ABSTRACT
Many plants accumulate compatible osmolytes at high levels in plant cells such as amino acids and/or develop special epidermal cell bladders which may serve as external water reservoirs and having small and thick-walled cells in response to water deficit. The objectives of the present investigation were: (i) to study effects of water stress on the anatomical traits and accumulation of free amino acids in quinoa leaves and (ii) to describe differences among drought tolerant and sensitive genotypes in such traits following the imposition of water deficit. A field experiment was carried out in the growing season 2015/2016, using a split plot design with five replications. Main plots were allotted to three irrigation regimes, i.e. well watering (WW) [95% field capacity (FC)], moderate water stress (WS) [65% FC] and severe water stress (SWS) [35% FC] and sub plots to five genotypes. Mean squares due to genotypes, irrigation regimes and their interaction were significant (p≤0.01) for studied leaf free amino acids and anatomical traits. Water stress caused a significant decrease in leaf thickness under WS and SWS, upper and lower epidermis under WS, palisade and spongy layers under SWS, but caused a significant increase in palisade and spongy layers under WS and upper and lower epidermis under SWS. The genotype CICA-17 (tolerant) had the thickest leaf and upper epidermis and second thickest lower epidermis, palisade and spongy layers. Contents of each amino acid were significantly increased due to water stress, except Leucine. Increases in amino acid content increased by increasing severity of water stress. Maximum increase (109.6%) was shown by Threonine under SWS, but minimum (8.08%) was by Arginine under WS. Under SWS, the tolerant genotype CICA-17 showed the highest mean increase percentage (47.9%) in total amount of amino acids relative to WW; it showed the highest increase in all amino acids, especially Proline, Methionine and Phenylalanine.