new cell types part_of pith, hypocotyl & tapetum

[planteome-user]

Need new terms for following cell types -tapetum/tapetal cell (http://www.ncbi.nlm.nih.gov/pubmed/21515697) -hypocotyl cell (http://www.plantcell.org/content/10/10/1623.abstract) -pith cell/pith parenchyma cell (http://www.pnas.org/content/107/51/22338.full.pdf) --root pith cell (-->part_of PO:0005040 : root pith) --shoot axis pith cell (-->part_of PO:0005041 : shoot axis pith )

There are some

Reported by: jaiswalp

Original Ticket: obo/plant-ontology-po-term-requests/503