Investigation on the effect of benzyladenine on the germination, radicle growth and meristematic cells of Nigella sativa L. and Allium cepa L.

The effect of different benzyladenine (BA) treatments which is a phyto-regulator or plant hormone on the cytology and growth of Nigella sativa L. (Black seed) and Allium cepa L. (onion) were investigated. Six concentrations of benzyladenine ranging from 5 to 55 ppm were applied for 6, 12, 18, 24, 36 and 48 h. The treatments elevate the germination percentages of Nigella sativa L. and Allium cepa L. and increase the root growth of both plants. In contrast concentrations higher than 60 ppm for 48 h were caused an inhibition effect for both plant. The root growth initiation was concentration and/or time dependent. The applied concentrations of BA showed a promotor effect on cell division in root tips of both plants and caused an increase in their mitotic index values (MI). The elevation in MI values in root tips of Nigella sativa L. was more evident than that of Allium cepa L. All treatments changed the frequency of mitotic phases as compared with the control values. All the applied concentrations of BA significantly induced a number of chromosomal aberrations in root tip cells of Nigella sativa L. and Allium cepa L. The total percentages of abnormalities in Nigella sativa L. root tip cells were more than that in Allium cepa L. with all concentrations of BA. The most dominant types of observed abnormalities were stickiness, bridges, and C-mitosis. BA treatments produced a number of mitotic abnormalities in dividing cells in root tips of both plants resulting from its action on the spindle apparatus such as C-mitosis, lagging chromosomes and multipolar at ana-telophases. Also, BA induced vacuolated nuclei and irregular prophases. The induction of chromosomal stickiness and chromosomal aberrations such as bridges indicates its action on the chromosome. Also, the induced chromosomal bridges at ana-telophases indicates true clastogenic potential of this chemical. It may be concluded that BA causes toxic effect on root tip cells of Nigella sativa L. and Allium cepa L. and this toxicity induces different types of genic and chromosomal variations.