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United States Department of Agriculture

Agricultural Research Service

Title: Delay of Leaf Senescence in Transgenic Alfalfa Plants Expressing a Gene for Cytokinin Biosynthesis

Authors
item Samac, Deborah
item Gan, Susheng - UNIVERSITY OF WISCONSIN
item Amasino, Richard - UNIVERSITY OF WISCONSIN

Submitted to: Keystone Symposia on Molecular and Cellular Biology
Publication Type: Abstract Only
Publication Acceptance Date: April 7, 1997
Publication Date: N/A

Technical Abstract: Significant yield losses can occur in alfalfa (Medicago sativa) stands due to defoliation caused by leaf senescence and foliar diseases. Leaf senescence is a type of programmed cell death that is affected by environmental conditions and infection by pathogens. We have tested the effect of expression of isopentenyl transferase (IPT), a key enzyme in cytokinin biosynthesis, on leaf senescence and disease resistance in alfalfa. Detached alfalfa leaves floated on water in darkness rapidly lost chlorophyll compared to control leaves held in the light. Application of 0.01 mM kinetin to dark treated leaves delayed chlorophyll loss. Transgenic alfalfa plants containing a chimeric gene composed of an Arabidopsis senescence specific promoter (SAG12) fused to the IPT coding region or the SAG12 promoter fused to beta-glucuronidase (GUS) were generated. Little to no GUS activity was observed in transgenic alfalfa plants indicating that the promoter is not highly active in this heterologous host. However, several plants containing the SAG12-IPT construct displayed a delay in leaf senescence. Detached leaves held in darkness retained twice as much chlorophyll as leaves from control plants. These plants are phenotypically normal except for a significant increase in stem number and a delay in flowering compared to control plants. The effect of this construct on resistance to several diseases and on forage yield and quality will be presented.

Last Modified: 10/1/2014
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