R. 1992. Diurnal patterns of respiration in the leaves of four forest tree species. -Physiol. Plant. 84: 361-366.Respiration along the cyanide-sensitive, cytochrome pathway and the cyanide-insensitive, alternative pathway was monitored over a 24-h period in the leaves of Acer rubrum, Betula papyrifera. Populus tremuloides and Quercus rubra excised in the field. Populus displayed the greatest rate of total re.spiration, followed by Betula, Quercus and Acer. All species displayed the capacity for the alternative pathway as well as some engagement of the pathway, although the level of engagement in Acer was very low. lo all species investigated there were no marked diurnal trends in any respiration variable measured. Leaf soluble sugar levels remained at a relatively constant level throughout the sampling period. It is concluded that respiration did not show diurnal fluctuations because substrate supply in the leaf was maintained at a constant level.

W. R. 1996. The rate of development of water deficits affects Saxifraga cernua leaf respiration. -Physiol. Plant. 96: 291-297.We allowed plant water deficits to develop at two different rates following the cessation of watering in order to investigate the effects of water stress on cytochrome pathway and alternative pathway respiration in the leaves of the arctic herb Saxifraga cernua. Plants were pretreated by growth in either a commercial organic (CO) mixture or a vermiculite-perlite (VP) mixture, which allowed the complete development of water deficits in 19 and 8 days, respectively. The rate of water potential reduction was approximately 0.11 MPa day"' in the leaves of CO plants, compai-ed to a reduction of 0,21 MPa day"' in leaves of VP plants. Osmotic adjustment occurred to a greater extent in leaves of CO plants and corresponded with an increase in ethanol-soluble sugars. In leaves of CO plants, cytochrome pathway activity gradually declined from that of control rates until day 11, and then declined more rapidly. In contrast, cytochrome pathway activity significantly increased in response to water deficits in leaves of VP plants. In leaves of both CO and VP plants, alternative pathway activity declined as water stress progressed. Relatively severe water deficits reduced alternative pathway capacity in leaves of botii CO and VP plants. We also investigated the effect of previous exposure to water deficits on leaf respiration. In piants that had previously experienced three cycles of water stress, the increase in cytoehrome pathway activity during the fourth water stress cycle was small compared to the increase obseri'ed in leaves of plants experiencing water stress for the first time. These results suggest that cytochrome pathway activity is differentially sensitive to the rate of development of plant water deficits and that respiratory responses to acute water stress are not necessarily similar to the responses to chronic water stress,

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