Auxin movement in corn coleoptiles

Formation of naphthaleneacetic acid-glucose (NAGlu) in detached leaves, floating on a-naphthaleneacetic acid-1-V4C (NAA, 0.05 microcurie per milliliter, 3.1 ,uM)-buffer solution (phosphate-citrate, pH 4.2) began immediately while there was a 2-to 4-hour lag before NAA-asparatate (NAAsp) could be detected. Subsequent increase in the NAAsp conjugate reflected a decrease in free NAA to 1 to 2 % of the total radioactivity taken up. Pretreatment with 31 gM 'C-NAA for 18 hours doubled NAAsp formation after transfer for 4 hours to '4C-NAA. Pretreatment with ethylene, as ethephon (up to 400 milligrams per liter) or ethylene gas (10 microliters per liter), did not induce NAAsp formation. In the presence of NAA, ethylene had no effect on NAA conjugation. Similarly, CO2 (5%) did not modify the formation of the conjugates. Rhizobitoxine (1.87 uM) inhibited NAA-induced ethylene production but did not prevent NAA-induced formation of NAAsp. We concluded that the conjugation of NAA with aspartic acid is not mediated by ethylene.

Section: Discussionmentioning

confidence: 71%

Mechanism of Naphthaleneacetic Acid Conjugation

Gören¹,

Bukovac²

1973

“…4), and the plateau in the dose-response curve is essentially unchanged. Further, 1-NAA is transported through sections almost as well as IAA while 2,4-D is not (7). The dose-response curve for 1-NAA does not show a plateau (Fig.…”

Section: Discussionmentioning

confidence: 96%

Auxin Concentration/Growth Relationship for Avena Coleoptile Sections from Seedlings Grown in Complete Darkness

Shinkle¹,

Briggs²

1984

ABSTRACIA biphasic auxin dose-response curve has been obtained for indoleacetic acid (IAA)-stimulated growth of subapical sections of coleoptiles from totally dark-grown oats (Arena sativa L. cv Lodi). The curve for growth at 6 h is composed of a log-linear phase and a modified bellshaped phase separated by a plateau. The curve is log-linear from 0.003 to 0.4 micromolar IAA when sections are incubated in pH 5.9 buffer. The plateau of IAA concentration-neutral growth is seen from 0.4 to 4.0 micromolar UIA. Further increase in growth occurs from 4.0 to 10 micromolar IAA. Changing the pH of the buffer from 5.9 to 5.5 or 6.2 changes the shape of the curve, shifting the plateau to lower IAA concentration, or abolishing it, respectively. The synthetic auxin 2,4-dichlorophenoxyacetic acid also shows a biphasic dose-response curve, but the synthetic auxin 1-naphthalene acetic acid does not. The plateau is not affected by the auxin-transport inhibitor 2,3,5-triiodobenzoic acid. The plateau is eliminated by taking sections from coleoptiles grown under continuous dim red light. We advance a model to account for these results based on two modes of auxin uptake into the cell: carrier-mediated uptake and uptake via chemiosmotic diffusion.There have been several interpretations of the dose-response curve for auxin-stimulated growth in oat (Avena sativa) coleoptiles. Over the last 50 years, these have ranged from analyses of the mode of auxin interaction with a putative auxin receptor/ enzyme (4), to assertions that changes in growth rates seen in whole plants are not linearly related to auxin concentration (20).In addition, the shape of the auxin dose-response curve for growth has been variously reported as: linear with concentration (24); linear with the log of auxin concentration (11); bell-shaped on a log auxin concentration scale (4); and sigmoidal on a log auxin concentration scale (1).One feature common to all of these studies was that the response of the tissue to varying auxin concentration yielded a single phase continuous dose-response curve. This common feature resulted in models of growth responses to auxin which postulated only single step/single receptor transduction as the mechanism of auxin action.We report here conditions yielding a biphasic dose-response curve for IAA-stimulated growth in oat coleoptile segments At 72 to 76 h after imbibition, seedlings were selected for uniform size by touch and were removed by hand from the seeds. The coleoptiles ranged from 1 to 1.5 cm in length. The coleoptiles, with some mesocotyl attached, were placed in a specially designed two-blade cutter assembly. The cutter removed a 3-mm tip section, leaving the next 5.7 mm between the blades. Primary leaves were not removed. These sections were then placed in 9 to 12 ml of 5 mm K-phosphate buffer containing 80 gM chloramphenicol and the appropriate test substances in a Petri dish on ice. Sections were collected for up to seven treatments (seven dishes) in a given harvest. By rotating delivery of 4 to 5 sections around all Petri d...

“…Some of these phenomena have been explained as being manifestations of the movement of the plant hormones known as auxins, which have been known to move polarly since 1928 (10,19). After it was shown (7,8,11,16) that even the synthetic auxin-type herbicide 2, 4-D moved through excised shoot tissues with a polarity like that of the endogenous auxin IAA, other classes of hormones were tested. Just recently, GA. was found to move with a polarity very similar to IAA through Coleus petioles and with opposite polarity to IAA through corn root sections (12)(13)(14).…”

mentioning

confidence: 99%

Polarity of Thiamine Movement through Tomato Petioles

Kruszewski¹,

Jacobs²

1974

Thiamine-"C moved through petiolar sections of Lycopersicon esculentum Mill. var. Michigan State Forcing with striking similarity in kinetics to auxins and gibberellic acid moving through similar sections of other green plants. Thiamine moved with strong basipetal polarity, at a velocity of 3 to 5 mm per hour, and emerged unchanged into the basal receiver agar block, judging by chromatography. This lends support to the hypothesis that polar movement is a property of several classes of plant hormones, rather than being restricted to the auxins (as previously believed).Multicellular plants show many polar phenomena during development and regeneration (e.g., regeneration of roots at the basal or "root" end of an excised stem section). Some of these phenomena have been explained as being manifestations of the movement of the plant hormones known as auxins, which have been known to move polarly since 1928 (10,19). After it was shown (7,8,11,16) that even the synthetic auxin-type herbicide 2, 4-D moved through excised shoot tissues with a polarity like that of the endogenous auxin IAA, other classes of hormones were tested. Just recently, GA. was found to move with a polarity very similar to IAA through Coleus petioles and with opposite polarity to IAA through corn root sections (12)(13)(14). Although early reports claimed polar movement of abscisic acid and a cytokinin (1, 4), the more quantitative later studies found sizeable movement in both directions, with no clear sign of polarity of these two classes of hormone (5,9,18 considered as confirmation of the hypothesis that in the intact plant thiamine was synthesized in the leaves and moved from there to the roots, which were unable to synthesize it but needed it for development. We could find no literature on the movement of thiamine through classical "transport sections." So that the results would be more useful for comparisons, we used the same general methods used earlier in this laboratory for studies of the movement of auxins, cytokinins, and GA3 (10-14, 16, 18). Sections 5.1 mm long were excised with a double-bladed cutter from the middle of petioles of leaves of tomato (Lycopersicon esculentum Mill. var. Michigan State Forcing). Tomato was used because of the numerous reports that its excised roots need thiamine for continued growth in culture. The excised petiolar sections were placed horizontally between donor and receiver blocks of 1.5% agar (see inset diagram of Fig. 1). Donor blocks contained thiamine, with stated specific radioactivity of 18.9 mc/mmole labeled with "4C in the thiazole 2 position, at a concentration of 15 uM. A donor block was placed against the apical ("leaf blade") end of the petiolar section when movement in the basipetal direction was being tested (as in inset diagram), and against the basal cut end (stem end) when acropetal movement was being tested. These transport systems were placed on glass slides in moist Petri dishes which were placed in a dark incubator at 26 to 27 C. After 2, 3, or 4 hr the receiver blocks were remo...