Effects of boron and calcium supply on calcium fractionation in plants and suspension cells of rape cultivars with different boron efficiency

In this study, the effects of boron (B) and calcium (Ca) supply on Ca fractionation in suspension cells and different tissues of rape (Brassica napus L.) plants of two cultivars with different B efficiency were studied, with a purpose to elucidate the mechanism by which B affects Ca concentration in plants. As Ca supply increased in nutrient solution or culture medium, the relatively easily extractable Ca fractions, that is H(2)O and 80% ethanol extractable Ca in leaves, 1 mol L(-1) NaCl extractable Ca in upper leaves, roots and suspension-cell were significantly increased. While the recalcitrant Ca fractions extracted by 2% acetic acid, 0.6 mol L(-1) HCl and Ca in the residue were not affected by Ca supply. Increasing B supply in nutrient solution or culture media significantly reduced 1 mol L(-1) NaCl extracted Ca in suspension cell and roots of both cultivars, which were most likely related to the alteration of cell wall metabolism. Calcium extracted by 2% acetic acid, 0.6 mol L(-1) HCl and Ca in residue in suspension-cell and roots of B inefficient cultivar Bakow were easily improved by B deficiency as compared to that of B efficient cultivar Tezao16. Increasing of these relative recalcitrant Ca fractions was related to the different response of cultivars to the B deficiency, which may reflected different extent that Ca deposited in the two cultivars due to impaired membrane integrity under B deficiency. The effects of B on Ca concentration in lower and upper leaves of the two cultivars were quite different and were the integrated effects of B on Ca metabolism, Ca transport in plants and growth of certain organ. Increasing B supply increased total Ca concentration in upper leaves of Bakow and reduced that of Tezao16, which might relate to the different adaptability of the two cultivars to comparatively higher B supply.