10. Snow algae of the Windmill Islands region, Antarctica

A list of the 24 species of snow algae identified from the region, a resume of what is currently known about the major species, and avenues for further research are provided. New species discovered include 2 Desmotetra spp., one Chlorosarcina sp., 2 Chloromonas spp. and a Palmellopsis sp. Several of these are from genera whose members have previously been found only in the soil flora. Not only was it necessary to elucidate the life cycle of these species, but it was also essential to examine them ultrastructurally to determine their taxonomic positions.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF DINOBRYON CYLINDRICUM (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Dinobryon cylindrioum Imhof. (UTEX no. LB 2266) was determined using serial section reconstruction. Four microtubular rootlet systems (R₁, R₂, R₃, and R₄)and a rhizoplast are present, following the general pattern found in other chrysophytes. The R₁ rootlet, containing seven microtubules, originates at the basal body of the long flagellum that bears mastigonemes (F₁). The R₁ rootlet forms an arc which curves in clockwise direction (when viewed from the anterior end of the cell) approximately halfway around the pit from which the short smooth flagellum (F₂) emerges. Numerous microtubules cascade from the exterior-facing side of this rootlet to the tail of the cell. The R₂ rootlet originates between the F₁ and F₂ basal bodies, is attached to the F₁ basal body by a fibrous connection, and forms a clockwise arc above the R₁ rootlet. This rootlet extends approximately one quarter of the way around the pit. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts, designated R₃ and R₃. Both parts circle the pit in counter-clockwise direction, pass beneath the F₂ basal body, and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material, passes diagonally over the top of the F₂ basal body, forms a clockwise loop at least three quarters of the way around the pit to the interior of the R₃ and R₃ rootlets, and ends in the cytoplasm. Similarities of rootlet origins and other details of the flagellar apparatus of D. cylindricum with those of other heterokont organisms reinforce the idea that these organisms are phylogenetically related.     

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF UROGLENA AMERICANA (CHRYSOPHYCEAE)1

The three-dimensional structure of the flagellar apparatus of Uroglena americana Calkins (Uroglenopsis americana [Calkins] Lemmerman) was determined using serial section reconstruction. The three microtubular rootlet systems (R₂, R₃, and R₄) follow the general pattern found in other chrysophytes. The R₂ rootlet originates between the basal bodies of the mastigoneme-bearing long flagellum (F₁) and the short smooth flagellum (F₂) and is attached to the former by a fibrous connection. The R₃ rootlet system originates as a trough-shaped band of six microtubules spanning the distance between the proximal ends of the F₁ and F₂ basal bodies. The six-membered rootlet splits into two parts (designated R₃ and R₃) which circle the depression from which the F₂ flagellum emerges in counter-clockwise direction. These two rootlets pass beneath the F₂ basal body and descend into the cell alongside the chloroplast. The R₄ rootlet originates in fibrous material which passes diagonally over the F₂ basal body, forms a clockwise loop about three-quarters of the way around the depression, and ends in the cytoplasm. In place of a typical chrysophyte R₁ rootlet, U. americana has a different array of microtubules attached to the F₁ basal body which we have designated the descending rootlet (DR). This rootlet is a hairpin-shaped structure lying just below the surface of the cell; its longitudinal axis is predominantly parallel to the longitudinal axis of the cell. The DR resembles the bypassing rootlet which occurs in phaeophyte zoospores. Other chrysophytes may possess rootlets which are similar to the DR found in Uroglena.     

ENTOSIPHON SULCATUM (EUGLENOPHYCEAE): FLAGELLAR ROOTS OF THE BASAL BODY COMPLEX AND RESERVOIR REGION1,2

The flagellar root system of Entosiphon sulcatum (Dujardin) Stein (Euglenophyceae) is described and compared with kinetoplastid and other euglenoid systems. An asymmetric pattern of three microtubular roots, one between the two flagellar basal bodies and one on either side (here called the intermediate, dorsal, and ventral roots), is consistent within the euglenoid flagellates studied thus far. The dorsal root is associated with the basal body of the anterior flagellum (F₁) and lies on the left dorsal side of the basal body complex. Originating between the two flagellar basal bodies, and associated with the basal body of the trailing flagellum (F₂), the intermediate root is morphologically distinguished by fibrils interconnecting the individual microtubules to one another and to the overlying reservoir membrane. The intermediate root is often borne on a ridge projecting into the reservoir. The ventral root originates near the F₂ basal body and lies on the right ventral side of the cell. Fibrillar connections link the membrane of F₂ with the reservoir membrane at the reservoir-canal transition level. A large cross-banded fiber joins the two flagellar basal bodies, and a series of smaller striated fibers links the anterior accessory and flagellar basal bodies. Large nonstriated fibers extend from the basal body complex posteriorly into the cytoplasm.     

THE FLAGELLAR APPARATUS OF HYMENOMONAS CORONATA (PRYMNESIOPHYTA)1

The ultrastructure of Hymenomonas coronata Mills was reinvestigated to determine the microarchitecture of the flagellar apparatus. Cell morphology and flagellar apparatus structure are very similar to those of Pleurochrysis. Some important variations occur. First, a crystalline root (= compound root) is absent on microtubular root 1. Second, a two-stranded microtubular root emanates at a right angle from microtubular root 2. Third, a fibrous root emanates from the dorsal region between the basal bodies and extends to the cell's right, paralleling microtubular root 3. These similarities and variations in flagellar apparatus characters are discussed in reference to known variations in the Prymnesiophyta.     

COMPARATIVE ANALYSES OF THE DINOFLAGELLATE FLAGELLAR APPARATUS. III. FREEZE SUBSTITUTION OF AMPHIDINIUM RHYNCHOCEPHALUM1

The flagellar apparatus of the marine dinoflagellate Amphidinium rhynchocephalum Anissimowa was examined using the techniques of rapid freezing/freeze substitution and serial thin section three dimensional reconstruction. The flagellar apparatus is composed of two basal bodies that are offset from one another and lie at an angle of approximately 150° The transverse basal body is associated with two individual microtubules that extend from the proximal end of the basal body toward the flagellar opening. One of these microtubules is closely appressed to a striated fibrous root that also extends from the proximal base of the transverse basal body. The longitudinal basal body is associated with a nine member microtubular root that extends from the proximal end of the basal body toward the posterior of the cell. The longitudinal microtubular root and the transverse striated fiber are connected by a striated connective fiber. In addition to the microtubules associated with the transverse and longitudinal basal bodies, a group of microtubules originates adjacent to one of the transverse flagellar roots and extends into the cytoplasm. Vesicular channels extend from the flagellar openings to the region of the basal bodies where they expand to encompass the various connective structures of the flagellar apparatus. The possible function and evolutionary importance of these structures is discussed.     

COMPARATIVE ANALYSES OF THE DINOFLAGELLATE FLAGELLAR APPARATUS. II. CERATIUM HIRUNDINELLA1

The three-dimensional structure of the flagellar apparatus in the gonyaulacoid dinoflagellate. Ceratium hirundinella var. furcoïdes (Schröder) Hub.-Pest. was determined using serial section electron microscopy. The flagellar apparatus is quite large and consists of several components. The two basal bodies nearly abut at their proximal ends and are separated by an angle of approximately 120° The broad longitudinal microtubular root extends from the cell's left edge of the longitudinal basal body and bends around the sulcal/cingular depression into the cell's left antapical horn. A transverse striated fibrous root is associated with the transverse basal body and a narrow electron dense extension is present along the anterior edge of the transverse basal body. This study revealed severa1 hitherto unreported fibrous components of the flagellar apparatus that link the various microtubular and fibrous components to themselves and to the two striated collars. A large striated fibrous connective links the two striated collars to one another. This fibrous connective is linked to another striated fibrous connective that originates from the longitudinal basal body and lies perpendicular to the longitudinal microtubular root. The readily identifiable and numerous components of the Ceratium flagellar apparatus are comparable to those of other dinoflagellates. The combined presence of well dpveloped striated collars, a striated collar connective, and a basal body angle of approximately 120° indicates that this flagellar apparatus is most like that described for Peridinioid dinoflagellates. Important similarities are also noticeable between this flagellar apparatus and that of Oxyrrhis marina.     

STRUCTURE AND PHYSIOLOGY OF THE HAPTONEMA IN CHRYSOCHROMULINA (PRYMNESIOPHYCEAE). I. FINE STRUCTURE OF THE FLAGELLAR/HAPTONEMATAL ROOT SYSTEM IN C. ACANTHA AND C. SIMPLEX1

The intracellular structural relationships between the flagella and haptonema in Chrysochromulina acantha Leadbeater & Manton (Prymnesiophyceae) were studied in detail and a reconstruction is presented. Three micro-tubular roots are associated with the flagellar apparatus. The largest, consisting of a sheet of approximately 20 microtubules, has its origins at the base of the left basal body. The main body of microtubules passes over the surface of a mitochondrion toward the left chloroplast and apparently terminates at a pair of microtubules oriented perpendicularly to it. Four microtubules diverge from the sheet and pass behind the left basal body. Two other roots–one consisting of a 2 + 2 + 1 arrangement of microtubules, the other of a single microtubule only—are associated with the right basal body. The two basal bodies are connected by distal and proximal fibers, and they are linked also to the base of the haptonema, three fibers extending from the haptonemal base to the right basal body, one only to the left. An additional fiber extending from the right basal body passes between the left basal body and the base of the haptonema, terminating at the largest microtubular root. Lateral extensions link this fiber to both the left basal body and the haptonematal base. Negative staining of isolated root systems of C. simplex Estep et al. shows that the arrangement of microtubules and fibrous connections is similar to that in C. acantha. The root system of C. acantha is compared to those of other members of the Prymnesiophyceae.