Lower Ploidy Levels Research Articles

Cytopalynology of Amaranthus L. and Chenopodium L. – The two pantoporate taxa

AbstractCytopalynological studies in the species, cytotypes, interspecific hybrids and amphiploids of Amaranthus L. and Chenopodium L. have been carried out using LM and SEM. It has been observed that in the cytotypes, the pollen grains at the lower ploidy level have a narrow size range. The size range widens with the increase of the ploidy level. The exine surface ornamentation is more prominent in the polyploids than in the diploids, and the 6x level exine pattern of the parent is expressed in the pollen of 6x level amphiploid. The triploid hybrid shows a high degree of variability with regard to pollen size and exine surface ornamentation. Such pollen characters may be used as markers in the biosystematic delimitation of cytotaxa occurring in nature.

Expression of wild-type GBSS transgenes in the off-spring of partially and fully complementedamylose-free transformants of potato

Theamylose-free (amf) potato mutant can easily be complemented through introduction of the wild-type gene coding for granule-bound starch synthase (GBSS). After iodine staining the starch of theamf mutant is red whereas that of the wild type and the complementedamf mutant is blue. The level of complementation of selected transformants and their sexual off-spring after backcrossing withamf was investigated using sporophytic tuber cells and gametophytic microspore cells. Two diploid and two tetraploid transformants with full complementation demonstrated the expected segregation patterns of 1:1 (one active insert) or 3:1 (two independently segregating active inserts) in the microspores and in the F1 offspring based on staining of tubers. All expected genotypes in the F1 generation were found, based on microspore segregation patterns of the individual F1 plants. Two transformants with partial complementation (mixed phenotypes) were investigated. One of them, B1, was tetraploid and duplex for the GBSS insert, which had originated through mitotic doubling of the transformed diploid cells. In the F1 generation three phenotypic classes were found:amf, fully complemented and partially complemented. The latter two classes exist independently of a simplex or duplex gene status. The second transformant with partial complementation, B10, appeared to have a complex molecular composition. One cluster of five transgenes caused the partial complementation. Fully and partially complemented phenotypic classes were found after crossing B10 with theamf mutant. Indications were found that the ploidy level of the tissue in which the genes were introduced and expressed played an important role. Firstly, partial complementation was found after transformation of the diploid and not of the tetraploidamf genotypes. Secondly, the level of complementation was higher in tissue with lower ploidy levels, as illustrated by the colour of the starch inin vitro tubers (2x–4x cells) versus field-grown tubers (16x–64x).

Biased mitochondrial segregation, independent of cell type used for fusion and of hybrid nuclear DNA content, was found in Brassica napus (+) B. oleracea somatic hybrids

To determine whether the cell type used for protoplast fusion influenced the mitochondrial segregation in somatic hybrids, mtDNA analysis was performed in Brassica napus (+) B. oleracea hybrid plants obtained from four different fusion combinations of hypocotyl and mesophyll protoplasts. In these fusions B. oleracea mitochondria were combined with B. campestris mitochondria since the B. napus cultivar had a cytoplasm derived from B campestris. Two mitochondrial gene probes, atp9 and atpA, were used to analyse mtDNA in the regenerated hybrids. In total, 96 plants were analysed. In all fusion categories, an overall biased segregation of mtDNA demonstrating a B. campestris specific pattern was found. No significant differences in segregation pattern of atp9 or atpA were found between the fusion categories. Thus, no major influence of the cell type used for protoplast fusion on mitochondrial segregation in the hybrids was found. Furthermore, nuclear DNA content analyses were available for 74 hybrids and we investigated whether the mitochondrial segregation patterns were different in hybrids exhibiting different ploidy levels. No significant difference in mitochondrial segregation was found between symmetric hybrids and hybrids with higher or lower ploidy levels. The overall strong bias of hybrids exhibiting a B. campestris RFLP pattern indicates that inherent differences of mitochondrial genomes from the different species exist, which affect the segregation in biparental cytoplasms.

Physiological Comparisons of Isogenic Diploid‐Tetraploid, Tetraploid‐Octoploid Alfalfa Populations1

Two isogenic paired sets of alfalfa (Medicago sativa L.), a diploid (2n = 2x = 16) and tetraploid (2n = 32) set plus a tetraploid and octoploid (2n = 8x = 64) set, were compared in two growth chamber experiments for photosynthesis, N fixation, and dry matter accumulation on a whole‐plant basis. In Experiment A, each plant was harvested when it had open flowers on two racemes. Plants were harvested on a weekly basis in Experiment B.Within each set, the higher ploidy level reached the harvest stage approximately 9 days earlier. This maturity differential affected the comparisons of dry matter accumulation in Experiment A. Fresh and dry weights of leaves, stems, and roots did not differ in Experiment A. In Experiment B, the 4x had significantly greater herbage fresh weight than the 2x, while the 4x and 8x pair did not differ significantly. Net CO2 exchange (NCE) on a whole‐plant basis was equivalent across ploidy levels in both experiments. Acetylene reduction on both a whole‐plant and nodule‐weight basis and nodule number and nodule weight did not differ significantly at the different ploidy levels in either experiment. For measurements taken only during Experiment A, NCE was greater in the 4x compared to the 8x on a chlorophyll basis; transpiration was significantly greater in the 8x than in the 4x, and the chlorophyll a:b ratio was lower in the 8x than the 4x. Root respiration did not differ. When nonhomogeneous variances between ploidy levels were compared, in 17 out of 18 comparisons the lower ploidy level had the greater variance.The ploidy level had little effect on physiological processes in the isogenic populations of this study. Because greater variance exists with lower ploidy levels, selection should be more easily performed at lower ploidy levels.

ON THE LIFE CYCLE, CYTOLOGY AND TAXONOMY OF CLADOPHORA CALLICOMA FROM INDIA

The present investigation deals with the cultural observations on the morphology, reproduction, life cycle, cytology and taxonomy of a freshwater Cladophora, C. callicoma (L.) Kütz, from India. There is a regular isomorphic alternation of generations between quadriflagellate zoospore‐producing diploid plants and biflagellate isogamete‐producing haploid plants, coupled with heterothallism in the latter. Chromosome numbers of n = 12 and 2n = 24 were determined respectively for gametophytes and sporophytes. Twelve bivalents were counted in meiosis where chiasmata varied from one to three. In light of above observations, the affinity of C. callicoma with C. glomerata, to which the former has often been assigned, has been discussed. It is proposed that the C. glomerata complex, which consists of intraspecific polyploid races, might have two distinct lines of evolution with regard to life cycle; one with forms having higher ploidy levels and lacking an alternation of generations, and the other with forms having low ploidy levels and alternation of generations.

CYTOGENETICS OF 6X-AMPHIPLOID × AVENA SATIVA L. F1 HYBRIDS

Avena abyssinica (2n=28) × A. strigosa (2n=14) 6x amphiploids were crossed with 13 different A. sativa (2n=42) varieties or selections. There was considerable variation in chromosome number within and among F1 plants. The mode was 40 in root tip cells and 41 in pollen mother cells (PMC's). The number of univalents in PMC's ranged from 10 to 27 with a mean of 18.9. The average number of bivalents was 7.1, ranging from 2 to 13. Multiple associations were common. Only 10.8% of the pollen grains contained normally developed nuclei, i.e. one vegetative and two elongated sperm nuclei. Forty of 41 F1 plants were completely self-sterile and only one seed was obtained from 16,950 florets. Seed set in backcross pollinations with A. sativa was 1.25%, providing some opportunity for perpetuation of desirable genes from lower ploidy levels.