Fleshy Storage Research Articles

Characterisation of Pectobacterium carotovorum causing soft rot on Kalanchoe gastonis-bonnierii in Malaysia

Soft rot disease can be found worldwide on fleshy storage tissues of fruits, vegetables and ornamentals. The soft rot Pectobacterium carotovorum subsp. carotovorum (Pcc) is an important pathogen of Kalanchoe spp. and other ornamental plants. The disease occurs on crops in the field, greenhouses and during transit, resulting great economic damages. The economic importance of crop loss by soft rot bacteria varies by severity of the disease and value of the crop. A destructive disease on Kalanchoe gastonis-bonnierii was observed in commercial ornamental plant greenhouses in Cameron highland and Melaka, Malaysia in 2011. Samples suspected to be infested with Pectobacterium spp. were brought to the laboratory. In pathogenicity test, a suspension of 106 CFU/ml of strains was able to cause soft rot on leaves and stems. A 434 bp banding pattern on 1% agarose gel was produced in polymerase chain reaction (PCR) amplification of pectate lyase encoding gene (Pel gene). PCR amplification of the intergenic transcribed spacer (ITS) (16S–23S rRNA) ITS region with G1 and L1 primers produced two main bands at about 540 and 570 bp. The ITS-PCR products were digested with RsaI restriction enzyme. For discrimination of the P. carotovorum subsp. carotovorum (Pcc) from P. carotovorum subsp. odoriferum (Pco), all isolates subjected to α-methyl glucoside test. All isolates were identified as Pcc based on phenotypic and molecular methods. This is the first report of soft rot disease caused by P. carotovorum subsp. carotovorum on K. gastonis-bonnierii, in Malaysia.

Evidence That Thaxtomin C Is a Pathogenicity Determinant of Streptomyces ipomoeae, the Causative Agent of Streptomyces Soil Rot Disease of Sweet Potato

Streptomyces ipomoeae is the causal agent of Streptomyces soil rot of sweet potato, a disease marked by highly necrotic destruction of adventitious roots, including the development of necrotic lesions on the fleshy storage roots. Streptomyces potato scab pathogens produce a phytotoxin (thaxtomin A) that appears to facilitate their entrance into host plants. S. ipomoeae produces a less-modified thaxtomin derivative (thaxtomin C) whose role in pathogenicity has not been examined. Here, we cloned and sequenced the thaxtomin gene cluster (txt) of S. ipomoeae, and we then constructed targeted txt mutants that no longer produced thaxtomin C. The mutants were unable to penetrate intact adventitious roots but still caused necrosis on storage-root tissue. These results, taken in context with previous histopathological study of S. ipomoeae infection, suggest that thaxtomin C plays an essential role in inter- and intracellular penetration of adventitious sweet potato roots by S. ipomoeae. Once inside the plant host, the pathogen uses one or more yet-to-be-determined factors to necrotize root tissue, including that of any storage roots it encounters.

The root-tuber anatomy of Asphodelus aestivus

The root tubers of Asphodelus aestivus consist mostly of enlarged fleshy storage tissue. They are bounded by a multiple-layered velamen, responsible for rapid water uptake, water loss reduction, osmotic and mechanical protection. In the cortex area, thin-walled idioblasts contain numerous raphides of calcium oxalate in their large vacuole with a distinctive tonoplast. Wide morphological variations are observed among the raphide cross sections. Electron-dense compounds penetrate the raphide surface and raphide groove. Raphides seem to be vital for the protection of the root tuber parenchyma from herbivores. The cells of uniseriate endodermis are heavily thickened possessing a few plasmodesmata. The vascular cylinder is 20–28-arch and the root xylem consists of vessels in short radial rows, alternating with clusters of phloem cells. The presence of cells, which contain soluble polysaccharides in their large vacuole, is conspicuous after employing the Schiff's reagent. Exodermis cells and all cell walls, especially the thick ones of the endodermis, are also stained. Numerous parenchyma cells, especially those around vascular bundles are stained intensely, when exposed to Sudan Black B. These cells occurring as solitary idioblasts abundantly accumulate oil. Electron-dense remnants are evident within the vacuoles of the storage cells especially near the vascular tissue. The morphological features of A. aestivus root tubers and the major part of the total plant biomass are responsible for the species’ occurrence and frequent dominance in a wide array of arid environments. A. aestivus possessing root tubers is proved to be very efficient in storing water during the long summer drought, less susceptible to climatic stress and well synchronized with the climatic fluctuations of the Mediterranean environment.

線虫寄生性細菌Ｐａｓｔｅｕｒｉａ ｐｅｎｅｔｒａｎｓによるネコブセンチュウ感受性の異なるサツマイモ品種のサツマイモネコブセンチュウ害抑制 ＩＩ． Ｐ．ｐｅｎｅｔｒａｎｓ施用後第７〜９作における線虫防除効果

We examined the suppressive effects of Pasteuria penetrans on Meloidogyne incognita on two sweet potato cultivars, 'Beniazuma' (moderately resistant) and 'Kokei 14' (highly susceptible), in field plots enriched with P. penetrans by six seasons of consecutive cropping from 1994 to 1997. Application of P penetrans significantly reduced population densities of the root-knot nematode in the 7th (1998) and 8th (1999) croppings of 'Beniazuma', and increased the marketable yields of fleshy storage root. However, there was a severe yield loss in the 9th (2000) cropping, through the application of 1, 3-D. The degree of adhesion of P penetrans endospores to J2 was low at every harvesting. Nematode-suppressive effects by P. penetrans were not conspicuous in the 'Kokei 14' cropping sequence.

Physicochemical characteristics of onion (Allium cepa L.) tissues.

The structure and mechanical properties of onions are important factors affecting their textural quality. The onion bulb consists of several layers of pigmented, papery scales surrounding fleshy storage scales that comprise an upper epidermis, an intermediate parenchyma tissue, and a lower epidermis. The purpose of this study was to examine the chemical composition of cell walls from the papery scales and outer fleshy scales of onion (Allium cepa L. cv. Sturon) in relation to their mechanical properties. Cell-wall material (CWM) was prepared from the component tissues and analyzed for its carbohydrate and phenolic composition. The CWMs were rich in uronic acid and glucose, with smaller quantities of arabinose, galactose, and xylose. In the fleshy scales, the lower epidermis contained relatively more galactose-rich pectic polysaccharides, whereas the upper epidermis and the papery scales contained virtually no galactose. Analysis of mechanical properties showed that the order of strength of the tissues was papery scales > fleshy scales, which were in the order lower epidermis > upper epidermis > intermediate parenchyma. The upper epidermis of fleshy scales was stronger in the vertical than the horizontal direction, and both orientations showed negligible notch sensitivity. Cyclohexane-trans-1,2-diaminetetraacetate-induced vortex-induced cell separation of the intermediate layer of fleshy scales indicated that calcium cross-linking may play an important role in cell-cell adhesion. A small but significant amount of ferulic acid was found in the walls, predominantly in the thick cuticle of the lower epidermis of fleshy scales. Alkali-labile wall-bound flavonoids were also detected.

First Report of Sweetpotato Scurf Caused by Monilochaetes infuscans in Italy.

In the last few years, in the Treviso area, the incidence and severity of a sweetpotato (Ipomoea batata) disease has increased to become a serious economic threat to this crop. The symptoms are small, dark brown to black spots on the surface of fleshy storage roots that under high relative humidity coalesce to completely cover the root surface. Affected roots may also develop small cracks and shrink in storage. In the past, the same symptoms were observed, but the low incidence of the disease did not cause significant economic losses, and therefore it was not considered worthy of investigation. In August 1998, an investigation was initiated to determine the causal agent of the disease and to provide growers with effective control strategies. Since the symptoms were similar to those incited by Monilochaetes infuscans, agent of sweetpotato scurf (1), samples of roots were collected and examined for the presence of the pathogen. Even though it is difficult to isolate, M. infuscans was consistently present in infected tissues. In pure culture on potato dextrose agar the pathogen formed typical, raised, domelike, dark gray to black colonies. Conidiophores were brown to black, unbranched, and support straight or curled chains of hyaline conidia. Traditional cultivation methods that ignore sanitary conditions probably caused the gradual increase in the incidence and severity of the disease. Sweetpotato scurf is common in the U.S., Japan, and some Pacific islands, but it has not been previously recorded in Italy. Reference(1): C. A. Clark and J. W. Moyer. 1988. Compendium of Sweet Potato Diseases. American Phytopathological Society, St. Paul, MN.

Structure of Panax quinquefolius L. (Araliaceae) Roots with Emphasis on Secretory Duct Formation

Primary and first-order lateral roots of Panax quinquefolius L. (American ginseng) were collected from plants in an experimental garden during their second year of growth and processed for light and transmission electron microscopy. Roots in primary growth had either a diarch or triarch primary xylem pattern, a pericycle, an endodermis with Casparian bands and subsequently a suberized cell wall, and a cortex of variable thickness with a suberized hypodermal layer. Both root types underwent rapid secondary growth and the primary root particularly formed a fleshy storage organ. The secondary phloem and secondary xylem had abundant parenchyma and few conducting elements. Secretory ducts differentiated in tissue derived from the pericycle and in the secondary phloem. Each schizogenous duct consisted of six to eight epithelial cells, which possessed dense, globular deposits but lacked starch. A phellogen, which produced several layers of suberized phellem, was initiated in the periphery of tissue derived from the pericycle. The results of this study clarify the anatomical localization of secretory duets in roots of this species.

Cell adhesion, cell separation and plant morphogenesis

A simplified and useful view of plant cell development is that it involves the spatial and temporal organization of cell division, cell expansion and cell differentiation all taking place within the constraints of a lack of cell migration. A facet of such development that has often been neglected, is understanding how the cells of a developing structure hold fast or adhere. Subsequently in development the adhered cells of apices or embryos give rise to more loosely attached cells in mature structures where the degree of cell separation and intercellular space formation is developmentally regulated. Recent cell biological studies, most significantly in the derivation of monoclonal antibody probes forthe plant cell surface (Knox, 1992; Roberts, 1990), have increased our awareness of the local modifications of cell walls and rekindled interest in aspects of plant cell wall adhesion and intercellular space formation. It seems timely to examine our current understanding of the mechanisms of cell adhesion and separation and their importance for plant morphogenesis. Molecular probes for cell surface components offer immense potential, not only for the specific study of the local wall modifications such as those resulting in cell separation but also as probes of molecular markers of cell identity relating to position and context. This essay attempts to draw some of the threads together regarding both the nature and importance of cell adhesion and cell separation in plant tissues.

Nutritional Studies of Christmas Bell

Eighteen-month-old seedlings of Christmas Bell (Blandfordia grandiflora Sm.) in 800-ml containers were top dressed with 8- to 9-month Osmocote controlled-release fertilizer 18N-2.6P-10K at 0, 0.625, 1.25, 2.5, 5.0, or 10 kg·m-3. Other plants were fertilized once or twice weekly with a complete liquid fertilizer supplying 100 mg N/liter based on an N : K ratio of either 1:0.6 or 1:1.5. The former ratio was the same as the Osmocote while the latter was the N : K ratio in tops of healthy wild-growing plants of B. grandiflora. The highest fresh weights occurred at the Osmocote rate of 5 kg·m-3 and with the once-weekly liquid feed of 1 N : 1.5 K ratio. Plants fertilized with low rates of Osmocote were pale green but had extensive root systems that were white and predominantly fibrous. As the rate of Osmocote was increased, plants became greener and produced smaller root systems in which fleshy storage organs were predominant over fibrous roots.

Cell wall storage polysaccharides in cotyledons ofLupinus angustifolius L. II. Mobilization during germination and seedling development

During germination and early seedling development, cotyledons of seeds ofLupinus angustifolius were modified from thick-walled, fleshy storage organs to leaf-like, expanded photosynthetic organs by the controlled collapse of groups of mesophyll cells. Cotyledon cell walls of imbibed seeds are PAS-negative, have a strong affinity for calcofluor, and a dense fibrillar ultrastructure. The first visible sign of the mobilization of cell wall polysaccharides occurs 5 days after imbibition, with the appearance of PAS-positive maculae in ordered rows on the inner surface of the thickened walls. These correspond in orientation and frequency with the folds and radial striations found in walls of mature seeds, and with areas with poor affinity for calcofluor. In the electron microscope, the maculae appear as electron-lucent, wedge-shaped areas of loosely-arranged fibrils which, as germination proceeds, spread throughout the walls. The evidence suggests that storage polysaccharides are mobilized from the matrix of the walls by the action of hydrolytic enzymes leaving a framework of structural components, and not by the erosion of cracks and fissures.

Some biophysical principles underlying the controlled atmosphere storage of plant material

SUMMARYControlled atmosphere (CA) storage is of use for commodities which potentially can undergo rapid and unacceptable biochemical change. In air, the oxygen status of most plant material, including fleshy storage organs and fruits, suffices, even in the centre, for cytochrome oxidase to be fully saturated. Conflict of evidence exists as to possible O2 and CO2 gradients in fruit which, though physiologically unimportant in air, could be important under CA conditions. CA storage gives possible control of internal O2 from o to about 80–95%; internal CO2 from about 3–4 to 100%; and both simultaneously to intermediate values. Calculated molarities of dissolved O2, CO2 and ethylene are given for various atmospheres.The differences in the O2 concentrations recommended for different varieties of apple are not readily explicable. Varietal differences in susceptibility to CO2 injury could possibly result from anatomical, rather than biochemical, differences. This could be determined partly by resolving the conflict of evidence mentioned above. Variability of plant material prevents precise control of intercellular atmosphere; recommended atmospheres can be designed only to avoid completely anaerobic conditions and a harmful level of CO2 in the centre of the least permeable individual fruit or vegetable. Effects of low O2 and high CO2 are briefly described.

Morphology of Humulus lupulus. II. Secondary Growth in the Root and Seedling Vascularization

Miller, Robert H. (U. Nevada, Reno.) Morphology of Humulus luppulus. II. Secondary growth in the root and seedling vascularization. Amer. Jour. Bot. 46(4): 269–277. Illus. 1959.—In the primary state the roots of Humulus lupulus L. have a diarch xylem plate with 2 strands of primary phloem lying on either side of the primary xylem. Secondary histogenesis is described for the primary root. Fibrous and fleshy storage roots are developed by the hop plant and their respective developmental and anatomical structures are described. Lateral roots are initiated in the pericycle opposite the protoxylem poles. The architecture of these secondary roots is similar to that of the primary root. The seedling develops a fleshy storage organ through secondary growth of the primary root and the hypocotyl. The hypocotyl eventually resembles a fleshy taproot throughout most of its extent. The vascular cambium differentiates large amounts of parenchymatous tissues. A relatively smaller amount of tracheary tissue is formed. The secondary phloem comprises a high percentage of phloem parenchyma and ray cells containing numerous large starch grains, and constitutes the larger portion of the fleshy storage root. Numerous thick-walled lignified fibers occur throughout the secondary vascular tissues. Resin and tannin cells are abundantly distributed. A phellogen is differentiated from the pericycle and develops a persistent periderm on the outer surface of the fleshy storage organ. A relatively short transition region occurs in the upper part of the hypocotyl. The transition takes place from a radially alternate arrangement of the vascular tissues in the root to a collateral arrangement in the cotyledons.

MORPHOLOGY OF HUMULUS LUPULUS. II. SECONDARY GROWTH IN THE ROOT AND SEEDLING VASCULARIZATION

Miller, Robert H. (U. Nevada, Reno.) Morphology of Humulus luppulus. II. Secondary growth in the root and seedling vascularization. Amer. Jour. Bot. 46(4): 269–277. Illus. 1959.—In the primary state the roots of Humulus lupulus L. have a diarch xylem plate with 2 strands of primary phloem lying on either side of the primary xylem. Secondary histogenesis is described for the primary root. Fibrous and fleshy storage roots are developed by the hop plant and their respective developmental and anatomical structures are described. Lateral roots are initiated in the pericycle opposite the protoxylem poles. The architecture of these secondary roots is similar to that of the primary root. The seedling develops a fleshy storage organ through secondary growth of the primary root and the hypocotyl. The hypocotyl eventually resembles a fleshy taproot throughout most of its extent. The vascular cambium differentiates large amounts of parenchymatous tissues. A relatively smaller amount of tracheary tissue is formed. The secondary phloem comprises a high percentage of phloem parenchyma and ray cells containing numerous large starch grains, and constitutes the larger portion of the fleshy storage root. Numerous thick‐walled lignified fibers occur throughout the secondary vascular tissues. Resin and tannin cells are abundantly distributed. A phellogen is differentiated from the pericycle and develops a persistent periderm on the outer surface of the fleshy storage organ. A relatively short transition region occurs in the upper part of the hypocotyl. The transition takes place from a radially alternate arrangement of the vascular tissues in the root to a collateral arrangement in the cotyledons.

The virulence of biochemical mutants of Erwinia aroideae for varieties of radish and turnip.

Summary: Biochemical mutants of Erwinia aroideae displayed a pattern of virulence and avirulence for varieties of radish and turnip similar to the pattern previously reported for different host species. Three types of host response were noted when slices of the fleshy storage organs were inoculated: uniformly resistant, uniformly susceptible, and a variable response in which individuals of a given variety may be resistant or susceptible to a specific mutant. Prototrophic reversions from an avirulent mutant requiring arginine and from an uncharacterized mutant with diminished virulence were as virulent as the parental strain for all varieties of radish and turnip.

A COMPARISON OF OSMOTIC CONCENTRATIONS OF SUPPLYING AND RECEIVING TISSUES AND ITS BEARING ON THE MÜNCH HYPOTHESIS OF THE TRANSLOCATION MECHANISM

Munch (I930) has recently proposed a mechanism which he thinks accounts for the movement of solutes through phloem tissue. In brief, the Munch hypothesis proposes that there is a mass flow of solution from the supplying cells to the receiving cells, that the flow from cell to cell in the phloem passes through the pores of the sieve plates, while for the less specialized supplying or receiving cells the flow is through the more minute plasmodesma. The hypothesis demands that the supplying cells have a higher turgor pressure than the receiving cells. This would mean that, except under rather special conditions, the supplying cells must have a higher osmotic concentration than the receiving cells. There are several points about the hypothesis that are in its favor and make it rather intriguing, but there are also several grave weaknesses involved. No attempt will be made in this paper to summarize these various points, because a rather extensive criticism will be included in a book by the senior author. that is shortly to appear and which deals with many of these and other interesting problems relating to solute translocation in plants. According to the Muinch hypothesis, the supplying cells must have a higher turgor pressure than the receiving cells so that there will be a pressure gradient forcing the solution along the channels leading to the receiving cell. General observations, however, give one the definite impression that receiving tissues are often more turgid than the supplying tissues. For example, the appearance of turgid sprouts developing from increasingly flaccid potato tubers is frequently to be seen, as is also the development of turgid shoots from storage roots, as of carrots, beets and turnips, and from other fleshy storage organs, such as bulbs and corms. The cotyledons of developing seedlings also appear less turgid than the receiving tissues. Quantitative data comparing osmotic concentrations of receiving and supplying tissues are not extensive. The senior author (I920) in experiments incident to translocation studies obtained data indicating an osmotic gradient but with the higher concentrations near the growing tissues which were at the same time the receiving tissues. Fernald (I925) in testing this point presents rather extensive data demonstrating such a reverse gradient leading from