Fine structure of mycota 12. Karyochorisis — somatic nuclear division — in Cordyceps militaris

Summary The literature on somatic nuclear division in the fungi consistently suggests that, with but one present exception, the process is non-mitotic. The correlation of previous electron microscopic studies of yeasts with the present study of Cordyceps militaris supports this interpretation and provides a possible mechanism, identified as karyochorisis (nuclear sundrance). During karyochorisis there are two successive invaginations of the inner and outer elements of the perinuclear cisterna. The invagination of the inner nuclear membrane divides the nucleoplasm into two or more subunits described by the new term karyome. The subsequent invagination of the outer nuclear membrane separates the karyomes into daughter nuclei. It is suggested that, in contrast to continued sterile efforts to prove that mitosis is the general mode of fungal somatic nuclear division, the hypothesis of karyochorisis raises new questions that offer new areas for future research. Four that are put forth are 1. the possibility of a correlation between nuclear size and the mode of division; 2. the nature of the mechanism of chromosome replication and separation; 3. the cause of nuclear elongation and the possibility that its initiation depends on a critical RNA volume; and 4. the possibility that colchicine produces polyploidy by blocking the invaginations of the nuclear envelope. In a concluding section the suggestion is made that the proposed hypothetical mode of fungal nuclear division, karyochorisis, may represent only a special example of a general phenomenon of division of double membrane organelles in primitive cells.It is a pleasure to acknowledge the technical assistance of Mrs. Barbara Raymond, Messrs. Lloyd Thibodeau and Philip Spencer of our Laboratory and to thank Professor R. Emerson and Mr. Robert Berman of the Botany Department for making available material of Blastocladiella.This investigation was supported by Postdoctoral Fellowships 9197-C2 and 2F2 AI 9197-04 from the United States National Institute of Allergy and Infectious Diseases, Dr. James H. McAlear, sponsor; and partly by grant AI-05514-01 from the same Institute.     

An extracellular polysaccharide produced by Palmella mucosa Kütz.

Summary An extracellular polysaccharide composed of glucose, fucose, arabinose and glucuronic acid in a molar proportion of 11:6:3:1 is a major end-product of photosynthesis by Palmella mucosa Kütz.The liberation of polysaccharide is related to the age of the culture. Glucose can substitute efficiently for CO₂ as the source of carbon for polysaccharide synthesis. Nitrate-nitrogen from sodium, potassium and calcium salts can be used in the mineral salts medium with little differences in carbon metabolism of the alga. Ammonium nitrate produces an acidic medium which limits polysaccharide production.The incorporation of C¹⁴ into the polysaccharide from NaHC¹⁴O₃ shows initially a trend toward intracellular synthesis. The C¹⁴ appears in the extracellular polysaccharide after prolonged exposure. Glucose-C¹⁴ is actively transformed to polysaccharide material which is an indication that glucose may play an important role in the synthesis of polysaccharide by Palmella mucosa Kütz.     

Treating seeds with activators of plant defence generates long-lasting priming of resistance to pests and pathogens

? Priming of defence is a strategy employed by plants exposed to stress to enhance resistance against future stress episodes with minimal associated costs on growth. Here, we test the hypothesis that application of priming agents to seeds can result in plants with primed defences. ? We measured resistance to arthropod herbivores and disease in tomato (Solanum lycopersicum) plants grown from seed treated with jasmonic acid (JA) and/or β-aminobutryric acid (BABA). ? Plants grown from JA-treated seed showed increased resistance against herbivory by spider mites, caterpillars and aphids, and against the necrotrophic fungal pathogen, Botrytis cinerea. BABA seed treatment provided primed defence against powdery mildew disease caused by the biotrophic fungal pathogen, Oidium neolycopersici. Priming responses were long-lasting, with significant increases in resistance sustained in plants grown from treated seed for at least 8 wk, and were associated with enhanced defence gene expression during pathogen attack. There was no significant antagonism between different forms of defence in plants grown from seeds treated with a combination of JA and BABA. ? Long-term defence priming by seed treatments was not accompanied by reductions in growth, and may therefore be suitable for commercial exploitation.     

Phosphorylation of the hinge domain of the nuclear hormone receptor LRH-1 stimulates transactivation

The nuclear receptor LRH-1 (NR5A2) functions to regulate expression of a number of genes associated with bile acid homeostasis and other liver functions, but mechanisms that modulate its activity remain unclear. We have found that mitogenic stimuli, including treatment with phorbol myristate (PMA), increase LRH-1 transactivation. This response maps to the hinge and ligand binding domains of LRH-1 and is blocked by the mitogen-activated protein kinase ERK1/2 inhibitor U0126. LRH-1 is a phosphoprotein and hinge domain serine residues at 238 and 243 are required for effective phosphorylation, both in vitro and in cells. Preventing phosphorylation of these residues by mutating both to alanine decreases PMA-dependent LRH-1 transactivation and mimicking phosphorylation by mutation to positively charged aspartate residues increases basal transactivation. Although serine phosphorylation of the hinge of SF-1 (NR5A1), the closest relative of LRH-1, confers a similar response, the specific targets differ in the two closely related orphan receptors. These results define a novel pathway for the modulation of LRH-1 transactivation and identify specific LRH-1 residues as downstream targets of mitogenic stimuli. This pathway may contribute to recently described proliferative functions of LRH-1.