Impact of the exodermis on infection of roots byFusarium culmorum

Patterns of infection withFusarium culmorum (W G Smith) Saccardo were observed in seedling roots of barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), maize (Zea mays L.) and asparagus (Asparagus officinalis L). Apical regions of the main roots were not infected. Since penetration into the root occurred several days after inoculation and the roots were growing during the experiment, these regions had apparently not been in existence long enough to be infected. In older regions of barley, wheat and asparagus, hyphae entered through the tips of lateral roots. In barley and wheat, which had not developed any suberin lamellae in their subepidermal layer, infection occurred randomly over the remainder of the root. In maize, the fungus penetrated the epidermis at many sites but did not breach the exodermis in which all cells possessed both Casparian bands and suberin lamellae. Maize roots, therefore, sustained only minimal infections. In asparagus, the fungus grew through the short (passage) cells but never the long cells of the exodermis. In doing so, it penetrated cells possessing Casparian bands but lacking suberin lamellae. The results support the hypothesis that suberin lamellae provide effective barriers to the growth ofF. culmorum hyphae.     

Studies of the inhibition of aldose reductase: evidence for multiple site binding

1. Comparison of structure-inhibition relationships and kinetic data between the N-[(4-benzoylamino)phenyl]sulfonyl]amino acids (BAPS-amino acids) and phenylsulfonylamino acids (PS-amino acids) suggests that the additional benzoyl moiety present in the BAPS-amino acids enhances inhibition by direct interaction with aldose reductase (EC 1.1.1.21) without altering the mode of interaction with the enzyme. 2. Also the 2-, 3- and 4-nitro regioisomers of BAPS-glycine (NBAPSG) display parallel structure- inhibition relationships with the 2-, 3- and 4-nitrobenzaldehyde substrates and the 2-, 3- and 4-nitroacetophenone competitive inhibitors. 3. Competition studies and multiple inhibition analyses demonstrate that the 4-nitrobenzoyl group of 4-NBAPSG binds at the substrate site of aldose reductase, while the PS-glycine moiety of 4-NBAPSG binds cooperatively at a distinct site.