Triacontanol stimulates nitrogen-fixation, enzyme activities, photosynthesis, crop productivity and quality of hyacinth bean ( Lablab purpureus L.)

Abstract

Hyacinth bean ( Lablab purpureus L.) serves as a good source of vegetable proteins in human diet, and its seeds and pods contain as much as 20–28% protein. The bean contains tyrosinase enzyme, which has potential use for the treatment of hypertension. However, plant biological yield appears to be comparatively low in Aligarh soil in this region of India (Western Uttar Pradesh). A hypothesis was designed to address whether foliar application of triacontanol (TRIA) could enhance the crop productivity as well as crop quality. TRIA is known to be a potent plant growth promoting substance for many agricultural and horticultural crops. The hyacinth bean plants grown in soil containing pots, were sprayed with five concentrations of TRIA (10 −0 (Control), 10 −8, 10 −7, 10 −6 and 10 −5 M) at 15-day intervals. The plant fresh and dry weights, leaf-area, number and dry weight of nodules per plant, total chlorophyll and carotenoid content, nitrate reductase activity, carbonic anhydrase activity, nodule-nitrogen content, leghemoglobin content and leaf N, P, K and Ca contents were analyzed at 60, 90 and 120 days after sowing (DAS). Net photosynthetic rate, transpiration rate and stomatal conductance were measured only at 90 DAS. The protein content plus carbohydrate and tyrosinase activity were analyzed in the seeds. Foliar spray of 10 −6 M TRIA significantly stimulated most of the studied attributes. At the highest concentration (10 −5 M TRIA), values of all attributes were significantly decreased at all three stages. For example, 10 −6 M TRIA increased seed-yield and -protein content by 56.3 and 14.5%, respectively when compared to unsprayed plants. TRIA also stimulated the activity of tyrosinase when compared to the control plants.