Seed vigor may be determinant for field performance, especially under water

restriction conditions. Sunflower is a crop subject to these conditions in the field and, therefore,

the aim of this study was to evaluate the physiological and antioxidant changes in sunflower

seeds under water restriction. Two lots of sunflower seeds (cv. Hélio 253) with different vigor

levels were used. After initial characterization, seeds were placed to germinate under water

potentials of 0.0, -0.2, -0.4, -0.6 and -0.8 MPa and evaluated by tests of germination, first

germination count, shoot length and primary root length. The activities of the antioxidant

enzymes SOD, CAT, POX and APX were also evaluated at 0, 2, 4 and 6 days after sowing. Water

restriction led to a decrease in germination and slower seedling growth, regardless of seed

vigor level. SOD activity was similar in the two lots, with reduction in activity four days after

sowing. CAT activity was affected differently during germination in the two lots, and it was

generally higher in the most vigorous lot. In higher vigor seeds, there was lower POX activity

in water restriction treatments compared to the control. In general, seeds of lower vigor have

lower capacity for activation of antioxidant enzymes, especially peroxidases.