Effect Of Chromosome Doubling Research Articles

The effect of induced polyploidy on phytochemistry, cellular organelles and the expression of genes involved in thymol and carvacrol biosynthetic pathway in thyme (Thymus vulgaris).

Induced polyploidy usually results in larger vegetative and reproductive plant organs. In order to study the effect of chromosome doubling on Thymus vulgaris, three levels of colchicine concentration including 0.1, 0.3 and 0.5% (w/v) were applied for 6, 12 and 24 hours on apical meristem of 2- and 4-leaf seedlings. Ploidy level was evaluated by flow cytometry and microscopic chromosome counting. Chemical composition of essential oils extracted by hydro-distillation was analyzed by gas Chromatography/mass spectrometry (GC/MS) and gas Chromatography (GC). The application of 0.3% colchicine at 4-leaf seedling for 6 hours resulted in the highest survival rate and the highest number of tetraploid plants. Cytogenetic and flow cytometry analyses confirmed the increase of chromosome number from 2n=2x=30 in diploids to 2n=4x=60 in induced tetraploids. Tetraploid plants had larger leaves, taller and thicker stems, dense branching, longer trichome, larger stomata, larger guard cells, and decreased number of stomata. The number of chloroplasts and mitochondria increased significantly in tetraploid plants by 1.66 and 1.63 times, respectively. The expression of CYP71D178, CYP71D180 and CYP71D181 increased in tetraploids by 3.27, 7.39 and 2.15 times, respectively, probably resulting in higher essential oil compounds, as tetraploids outyielded the diploid plants by 64.7% in essential oil, 40.9% in thymol and 18.6% in carvacrol content.

Tetraploid Induction with Leaf Morphology and Sunburn Variation in Sorbus pohuashanensis (Hance) Hedl

Sorbus pohuashanensis (Hance) Hedl. is an important forestry species valued for its ornamental, medicinal, and ecological properties. Polyploidy breeding is an important method of germplasm innovation; however, polyploidy induction and phenotypic variation caused by chromosome doubling in S. pohuashanensis are poorly understood. In this study, S. pohuashanensis seeds were used to explore the effects of different colchicine concentrations, cold stratification times, and seeds from different sources on polyploidy induction. Ploidy levels of the regenerated plants were determined by flow cytometry. The results showed that the tetraploid induction effect of S. pohuashanensis seeds was significantly affected by colchicine concentration, and the highest tetraploid induction rate of 24.75% was achieved by immersion in 0.2% (w/v) colchicine for 48 h. After 2 years of induction, 77 tetraploid plants were obtained. Compared to diploids, tetraploid plants showed significant variations in plant height, leaf morphology (apical leaflet width, middle leaflet width), and diameter of the middle petiole. The stomatal size and chloroplast number increased with chromosome doubling whereas the stomatal number and density decreased. In addition, significant differences in the percentage of sunburn associated with ploidy changes were observed. This study provides a technique for tetraploid induction of S. pohuashanensis seeds, showing the variation in traits caused by polyploidization and the effect of chromosome doubling on sunburn resistance. Tetraploidy induction provides a new direction for S. pohuashanensis germplasm innovation.

Effect of gamma irradiation on nucleolar activity in root tip cells of tetraploid Triticum turgidum ssp. durum L.

Ionizing irradiation induces positive or negative changes in plant growth (M1) depending on the amount of irradiation applied to seeds or plant parts. The effect of 50-350Gy gamma irradiation of kernels on nucleolar activity, as an indicator of metabolic activity, in root tip cells of tetraploid wheat Triticum turgidum ssp. durum L. cv. Orania (AABB) was investigated. The number of nucleoli present in nuclei and micronuclei as well as the mitotic index in the different irradiation dosages was used as an indicator of the cells entering mitosis, the chromosomes with nucleolar organizer regions that are active as well as chromosome doubling in the event of unsuccessful mitotic division. Nucleolar activity was investigated from 17.5 to 47.5h after the onset of imbibition to study the first mitotic division and its consequences on the cells that were in G2 and G1 phases at the time of gamma irradiation. Untreated material produced a maximum of four nucleoli formed by the nucleolar organizing regions (NORs) on chromosomes 1B and 6B. In irradiated material, additional nucleoli were noted that are due to the activation of the NORs on chromosome 1A in micronuclei. The onset of mitosis was highly significantly retarded in comparison to the control due to checkpoints in the G2 phase for the repairing of damaged DNA. This study is the first to report on the appearance of nucleoli in micronuclei as well as activation of NORs in the micronuclei that are inactive in the nucleus and the effect of chromosome doubling on nucleolar activity in the event of unsuccessful mitotic division.

Investigation of genes associated with petal variations between diploid and autotetraploid in Chinese cabbage (Brassica rapa L. ssp. pekinensis) by RNA-seq and sRNA-seq.

Polyploidy promotes morphological, physiological, and reproductive diversity in plants. The imminent effect of chromosome doubling in plants is the enlargement of organs such as flowers and fruits, which increases the commercial value of crops. Flowering plays a vital role in the growth and development of angiosperms. Here, we prepared an isolated microspore culture of 'FT', a doubled haploid (DH) line of Chinese cabbage (Brassica rapa L. ssp. pekinensis), and obtained diploid and autotetraploid plants with the same genetic background. Compared with diploids, the autotetraploids were characterized by large floral organs, dark petals, delayed flowering, and reduced fertility. The indole-3-acetic acid (IAA) and jasmonic acid (JA) levels in autotetraploid petals were significantly higher and the abscisic acid (ABA) level was significantly lower than those in the diploid petals. The lutein level in autotetraploid petals was nearly two times higher than that in the diploid petals. A comparative transcriptome analysis revealed 14,412 differentially expressed genes (DEGs) between the diploids and autotetraploids, and they were enriched in 117 Gene Ontology terms and 110 Kyoto Encyclopedia of Genes and Genomes pathways. We detected 231 DEGs related to phytohormone signal transduction and 29 DEGs involved in carotenoid biosynthesis. An miRNA-target mRNA analysis showed that 32 DEGs regulated by 16 DEMs were associated with flowering timing (BraA03000336, BraA09004319, and BraA09000515), petal development (BraA05002408, BraA01004006, BraA09004069, and BraA04000966), flower opening (BraA07000350), and pollen development (BraA01000720, BraA09005727, and BraA01000253). This study provides information to help elucidate the molecular mechanisms underlying phenotypic variations induced by autopolyploidy in Chinese cabbage.

Changes of Phenolic Acids and Antioxidant Activities in Diploid and Tetraploid Echinacea purpurea at Different Growth Stages

Phenolic acids are the main active substances that contribute to the antioxidant activity of Echinacea purpurea (L.) Moench, Asteraceae. However, the effect of chromosome doubling and developmental growth stage on the phenolic acid accumulation and the antioxidant capabilities of E. purpurea has remained unclear. Our systematic studies indicate that the dry weight of tetraploid plants is significantly higher than that of diploid plants, leading to higher yields of cichoric acid, caffeic acid, chlorogenic acid, caftaric acid, and 1,5-dicaffeoyl quinic acid compared with diploid plants, at different growth stages. Cichoric acid and caftaric acid are the predominant compounds in diploid individuals. The period with the higher yields of cichoric acid and caftaric acid are coincided with that of total phenolic acids in four investigated organs (root, leaf, stem, and flower), which mostly observed during the flowering period (August). Furthermore, antioxidant activities in four different organs of tetraploid individuals were higher than those in diploid plants, at each growth stage. The changes in the antioxidant activity in different organs (flower, root, leaf, and stem) of diploid individuals were significantly and positively correlated with the trends in the content changes of total phenolic acids throughout different growth stages. Blooming time should be chosen as the best harvest time for both diploid and tetraploid plants, and the flowers and leaves may be used as raw materials for the extraction of total phenolic acids and development of antioxidant supplements to stimulate the immune system.

A ploidy chimera reveals the effects of tetraploidy in date palm

In the oasis of Tozeur (Tunisia) a peculiar date palm ploidy chimera was discovered, showing a diploid (2n = 2x) and a tetraploid (2n =4x) sector and a uniform tetraploid offshoot. This chimera allowed to describe the effects of chromosome doubling on some selected features. Because both ploidies occur within one plant, there was no environmental bias. Tetraploid leaves are longer, bear larger leaflets and spines and have a thicker rachis than normal diploid leaves. During three seasons, tetraploid inflorescences appeared ten days later than their diploid counterparts. The tetraploid sector formed bunches with stalks bearing larger fruits, with a higher percentage of inedible parthenocarpic fruits, than bunches that arose from the diploid sector. Tetraploid fruits are significantly longer, wider and heavier than diploid fruits, with a larger pulp diameter, irrespective of whether they are seeded or parthenocarpic. Diploid parthenocarpic fruits are longer than seeded fruits, while tetraploid parthenocarpic and seeded fruits both show the same size. The occurrence of tetraploidy opens new perspectives in date palm breeding. Pollination of tetraploid pistils with pollen from diploid males gave rise to a relatively low number of triploid plantlets, suggesting a triploid block.

Artificial Chromosome Doubling in Allotetraploid Calendula officinalis.

Calendula officinalis L. is known as an ornamental plant as well as a source of biochemical compounds used in cosmetics and industry. C. officinalis has a complex karyotype. Published chromosome numbers differ between 2n = 4x = 28 or 32. We have estimated genome sizes in nine commercial cultivars and evaluated the ploidy level by karyotyping and fluorescent in situ hybridization (FISH) using 5S and 45S rDNA loci. The detection of chromosome sets of two rather than four homologues would suggest that C. officinalis has an allotetraploid background. In addition, four signals for 45S but only two for 5S were found by using FISH. Artificial chromosome doubling is a common technique in plant breeding, as polyploidization results in several consequences for plant growth and development. Especially the suggested allotetraploid background in C. officinalis is interesting when examining the effect of chromosome doubling on the plant phenotype. Here we describe chromosome doubling of three allotetraploid cultivars of C. officinalis, ‘Nova,’ ‘WUR 1553-7’ and ‘Orange Beauty’. Three antimitotic agents – colchicine, oryzalin and trifluralin - were used in different concentrations to find the combination of the best agent and the best dosage to obtain octaploids. For all three cultivars a few octaploids were obtained. A concentration of 200 and 400 ppm of colchicine was most efficient for chromosome doubling in ‘Nova’ and ‘Orange Beauty,’ respectively. For ‘WUR 1553-7’ the treatment with 20 ppm oryzalin was also effective. Cell numbers and first observations of the phenotype in the chromosome doubled plants show thicker leaves and bigger cells, as commonly observed after ploidy doubling. Due to the low number of chromosome doubled plants obtained more elaborate phenotyping will be performed on following generations cultivated under field conditions.

Chromosome doubling of Sedum alfredii Hance: A novel approach for improving phytoremediation efficiency

Sedum alfredii Hance is a cadmium (Cd)/zinc (Zn) hyperaccumulator native to China. However, its relatively low biomass restricted the large-scale application for heavy metal contamination remediation. The chromosome set doubling of S. alfredii in vitro was achieved by 0.1%-0.2% (W/V) colchicine treatment. The plant DNA ploidy was analyzed by flow cytometry and chromosome set doubling plants (CSD) were identified based on the obvious different sharp peak. A tissue culture experiment with different Cd treated levels and a field trial with natural polluted mined soil were conducted to study the effects of chromosome doubling on plant biomass and Cd accumulation in shoots. The results suggested that S. alfredii is a mixoploid. Compared with the wild type plants (WT), CSD exhibited typical "gigas" characteristics in morphology including stem thickness, root hair production, number of leaves and size of stoma guard cell. Fresh weight and dry weight of CSD were increased to 1.62-2.03-fold and 2.26-3.25-fold of WT. And Cd content of CSD showed a 17.49%-42.82% increase and 59% increase under tissue culture and field condition, accordingly. In addition, the TF and in BCF of CSD were 2.37- and 1.59-fold of WT, respectively. These results proved that it is feasible to promote phytoextraction efficiency of S. alfredii in Cd contaminated soils through chromosomal engineering, which provides a novel approach for hyperaccumulator application in phytoremediation.

A comparative study of the dynamic accumulation of polyphenol components and the changes in their antioxidant activities in diploid and tetraploid Lonicera japonica

Polyploidization is an effective method to achieve a higher yield of secondary metabolism active ingredients in medicinal plants. Polyphenols are the main active substances that contribute to the antioxidant activity of Lonicera japonica. For studying on the effect of chromosome doubling and harvest time on the dynamic accumulation of the main active substances and antioxidant capabilities of L.japonica, the polyphenol composition contents (7 phenolic acids and 3 flavonoids) and the antioxidant capacity in buds and flowers of diploid and tetraploid L.japonica at six different growth stages were determined by HPLC-DAD and three common antioxidant assays (FRAP, OH RSC and DPPH ARP), and the correlation between the dynamic accumulation of the polyphenol components and antioxidant capacity was also analyzed in current research. The results indicated that the content of the most determined phenolic acids and flavonoids and the antioxidant capacity in most of the growth stages from tetraploid plants were significantly higher than those in the diploid plants. Furthermore, the changes in the antioxidant activity presented a significant positive correlation with the variations in the chlorogenic acid, rutin, hyperoside, luteoloside in the two ploidy levels of L.japonica plants. The higher yields of chlorogenic acid (158.97, 164.00, 199.85mg), luteoloside (5.44, 4.03, 6.31mg), hyperoside (1.15, 1.06, 1.30mg) and total flavonoids (9.87, 8.67, 11.10mg) from 100 buds or flowers in tetraploid plants occurred during the S3-S5 stages, and these stages also exhibited higher antioxidant activities. Therefore, the stages of S3-S5 are recommended as the best time for harvesting high-yield, high-quality tetraploid Flos Lonicerae Japonicae.

Induction, regeneration and characterization of tetraploids and variants in ‘Tapestry’ caladium

Caladium (Caladium × hortulanum Birdsey) is an important ornamental aroid that is valued for its long-lasting colorful foliage. Genetic improvement and cultivar development in caladium have been primarily achieved through sexual hybridization, and there is a strong need to explore in vitro-based approaches to generate novel phenotypic variations in caladium. This study was conducted to develop an efficient in vitro chromosome doubling technique for caladium, to assess the effects of chromosome doubling on caladium leaf morphology, and to identify promising caladium tetraploids for breeding. Leaf segments of ‘Tapestry’ caladium were pre-cultured in vitro, treated with colchicine, and then cultured to regenerate tetraploid plants. Out of 501 established plants, 56 showed considerable variation from the wildtype in leaf shape, color, coloration pattern, and/or thickness. Ploidy analysis showed that 48 appeared to be tetraploids, and the remaining eight appeared to be diploids. In two treatments with 0.1 or 0.2 % (w/v) colchicine for 4 days, 13.74 and 24.14 % of the regenerated plants were tetraploids. Caladium tetraploids exhibited round and thick leaves with thick petioles. These morphological changes were a reliable morphological indicator for visual screening for tetraploids in caladium. Based on observed morphological changes, the eight diploid variants were categorized into five variant types (VT1–VT5), and the 48 tetraploid variants were categorized into another five variant types (VT6–VT10). Most caladium plants in VT1, VT2, VT3, VT6, and VT7 showed much improved ornamental values and held potential as promising new selections for container and landscape performance trials and tuber yield tests. Nuclear DNA content and chromosome number analysis were conducted on 17 representative variants; results revealed the two diploid variants had gained one or two additional chromosomes, one tetraploid variant gained four additional chromosomes, and two tetraploid variants lost two or four chromosomes. These results demonstrate for the first time in caladium that in vitro induction of tetraploids is a very powerful tool for generating novel phenotypes for genetic improvement and breeding and that chromosome gain or loss is a common type of cytological variation in caladium.

Seed attributes in fruit of colchicine-induced tetraploids of Actinidia chinensis

Seed characteristics are important in kiwifruit breeding and production as they affect the efficiency of cross breeding and commercial fruit size and quality. Following a study of the size, shape and quality attributes of induced tetraploid kiwifruit, three methods for seed evaluation were compared to uncover the effect of chromosome doubling on seed development, quantity and quality in induced tetraploids of Actinidia chinensis. Results over 3 years consistently showed that colchicine-induced tetraploids had a significantly lower seed density in transverse sections of fruit, fewer normally filled seeds, and more unfertilized and aborted seeds than their diploid progenitors. The weight of filled seeds of colchicine-induced tetraploids from the commercial gold-fleshed kiwifruit cultivar ‘Hort16A’ was significantly (33%) higher than that of their diploid progenitor. In contrast, the weight of filled seeds from the fruit of colchicine-induced red-fleshed A. chinensis tetraploids was significantly lower than that of their respective diploid progenitors. Seed size may have been related mainly to the availability of pollen from nearby males of the same ploidy. The dry seed coat colour of colchicine-induced tetraploids was brown in comparison to the black seeds of diploids. This is the first time that the reproductive nature of autotetraploid kiwifruit has been systematically characterized. I have shown that chromosome doubling significantly reduces seed numbers and affects seed development inside kiwifruit.

Fruit Quality in Induced Polyploids of Actinidia chinensis

Fruit of colchicine-induced tetraploids of Actinidia chinensis were 50% to 60% larger than those of their diploid progenitors. In addition to fruit size, fruit quality is a key issue in any commercialization of these autotetraploids. We have made the first detailed study of the effects of chromosome doubling on fruit quality parameters other than size: these attributes include flesh firmness, color, soluble solid content (SSC), dry matter content (DM), vitamin C content, fruit skin thickness, and red pigmentation distribution in red-fleshed kiwifruit. Four selections from colchicine-induced tetraploids from the yellow-fleshed kiwifruit cultivar Hort16A were trialed for the stability of their fruit quality. Analysis of fruit at harvest over 3 years showed that fruit of the induced autotetraploids were significantly softer (lower flesh firmness), had lower DM, and had a less intense golden flesh color than fruit of their diploid progenitor. During development, SSC of fruit of the autotetraploid plants started to increase earlier than in the diploid ‘Hort16A’. This has been confirmed by replicated trials. No difference was found in vitamin C content between fruit of autotetraploids and diploids. Autotetraploids had significantly thicker skins than diploid ‘Hort16A’. Induced autotetraploids from three female genotypes of red-fleshed A. chinensis showed similar trends to autotetraploids of ‘Hort16A’ in fruit flesh firmness and outer pericarp flesh color, DM, SSC, and vitamin C. All the traits analyzed indicated that fruit of the autotetraploid plants matured earlier than those of their diploid progenitors. Furthermore, red pigmentation, one of the most important traits for red-fleshed kiwifruit breeding, showed a reduction in both intensity and distribution in the autotetraploids compared with their diploid progenitors. There was considerable variation among fruit of autotetraploid plants regenerated from each diploid progenitor. Therefore, selection among the regenerants may be required to achieve the best outcome after ploidy manipulation in kiwifruit breeding.

The effects of chromosome-doubling on selected morphological and phytochemical characteristics of Cichorium intybus L.

SummaryThe artificial induction of polyploidy is an efficient method by which to increase the production of secondary metabolites in various plant species, but it is often accompanied by changes in morphological and phytochemical characteristics. In this study, various concentrations of colchicine [0.00, 0.05, 0.10, 0.25, or 0.50% (w/v)] were applied to the seeds or shoot apical meristems of young seedlings of Cichorium intybus L. to induce tetraploidy. Microscopic studies were used to select putative polyploids, and flow cytometry analysis was conducted to confirm ploidy levels. Comparisons were made between selected structural and phytochemical characteristics of the parental diploid and induced tetraploid chicory plants. Based on the numbers of tetraploids obtained, treatment of shoot apical meristems was found to be more efficient than seed treatment. Structural characteristics such as the sizes of leaves, flowers, stomatal guard cells, pollen grains, and numbers of chloroplasts in paired guard cells were affected by an increase in ploidy level. These measurements also indicated that the induction of autotetraploidy in C. intybus L. had a significant effect on total phenolic compound and chlorogenic acid concentrations in leaves.

Induced polyploidy dramatically increases the size and alters the shape of fruit in Actinidia chinensis

Some otherwise promising selections of Actinidia chinensis (kiwifruit) have fruit that are too small for successful commercialization. We have therefore made the first detailed study in diploid kiwifruit of the effects of chromosome doubling induced by colchicine on fruit size, shape and crop loading. Flow cytometric analysis of young leaves and chromosome analysis of flower buds and root tips was used to confirm the stability of induced autotetraploids. Fruit weight, size and crop load were measured in the third year after planting in the field and for three consecutive years. DNA fingerprinting was used to confirm the origin of the material. There was a very significant increase in fruit size in induced autotetraploids of different genotypes of A. chinensis. With the commercially important diploid cultivar 'Hort16A', most regenerants, Type A plants, had fruit which were much the same shape as fruit of the diploid but, at the same fruit load, were much larger and heavier. Some regenerants, Type B plants, produced fruit similar to 'fasciated' fruit. Fruit of the autotetraploids induced from three female red-fleshed A. chinensis selections were also 50-60 % larger than fruit of their diploid progenitors. The main increase in fruit dimensions was in their diameters. These improved fruit characteristics were stable over several seasons. Chromosome doubling has been shown to increase significantly fruit size in autotetraploid A. chinensis, highlighting the considerable potential of this technique to produce new cultivars with fruit of adequate size. Other variants with differently shaped fruit were also produced but the genetic basis of this variation remains to be elucidated. Autoploids of other Actinidia species with commercial potential may also show improved fruit characteristics, opening up many new possibilities for commercial development.

Photosynthetic characteristics of diploid honeysuckle (Lonicera japonica Thunb.) and its autotetraploid cultivar subjected to elevated ozone exposure

In order to investigate the effect of chromosome doubling on ozone tolerance, we compared the physiological responses of a diploid honeysuckle (Lonicera japonica Thunb.) and its autotetraploid cultivar to elevated ozone (O3) exposure (70 ng g-1, 7 h d-1 for 31 d). Net photosynthetic rate (P N) of both cultivars were drastically (P<0.01) impaired by O3. Although there were significantly positive correlation between P N and stomatal conductance (g s) in both cultivars under each treatment, the decreased g s in O3 might be the result rather than the cause of decreased P N as indicated by stable or increasing the ratio of intercellular to ambient CO2 concentration(C i/C a). P N under saturating CO2 concentration (P Nsat) and carboxylation efficiency (CE) significantly decreased under O3 fumigation, which indicated the Calvin cycle was impaired. O3 also inhibited the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (Fv/Fm), actual quantum yield of PSII photochemistry (ΦPSII), electron transport rate (ETR), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), the maximum in vivo rate of Rubisco carboxylation (Vcmax) and the maximal photosynthetic electron transport rate (Jmax) which demonstrated that the decrease in P N of the honeysuckle exposed to elevated O3 was probably not only due to impairment of Calvin cycle but also with respect to the light-harvesting and electron transport processes. Compared to the diploid, the tetraploid had higher relative loss in transpiration rate (E), (g s), (P Nsat), Vcmax and Jmax. This result indicated that the Calvin cycle and electron transport in tetraploid was damaged more seriously than in diploid. A barely nonsignificant (P=0.086) interaction between O3 and cultivar on P N suggested a higher photosynthetic sensitivity of the tetraploid cultivar.

Apomixis and sexuality in the Potentilla argentea complex III. Euploid and aneuploid derivatives (including trisomics) of some apomictic biotypes

Three apomictic biotypes belonging to the Potentilla argentea complex formed the basis of this investigation, one of them diploid, one tetraploid and one hexaploid. The effects of chromosome doubling and other changes in chromosome number were studied. Hybrids between the same biotypes were discussed in a previous paper. The diploid was a facultative apomict, but autotetraploids produced by colchicine treatment were totally sexual. This was also true of autotriploids, probably also of trisomics and other aneuploids. Five out of seven possible primary trisomics were obtained; they were morphologically well separated from each other and from the diploid. As shown by the result of test-crosses, facultative apomixis was restored in “recombined diploids” in progenies from triploids and trisomics. This indicates that apomixis is partly dependent on homozygosity for recessive genes, but that also the degree of ploidy as well as chromosomal and genic balance directly influence the mode of reproduction. — In the more strictly apomictic tetraploid (2n= 28) biotype, unreduced egg cells were fertilized in exceptional cases, whereas the chromosome-doubled plants formed some aberrants by fertilization of reduced egg cells. However, an “autotriploid” (2n= 42) formed half of its offspring by fertilization of unreduced and reduced egg cells. Aberrants with 2n= 35 and 2n= 63 were obligate apomicts. — The hexaploid was obligately apomictic, whereas the poorly fertile plants resulting from chromosome doubling gave rise to one plant with further increased chromosome number; thus, even here apomixis was interfered with to some extent. — The concluding discussion also deals with problems of mitotic and meiotic instability, crossing barriers in pseudogamous taxa, and viewpoints on the mechanisms and regulation of apomixis.

Photosynthetic responses to chromosome doubling in relation to leaf anatomy in Lonicera japonica subjected to water stress.

Gas exchange, chlorophyll fluorescence, and contents of some metabolites in two Japanese honeysuckle (Lonicera japonica Thunb.) cultivars, Damaohua (2n = 2x) and Jiufengyihao (2n = 4x), were compared with explore the function of chromosome doubling under water stress conditions. Water stress significantly decreased net photosynthesis rate, stomatal conductance, and transpiration rate of both cultivars. It also decreased electron transport rate, effective quantum yield of Photosystem II, photochemical quenching, and starch content, but increased non-photochemical quenching and contents of total soluble sugars, proline, and malondialdehyde. However, the tetraploid cultivar showed higher resistance to water stress than the diploid, as indicated by the fact that gas exchange, chlorophyll fluorescence, and metabolites were less affected for the tetraploid than the diploid. Moreover, the tetraploid recovered more quickly than the diploid after re-watering. Morphological and anatomical analysis further revealed that the tetraploid possessed less whole plant leaf area, higher leaf mass per unit area, thicker epidermis (both upper and lower) and palisade tissue, as well as denser pubescence. All of those specialised structures caused by chromosome doubling might lead to greater capacity in coping with drought stress. Our findings suggest that the effect of chromosome doubling on drought resistance in L. japonica could attribute to the improvement of structure and photosynthesis-related traits.

Effects of polyploidy on photosynthetic properties and anatomy in leaves of Phlox drummondii.

Polyploidy affects photosynthesis by causing changes in morphology, anatomy and biochemistry. However, in newly developed polyploids, the genome may be unstable. In this study, diploid (2×) and synthetic autotetraploids in initial (4×-C0) and 11th generations (4×-C11) of Phlox drummondii Hook were used to study the effects of chromosome doubling and genome stabilisation on leaf photosynthesis and anatomical properties. The light-saturated photosynthetic rate on a leaf area basis at 360 µmol CO2 mol-1 air (A360) was highest in 4×-C11 leaves, intermediate in 4×-C0 leaves, and lowest in 2× leaves. Rubisco amounts, CO2-saturated photosynthetic rate at 1200 µmol CO2 mol-1 air at PPFD of 1000 µmol m-2 s-1 (A1200, representing the capacity for RuBP regeneration), cumulative surface areas of chloroplasts facing intercellular spaces (Sc), all expressed on a leaf area basis, were all higher in 4× leaves than in 2× leaves, and stomatal conductance (gs) at 360 µmol CO2 mol-1 air was only higher in the 4×-C11 leaves. A360 for the 4×-C11 leaves was greater than that in the 4×-C0 leaves despite having similar amounts of Rubisco. This was presumably associated with a greater RuBP regeneration capacity, as well as an increase in Sc and gs, which would increase the CO2 concentration of Rubisco. These results indicate that the higher rate of photosynthesis in 4×-C11 leaves was not an immediate outcome of chromosome doubling; rather, it was due to adjustment and adaptation during the process of genome stabilisation.

Variation of Both DNA Genetic Structure and Reproduction Traits of Plant Autotetraploid

Due to the effect of chromosome doubling, the DNA genetic structures of autotetraploid vary from its original diploid, and thus autotetraploid phenotype changes correspondingly. Compared with original diploid, the phenotype changes of autotetraploid were as follows. The part of its male and female gametes was of abortion. Its pollen (diplo-haplont) was significantly bigger. The number of egg cells or synergids or antipodal cells in its embryo sacs increases or reduces. While self-crossing procreation of it, pollen tubes and the fertilization processes of polar nucleus and the fertilized cells development were partly abnormal. Its reproductive capacity (or seed setting rate) dropped to some extents, which can be gradually improved with generations. For some plant species, it has a better cross-compatibility in distant hybridizations.

Production of Doubled Haploids from Androgenic Embryoids and Plantlets of Tobacco

In four experiments, the chromosome doubling effect of acenaphthene vapour was tested on androgenic embryoids and/or plantlets of tobacco. The maximum rate of plants with doubled chromosome numbers (41.3 % diploids plus 2.7 % tetraploids) was recorded when approx. 100 mg acenaphthene in small and sterilized cheese-cloth bags were hanged for 72 h, into the culture jars (6.0 × 11.5 cm), containing 4 - 6 androgenic plantlets newly transferred from culture tubes. Acenaphthene treatments performed at the earlier stages of culture resulted in lower percentages (from 0.0 to 6.3 %).