Long-Term Phosphate Starvation and Respiratory Metabolism in Suspension-Cultured Catharanthus roseus Cells

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In order to clarify the metabolic adaptation of respiratory pathways in plants to limited levels of P_i, the effects of long-term starvation of P_i On the activities of various enzymes related to respiratory metabolism were examined in suspension-cultured Catharanthus roseus cells. When the activities were expressed as units per g fresh weight, only those of phosphoenolpyruvate-hydrolyzing (PEP-hydrolyzing) enzyme (which may possibly be equivalent to the acid phosphatase activity derived from vacuoles) and PEP carboxylase were higher in the P_i-starved cells than in control cells. Activities of other enzymes in the P_i-starved cells were lower than or similar to those of the control cells. Time-course studies indicated that PEP-hydrolyzing activity was inducible by starvation of P_i. However, in contrast to the results reported by Duff et al. [(1989a) Plant Physiol. 90: 1275.], fluctuations in the activity of PP_i:fructose-6-phosphate 1-phosphotransferase during starvation of P_i were similar to those in levels of phosphofructokinase and 6-phosphogluconate dehydrogenase. These data suggest that the concept of the phosphate starvation-inducible 'bypasses', which are engineered via the coarse control (i.e., induction) of specified enzymes and were proposed initially by Duff et al. in Brassica nigra cells, is not directly applicable to Catharanthus roseus cells in suspension. Tracer experiments using [U-^<14>C]glutamine indicated that a significant proportion of respiratory substrates could be supplied from the enlarged pool of amino acids during starvation of P_i. These assumptions are supported by the observed fluctuations in levels of free amino acids and of protein in P_i-fed and P_i-deficient Catharanthus roseus cells.
日本植物生理学会の論文

Long-Term Phosphate Starvation and Respiratory Metabolism in Suspension-Cultured Catharanthus roseus Cells

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