Effect of oxygen deficiency on mineral nutrition of excised tomato roots

The influence of oxygen deficiency on uptake of water and mineral elements through root system was studied on detopped tomato plants for 48 It. The root exudates and the nutrient solutions were collected and analyzed every two hours after decapitation of the shoots at the early fruiting stage. The lack of oxygen in the nutrient solution induced the appearance of nitrite ions in the nutrient medium and in the xylem sap. Nitrites were derived from nitrate reduction by tomato root cells. This mechanism, called "nitrate respiration", should be an alternative pathway to have oxygen as electron acceptor during root anoxia and could be a transient adaptation to hypoxic conditions. The lack of oxygen in the nutrient medium caused a 42% reduction of water consumption by excised tomato roots during the experiment. The deprivation of oxygen induced also an efflux of potassium, magnesium, phosphate and sulfate in the nutrient solution. So, this experimentation allows to obtain information about macronutrient uptake mechanisms by excised tomato roots. The uptake of potassium, magnesium, phosphate and sulfate is an "active process", directly linked to the energetic catabolism. On the opposite, the absorption of calcium is a "passive process", in the pathway of the electrochemical gradient via the water xylem flow.