Effect Of Solution PH And Nitrogen Forms On Iron Nutrition Of Tissue Cultured Apple

The effects of solution pH and nitrogen forms (N03^--N and NH₄-N) on tissue cultured apple tree (Malus pumila Mill) were studied in nutrient solutions under HC03^- controlled condition. The 59Fe isotopic method was also used to identify the iron reutilization efficiency. The results showed that in iron sufficient condition, iron would accumulate in root and shoot, in which reached 97. 55% in whole iron content of plant. Compared with NH₄⁺-N, supply N03^--N the root Fe(III)-reduction capacity would decrease, that would also occur in high pH solution. Thus result iron accumulated in root apoplastic that cannot mobile freely to up plant. In iron-deficient condition, the higher solution pH the lower the active iron in leaves. When solution pH were not access 7. 7, the root Fe (III)-reduction capacity fed with N03^--N were higher to which in NH₄⁺-N solution; but the root Fe(III)-reduction capacity were higher in NH₄⁺-N solution under pH8. 7 solution. When no iron in solution, fed with NH₄⁺-N could increase the reutilization of root apoplastic iron. If there were no HCO₃^- in solution, after fed with NH₄⁺-N lOd, the 59Fe content in root decreased 17.57% in whole plant, fed with N03^--N decreased 6.43%. If HCO3^- exist in solution, fed with NH₄⁺-N the 59Fe content in root decreased 10.37%, fed with N03^--N decreased 2.54%. Analyzing showed root apoplastic iron content was negative correlation with the chlorophyll content in leaves when no iron in solution. Fed with NH₄⁺-N the active iron and chlorophyll content were much higher than with N03^--N.