Dependence of Basipetal Polar Transport of Auxin upon Aerobic Metabolism

Abstract

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.

Phospholipase Dζ2 Drives Vesicular Secretion of Auxin for Its Polar Cell-Cell Transport in the Transition Zone of the Root Apex

“…Early papers revealed that auxin transport is an active process requiring continuous respiration, supply of cellular energy in form of ATP, and physiological temperatures. [3][4][5] Here we provide in vivo pharmacological and genetic evidence that substantial portion of the polar transport of auxin in root apices is driven by vesicle-mediated secretion regulated by the PLDζ2 activity and its product PA. In the PLD2 mutant and after 1-butanol treatment, auxin fluxes measured by the IAA-sensitive microelectrode are strongly supressed despite undisturbed PINs localization.…”

“…The secretory theory deals with the active auxin efflux whereas the chemiosmotic theory deals mainly with the passive auxin influx due to lipophilic weak acid nature of auxin and pH differences between the cytoplasm and cell wall. Ever since the polar auxin transport was shown to be dependent on active respiration and continuous ATP supply, [4][5][6] with the efflux being the decisive process, auxin efflux carriers were postulated and looked for. 8,9 Recently, manipulation of secretory activities, via phospholipase Dζ2 mutant and overexpressing lines 10 as well as its signalling product phosphatidic acid (PA), supported our earlier auxin immunolocalization data 11 that the vesicular recycling and secretion, and not just the bare presence of PINs at the plasma membrane, are essential for polar cell-cell auxin transport.…”

Influence of Gamma Radiation on the Transport of Indolyl‐3‐Acetic Acid in Bark Tissue from Apple Trees

“…Several external factors, e.g. pH, temperature, and anoxia have been investigated (Gregory and Hancock 1956, Wilkins and Martin 1967, Goldsmith 1966, 1969, Smith and Jacobs 1968. There is also a suggestion that membrane function is responsible for polar movement.…”