Effect of salicylic acid on biochemical changes in wheat plants under khat leaves residues

Residues of khat (Catha edulis Forskal) leaves in the soil showed an inhibitory effect on the dry mass, pectin and cellulose of wheat shoots and roots and cell wall-associated proteins of roots. The dry mass of shoots and roots significantly reduced and the reduction in roots was greater than in shoots. On the other hand, the contents of hemicellulose and lignin in both shoots and roots and cell wall-associated proteins of shoots were stimulated by the amount of khat leaves added to the soil. Soaking wheat caryopses in salicylic acid (SA) counteracted partially or completely the adverse effect of khat leaves residues on pectin and cellulose composition. The dry mass of wheat shoots and roots increased by SA to about 1.5–3 folds of SA-untreated plants. The content of hemicellulose and lignin of shoots and roots was antagonistically lowered by the application of SA. The application of SA was generally associated with a marked increase in the biosynthesis of cell wall-associated proteins of shoots and roots of wheat plants. Soluble proteins, proline and free amino acids increased significantly in plants growing in soil amended with khat leaves residues; however, SA inhibited this stimulatory effect. Soaking of wheat caryopses in SA had a favorable effect on the accumulation of nutritive cations; it also ameliorated the effect of more distressing ions, especially Na, accumulated in wheat plants due to mixing khat leaves residues with the soil.