Biochemical composition of Tunisian Nigella sativa L. at different growth stages and assessment of the phytotoxic potential of its organic fractions

The present study was conducted to study some biochemical characteristics of Tunisian Nigella sativa at different developmental stages of plant growth (vegetative, flowering and fruiting stages) and to screen the chemical constituents and the phytotoxic activity of their organic extracts on lettuce (Lactuca sativa L.). The GC-MS analysis of petroleum ether fractions revealed that N. sativa seeds were rich in linoleic acid (58% of total fatty acids), oleic acid (22% of total fatty acids) and palmitic acid (12% of total fatty acids). The fatty acid composition of aerial parts showed an increase in the level of saturated fatty acids accompanied by a concomitant decrease of polyunsaturated fatty acids levels during the developmental stage. The phytochemical investigation showed that among the organic extracts, the methanolic extract from aerial parts harvested at the fruiting stage contained the highest amounts of phenolic and flavonoid compounds. The phytotoxic study revealed that N. sativa negatively affected the growth of lettuce plants. This effect was largely dependent on the developmental stage at which material was collected and the nature of extracting solvent. The methanolic extract of aerial parts harvested at the vegetative stage was the most active on seedling growth of lettuce.