Cytogenetical and Physiological Effects of L-tryptophan in Onion ( Allium cepa L.) Exposed to Salt Stress
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Cytogenetical and Physiological Effects of L-tryptophan in Onion (Allium cepa L.) Exposed to Salt Stress Dilek Çavuşoğlu*, ** Department of Plant and Animal Production, Plant Protection Program, Atabey Vocational High School, Isparta University of Applied Sciences, Isparta, 32670 Turkey *e-mail: [email protected] **e-mail: [email protected] Received November 13, 2019
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. Keywords: L-tryptophan, mitotic index, seed germination, chromosomal aberrations, salt stress DOI: 10.3103/S1068367420040059
INTRODUCTION In most of the world’s arid and semi-arid regions, soil salinity is seen due to irrigating the crop with saline water or natural processes. 20% of the cultivated areas in the worldwide are negatively affected by high salt concentration, which inhibits plant growth and yield. Furthermore, the salinized areas are increasing at a rate of 10% annually. It has been estimated that more than 50% of the arable land would be salinized by the year 2050. Due to high water losses exceeding precipitation, salt concentration in the upper soil layer increases in dry areas and warm regions. To maintain agricultural sustainability and crop production, salinity stress is a fundamental issue to overcome in these regions [1, 2]. Tryptophan (Trp) is the largest and the most hydrophobic amino acid. Because of the structural similarities, this amino acid is commonly considered to be a precursor to IAA therefore, it also contributes actively in forming growth hormones (i.e. auxin) in plant
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