LOW SULFUR ALTERS BORON METABOLISM OF MUSTARD

Abstract

Mustard (Brassica campestris L. var. Sarson) was grown in refined sand at three levels, deficient (0.3), normal (30), and excess (300) μM boron, each at low (0.02) and normal [2] mM sulfur. In mustard, dry matter and reproductive yield were highest at combined supply of adequate boron and sulfur. Foliar symptoms of boron deficiency were accentuated by low sulfur. Boron (B) deficiency at normal sulfur (S) reduced flowering, dry matter, pod yield, tissue boron, chlorophyll content, Hill reaction activity, protein and organic labile, and lipid phosphorus fractions, and increased the concentration of inorganic phosphorus, reducing and non-reducing sugars, phenol content, and the activities of peroxidase, acid phosphatase, and ribonuclease. A synergism between boron and sulfur was reflected when boron deficiency effects were accentuated further by combined deficiency of both nutrients. No seeds were formed in boron deficiency regardless of sulfur levels.The foliar symptoms of boron excess were initiated earlier than its deficiency and were more severe at low sulfur levels. At excess boron, the decreases in biomass, pod yield, chlorophyll, and lipid P concentrations were more pronounced at low sulfur level. Also an increase in leaf boron, reducing and non-reducing sugars, phenols, and activity of ribonuclease and peroxidase occurred, indicating a synergistic role of boron and sulfur in mustard.