POLAR DISTRIBUTION OF RESPIRATORY RATE IN THE ONION ROOT TIP

Since the root tip of Allium cepa is being used more and more in physiological investigations, it was considered of value to investigate and compare the respiratory rate of different regions in this polar tissue. LUND and KENYON (8) observed that the region of active mitotic division in the root tip had the greater rate of reduction of methylene blue when compared to more basal regions and that this apical region was electropositive to the higher regions of the root. They also found that there wias the same polar distribution in the production of acid (CO2) when tested with phenol red. These factors were given as evidence in support of the theory of the origin of bioelectric potentials as oxidative-reductive systems in flux equilibrium. MARSH (9) showed that the electrical potential difference between apical and basal contacts on the root could be depressed by KCN, and ROSENE and LUND (11) found that the displacement of oxygen with hydrogen around the root also lowered the E.M.F. The readmission of oxygen gave a "rebound" effect in the p.d. of the root which was interpreted as resulting from a greater accumulation of oxidizable material in the apex as compared to the base. BERRY and HOYT (1, 2) observed that an onion root under anaerobic conditions could not be stimulated when direct or alternating current was passed through the root. ROSENE (13) has recently reported the inhibiting effect of KCN on the rate of exudation in excised onion roots. The present paper evaluates the normal respiratory rate of three segments of the root and the problems associated with measurements of this type. There is also included a preliminary estimate of the effects of eyanide and methylene blue on oxygen consumption in these segments.