Xylem loading process is a critical factor in determining Cd accumulation in the shoots of Solanum melongena and Solanum torvum

Cadmium (Cd) concentration in eggplant (Solanum melongena) fruits can be drastically reduced by grafting them with Solanum torvum rootstock. We thus examined the characteristics of Cd absorption in roots and Cd translocation from roots to shoots between S. melongena and S. torvum over 7 days using a hydroponic culture. Although there is no significant difference in Cd concentration in the roots of S. melongena and S. torvum, Cd concentration in the shoots and xylem sap was higher in S. melongena than in S. torvum. By evaluating symplastic Cd absorption in roots, using enriched isotopes ¹¹³Cd and ¹¹⁴Cd, and measuring the kinetics in xylem loading, we characterized Cd absorption and translocation for S. torvum (low Cd translocation) and S. melongena (high Cd translocation). A concentration-dependent study in roots indicated that K_m values were almost the same for species, but the V_max value was 1.5-fold higher in S. melongena than in S. torvum. A concentration-dependent study in xylem loading indicated that V_max was almost the same, but K_m values were approximately 7-fold higher in S. torvum compared to S. melongena. These results, together, suggest that the affinity for Cd in the xylem loading process is a critical factor for determining the different Cd concentrations in the shoots between both plants under low Cd concentration conditions. In addition, a metabolic inhibitor, carbonyl cyanide-m-chloro-phenyl-hydrazone (CCCP) inhibited Cd absorption and translocation from roots to shoots in both plants. This suggests that Cd absorption in roots and Cd translocation from roots to shoots via the xylem loading process, under low Cd concentration conditions, are partly mediated by an active energy-dependent process in both plants.     

Comparison between Solanum torvum Sw. and S. melongena L. after Ralstonia solanacearum inoculation

Bacterial wilt, caused by Ralstonia solanacearum, is one of the most devastating plant diseases, affecting some economically important Solanaceae crops. In contrast, Solanum torvum, also known as wild eggplant, does not wilt when infested with R. solanacearum. In order to describe the mechanism underlying the response of S. torvum, it was compared with the cultivated eggplant, S. melongena, when both were infected with the same R. solanacearum strain. No wilting occurred in S. torvum, although the bacteria colonised roots and stems in both species within the first 24 h. There were marked differences beyond 24 h, consisting of high bacterial mortality in S. torvum. Using the calli model, our investigations revealed an increase in cell wall monoamine oxidase activity in S. torvum after R. solanacearum inoculation, which did not occur in S. melongena.     

Potential of Tissue Culture for Breeding Root-Knot Nematode Resistance into Vegetables

Plant protoplast technology is being investigated as a means of transferring root-knot nematode resistance factors from Solanum sisymbriifolium into the susceptible S. melongena. Solanum sisymbriifolium plants regenerated from callus lost resistance to Meloidogyne javanica but retained resistance to M. incognita. Tomato plants cloned from leaf discs of the root-knot nematode resistant ''Patriot'' were completely susceptible to M. incognita, while sections of stems and leaves rooted in sand in the absence of growth hormones retained resistance. Changes in resistance persisted for three generations. It is postulated that the exogenous hormonal constituents of the culture medium are modifying the expression of genetic resistance.     

STUDIES ON THE ROOT OF HORDEUM VULGARE L.– ULTRASTRUCTURE OF THE SEMINAL ROOT WITH SPECIAL REFERENCE TO THE PHLOEM

Seminal root tissue of Hordeum vulgare L. var. Barsoy was fixed in glutaraldehyde and osmium tetroxide and studied with the light and electron microscopes. The roots consist of an epidermis, 6–7 layers of cortical cells, a uniseriate endodermis and a central vascular cylinder. Cytologically, the cortical and endodermal cells are similar except for the presence of tubular-like invaginations of the plasmalemma, especially near the plasmodesmata, in the former. The vascular cylinder consists of a uniseriate pericycle surrounding 6–9 phloem strands occurring on alternating radii with an equal number of xylem bundles. The center of the root contains a single, late maturing metaxylem vessel element. Each phloem strand consists of one protophloem sieve element, two companion cells and 1–3 metaphloem sieve elements. The protophloem element and companion cells are contiguous with the pericycle. Metaphloem sieve elements are contiguous with companion cells and are separated from tracheary elements by xylem parenchyma cells. The protoplasts of contiguous cells of the root are joined by various numbers of cytoplasmic connections. With the exception of the pore-plasmodesmata connections between sieve-tube members and parenchymatic elements, the plasmodesmata between various cell types are similar in structure. The distribution of plasmodesmata supports a symplastic pathway for organic solute unloading and transport from the phloem to the cortex. Based on the arrangement of cell types and plasmodesmatal frequencies between various cell types of the root, the major symplastic pathway from sieve elements to cortex appears to be via the companion and xylem parenchyma cells.     

Somatic hybrid plants produced by electrofusion between Solanum melongena L. and Solanum torvum Sw

Summary Somatic hybrid plants between eggplant (Solanum melongena) and Solanum torvum have been produced by the electrofusion of mesophyll protoplasts in a movable multi-electrode fusion chamber. Using hair structure as a selection criteria, we identified a total of 19 somatic hybrids, which represented an overall average of 15.3% of the 124 regenerated plants obtained in the two fusion experiments. Several morphological traits were intermediate to those of the parents, including trichome density and structure, height, leaf form and inflorescence. Cytological analyses revealed that the chromosome numbers of the somatic hybrids approximated the expected tetraploid level (2n=4x=48). Fifteen hybrid plants were homogeneous and had relatively stable chromosome numbers (46–48), while four other hybrids had variable chromosome numbers (35–48) and exhibited greater morphological variation. The hybridity of these 19 somatic hybrid plants was confirmed by analyses of phosphoglucomutase (Pgm) and esterase zymograms.     

白鲜根的发育解剖学研究

应用半薄切片、常规石蜡切片并结合离析法,对药用植物白鲜(Dictamnus dasycarpus Turcz.)根的发生发育过程进行了研究。结果表明:白鲜根的发生发育过程包括4个阶段,即原分生组织阶段、初生分生组织阶段、初生结构阶段以及次生结构阶段。原分生组织位于根冠内侧及初生分生组织之间,衍生细胞分化为初生分生组织。初生分生组织由原表皮、基本分生组织以及中柱原组成。原表皮分化为表皮,基本分生组织分化为皮层,中柱原分化为维管柱,共同组成根的初生结构;在初生结构中,部分表皮细胞外壁向外延伸形成根毛,皮层中分布有油细胞,内皮层有凯氏带,初生木质部为二原型或偶见三原型,外始式;根初生结构有髓或无。次生结构来源于原形成层起源的维管形成层的活动以及中柱鞘起源的木栓形成层的活动;白鲜次生韧皮部宽广,其中多年生根中可占根横切面积的85%,另外除基本组成分子外,还分布有油细胞;周皮发达,木栓层厚;初生皮层、次生木质部和次生韧皮部薄壁细胞中常充满丰富的淀粉粒。     

Cadmium accumulation in relation to organic acids in leaves of Solanum nigrum L. as a newly found cadmium hyperaccumulator

The influence of various cadmium concentrations on organic acid levels in leaves of the Cd hyperaccumulator, Solanum nigrum L. and a closely related species, Solanum melongena L., were investigated. In particular, the relationship of organic acids with Cd accumulation in the two plants was investigated. The results showed that Cd accumulation in the shoots of S. nigrum was significantly higher than that of S. melongena. The accumulation of Cd in the leaves of S. nigrum ranged from 2.0 to 167.8 μg g⁻¹ dry weight (DW), but only from 1.2 to 64.0 μg g⁻¹ DW in S. melongena. Solanum melongena was considerably less tolerant to Cd than S. nigrum. Approximately 20% of the total Cd in S. nigrum leaves was water-soluble, suggesting that some accumulated Cd was associated with water-soluble compounds such as organic acids. Malic acid in the leaves of S. nigrum was the most abundant organic acid [up to 115.6–145.7 μmol g⁻¹ fresh weight (FW)], but this acid was not significantly affected by the Cd concentration in soil. However, the level of malic acid in S. melongena plants was much lower, only 16.3–75.4 μmol g⁻¹ FW. The significant positive correlations between total Cd and water-soluble Cd concentrations and both acetic and citric acid concentrations in the leaves of S. nigrum were observed. In contrast, there was no correlation between concentrations of the two acids and Cd concentrations in the leaves of S. melongena. These results indicated that acetic and citric acids in the leaves of S. nigrum might be related to its Cd hyperaccumulation.     

GISH confirmation of somatic hybrids between Solanum melongena and S. torvum: assessment of resistance to both fungal and bacterial wilts

Interspecific somatic hybrids between Solanum melongena L. (2n = 2x = 24) and two accessions of Solanum torvum Sw. (2n = 2x = 24) were produced in view of transferring resistance to two soil-born pathogens, Ralstonia solanacearum and Verticillium dahliae, from the wild species into the cultivated eggplant. All somatic hybrids were phenotypically homogenous and intermediate between the parents. Their hybrid nature was confirmed by analysis of isozymes and RAPDs. They showed reduced pollen viability, and all but one possessed the chloroplasts from either one or the other parent. As S. melongena and S. torvum chromosomes were morphologically indistinguishable, genomic in situ hybridisation (GISH) was applied to recognise the chromosomes from each parent in the hybrids. As expected, the selected tetraploid plants contained one complete set of chromosomes from each fusion partner. On spread preparations, the two parental genomes were not spatially separated at any time of the cell cycle. Translocation or recombinant chromosomes could not be demonstrated in the mitotic metaphase. Tests for resistance performed in vitro by using suspensions of two strains of R. solanacearum (race 1 and 3) and filtrate of culture medium of one strain of V. dahliae, revealed that S. melongena was susceptible, whereas both accessions of S. torvum had high levels of resistance. Except for two hybrid clones, which were found susceptible to race 3, as was S. melongena, all somatic hybrids tested showed good levels of bacterial and fungal resistance, either intermediate or as high as that of the wild parent.     

Random amplified polymorphic DNA variation in the eggplant,Solanum melongena L. (Solanaceae)

RAPD analysis was carried out on 52 accessions of Solanum melongena (eggplant) and related weedy forms known as insanum. Twenty-two primers amplified 130 fragments. Solanum melongena exhibited 117 of the fragments, all of which were also present in insanum. Insanum displayed an additional 13 fragments not found in S. melongena. Overall, the insanum accessions were more diverse than those of S. melongena. The calculated similarity between them was 0.947. The RAPD results were closely concordant with the results of an electrophoretic isozyme survey performed on the same accessions. The concordance of the results shows that even though S. melongena and insanum are highly diverse morphologically, it is no longer appropriate to distinguish them taxonomically.     

茄子野生近缘种托鲁巴姆试管微扦插繁殖技术研究

嫁接栽培是茄果类蔬菜防治土传病害和提高产量的重要措施之一。茄子野生近缘种托鲁巴姆(Solanums torvum)因综合抗性强,成为茄子和番茄嫁接的常用优良砧木。但是,由于托鲁巴姆种子的发芽率、发芽势和发芽指数较低,苗龄较长,限制了其在工厂化育苗中的大规模应用,因此迫切需要开发其他方法及相应技术体系提高托鲁巴姆的育苗效率,降低育苗成本。为优化托鲁巴姆微扦插技术,该研究探索并优化了试管内微扦插繁殖托鲁巴姆技术,以无菌播种获得初代无菌苗的茎段为外植体,通过在培养基中添加植物生长调节剂,对比不同浓度植物生长调节剂对托鲁巴姆微扦插繁殖过程中的影响。结果表明:(1)托鲁巴姆在不同培养基中,腋芽诱导、继代增殖和生根培养的效果存在显著差异,初代芽诱导的最佳培养基为MS+KT 0.5 mg·L^-1+IBA 0.1 mg·L^-1,出芽率达90%。(2)继代扦插最佳培养基为MS+IBA 0.4 mg·L^-1,培养30 d的增殖系数达6.11,植株长势健壮。(3)最佳生根培养基为1/2MS+IBA 0.2 mg·L^-1,生根培养30 d,单株一级根数4.56条,最长根长125.80 mm、根粗0.50 mm,根系发达。采用试管内微扦插技术繁殖托鲁巴姆种苗,操作简单,增殖系数较高,可满足快速繁育种苗的要求。该研究结果为托鲁巴姆的工厂化规模育苗提供了新途径。     

Transfer of fungal tolerance through interspecific somatic hybridisation between Solanum melongena and S. torvum

Tolerance to Verticillium wilt is found in a wild relative of eggplant, Solanum torvum. To transfer this tolerance to eggplant (S. melongena), protoplast fusions between eggplant and irradiated S. torvum protoplasts were performed. Putative hybrids were regenerated and evaluated for Verticillium tolerance and field value. A total of 12 plants were eventually selected to be incorporated into the breeding program, as they showed a high degree of Verticillium tolerance under field conditions combined with the morphological characters of eggplant, including normal seed set. DNA analysis showed one of these tolerant plants to have a changed pattern, with some changes corresponding to specific pattern characteristics of S. torvum. Received: 12 April 1998 / Revision received: 9 September 1998 / Accepted: 29 November 1998     

Increased resistance to fungal wilts in transgenic eggplant expressing alfalfa glucanase gene

The wilt diseases caused by Verticillium dahliae and Fusarium oxysporum are the major diseases of eggplant (Solanum melongena L.). In order to generate transgenic resistance against the wilt diseases, Agrobacterium-mediated gene transfer was performed to introduce alfalfa glucanase gene encoding an acidic glucanase into eggplant using neomycin phosphotransferase (npt-II) gene as a plant selection marker. The transgene integration into eggplant genome was confirmed by Polymerase chain reaction (PCR) and Southern blot analysis and transgene expression by the glucanase activity and western blot analysis. The selected transgenic lines were challenged with V. dahliae and F. oxysporum under in vitro and in vivo growth conditions, and transgenic lines showed enhanced resistance against the wilt-causing fungi with a delay of 5–7 days in the disease development as compared to wild-type plants.     

Comparison of Compatible and Incompatible Response of Potato to Meloidogyne incognita

One susceptible (D6) and two resistant (E2 and N4) clones of Solanum sparsipilum × (S. phureja × haploid of S. tuberosum) were used to study the responses of potato roots and tubers to race 1 of Meloidogyne incognita (Kofoid &White) Chitwood. The compatible response was characterized by rapid penetration of large numbers of second-stage juveniles (J2) into roots, cessation of root growth, and occasional curving of root tips. The life cycle of M. incognita in the susceptible clone was completed in 25 days at 23-28 C. The incompatible response was characterized by penetration of fewer J2 into roots, necrosis of feeding sites within 2-7 days, and lack of nematode development. There were no differences in response of tubers from resistant and susceptible clones to nematode infection. Small numbers of J2 were detected in tubers, but they did not develop.     

Immunofluorescent Localization of Plasma Membrane H-ATPase in Barley Roots and Effects of K Nutrition

The plasma membrane H⁺-ATPase (PM-H⁺-ATPase) of barley (Hordeum vulgare L. cv Klondike) roots was assayed by cross-reaction on western blots and cryosections with an antibody against the PM-H⁺-ATPase from corn roots. Under conditions of reduced K availability, which have previously been shown to increase K influx by greater than 25-fold, there were only minor changes detected in PM-H⁺-ATPase levels. Antibody labeling of cryosections showed the relative distribution of PM-H⁺-ATPase among cell types in root tips and mature roots. Epidermal cells, both protoderm and mature root epidermis, including root hairs, had high levels of antibody binding. In mature roots, the stelar tissue showing the highest antibody binding was the companion cells of the phloem, followed by pericycle, xylem parenchyma, and endodermis.     

An easy method for cutting and fluorescent staining of thin roots

Background and Aims

Cutting plant material is essential for observing internal structures and may be difficult for various reasons. Most fixation agents such as aldehydes, as well as embedding resins, do not allow subsequent use of fluorescent staining and make material too soft to make good-quality hand-sections. Moreover, cutting thin roots can be very difficult and time consuming. A new, fast and effective method to provide good-quality sections and fluorescent staining of fresh or fixed root samples, including those of very thin roots (such as Arabidopsis or Noccaea), is described here.

Methods

To overcome the above-mentioned difficulties the following procedure is proposed: fixation in methanol (when fresh material cannot be used) followed by en bloc staining with toluidine blue, embedding in 6 % agarose, preparation of free-hand sections of embedded material, staining with fluorescent dye, and observation in a microscope under UV light.

Key Results

Despite eventual slight deformation of primary cell walls (depending on the species and root developmental stage), this method allows effective observation of different structures such as ontogenetic changes of cells along the root axis, e.g. development of xylem elements, deposition of Casparian bands and suberin lamellae in endodermis or exodermis or peri-endodermal thickenings in Noccaea roots.

Conclusions

This method provides good-quality sections and allows relatively rapid detection of cell-wall modifications. Also important is the possibility of using this method for free-hand cutting of extremely thin roots such as those of Arabidopsis.     

Life Cycle,Pathogenicity, Histopathology,and Host Range of Race 5 of the Barley Root-Knot Nematode

The optimum temperature for development of race 5 of Meloidogyne naasi was 26 C. A life cycle was completed in 34 days. Growth of sorghum was suppressed when inoculated with M. naasi. Observations of M. naasi-infected sorghum roots demonstrated that roots were penetrated just behind the root cap; giant cells were generally initiated either in the procambial region or in very young phloem. When giant cells developed in the cortex, corresponding areas of the vascular system did not have an endodermis, pericycle, or phloem fibers. Nineteen plant species were tested for suitability as hosts for race 5 of M. naasi. Reproduction occurred on 11 of 12 monocotolydenous hosts and none of 7 dicotolydenous hosts. Reproduction often occurred without gall development.     

Metabolic inhibitors induce symplastic movement of solutes from the transport phloem of Arabidopsis roots

The distribution of the phloem-mobile fluorescent probe carboxyfluorescein(CF) within the primary root of Arabidopsis thaliana was imagedusing a confocal laser scanning microscope (CLSM) and the tissueand subcellular distribution of the probe was shown to be influencedby treatment with a number of metabolic inhibitors. Sodium azidecompletely inhibited the phloem transport of CF into the treatedregion of root. Treatment with both CCCP and probenecid inducedthe lateral movement of CF from the transport phloem to theadjacent cell layers, and the probe accumulated in the cytoplasmof the pericycle, endodermis, cortex, and epidermis. This lateraltransfer of CF was restricted to the pericycle in the presenceof plasmolysing concentrations of sorbitol. Ultrastructuralinvestigations demonstrated the presence of a plasm odesmatalpathway leading from the sieve elementcompanion cell complex(SE-CC) out into the cortex. The results are consistent withthe operation of this symplastic pathway under conditions ofmetabolic energy reduction and are discussed in relation tothe regulation of plasmodesmatal conductance in the transportphloem. Key words: Arabidopsis, confocal laser scanning microscopy (CLSM), metabolic inhibitors, phloem transport, symplastic phloem unloading