A combined study of morphology, stem anatomy and isozyme patterns was used to reveal the identity of sterile plants from two rivers on the Germany/France border. A detailed morphological examination proved that the putative hybrid is clearly intermediate between Potamogeton natans and P. nodosus. The stem anatomy had characteristics of both species. The most compelling evidence came from the isozyme analysis. The additive “hybrid” banding patterns of the six enzyme systems studied indicate inheritance from P. natans and P. nodosus. In contrast, other morphologically similar hybrids were excluded: P. ×gessnacensis (= P. natans × P. polygonifolius) by all the enzyme systems, P. ×fluitans (= P. lucens × P. natans) by AAT, EST and 6PGDH, and P. ×sparganiifolius (= P. gramineus × P. natans) by AAT and EST. All samples of P. ×schreberi are of a single multi-enzyme phenotype, suggesting that they resulted from a single hybridization event and that the present-day distribution of P. ×schreberi along the Saarland/Moselle border was achieved by means of vegetative propagation and long-distance dispersal. Neither of its parental species occur with P. ×schreberi or are present upstream, which suggests that this hybrid has persisted vegetatively for a long time in the absence of its parents. The total distribution of this hybrid is reviewed and a detailed account of the records from Germany is given. P. ×schreberi appears to be a rare hybrid. The risk of incorrect determination resulting from the identification of insufficiently developed or inadequately preserved plant material is discussed.
The review incorporates recent information on carbonic anhydrase (CA, EC: 4.2.1.1) pertaining to types, homology, regulation, purification, in vitro stability, and biological functions with special reference to higher plants. CA, a ubiquitous enzyme in prokaryotes and higher organisms represented by four distinct families, is involved in diverse biological processes, including pH regulation, CO2 transfer, ion exchange, respiration, and photosynthetic CO2 fixation. CA from higher plants traces its origin with prokaryotes and exhibits compartmentalization among their organs, tissues, and cellular organelles commensurate with specific functions. In leaves, CA represents 1-20 % of total soluble protein and abundance next only to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) in chloroplast, facilitating CO2 supply to phosphoenol pyruvate carboxylase in C4 and CAM plants and RuBPCO in C3 plants. It confers special significance to CA as an efficient biochemical marker for carbon sequestration and environmental amelioration in the current global warming scenario linked with elevated CO2 concentrations. and A. Tiwari ... [et al.].
Evidence from isozyme electrophoresis confirmed previous hypothesis on the occurrence of interspecific hybridization between Potamogeton natans L. and P. lucens L. formulated on the basis of morphology and stem anatomy. Isozyme phenotypes of the morphologically intermediate plants were compared with those obtained from the putative parents growing in the same locality. P. natans and P. lucens differed consistently in at least 12 loci and possessed different alleles at 7 loci. The hybrid had no unique alleles and exhibited an additive “hybrid” isozyme pattern for all 7 loci that could be reliably analysed and where the parents displayed different enzyme patterns. Both true parental genotypes were detected among samples of plants of P. lucens and P. natans from the same locality. The hybrid plants represent a recent F1 hybrid generation resulting from a single hybridization event. Consistent differences in enzyme activity between submerged and floating leaves of P. natans and P. ×fluitans were observed in all interpretable enzyme systems.
Haploid parthenogenesis in facultatively apomictic Pilosella generated polyhaploid progeny (with half the maternal chromosome set) both in natural populations and garden experiments. Production of polyhaploids varied considerably among different species, hybridogenous species and hybrids. In the field (14 localities), the highest frequency of polyhaploids exceeded 80% of the total seed progeny produced by some recent hybrids. A similar diversity in the production of polyhaploids was also recorded in garden experiments. A two-step process by which new genotypes of both P. aurantiaca (tetraploid) and P. rubra (hexaploid) were formed under garden conditions during a polyploid–polyhaploid–polyploid cycle is described. In the first step, the maternal plants generated dihaploid and trihaploid F1 progeny, respectively. Although a substantive part of this polyhaploid progeny was either non-viable or sterile, the apomictic polyhaploids occasionally doubled their genome. Consequently, the F2 progeny resulting from the second step had a double ploidy level, identical to that of the original maternal parent. The complete process was autonomous, without contribution of pollen from parent genotype. This cycle necessarily implicates increasing homozygosity in F2 progeny compared to the original maternal polyploid plant. The probabilities of particular steps of this process occurring in Pilosella and the variation in polyhaploids are estimated and described, and the ability of polyhaploid plants to survive under field conditions discussed. Probability of the complete cycle (haploid parthenogenesis followed by doubling of the genome), which occurred under garden conditions in P. rubra, is estimated to be in the order of hundredths of percent. Despite this low probability, it can result in the production of new homozygous genotypes in populations of apomicts, especially in those occurring in disturbed habitats with little competition.