Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 20, 1997
Publication Date: N/A
Interpretive Summary: When plants experience water shortages their growth slows down and, even after rewatering, some amount of time passes before normal growth resumes. Some plants that are called desiccation-tolerant can undergo severe water loss and recover normal metabolism within minutes of rewatering. In this study, the effect of water loss on the enzyme nitrate reductase from a desiccation-tolerant moss (Tortula ruralis) was determined. The enzyme recovered after water application within minutes. This compares to a recovery period of days for same enzyme from cotton. In addition to its rapid recovery following rewatering, the enzyme maintained its activity during the initial stages of water loss. In other plants this enzyme is one of the first to be affected during water loss. These results indicate significant differences in this enzyme between desiccation-tolerant and intolerant plants and suggest mechanisms for the improvement in the rate of recovery of plants following the alleviation of water loss.
Technical Abstract: The activity of the enzyme nitrate reductase (EC 18.104.22.168) is generally reduced in plants experiencing water deficits. Upon the alleviation of the water stress, its activity recovers to control levels in periods ranging from 1-7 days. A reduction in the time required for the reestablishment of nitrate reductase activity may improve recovery of plants from water stress. In desiccation-tolerant plants metabolic recovery can occur within hours following rehydration. In this study, the rate of recovery of nitrate reductase activity in the desiccation tolerant moss Tortula ruralis has been investigated. Nitrate reductase activity was detectable in fully hydrated moss samples at levels that are approximately 50% of those reported for other plant species. Nitrate reductase activity declined rapidly during dehydration of the moss tissue and was not detectable in dried moss samples. The recovery of nitrate reductase activity following rehydration was dependant on the rate of the preceding dehydration. In slow-dried moss the activity recovered to control levels in less than 8 hours while rapid-dried samples required 24 hours for full recovery. Nitrite accumulates during slow dehydration but does not accumulate if desiccation is rapid. Following rehydration of slow-dried moss the amount of nitrite declines and reaches a control level within 1 hour. Attempts to measure immunologically reactive nitrate reductase protein levels or nitrate reductase mRNA levels using heterologous DNA probes were unsuccessful, suggesting that the Tortula nitrate reductase may be significantly different from that found in algae and higher plants.