Genetic variability in recovery growth and synthesis of stress proteins in response to polyethylene glycol and salt stress in finger millet

Abstract

Marked differences were found among 28 finger millet genotypes (Eleusine coracana Gaertn.) in acquired tolerance to osmotic stress as assessed by the recovery of root growth from severe stress [-1.2 MPa polyethylene glycol, (PEG) or 400 mM NaCl]. However, these differences in tolerance were observed only when the seedlings were subjected to a preceding mild induction stress (-0.6 MPa PEG or 200 mM NaCl). In two contrasting genotypes, synthesis of stress-induced proteins was studied. Proteins with apparent molecular weight of 70-72, 52, 37, 34 and 23 kDa were synthesized in the highly responsive genotype (GE 415) and poorly responsive (VL 481) genotype following a mild induction stress (200 mM NaCl). However, GE-415 synthesized a 54 kDa protein that was not observed in VL-481. Addition of abscisic acid (ABA) to the induction medium containing 200 mM NaCl enhanced the acquired tolerance of finger millet seedlings over those without ABA in association with the appearance of several ABA-responsive proteins. GE-415 required much less ABA than VL-481 to obtain the same response. With 10 μM ABA + 200 mM, A NaCl induction stress, GE-415 had significantly higher endogenous ABA. In association with higher levels of ABA, GE-415 had greater recovery root growth following severe stress from 600 mM NaCl. Pretreatment with 10 μM ABA + 200 mM NaCl induced several proteins with apparent molecular weights of 70-72, 54, 45, 36, 29 and 21 kDa in both genotypes. Qualitatively, GE-415 synthesized a unique 23-24 kDa protein and quantitatively there was significantly more of the 21 kDa protein in GE-415 compared to VL-481. The results indicate that the synthesis of stress proteins is correlated with the observed variation in acquired tolerance of the two genotypes.