PRIMING-INDUCED METABOLIC CHANGES IN THREE ANNUAL MEDICS SPECIES IMPROVE GERMINATION AND EARLY GROWTH UNDER DROUGHT AND SALT STRESS CONDITIONS

摘要

The effects of seed priming chemicals such as urea and potassium nitrate on prolinecontent, germination and early growth characteristics of three annual medics plants under drought and salt stress were studied in controlled conditions during 2010-2011. Treatments consisted of stress type and intensity at five levels: moderate drought (MD), severe drought (SD), moderate salt (MS), severe salt (SS), and control (C, without stress). Seed priming was applied at threelevels: water (control), KNO_3 and urea. Three annual medics species {Medicago scutellata, M. rigidula and M. polymorpha L.) were used in the study. The results showed that the highest germination percentage (Ger %), germination rate (GR), seedling length (SL), radical length (RL) and seedling to radical length ratio (S/R) were achieved in control treatments while the highest proline and protein contents were measured in the severe drought treatment. Urea priming led to higher Ger %, GR, SL and RL followed by KNO_3 priming. Priming had no effect on S/R and proline content. Among the three annual medics species studied Medicago scutellata showed the highest Ger %, GR, SL, RL, proline and protein contents. Salt stress affected Ger %, GR and RL to a higher extent than drought stress whereas drought stress affected S/R more strongly than salt stress. Both types of stress decreased all measured parameters except for protein and proline contents that were increased remarkably. Drought stress increased proline content more strongly than salt stress. Generally, in both drought and salt stress conditions, potassium nitrate and urea led to increased Ger %, GR, SL and RL. Therefore, seed priming can be recommended to combat the effects of drought and salt stress.