Genotypic Responses in Sorghum to Drought Stress. III. Free Proline Accumulation and Drought Resistance1

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Abstract
We explored a possible association between free proline amino acid accumulation in water‐stressed leaves and the drought resistance of various grain sorghum [Sorghum bicolor (L.) Moench] cultivars.Eight sorghum cultivars were grown in a growth chamber under a drying cycle (to a leaf water potential of −18 to −21 bars) and a subsequent recovery phase. Free proline, free ammonia, dark respiration rate, and recovery rating were recorded, as well as desiccation tolerance of each cultivar when grown in the field.Free proline accumulation was initiated in leaves of all cultivars as leaf water potential was reduced to −14 to −16 bars. Free ammonia concentration in leaves of all cultivars did not change appreciably during the drying cycle. Upon rewatering, free proline content was reduced and free ammonia concentration was increased, both rather abruptly. Cultivars difered significantly in maximum free proline accumulation and post‐stress free ammonia concentration, dark respiration rate, and recovery rating.Correlations indicated that desiccation tolerance was not related to any of the attributes measured, or even to recovery rating. Free proline accumulation during water stress was correlated significantly with post‐stress recovery rating, free ammonia concentration, and dark respiration rate.It is suggested that accumulated free proline in water‐stressed sorghum leaves is related to the ability of a cultivar to recover upon the relief of stress, possibly by way of proline's role as a source of respiratory energy in the recovering plant.