Most plant pathogens invade the apoplasm by releasing pectolytic enzymes which facilitate the spread of the invading organism. Bacteria frequently infect plants by gaining entry to the tissue via the stomata. Having entered the plant they spread and multiply in the intercellular spaces. With bacterial vascular diseases, the infection is spread within the plants through the xylem.
Once within the plant, the bacteria need to be able to scavenge iron from the two main iron-transporting ligands, nicotianamine and citrate. To do this they produce siderophores, thus the enterobacterial Erwinia chrysanthemi produces two siderophores, chrysobactin and achromobactin. Xanthomonas group of plant pathogens produce xanthoferrin siderophores to scavenge the iron.
Like in humans, plants also possess siderophore binding proteins involved in host defense, like the major birch pollen allergen, Bet v 1, which are usually secreted and possess a lipocalin-like structure.