Physiological and biochemical mechanisms of allelochemicals in aqueous extracts of diploid and mixoploid Trigonella foenum-graecum L.

This study was conducted to evaluate the effect of shoot aqueous extracts of diploid and mixoploid fenugreek at vegetative, flowering and fruiting stages on some physiological and biochemical processes in lettuce. The allelochemicals stress was registered as the result of aqueous extract application, which was added to the Hoagland nutrient solution at concentration corresponding to IC50 (50% inhibition of germination or root growth). The germination inhibition seems to be correlated with membrane deterioration as proved by a strong electrolyte leakage, increase in malondialdehyde (MDA) content, and mitochondrial respiration disruption due to a decrease in dehydrogenases activity. These disruptions were recorded with all test extracts, especially fruiting stage extract of diploid and mixoploid plants. For seedling growth inhibition, the roots showed the same interference, especially in the presence of aqueous extract of plant material harvested at the vegetative stage for diploid and at flowering of mixoploid plants. Chlorophyll content was slightly reduced while carotenoid content was significantly reduced. The lettuce seedlings have circumvented the allelochemicals stress, by i) increasing the phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activity, ii) accumulation of proline and iii) the production of secondary metabolites with antioxidant potent, such as polyphenols, flavonoids and alkaloids. The importance of these phenomenons varied with the extract origin and target organ, which is in favor of speculating on the allelochemicals specificity and on the change in the chemical composition of different extracts. Also, understanding of the different mechanisms of allelochemicals may provide a basis for the development of growth regulators and natural pesticides to boost up production in sustainable agriculture.