FURTHER EXPERIMENTS ON THE ABSORPTION OF IONS BY PLANTS,INCLUDING OBSERVATIONS ON THE EFFECT OF LIGHT

1. The conditions of illumination were found to exert a very significant influence on absorption of ions from dilute solution by Nitella. These conditions were also found to influence the penetration of Br and NO₃ into the cell sap. 2. It is concluded that absorption of ions by plants from dilute solutions involves energy exchanges, with light as the ultimate source of the energy. It is suggested that the absorption is intimately related to growth and metabolism. 3. One ion may affect the removal from solution or penetration into the cell sap of another ion present in the same solution, even in solutions of extremely low concentration. It is probable that all three types of relations may exist—anion to anion, cation to cation, and anion to cation. 4. The sulfate and phosphate ions exerted far less influence on the absorption of nitrate than did chlorine and bromine ions. It is suggested as a possibility that sulfate does not penetrate readily to those surfaces at which chlorine, bromine, nitrate, and other ions may become effective.     

ELECTRICAL RESPONSES FROM THE LATERAL-LINE NERVES OF FISHES : V. RESPONSES IN THE CENTRAL NERVOUS SYSTEM

Records of spontaneous discharge of nerve impulses, similar to that previously described in catfish and in trout, have been obtained from lateral-line nerves of goldfish and perch, by the use of concentric micro electrodes slipped under the nerve in situ. These impulses have been followed into the central nervous system. They enter the tuberculum acusticum and thence apparently spread diffusely through the cerebellum. Cutting the lateral-line nerve on one side silences the ipsilateral tuberculum acusticum, but only reduces the intensity of ipsilateral cerebellar activity. Cutting the remaining lateral-line nerve silences activity throughout the tuberculum acusticum and the cerebellum. The maintenance of tonic activity in the tuberculum acusticum by way of lateral-line discharge may account for the inhibitory effects of the lateral-line system on auditory responses.     

ADAPTATION OF CUTANEOUS TACTILE RECEPTORS. III

Further experimental evidence is presented indicating that the peripheral inhibitory phenomenon known as sensory adaptation, as it is manifested in tactile receptors in frogs'' skin, is produced by a neurohumor released by non-nervous cells of the skin when they are pressed upon. 1. Adaptation is not produced by electrically initiated antidromic impulses backfired into the axon branches. 2. Intermittent air jet stimulation of a region of skin several millimeters distant from a responsive single ending produces failure of response of the ending to a similar direct intermittent stimulus applied to the skin containing the ending immediately afterward. 3. Constant pressure causes an ending to adapt but no spread of the effect, as described in the above paragraph, is found. This implies that the spread is the result of the vibratory movement of the skin. 4. The time curves of recovery from adaptation are inconsistent with any known properties of isolated nerve.     

A mass mortality of fishes caused by receding water levels in the vegetated littoral zone of the West Kleinemonde Estuary,South Africa

On 15 November 2017 the mouth of the West Kleinemonde Estuary breached following heavy catchment rains and increased river flow. The water level in the estuary following mouth opening decreased by 1.65 m within 24 h, resulting in an almost complete draining of the littoral zone where large beds of the aquatic macrophyte Ruppia cirrhosa and mats of the associated filamentous algae were present. As the water depth within the plant beds decreased, the macrophytes, together with the algal filaments, created an increasingly dense mat, trapping fish that were resident, foraging or passing through the littoral zone. By 16 November 2017 large numbers of fishes belonging to at least 20 species were trapped in pools and depressions within the littoral, as well as within the R. cirrhosa beds and filamentous algal mats in the lower reaches of this system. Other affected taxa included crustaceans, especially isopods, and large numbers of small bivalves attached to macrophyte vegetation. Beneficiaries of the fish kill, in terms of unexpected food availability, included a variety of piscivorous bird species and the Cape clawless otter Aonyx capensis. This is the first documented account of a diverse species fish kill associated with estuary mouth breaching.     

Extracellular Matrix Assembly in Diatoms (Bacillariophyceae) (II. 2,6-Dichlorobenzonitrile Inhibition of Motility and Stalk Production in the Marine Diatom Achnanthes longipes)

The cellulose synthesis inhibitor 2,6-dichlorobenzonitrile (DCB) and the DCB analogs 2-chloro-6-fluorobenzonitrile, 3-amino-2,6-dichlorobenzonitrile, and 5-dimethylamino-naphthalene-1-sulfonyl-(3-cyano-2, 4-dichloro)aniline (DCBF) inhibited extracellular adhesive production in the marine diatom Achnanthes longipes, resulting in a loss of motility and a lack of permanent adhesion. The effect was fully reversible upon removal of the inhibitor, and cell growth was not affected at concentrations of inhibitors adequate to effectively interrupt the adhesion sequence. Video microscopy revealed that the adhesion sequence was mediated by the export and assembly of polymers, and consisted of initial attachment followed by cell motility and eventual production of permanent adhesive structures in the form of stalks that elevated the diatom above the substratum. A. longipes adhesive polymers are primarily composed of noncellulosic polysaccharides (B.A. Wustman, M.R. Gretz, and K.D. Hoagland [1997] Plant Physiol 113: 1059-1069). These results, together with the discovery of DCB inhibition of extracellular matrix assembly in noncellulosic red algal unicells (S.M. Arad, O. Dubinsky, and B. Simon [1994] Phycologia 33: 158-162), indicate that DCB inhibits synthesis of noncellulosic extracellular polysaccharides. A fluorescent probe, DCBF, was synthesized and shown to inhibit adhesive polymer production in the same manner as DCB. DCBF specifically labeled an 18-kD polypeptide isolated from a membrane fraction. Inhibition of adhesion by DCB and its analogs provides evidence of a direct relationship between polysaccharide synthesis and motility and permanent adhesion.     

Norian-Rhaetian reefs in Argolis Peninsula,Greece

Summary Upper Triassic to Lower Jurassic shallow-water carbonate sequences of the ‘Pantokrator limestones’ are widely distributed in the Argolis Peninsula, southern Greece. Within this sequence are some reef or reefal structures. In the Mavrovouni Mountains, near Sarmeika, 6 km SE of the ancient theatre of Epidavros (Argolis Peninsula), a Norian-Rhaetian reef complex has been identified. This is the first well-documented Norian-Rhaetian reef in Greece. The main reef builders are coralline sponges (‘sphinctozoans,’ ‘inozoans’, and sclerosponges), followed by dendroid, cerioid, and solitary corals, and algae. The reef type corresponds to a ‘sponge-coral reef’.     

Changes in benthic community composition in response to reservoir aging

The effects of reservoir aging on the benthic macroinvertebrate community in Pawnee Reservoir were documented by comparing species composition and biomass of samples collected from October 1991 through September 1992, to a similar survey conducted in 1968–70 by Hergenrader & Lessig (1980). Filling of the basin with sediment and associated material and the subsequent change in the benthic environment, has resulted in a relatively homogenous bottom substrate at each of the three sampling transects (dam, middle, and inflow). Sediment enrichment has limited the benthic fauna to species tolerant of brief periods of bottom anoxia and increased levels of organic matter, which has resulted in the disappearance of many taxa and a decrease in the abundance of remaining invertebrates. Significant differences in total biomass were found at each transect, as well as for the whole lake, between study periods. The dam, middle, inflow and total biomasses for the 1968–70 study period were 2.4, 1.5, 2.3 and 2.0 g m^–2, respectively, compared to 0.2, 0.2, 0.3, and 0.2 g m^–2 for the 1991–92 study period. The total disappearance of eight invertebrate taxa, in particular two sphaerid clam species, and significant declines in other dominant taxa such as Chaoborus punctipennis and Chironomus sp. accounted for these major differences in biomass between study periods. Reductions in the number of taxa present has resulted in an increase in benthic faunal similarity at each transect, with tubificid oligochaetes, Coelotanypus sp., C. punctipennis, and Chironomus sp., comprising 90% of both the total density and biomass of benthic invertebrates in Pawnee Reservoir.     

Temporal scaling of molecular evolution in primates and other mammals

Molecular clocks are routinely tested for linearity using a relative rate test and routinely calibrated against the geological time scale using a single or average paleontologically determined time of divergence between living taxa. The relative rate test is a test of parallel rate equality, not a test of rate constancy. Temporal scaling provides a test of rates, where scaling coefficients of 1.0 (isochrony) represent stochastic rate constancy. The fossil record of primates and other mammals is now known in sufficient detail to provide several independent divergence times for major taxonomic groups. Molecular difference should scale negatively or isochronically (scaling coefficients less than 1.0) with divergence time: where two or more divergence times are available, molecular difference appears to scale positively (scaling coefficient greater than 1.0). A minimum of four divergence times are required for adequate statistical power in testing the linear model: scaling is significantly nonlinear and positive in six of 11 published investigations meeting this criterion. All groups studied show some slowdown in rates of molecular change over Cenozoic time. The break from constant or increasing rates during the Mesozoic to decreasing rates during the Cenozoic appears to coincide with extraordinary diversification of placental mammals at the beginning of this era. High rates of selectively neutral molecular change may be concentrated in such discrete events of evolutionary diversification.      

Alternaria cassiae Alters Phenylpropanoid Metabolism in Sicklepod (Cassia obtusifolia)

Phenylpropaniod metabolism has been implicated in plant defence mechanism(s) against pathogen attack. In this study, phenylpropanoid metabolism was examined over a 72 h time course in the weed sicklepod (Cassia obtusifolia) in relation to pathogenic effects of the fungus Alternaria cassiae. When 3- to 4-week old seedlings were challenged by the pathogen, extrable phenylalanine ammonia-lyase (PAL, E.C. 4.3.1.5) activity was dramatically increased above that in uninfected plants severalhours after inoculation and exposure to dew. Greatest increases of enzyme activity (3-fold, specific activity basis) occurred at ca 15–23 after treatment with fungal spores. After this peak of activity, PAL activity declined with time in infectedtissue, but remained greater than in uninfected plants through 65 h after treatment. Total methanol-soluble hydroxyphenolic compound levels (PAL products) were higher in shoots (stems and leaves) of infected plants at 48–72 h. Leaves contained a higherconcentration (per gram fresh weight) of hydroxyphenolic compounds than did stems, and infected leaves exhibited a phenolic content greater than that of uninfected leaves at ca 27–72 h. Increased soluble phenolic compound production correlated with the appearance of lesions and necrotic spots on leaves and stems. UV irradiation examination and spectrofluorometric analysis of thin layer chromatographic separations of methanolic exatracts revealed a substantial increase of several components ininfected tissue 48 h after inoculation. Results support the view that PAL activity increases correlate with increased phenolic compound production in this host/pathogen interaction.