Pedosphere 28(1): 16--34, 2018
ISSN 1002-0160/CN 32-1315/P
©2018 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Perspectives of Using L-Tryptophan for Improving Productivity of Agricultural Crops: A Review
Ayesha MUSTAFA, Muhammad IMRAN, Muhammad ASHRAF, Khalid MAHMOOD
Soil and Environmental Sciences Division, Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad 38000 (Pakistan)
      Plant growth regulators are biologically active signaling molecules that regulate a number of plant physiological processes. Auxin (indole-3-acetic acid) is an important plant growth regulator and is synthesized within plant tissues through L-tryptophan (L-TRP)-dependent and -independent pathways. It has been found that plants respond to exogenously applied L-TRP due to insufficient endogenous auxin biosynthesis. The exogenous application of L-TRP is highly significant for normal plant growth and development. L-tryptophan is applied through foliar spray, seed priming, and soil application. Soil-applied L-TRP is either directly taken up by plants or metabolized to auxin by soil microbiota and then absorbed by plant roots. Similarly, foliar spray and seed priming with L-TRP stimulates auxin synthesis within plants and improves the growth and productivity of agricultural crops. Furthermore, L-TRP contains approximately 14% nitrogen (N) in its composition, which is released upon its metabolism within a plant or in the rhizosphere and plays a role in enhancing crop productivity. This review deals with assessing crop responses under the exogenous application of L-TRP in normal and stressed environments, mode of action of L-TRP, advantages of using L-TRP over other auxin precursors, and role of the simultaneous use of L-TRP and auxin-producing microbes in improving the productivity of agricultural crops. To the best of our knowledge, this is the first review reporting the importance of the use of L-TRP in agriculture.
Key Words:  auxin biosynthesis,auxin precursors,auxin-producing microbes,crop productivity,indole-3-acetic acid,plant growthpromoting rhizobacteria,plant response to abiotic stresses
Citation: Mustafa A, Imran M, Ashraf M and Mahood K. 2018. Perspectives of using L-tryptophan for improving productivity of agricultural crops:A review. Pedosphere. 28(1):16-34.
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