The effect of manganese and EDTA on the balance of nitrogen in maize xylem exudate

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Abstract
The effect of manganese chloride (10 mg Mn l-1), EDTA (18 mg l-1) and a mixture of these compounds on the nitrogen balance in maize xylem exudate was investigated. The compounds were applied as experimental solutions to the roots of 20 day old plants 24 h before excision. Application of Mn resulting in a lowered nitrogen level in the xylem exudate increased the relative content of the organic N-compounds in the exudate, particularly that of free amino acids. EDTA appreciably enhanced the content of total nitrogen in xylem exudate, however no significant changes were found in the proportion of inorganic and organic N-compounds in comparison with the water control. The significant features of the free amino acid exudate fraction of all experimental variants were, among others, the relatively high lysine content and the absence of proline arid sulphur containing amino acids. By gel filtration on Sephadex G-25 of xylem exudates UV (254 nm) absorbing fractions, four in the water control, five in Mn and six in EDTA variants were isolated. The UV absorbing fractions with the exception of one in each experimental variant (Kav 0.73 in water control, Kav 0.61 in Mn-variant, Kav 0.75 in EDTA and Mn + EDTA variant) were of peptide character, proline and sulphur-containing amino acids were missing in them. In the exceptional UV absorbing fractions (Kav 0.61–0.75) in spite of their high N-content (10.23%) after hydrolysis practically no amino acid could be detected.