An image orientation is subject to its photographer. One thing I thoroughly enjoy about abstract macro is there are no rules for orientation like in landscape or portrait photography. If there are strong vertical lines, present it vertically. If the shadows work better presented upside down - do it. It is up to you the photographer to decide. There are times I am unsure of a photo I have taken and will rotate it in all orientations to find the most dramatic composition. In abstract macro, your final image is more about the creative concept and less about what object was photographed.