METABOLIC RESPONSE OF MEDICAGO-SATIVA L AND LOTUS-CORNICULATUS L ROOTS TO ANOXIA

Differential rates of fermentation and energy production have been implicated in the response of plant species to extended root anoxia. This study describes the metabolic response to anaerobiosis of waterlogging-tolerant birdsfoot trefoil (Lotus corniculatus L.) and waterlogging-sensitive alfalfa (Medicago sativa L.). Studies were carried out on glasshouse-grown plants subjected to root anaerobiosis in nutrient solution. Rate of fermentation, as estimated by CO2 evolution, declined significantly upon anaerobiosis in both species but was proportionally less, relative to the aerobic control, in trefoil. Another indicator of carbon flux through glycolysis, the concentration of glucose-6-phosphate, was also significantly lower in trefoil roots relative to aerobic controls. Both species showed significantly increased root exudation of K+, sugars and amino-N, especially during the first 2 d of root anaerobiosis, indicating changes in membrane selective permeability. The energy status of roots subjected to anaerobiosis declined sharply in both species but trefoil roots maintained higher ATP/ADP ratios for up to 4 d of anaerobiosis. The results are consistent with the hypothesis that increased fermentation activity maintains a more favourable root energy status. This higher energy status may facilitate survival by maintaining crucial root activities, such as maintenance of membrane stability.