A structural investigation of the ovule in sugar beet, Beta vulgaris: The micropylar nucellus

At the mature stage of ovule development the micropylar part of the crassinucellate nucellus in sugar beet, Beta vulgaris has been investigated by light and electron microscopy. Compared to the main body of the nucellus the columnar cells in the micropylar part appear more meristematic and display a number of structural characteristics indicative of high metabolic activity, e.g. abundant mitochondria, dilated endoplasmic reticulum, numerous dictyosomes and coated vesicles often fusing with irregular and strongly PAS+ cell walls. This tissue undergoes a gradual degeneration after having reached the mature stage and this degeneration seems to be independent of both pollination and fertilization. The cuticle structure of the apical cells in the micropylar nucellus is very similar to cuticles of stigmatic papillae in other plants, which may be related to this tissue being predetermined to be recognized and penetrated by pollen tubes. The ultrastructural features of the micropylar nucellus cells are well in accordance with a secretory activity related to penetration and guidance of pollen tubes. It is discussed whether mitochondrial conversion of ACC to ethylene in these cells might be involved in pre- and postfertilization processes.     

A structural investigation of the ovule in sugar beet, Beta vulgaris: Integuments and micropyle

The micropyle and the integuments of sugar beet (Beta vulgaris) ovules have been investigated by light and electron microscopy during differentiation and maturation of the ovule. The micropyle itself is formed by the inner integument which is surrounded by the outer integument at its base. The micropyle containts a fibrillar PAS+ substance and is often covered by a thin sheet or hymen. Both integuments are cuticle-covered thin sheets, each 2-few cell layers in thickness. In the outer integument an increase in starch accumulation occurs during ovule maturation and probably functions as nutrient storage for embryo development. The inner epidermis of the inner integument differentiates as the most conspicuous cell layer of the beet ovule. During growth and maturation of the ovule a system of small perinuclear vacuoles containing dense material increases steadily in these cells. At maturity this system fills up more than half of each cell and very dense material has accumulated in each vacuole. This vacuole content is highly refractive and contains tannins and/or polyphenols.     

Molecular genetic investigation of sugar beet (Beta vulgaris L.)

Molecular genetic studies of sugar beet (Beta vulgaris L.) are reviewed as a basis for the development of genomics of this species. The methods used to study structural and functional genomics are considered. The results and their application to increase the efficiency of sugar beet breeding are discussed.     

A linkage map of sugar beet (Beta vulgaris L.)

Summary We have established a first linkage map for beets based on RFLP, isozyme and morphological markers. The population studied consisted of 96 F₂ individuals derived from an intraspecific cross. As was expected for outbreeding species, a relatively high degree of polymorphism was found within sugar beet; 47% of the DNA markers were polymorphic for the chosen population. The map consists of 115 independent chromosomal loci designated by 108 genomic DNA probes, 6 isozyme and one morphological marker. The loci cover 789 cM with an average spacing of 6.9 cM. They are dispersed over nine linkage groups corresponding to the haploid chromosome number of Beta species. Eighteen markers (15.4%) showed distorted segregation which, in most instances, can be explained by gametic selection of linked lethal loci. The application of the linkage map in sugar beet breeding is discussed.     

Cytogenetics of autotetraploid sugar beet (Beta vulgaris L.)

Summary Autotetraploid and diploid varieties of sugar beet were investigated for morphology, plant development, root and seed yield. The results obtained from the tetraploid varieties were evaluated according to the number of euploid and aneuploid plants found in each variety. Aneuploid plants often are characterized by delayed growth and poor root or seed yield, which reflects in the average yield of the tetraploid variety. Eutetraploid plants will compete successfully with their diploid counterparts. Until chromosomal stability of euploid plants will be found, aneuploid plants can be eliminated by mechanical selection only, which has to be repeated in each generation. A mechanical selection for euploidy will not only lower the amount of aneuploids in the tetraploid varieties, but also among the triploid hybrid seeds.

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Zusammenfassung Autotetraploide und diploide Zuckerrübensorten wurden auf Morphologie, Wachstum sowie Rüben-und Samenertrag untersucht. Die Ergebnisse der tetraploiden Sorten wurden gemäß den in ihnen gefundenen Anteilen von euploiden und aneuploiden Pflanzen ausgewertet. Aneuploide Pflanzen sind oft durch verlangsamtes Wachstum und schlechten Rüben- oder Samenertrag gekennzeichnet, was sich im Durchschnittsertrag der tetraploiden Sorten widerspiegelt. Eutetraploide Pflanzen können erfolgreich mit den entsprechenden diploiden konkurrieren. Ehe nicht chromosomal stabile eutetraploide Pflanzen gefunden werden, können Aneuploide nur durch mechanische Selektion ausgelesen werden. Diese muß in jeder Generation wiederholt werden. Eine mechanische Selektion auf Aneuploide wird die Anzahl der Aneuploiden nicht nur in den tetraploiden Sorten herabsetzen, sondern auch unter den triploiden Hybridsamen.

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Resumen Se investigó variedades autotetraploides y diploides de remolacha azucarera en relación con la morfología, el desarrollo y el rendimiento en raíz y semilla. Los resultados obtenidos de la variedad tetraploide se evaluaron de acuerdo con el número de plantas euploides y aneuploides halladas. Las plantas aneuploides se caracterizan frecuentemente por un crecimiento retardado y una producción pobre en raíz o semilla, propiedades que se reflejan en el rendimiento medio de las variedades tetraploides. Las plantas eutetraploides pueden competir con éxito con sus correspondientes diploides. Mientras no se alcance la estabilidad cromosómica de las plantas euploides, las aneuploides pueden únicamente eliminarse por medio de una selección mecánica, selección que debe repetirse en cada generación. Una selección mecánica para euploidía no sólo rebajará la proporción de aneuploides en las variedades tetraploides sino tambien dentro de las semillas híbridas triploides.

     

Comparison of aerobic heterotrophic taxa isolated from four root domains of mature sugar beet (Beta vulgaris)

Abstract: The distribution of bacteria in the rhizosphere, rhizoplane, interior root tissues (core) and lower root (all tissues) of mature sugar beet roots ( Beta vulgaris ) was compared. Of 556 isolates, 102 species from 40 genera were identified by fatty acid methyl ester gas-chromatographic (FAME-GC) analysis. The ten most common genera ( Bacillus , 14%; Arthrobacter , 12%; Pseudomonas , 11%; Aureobacterium , 9%; Micrococcus , 6%; Xanthomonas , 5%; Alcaligenes , 4%; Flavobacterium , 3%; Agrobacterium , 3%; Microbacterium , 3%) accounted for 70% of isolates, and were found in each of three root domains (rhizosphere, rhizoplane and interior root tissues) on the two principal sampling occasions. Gram-positive strains were more abundant in the rhizosphere than the rhizoplane. Compared to the rhizoplane, rhizosphere bacterial communities were represented by a less diverse, more hierarchical distribution of species where twice as many isolates formed late developing colonies on isolation plates. Between October and January, the bacteria isolated from root interior tissues acquired a distinct change in taxonomic pattern, with decreased diversity and increased hierarchy. A bacterial continuum of similar taxa was observed which extended from the rhizosphere to interior root tissues.     

Intraspecific diversity of sugar beet (Beta vulgaris) mitochondrial DNA

Summary Mitochondrial (mt) DNA, isolated from different sugar beet populations, was analyzed using BamHI and EcoRI restriction enzymes. It was shown that plants possessing the new mtDNA types are revealed among O-type fertilizers quite frequently. Among cytoplasmic male sterile (cms) plants, which evolved during cultivation of O-type fertilizers, plants with altered mt genome were found.     

Plant regeneration from protoplasts of sugar beet (Beta vulgaris)

Mesophyll protoplasts from two of five sugar beet lines tested were regenerated into plants. Mesophyll protoplasts of all lines showed high plating efficiencies up to 4.0% developed hard compact callus, and two of the lines also developed white, soft and friable callus consisting of starch grain-containing cells. Whereas the compact callus never regenerated into plants, the white friable ones frequently developed globular structures, which became green in the light and formed adventitious shoots after cytokinin (BAP or thidiazuron) treatment. Genetic analysis by PCR-fingerprinting and flow cytometry showed uniformity and unchanged ploidy levels in 15 independently regenerated plantlets in line NF. but altered ploidy level (from diploid to triploid) in a regenerated plantlet of clone VRB.     

The "crystals" in the sugar beet (Beta vulgaris L.) leaves

Crystal containing cells widely distributed in plant tissues, though the origin of the crystals and their functions are still opened to question. Membrane vesicles in beet leaves are visible in electronic microscope. They originate in cytoplasm and penetrate into vacuole by pinocytosis with participation of tonoplast. In light microscope, vesicles are luminous likewise crystals in crystal cells. Such vesicles-"crystals" fulfill crystal cells also. The content of vesicles-"crystals" are electronic transparent at every path of leaf development. It was proposed that distinct vesicles-"crystals" in cytoplasm and vacuole and mass of them in crystal cells, vein bundles, and epidermal cells--all of them are lytic compartments. Later, obviously, true crystals are formed.     

Intraspecific variation of Myzus persicae on sugar beet (Beta vulgaris)

Differences in inherited resistance among seven sugar-beet stocks had similar effects on Myzus persicae clones representing the range of variation in aphid response to resistant and susceptible sugar beet observed in fifty-eight clones collected between 1969 and 1971. Three sugar-beet stocks were consistently resistant. Statistically significant interactions between beet stocks and aphid clones did not indicate the existence of biotypes with specific abilities to overcome resistance. M. persicae clones differed in their vigour of colonizing sugar beet, irrespective of the differences between beet stocks. The readiness of adult aphids to settle determined the size of aphid population produced and included a component related to the response of the aphid clone to sugar beet as a host, and a component related to the resistance ranking of the beet stock. Breeding sugar beet with resistance to aphids will be simplified, as the results indicate that, at present, differences between aphid biotypes need not be considered a problem.     

Cadmium effects on leaf transpiration of sugar beet (Beta vulgaris)

Seedlings of sugar beet ( Beta vulgaris L. cv Monohill) were cultivated for 4 weeks in nutrient solution containing different concentrations of CdCl₂ (0 to 10 μ M ). The effects of Cd on appearance and function of stomata and leaf cuticle were investigated by water loss measurements and microscopy. The leaf transpiration rate increased with increasing Cd concentrations while the sum total of stomatal aperture area per unit leaf area decreased. Already at low Cd levels. an increase of defective and undeveloped stomata was found in Cd treated plants. These stomata are closed or have small apertures and probably lack a functional closing mechanism. The number of intact stomata per unit leaf area was lower in leaves of Cd treated plants than in controls, and Cd induced closure of intact stomata. The total number of stomata per leaf area slightly increases with increasing Cd concentration. as does the percentage of small stomata. Furthermore. specific leaf area increased, while the density of leaf structure was decreased by Cd. From this observation we conclude that the increase in transpiration rate caused by Cd is primarily due to effects on the permeability of the leaf cuticle to water.     

A refined method for ovule culture in sugar beet (Beta vulgaris L.)

Induction of gynogenesis through ovule culture is a valuable tool to produce haploid and doubled haploid plants in sugar beet (Beta vulgaris L.). However, there is still large room for refining the method. In this study we investigated the gynogenic response of cultured ovules of three sugar beet genotypes, the effect of the application to inflorescences of different pretreatments with mannitol at 4ºC and with 5-azacytidine and 2,4-D, and the effect of the use of different basal culture media and sucrose concentrations. The response was evaluated in terms of percentages of induction of gynogenesis, embryogenesis and callogenesis, as well as of regenerated plants. We showed that a pretreatment with 0.5 M mannitol at 4 °C for 4 days, and with 50 µM 5-AzaC for 1 h, notably improved the percentage of embryogenesis and plant regeneration. Besides, the use of MS basal medium and 60 g/L sucrose was also found beneficial. This study provides new ways to improve the efficiency of haploid induction and plant regeneration through ovule culture in sugar beet, and is potentially applicable to ovule culture in other crops.

     

Selection in vitro for UV-tolerant sugar beet (Beta vulgaris) somaclones

With a reduced stratospheric ozone concentration, the generation of UV-tolerant plants may be of particular importance. Among different crop plants there is large variation in sensitivity to UV-B radiation. This study was undertaken to investigate the possibilities of using somaclonal variation and selection in vitro for improving UV-B tolerance in sugar beet (Beta vulgaris L.). Sugar beet callus was exposed to UV radiation (280–320 nm, 0.863–5.28 kJ m^-2 day^-1, unweighted) and resultant shoots were selected from surviving cells. After establishment of the plants, they were grown under either visible radiation (114 μmol m^-2 s^-1 PAR) or with the addition of UV radiation (6.3 kJ m^-2 day^-1 biologically effective UV-B). Screening of regenerants in vivo for tolerance to UV radiation was undertaken 10 months after termination of the UV selection pressure. Screening was done visually and by using a number of physiological parameters, including chlorophyll fluorescence induction, ultraweak luminescence, pigment analysis and total content of UV-screening pigments. A clear difference between the unselected and the UV-selected somaclones was observed when visually studying the UV damage and other leaf injury. The observations were supported by the ultraweak luminescence measurements. Unselected plants showed significantly greater damage when subjected to subsequent UV radiation as compared to the selected plants. The clones subjected to UV selection pressure displayed a significantly higher concentration of UV-screening pigments under subsequent UV radiation. The unselected plants under subsequent UV treatment showed a lower carotenoid concentration when compared to selected plants. However, no significant difference between treatments was found for chlorophyll a/b, or F/F_max, a measure of photosynthetic quantum yield.     

Comparison of chloroplast and mitochondrial DNA from five morphologically distinct Beta vulgaris cultivars: sugar beet,fodder beet,beet root,foliage beet,and Swiss chard

Summary Two cytoplasms, N and S, are used in the breeding of sugar beet, Beta vulgaris var. altissima. These cytoplasms can be distinguished by their mitochondrial DNA. In an attempt to detect new cytoplasms, we compared the restriction profiles of chloroplast and mitochondrial DNA from five different cultivars of Beta vulgaris. All restriction patterns of chloroplast DNA were identical. With the exception of sugar beet with S-cytoplasm, all cultivars studied showed the same restriction profile of mitochondrial DNA, indicating that these cultivars all contain the N-cytoplasm. These results are discussed with regard to the large morphological differences of the cultivars and the cytoplasmic variability found in natural populations of the wild beet, Beta maritima.     

Histological and semi-quantitative approaches to in vitro cellular responses of ovule,embryo and endosperm in sugar beet,Beta vulgaris L.

Summary Fertilized ovules from sugar beet, Beta vulgaris L., of different intra- and interspecific crosses have been grown under in situ and in vitro conditions and investigated by light microscopy. Selected anatomical parameters were observed and entered in a computer program for statistical treatment. After a few days in culture the cells of the inner integument epidermis develop reticulate wall thickenings and their content of tannins decrease. Likewise, the starch content in the outer integument decreases and no real seed coat is formed. The funiculus tissue increases its metabolic activity, i.e., abundant accumulation of protein and starch. Callus or callus-like proliferations develop in the nucellus and the suspensor, but only rarely in the embryo or endosperm. However, the embryo may show an irregular morphology. Very rapid metabolism of starch in the suspensor may be related to the ability of the embryo to survive the first days in culture. Generally, the cellular responses, most significant in the maternal sporophytic tissue and the suspensor rather than in the embryo and endosperm, can be explained as structural adaptations to alternative pathways of nutrient supply.     

Variability of cathodic peroxidases in sugar beet (Beta vulgaris L.) cultivars

Eighteen varieties of sugar beet (Beta vulgaris L.), originating from various European countries, were compared in respect of peroxidase variability level. They were cultivated in the same experimental plot. The cultivars differed in ploidy level: one variety was tetraploid, three were diploid and 14 varieties were triploid. The cathodic peroxidase system is controlled by four independent genes, of which only one is polymorphic. Consequently, the varieties were characterised by frequencies of 3 allozymes belonging to one locus. Only one variety proved to be fully monomorphic. Genetic similarities between the cultivars were illustrated by a dendrogram (UPGMA) and show different groups of varieties not related to their ploidy level.     

A new cytoplasmic male sterile genotype in the sugar beet Beta vulgaris L.: a molecular analysis

Summary Mitochondrial DNA (mtDNA) from fertile (N) and possibly new cytoplasmic male sterile (CMS) genotypes was studied in the sugar beet Beta vulgaris L. It was found by restriction endonuclease analysis that BMC-CMS, a cytoplasm that was derived from the wild beet Beta maritima, contained a unique type of mtDNA which is distinguishable from both the N and S-CMS, the only other CMS genotype that is currently availabe in B. vulgaris L. The organization of three genes: coxI, coxII and cob, was analyzed by hybridization with heterologous probes from maize. These genes have a similar structure in N and BMC-CMS that is different from S-CMS. It is concluded that BMC-CMS is a novel CMS genotype in the sugar beet.     

Biolistic transformation of highly regenerative sugar beet (Beta vulgaris L.) leaves

Leaves of greenhouse-grown sugar beet (Beta vulgaris L.) plants that were first screened for high regeneration potential were transformed via particle bombardment with the uidA gene fused to the osmotin or proteinase inhibitor II gene promoter. Stably transformed calli were recovered as early as 7 weeks after bombardment and GUS-positive shoots regenerated 3 months after bombardment. The efficiency of transformation ranged from 0.9% to 3.7%, and stable integration of the uidA gene into the genome was confirmed by Southern blot analysis. The main advantages of direct bombardment of leaves to regenerate transformed sugar beet include (1) a readily available source of highly regenerative target tissue, (2) minimal tissue culture manipulation before and after bombardment, and (3) the overall rapid regeneration of transgenic shoots.     

Restriction fragment map of sugar beet (Beta vulgaris L.) chloroplast DNA

Summary A restriction endonuclease fragment map of sugar beet chloroplast DNA (ctDNA) has been constructed with the enzymes SmaI, PstI and PvuII. The ctDNA was found to be contained in a circular molecule of 148.5 kbp. In common with many other higher plant ctDNAs, sugar beet ctDNA consists of two inverted repeat sequences of about 20.5 kbp separated by two single-copy regions of different sizes (about 23.2 and 84.3 kbp). Southern hybridization analyses indicated that the genes for rRNAs (23S+16S) and the large subunit of ribulose 1,5-bisphosphate carboxylase were located in the inverted repeats and the large single-copy regions, respectively.     

Flavin excretion from roots of iron-deficient sugar beet (Beta vulgaris L.)

The characteristics of flavin excretion from iron-deficient sugar-beet roots have been studied. Roots from iron-deficient sugar beet excreted flavins when plants were allowed to decrease the pH of the nutrient solution, but not when plants were grown in nutrient solutions buffered at high pH. As shown by reversed-phase high-performance liquid chromatography, the two major flavins whose excretion was induced by iron deficiency were different from riboflavin, FMN and FAD. These flavins have been identified as riboflavin 3′-sulfate and riboflavin 5′-sulfate by electrospray-mass spectrometry, inductively coupled plasma emission spectroscopy, infrared spectrometry and¹H-nuclear magnetic resonance. We have characterized the time courses of accumulation of the different flavins in the nutrient solution and considered several possible roles for flavin excretion in iron acquisition.