Metabolic Activity and Energy Charge of Excised Maize Root Tips under Anoxia

Abstract

Energy charge and fermentative metabolism under anoxia were monitored in excised maize root tips after various times of aging in air and were related to their soluble sugar content. The energy charge value, which was 0.9 in air irrespective of the time of aging, dropped to a lower value within minutes of transfer to a nitrogen atmosphere. This value was dependent upon sugar content of the tissues which was itself a function of aging. The energy charge value after transfer to nitrogen was 0.6 in freshly excised tissue but only 0.2 in tissue aged for 4 hours. When aged tissues supplied with 0.2 molar glucose were transferred to nitrogen, the energy charge was 0.6, irrespective of the time of aging. When 0.2 molar glucose was added under nitrogen, energy charge rose to 0.6. This rise was faster in root tips aged for 8 hours than those aged for 24 hours.The rate of ethanol plus lactate production (representing 60 and 10%, respectively, of the total sugar consumption in anoxia) was closely correlated to the level of energy charge. It is concluded that, in anoxia, there is a quantitative relationship between the energy charge value and the level of metabolic activity via fermentative pathways.