Seeds germination and shoot growth responses of a threatened poaceae (Cenchrus ciliaris L.) to increasing salt stress

Abstract

Cenchrus ciliaris L. (Buffel Grass), a perennial Poaceae, is a threatened species in arid regions of Tunisia. In the present work, involvement of soil salinization on its scarcity is evaluated through studying seeds germination and shoot growth ability under NaCl stress (0, 50, 100, 200 and 300 mM). Our results showed that at moderate stress including 50 and 100 mM NaCl, C. ciliaris sustained sufficient germination capacity (GC), adequate germination mean time (GMT ) and recovery aptitude (13 %) after transferring seeds to distilled water. Shoot growth was reduced to 50 % by 50 and 100 mM NaCl treatments relative to control, inducing neither lipid oxidation nor tissues dehydration. Salt-induced stimulation of gaïacol peroxidase (GPX, EC. 1.11.1.7) activity seemed to be efficient against oxidative stress. Severe stress, including 200 and 300 mM NaCl, lengthened seeds dormancy, decreased GC and germination rate (increasing GMT) with low germination recovery. While plant growth was not severely affected, increasing malonydialdehyde (MDA) production indicated that 200 and 300 mM NaCl provoked lipid oxidation and that GP X could no longer overcome oxidative stress. It seems that soil salinization with doses greater than 100 mM NaCl may contribute to C. ciliaris scarcity by lowering germination capacity and seedlings growth and establishment.