3d printing has been all about body parts. Why start there? The technology is far to immature at this point for successful implementation of engineered tissues. Let's start with something a little easier. I will bet that a plant or tree can be successfully created by extruding wood filament. Plants are much easier to make.
I don't know a lick about this, but I hope some one out there has an idea on how to go about it. The applications for printing plants could be ground breaking. World hunger, global warming, teraforming mars, who knows?
There's more grant money available to develop human tissues - so the research is on human tissue and not plant.
There is also the the environment to consider. You mess up a human tissue you kill one human. You mess up a
plant tissue and it gets loose in the wild and you can wipe out a whole species of plants. See American Chestnut Trees.
While breeding selects only the 'normal' variations of the genome -- GM can be a complete recreation or mixing sequences from different species: e.g. 'strawberry flavour' in tomatoes ... or human genoms in pig embryos for medical experimentation
This 'intemixing' or complete new/unknown genoms can cause severe problems when interacting with bacteria and viruses or simply by creating toxic (or 'wrong' as with CJD or BSE) proteins when spreaded and 'copied' with RNA
Back track. Let's try something simple for now. I'm looking for an automatic seed planting machine. I will put up $500 dollars to somebody who comes up with a device that can plant a 32' x 16' (or 512 sq ft) area of land with 2 types of seeds. The rules are simple; The first person to post a video and designs of a robotic planting machine in action, wins.
Why? Because I want to see it and I think it's important. An open source robot that could one day feed millions of people. I think it's worth 500 bucks.
It's not that complicated. Take Soy and Corn. Two symbiotic plants that we all depend on. They all require a lot of labor to plant. If there was a robot that could plant a small garden, just think of the "food miles" that could be eliminated. It's a long shot that this post will get to anyone with the volition to undertake such a mad project, but, it's worth a shot.
Definitely an intersting idea, and it's quite smart to take plant cells as most of them are pluripotent anyways (the charactersitic that mammal cells only have as embryonic stem cells (and cancer cells)).
The point is that just printing them wont give them an environment that tells them what they should do and so nothing will happen. And just plotting seeds.... well in my opinion what you want sound more or less like a improved sewing machine.
You could try to 3D print with quickly gelating hydrogels and include some bacteria for the first step. Thats not what you had in mind but it's a beginning.
I'm not sure what 3D printing trees is about, but suppose someone wants to make a complex shape from wood. Grid up some live tree root into sawdust, add root growth hormone, nutrient solution. Pack the sawdust, hormone, nutrient mixture into a form (mold), and let it grow for a few days. If any growth occurs, it should fuse into a sold piece of wood the shape of the form. IDK if it would work.