Tolerance to the fungal pathogen Rhizoctonia solani AG4 of transgenic tobacco expressing the maize ribosome-inactivating protein b-32

The maize b-32 protein is a functional ribosome-inactivating protein (RIP), inhibiting in vitro translation in the cell-free reticulocyte-derived system and having specific N-glycosidase activity on 28S rRNA. Previous results indicated that opaque-2 (o2) mutant kernels, lacking b-32, show an increased susceptibility to fungal attack and insect feeding and that ectopic expression in plants of a barley and a pokeweed RIP leads to increased tolerance to fungal and viral infection. This prompted us to test whether b-32 might functi on as a protectant against pathogens. The b32.66 cDNA clone under the control of the potato wun1 gene promoter was introduced into tobacco by Agrobacterium tumefaciens-mediated transformation. Out of 23 kanamycin resistant regenerated shoots, 16 contained a PCR fragment of the corrrect size spanning the boundary between the promoter used and the coding region of the b-32 gene. Eight independently transformed tobacco lines were randomly chosen for protein analysis: all of them expressed b-32 protein. The data presented indicate that transgenic tobacco plants expressing b-32 show an increased tolerance against infection by the soil-borne fungal pathogen Rhizoctonia solani Kuhn     

Content and Aggregation of Ribosomes during Formation, Dormancy and Sprouting of Tubers of Helianthus tuberosus

The ribosomes and their qualitative (monosomes-polysomes) and quantitative variations over a whole vegetative period of the tuber of Helianthus tuberosus L. (cv. OB 1) were examined. Tubers in different phases of growth, dormancy and sprouting or slices of dormant tubers activated with 2 x 10^-6M indol-3-acetic acid were used. The ribosomes were analyzed by a linear sucrose gradient. During flowering, polysomes of tuber disappeared almost completely and rRNA decreased in comparison with the level present at the beginning of tuber formation. After flowering, there was a new synthesis of monosomes and polysomes until the onset of dormancy; this last period was characterized by a marked increase in polysomes and a proportional increase in monosomes. The level remained almost constant till the break of dormancy. When the tubers sprouted, ribosomes, present almost exclusively as monosomes, decreased considerably; on the contrary the non-photosynthetic sprouts contained many monosomes and polysomes. The first phases of activation (3 h) of tuber slices were characterized by a RNA synthesis, which occurred during one hour, in the subunit region of the gradient. Successively (10 h of activation) the ³²P incorporation was seen also in the polysome region and increased with time. Some possible interpretations of these last results are discussed.