الفهرس 
Introduction
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Abstract
A study on nitrogen nutrition of wheat ( Triticum aestivum L.) sakha 93 was conducted to perform such study, three experiment hav been followed up. In the first experiment, wheat seedlings were grown with varying levels of nitrogen (0.3, 3, 10, and 25 mM) either as NH4 + or NO3 as a sole nitrogen source in a hyDROPonics culture. Growth of wheat was adversely affected by NH4 + particularly at high doses with progress of age. Roots were affected to a greater extent than shoots, resulting in a markedly lower root to shoot dry weight ratio of NH4 + grown plants than in those fed with NO3 . Also, water content of shoots and roots as well as root length were lower in NH4 +fed plants than in those fed with NO3 . The optimum N concentration for wheat growth was found to be 10 mM as NO3 and 3 mM as NH4 +, with higher doses leading to growth reduction. NH4 + at the lowest level (0.3 mM) appeared to be more beneficial to wheat seedlings than NO3 . In the second experiment, wheat seedlings were grown with two different levels of K+, Na+, Ca2+, Mg2+ (each at 0.3 and 9 mM) in combinations NH4 + at the same two levels. The cations used, particularly K+ and Ca2+ and to a lesser extent Mg2+ improved plant growth under NH4 + nutrition whereas Na+ reduced growth further. However, growth improvement was not associated with reduced NH4 + uptake by cations. The reverse, i.e. inhibition of cation uptake by NH4 +, was evident. The third experiment demonstrated the presence of two affinity NO3 uptake systems (high and low) as well as a constitutive and inducible uptake systems. The high affinity uptake system operated in the low range of NO3 concentration (up to 300 <U+00B5>M ) and the low affinity system at higher levels. Presence of NH4 + in the uptake solution led to promotion of nitrate uptake rates for both constitutive and inducible systems. NH4 + uptake was lowered by NO3 up to 600 <U+00B5>M then raised again with further increase in NO3 concentration. Rates of uptake of K+ and Ca2+ were increased in response to NO3 upto a certain level beyond which they were reduced. The response of Na+ uptake to NO3 differed between plants with constitutive and those with inducible NO3 uptake system.