plt1 = plot(x1,y1,'-r','LineWidth',3,'Marker','.','MarkerEdgeColor','r');
When you plot() a vector of one variable against a constant in the other, plot creates a line object for each element of the vector and a single pixel marker simply isn't large enough to show up; there is no line created because there are (in this case 5) separate line objects, each consisting of only a single point.
You also have the sequence of commands in wrong order; or you need a hold on first after setting the axes limits and orientations or plot will cause refreshing the limits of the plot to match the plotted data.
If you want to plot a single vertical or horizontal line; the xline or yline functions are the better way to do so; they're relatively recent but get around the need to duplicate the constant data value manually (but cross the entire axis in extent so not helpful here -- Addendum/Correction --dpb)
Try something more like
xlim([0 361]),ylim([0 361])
and joy should ensue.