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)
Corresponding Author:Ayesha MUSTAFA
      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: Ayesha, M., Muhammad, I., Muhammad, A. and Khalid, M. 2018. Perspectives of Using L-Tryptophan for Improving Productivity of Agricultural Crops: A Review. Pedosphere. 28(1): 16-34.
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