Response of Thmarindus indica L. to iso-osmotic solutions of NaCl and PEG during germination

The effects of reduced external water potentials (0, -0.3, -0.6, -0.90 and -1.30 MPa) generated by either NaCl or polyethylene glycol-6000 (PEG) on water uptake and germination characteristics of Tamarindus indica seeds were investigated under laboratory conditions. Water uptake and final germination percentage (G(F)) decreased, while number of days to 50% germination (D-50) and mean germination time (MGT) increased significantly with reducing osmotic potentials of both NaCl and PEG. At each iso-osmotic solution, PEG appeared to be more inhibitory to water uptake than NaCl, especially at the lowest water potential (-1.2 MPa). At this water potential, no germination was observed in both NaCl and PEG solutions. At all other treatments, NaCl resulted in lower G(F), and higher D-50 and MGT values than did iso-osmotic solutions of PEG. These results suggest that the main effect of PEG occurred via an inhibition of water uptake while detrimental effects of NaCl may be attributed mainly to accumulated toxic ions.