The Pro Arte Quartet concert Saturday night in the Wisconsin Union Theater was among the most poignant of this year?s centennial performances. According to Union Theater director Ralph Russo, an early iteration of the Pro Arte helped open the theater 73 years ago, at a spring arts festival. (The theater will soon close for a two-year renovation, set to be complete in fall 2014.) After a discussion with guest composer William Bolcom and New York Times music critic Anthony Tommasini, the concert itself opened with a dedication to violist James Crow.