Electrical Events Correlated with Contractile Vacuole Activity in the Suctorian, Heliophrya

SYNOPSIS. The surface membrane potentials of suctorian genus Heliophrya were studied with intracellular electrodes. Resting membrane potentials averaged -32 mV, and spontaneous depolarizing potentials occurring at apparently random intervals and having a variety of waveforms were routinely observed. Such spontaneous potentials were correlated in time with visually monitored contractile vacuole activity. Individual contractile vacuoles had unique, although somewhat variable, electrical signatures. In the presence of an intracellular electrode all vacuoles contracted independently, but at approximately the same frequency. The amplitude of the electrical potentials increased when the membrane was hyperpolarized and decreased when it was depolarized. The sign of such potentials reversed at between -10 mV and the zero membrane potential. A 20% decrease in the membrane resistance was measured at the peak of the spontaneous depolarizing potentials.     

Effect of Photoperiod and Irradiance Changes Upon Development of Freezing Tolerance and Accumulation of Soluble Carbohydrate in Seedlings of Lolium perenne Grown at 2 {degrees}C

Two contrasting cultivars of Lolium perenne were exposed toa range of daily radiation integrals during hardening at 2°Cfor 15 d. The maximum induced freezing tolerance measured asLT₅₀ (temperature for 50 % kill) differed markedly between thecultivars. The observed LT₅₀ values were unaffected by changesin the radiation integral above 10 mol m^–2 d^–1,whereas accumulation of water-soluble carbohydrate showed astrong positive correlation with the radiation integral overthe entire range of the experiment. The correlation betweenLT₅₀ and soluble carbohydrate content at the end of the hardeningperiod was poor and showed no obvious connection with genotype.Fructan polymers and sucrose were the major components of thesoluble carbohydrates in both cultivars. The depression of freezingpoint attributable to the accumulation of soluble, osmoticallyactive carbohydrate was not sufficient to account for the observedchanges in LT₅₀ in the hardy genotype. These results are discussedin relation to the interactions between growth, photosynthesisand assimilate partitioning during hardening. Lolium perenne, hardening, freezing tolerance, irradiance, carbohydrate, fructan     

Variation in growth of overwintered stolons of contrasting white clover populations in response to temperature, photoperiod and spring environment

The response of overwintered stolons of nine contrasting white clover populations to temperature, photoperiod and natural conditions was studied in six environments during the spring. Rate of leaf appearance, leaflet length, petiole length, stolon internode length, dry matter distribution within the plant and total dry weight were measured on 15 plants of each population/environment combination. Most characters, except leaf size and proportion of dry matter allocated to leaf, responded positively to temperature in the range 10 – 20°C. A positive effect of photoperiod extension was also found for all characters except rate of leaf appearance, internode length and distribution of dry matter to leaf. Population differences in response to environment were found which were related to both leaf size classification and origin. Stolon dry weight was positively correlated with leaf length, petiole length and stolon internode length in most environments. The relationships between the eight characters were often complex and canonical variate analysis provided a convenient way to discriminate between the populations based on all eight characters.     

Physiological studies of a hybrid between populations of Dactylis glomerata from contrasting climatic regions. I. Inter population differences

A study of the physiological responses of a hybrid between a North European population and a colchicine-induced autotetraploid of a Portuguese population of Dactylis glomerata subspecies lusitanica showed an intermediate response of the hybrid for many characters. However, the hybrid resembled one or other of the parents in the more favourable expression of certain characters in controlled environments at 20°C, 16 h photoperiod and 8 °C, 8 h photoperiod. Rate of dry-matter production of the hybrid did not differ significantly from that of the northern parent at 20 °C, 16 h and that of the Portuguese parent at 8 °C, 8 h. Leaf growth of the hybrid at 8 °C, 8 h was greater than that of the northern parent and together with the high percentage survival in a freezing test may indicate a role for similar hybrids in the development of potential varieties with improved seasonal distribution of dry-matter production.     

Time Changes of Relative Growth-rate in two Natural Populations of Dactylis glomerata L.

Changes in the relative growth-rate (RGR) between successiveharvests were studied in two natural populations of Dactylisglomerata, one from Norway and the other from Portugal, grownat four temperatures in a 16-h photoperiod. Young seedlingswere harvested at six equal intervals of 7 days at 5 and 10°C and 3.5 days at 20 and 30 °C. Quadratic curves werefitted to log_e dry weight by a method employing inverse matrices.There was a decline in RGR with time and the magnitude of thisdecline differed for the two populations with an intersectionof the curves at each temperature. At 5 and 10 °C the RGRof the Portuguese population was greater than that of the Norwegianat the initial harvests, but it declined more rapidly than theRGR of the Norwegian population. This relationship was reversedat 20 and 30 °C, with the RGR of the Norwegian populationbeing greater when the plants were small, and declining morerapidly with time. The implications of these changes in RGRare discussed in relation to earlier growth-analysis experimentswhere only two harvests were taken.     

Systemic Responses Arising From Localized Heat Stimuli in Tomato Plants

Localized application of heat to the terminal leaflet of leaf1 of tomato (Lycopersicon esculentum) seedlings induced bothpropagated electrical activity and the systemic production ofproteinase inhibitors. Aspirin and related compound inhibitedboth the propagated electrical activity and the systemic response.An electrical signal therefore remains a candidate for the systemicsignal in the wound response of tomato plants Proteinase inhibitor, propagated electrical activity, aspirin, tomato, Lycopersicon esculentum     

Diurnal Fluctuations in Growth and CO2 Exchange in Dactylis glomerata

Diurnal fluctuations in dry matter accumulation and leaf extensionof seedlings of Dactylis glomerata were followed through a 16-hlight period and a subsequent 8-h dark period at 20 °C.Themeasured increase in dry weight during the light period andthe decrease during the dark period showed a very good agreementwith calculated dry weight changes derived from the rates ofcarbon dioxide exchange of whole seedlings. Although dry weightof the leaf blades decreased during the dark period, leaf expansioncontinued throughout the 24-h period with associated changesin the ratio of fresh weight to dry weight of the leaf blades.     

Quantitative Analysis of Cold Hardening and Dehardening in Lolium

The change in cold hardiness of three Lolium multiflorum Lam.varieties was followed in plants exposed to hardening or dehardeningconditions at a range of temperatures. Hardening and dehardeningwere analysed as quantitative processes dependent upon temperatureand time. Their time courses changed exponentially to an asymptotewhich was logistically related to temperature. Both componentsof the model were fitted simultaneously. Parameters of biologicalinterest, such as the initial rates of hardening and dehardeningfor a given temperature and the percentage of the process completedin a given time, were derived and compared for varieties ofcontrasting hardiness. The analysis demonstrated the importanceof dehardening in determining hardiness. Similar results wereobtained when the model was applied to hardening and dehardeningdata for Lolium perenne L. The potential of this quantitative analysis for distinguishingbetween possible mechanisms of cold hardiness is discussed andfurther experiments required to characterise the kinetics ofhardening and dehardening more fully are identified. Lolium multiflorum, Lolium perenne, cold hardening, cold dehardening, processes, model, varieties     

A Manometric Technique for Determination of Apparent Photosynthesis of Lolium

A manometric technique for measuring photosynthesis of detachedleaves of Lolium is described. Results are compared with infra-redgas analysis data and ¹⁴CO₂ assimilation by attached leavesfrom similar plant material. All three methods gave similarcomparative estimates of apparent photosynthesis.