EFFECT OF BORON ON THE GROWTH AND MINERAL ECONOMY OF SOME HALOPHYTES AND NON-HALOPHYTES

Growth of halophytes in nutrient solutions with increasing boron concentrations was less reduced than that of some non-halophytes. Boron (B) concentrations occurring in sea water (0.350 mol m-3 B) depressed growth of glycophytic plant species strongly, while growth of halophytes did not significantly differ from that under control conditions (Hoagland's nutrient solution containing 0.025 mol m-3 B). With increasing boron concentrations in the medium, the total boron concentrations in the shoot tissue increased up to 35-mu-mol B g-1 d. wt (350 mg kg-1 B d. wt basis) in the non-halophytic species and were lower in most of the halophytic species examined. Sodium chloride (200 mol m-3) in the culture medium depressed the total B content of the shoot in the halophytic species. In most halophytic species, the water-insoluble B fraction in the shoot and root tissue was higher than in the non-halophytic species tested with the exception of Phaseolus vulgaris. When the plants were grown in culture solution containing 200 mol m-3 NaCl, the ratio of insoluble: total B in shoot and root tissue increased. The resistance of halophytes to excess B and the possible detoxification of excess borate by complexation, either with cis-diol groups of carboxyl groups in the cell walls or with dissolved compounds such as sorbitol in the halophytic Plantago maritima is discussed. The mechanism by which B tolerance in the halophytes might be accomplished is also discussed.