PLANT PHYSIOLOGY , Vol 106, Issue 4 1541-1546, Copyright © 1994 by American Society of Plant Biologists
|
METABOLISM AND ENZYMOLOGY |
Immediate Activation of Respiration in Petroselinum crispum L. in Response to the Phytophthora megasperma f. sp. Glycinea Elicitor
E. G. Norman, A. B. Walton and D. H. Turpin
Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 (E.G.N., A.B.W.)
Treatment of parsley (Petroselinum crispum L.) cell cultures with the
Phytophthora megasperma elicitor isolated from the fungus Phytophthora
megasperma f. sp. Glycinea caused an immediate increase in the rate of
respiratory CO2 evolution in the dark. The respiratory response was
biphasic, showing a rapid enhancement in the first 20 min and then a slower
increase until a steady rate was attained 60 min posttreatment. The
enhanced rate of CO2 evolution corresponded to the activation of
phosphofructokinase and glucose-6-phosphate dehydrogenase, key enzymes in
the regulation of carbohydrate flow to glycolysis and the oxidative pentose
phosphate (OPP) pathway, respectively. The increased rate of CO2 evolution
and the activation of phosphofructokinase and glucose-6-phosphate
dehydrogenase were maintained for the duration of the experiments,
indicating long-term stimulation of respiration through both glycolysis and
the OPP pathway. A 23% decrease in the C6:C1 ratio of 14CO2 evolution from
labeled glucose 60 min after the addition of Phytophthora megasperma
elicitor is consistent with an increased contribution of the OPP pathway to
cellular respiration. Long-term activation of the OPP pathway following
elicitation could serve to maintain the pools of substrates necessary
during activation of the shikimic acid pathway, leading to the production
of defensive compounds.
