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Endogenous and Exogenous Respiration of Conidia of Verticillium albo-atrum. G. O. Throneberry, Department of Botany and Entomology, New Mexico State University, Las Cruces 88001. Phytopathology 60:143-147. Accepted for publication 25 August 1969. DOI: 10.1094/Phyto-60-143.

Conidia of Verticillium albo-atrum harvested from shake cultures maintained a consistent respiratory response to glucose after up to 6 hr starvation, with RQs near 1.2. Endogenous respiration decreased consistently with starvation time with a concomitant decrease in RQ from 0.9 to 0.7, indicating a transition to lipid utilization. Cells treated to induce germination responded similarly to glucose, but had slightly lower RQs. Their unstarved endogenous respiration, expressed as a percentage of comparable exogenous respiration, was less than for unstarved noninduced cells. With increasing starvation time, however, the decrease in endogenous relative to exogenous respiration was less than with equally starved noninduced cells. Furthermore, there was no evident decrease in RQ. Respiratory response to glycerol was initially similar to that of glucose, but was greater than with glucose after 3-hr exposure to these substrates. On a dry wt basis, respiratory activity of cells from progressively older cultures decreased through 14 days, with the most evident decreases at 2 to 3 days. On a per cell basis, comparable decreases occurred through 6 days, but respiratory rates then increased with further culture age. Correspondingly, dry wt per cell was relatively constant through 6 days, then increased markedly. Responses to inhibitors and other added materials varied with the endogenous or exogenous nature of the substrate. Endogenous respiration generally showed a greater response to stimulatory materials, whereas the effect of inhibitory materials was usually more evident with glucose present. Membrane permeability effects and endogenous-exogenous respiration differences are considered as possible influencing factors, though the data preclude strong support of either case.