Nitrogen assimilation in mycorrhized durum wheat plants

Arbuscular mycorrhizae (AM), the most common symbiotic associations between fungi and higher plants, plays pivotal role in the acquisition of mineral nutrients. While many studies have been focused on P nutrition and mycorrhizal infection, only a few have considered the contribution of mycorrhiza to N assimilation and partitioning, particularly in neutral and alkaline soils. The study aimed to assess comparatively nitrogen assimilation and partitioning in mycorrhized durum wheat (Triticum durum Desf., cv. Creso). Plants inoculated and not inoculated with Glomus sp fungal spores were grown in medium-textured soil in cell chamber under controlled conditions. Leaf and root samples were collected during growth and used for the analysis of free amino acids, proteins and nitrogen and phosphorous compounds. Data supported that mycorrhizal colonization was high in low P soils and strongly suppressed in P fertilized soils. Mycorrhized plants (MP) compared not mycorrhized ones (NMP) showed a lower growth in the tilling stage, but an overall higher one in the emergence stage. Free amino acid distribution and contents as well as nitrate reductase and glutamine synthetase activities supported that nitrate reduction was mainly carried out by the fungal nitrate reductase, while ammonium assimilation occurred through the GS – GOGAT and the arginine synthesis pathways in the MP roots. In the MP leaves where carbon skeletons and energy were largely available, instead, GS-GOGAT cycle was very active. Glutamine, aparagine, arginine, occurred at high level in the MP roots, while larger pools of glutamate and other nitrogen compounds including phosphoorganic coenzymes were found in the leaves. Protein content was also higher in the overall MP plants. So mycorrhiza improved also nutritional values of durum wheat plant tissues.