Proline accumulation in response to dehydration and diurnal hydration cycles varies among maize genotypes

Proline is a compatible solute that may help plants adapt to water stress b y preserving enzyme activity in desiccated tissues. To learn about the gene tic variation of proline accumulation that occurs with rapidly developing w ater stress or diurnal water stresses, 21 field-grown maize (Zea mays L.) g enotypes were evaluated for free proline concentration in leaves before and after detachment and dehydration. Genotypes differed significantly for pro line accumulation in the detached leaves which varied from 58 to 208% over initial concentrations. Within sampling times proline concentration was nor significantly correlated with relative water content (RWC) or solute poten tial normalized for RWC (Psi (s100)). In a related experiment, six maize ge notypes received well-watered and water-stressed treatments. These included four topcrosses selected from the first experiment and two hybrids known t o differ for response to water stress. Determinations were made of free pro line concentration, RWC, and Psi (s100) on attached leaves at the beginning ("dawn") and after 9 to 10 h of the 16-h photoperiod ("midday"). Proline c oncentrations ar dawn and midday varied in genotype-specific patterns. Leaf proline concentration was negatively correlated with dawn (r=-0.41**, P le ss than or equal to0.01) and midday (r=-0.28*, P less than or equal to0.05) RWC of plants in the water-stressed treatment, but not in the well-watered treatment. Final shoot weight of plants in the water-stressed treatment wa s negatively correlated with dawn proline concentration (r=-0.31*) but not midday proline concentration. Comparing the two hybrids chosen for their di fferent water stress responses, the water-stress sensitive hybrid had a sig nificantly lower final shoot weight and a significantly higher midday proli ne concentration. Generally, proline concentration did not appear to be a r eliable predictor of water-stress tolerance in maize.