|Stephens, Brian - BAYLOR COLLEGE OF MED|
|Cook, Douglas - TEXAS A&M UNIVERSITY|
|Penmetsa, R - TEXAS A&M UNIVERSITY|
Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 1998
Publication Date: N/A
Technical Abstract: We wish to understand processes of micronutrient metal homeostasis in higher plants and have found that metal mutants provide useful tools. Screening for metal hyperaccumulators is fairly easy because leaf metal toxicity results in readily visualized necrotic lesions. However, in order to achieve toxic levels, sufficient metal influx must occur via the roots. Thus, we have searched for a plant model in which a large portion of the root system is involved in metal influx. Medicago truncatula is a diploid autogamous legume species with a short generation time and a small genome size that has been proposed as a model genetic system. In M. truncatula, we found that Fe acquisition processes can be induced throughout much of the root system in response to Fe-deficiency. This differs from that in Arabidopsis, where Fe acquisition processes are localized only to regions near the root apices. Based on these results, our initial screen was focused on the identification of Fe mutants. Our screening procedure has been to grow M2 mutant plants to 4 weeks of age in vermiculite fertilized with a complete nutrient solution containing 100 uM Fe(III)-citrate. A screen of 3000 mutants yielded 5 plants with severe leaf necrosis; in all cases, leaf concentrations of Mn and Zn (but not Fe) were elevated 10- to 15-fold relative to wildtype. Transferring plants to hydroponic media with low levels of Mn and Zn accelerated plant growth and reduced the level of necrosis. M3 plants derived from each of the mutants also showed the necrotic phenotype. We will present an overview of our screening protocol and will provide mineral analysis, genetic, and physiological data on the metal hyperaccumulators. This work was funded by USDA-ARS Cooperative Agreement No. 58-6250-1-003.