Betaine accumulation in salt-stressed sorghum

Two analytical methods for measuring betaine were compared in a study of betaine accumulation in salt-stressed sorghum. Spectrophotometric determination of betaine as the p -bromophenacyl ester is highly sensitive and specific. However, a periodide assay was found to be more convenient for screening numerous plant samples without undue sacrifice in accuracy.
The accumulation of betaine in grain sorghum [ Sorghum bicolor (L.) Moench] cvs NK 265 and Double TX was measured in salt-stressed plants grown hydroponically and in the field and in drought-stressed potted plants. Neither drought nor mild salinity (-0.2 MPa) stress was effective in stimulating betaine accumulation. However, when the osmotic potential of the culture solution was lowered to -0.8 MPa, betaine levels in the shoots rose rapidly for 12 days after initiation of salination, and then declined, apparently because of dilution by plant growth. In young leaf blades, betaine was strongly accumulated up to 70–75 μmol (g dry weight)⁻¹; the concentration in leaf sheaths was less than 6 μmol (g dry weight)⁻¹.
In the field, betaine levels in salt-stressed sorghum increased 6- to 7-fold over the basal level of the control plants. In a comparable study of two wheat species ( Triticum aestivum L. cv. Probred and T. durum Desf. cv. 1000-D), betaine increased only 3- to 4-fold over unstressed plants.