Efeitos da inclusão da lectina de sementes de Cratylia floribunda Mart. em dietas para ratos e sua participação no mecanismo de defesa da planta

Abstract

The Cratylia floribunda Mart. lectin has insecticidal action against the larvae of the bruchid beetle (Callosobruchus maculatusy which spoiled the storage cowpea [Vigna unguiculata (L.) Walp], suggesting a defensive physiological role for this protein. However, it is questioned if the expression of this lectin in seeds of transgenic plants, for expie, in cowpea, will bring about some deleterious effects upon men and their domestic animals. The hypothesis which directed the present work asked if this lectin was able to cause deleterious effects upon another experimental model, reinforcing the idea of its involvemem in plant defense mechanisms against herbivory. To test this hypothesis, diets containing the Cratylia floribunda lectin were offered to growing rats. The rats fed on the diet containing Cratylia flori bunda flour, as the sole source of protein, induced stunted growth of the animais even more expressive than that observed for rats fed the protein free diet (NPC). Furthermore the protein digestibility, NPU and biological value were very much lower than those observed for the control diet (Egg-white). In addition, the rats suffered from enlargement of stomach, small intestine, caecum + colon, kidneys, liver, pancreas, heart and lungs and thymus atrophy. These redemonstrated that the seed flour of Cratylia floribunda is a very poor protein source as compared to animal protein. The rats on the diet containing the lectin purified from Cratylia floribunda seeds ate slightly less diet than those fed on control diet. They had a good growth and showed fitness and vitality similar to rats fed on egg-white. However, detailed analyses revealed that the Cratylia floribunda lectin was resistant to in vivo proteolytic cleavage and induced metabolic changes, identified by a slight reduction on protein digestibility, and biological value, besides to enlargement of stomach, small intestine, caecum + colon, kidneys, pancreas, heart and lungs. Furthermore immunohistochemical analyses showed that the lectin interacted with the gut epithelium. This interaction may have afed the morphology and function of the gut leading to systemic alterations. These results suggest that the Cratylia floribunda lectin is related to the plant ensive role against herbivory. Thus, although this lectin inhibited the development of larvae of Callosobruchus maculatus, the cowpea weevil, transgenic plants expressing this protein could not be safe for consumption. However, due to its insecticidal action and economic and ecological advantages in place of synthetic insecticides and, also, because of the possibility of elirnination of the deleterious effects caused by this lectin, it is important to produce transgenic cowpea and to evaluate its toxicity.