Among the stock activity stories for Wednesday, Sept. 9, from AP Financial News:

NEW YORK (AP) ¿ Shares of medical device maker Stryker Corp. rose after a Deutsche Bank analyst upgraded the stock to "Buy" from "Hold."

NEW YORK (AP) ¿ Educational services provider K12 Inc. tumbled more than 14 percent in afternoon trading, making it the biggest decliner on the New York Stock Exchange in percentage terms, after issuing disappointing guidance for fiscal 2010.

SCOTTSDALE, Ariz. (AP) ¿ JDA Software Group Inc. said it has repurchased all of its series B convertible preferred stock.

NEW YORK (AP) ¿ Shares of Hutchinson Technology Inc. soared after the company released upbeat preliminary fourth-quarter results.

MILWAUKEE (AP) ¿ Shares of Cott Corp. rose sharply after an analyst upgraded the company's stock to "Buy", saying the private-label beverage manufacturer has more financial flexibility.

NEW YORK (AP) ¿ Shares of eBay Inc. gained after Sanford Bernstein upgraded the stock, pointing to improvements in the company's core online marketplace business, positive signs for used car sales and the proposed sale of Skype, the online telecommunications service.

SIOUX FALLS, S.D. (AP) ¿ Shares of DuPont Co. edged lower after a Goldman Sachs analyst downgraded the stock, saying it appears fairly valued.

NEW YORK(AP) ¿ Shares of Casey's General Stores Inc. rose after the convenience-store operator said first-quarter results came in above analyst expectations.

Copyright 2009 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.