Effect of soil applied L‐tryptophan on growth and chemical composition of cotton

Abstract

Addition of L-tryptophan (L-TRP) to soil can have an ecological impact on the growth and development of some plants through its catabolism into auxins by rhizosphere microflora. A pot experiment was conducted to assess the influence of L-TRP on growth and chemical composition of cotton (Gossypium hirsutum L.). Seven L-TRP levels (10 -7 to 10 -1 g/kg soil) were applied as a soil drench in addition to a control. Data obtained revealed that specific growth parameters were significantly promoted, such as plant height (27.3%), dry weights of shoot (45.7%) and root (35.8%), biomass (43.3%), and number of branches (37.5%), flowers (63.3%) and bolls per plant (22.4%) in response to L-TRP treatments. Similarly, the nitrogen (N), phosphorus (P), and potassium (K) concentrations in plant tissues and their uptake were also significantly affected by the exogenous application of L-TRP. Significant linear or quadratic doseresponse relationships were found when root mass, branches, flowers, bolls, and NPK concentrations in plant tissues and their uptake, were regressed against log[L-TRP] excluding the control. The effects of L-TRP could be most likely attributed to its conversion into auxins by the rhizosphere microflora upon direct uptake by plant; however, other mechanisms such as direct uptake of L-TRP by plant roots with subsequent auxin production within plant tissues or a change in the balance of rhizosphere microflora affecting plant growth cannot be excluded.

Improving Crop Yields by the Application of an Auxin Precursor L-tryptophan

“…However other possibilities such as direct uptake of these precursors by plant roots and subsequent conversion into respective phytohormones within the plant tissues and/or change in the balance of rhizosphere microflora affecting plant growth cannot be excluded. Our results are in agreement with previous studies in which L-TRP application affected the growth and yield of radish, melon, cantaloupe, pepper, maize, wheat, soybean and cotton (Frankenberger et al, 1990;Frankenberger and Arshad, 1991 a,b;Sarwar and Frankenberger, 1994;Martens and Frankenberger 1992: Arshad et al, 1994, 1995.…”

Azotobacter and L-tryptophan Application for Improving Wheat Yield

“…It is now well established that various Azotobacter species are capable of synthesizing plant hormones and is considered the most plausible mechanism of action. Significant yield increase in response to L-TRP application in present study is in agreement with the findings of many other workers (Martens and Frankenberger, 1994;Arshad et al, 1995). The increased N concentration and uptake in grain and straw in our study is also in accordance with the findings of many other workers (Arshad et al, 1994a,b;Zahir et al, 1997).…”

Nitrogen Uptake from Amino Acids in Maize through Arbuscular Mycorrhizal Symbiosis

“…It has been suggested that amino acids affect plant growth differently [15]. For example, Trp and Met applied to soil had a positive impact on plant growth [16][17][18]. The application of Glu increased maize growth and N content both with and without AMF in our experiment.…”