Diatom cells

Fig. 5.1 SEM micrograph of the silica shell of a Coscinodiscus sp. diatom cell...

Hecky, R.E., K. Mopper, P. Kilham, and E.T. Degens. 1973. The amino acid and sugar composition of diatom cell-walls. Marine Biology 19 323-331. 

Auxospore A form of reproductive cell in diatoms usually resulting from the union of two diatom cells. 

Fig. 47. Diatom cell walls after sonication and staining with phosphotunestic acid (a) Xavicula pelliculosa (b)Nitzschia brevirostris (c d) Cyclotella cryptica (llecky et a/.548 ). Around the circumference of the large pores, where there is no underlying silica, a hi-layer membrane can be recognized with grains showing an 80 A periodicity. For discussion of this periodicity see Ref.48 ...

Fig. 49. Hypothetical arrangement of organic layers in the diatom cell wall Gl glucose, M mannose, Fu fucose, X xylose. Ser serine, Asp aspartic acid, Gly glycine, Thr threonine hatched lines represent hydrogen bonds (Hecky etal54 ))...

Lewin, J. C. The dissolution of silica from diatom cell walls. Geochim. Cosmochim. Acta 21, 182-189 (1961). 

Despite potential Phaeocystis spp. cell C dominance in the water column, vertical export of diatom cell C was always larger than that Phaeocystis spp. cell C at 100 m depth, unless deep mixing short-circuits retention. 

Under similar cyclization conditions (2S, 3R)-2-/< r/-butoxycarbonylamino-3-hydroxy-4-pentenoic acid (32) gives the corresponding (3S, 4S, 5.R)-bromolactone in low yield. On the contrary, the lactonization performed with mercury(Il) acetate in tetrahydrofuran, followed by treatment with bromine, exclusively produces the (SS S /Q-lactone 33 in 56% yield. The (35,45,5/ )-lactone was converted into (25,3S,4S )-3,4-dihydroxyproline (34), a compound isolated from diatom cell walls. These transformations thus provide an effective method for the synthesis of substituted prolines35. 

Several studies have suggested that the extent of organic matter degradation may be imprinted on the relative distribution of amino acids. For example, the depth-dependant relative enrichment of certain amino acids in POM has been interpreted as enhanced preservation of particular proteins. Hecky et al. (1973) showed that diatom cell wall proteins were relatively enriched in serine and glycine Cowie and Hedges (1992) found that these amino acids were relatively unreactive in sinking POM and concluded that the observed pattern represented selective preservation of diatom cell wall material within POM. Glycine is enhanced in HMWDOM relative... 

Leynaert, A., BucciareUi, E., Claquin, P., Dugdale, R. C., Martin-Jezequel, V., Pondaven, P., and Ragueneau, O. (2004). Effect of iron deficiency on diatom cell size and silicic acid uptake kinetics. 

Laboratory work suggests, however, that Fe limitation probably does not directly inhibit N03 uptake by compromising nitrate reductase activity (Milligan and Harrison, 2000). Instead, Fe limitation may block the N03 reduction pathway further downstream, by preventing nitrite (N02 ) reduction to NH4+ due to insufficient supplies of photosyntheticaUy-produced reductant. This study showed that Fe-deficient diatom cells continue to take up and reduce N03 to nitrite. 

As in many protists, reproduction in diatoms is by binary fission, an asexual method in which the parent cell divides into two identical cells. Asexual reproduction involves only one parent, and the two offspring are clones, or exact duplicates of the parent. During fission, a diatom cell experiences challenges that cells of other species of protists do not face it also has to divide its frustule. 

Sexual reproduction can occur in several ways. In some species, a small diatom cell breaks into little pieces, each of which swims around until it finds another diatom cell with which it can fuse. The product of their fusion builds the new frustule. In other species, two adult diatom cells line up beside each other. Each cell undergoes division, and then they exchange one daughter cell. The new pairs of daughter cells fuse, resulting in two new cells, each possessing genetic material from two parents. 

Along both temperate and tropical shores, an unusual variety of diatom forms mucuslike sheaths, or tubes, that hold colonies of cells. These tubes resemble the long, thin threads of filamentous brown algae, but a close look under a microscope shows that the tubes hold large diatom cells. Unlike free-living diatoms, the cells of most tube-dwelling species are not covered with silicon frustules. 

A.G.J. Buma, E.J. van Hannen, M.J.W. Veldhuis, L. Roza, W.W.C. Gieskes (1995). Monitoring UV-B induced DNA damage in individual diatom cells by immuno-fluorescent thymine dimer detection. J. Phycoi, 31, 314-321. 

Fig. 7 An image of diatom algae Navicula ramosissima macrocolonies - tubedwelling diatom. Cells are located inside mucilage tubes of their own making. Western basin, November 2002...

November, 2002. On the macrophyte thalli, we observed that both trichomal surfaces of C. fracta and V. cf. dichotoma and polymeric tubes of N. ramosissima were settled by microepiphytic assemblages. The structures of microepiphytes developing on clay surfaces covered with brown fur were most complex. The papillar non-branched shoots of V. cf. dichotoma were completely covered with Tabularia fasciculata. These needle-shaped diatom cells formed palisade-like layers at the surface of the host. This amalgamation increased the volume of the epiphyte/basiphytic complex by 2-2.5-times when compared to the volume of the basiphyte alone. At some sites, the curly shoots of V. cf. dichotoma were covered with a layer of Cocconeis placentula var. euglipta cells. 

Bacillariophyta/ -phyceae Diatoms cells with box-like silicified wall, often forming loose chains, almost all PA... 

Dideoxy-l,4-imino-L-xylitol [(25, 3ii ,4ii )-2-hydroxymethyl pyrrolidine-3,4-diol, 4] was isolated from diatom cell walls md Amanita vitosa mushrooms. 2-Hydroxymethyl-... 

---