The Change Of Protein And Amino Acids Metabolism In Xylem Sap Of Maize Seeding Under Alternative Split-Root Osmotic Stress

Some research have shown that when plant roots sense the change of soil water condition, it would produce a few signals and transfer to leaves with transpiration stream to control the stoma behavior, so that plants can use water optimumly, At present, many people take ABA as an important root signal, but whether it is an only signal is still a controversial issue, because of other substances, such as pH, amino acid, sugar et al, are also thought as signals act together with ABA. Using maize (zea mays.L) as material, we have researched the relationship between osmotic stress, stress time and amino acids, protein in leaves, xylem sap and roots of maize seedlings using alternative split-root osmotic stress under solution culture, discussed the role they played in whole plant, the results showed:Maize leaves water potential are higher under –0.2MPa and –0.5MPa alternative split-root osmotic stress than those under whole root osmotic stress. Among them, those under –0.2MPa alternative split root stress are closer with those under contrast, and the same results are gotten under –0.5MPa alternative split-root stress compared with –0.2MPa whole root osmotic stress, which showed that alternative split-root osmotic stress can increase leaf water potential. The change of soluble sugar and free amino acids are similar under different osmotic stress, that is, the content would increase with the stress degree stronger and the stress time longer, especially under –0.5MPa alternative split-root osmotic stress.The amount of Asp, Ser, Thr, Glu and Ala are over 50% of total free amino acids, and which would increase with the stress degree stronger and the stress time longer. Furthermore, the amount of Gly and His is higher in leaves, also the Val and His in roots, the Val ,Ile, Leu,and Lys in xylem sap. The Thr and Ser change greatly with the increasing of stress degree. For example, their two independent peaks emerged into one peak in chromatography. The amount of Pro change significantly compared with other amino acids, which present in leaves from 26.65 to 143.09 mg∕100g, and in roots from 6.14 to 23.57 mg∕100g.Among all the treatments, some amino acids are undetected, such as Asp in leaves Cys in roots, and the amount of Met is always remained in 0.2mg∕100g or so in roots.With the stress degree stronger and the stress time longer, the protein in xylem sap changed among 14.4~31KD for all alternative split-root osmotic stress.For roots under –0.5MPa alternative split-root osmotic stress, the amount of amino acids were increased in the stress part, but which were decreased significantly when putting them into common solution; when the condition change to stress again the amount increase again, taken together, the amount of free amino acids increase in a wave way in roots of maize seedlings Under alternative split-root osmotic stress. The amount of free amino acids increase with the increased treatment time in roots grow in usual condition under –0.5MPa fixed osmotic stress, but lower than that under alternative split-root treatment; the amount in roots grow in stress show the same tendency, but higher than that under alternative split-root treatment and lower than while root stress.