There is far more in wheat than gluten.  Seeds of many kinds are filled with specific chemical compounds that are toxic to mammals.  Plants actively participate in chemical warfare at many levels, via the roots, leaves and seeds.
<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Seed_predation#Seeds_and_their_defenses" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Seed_predation#Seeds_and_their...</a>