Abstract
The Arabidopsis loss-of-function mutant of MSG2/IAA19 is defective in tropistic responses of hypocotyl. We examined staining pattern of MSG2 promoter::GUS in 4-day-old etiolated seedlings in response to unilateral irradiation with 0.06 umol/m2/s blue light. Without the photostimulus hypocotyls of 83% seedlings were uniformly stained. However, number of seedlings with differential staining increased in proportion to phototropic curvature. After 24-hr stimulation, 58% of seedlings showed differential staining, which appeared to develop by disappearance of the staining mainly in epidermis and cortex of the irradiated side of hypocotyls. Similar results were obtained in gravitropism. Because it was difficult to detect change of staining with the 90° reorientation, seedlings were reoriented 135° to induce stronger gravitropism. After 24-hr stimulation, 49% of seedlings exhibited differential staining. We also carried out the same experiments with the DR5::GUS seedlings. GUS staining was too faint to detect asymmetric staining in this case.
