on leaf protein metabolism. He found that development of adventitious roots on the petioles of detached leaves caused a reduction in the rate of protein breakdown (3). Richmond and Lang (26) discovered a chemical basis -for senescence retardation when they showed that kinetin delayed yellowing of detached Xanthium

Inhibition of Auxin-induced Deoxyribonucleic Acid Synthesis and Chromatin Activity by 5-Fluorodeoxyuridine in Soybean Hypocotyl

“…Hawkeye 63) were germinated in moist vermiculite for 3 days at 30 C. Rootless seedlings, 4.5 cm long, were prepared as described previously (3). The tissue between 2 and 4 cm below the cotyledons was used in these studies and is referred to as the basal section.…”

“…In order to determine whether DNA synthesis contributes to auxin-induced chromatin activity, we used rootless soybean seedlings as a test system (3). The conditions were regulated so that the basal hypocotyl tissue of both intact and rootless seedlings responded similarly to auxin.…”

Asparate Transcarbamylase Activity in Etiolated Cowpea Hypocotyls Treated with 2,4-Dichlorophenoxyacetic Acid

“…DNA was determined on the KOH-nonhydrolyzable materials from the RNA extracts, following hydrolysis for 1 hr at 70 C in 1 N HC1O4 (8). The diphenylamine procedure of Burton (3) was used, with hydrolyzed salmon sperm DNA as a standard.…”

Temperature-dependent interaction of auxin and ethylene in soybean hypocotl elongation

“…However, antagonistic interactions also have been observed (16,38). Auxin levels in epicotyls of etiolated pea seed lings were diminished by 50% when they were treated with ethylene (58).…”

“…In fact, some of the ef fects formerly attributed to auxin are now known to be due to auxin-induced ethylene evolution (23,37,63,74). It is well-established that supraoptimal concentrations of auxin induce ethylene evolution in a wide variety of plant tissues (1,2,12,15,18,37,38,44,60,67,75). Auxin stimu lation of ethylene evolution has a lag period (15,45,60,74), and, since inhibitors of protein synthesis can inhibit auxin-induced ethylene evolu tion (30,44,60,75), it is concluded that auxin induction of ethylene evolution involves protein synthesis.…”