Plants don't only use gravity as a reference for "up". They also use the source of light.
Here is an experiment you can try with sprout seeds. Get a shoebox, divide in three with cardboard partitions. Under one section, open the top. Under another section, open the side, and under the middle section, keep it closed.
After growing the seeds in their moist paper towels, observe. You see no growth in the dark section. You see upward growth in the open top section, and curiously, you see a diagonal growth in the side-open section.
YET, they all were grown in the same gravitational field. Interesting.