BUZZ-LSE: best day in 7 yrs, in talks with Deutsche Boerse-sources
** London Stock Exchange (Other OTC: LDNXF - news) turns positive, +12.6%, poised for biggest one-day rise since March 2009 and easily top of FTSE 100 riser
** LSE and Deutsche Boerse (LSE: 0H3T.L - news) exploring a possible merger, company and financial sector sources say
** Deutsche Boerse shares +3.9%
** Source tells Reuters talks between cos at an early stage
** Both cos were earlier trading down, in line with the broader market (venkateshasoumithri.mamidipudi.thomsonreuters.com@reuters.net)