Studies on the Biochemistry and Fine Structure of Silica Shell Formation in Diatoms. Chemical Composition of Navicula pelliculosa during Silicon-Starvation Synchrony

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

Transcript level coordination of carbon pathways during silicon starvation‐induced lipid accumulation in the diatom Thalassiosira pseudonana

“…Studies aimed at elucidating changes in transcript abundance during nutrient‐limited lipid accumulation often use nitrogen as the limiting nutrient, which is a stressful condition and induces massive cellular changes such as chlorosis and an associated down‐regulation of photosynthesis (Sun et al ., 2013; Abida et al ., 2015; Levitan et al ., 2015). In contrast, short‐term (24 h) silicon starvation has been used as a method to synchronize diatom cultures, and is not generally considered a stressful condition (Coombs et al ., 1967; Hildebrand et al ., 2007; Shrestha et al ., 2012). Silicon starvation‐induced changes in transcript abundance are more likely to reflect the cellular processes that occur as T. pseudonana arrests growth, rather than a response to stress.…”

“…We suggest that the observed TAG accumulation after 8–12 h of starvation in T. pseudonana is the result of ongoing production of fatty acids with a decrease in cellular requirements for membrane biosynthesis. Other studies have shown that after returning to nutrient‐replete conditions after a short exposure to depleted conditions, diatoms rapidly draw down accumulated lipid stores and resume growth (Coombs et al ., 1967; Valenzuela et al ., 2013). Bioenergetically, it would be more efficient for these stored lipids to be utilized as precursors for membranes or other molecules rather than to be catabolized completely.…”

“…Increases in cellular pigmentation and chloroplast replication have previously been documented under silicon‐induced growth arrest in diatoms (Holmes, 1966; Coombs et al ., 1967; Harrison et al ., 1977; Traller & Hildebrand, 2013). This is in strong contrast to the response of nitrogen limitation in which many photosynthetic taxa become chlorotic (Abida et al ., 2015).…”

Fluctuations in the Organic Carbon to Chlorophyll a Ratios for Estuarine Benthic Diatom Populations

“…Harvey (1953), Brown and Richardson (1968), Beale and Appleman (1971) and Sheridan (1972) found an inverse proportion between light intensity and chlorophyll a concentrations for algal cells. Steele and Baird (1962), Antia et al (1963), Coombs et al (1967), Eppley (1968), Strickland et al (1969), Hobson and Pariser (1971), Thomas and Dodson (1972) and Peny (1976) showed that deficiency of P, N and Si could lead to a considerable increase in the organic carbon to chlorophyll a ratios. Caperon and Meyer (1972), Eppley and Renger (1974) and Perry (1976) described a negative correlation between specific growth rate and the organic carbon to chlorophyll a ratio.…”

The relationship between light intensity and nutrient uptake kinetics in six freshwater diatoms

“…Surge uptake occurred when intracellular Si level was very low and the maximum uptake rate could be obtained in this process (Conway and Harrison, 1977;Conway et al, 1976). Energy for Si uptake came from respiration (Coombs et al, 1967). Krause et al (2012) pointed that the kinetics parameters of Si uptake (values of V m(Si) and V m(Si) :K m(Si) ) in phytoplankton were coupled with ambient light availability and they increased with the increasing of irradiance at two of the three field stations.…”