1. There are a lot (I mean A LOT) of areas in Plant Science. For examples, plant molecular biology, plant breeding, plant genetics, plant cell biology, .........etc. Different people have their own interested subjects. It is very hard for people to determine 'which area is interesting' for you. You have to find out 'which one is interesting' for yourself.
2. I don't know whether 'rotation' is available in your University. That means that you can spend some time 'rotate' from one lab to another lab (ex. stay a few weeks in one lab) to see what they are doing (researches), and indirectly help you to find out which 'subject' interest you. If not, probably you can just go to different labs and spend some time to talk to those people, such as a PI, a post-doc or a graduate student.
you can search resent trends in plant science and plant research then you should find the interested area and discuss with ur professors and seniors .....