Changes in Free Amino Compounds during the Development of Two Wheat Cultivars Subjected to Different Degrees of Water Stress

The changes of total nitrogen and free amino compounds, except proline, in leaves, stems, roots and ears of the wheat cultivars Yecora and Generoso were followed during the development in the field with and without irrigation. The time course of the sum of the amino compounds was similar in stems and roots, but was different in the leaves and ears. The levels of particular compounds for a given cultivar varied with plant development, organ and water stress. Glutamate, alanine, aspartate, and serine were found at high concentrations in all organs, although their proportion was substantially lower in the stems and roots where glutamine and asparagine were also detected in considerable amounts. Large amounts of glutamine were also found in the ears. The concentrations of some compounds increased in the periods of more severe water stress, although the concentration of total nitrogen did not show a similar response. From correlations between Ψ1, and the values of specific compounds, as well as from the examination of the time courses in the two treatments, it was found that glutamine, alanine, serine, leucine plus valine, asparagine and γ-aminobutyric acid accumulated to a greater extent during water stress. The response of these compounds to water shortage differed between cultivars, organs, and stage of development, but it was less marked in comparison with proline. The sensitivity of any of the examined cultivars to water stress was different before and after heading: the early and semi-dwarf Yecora reacted more readily than the late and taller Generoso to water shortage in the vegetative phase, while the opposite situation was observed in the reproductive phase.