Chromosome variation in dividing protoplasts and cell suspensions of wheat

Nonrandom chromosome variation and morphogenic potential in cell lines of bread wheat (Triticum aestivum L.)

A cytogenetical analysis of 18 cell lines, 9 microspore derived, 6 anther derived, and 3 immature-embryo derived, of bread wheat (Triticum aestivum L.) varying in their morphogenic potential was undertaken. Chromosome variation, both structural and numerical, was detected in all lines studied. Variation was present and, in some cases quite extensive, in the earliest samples taken (only 12 weeks after initiation of the suspensions). Within any culture, the pattern and extent of variation changed throughout the course of the study and cells with a euploid constitution generally decreased in frequency with culture age. Among the nine microspore-derived suspensions, morphogenic lines generally showed a more restricted range of chromosome numbers and higher proportions of euploid cells than nonmorphogenic lines. The patterns of distribution of chromosome numbers among the anther-derived cultures were similar to those of the microspore-derived lines but the correspondence between instability and regenerative capacity was less. The immature embryo derived lines, which were neither regenerable nor morphogenic, were all unstable. The anther-derived lines were sampled over several months to determine whether loss of morphogenic potential was related to changes in chromosome instability of specific lines. Analysis of the "elite" line Fl.7, initially capable of regenerating green plants, showed that substantial decreases in the frequencies of normal euploid cells (from 45 to 5%) occurred over the period when morphogenic capacity was lost. However, whether the chromosome instability resulted in loss of morphogenicity or vice versa was not clarified. C-banding analyses of lines Fl.7 and C82d indicated that instability was not random with respect to the three genomes (A, B, and D) of wheat nor to the different chromosomes within the genomes. Chromosomes of the B genome were most often lost or involved in rearrangements, with breakpoints located at, or near, the heterochromatic blocks. Because of the heterogeneity of the cell lines, extensive analyses of large numbers of cells would be required before it would be possible to determine whether loss of morphogenic potential arises as a result of specific chromosome loss(es).

Primary callus as source of totipotent barley (Hordeum vulgare L.) protoplasts

Primary callus of barley (Hordeum vulgare L.) derived from scutella (cv. 'Dissa') and anthers (cv. 'Igri') was used for protoplast isolation and plant regeneration. The protoplasts were embedded in agarose and cultured with nurse cells. The plating efficiency varied from 0.1% to 0.7%. Shoots regenerated from the developing callus. Plantlets were transferred to soil and cultivated in the greenhouse three to five months after protoplast isolation. All plants were normal in morphology, and most of them flowered and set seeds.

Chromosome 5D instability in cell lines of Triticum tauschii and morphological variation in regenerated plants

Immature embryos of Triticum tauschii cultured on L2 medium with 30 g∙L−1maltose gave rise to compact and highly structured callus that readily regenerated shoots when transferred to MS medium supplemented with zeatin and indole-3-acetic acid. Two cell suspensions were initiated from the callus induced on L2 medium. An analysis of chromosome number in these cell suspensions after 3 months of culture showed that 95 and 75% of the cells had a normal complement. After 5 months, in both lines the majority of cells had chromosome complements of 2n = 13 and many of these aneuploid cells possessed a dicentric chromosome. C-banding indicated that the dicentric was often formed from chromosomes 2D and 5D. Fifty-six plants regenerated from callus were grown to maturity. Variation was observed in tiller number, flowering time, and seed-set; in two cases, the variation in early flowering was shown to be heritable. All the regenerants analysed had normal chromosome counts (2n = 2x = 14) and meiotic analyses of 35 plants revealed no obvious structural rearrangements.Key words: immature embryo culture, regeneration, chromosome, cell suspension, Triticum tauschii.

Sensitivity of random amplified polymorphic DNA analysis to detect genetic change in sugarcane during tissue culture

Random amplified polymorphic DNA (RAPD) analysis using 10-mer oligonucleotide primers efficiently differentiated sugarcane cultivars and proved suitable for detecting gross genetic change such as that which can occur in sugarcane subjected to prolonged tissue culture, for example in protoplast-derived callus. However, RAPD analysis was not sufficiently sensitive to detect smaller genetic changes that occur during sugarcane genetic transformation. The length of DNA scored for polymorphism per primer averaged 13.2 kb, or 0.0001% of the typical sugarcane genome size of 1.2 × 107 kb (2C). RAPD analysis of sugarcane plants regenerated from embryogenic callus revealed very few polymorphisms, indicating that gross genetic change is infrequent during this tissue culture procedure, although epigenetic effects result in transient morphological changes in regenerated plants. More sensitive variations on the RAPD technique may increase the practicality of DNA-based screening of regenerated plant lines to reveal somaclonal variants.

Chromosomal variation in dividing protoplasts derived from cell suspensions of barley (Hordeum vulgare L.)

Numerical and structural chromosome variation was analysed in dividing protoplasts isolated from suspension cells of barley. Five cell lines exhibited distribution patterns in chromosome number with different peaks and ranges. Embryogenic/morphogenic cell lines showed a peak at 2n = 14 (ca. 50%) after 6-7 months in culture, while older non-embryogenic cell lines had peaks at aneuploid or polyploid chromosome numbers. Culture duration had a clear effect on numerical and structural chromosome variation in embryogenic cell lines. With ageing of the cultures chromosome variation accumulated and the proportion of 2n = 14 cells decreased. The effect of protoplast isolation and culture on chromosome variation was examined; more cells with normal chromosome sets (12%) were maintained in protoplast-derived colonies than in source suspension cells (4%) of the same culture age.

Cytogenetic studies of Haplopappus gracilis in both callus and suspension cell cultures

Investigations have been carried out on karyotype change in both callus and suspension cell cultures of Haplopappus gracilis (2n=4). It has been found that polyploidization arises directly in culture to give up to six times the normal diploid chromosome number in some cultures. In polyploid cultures, both chromosome loss and chromosome rearrangements occur to give rise to aneuploid karyotypes displaying chromosomes which differ in morphology from the diploid set. Whole or partial chromosome loss has been observed in the form of lagging chromosomes and chromosome bridges at anaphase, and micronuclei, ring chromosomes and chromosome fragments at other stages in mitosis. C-banded preparations have confirmed the occurrence of chromosomal rearrangements. Comparative investigations suggest that (i) more polyploidy occurs in callus cultures than in suspension cell cultures, and (ii) the presence of cytokinin (kinetin) in the culture medium may reduce the extent of karyotype change.

Initiation of morphogenic cell-suspension and protoplast cultures of barley (Hordeum vulgare L.)

Cell-suspension cultures were initiated from embryogenic calli of various barley cultivars. Seven fast-growing suspension lines were obtained from four different cultivars (cvs. Dissa, Emir, Golden Promise and Igri). Two of these cell suspensions showed morphogenic capacity. From a cell suspension of cv. Dissa, albino plantlets were regenerated when aggregates were cultured on solid medium. Aggregates of cv. Igri usually stopped differentiation at the globular stage, but occasionally formed scutellum-like structures. Five suspension lines were used for protoplast isolation and culture. Dividing protoplasts were obtained from all lines, but with cv. Igri a few divisions only and no further development were observed. Protoplasts from the various lines differed in the time of first division (2-14 d), division frequency (0.09-70.9%) and efficiency of colony formation (0.09-7.3%). Protoplasts isolated from the morphogenic cell suspension of cv. Dissa developed compact calli which sporadically regenerated albino plantlets.