Plant Stress and Defense Mechanisms - 4 Plant Responses to their Biotic Environment Plants are constantly under attack. The dermal tissues function to defend plants from mechanical damage, but are limited in their ability to do so. Predators with sharp mouthparts munch on plants, or penetrate through vulnerable spots. The mechanical protection afforded by spines, thorns and other offensive surface structures is also limited. Plant Predators Fungal spores readily enter through stomatal openings and take advantage of the spongy mesophyll to rapidly spread through the leaf tissue. Nematodes are infamous root parasites, biting through the epidermis. The ease with which aphids penetrate into phloem of soft tissues has been discussed previously. Following the strategy that the best defense is a good offense, plants respond to many predator attacks with a chemical offense, the secondary metabolites. Chemical Toxins – Secondary Metabolites
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