Evidence for Essential Maintenance Respiration of Leaves ofXanthium Strumariumat High Temperature

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Abstract
Mesophyll resistance to photosynthetic carboxylation (r'm) was used as a criterion for leaf integrity. It was measured, at 25 °C, in the light, before and after periods of high temperature (3 h at 38 °C) in the dark. During the high temperature periods, respiration (RD) of attached leaves of Xanthium strumarium was suppressed from 27%-36% by either low [O2] (1.04% or 0.21% v.v.) or high [CO2] (840 μl 1−1) in the ambient air. Neither treatment affected rates of RD or photo-respiration during the second period at 25 °C. There was no significant increase of r'm when RD was not suppressed during the high temperature treatment. When RD was suppressed at high temperatures, r'm increased from about 3s cm−1 before, to about 26 s cm−1 after the high temperature treatment. The increase depended upon the degree of suppression. It is concluded that increased RD at high temperature in Xanthium leaves is partly the result of an increase of energy demanding maintenance. The subsequent rate of carbon dioxide fixation is reduced when this increase of maintenance-induced respiration is inhibited.

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