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THE SULPHUR REQUIREMENTS OF PLANTS AS EVIDENCED BY THE SULPHUR-NITROGEN RATIO IN THE ORGANIC MATTER A REVIEW OF PUBLISHED DATA

W. DIJKSHOORN and A. L. VAN WIJK
Plant and Soil
Vol. 26, No. 1 (February 1967), pp. 129-157
Published by: Springer
Stable URL: http://www.jstor.org/stable/42949510
Page Count: 29
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THE SULPHUR REQUIREMENTS OF PLANTS AS EVIDENCED BY THE SULPHUR-NITROGEN RATIO IN THE ORGANIC MATTER A REVIEW OF PUBLISHED DATA
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Abstract

From a review of published data on S-and N-fractions it has been shown that on a gram atom basis these elements occur in organic forms in a ratio ranging from 0.025 (legumes) to 0.032 (gramineous plants) and that this is the same as the S : N ratio in the proteins which constitute about 80 per cent of the organic S and N present. In plants deficient in sulphur, the ratio organic-S : organic-N becomes less than normal due to an increase in the proportion of non-protein organic-N compounds low in sulphur. With sulphur deficiency the cytoplasmic proteins decrease out of proportion to the chloroplast proteins of a higher S content so that the ratio of protein-S to protein-N tends to increase. A similar change may occur during the fall in tissue protein content with increasing plant age. Sulphur-deficient plants show a subnormal ratio of organic-S to organic-N in the absence of sulphate in the tissues. Plants in which the protein content is decreased by proteolysis may have subnormal organic-S : organic-S ratios in the presence of sulphate in the tissues, i.e. without S shortage. This may occur during dark starvation or in seedlings drawing upon reserve proteins in the seeds. The S-requirements for growth are reflected in the normal ratio of organic-S to organic-N. In most species investigated, organic-S occurs mainly as cystine and methionine and is directly related to protein metabolism. Because of the presence of other forms of organic-S, the organic-S : organic-N ratio in the Brassica species is higher.

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