Secondary compound, etc.

How does secondary compound provide defense for a plant if it's supposed to attract pollinators? Also, what is a submucosa and a D segment? Thanks.

secondary compounds are just a large class of compounds. I believe primary ones are for metabolism, and so secondary compounds are ones that serve to attract pollinators some can fight infections, etc.

Submucosa is a layer underneath the mucosa, which is a epithelial layer. the submucosa has connective tissue and blood vessels and nerves. I believe depending where it is it has different function, but you can imagine with such vessels its role is to aide in absorption and secretion (depending on where it is). (I'm not sure of the detail necessary here, but I think conceptually this will help)

D segments are part of the gene that makes the receptors of lymphocytes. It is like unto the V and J segments, which add variability to the receptor. The order on the gene is V, D, J, and C(constant) (check out immunogloblin gene rearrangement pg. 906, though this pic doesn't have D)

Hope this helps,
Sean

It might be better to think of "plant defenses" in this context as not only protecting it from harmful factors, but in general supporting the health and life of the plant. Many secondary compounds may have bitter taste or toxic effects that help defend against herbivores and parasites, but others that attract pollinators is ultimately supporting the the life of the species.

One thing to keep in mind about the gene rearrangement section on pg. 906 is that it is only referring to light-chain polypeptides. The heavy-chain segments are a combination of V, D, and J.