Analysis of glycinebetaine accumulation and its relation to salinity tolerance in sorghum
Abstract
Ultimately, if a plant is to survive prolonged exposure to osmotic stress, it must lower its cellular osmotic potential to equal that of the external environment. This can be achieved by the synthesis of compatible solutes. Glycinebetaine (GB) is a compatible solute produced in a number of plant families, including some grasses such as sorghum (Sorghum bicolor L. Moench). A recombinant-inbred (RI) population was developed from a cross between a GB-deficient (IS2319) and a GB-accumulating (P932296) lines of sorghum. Chi-square analysis of GB levels within both the F5and F7:8 generations indicated higher than expected numbers of GB-accumulating lines. When grown under controlled conditions, GB accumulation levels varied as much as 10-fold within these populations, suggesting genetic control not only of the presence of GB, but also of level. We tested this hypothesis by analyzing individual plants from lines determined to be low-, medium-, or high-accumulating GB lines in the RI screens. This analysis demonstrated a conserved level of GB accumulation within lines. From the RI population, two pairs of near-isogenic lines (NILs) were developed. The homogenisity of the GB trait and the isogenicity of the NILs was confirmed with progeny tests and RAPD analysis, respectively. The deficiency in GB accumulation appears to be at the choline oxidation step, based on labeling studies conducted with the NILs and parents of the population. Although salinity tolerance (based on physiological measurements) was consistently greater in the GB-accumulating parental line (P932296) than the GB-deficient parent (IS2319) in several experiments, this tolerance was not displayed in GB-accumulating lines of the RI population or in the GB-accumulators within the NIL pairs. This lack of tolerance could be attributed to inappropriate genetic backgrounds for those plants in which the GB trait was expressed. This is unlikely, however, due to the number of lines examined (eight RI lines and two pairs of NILs), and the lack of tolerance is more likely an indication of the small contribution of GB to salinity tolerance relative to other tolerance mechanisms in this species or inappropriate environmental conditions to allow expression of GB-mediated tolerance.
Degree
Ph.D.
Advisors
Goldsbrough, Purdue University.
Subject Area
Botany
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