Physiological responsees of corn and grain sorghum under moisture stress and during rewatering

Grain sorghum (Sorghum bicolor (L.) Moench) and corn (Zea mays L.) seedlings were grown hydroponically for two weeks in a growth chamber. Moderate and severe moisture stress treatments were then applied to the plant roots by additions of polyethylene glycol to the growth media. After six days of moderate and three days of severe moisture stress, the osmotica were replaced with nutrient solution only. Changes in shoot length, weight, leaf water potential, and protein, nucleic acid and carbohydrate content were measured prior to, during and following exposure to moisture stress conditions. The effects of moisture stress and rewatering on these parameters were compared within and between species in an attempt to learn more about the species' drought resistance. Grain sorghum seedlings exhibited larger reductions in leaf water potentials during stress periods than corn. Shoot elongation was re-tarded more in corn by smaller decreases in leaf water potential than in sorghum. Dry matter and protein accumulations of grain sorghum were not affected during the moderate stress period but were significantly reduced in corn. Dry matter and protein accumulations were reduced the same in both species during the severe stress period. Upon rewatering, the leaf water potentials of both species returned to normal. Dry matter and protein accumulations following exposure to moderate stress were the same in both species. Dry matter accumulations were the same in both species during and following exposure to severe stress, however, protein concentrations were lower in sorghum than in corn. Total RNA and DNA contents per unit dry weight were not affected by either moisture stress or rewatering. Water stress had no consistent effect on either total sugar or total nonstructural carbohydrate content of either species. The internal water status of grain sorghum appeared to be characteristic of a drought resistant plant species. Growth responses following exposure to water stress were the same in both com and grain sorghum. Total RNA and DNA concentrations were not affected by moisture stress conditions in either species, but protein concentration was affected more in sorghum than corn during recovery from severe stress. No major biochemical differences were found between corn and grain sorghum that would explain sorghum's greater ability than corn's to resist drought under natural conditions.