The effects of gibberellic acid (GA 3 ), kinetin (KIN), benzyladenine and ethylene (E) on mitotic activity and chromosomal aberrations in root tips of barley seeds (Hordeum vulgare L. cv. ''Bülbül 89'') germinated under salt stress were investigated. It was determined that all of these plant growth regulators (PGRs) decreased mitotic index in root tips of barley seeds germinated at 20°C and in distilled water. Furthermore, some of the PGRs studied increased significantly the frequency of chromosomal aberrations. The frequency of chromosomal aberrations in seeds treated with E and KIN was considerably higher than in the seeds germinated under nonstress conditions. The inhibitory effect of salt stress on mitotic index increased with increasing salt concentration (0.30, 0.35, 0.40 and 0.45 molal, m). GA 3 and KIN pretreatments showed a successful performance in ameliorating the negative effects of increasing salinity on mitotic activity. The number of chromosomal aberrations also increased with increasing NaCl concentration. However, most of the PGR pretreatments studied alleviated the detrimental effects of increasing salinity on chromosomal aberrations. KIN pretreatment at 0.30 and 0.35 m salinity could not rescued the cytogenetic activity of salt stress on this parameter.

Cytogenetic response of 24-epibrassinolide (EBR) and different NaCl concentrations (0.30, 0.35 and 0.40 M, molar) on root meristem cells of barley were analysed. Plants grown on media containing 0.30, 0.35 and 0.40 M NaCl showed a significant decrease of mitotic index and higher number of chromosomal abnormalities as compared to those of control conditions. Also, the mitotic index approximately 50% decreased in EBR-treated samples and chromosomal abnormalities almost tipled those of control. EBR pretreatment in higher concentrations of salt (0.40 M NaCl) caused total inhibition of mitotic activity in roottip cells. However, comparison of all concentrations of salt and control revealed to have a successful performance in ameliorating of the detrimental effects of salinity on chromosomal abnormalities.

The effects of exogenous polyamines (PAs): spermine (Spm), spermidine (Spd), cadaverine (Cad) and putrescine (Put) on mitotic activity and chromosomal aberrations in root meristem cells of Hordeum vulgare L. (barley) seeds exposed to salinity were analyzed. The PAs significantly inhibited cell division in distilled water. Furthermore, most of these PAs (except for Spd) caused a significant increase in the frequency of chromosomal aberrations as compared to control group. Seeds treated with Put caused the highest percentage of mitotic abnormalities in total. The negative effect of salinity on mitotic index and the frequency of chromosomal aberrations increased with increasing salt concentration. PAs studied could not be successful in ameliorating of the negative effect of salinity on mitotic activity. Particularly, exposure to Cad and 0.40 M NaCl caused a complete block of cell division in total. However, most of the PA studied showed a perfectly performance in alleviating the detrimental effects of increasing salinity on chromosomal aberrations.

doi:10.3906/bot-1311-3

SummaryThe present study was performed to evaluate the role of Aloe vera L. leaf extract (AvLE) on some physiological and cytogenetical parameters of Allium cepa L. seeds exposed to salinity. The radicle length of the seeds germinated in the medium with AvLE alone increased as compared with ones of the control seeds germinated in distilled water medium, while their radicle number and fresh weight reduced according to the control. In addition, the germination percentage of the mentioned seeds statistically was the same as the control seeds. Furthermore, the seeds germinated in the media containing 0.1 mg/L AvLE alone showed a significant increase of mitotic index, although they exhibited a higher number of chromosomal aberrations and micronucleus (MN) formation as compared with the seeds germinated in control conditions. On the other hand, salt stress considerably inhibited the seed germination and seedling growth of A. cepa. Moreover, salinity markedly decreased the mitotic index in root tip meristems of the seeds and increased the number of chromosomal aberrations. The negative effect of salt on the seed germination, seedling growth, mitotic activity and MN formation was alleviated in dramatically varying degrees by AvLE application. In contrast, the detrimental effects of salt on the chromosomal aberrations greatly increased with this treatment. Consequently, we reported that the application of AvLE alone induced chromosomal aberrations and MN formation, which are an indicator of genotoxicity, and had cytotoxic activity in normal conditions. However, the frequency of MN is greatly reduced in root tip cells of the seeds germinated in the medium containing 0.1 mg/L AvLE +0.15 M NaCl.

The effect of exogenous hydrogen peroxide (H 2 O 2 ) on mitotic activity and chromosomal aberrations in root tip meristems of barley (Hordeum vulgare L. var. Tokak 157/37) germinated under salinity was analyzed. The inhibitory effect of salinity on mitotic index and the frequency of chromosomal aberrations increased with increasing salt concentration (0.00 control, 0.35, 0.40, 0.45 M, molal NaCl). The frequency of chromosomal aberrations of seeds germinated in medium with 0.40 M NaCl after pretreatment with H 2 O 2 (30 lM, micromolal) was significantly higher than the control group. The highest concentration of NaCl (0.45 M) together with H 2 O 2 caused total inhibition of germination. In this study, the intention was to determine the performance of H 2 O 2 in alleviating detrimental effect of salt stress on mitotic activity and chromosomal aberrations. However, H 2 O 2 did not reduce the detrimental effect of NaCl on these parameters. Also, it caused higher chromotoxic effect compared to those of control groups.

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