Hydrolysis products of glucosinolates in Brassica napus tissues as inhibitors of seed germination

Abstract

Enzymatic hydrolysis of glucosinolates, a class of compounds found in Brassica species, results in a number of products with potential to inhibit seed germination. To investigate the impact of both volatile and watersoluble allelochemicals, germination bioassays using Lactuca sativa seeds were conducted with root and combined leaf and stem tissues of Brassica napus. Tissues in which glucosinolates were hydrolyzed to remove volatile glucosinolate degradation products were compared with intact tissues and water controls. Only tissues containing glucosinolates produced volatiles that inhibited germination. Volatiles were trapped and identified using GC-MS. Volatiles produced in greater quanitity from intact tissues than from tissues without glucosinolates were almost exclusively glucosinolate hydrolysis products. Water-soluble components also inhibited germination. Chemical analysis of extracts confirmed the presence of glucosinolate hydrolysis products, but indicated the involvement of additional allelochemicals, especially in leaf and stem tissues. Results support the proposal that glucosinolatecontaining plant tissues may contribute to reductions in synthetic pesticide use if weed seeds are targeted.

Effects of Plant Residue, Root Exudate and Juvenile Plants of Rapeseed (Brassica napus L.) on the Germination, Growth, Yield, and Quality of Subsequent Crops in Successive and Rotational Cropping Systems

“…Brown and Morra (1996) reported that the volatiles produced in intact roots of rapeseed inhibited the germination of lettuce seed by 70% on blotter paper (at a concentration of 5.5 g dry wt per 72.25 cm 2 ). The major glucosinolate in the roots was gluconasturtiin, (4.5 mol g -1 dry wt).…”

Glucosinolate Content in Rapeseed in Relation to Suppression of Subsequent Crop

“…Waligora (1996) reported that rapeseed GSLs reduced seed germination rate and seedling growth of lettuce. Brown and Morra (1996) reported that volatiles from intact roots (5.5 g in dry weight) of rapeseed inhibited the germination of lettuce. The germination rate was about 30% of control on 8.5-cm ×8.5-cm blotter paper (the area was 72.25 cm 2 ).…”

“…The experiments were conducted in a rotational paddy field in upland Composed from Brown and Morra (1996) and Vierheilig et al (2000).…”

“…In addition, volatilization of isothiocyanate (ITC), one of the GLS degradation products from turniprape mulch, in soil reduced weed seed germination (Peterson et al, 2001). Both volatile and water-soluble hydrolysis products of GSLs inhibited seed germination (Brown and Morra, 1996). Oleszek (1987) reported that volatiles from B. napus leaves inhibited the germination and the root growth of some weeds and crop plants, but did not study double-low cultivars or other plant parts.…”

Allelopathic Weed Suppression Through the Use of Cover Crops

“…Glucosinolates, secondary metabolites containing sulfur and nitrogen, are enzymatically hydrolyzed by myrosinase in the presence of water to form isothiocynates, the active allelochemicals (Haramoto and Gallandt 2005;Norsworthy and Meehan 2005;Petersen et al 2001;Price et al 2005). Previous research examining extracts from glucosinolate-producing plant species have shown inhibition of other species through reduced germination, reduced seedling emergence and reduced size, as well as delayed seed germination (Al-Khatib et al 1997;Brown and Morra 1996;Malik et al 2008;Norsworthy et al 2007;Wolf et al 1984). A l t h o u g h s p e c i f i c m o d e s o f a c t i o n h a v e n o t been thoroughly investigated for each compound, it is evident that some plant species are able to tolerate these allelochemicals more readily than other species (Norsworthy and Meehan 2005).…”