How do the nitrogen-fixing genera Azospirillum and Rhizobium associate with plant roots?
1) Azospirillum stays on the outside of the roots of tropical grasses, while Rhizobium grows inside the roots of legumes.
2) Azospirillum and Rhizobium both grow inside specialized root cells.
3) Azospirillum stays on the outside of the roots of tropical grasses, while Rhizobium grows inside the roots of legumes.
4) Azospirillum and Rhizobium both stay on the outside of roots.