02 consumption by the desiccation-tolerant moss Tortula ruralis and the desiccation-intolerant Cratoneuronfidicinum increased markedly during the latter stages of desiccation. ATP content of the mosses during desiccation was not correlated with 02 consumption, but was influenced by the rate at which the mosses lost water. The more rapid the water loss, the more ATP that was present in the dry mosses. The pattern of 02 consumption on rehydration also was influenced by the previous rate of desiccation. After rapid desiccation of T. ruralis 02 consumption upon rehydration was considerably elevated, and for up to 24 hours. After very slow desiccation the elevation was small and brief. Normal 02 consumption did not occur in C. fdhicwum after rapid desiccation, but did so within a few hours of rehydration after slower speeds of drying. ATP levels in T. rralis returned to normal within 5 to 10 minutes of rehydration. In C. fiicinum, increases in ATP were closely correlated with 02 consumption. These observations are considered to be related to differential damage caused to mitochondria and to cellular integrity by different speeds of water loss. The desiccationtolerant moss appears to be able to repair the severe damage imposed by rapid desiccation whereas the desiccation-intolerant moss cannot.Upon rehydration after desiccation, respiration by desiccationtolerant lower plants characteristically is stimulated above normal (3,24). This respiratory burst (or resaturation respiration [23]) has been reported in bryophytes (6, 8, 16, 27), ferns (20, 25), and lichens (10, 21-23). It has been observed that sometimes this burst is more pronounced in species less tolerant of desiccation (8, 23). Also, the magnitude of the burst is related to the severity and duration of the desiccation period (9,16,23 containing "energy-rich macroerg bonds" (i.e. ATP) during drying. In the second study (4), it was suggested that tolerance of desiccation may not depend so much upon the maintenance of high ATP levels during drying, but rather upon the ability to resume ATP synthesis rapidly on rehydration.Generally there has been a lack of attention to the relationships between respiration and ATP synthesis under any conditions of water stress and upon relief of them. In this paper, results are presented on the correlation between 02 uptake, CO2 evolution, and ATP levels during desiccation in a desiccation-tolerant moss, Tortula ruralis, and a desiccation-intolerant moss, Cratoneuron filicinum. The consequences of different rates of desiccation were tested, since there is evidence that rate of water loss has a profound influence upon the recovery of metabolism and ofcellular integrity when these mosses subsequently are rehydrated (5, 7, 13, 19).
MATERIALS AND METHODSThe collection and preparation of the gametophytes of T. ruralis ([Hedw.] Gaertn., Meyer, and Scherb.) and C. filicinum ([Hedw.] Spruce) (formally misidentified as Hygrohypnum luridum [Hedw.] Jenn.) have been described elsewhere (1, 2). Moss pieces were subjected to three...