Cytogenetical and Physiological Effects of L-tryptophan in Onion (Allium cepa L.) Exposed to Salt Stress

Abstract

In this study, 10 mg L–1 L-tryptophan effects on the seedling growth (fresh weight, radicle length and radicle number), seed germination, chromosomal aberrations and mitotic activity in Allium cepa L. germinated in salinity (0.175 M NaCl) conditions were investigated. In only L-tryptophan medium, the radicle length and radicle number of the seedlings were partially reduced compared to the control seedlings grown in the pure water medium, the germination percentage and fresh weight indicate statistically the same values as the control. Moreover, the chromosomal aberrations and mitotic index in the root tip meristem cells of Allium cepa seeds germinated in alone L-tryptophan medium showed increase compared to the control seeds germinated in the pure water medium. On the other hand, salt stress significantly inhibited the germination rate, radicle length, radicle number and fresh weight of Allium cepa L. In addition, it important reduced the mitotic index (activity) and increased the chromosomal aberrations in root tip meristems of the seeds. Nevertheless, the inhibitory effects of salt stress on all the mentioned parameters were dramatically alleviated by L-tryptophan application. The germination percentage, radicle length, radicle number, fresh weight, mitotic index and chromosomal aberrations of the seedlings grown in 0.175 M salinity were 23%, 10.3 mm, 12.7, 7 g, 1.2 and 17% respectively, while these values became 77%, 15.3 mm, 16.7, 15.2 g, 11.6 and 14.6% in the seedlings treated with 10 mg L–1 L-tryptophan.