32Starch metabolism in potato Solanum tuberosum L.

Starch is a major storage carbohydrate in plants. It is an important source of calories in the human and animal diet. Also, it is widely used in various industries. Native starch consists of water-insoluble semicrystalline granules formed by natural glucose polymers amylose and amylopectin. The physicochemical properties of starch are determined by the amylose:amylopectin ratio in the granule and degrees of their polymerization and phosphorylation. Potato Solanum tuberosum L. is one of the main starch-producing crops. Growing industrial needs necessitate the breeding of plant varieties with increased starch content and specified starch properties. This task demands detailed information on starch metabolism in the producing plant. It is a complex process, requiring the orchestrated work of many enzymes, transporter and targeting proteins, transcription factors, and other regulators. Two types of starch are recognized with regard to their biological functions. Transitory starch is synthesized in chloroplasts of photosynthetic organs and degraded in the absence of light, providing carbohydrates for cell needs. Storage starch is synthesized and stored in amyloplasts of storage organs: grains and tubers. The main enzymatic reactions of starch biosynthesis and degradation, as well as carbohydrate transport and metabolism, are well known in the case of transitory starch of the model plant Arabidopsis thaliana. Less is known about features of starch metabolism in storage organs, in particular, potato tubers. Several issues remain obscure: the roles of enzyme isoforms and different regulatory factors in tissues at various plant developmental stages and under different environmental conditions; alternative enzymatic processes; targeting and transport proteins. In this review, the key enzymatic reactions of plant carbohydrate metabolism, transitory and storage starch biosynthesis, and starch degradation are discussed, and features specific for potato are outlined. Attention is also paid to the known regulatory factors affecting starch metabolism.

[A comparative genetic and cytogenetic mapping of wheat chromosome 5B using introgression lines].

The genetic map of chromosome 5B has been constructed by using microsatellite (SSR) analysis of 381 plants from the F2 population produced by cross of the Chinese Spring (CS) and Renan cultivars. Initially, 180 SSR markers for the common wheat 5B chromosome have been used for analysis of these cultivars. The 32 markers able to detect polymorphism between these cultivars have been located on the genetic map of chromosome 5B. Cytogenetic mapping has involved a set of CS 5B chromosome deletion lines. Totally, 51 SSR markers have been located in ten regions (deletion bins) of this chromosome by SSR analysis of these deletion lines. Five genes--TaCBFIIIc-B10, Vrn--B1, Chi--B1, Skr, and Ph1--have been integrated into the cytogenetic map of chromosome 5B using the markers either specific of or tightly linked to the genes in question. Com- parison of the genetic and cytogenetic maps suggests that recombination is suppressed in the pericentromeric region of chromosome 5B, especially in the short arm segment. The 18 markers localized to deletion bins 5BL16-0.79-1.00 and 5BL8-0.66-0.79 have been used to analyze common wheat introgression lines L842, L5366-180, L73/00i, and L21-4, carrying fragments of alien genomes in the terminal region of 5B long arm. L5366-180 and L842 lines carry a fragment of the Triticum timopheevii 5GL chromosome, while L73/00i ? L21-4 lines, a fragment of the Aegilopsspeltoides 5SL chromosome. As has been shown, the translocated fragments in these four lines are of different lengths, allowing bin 5BL18-0.66-0.79 to be divided into three shorter regions. The utility of wheat introgression lines carrying alien translocations for increasing the resolution of cytogenetic mapping is discussed.

[Analysis of 5S rDNA changes in synthetic allopolyploids Triticum x Aegilops].

By the example of three synthetic allopolyploids: Aegilops sharonensis x Ae. umbellulata (2n =28), Triticum urartu x Ae. tauschii (2n =28), T. dicoccoides x Ae. tauschii (2n =42) the 5S rDNA changes at the early stage of allopolyploidization were investigated. Using fluorescent in situ hybridization (FISH), the quantitative changes affecting the separate loci of one of the parental genomes were revealed in plants of S3 generation of each hybrid combination. Souther hybridization with genomic DNA of allopolyploid T. urartu x Ae. tauschii (TMU38 x TQ27) revealed lower intensity of the fragments from Ae. tauschii compared with the T. urartu fragments. It may be confirmation of the reduction of signal on 1D chromosome that was revealed in this hybrid using FISH. Both appearance of a new 5S rDNA fragments and full disappearance of fragments from parental species were not showed by Southern hybridization, as well as PCR-analysis of 5-15 plants of S2-S3 generations. The changes were not found under comparison of primary structure of nine 5S rDNA sequences of allopolyploid TMU38 x TQ27 with analogous sequences from parental species genomes. The observable similarity by FISH results of one of the studied synthetic allopolyploids with natural allopolyploid of similar genome composition indicates the early formation of unique for each allopolyploid 5S rDNA organization.

[Genomic changes at early stages of formation of allopolyploid Aegilops longissima x Triticum urartu].

Using the model of synthetic allopolyploid Aegilops longissima TL05 x Triticum urartu TMU06 of the first generation, the degree and character of changes in subtelomeric, microsatellite and random amplified DNA sequences (RAPD) on early stage of polyploidization was estimated. Study of genome changes was performed by comparing of PCR spectra obtained while amplifying genome DNA of allopolyploid and its parental forms. For analysis of subtelomeric DNA, we used 66 pairs of primers composed of 11 singular primers designed for subtelomere DNA sequences of cereals. RAPD analysis was performed with usage of 38 primers, in microsatellite (SSR) analysis 23 primer pairs were used. RAPD analysis appeared to be a more effective PCR-based method to identify genome changes. Absence of some PCR fragments typical for parental genome in RAPD specters of allopolyploid TL05 x TMU06 was shown using 13 primers of 38 (34%), and with usage of subtelomere primers such changes in PSR specters were shown only for one of 66 pays of primers (1.5%). SSR loci were stable during the polyploidization process. Subsequent analysis of PCR fragments absent in specter of synthetic allopolyploid showed that high level of genome changes in RAPD analysis is probably connected with more effective ability of this method to reveal point mutations. Some data was found suggesting that not all genome changes observed in experimentally synthesized allopolyploids of the first generation are consequences of coadaptation of few genomes in one nucleus.