| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1998: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1997: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
We isolated an Arabidopsis mutant, msg1, which was defective in growth curvature response of hypocotyl induced by unilateral application of auxin. Msg1 was found allelic to the nonphototropic mutant, nph4 (Liscum and Briggs, 1995). msg1 hypocotyls were impaired in gravitropism as well as the auxin-induced growth curvature and phototropism ; they were resistant to auxin. msg1 was similar to wild type in shape except for epinastic or hyponastic rosette leaves. These results indicate that msg1 is defective in auxin-specific growth curvature responses. We checked many growth mutants of Arabidopsis with respect to the auxin-induced growth curvature response. But, we found that only axr1 lacked the growth response. Axr1 hypocotyls were impaired in both gravitropism and phototropism, indicating that axr1 was another auxin-specific growth curvature mutant. in order to determine the relationship between MSG1 and AXR1 in the auxin-dependent growth curvature response, we constructed a double muta
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nt between msg1 and axr1, and measured its growth curvature responses. Both msg1 and axr1 single mutants lost phototropism of hypocotyl partially ; msg1 axr1 double mutants displayed no phototropism of hypocotyl. Gravitropism of both single mutants was affected partially ; defects in hypocotyl gravitropism of the double mutant were larger than those of either single mutant. Axr1 rosette leaves were wrinkled, while msg1 leaves were epinastic ; leaves of msg1 axr1 double mutant were wrinkled and epinastic. These results indicate that effects of mutations in msg1 and axr1 were additive. In other words, we can conclude that MSG1 and AXR1 act independently in auxin-specific growth curvature responses.
We also investigated effects of indole-3-acetic acid, 2,4-dichhlorophenoxyacetic acid and 1-naphthaleneacetic acid on abberant gravitropism of aux1 roots. It was found that only an addition of naphthaleneacetic acid restored aux1 gravitropism. This finding as well as the predicted amino acid sequence of AUX1 protein Q3ennett et al., 1996) indicates that A UX1 probably encodes an auxin influx carrier. Less
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