Shelves and other load supporting panels are releasably mountable between pairs of uprights by sandwiching the rear ends of the panels between an upper, rear mounting bracket and a lower, forward mounting bracket at each end of the panels. Each pair of upper and lower mounting brackets are mounted to an upright so as to be in opposed facing relation to another pair of upper and lower mounting brackets or an adjacent upright. A protuberance on one mounting bracket of each pairs engages into a corresponding indentation on the panel to prevent the panel being inadvertently slid outwardly horizontally from its position cantilevered from between the uprights.