Resistance to Phytophthora infestans in somatic hybrids of Solanum nigrum L. and diploid potato.

In breeding for resistance to late blight, ( Phytophthora infestans Mont. de Bary), an economically important disease affecting potatoes, the search for new sources of durable resistance includes the non-host wild Solanum species. The aim of this work was to evaluate the resistance to P. infestans in the somatic hybrids between S. nigrum L. and diploid potato clone ZEL-1136. Sixteen somatic hybrids, their fusion parents, and three standard potato cultivars were screened for resistance to P. infestans in two types of tests-on whole plants and detached leaves-with two highly aggressive and virulent isolates of P. infestans, US8 and MP322. In the whole plant assay, the foliage of the somatic hybrids showed no symptoms of infection, while the foliage of the potato fusion parent and the standard cultivars was infected with P. infestans. In the detached leaflet assay, the breaking-down of resistance of the S. nigrum L. parent and the variable response of individual hybrid clones were noted. Nine S. nigrum L. (+) ZEL-1136 hybrids showed a resistance that was significantly higher than that of S. nigrum, while six clones expressed a resistance to P. infestans similar to that of S. nigrum. The results confirm the effective transfer of late blight resistance of S. nigrum into its somatic hybrids with potato.

Somatic hybrids Solanum nigrum (+) S. tuberosum: morphological assessment and verification of hybridity.

Somatic hybrids between the cultivated potato diploid hybrid clone, ZEL-1136, and hexaploid non-tuber-bearing wild species Solanum nigrum L. exhibiting resistance to Phytophthora infestans were regenerated after PEG-mediated fusion of mesophyll protoplasts. The objective was to transfer the late-blight resistance genes from the wild species into plants of the cultivated potato clone. From a total of 59 regenerants, 40 clones survived and have been maintained in vitro on hormone-free MS/2 medium. Thirty-two somatic hybrids were identified by their intermediate morphology (leaves of nigrum type and flowers of tuberosum type) and verified by flow cytometry and random amplified polymorphic DNA (RAPD) patterns. The RAPD analysis of nuclear DNA confirmed the hybrid nature of 29 clones. Flow cytometry revealed a wide range of ploidy in the generated hybrids, from nearly the tetra- to decaploid level. Most of the hybrid clones were stable in vitro, grew vigorously in soil, and set flowers and parthenocarpic berries. However, all of the flowering hybrids were male-sterile. Nine hybrid clones produced tuber-like structures in soil. The most vigorous flowering somatic hybrids were selected for assessment of the late-blight resistance.

Transgenic potato plants expressing soybean beta-1,3-endoglucanase gene exhibit an increased resistance to Phytophthora infestans.

Soybean beta-1,3-endoglucanase represents a model system for studies on early plant responses to infection by fungal pathogens, and it has been implicated in the release of elicitors from fungal cell walls. In the present study, potato plants were transformed with the soybean beta-1,3-endoglucanase cDNA via Agrobacterium delivery system. The transfer of the gene into potato genome was confirmed by (i) PCR amplification, (ii) Northern blot analyses, and (iii) an increase in the activity of beta-1,3-endoglucanase in transgenic plants. The transformation resulted in an increased resistance of selected transgenic plants to infection by Phytophthora infestans, an important pathogen.

Protein-synthesizing activity of maize-shoot chromatin : I. Conditions and component requirements.

The evidence presented in this paper suggests that purified plant chromatin, similar to mammalian (SR Umansky et al., Eur J Biochem 1980 105: 117-129), has the ability to incorporate amino acids into acid precipitable material. The polypeptide-synthesizing system of chromatin seems to differ substantially from the classical polyribosomal translation mechanism in cytoplasm. When chromatin purified from 5-day-old etiolated maize (Zea mays) shoots was incubated with (14)C-labeled amino acids, label was incorporated into the trichloroacetic acid precipitable product. Chloramphenicol, pactamycin, and actinomycin D inhibited the incorporation almost completely, whereas treatment with cycloheximide, puromycin, or aurintricarboxylic acid did not affect the labeling. Preincubation with pancreatic RNase was also without effect, but treatment of chromatin with DNase I caused about 25% depression of label incorporation. A wheat germ translation system or its single components have no effect on the chromatin polypeptide-synthesizing activity beyond that expected for a simple addition. The protein-synthesizing system is tightly bound to chromatin and could not be removed by dissociation in 1 molar NaCl. The mean molecular weight of the major protein fraction synthesized in the presence of chromatin was 21 to 24 kilodaltons.

Gibberellic Acid Activates Chromatin-bound DNA-dependent RNA Polymerase in Wounded Potato Tuber Tissue.

Chromatin-bound DNA-dependent RNA polymerases react upon wounding of white potato tuber tissues with an increase in activity, which is additionally enhanced to 300% in the presence of 0.1 micromolar gibberellic acid (GA(3)). 2,4-Dichlorophenoxyacetic acid is only weakly effective and indoleacetic acid not at all. Wounding and treatment with GA(3) affect template availability of chromatin only slightly. The hormone has no effect on chromatin-bound RNA polymerases, if added in vitro.The enzymes from intact, wounded, and hormone-treated tissues possess similar characteristics: their activity is dependent on the presence of all four ribonucleotides and a divalent cation such as Mg(2+) or Mn(2+). However, the sensitivity of the enzymes from different preparations toward alpha-amanitin differs. Total RNA polymerase activity of chromatin was inhibited by alpha-amanitin to about 44% in intact, to about 22% in wounded, and only 15% in GA(3)-treated tissues. The relative activities of polymerases I and II were estimated by varying the (NH(4))(2)SO(4) and alpha-amanitin concentrations in the assay system. It is evident that GA(3) preferentially stimulates polymerase I and hence ribosomal RNA synthesis. RNA polymerase II is but slightly affected by GA(3). Nearest neighbor frequency analysis revealed that the RNA synthesized by the enzymes from the intact tuber is different from that of wounded or GA(3)-treated tissues.

Enhancement of polyribosome formation and RNA synthesis of gibberellic Acid in wounded potato tuber tissue.

As part of a more detailed study on plant tumorigenesis, the action of gibberellic acid (GA(3)) in wounded potato tuber tissues as a model system has been evaluated. GA(3) stimulates total RNA synthesis in wounded tissues, the optimal concentration being 0.1 micromolar. The responsiveness of the tissue toward the hormone develops with time after wounding. Whereas freshly wounded tissue does not respond at all to the hormone, it becomes competent after about 6 hours, the competence being maximal after 1 day of wound healing.GA(3) enhances the formation of polyribosomes in wounded tissues and stimulates the synthesis of both ribosomal RNAs, transfer RNAs, 5S RNA, and a fraction, which in sucrose density gradients sediments between 18S rRNA and 5S RNA. This fraction contains presumptive mRNA.The hormone, then, is somehow recognized by wounded potato tissue in a time-specific way; the signal is transferred to the genome and triggers the synthesis of various RNA species.

Rhythmic changes in transcriptional activity during the development of potato tubers.

Chromatin-bound, DNA-dependent RNA polymerase (EC 2.7.7.6) activity and chromatin template availability, as measured with saturating amounts of E. coli RNA polymerase, changes rhythmically during the formation, dormancy, and sprouting of potato tubers. Active growth processes coincide with the highest RNA polymerase activity as well as the greatest template accessibility, during tuberization and sprouting. Consequently, chromatin-associated RNA and protein content is highest in young developing tubers and in old tubers at the onset of sprouting. Ribosomal RNA content, in turn, is maximal in small tubers, remains constant during dormancy, and decreases when sprouting begins, probably due to the translocation of rRNA into the sprouts. The nucleolus changes its shape and size concomitantly with the process of tuberization.

Age-dependent variations in transcriptional response to wounding and gibberellic acid in a higher plant.

The reaction of potato tuber tissue upon wounding and gibberellic acid (GA3) treatment is strictly dependent on the tuber age. Young, rapidly growing tubers decline both chromatin-bound, DNA-dependent RNA polymerase (EC 2.7.7.6) activity and template availability as a consequence of wounding and are not responsive toward GA3. At the onset of dormancy, ripened tubers do not at all respond to wounding or hormones, but later on develop the ability to increase their transcriptional rate and template accessibility, both after injury and treatment with 10(-7) mol l(-1) GA3. The size of the nucleolus and the rRNA content of the ribosomal population follows the same pattern.