Phosphorus stress alters boron metabolism of mustard

The study has been made to understand the role of phosphorus in changing the boron (B) metabolism of mustard (Brassica campestris L.) cv. T9 by growing the plants in refined sand at deficient (0.3 muM), adequate (30 muM) and excess (300 muM) levels of boron, each at three levels of phosphorus (P), low (0.15 mM), normal (1.5 mM) and excess (3.0mM). The synergy between B and P was reflected when low phosphorus accentuated the effects of B deficiency by lowering further the reduced dry weight, total seed. yield and increased further the concentration of reducing sugars, phosphorylated protein and activities of acid phosphatase and ribonuclease in B. deficient leaves. The effects of excess boron in mustard, viz., reduction in dry weight, seed weight, contents of reducing sugars, organic P, oil content, activity of ribonuclease and stimulating leaf boron, content of inorganic P, phosphorylated protein were accelerated further by combined toxicity of both nutrients. No seeds were produced at deficient B even on increasing the P supply to twice that of adequate amount. The synergy was again observed between B and P when low phosphorus accentuated boron excess effects, i.e., the depression in dry weight, seed yield, reducing sugars, organic P, and oil content and increasing further B and activity of ATPase in young leaves in low P-excess B treatment in mustard.