Ultrastructure of the Harmful Unarmored Dinoflagellate Cochlodinium polykrikoides (Dinophyceae) with Reference to the Apical Groove and Flagellar Apparatus

ABSTRACT. The external and internal ultrastructure of the harmful unarmored dinoflagellate Cochlodinium polykrikoides Margalef has been examined with special reference to the apical groove and three‐dimensional structure of the flagellar apparatus. The apical groove is U‐shaped and connected to the anterior sulcal extension on the dorsal side of the epicone. The eyespot is located dorsally and composed of two layers of globules situated within the chloroplast. A narrow invagination of the plasma membrane is associated with the eyespot. The nuclear envelope has normal nuclear pores similar to other eukaryotes but different from the Gymnodinium group with diagnostic nuclear chambers. The longitudinal and transverse basal bodies are separated by approximately 0.5–1.0 μm and interconnected directly by a striated basal body connective and indirectly by microtubular and fibrous structures. Characteristic features of the flagellar apparatus are as follows: (1) a nuclear extension projects to the R1 (longitudinal microtubular root) and is connected to the root by thin fibrous material; (2) fibrillar structures are associated with the longitudinal and transverse flagellar canal; and (3) a striated ventral connective extends toward the posterior end of the cell along the longitudinal flagellar canal. We conclude, based on both morphological and molecular evidence, that Cochlodinium is only distantly related to Gymnodinium.     

Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes

1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36–68°N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid‐European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large‐sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid‐tolerant species were also occasionally abundant. Small‐sized, benthic‐associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species‐specific preferences for habitat and environmental conditions in the Mid‐European group of lakes. Taxon richness was low in the southern‐most, high‐conductivity lakes as well as in the two northern‐most sub‐arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human‐related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.     

Seedling Growth and Storage Characteristics of Seeder and Resprouter Species of Mediterranean-type Ecosystems of S. W. Australia

Juvenile (2–4 years old) plants of a taxonomically diverserange of dicotyledonous species were examined following recruitmentfrom seed in recently burnt habitats in S.W. Australia. Obligateseeder species (those succumbing to fire) had on average, analmost threefold greater total plant d. wt and more than a fourfoldgreater shoot: root d. wt ratio than comparably-aged, cohabiting,resprouter species (those capable of surviving fire). Starchwas generally much more concentrated in root dry matter of resproutersthan seeders, and both categories exhibited greater starch storagecapacity in roots than shoots. Members of the Myrtaccae wereexceptional in not showing a greater root starch reserve inresprouter than in seeder species. and in carrying as high,or higher, starch levels in shoots as in roots. Anatomical investigationson roots provided instances of zero starch storage, storage,only in rays or in cortex, in rays and in xylem parenchyma,in rays and in cortex, or in all three locations. High starchratings of resprouter roots related mostly to higher starchgrain packing density at storage sites, but in certain instancesthese also reflected proportionally greater areas of tissuespecifically devoted to storage. Dry matter of shoots of bothseeders and resprouters generally contained higher levels ofN, P, K, Ca and Mg than that of roots, but there was no significantevidence of elements being more concentrated in resproutersthan in seeders. Fire response, seedlings, resprouter, obligate seeder, shoot: root ratio, starch storage, mineral nutrition     

The Influence of Temperature on a K+-Channel and on a Carrier-Type Transporter in Nitella

Fisahn, J. and Hansen, U-P. 1986. The influence of temperatureon a K⁺ -channel and on a carrier type transporter in Nilella—J.exp. Bot. 37. 440–460. In Nitella, the effects of temperature on membrane potentialand on resistance consist of several components. The evaluationof their associated time-constants measured in linear(ized)temperature responses at a resting potential of–120 mVprovides an approach to their identification. For changes slowerthan c. 1 s, the temperature effect on membrane potential andresistance does not originate from temperature action on theinvolved transporter, but is mediated by signals from temperaturesensitive metabolic processes. In the case of potential, theseprocesses seem to be identical to those which also mediate thelight effect: pH-regulation, and two direct signals from photosynthesis,as indicated by the similarities of the related time-constants( respectively). The temperature effect on resistance displays only one time-constant of 40 sinmost experiments. The related process is unknown. The non-coincidenceof the time-constants of the effect on potential and on resistanceimplies the involvement of a carrier-type transporter (H+-pumpor cotransporter) in the effect on potential, and of a K+channelin the effect on resistance. The K+-channel is identified bythe reversal potential of the effect on membrane potential measuredin cells depolarized or hyperpolarized by an injected electricalcurrent Under these conditions the temperature effect on resistancedominates the effect on potential. Key words: H⁺-pump, K⁺-channel, kinetic analysis, Nitella, oscillation, pH-regulation, reversal, potential, temperature, time-constants