How do plant cell divide without centrioles?
There are many different ways to make a spindle in plant cells: 


  Mitotic spindles may be organized at centriolar centrosomes (only in final divisions of spermatogenesis), polar organizers (POs), plastid MTOCs, or nuclear envelope MTOCs (NE-MTOCs).


Of these, only the latter has been observed in angiosperms (flowering plants). For more info (and the source of the quote), see Brown &amp; Lemmon, "The Pleiomorphic Plant MTOC: An Evolutionary Perspective"