ASCORBIC ACID AND ASCORBIC ACID OXIDIZING ENZYMES OF GREEN BEAN PLANTS DEFICIENT IN MANGANESE

Recently in this laboratory (1) soybeans grown on manganese-deficient field plots were analyzed for ascorbic acid and ascorbic acid-oxidizing enzymes. Contrary to some reports in the literature, no consistent relationship was found between manganese deficiency symptoms and ascorbic acid or the enzymes which oxidize it. The present study was performed with solution cultures to provide a more rigid deficiency of manganese. Stringless green pod beans (Asgrow) were germinated in controlled temperature cabinets in paper rolls moistened with distilled water. Seedlings were transferred at 10 days to solution culture vessels. The continuous solution renewal method which automatically aerates the solution, as described by SHIVE and STAHL (4), was employed with some modification. Sixteen units of six culture vessels each were arranged on greenhouse benches by randomizing the order of three reservoir jars, one from each of the three experimental treatments. Each reservoir jar supplied two culture vessels. Macronutrient elements were supplied in the amounts used by SOMERS et al. (5) in a study of the effects of iron-manganese ratios on soybean plants. In millimolar concentrations these were: KH2PO4-0.58, K2SO40.82, Ca(NO3) 2-4.50, and MgSO4-2.30. Iron as FeSO4 (low Mn) and manganese as MnSO4 were added in the ratios of 4.0 to 0.00, 4.0 to 0.01, and 4.0 to 2.00 (p.p.m.). Micronutrient elements other than manganese were supplied in the following amounts and forms: 1.0 p.p.m. zinc (ZnSO4), 0.5 p.p.m. boron (H3BO3), and 0.1 p.p.m. copper (CUSO4). Distilled water and analytical grade reagents were used throughout. The cultural solutions which were made each morning from concentrated reagent solutions were maintained at pH 4.0 to 4.2. Acidified ferrous sulphate solution was prepared fresh from the dry salt each morning immediately prior to addition to the cultural solutions. The greenhouse temperature was maintained at 80° F in day and 70° F at night. Since the experiment was performed during the winter months, six hours of supplementary lighting from incandescent lamps was provided each clear day and thirteen hours on cloudy days. Parathion (0, 0-diethyl