No abstract

Summary. iChanges are reported in total cellular organic carbon, nucleic acids, proteins, carfbohydrates, lipids and chlorophylls during the course of silicon-starvation synchrony of Navicula pelliculosa. All constituents increased at the same rate, relative to cel1 number, for 30 hours of exponential growth during which silicon was depleted from the medium. Increase in cell number then stopped. but net synthesis of most components continued for a further 5 to 7 hours before ceasing. Deoxyribonucleic acids and lipids accumulated throughout the 14 hour silicon-starvation period. When silicon was resupplied, lipid synthesis ceased and organic carbon anld carbohydrates decreased slightly. Net synthesis remained low during the 4 hour silicon uptake period but was resumed at higher rates as cell num-ber began to rise. In cultures transferred to the dark 1 hour prior to readdition of silicon, total carbon, carbohydrates, and lipids decreased markedly during silicon uptake and cell separation. This was due in,part to con'version of protein which maintained the protein level of the dark cells close to that of cells kept in the light. Mechanisms by which silicon starvation and reintroduction of silicon might affect rates of cellular synthesis are discussed.Silicon is a major component of the cell wall in almost all diatom species and is essential for their growth, but whether it is required only as a wall constituenit or affects other metabolic processes as well is not known. Studies conducted, in this laboratory (4, 17), primarily to investigate the metabolism of silicon in wall formation, have shown that in the fresh water diatom, Navlicula pelliculosa, cell separation ceases once the medium is depleted of silicon.However, cellular development is not arrested until after cytokinesis has taken place and deposition of new walls has ibegun. Thus after 14 hours of silicon starvation more than 70 % of the cell population consists of bi'protoplastic cells, i.e., 2 daughter protoplasts, each surrounded by a new plasmalemma and separated by an intercellular space, contained within the parent frustule. When silicon is resupplied there is a 4 hour period of rapid silicon uptake after which

Muscodor albus strain GBA is a newly isolated endophytic fungus from Ginko biloba (family Ginkoaceae) collected in Newport, RI, USA. The cultural characteristics (color, growth pattern) and mycelial/hyphal characteristics resemble many isolates of Muscodor albus. The ITS rDNA sequence of the strain has at least 98% similarity with other isolates of M. albus and M. crispans. This xylariaceaous species effectively inhibits and kills certain test microbes via a mixture of volatile organic compounds (VOCs) that it produces. Some of the target test microbes were totally inhibited by M. albus strain GBA and not by other M. albus isolates, making this isolate unique in its biological activity. The VOCs of this fungus were identified by gas chromatography/mass spectrometry as esters, lipids, alcohols, acids and ketones, including proportionally large quantities of 1-butanol, 3-methyl-, acetate. A terpenoid, not observed in other strains of this fungus, vitrene was tentatively identified in the VOCs of this organism. This is the first record of M. albus in Ginko biloba and is the first report of any M. albus strain from the United States. The organism is normally found in tropical latitudes (16° north/ south) but the plant host M. albus strain GBA is located at 41° north latitude. Most importantly, however, the discovery of M. albus in the USA has enormous implications vis-a.vis governmental regulation of M. albus for use as a biological control agent in agriculture and industry, as this organism naturally occurs in the USA. A discussion on the relationship of this taxon with its host is also included.

Rates of photosynthesis, measured by oxygen electrode or by (14)CO(2) fixation, dark respiration and (32)P-phosphate incorporation are reported for the silicon-starvation synchrony of the fresh water diatom Navicula pelliculosa. During late exponential growth the rates were consistent with increase in carbon mass. During silicon starvation, rates of carbon dioxide fixation, oxygen evolution and (32)P incorporation fell, and the saturating light intensity decreased from 27,000 lux to 5000 lux. Reintroduction of silicon led to immediate transients in all parameters studied, followed by a prolonged increase in rate of dark respiration and a gradual increase in apparent photosynthesis. During release of daughter cells, the rates of dark respiration decreased as photosynthesis and (32)P incorporation increased. These results are discussed in relation to effects of silicon on the energy metabolism of the diatom.