Molecular, biochemical and physiological responses of sorghum to pre-flowering drought stress: The role of dehydrins, glycinebetaine and osmotic adjustment as protective mechanisms
Abstract
Sorghum, Sorghum bicolor (L.) moench, is an important agricultural plant and is one of the most drought tolerant grain crops. Sorghum possesses various mechanisms which enable the plant to not only survive, but thrive, under conditions deleterious to other crop plants. Sorghum, therefore, is an excellent model plant for studying the complex phenomenon of drought tolerance. Two important, protective mechanisms are the accumulation of compatible organic solutes and the induction of protective gene products. The effect of drought stress was compared between a drought-tolerant (P954035) and drought-susceptible (P721N) sorghum genotypes. Gas-analysis and leaf water potential ($\Psi\sb{\rm w}$) measurements indicate clear phenotypic differences between the genotypes. Labeling studies with ($\sp{35}$S) -methionine and western blot analysis (using an anti-dehydrin antibody) identified a drought stress-inducible 21 kDa protein. A sorghum dehydrin cDNA, DHN1, was isolated from drought stressed sorghum seedlings and characterized. DHN1 encodes a small, hydrophillic protein of approximately 16.3 kDa. DHN1 mRNA expression and the accumulation of dehydrin protein in response to drought stress were investigated in sorghum seedlings and mature sorghum plants. The accumulation of glycinebetaine is induced by drought stress in sorghum. Two sorghum cDNA clones (BADH1 and BADH15) encoding betaine aldehyde dehydrogenase (BADH) were isolated and characterized. BADH1 is a truncated cDNA 1376 bp in length. BADH15 is a full-length cDNA clone predicted to encode a protein of approximately 53.6 kDa. The predicted peptide sequences of BADH1 and BADH15 share significant homology with other plant BADHs. The effects of pre-flowering drought stress upon BADH mRNA expression, leaf water relations, solute composition and osmotic adjustment (OA) were investigated in mature sorghum plants (P954035). In response to drought stress, proline levels increased 108-fold and glycinebetaine levels increased 26-fold. BADH1 and BADH15 mRNA are both drought stress-inducible and the expression correlates with the observed glycinebetaine accumulation. Accumulation of these compatible solutes contributes to osmotic potential ($\Psi\sb\pi$) and allowed P954035 to develop a maximal OA of 0.405 MPa. Finally, a restriction fragment-length polymorphism (RFLP) associated with BADH1 was mapped in Zea mays to the centromere of chromosome 4. The locus was designated bet2.
Degree
Ph.D.
Advisors
Goldsbrough, Purdue University.
Subject Area
Botany|Molecular biology
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