Linda Sicko-Goad

A morphometric method for correcting phytoplankton cell volume estimates

SummaryCell volume calculations are often used to estimate biomass of natural phytoplankton assemblages. Such estimates may be questioned due to morphological differences in the organisms present. Morphometric analysis of 8 species representative of phytoplankton types found in the Great Lakes shows significant differences in cell constituent volumes. Volume of physiologically inert wall material ranges from nil, in some flagellates, to over 20% of the total cell volume in certain diatoms. Likewise, “empty” vacuole may comprise more than 40% of the total cell volume of some diatoms, but less than 3% of the volume of some flagellates. In the organisms investigated, the total carbon containing cytoplasm ranged from 52% to 98% of the total cell volume and the metabolizing biovolume ranged from 30% to 82%. Although these differences complicate direct biomass estimation, morphometric analysis at the ultrastructural level may provide ecologically valuable insights.

A MORPHOMETRIC STUDY OF LEAD AND COPPER EFFECTS ON DIATOMA TENUE VAR. ELONGATUM (BACILLARIOPHYTA) 1

Polyphosphate bodies containing lead were induced in laboratory cultures of Diatoma tenue var. elongatum Lyngb. by the addition of phosphorus and 0.05 μg‐atoms/l Pb to P deficient medium. Morphometric analysis of cells exposed to Pb showed a significant decrease in number of mitochondria with a concomitant increase in their volume and an increase in membranous organelles in the vacuole compared to phosphorus starved and phosphorus sufficient controls. Exposure of cultures to 0.08 μg‐atoms/l copper resulted in reduction of the number of polyphosphate bodies formed during luxury uptake but no other significant morphological changes in cellular organelles. Ecological implications of the interactions between nutrients and low level trace metal contamination are discussed.

REJUVENATION OF MELOSIRA GRANULATA (BACILLARIOPHYCEAE) RESTING CELLS FROM THE ANOXIC SEDIMENTS OF DOUGLAS LAKE, MICHIGAN. I. LIGHT MIGROSCOPY AND 14C UPTAKE 1

Resting cells of Melosira granulate (Ehr.) Ralfs were collected from the anoxic sediments of Douglas Lake, Michigan. Sediment containing M. granulata was inoculated into distilled water and incubated in a growth chamber for one week during which observations were made on the cytological differentiation process. Cells classified as “condensed,” i.e. containing a dark brown cytoplasmic mass were identified as resting cells. The differentiation process consisted of a series of gradual cytological changes that included elongation of the cytoplasmic mass and recognition of definable organelles to the point where the cells were non‐distinguishable from water column vegetative cells. Differentiating cells accumulated large polyphosphate and lipid granules. However, these granules disappeared just prior to cell division. The complete differentiation or rejuvenation sequence occurred in some cells in less than 24 h. However, not all dormant cells rejuvenated at the same time and it was observed that the lag period for rejuvenation increased with resting cell age (depth of burial in sediments). In the 14C uptake studies, label was initially observed in condensed state cells. The label gradually progressed to the more differentiated forms. Total carbon uptake during the rejuvenation process was initially lower in the rejuvenating cells, but roughly equal to water column populations after 8 h, indicating a period of high metabolic activity in the rejuvenating cells between 1 and 8 h.

A Morphometric Analysis of Algal Response to Low Dose, Short-Term Heavy Metal Exposure

SummaryThree algae,Melosira granulata, Fragilaria capucina, andAnacystis cyanea, collected as part of a natural phytoplankton assemblage were found to differ in their cytological responses to low dose short-term exposure to copper and lead. In general, all were more sensitive to copper than to lead.Fragilaria was more sensitive to both metals than the other species examined. Most immediate changes in relative volume categories can be ascribed to changes in vacuole volume that are most likely the result of changes in membrane permeability. There was some degree of accommodation in all three species at 24 hours. These results are discussed in view of the natural environment of the algae, as well as in relationship to previous studies.

A Systematic, Quantitative, and Ecological Comparison of Melosira Islandica O. Müll. with M. Granulata (EHR.) Ralfs from the Laurentian Great Lakes☆

Abstract Melosira granulata and M. islandica occur sympatrically in the Laurentian Great Lakes, but maximum population abundance of the two species occurs at opposite ends of the range of seasonal and trophic conditions found in the system. Both species are polymorphic, but are distinguishable on the basis of a number of morphological characteristics. Their distribution and the range of morphologic variation encountered in populations from the Great Lakes is summarized and discussed. Although ranges in size and computed cell volumes of populations of the two species overlap, there are significant differences in cellular composition. Cells of M. islandica contain a much larger fraction of living cytoplasm and cell wall material than cells of M. granulata .

EFFECT OF GROWTH AND LIGHT/DARK CYCLES ON DIATOM LIPID CONTENT AND COMPOSITION1

Total extractable lipid (TEL) and lipid composition were studied throughout the growth cycle in three freshwater diatoms‐Cyclotella meneghiniana Kütz., Melosira varians C. A. Ag., and Stephanodiscus binderanus (Kütz.) Krieg under three light regimes (16:8 h LD, 20:4 h LD, and 12:12 h LD) at 20°C. Two of the diatoms demonstrated strong daylength preferences for growth; C. meneghiniana grew best under long‐day (20: 4‐h LD) conditions, whereas S. binderanus grew best under short‐day (12:12‐h LD) conditions. The lipid composition of the diatoms was similar throughout the growth cycle. Aged (2‐month‐old) cells were high in total lipid and triacylglycerols. Before the onset of active growth and during the early part of active growth, there was a reduction in total neutral lipids, primarily triacylglycerols, and an increase in all polar lipids, including chlorophyll a, acetone‐mobile polar lipids, and phospholipids. While cell numbers were still increasing, triacylglycerols increased and polar lipids decreased to levels near those found in aged cultures, Results suggest that increased triacylglycerol content of freshwater diatoms is not necessarily indicative of senescent populations.

Viroplasm and large virus-like particles in the dinoflagellateGymnodinium uberrimum

SummaryVirus-like particles (VLPs) measuring 385±5 nm in diameter are described in the freshwater dinoflagellateGymnodinium uberrimum. The VLPs are found in association with, and “budding” from a vesicular viroplasmic area. A similar viroplasm was also found in a chrysophycean alga,Mallomonas sp. collected from the same general area in Saginaw Bay of Lake Huron. The nature of these VLPs and their virogenic stroma, in these algae from the Laurentian Great Lakes are discussed in the present report.

Effects of chlorinated benzenes on diatom fatty acid composition and quantitative morphology. II: 1,3,5-trichlorobenzene

Cells of the diatomCyclotella meneghiniana were exposed in a closed system to 0.245 ppm 1,2,4-trichlorobenzene. Response to this chlorinated benzene was monitored over a period of 5 days by quantitative ultrastructure and fatty acid percent composition. Over the time period examined, 41 significant morphological changes and 12 significant changes in fatty acid composition were observed. Autophagic-like vacuoles were frequently observed, indicating lysis of cellular constituents. In general, there was an increase in the C20:5 fatty acid, which may be indicative of photosynthetic impairment, since this fatty acid probably substitutes for linolenic acid in diatoms. The most significant numbers of changes were observed after 8 hr of exposure to this lipophilic toxicant, and these changes occurred in membranous organelles. It is suggested that the daily photoperiodic variation in lipid content of phytoplankton may be an important consideration in evaluating effects of lipohilic toxicants.

Quantitative ultrastructural changes associated with lead-coupled luxury phosphate uptake and polyphosphate utilization

Quantitative electron microscopy (stereology) was used to assess the ultrastructural response of three algae representative of the classes Chlorophyceae, Cyanophyceae, and Bacillariophyceae to lead-coupled polyphosphate degradation. The organisms were exposed to a culture medium concentration of 20 ppb Pb for 3 hr at the time of luxury phosphate uptake and subsequently transferred to phosphorus and lead-free medium. A differential sensitivity was observed as follows:Plectonema > Scenedesmus > Cyclotella. InPlectonema andScenedesmus, detrimental cytological changes were observed when the polyphosphate relative volume dropped below 0.5%, which was approximately the P-starvation level of polyphosphate. Few significant ultrastructural changes were observed inCyclotella after one week in P-deficient medium. At this time, the relative volume of polyphosphate was still 1.5%. Although a few significant ultrastructural changes occurred with phosphate deprivation, the greatest numbers of changes occurred in cells that had been exposed to a short-term (3 hr) low level of Pb. Changes in the relative volume of polyphosphate in all three organisms suggest thatPlectonema andScenedesmus have higher phosphate nutrient requirements thanCyclotella. The ecological implications of metal sequestering by polyphosphate are discussed.

The Need for Uniform Terminology Concerning Phytoplankton Cell Size Fractions and Examples of Picoplankton from the Laurentian Great Lakes

Abstract A variety of terms are used to describe phytoplankton cell size fractions in the freshwater and marine literature. To eliminate misinterpretations, it is strongly suggested that a uniform terminology be adopted by limnologists and phycologists working in the Great Lakes. This terminology is in accord with SI units of dimension and mass. Some examples of the importance of picoplankton are discussed.