Tuberization in potato is a complex developmental process involving the expression of a specific set of genes leading to the synthesis of tuber proteins. We here report the cloning and analysis of mRNAs encoding tuber proteins. From a potato tuber cDNA library four different recombinants were isolated which hybridized predominantly with tuber mRNAs. Northern blot hybridization experiments showed that three of them, pPATB2, p303 and p340, can be regarded as tuber-specific while the fourth, p322, hybridizes to tuber and stem mRNA. Hybrid-selected in vitro translation and nucleotide sequence analysis indicate that pPATB2 and p303 represent patatin and the proteinase inhibitor II mRNA respectively. Recombinant p322 represents an mRNA encoding a polypeptide having homology with the soybean Bowman-Birk proteinase inhibitor while p340 represents an mRNA encoding a polypeptide showing homology with the winged bean Kunitz trypsin inhibitor. In total, these four polypeptides constitute approximately 50% of the soluble tuber protein. Using Southern blot analysis of potato DNA we estimate that these mRNAs are encoded by small multigene families.

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Donor plants of Hordeum vulgare L. cv. Igri were grown in a conditioned environment to minimise fluctuations in the composition of the microspore population. After isolation different types of microspores were identified within each population, amongst others an embryogenic subpopulation. It was shown that the optimum plating density is achieved by adjusting the density to 2×10(4) embryogenic microspores per ml, with a lower threshold at 5×10(3) per ml. By increasing the osmolality of the pretreatment solution to 440 mOs.kg(-1) and that of the culture medium to 350 mOs.kg(-1), up to 15% of the population developed into embryo-like structures. When microspores of cv. Igri were cultured under the optimized conditions, the ratio of green/albino plants increased from 1∶1 to 34∶1, and 50 green plants per anther were formed.

The nucleotide sequence of the tmr gene, encoded by the octopine Ti plasmid from Agrobacterium tumefaciens (pTiAch5), was determined. The T-DNA, which encompasses this gene, is involved in tumor formation and maintenance, and probably mediates the cytokinin-independent growth of transformed plant cells. The nucleotide sequence of the tmr gene displays a continuous open reading frame specifying a polypeptide chain of 240 amino acids. The 5'- terminus of the polyadenylated tmr mRNA isolated from octopine tobacco tumor cell lines was determined by nuclease S1 mapping. The nucleotide sequence 5'-TATAAAA-3', which sequence is identical to the canonical "TATA" box, was found 29 nucleotides upstream from the major initiation site for RNA synthesis. Two potential polyadenylation signals 5'-AATAAA-3' were found at 207 and 275 nucleotides downstream from the TAG stopcodon of the tmr gene. A comparison was made of nucleotide stretches, involved in transcription control of T-DNA genes.

Tuber discs of Solanum tuberosum cv Bintje and Désirée were cocultivated with an Agrobacterium tumefaciens binary vector, carrying both the neomycine phosphotransferase and the E. coli β-glucuronidase gene fused to resp. the nopaline synthase and Cauliflower mosaic virus 35S promotor.Inoculated tuber discs produce transgenic shoots in selective media containing kanamycin. The transgenic plants are phenotypically normal and contain the euploid number of chromosomes. Both the neomycin phosphotransferase as well as the β-glucuronidase gene are expressed conferring resp. kanamycin resistance and β-glucuronidase activity to the plants.