Growth and Vegetative Development
Lewis, Daniel , Spalding, Edgar .
Identification of an MDR1-dependent auxin transport stream required for normal cotyledon development in Arabidopsis.
The formation and subsequent development of cotyledons are dependent upon the distribution of the phytohormone auxin. During embryogenesis asymmetric localization of the auxin efflux complex directs auxin through the epidermis to the incipient cotyledon where it accumulates at the periphery and drives development. MDR1 is an ABC transporter that directly participates in and/or regulates auxin movement. In addition to previously described epinasty, mdr1 cotyledons appear smaller with less peripheral auxin-responsive promoter (DR5) activity. Localized auxin application experiments coupled with qualitative and quantitative observation of DR5 activity in wild type and mdr1 suggested that auxin is imported from the shoot apex through the cotyledon petiole in an MDR1-dependent manner to form the observed auxin accumulation pattern. This hypothesis was tested by applying radiolabeled auxin to a cut petiole and quantifying the radioactivity in the distal half of the cotyledon. mdr1 cotyledons transported 50% less auxin than wild type. This defect is correlated with a 60% decrease in the cotyledon enlargement rate. However, mean epidermal cell size was approximately 85% of wild type. These results demonstrate that cotyledon expansion depends on polar auxin transport to create a peripheral auxin accumulation zone that drives cotyledon growth. The 15% decrease in cell size at day 5 is insufficient to account for the difference in mdr1 cotyledon size at this developmental stage (45-50%). Therefore we infer that MDR1-dependant auxin transport causes peripheral auxin accumulation that affects cotyledon expansion primarily through its well documented impact on cellular division in aerial organs.
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1 - University of Wisconsin, Botany, B136 Birge Hall, 430 Lincoln dr., Madison, WI, 53703, U.S.A.
2 - University of Wisconsin, Botany, B135 Birge Hall, 430 Lincoln dr., Madison, WI, 53703, U.S.A.
MDR1 = PGP19.
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM