Heritable somaclonal variation in wheat

Summary Efficient tissue culture and regeneration methods were established using immature wheat embryos as expiants. Genotype differences in culturability were evident, and from the ten accessions most amenable to culture, a total of 2,846 plants were regenerated. Extensive somaclonal variation for morphological and biochemical traits was observed among 142 regenerants of a Mexican breeding line, Yaqui 50E, and their progeny. Variant characters included height, awns, tiller number, grain colour, heading date, waxiness, glume colour, gliadin proteins and -amylase regulation. The variant characters were heritable through two seed generations and included traits under both simple and quantitative genetic control. Segregation data suggested that mutations both from dominance to recessiveness, and from recessiveness to dominance, had occurred. Most mutations in the primary regenerants were in the heterozygous state but some were true-breeding and presumed to be homozygous. Chromosome loss or addition did not account for the variation and none of the variant phenotypes was observed in over 400 plants from the parental seed source. The distinctive parental gliadin pattern was maintained in the somaclones thus excluding seed contamination or cross-pollination as a source of the variation.Abbreviations 2,4-D 2,4-dichlorophenoxy acetic acid - 2,4,5-T 2,4,5-trichlorophenoxy acetic acid - IAA indole acetic acid - BAP 6-benzyl amino purine - ABA abscisic acid - GA₃ gibberellic acid - DAP days after planting     

Somaclonal variation in wheat: genetic and cytogenetic characterisation of alcohol dehydrogenase 1 mutants

Summary The progeny of 551 regenerants of the hexaploid wheat cultivar Millewa were analysed for somaclonal mutants at the threeAdh-1 loci in hexaploid wheat. Seventeen regenerants gave rise to progeny having altered ADH1 zymograms. Progeny with altered zymograms in 13 of these regenerants were aneuploid. The remaining 4 regenerants gave rise to euploid progeny with altered ADH1 zymograms. The genetics of three of these somaclonal mutants is described in detail. These regenerants were interpreted to possess a 4A isochromosome, a 3BS/4A translocation and a 7BS/4A translocation, respectively.This research was partly supported by the Rockefeller Foundation and a Reserve Bank of Australia Rural Credit Development Fund research grant     

Somaclonal variation in rice – Submergence tolerance and other agronomic characters

The ability to withstand complete submergence was studied in R₂ seedlings raised by self-pollination from 158 R₁ plants regenerated from callus of mature rice seeds (cultivars FR13A and Calrose). Compared to parental controls, significant improvement in submergence tolerance as assessed by percentage survival, number of new leaves and chlorophyll content of the third leaf, was found in 5 of the 115 cv. FR13A somaclones and 3 of the 43 cv. Calrose somaclones tested using an aquarium system in a controlled-temperature glasshouse. With some exceptions these improvements were also observed in the R₃ generation when tested under field conditions in Thailand. Variation in other agronomically important characters was observed in the R₂ plants grown in a temperature glasshouse under 2 contrasting environments.     

High Protein Somaclones Seleted from Somaclonal Varients in Triticum aestivum L.

Calli were induced from the explants of young inflorescences of a haploid wheat pollen plant of wheat (Triticum aestivum L.). The calli were subcultured and 138 regenerated plants were differentiated from them. Among the plants 5 set 42 seeds from which 34 R2 plants were obtained. The R2 plants varied in plant height, awnedness, waxiness and maturation period. In R3 generation some somaclone lines segregated but most of them were more or less stable. All clone lines were stable in R4 generation. According to the assay of seed prorein content of 82 selected clones from over 100 R5 stable clones, 5 clones with high protein content, which varied from 19.16% to 21.33%, were discovered. Repeated assay in R6 generation confirmed the results. Differences in electrophoresis pattern of seed protein and amino acid content among clones were also recorded.     

Somatic cell culture of rice cultivars with different grain types: Somaclonal variation in some grain and quality characters

Variations in some grain and quality characters in progenies of regenerated rice plants were studied. Grain length and weight decreased significantly, yet gel consistency increased. Variations in these quantitative characters of all cultivars studied were consistent, showing the tendencies of the variations. Grain protein contents of the somaclones were higher in one cultivar. Variability of most traits was increased by combining low-dosage radiation and tissue culture.     

Somaclonal variation in high tannin sorghums

Summary Genetic variants were found among over 6,000 primary plants (R₁) regenerated from embryogenic tissue cultures of eight high tannin sorghums [Sorghum bicolor (L.) Moench]. Field assessment of somaclonal variation has progressed to the R₂ population, with over 48,000 R₂ seedlings (27,000 plants) in 1,126 rows from 1,055 R₁ plants. A total of 43 variant phenotypes was recovered, including several types of chlorophyll deficiencies, dwarfism, short culm, sterility, narrow leaf, and several previously unreported variants, such as ragged leaf, multibranched heads, and Hydra, a developmental variant which produces large numbers of panicles. Variation production greatly depends on parent genotype and appears to increase with increasing time in cultures. The toal average somaclonal variation rate (based per 100 R₁ plants) and somaclonal variant frequency (based per 100 R₂ plants) estimated in the tested population were 11.3 and 1.6, respectively. Chimerism was found in regenerants. The estimated size of the mutated sector carried by mutant regenerants ranged from the whole plant to less than 3% of a single head. The average proportion of mutated R₁ heads carrying large (80%–100%), medium (40%–80%), and small (<40%) mutated sectors was 38.7%, 26.0% and 35.3%, respectively. Some sector mutations do not appear until the R₃ generation. In order to avoid losing variants, the population for selecting somaclonal variation should be as large as possible. Some of these variants found may be useful for further study or for use in breeding programs.     

小麦体细胞无性系Glu-1基因突变体的遗传分析

对 Glu-1基因的Glu-Al和Glu-Bl位点都发生突变的1个小麦体细胞无性系后代的高分子量谷蛋白亚基组成进行的分析结果,进一步证实了体细胞无性系发生了基因突变, 且发现同源染色体的等位基因易发生相同突变,突变体多是纯合基因型。认为这是体细胞无性系变异稳定快的遗传根源。 Abstract:Evidence for specific gene mutation has been obtained in our previous research by analyzing high-molecular-weight glutenin subunits(HMW-GS)controlled by Glu-1 gene in wheat somaclons.On the basis of the result,the present study detected in the offspring of a HMW-GS somaclone the mutants at both Glu-A1 and Glu-B1 loci.The occurrence of gene mutation in wheat somaclones was further proved.The results showed that a allele on homologous chromosomes often mutated identically.Genotype of this kind mutation migh be pure.Thie is considered to be genetic reason for quickly stabilizing of somaclonal variation.     

Somaclonal variation for freezing tolerance in a population derived from norstar winter wheat

Summary Progeny of 66 plants regenerated from callus cultures derived from immature embryos of Norstar winter wheat were evaluated as seedlings for tolerance to controlled freezing. Greater freezing tolerance than the parent cultivar was observed in both R₂ and R₃ regenerate families. LT₅₀ values (predicted temperatures at which mean survival frequencies are 50%) for four families in the R₂ generation and three families in the R₃ were significantly lower than that of Norstar. In both R₂ and R₃ generations, most families did not differ significantly from the cultivar Norstar, by three separate measures of tolerance. Significant variation among families was observed in both R₂ and R₃ generations for survival, but not for plant height. Variation within family in the R₃ generation was also significant, though smaller than that among families. In the R₃ generation, eighteen families were significantly less freezing tolerant than Norstar according to LT₅₀, while thirteen were significantly less tolerant according to survival at a minimum temperature of-17 °C.NRCC No. 28387. This publication describes research performed as part of the program of the Plant Biotechnology Institute of the National Research Council of Canada through Plant Biotechnology Fund contract No. 31964-4-0021 awarded to T. H. H. Chen and M. D. Lazar, Alberta Research Council, Edmonton, Canada     

Somaclonal variation versus chemically induced mutagenesis in tomato (Lycopersicon esculentum L.)

Summary A comparison was made of the type and frequency of mutational events found in the progeny of tomato plants regenerated after one passage in vitro with those induced by chemical mutagenesis with ethyl methane sulphonate. Several mutants were recovered in the progeny of regenerated and mutagenized plants of two cultivars of tomato. They can be grouped into the following categories: seedling lethality, male sterility, resistance to Verticillium, short stature, change in number of lateral shoots or in leaf shape. The results indicate that the two sources of variability differ in their effect, changing the spectrum and frequency of the mutants as well as, at least in some cases, their pattern of segregation.     

Somaclonal variation in Solanum tuberosum detected at the molecular level

Summary The many reports of phenotypic variation among plants regenerated from tissue culture suggest underlying alterations at the DNA level. This hypothesis was tested with protoplast-derived Solanum tuberosum plants. Random potato-DNA clones were used to probe the genome of individual plants at specific sites. Two out of twelve plants were shown to be variant by Southern-hybridisation with one of the tester-clones. As this clone turned out to represent 25S-rDNA, both somaclonal variants can be regarded as mutants deficient in ribosomal RNA-genes.     

小麦籽粒品质性状的杂种优势和相关分析

以6个小麦品种（系）组配的6个杂交组合F1为供试材料,对其籽粒品质性状进行了杂种优化、性状相关和亲子相关分析。结果表明：（1）粉质参数中的形成时间和稳定时间杂种优势最强,分别为56.49％和32.23％;籽粒蛋白质含量和硬度的优势最弱,分别为-2.73％和-0.9046％;沉淀值和湿面筋含量的优势居中,分别为6.88％和5.88％。（2）粉质参数中的吸水率、稳定时间同其它几个指标之间呈显著或极显著相关;沉淀值与籽粒蛋白质含量呈正相关,但不显著,与湿面筋含量呈显著负相关;湿面筋含量与籽粒蛋白质含量呈显著负相关。（3）杂种F1的籽粒Zeleny沉淀值与高亲值,低亲值和中亲值呈显著和极显著正相关;籽粒蛋白质含量和湿面筋含量与高亲值,低亲值和中亲值呈负相关或不相关。     

Somaclonal variation in the progeny of transgenic barley

 Somaclonal variation (SCV) in transgenic plants may slow the incorporation of introduced genes into commercially competitive cultivars. Somaclonal variation in transgenic barley (Hordeum vulgare L.) was assessed in one experiment by comparing the agronomic characteristics of 44 segregating transgenic lines in the T₂ generation to their non-transformed parent (‘Golden Promise’). A second experiment examined the agronomic characteristics of seven transgenic-derived, null (non-transgenic) segregant lines in the T₂ and T₄ generations. Compared to their uncultured parent, Golden Promise, most of these lines were shorter, lower yielding, and had smaller seed, and the variability among individual plants was higher. The frequency and severity of the observed SCV was unexpectedly high, and the transformation procedure appeared to induce greater SCV than tissue culture in the absence of transformation. Attempts to understand the sources of SCV, and to modify transformation procedures to reduce the generation of SCV, should be made. Received: 26 June 1997 / Accepted: 31 October 1997     

Problems of interpreting results obtained in studies of somaclonal variation in gliadin proteins in wheat

Summary It is quite likely that somacloning increases the frequency of mutations: this has, in fact, been claimed for gliadin proteins. However, in such instances it is important to distinguish between true mutations and presumed changes in regenerants due to cross pollination or admixture. We present herein arguments that some so-claimed somaclonal variants in gliadincoding genes are unlikely to be due to mutations since they would have had to involve directed changes at several loci simultaneously.     

水稻体细胞无性系变异

水稻体细胞无性系变异研究取得了很大进展 ,获得了大量抗病、抗逆、优质、矮杆等突变体。对这些突变体遗传分析表明 ,大多数突变性状由 1对或 2对基因控制。水稻体细胞无性系变异的发生与基因型、性状、继代时间、培养方式等有关 ,并具有内在的机制 ,点突变和反转录转座子插入可能是引起水稻无性系变异的两个重要原因。     

Somaclonal variation in oil palm (Elaeis guineensis Jacq.): the DNA methylation hypothesis

Elaeis guineensis Jacq.) currently hampers the scaling-up of clonal plant production. In order to investigate the relationship between the “mantled” somaclonal variant and possible alterations in genomic DNA methylation rate, two complementary approaches have been used. HPLC quantification of relative amounts of 5-methyl-deoxycytidine has shown that global methylation in leaf DNA of abnormal regenerants is 0.5–2.5% lower than in their normal counterparts (20.8% vs 22%, respectively). When comparing nodular compact calli and fast growing calli, yielding respectively 5% and 100% of “mantled” plantlets, this decrease was up to 4.5% (from 23.2 to 18.7%). An alternative method, the SssI-methylase accepting assay, based on the enzymatic saturation of CG sites with methyl groups, gave convergent results. This work demonstrates that a correlation exists between DNA hypomethylation and the “mantled” somaclonal variation in oil palm. Received: 9 July 1999 / Revision received: 15 October 1999 / Accepted: 26 October     

Somaclonal variation in tomato: effect of explant source and a comparison with chemical mutagenesis

Summary Plants were regenerated from leaf, cotyledon, and hypocotyl explants of tomato cv Moneymaker. Various phenotypic alterations were observed among regenerated plants (R₁), but were not transmitted to the progenies, except for ploidy variation. Variation in ploidy level, mainly tetraploidy, occurred in R₁ plants and their R₂ progenies, and the frequency of polyploid plants depended on the explant source. More than 50% of the regenerants derived from hypocotyl explants were found to be polyploid. A correlation was observed between the percentage of polyploid cells present in the explant material in vivo and the frequency of polyploid plants. Several monogenic mutations were recovered in the R₂, four of which were shown to be allelic to known, recessive, single-gene mutants. No significant effect of explant source or duration of tissue culture period on mutant frequency or spectrum was found. For several mutant types that could be scored unambiguously, somaclonal variation was compared to variation induced by treatment of seeds with ethyl methane sulphonate (EMS). The results showed that the mutant frequencies were higher after EMS treatment than those generated through tissue culture. With respect to the mutant spectrum, no clear differences were observed between the spectra obtained after EMS treatment and those after tissue culture. However, tissue culture gave rise to polyploid plants, whereas no ploidy variants occurred after EMS treatment.     

具野稻细胞质的胞质型雄性不育系的体细胞克隆变异II.体细胞克隆温敏核不育突变

在胞质型水稻雄性不育系IR66707A和IR69700A经离体培养而获得的136个体细胞克隆中,发现了温敏核不育突变5例。这类突变体在广州地区的自然气候下,早季至晚季前期表现为不育,晚季后期表现为可育。盛夏,在幼穗发育至花粉形成阶段对部分突变材料进行短日照处理,发现对短日照敏感的不育系农垦58S转换为可育,而供试的5例突变及另一对照培矮64S却与未经处理的材料一样仍表现为不育,表明它们的育性与日照长度的变化无关。在同一发育时期进行低温处理的结果显示,低温处理10d及10d以上者可发生育性转换,自交结实率在17.23%-42.19%之间,而未经处理的材料仍然表现不育,表明它们的育性转换与温度有关。以正常品种为父本与突变体杂交,F1全部为可育;F2可育与不育个体的分离比为3:1;以F1为父本与之测交,TF1代中可育与不育个体的分离比为1:1。遗传分析表明,这种温敏核不育突变为一对隐性核基因所控制。获得了由胞质型雄性不育变为胞核型雄性不育的突变体,这在体细胞克隆变异领域中是一种典型的突变。     

植物体细胞无性系变异的细胞学和分子生物学研究进展

植物体细胞无性系变异是植物组织培养中的普遍现象,关于这些变异的起源存在多种观点,如转座因子的活化、ＤＮＡ甲基化等。本文综述了植物体细胞无性系的研究进展,从细胞学和分子生物学两个层次对无性系变异的起源进行了讨论     

Genetical analysis of chromosome 5A of wheat and its influence on important agronomic characters

Summary Chromosome 5A of bread wheat, Triticum aestivum carries the major gene, Vrnl, which is one of the main determinants of the winter/spring growth habit polymorphism in this species. Genetical analysis of this chromosome has been carried out using single-chromosome recombinant lines to establish the pleiotropic effects of this locus and two other major genes, q determining ear morphology and bl determining the presence of awns, on important agronomic characters. The three major genes were located on the long arm of chromosome 5A with a gene order of: centromere -bl-q-Vrnl. Analysis of quantitative characters from a winter sowing revealed pleiotropic effects of Vrnl or the effects of closely linked loci on the characters plant height, tiller number and spikelet number. However effects on ear emergence time were not associated with Vrnl but with q as were effects on spikelet number and ear length. In addition a locus determining yield/plant was located between Vrnl and q. Independant loci determining height and ear length were apparent on the short arm of chromosome 5A. From a spring sowing, however, there was a large pleiotropic effect of Vrnl on ear emergence time, as well as the effects previously detected. In addition, associated with q were effects on plant height and grain size which were not expressed from the winter sowing.