Formation Of Ingrowths Research Articles

Two tomato endoglucanases have a function during syncytium development

<em>Globodera rostochiensis</em>, as well as other cyst nematodes, induces formation of a multinucleate feeding site, called syncytium, in host roots. In tomato roots infected with a potato cyst nematode, the syncytium is initiated in the cortex or pericycle. Progressive cell wall dissolution and subsequent fusion of protoplasts of newly incorporated cells lead to syncytium formation. Expansion and development of a syncytium strongly depends on modifications of a cell wall, including its degradation, elongation, thickening, and formation of ingrowths within it in close contact with tracheary elements. Recent reports have demonstrated that during formation of syncytium, numerous genes of plant origin, coding for cell wall-modifying enzymes are up-re-gulated. In this research, we studied a detailed distribution and function of two tomato 1,4-β-endoglucanases in developing feeding sites induced by <em>G. rostochiensis</em>. In situ localization of tomato LeCel7 and LeCel8 transcripts and proteins demonstrated that these enzymes were specifically up-regulated within syncytium and in the cells adjacent to the syncytium. In non-infected roots an expression of LeCel7 and LeCel8 was observed in the root cap and lateral root primordia. Our data confirm that cell wall-modifying enzymes of plant origin have a role in a modification of cell wall within syncytia, and demonstrate that plant endoglucanases are involved in syncytia formation.

Arabidopsis endo‐1,4‐β‐glucanases are involved in the formation of root syncytia induced by Heterodera schachtii

Cyst nematodes induce root syncytia with specific features such as hypertrophy, increased metabolic activity and fusion with adjacent cells. Cell walls of the syncytia undergo massive changes such as thickening, local dissolution and formation of ingrowths. Cell wall degrading and modifying proteins are apparently involved in syncytium formation but detailed knowledge of this is still limited. Therefore, we studied the regulation and function of the entire Arabidopsis endo-1,4-beta-glucanase gene family in syncytia induced by Heterodera schachtii. Endo-1,4-beta-glucanases hydrolyze the 1,4-beta-glucosidic linkages between glucose residues. Using semi-quantitative and quantitative approaches we identified seven genes that are upregulated in syncytia. Two of these genes, coding for secreted AtCel2 and membrane-bound KOR3, are shoot-specific but show high expression in syncytia at different developmental stages. In silico analysis of the promoter regions of both genes compared with other genes with modified regulation in nematode feeding sites did not reveal specific cis-acting elements that could be related to specific transcription in syncytia. However, motifs responsive to sugar and different plant hormones were identified. Accordingly, treatments with sucrose, gibberellic acid and NAA induced upregulation of AtCel2, whereas ABA triggered downregulation of both AtCel2 and KOR3 in roots. As AtCel2 is related to degradation of the cell wall matrix, we analysed the hemicellulose content in syncytia. The measured values resembled the expression pattern of AtCel2. A distinctly reduced number of females developed in cel2 and kor3 T-DNA mutants, and we therefore conclude that endo-1,4-beta-glucanases play an important role in the formation and function of syncytia.

Ultrastructure of Initial Response of Graminaceous Roots To Infection By Heterodera a Venae

Ultrastructural changes induced by two pathotypes, Ha 22 and Ha 71 (Spanish populations), of the cereal cyst nematode Heterodera avenae on wheat cv. Anza and on oat cv. Cometa are described from 24 h to 5 days after nematode inoculation. Pathotype Ha 22 selected as a feeding site the stelar parenchyma cells of wheat roots, which responded with extensive hypertrophy, increase in cellular organelles and formation of elaborate ingrowths of the cell walls adjacent to xylem tracheal elements as seen in a 5 day-old syncytium. On the same host, pathotype Ha 71 fed upon xylem parenchyma cells that reacted early (24 h) with callose-like and osmiophilic granule deposits on their walls, leading to the degradation of the induced syncytium within 5 days. Feeding of both pathotypes on oat roots induced a hypersensitive host reaction, characterized by extensive necrosis of the endodermis and pericycle. Pathotype Ha 22 induced small syncytia in the stele where cellular response was expressed through involution of the cytoplasmic content, indicating a lack of nutrients from plant to nematode. Pathotype Ha 71 did not form syncytia in the stelar tissue and fed only on cortical cells, which were transformed into secretory transfer-like cells.

Tissue response induced by Heterodera schachtii (Nematoda) in susceptible and resistant white mustard cultivars

The anatomy and ultrastructure of syncytia induced in white mustard (Sinapis alba L.) by the beet cyst nematode (Heterodera schachtii Schmidt) were studied in the nematode-susceptible cultivar Trico and the nematode-resistant cultivar Maxi. Although syncytia in both cultivars could reach similar volumes, they differed considerably in their ultrastructure. In the susceptible cultivar, xylem parenchyma cells responded with extensive hypertrophy, an increase in plastids and tubular smooth endoplasmic reticulum, and formation of elaborate ingrowths of the cell walls abutting the xylem tracheary elements. In the resistant cultivar, xylem parenchyma cells, occasionally incorporated into the syncytium, necrotized. Normally, however, these cells resisted incorporation and stopped the syncytia from reaching the xylem tracheary elements. This resulted in the differentiation of cell wall ingrowths on the inner tangential walls of neighbouring stelar parenchyma cells. The improper coordination of syncytium differentiation with xylem morphogenesis, the malfunction in the symplast–apoplast interaction with an abnormal deposition of protoplasmic constituents into the apoplast, the small number of plastids, the lack of tubular smooth ER and degradation processes, further demonstrated the incompatible nature of the host–parasite interaction in the resistant cultivar Maxi. Key words: Sinapis alba, Heterodera schachtii, ultrastructure, resistance.

Cytokinesis in microspore mother cells of Impatiens sultani

Cytokinesis in Impatiens sultani microspore mother cells is simultaneous. It starts with the formation of small ingrowths of the surrounding callosic wall. Next, an incomplete cell plate is formed by fusion of small dictyosome vesicles. The cell plate consists of a network of anastomosing tubules and sacs. Aggregates of fusing vesicles are associated with bundles of microtubules, which are oriented perpendicular to the plane of the future cell walls. In the sacculate parts of the cell plate, some callose is deposited, while the associated microtubules disappear. The cell walls ultimately develop by enlargement of the previously formed wall ingrowths, which successively incorporate the elements of the cell plate. The enlargement and thickening of the walls is not accompanied by a further fusion and incorporation of dictyosome vesicles.

Ontogeny of external glands in the bladderwortUtricularia monanthos

The development of external glands on traps and stolons ofU. monanthos has been studied using transmission electron microscopy. During early differentiation of the epidermis some cells remain narrow and develop a protuberance which subsequently divides into a terminal and a pedestal cell, with the remainder of the original cell forming the basal epidermal cell of the gland. The lateral wall of the pedestal cell soon becomes densely impregnated throughout its thickness, and this is followed by the formation of discontinuous cuticular deposits within the primary wall of the terminal cell. The outer wall of the terminal cell then usually undergoes extensive secondary wall thickening beginning with the formation of ingrowths which for a period characterize the cell as a transfer cell. Later, at the stage when traps begin capturing prey, these ingrowths are overlain by further layers of secondary wall material. Concomitantly, in the pedestal cell, wall ingrowths become fully differentiated on the outer transverse wall and persist throughout the remaining life of the gland. The function of external glands during early ontogeny is discussed. At the stage when the terminal cell is differentiated as a transfer cell it is suggested that the gland is mainly responsible for absorbing solutes from the external medium. Once traps commence capturing prey the gland may become modified for a role in water secretion, facilitated by the differentiation of the pedestal cell as a transfer cell, and by the formation of a thick outer wall in the terminal cell.

Is Ant. Pituitary Hormone Demonstrable in Urine of Graves Disease, in Urine of Guinea Pigs Injected With Ant. Pituitary Extract?

Loeb and Bassett1 have shown that an acid extract of cattle anterior pituitary produces hypertrophy of the thyroid gland of guinea pigs. They noted that this experimentally produced hypertrophy characterized by an enlargement of the acinar cells, softening and absorption of colloid, and an irregular and often slit-like shape of the acini, and by the formation of papillary ingrowths into the acini resembles the pathological change in the thyroid gland in Graves disease. In a series of papers from this laboratory this similarity between the effects produced by the injection of extracts of the anterior pituitary gland of cattle and the symptoms of Graves disease has been further emphasized. Loeb and Friedman2 have produced exophthalmos in guinea pigs by repeated intraperitoneal injections of acid extract of the anterior pituitary. Siebert3 showed that this extract produced a rise in metabolism which was counteracted by the administration of potassium iodide, observations which accorded with the depressing ef...