Auxin Transport and Geoelectric Potential in Corn Coleoptile Sections

Naqvi, S. M.; Dedolph, R. R.; Gordon, Solon A.

doi:10.1104/pp.40.5.966

Cited by 13 publications

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“…In N., about 5 % moved 10 mm wtithin 2 houirs, as compared to 70 % in air. The resuilts of Naqvi et al ( 13) At presenit there are iuo firm grouniids for choosinig betweeni these 2 alterniatives, however, the fact that the rate of movemenit ill N., remains abouit the same (duirinig 4 hours, wvhereas the available )., mulst conitillute to (lecr-ease favors the latter ilnterpretationi. Fuirthernmore, gro th is reversibly abolishe(d 1)b alnaerobic cond(litionis ( 10,14), and( in the presenit experimenits, the cornl coleoptiles duiring the 4 bolrn pt-riod ill N., lnot onfly failed to grow buit even (lecreased inl lenigth by I to 2 mm.…”

Section: Resultsmentioning

confidence: 99%

“…IUptake (4,13) anid( exit (3) are kno-wn to l)e inihibited bv anaerobic con(ditions, but 1)oth inecessitate passage across iinjulred cells and may involve processes w-hich are not characteristic of transport throuigh the bulk of the tissuie. Stuidies of the movement of applied atuxinl after it has entered the sectiotn are lacking, although this transit shoulld 1 TIis research -*as supported in part by grant GM-08886 from the Division of General Medical Science, Unlited States Public Health Service.…”

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Movement of Pulses of Labeled Auxin in Corn Coleoptiles

Goldsmith

1967

Plant Physiol.

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Summnary. The transit of indole-3-acetic acid through 20-mm sections of corn coleoptiles can be separated from processes involved in the uptake of auxin by the section and the exit of auxin from the section. Aerobic sections are supplied with an exogenous source of 14C IAA for a limited time, and after the source is removed, a pulse of 14C IAA moves down at 12 to 15 mm/houir. After transfer to nitrogen, movement of the ptulse at the aerobic rate persists for about 10 minutes; thereafter drops to only 1 to 2 mm/houir and remains at this level during the next 4 hours. Within 2 hours, 70 % of the total 14C in aerobic sections has moved 10 mm or more down the section from the position of the initial peak, whereas after the same time in nitrogen less than 10 % of the total 14C has moved as far.During the migration down the coleoptile, the peak of radioactivity becomes broader and less distinct. This dispersion is more rapid in aerobic than anaerobic sections, but appears to be nonpolar and to occur along the existing concentration gradients. Diffusion probably contributes to this dispersion.In both inhibited and tuninhibited sections, the movement of the peak, in contrast to its dispersion, is A) polar (downward) and B) independent of existing concentration gradients. Thus transit within the section possesses the fundamental properties of the overall transport system. The reduced amotunt of transport in inhibited sections is more likely maintained by glycolysis than by a low level of aerobic respiration depetndent on the residuial oxygen in the tissule.The tranisport of iindole-3-acetic acid in coleoptiles is of iinterest becatuse it possesses a high degree of polarity and is independent of the prevailing concentratioin gradienit (11,12,15,16 258be more comparable to the movement of endogenotus atuxin than the overall transport from (lonor to receiver. The effect of reduiced oxygen tensions on the movement of endogenouis auxin has beeu stul(lie(l in shoots of pine (1) and crab apple (9) with conflicting results. To determine if the transit of auixin in corn coleoptiles could be inhibited directly, the transit was separated from both tuptake and exit by following the movement of a ptulse of labeled atuxinl down the section. In these experiments, movement of the ptulse is sharply re(luce(l )-.-anaerobic conditions buit retuirns to the normal aerobic rate onl rea(lmission of air (6). Thuis aerol)ic metabolism is niecessary for transit within the sectioni as well as uiptake and exit at the ends of the section. This paper presents the evidence that this transit is transport and that in pre-timably anaerobic sections it canl not be totally abolished. Materials and MethodsSections 20 mm long were cuit starting 3 mm Il)elow the tip of etiolated 6 day old corn coleoptiles (8). Each stuch section was supported vertically with its basal end resting on a receiver block (16 ul) of 1.5 % agar gel alnd containing 2 % suicrose. D)iri-ng the uiptake period, the apical enlds of each www.plantphysiol.org on May 13, 2018 -Published by ...

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Section: Resultsmentioning

confidence: 99%

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Movement of Pulses of Labeled Auxin in Corn Coleoptiles

Goldsmith

1967

Plant Physiol.

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“…Grahm and( Hertz (11) andci Woodcock and Wilkins ( unpublished) have sliov-n that the geoelectric effect (loes not occtir tln(ler anaerobic coniditionis. 'Nacqvi et al (15) claim that the lateral tranisport of IAA dturiing geotropic stimuilation occurs as readly uniider anaerobl)ic C'Onl dlitions as it dloes in air. They therefore arguie that the geoclectric effect cannot be a mandatory conse(quieince of the lateral transport of IAA.…”

Section: Discussionmentioning

confidence: 99%

“…Their (lata for the dlependeince of lateral tranisport of IAA uiponl aerobic metabolism muist therefor-e be -iexx-ed with reservatioin uinti1 inldepel lelnt con firmation is avlailable. The argument of NaqvNi et al (15) that the geoelectric effect caninot l)e a mandatory coinsequlenice of lateral traniFport of lAA in shoots is, therefore, oln the basis of presenit evidence, somewhat tenuiiouis; it would have been muich stroniger hal(l they actually (letermine(l xwhether or Inot the geoelectric effect (lexvelopedI in the coleoptile sections from which their IAA transport data xwere obtained.…”

Section: Physiologymentioning

confidence: 99%

Dependence of Basipetal Polar Transport of Auxin upon Aerobic Metabolism

Wilkins

Martin

1967

Plant Physiol.

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Suiiiiiwiiiry. The movement of IAA-14C through coleoptile segments of Avean and Zca has been investigated under aerobic and anaerobic conditions. The results are as follows: Zea. Using a 5-mm segment and a 2-hour transport period anlaerobic conditions reduced the total uptake of 14C from an apical donor by 74 % and the proportion of the total found in the receiving block by at least 45 %. Anaerobic conditions reduced total uptake from a basal donor by 58 % but no 14C reached the apical receiving block in either air or N2. Uptake from apical and basal donor blockks in N'.. is closely similar.The presence of 14C in the basal receiving blocks, and its absence in the apical receiving blocks, in 'N, suggests that even in anaerobic conditions movement of IAA is polarized basipetally, although the movement occurs at only a fraction of the rate foutnd in air.Anaerobic conditions induced a similar reduction in basipetal movemient of IAA nin upper and lower 5-mm segments taken from the apical 10 mm of a Zea coleoptile.Using 10-mm Zea segments no 14C was recovered in the receiving blocks at the basal end of the segment after 2 and 4 hours in No whereas large amounts were recovered in air.Avena: Using 5-mm segments and a 2-hour transport period the total uptake of 'C from an api,cal donor is reduced by 83 %. Movement of 14C into the basal donor :s totally inhibited in N.. Total tuptake of '4C from a basal donor is reduced by 61 % in nitrogen and no 14C reached the apical receiving blocks regardless of the atmospheric conditions.A t:me course for the movement of 14C into the basal and apical receiving blocks throuigh 5-mm segments showed that in air the amount in the basal receivers increased for 4 hours and then remained approximately uniform. In N2 no significant 14C reached the receivers until 6 to 8 hou,rs after the application of donors but even then the amounts were about 12 to 14 % of that in aerobic receivers. Movement of 14C into apical receivers was similar in air and in nitrogen and even after 6 to 8 hours the amolint of radioactivity barely reached significant level's.The extent to which the polarity of auxin transport in shooits depends upon aerobic metabolism hias been the stubject of several investigations in which metabolic inhibitors and anaerobic conditions have been used. Inhibitors of metabolism such as DNP, KCN, -NaN, and indoacetate have been shown generally to reduce the ra.te of basipetal transport of auixin ( 16,18 with Zea wiiays coleoptiles, Hertel aindl Leopold (13) found that the amount of labelled IAA passing through a 5-mm segment is reduced by 66 % in an atmosphere of No, whereas Naqvi, Dedol'ph, and Gordon (15) used 10-mm segments and concluided that the rate of basipetal trancport of labelled IAA is the same under aerobic and anaerobic conditions. Goldsmith (5) has found the basipetal transport of labelled IAA through 10-mm segments of Avena sativa coleoptiles to be totally inhibited un(ler anaerobic conditions.

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“…These large blocks were then divided inlto 12. (14 ) anid pine shoots (4) are correlated vith metabolic activity anid aitxinl tran)iport is niot, perhaps the reputed strict basipolaritv of auxin transport (7,16) …”

Section: Methodsmentioning

confidence: 99%