The main difference is the absence of gravity. This is interesting to researchers as it is the only way we can find out what the effect is of gravity on plants.

Experimenters were surprised to find that plants can grow with roots downwards and leaves upwards without gravity, originally thought that gravity was needed for this.

For details: How Do Plants Grow In Zero Gravity?

http://www.esa.int/Our_Activitie...

Page on gravitationalandspacebiology.org

However there are many changes in how they function. Within 2 minutes of starting a centrifuge in the ISS, the cells in the plants change gene expression of numerous genes. So when checking effects of various levels of gravity - they have to preserve the cells within minutes of stopping the centrifuge - or actually in the centrifuge. http://www.mdpi.com/2223-7747/4/...

Plants are also sensitive to tiny amounts of gravity. For instance in an experiment with lentil seedlings, they responded to two thousandths of a g, and interpolation suggests they are sensitive to levels of less than a ten thousandth of a g. Page on researchgate.net

Which - just putting a personal view here - leads me to wonder - is there any potential in generating micro g as a way of solving plant growth problems in space? Instead of engineering plants so they can grow in zero g, why not work on ideas for very slowly rotating "spin drier" type centrifuges in space, say enough for a hundredth of a g?

A 1 meter diameter centrifuge rotating at 1 rotation per minute would generate a bit over a hundredth g, so why not grow all the plants in slow centrifuges like that? It wouldn't take much power to spin the centrifuges, especially in zero g, and the centrifuges themselves could be light weight, and no hazard at all at those speeds. And it could let us grow plants that can't currently grow under zero g.

(I think there is a good chance that in future we'll have artificial g for humans too. For instance, for all we know, even a hundredth g might make some difference for humans also - or there again, it might not help at all, we won't know answers until we do tests in space with humans staying long term in low g, or variable and temporary g conditions - also small centrifuges like that with variable g which you can set according to your personal spin tolerance and comfort levels could help health and add to comfort while eating, drinking, using a space toilet)

It's just a thought. (you can work out levels of artificial g using SpinCalc)