Assessment of the dose-dependent cytotoxic effects of L-homoarginine using onion root apical meristem

Homoarginine is a toxic non-protein amino acid that occurs naturally in plants and adversely affects plant growth and development. In this study, it was aimed to investigate the effects of different externally applied L-homoarginine doses (10, 50, and 100 mM) on various physiological, cytogenetic, biochemical, and anatomical parameters of onion (Allium cepa L.) bulbs. All L-homoarginine doses caused a decrease in the physiological parameters examined (germination percentage, root length, root number, and fresh weight), a rise in chromosomal aberrations and micronucleus frequency, and a decrease in the mitotic index. L-Homoarginine applications promoted chromosomal aberrations such as cellular budding, accumulation of micronuclei, C-metaphase, chromosomal stickiness, chromatid bridges, vagrant chromosomes, unequal separation of chromosomes, and polar slip in the root meristem cells. In addition, this non-protein amino acid caused an enhancement in the free proline, catalase, superoxide dismutase, and malondialdehyde contents in the root cells of onion bulbs. Moreover, this toxic amino acid revealed some serious damage and changes such as the epidermal and cortex cell deformations, wall thickening in the cortex layer cells, accumulation of some chemical compounds in cortex layer cells, flattening of the cell nuclei, and deformation of the cell nuclei in the anatomical structure of onion roots. In summary, it was concluded that L-homoarginine is an amino acid with inhibitory effects and that the A. cepa test is a useful bioindicator for monitoring these effects.