Oxalic acid induced cytological alterations differ in beans tolerant or susceptible to white mould

Se trataron tejidos foliares de dos cv. de frijol blanco, uno susceptible y el otro tolerante al moho blanco (Sclerotinina sclerotiorum), en diferentes ocasiones, con acido oxalico. Los tejidos se prepararon para microscopia electronica mediante las tecnicas de corte delgado y fractura por congelacion. La membrana plasmatica del cv. resistente fue mas tolerante al dano inducido por el acido oxalico que la del cv. susceptible. A la misma concn. de acido oxalico, la membrana plasmatica y los cloroplastos del cv. susceptible se afectaron mas y presentaron un rompimiento mas rapido que los del cv. tolerante. En los cortes delgados, los organelos desintegrados se encontraban parcial o totalmente desorganizados. En repeticiones de las preparaciones obtenidas de la membrana plasmatica, mediante fractura por congelacion, mayores no. de protrusiones, arrugas, y rupturas se asociaron con la creciente exposicion a acido oxalico. El dano fue mas severo en la membrana plasmatica del cv. susceptible que en la del cv. tolerante. Las mediciones de conductividad en discos foliares de los dos cv., remojados en agua, mostraron que el cv. susceptible presento mayor conductividad que el resistente, lo que indica que el dano y la ruptura de la membrana plasmatica se relacionan estrechamente con la estabilidad de la membrana. (RA-CIAT) spa

Leaf tissues of two white bean (Phaseolus vulgaris L.) cultivars, one susceptible and one tolerant to white mould (Sclerotinia sclerotiorum (Lib.) de Bary), were treated for different times with oxalic acid. Tissues were prepared by both thin sectioning and freeze-fracture techniques for electron microscopy. The plasma membrane of the resistant cultivar appeared more tolerant to damage induced by oxalic acid than that of the susceptible cultivar. At the same concentration of oxalic acid the plasma membrane and chloroplasts of the susceptible cultivar were affected more, and ruptured more quickly, than those of the tolerant one. In thin sections, the ruptured organelles were partially or completely disorganized. In replicas of freeze- fractured preparations of the plasma membrane, increased protrusions, wrinkles, breakages and ruptures were associated with increasing exposure to oxalic acid. Damage was more severe in the plasma membrane of the susceptible cultivar than in that of the tolerant one. Measurements of the conductivity of water bathing leaf discs of the two cultivars showed that the susceptible cultivar led to a higher conductivity than the resistant one, indicating that the injury and rupturing of the plasma membrane were closely related to membrane stability. (AS) eng