Abstract

Salinity is one of the major environmental stress factors that cause many adverse effects on growth and productivity of plants. The objective of the present study was to investigate the effects of salinity levels on seed germination indices and protein patterns in Melissa offcinalis seedlings. An experiment was carried out based on randomized complete block design with five concentrations of NaCl and four replicates with sand medium. The results indicated that salt stress had negative effects on the seed germination percentage (GP), mean germination time (MGT) and germination rate (GR), primary shoot and root length, as well as the protein content. After two days of salt exposure, the lowest (0%) GP was obtained for seeds treated with 12 dSm^-1 salinity, as compared to the control (48.5%). Although, high salinity levels delayed seed germination, but during the experimental period GP increased and no significant differences were observed among the treatments in terms of GP after two weeks. The highest MGT (4.97 days) was obtained for plants stressed with 12 dSm^-1 salinity level, as compared to the control (1.89 days). Analysis of the protein bands revealed that salinity suppressed the expression of two proteins with the size of 45 (Y1), and 40 kDa (Y2) and protein of 60 kDa (D1) was down-regulated. Also, the synthesis of four proteins of 70 (X1), 30 (X2), 25 (X3), and 20 kDa (X4) was induced in the seedlings under salinity stress. The changes in protein pattern under salinity stress indicated that the synthesis of new proteins may be associated to the stress specific proteins.

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