Medium acidification by auxin treated and fusicoccin treated peeled stem segments from etiolated seedlings of pisum sativum cultivar alaska
Brummell, D.A.; Hall, J.L.
Journal of Experimental Botany 32(128): 635-642
ISSN/ISBN: 0022-0957 Accession: 005873065
Several reports have suggested that peeling off the epidermis from dicotyledonous stems removes the capacity of these segments to show an auxin-induced elongation response. This could be due either to the removal of the auxin-responsive tissue or to the loss of H+ into the medium when the impermeable cuticle is removed. Medium acidification by peeled etiolated segments of P. sativum L. cv. Alaska and the effects of IAA and fusicoccin (FC) on this process were investigated. Medium acidification occurred even with control segments and only in the presence of the divalent cations Ca2+ or Mg2+ did IAA give any enhancement of acidification. Under these conditions, the main effect of IAA was a reduction in the lag time between IAA addition and an observed acidification response. Addition of these ions is not required to obtain normal auxin-induced growth. Similarly, peeled segments of mature non-elongating tissue acidified the medium. FC gave some enhancement of medium acidification even in the absence of Ca2+ and Mg2+. With both IAA and FC, lag times before observable acidification occurred were reduced (from .apprx. 40-50 min to 20 min and 2-4 min, respectively), in the presence of Ca2+ or Mg2+. These ions appeared to exert similar effects. IAA, when added once a stabilized pH was attained, had little effect on pH, FC caused a further drop of .apprx. 0.5 unit. Auxin has little appreciable effect on the acidification of the medium caused by peeled segments, either of non-elongating or of growing stems and peeling apparently must remove the auxin-responsive tissue in pea stem.