Flowering phenology,seed set and bird pollination of five Western Australian Banksia species

Flowering phenology and seed set characteristics of five species of Banksia were studied in relation to the nectarivorous birds which feed at their inflorescences. Within the Banksia woodland at the study site near Perth, the flowering seasons of the Banksia species were sequential and only slightly overlapping, providing a year-round nectar source. Although honeyeaters visited alt five species, seed set was very low in each case. Caging experiments indicated that, in B. attenuata at least, alternative pollinators may play a more important role in pollination than do nectar-feeding birds. It is suggested that non-avian pollinators, predatory insects, and characteristics of the breeding system may also have been important in the evolution of the observed flowering phenology and patterns of seed set.     

Effect of temperature on phytochrome—mediated anthocyanin synthesis in red cabbage

Abstract. A brief high temperature treatment (45 C) promoted anthocyanin synthesis in 2-d-old dark-grown red cabbage seedlings. The increased effectiveness of a temperature/red light treatment as opposed to the reverse sequence suggests that an elevated temperature 'induces' some component which facilitates the phytochrome response.     

Ozone-induced ultrastructural changes in the plasma membrane of Chlorella sorokiniana

Abstract. Modifications in plasma membrane structure and permeability were observed in Chlorella sorokiniana following exposure to 0.2 gm⁻³(140 p.p.m.) O₃ for 30 min. Sixty-eight per cent of the cells were plasmolysed after 15 min O₃ exposure with disruption of organelles similar to that previously described in higher plants. Freeze-fracture exposed large areas of plasma membrane in 90% of the control cells and those exposed to O₃for short periods. After 20 min O₃ 90% of the cells cross-fracture, which indicates a change in molecular interactions in the membrane exposed to O₃ The earliest observed ultraslructural alteration is an aggregation of particles on the plasma membrane P face, statistically significant after 10 min O₃ Changes in ⁸⁶Rb influx occur during a similar time. After more extended exposure to O³ the plasma membrane P face shows regions of lipid phase transition to the crystalline state.     

The Role of Extracellular Ca2+ in the Activation of Pectinaria Oocytes

Several events are associated with fertilization in oocytes. Two such events are an increase in cytoplasmic Ca²⁺ concentration and the resumption of meiosis. Oocytes of the marine annelid, Pectinaria gouldii , are in metaphase I arrest when they are spawned. In this report we investigate the relationship between Ca²⁺ and resumption of meiosis in this species. Meiosis in unfertilized oocytes could be re-initiated with the divalent cation ionophore, A23187. Oocytes in Ca²⁺ free sea water, however, did not resume meiosis in the presence of the ionophore. Furthermore, it was observed that Ca²⁺ must be present for at least 15 min following ionophore treatment for meiosis to resume. These results suggest that extracellular Ca²⁺ is required for the re-initiation of meiosis in this species.     

The Effects of Salinity upon Galactosyl-Glycerol Content and Concentration of the Marine Red Alga Porphyra purpurea (Roth) C.Ag.

Changes in the major alcohol-soluble, low molecular weight carbohydratesof P. purpurea, O--D-galactopyranosyl-(1-2)-glycerol (‘floridoside’)and O--D-galactopyranosyl-(1-1)-glycerol (‘isofloridoside’),have been examined in response to salinity variation. ‘Floridoside’is shown to vary in absolute amount, increasing in hypersalineand decreasing in hyposaline media. ‘Isofloridoside’content per cell does not change in a similar manner. Responsesare almost identical under light or dark conditions, ‘floridoside’changes being complete within 24 h. Decreasing the externalwater potential using ionic and non-ionic solutes has the sameeffect upon galactosyl-glycerol content. The amount of ‘floridoside’synthesized, and degraded under hypersaline and hyposaline conditionsrespectively is shown to be insufficient to restore cell volumeto its original value. It is therefore suggested that the primaryfunction of ‘floridoside’ increases in concentratedsea-waters is that of a compatible solute, serving to protectthe cell during periods when the external salt content is increaseddramatically.     

Inhibition of Pinus radiata Primary Needle Epicuticular Wax Biosynthesis by Trichloroacetate

High concentrations (1000 parts 10^–6) of trichloroacetate(TCA) inhibit germination of Pinus radiata seed. Seedlings growingin the presence of lower concentrations (100 parts 10^–6)take up TCA where it becomes concentrated in cotyledons anddeveloping primary needles. TCA inhibits biosynthesis of nonacosan-10-oland long chain diol constituents of the primary needle epicuticularwax concomitant with a reduction in appearance of tubular waxexcept around stomatal pores. Epicuticular wax from TCA-treatedplants consists mainly of alkyl esters, and is amorphous. Itis suggested that P. radiata stomatal subsidiary cells possesstubular epicuticular wax chemically distinct from that of epidermalcells.     

Effects of Visible and Ultraviolet Light on Carotene-deficient Mutants of Crypthecodinium cohnii

Synopsis.
The ability of carotenoids to protect a heterotrophic dinoflagellate, Crypthecodinium cohnii , from photodynamic damage by sunlight in the presence of an exogenous dye was demonstrated. Wild-type C. cohnii and 2 carotcnoid-deficient mutants were plated on agar-solidified media and exposed to natural sunlight. The wild-type strain, which synthesizes γ–carotene and β–carotene, had the lowest mortality. Mutant car 17 which accumulates mainly §–carotene had an intermediate mortality rate while the albino mutant, car 3, which contains only phytoene, lost viability most rapidly. Wild-type cells treated with diphenylaminc, a carotenogenic inhibitor, were killed at the same rate as mutant car 3. The survival rate of mutants on exposure to sunlight was dependent upon the chromophore length of the accumulated carotenoids. The 3 strains showed no difference in rate of mortality when exposed to ultraviolet light. Protection from sunlight by accumulation of carotenes may be an important ecological factor for this species whose natural habitat is tidepools.     

Inotropism and Contracture of Aplysiid Ventricles as Related to the Action of Neurohumors on Resting and Action Potentials of Molluscan Hearts

The postsynaptic actions of neurohumors on molluscan musclemay be exerted through control of force as well as by meansof excitation and inhibition. The control of force may appearas potentiation of the response to excitation, as increasedinotropism in spontaneous contractions, or as an increase intonus. We have directed our attention to the alterations offorce induced in aplysiid ventricles by applied postulated neurohumors.The results are interpreted in terms of the known effects ofneurohumors on resting potential and action potentials of molluscanhearts. We recorded compound membrane potentials of aplysiidventricles extracellularly, using a single sucrose gap apparatustogether with a force-displacement transducer to measureforcein contractions or contracture. Aplysia californica ventriclehas a membrane potential of –52.5 ± 9.4 mV. Ventriclesof Aplysia dactylomela or Aplysia californica are depolarizedby increased concentrations of external potassium ion, withan accompanying contracture. After incubation in calcium-freemedium, KCl contracture-force is directly dependent on calciumion concentration. A depolarization of 8.3 ±2.14 mV inpotassium-free medium is blocked by substitution of lithiumfor sodium in the medium, suggesting an electrogenic sodiumpump. There is a sustained depolarization in low chloride medium,which suggests a significant chloride contribution to the restingpotential. Ventricles of Dolabella auriculana or Aplysia dactylomelaare depolarized by acetylcholine (ACh). Threshold for depolarizationis lower than threshold for contracture-force. The ventricleof A. dactylomela is depolarized by 5- hydroxytryptamine (5HT)with threshold at 10^–9 M and a maximum depolarizationof 30 mV at 10^–4M. Depolarization by 5HT may induce beatingbut does not induce contracture. Ventricles of Aplysia californicaare not depolarized by ACh although beating ventricles are inhibited,and a depolarized ventricle in a tonic contracture may be hyperpolarizedand relaxed by low concentrations. The force of contractionof the ventricle of Dolabella auricularia is dependent on theduration of the plateau phase of the cardiac action potential.The plateau is lengthened by 5HT with an accompanying increasein force of beat, and shortened by ACh, with an accompanyingdecrease in force of beat. The action potential in the ventricleof Aplysia californica is not differentiated into spike andplateau phases, and neither ACh nor 5HT has any marked effecton the form of the action potential. Nevertheless, isolatedventricles of Dolabella auricularia, Aplysia dactylomela, andAplysia californica are all excited by 5-hydroxytryptamine,with a threshold at about 10^–M. Both spontaneous beatingand excitation induced in A. californica ventricles by 5HT areblocked by lack of the sodium ion, which may be responsiblefor pacemaker potentials in molluscan hearts.     

The Effect of Metabolic Poisons on ATP Level and on Active Phosphate Uptake in Chlorella pyrenoidosa

Influence of light and dark aerobic conditions and of various metabolic poisons [3-(3,4-dichlorophenyl)1,1-dimethylurea (DCMU), 2,4-dinitrophenol (2,4-DNP), carbonyl cyanide-m-chlorophenylhydrazone (m-CCCP), α,α′bis(hexafluoroacetonyl) acetone (1799), N,N′-dicyclohexylcarbodiimide (DCCD), sodium azide, fatty acids] on the active phosphate uptake and on the ATP level has been investigated. Cells in the dark have the same level of ATP as in the light though the phosphate transport is decreased. Similar findings are observed with DCMU. Other poisons used inhibit phosphate uptake and decrease ATP level. However their effect is more drastic on phosphate transport than on the ATP level. There is no good correlation between the ATP level and phosphate transport.     

Respiration of maleic hydrazide treated and untreated onion bulbs during storage

Respiration rates were determined at a range of temperatures on onion bulbs cv. Rijnsburger sampled from a cool-stored bulk over a period of 8 months. In the first 5 months of storage, respiration rates were low and showed a small increase with temperature. During this period there was little or no difference between untreated bulbs and those treated with maleic hydrazide (MH) prior to harvest. Subsequently there was a rise in respiration rates, which preceded sprouting, but this was not evident in MH-treated bulbs. A relationship between respiration and dormancy was suggested by the correlation between respiration rate in January and sprouting in June for four cultivars.