Mitochondria from the Mesophyll Cells of Zea mays Leaves.

Improvements in preparative techniques have made it possible to isolate and purify mitochondria from the mesophyll cells of Zea mays leaves. Contamination by mitochondria from the bundle sheath cellswas insignificant. The use of a self-generatedPercoll gradient allowed the purification of washed mitochondria from the mesophyll cells and considerably reduced the contamination by broken thylakoids and peroxisomes. Mitochondrial activity was improved without disturbance of the characteristic oxidative properties of these mitochondria. Mitochondria from mesophyll cells exhibit original properties, namely an NADPH oxidation that is Ca(2+)-dependent, and an auto-inhibition of malate and succinate oxidations. These properties could be related to the C(4) metabolism of these plants. Whereas NADH and Ca(2+)-dependent NADPH oxidations remain rather constant, malate, and even succinate oxidation seems to be sensitive to control by oxaloacetate. This effect could contribute to maintaining the level of the malate pool in the mesophyll cells and favor malate export towards the bundle sheath cells.