Environmental Factors Controlling Flower Opening and Closing in aPortulacaHybrid

To examine flower opening and closing of aPortulacahybrid, flowerbuds were placed in darkness for 12 h (2030–0830 h) at20 °C and then exposed to various light-temperature conditions.Flower buds exposed to light at 25, 30 or 35 °C opened within1 h, and wilted 10–14 h later. Flower buds exposed tolight at 20 °C started to open after 4 h but opened slowlyand not completely. Flower buds subjected to 25, 30 or 35 °Cin darkness also opened rapidly, but did not reach full opening.Flowers opened at 30 °C in light, and partially closed andopened repeatedly in response to cycles of a 2-h exposure to20 °C and a 2-h exposure to 30 °C at any time between1000 to 1600 h. Similar phenomena were observed when the flowersopened at 30 °C in light and then were subjected to darknessand light alternately at 30 °C, although the effect of lightwas less obvious than that of alternating temperature. Floweropening and closing were not affected by relative humidity.These results indicate that a rise in temperature is requiredfor rapid flower opening in the buds kept at 20 °C, andthat light intensifies the effect of high temperature. Exposureto light without a temperature change delayed and slowed floweropening which was never complete. The involvement of an endogenousrhythm in flower opening byPortulacais indicated. Portulacahybrid, flower opening, flower closing, temperature shift, endogenous rhythm.     

Sink-Regulation of Photosynthesis in Relation to Temperature in Sunflower and Rape

Stimulation of the rate of photosynthesis at 2·0 kPaO₂ in comparison with 21 kPa O₂ and carbohydrate accumulationover 4h were measured during exposure of sunflower (Helianthusannuus L.) and rape (Brassica napus L.), grown at 30 °Cand 13 °C, to temperatures between 7 °C and 35 °C.The effect of reducing source: sink ratio by shading on theresponse of photosynthetic rate to temperature was also determined.Stimulation of photosynthesis by 2·0 kPa O₂ in comparisonwith 21 kPa O₂ decreased over 4 h at cool temperatures in sunflowerplants grown at 30 °C but not in rape grown at 30 °C.Stimulation did not decrease over 4 h in plants grown at 13CC. Sucrose was the main carbohydrate accumulated over 4 h;its accumulation increased with decreasing temperature. Starchaccumulation either decreased or remained the same with decreasingtemperature. In plants grown at 30 °C more carbohydrateaccumulated between 8 °C and 21 °C in sunflower thanin rape, but more carbohydrate accumulated at 30 °C in rapethan in sunflower. In plants grown at 13 °C much less carbohydrateaccumulated between 13 °C and 23 °C than in plants grownat 30 °C. Photosynthetic rate in plants grown at 30 °Cexposed to between 20 °C and 35 °C over 32 h (14 h light-10h dark-8 h light), declined over 32 h at 20 °C and 25 °Cin sunflower and at 20 °C in rape. This fall over 32 h,especially at 20 °C in sunflower, was significantly reducedby shading the rest of the plant. Shading had little effecton photosynthetic rate above 25 °C. The work confirms thatlow temperature imposes a sink-limitation on photosynthesiswhich occurs at higher temperatures in sunflower than in rape.This limitation may be relieved by decreasing the source:sinkratio. Key words: Sunflower, rape, photosynthesis, carbohydrates, sink demand, temperature     

The Effect of Heat Stress on Wheat Leaf and Ear Photosynthesis

The effect of heat-hardening on carbon exchange rate per unitarea (CER) of flag leaves, whole ears, and ears with the awnsremoved, was measured in hexaploid (Triticum aestivum L.) andtetraploid (T. turgidum L. and T. dicoccoides) wheat varieties.The CER for awns was calculated by the difference. For the non-hardened hexaploid cv. ‘H-895’ the CERfor the leaves and glumes had an optimum temperature of 25°C.By contrast, the CER for the awns increased from 25°C to32°C, indicating an optimum at 32°C or more. Heat-hardeningdecreased the CER of leaves and glumes at the optimum temperature,but increased the CER especially in leaves at supra-optimaltemperatures. Thus, leaf CER in hardened plants became essentiallyindependent of temperatures between 25°C and 32°C. AwnCER was little affected by heat-hardening. For all 12 varieties, leaf and ear CER was smaller in hardenedplants at 30°C than in non-hardened plants at 22°C.Leaf and ear CER measured at 30°C differed significantlybetween varieties within a species. Whole ear CER at 30°Cwas negative in most varieties although the calculated valuefor the awns was positive. Thus, the high temperature optimumfor CER of the awns was a major factor in the variation amongwheat varieties in tolerance of ear CER to heat. The biochemicalattributes of the photosynthetic mechanism in awns responsiblefor the high temperature optimum were already present in wildtetraploid wheat. There was a positive correlation across allvarieties between ear CER at 30°C and the percentage ofawns in total ear area (r = 0930, P = 0 This together with previousresults (Blum, 1985a), suggests that a large amount of awnsin the ear is a sensible selection index in wheat for improvedproduction in hot, dry environments. Key words: Carbon exchange rate, photosynthesis, awns, heat, stress, wheat, breeding     

Mechanisms of the acido- and thermo-phily of Cyanidium caldarium Geitler II. Physiological role of the cell wall

1) A partially disintegrated cell preparation of Cyanidium caldarium(i.e. the 100G fraction; cells from which the outer parts ofthe cell wall had been removed) was obtained by differentialcentrifugation of a cell suspension treated with a French press.2) The 100G fraction cells had completely lost the outer partsof their cell walls, but retained their subcellular structureunchanged and had Hill activity that was equally as high asthat of the intact cells. 3) The Hill activity of the 100G fractionshowed an optimum at pH 7.0 and at 35°C. This activity waslost under acid and high temperature conditions (e.g. pH 3,50°C) under which intact cells showed high activity. 4)The Hill activity of the 100G fraction was lost by heat treatment(55°C, 10min), acid-treatment (pH 3.0, 10 min) or pre-illumination(3xl0⁵lux, 30 min) though intact cells were not inactivatedby these treatments. However, no remarkable difference in sensitivitytowards inhibitors was found between the 100G fraction and intactcells. 5) We thus concluded that the cell wall plays an importantrole in the acido- and thermo-phily of Cyanidium cells. (Received August 19, 1974; )     

The Influence of Temperature on Root Hair Infection of Trifolium parviflorum and T. glomeratum by Root Nodule Bacteria: I. THE EFFECTS OF CONSTANT ROOT TEMPERATURE ON INFECTION AND RELATED ASPECTS OF PLANT DEVELOPMENT

The onset and rate of infection in root hairs of T. parviflorumand T. glomeratum inoculated with Rhizobium trifolli strain5 varied much with root temperature. At moderate root temperature(18, 24, and 30 °C) infections were initiated earlier andin larger numbers than at low (6 and 12 °C) or moderatelyhigh (36 °C) temperatures. Both species showed a broad temperatureoptimum between 18 and 30 °C. The site of thread initiation(apically or laterally in a hair) was independent of temperature,as was also the proportion of successful threads penetratingthe root cortex, which increased with seedling age. Threadsgrew more slowly at low temperatures. The size of hair nucleinear infection threads remained unaffected by temperature, butnuclei associated with laterally originating threads were largerthan those associated with apical threads. Infection was non-randomly distributed along the main root atall temperatures. More zones of infection were found at moderatetemperatures than at temperature extremes (6–12 or 36°C). Probit plots of numbers of infections for individualplants were steplike, the linear sloping parts correspondingto normal distributions of infection within zones. Between 18 and 30 °C numbers of infections increased exponentiallyin two phases, the first more rapid phase ending at about thetime nodules appeared. A model devised for the infection processand fitted to the data suggested the existence of two kindsof infections: primary ones occuring randomly at a slow rateand probably not affected by temperature and secondary infectionsthat appeared to increase with rising temperatures in the range12 to 30 °C. Nodule numbers were relatively more sensitive to high and lowtemperatures than infection. The numbers of infections and nodulesand the root lengths of T. parviflorum were twice those of T.glomeratum except at the temperature extremes. Numbers of infectionswere otherwise unrelated to root length or cotyledon or leafareas. The development of lateral organs (primordia, lateralroots, and nodules) was reduced at temperatures below 18 °Cand above 30 °C.     

The Effects of Temperature on Leaf Growth in Cyperus longus, a Temperate C4 Species

Plants of the C₄ sedge Cyperus longus L. were grown at 10, 20and 30 °C. An asymptotic growth curve, the Richards function,was fitted to growth data for successive leaves. The mean rateof leaf appearance was a linear function of temperature with0.014 leaves appearing per day for every 1 °C increase intemperature. The instantaneous relative rate of leaf extensionshowed a marked ontogenetic drift which was most rapid at 30°C and slowest at 10 °C. The mean absolute extensionrate for foliage had a temperature coefficient of 0.16 cm d^–1° C^–1 in the range from 10 to 30 °C. The durationof leaf growth was independent of leaf number at 10 and 20 °Cbut increased linearly with leaf number at 30 °C. The smalldifferences in relative growth rate at the three temperaturesresulted in large differences in foliage area produced at theend of a 30 d growth period. The final foliage areas at 20 and10 °C were 51 and 9% respectively of that at 30 °C. Cyperus longus, temperature, leaf growth, Richards function, growth analysis     

Effects of High Temperatures on the Permeability and Germinability of the Hard Seeds of Rhus javanica L.

The effects of temperature, 40–85 °C, on the permeabilityand germinability of the hard seeds of the pioneer tree Rhusjavanica L. with a fire syndrome were studied. The temperatureeffective for removal of the water-impermeable coat dormancyof the seeds was 55 ± 7·4 °C. With increasingtemperature, shorter exposure became sufficient to render theseeds permeable, but at temperatures above 75 °C, heat impairmentof germinability resulted in less than 60% germinability, evenwith long exposure. The most favourable regimes among thosetested were temperatures of 65–75 °C for durationsof 30–120 min, which frequently occur on denuded groundduring the midday hours of clear spring or summer days. Rhus javanica L., water-impermeable coat dormancy, seed germination, high temperature     

Influence of Temperature on the Effects of Water Stress on Quercus Species

Quercus coccifera L. and Q. ilex L. leaves, collected in winter,when the plants were in full turgor, were treated with polyethyleneglycol (PEG) with a water potential of –48 and –65bar, at 15 °C and at 30 °C, for 2 days. The responseof each species differs with temperature as far as the plastidpigment, anthocyanin and soluble sugar content is concerned.Thus Q. ilex is affected more at 15 °C rather than at 30°C, while in Q. coccifera, apart from a small increase inanthocyanins, no significant change was observed at 15 °C.On the contrary, at 30 °C significant changes were observedin all studied parameters. Chloroplast pigments decreased generallyon the first day and their content either dropped further orincreased to reach the control values on the second day. Alltreatments resulted in an increase in anthocyanin content. Solublesugar content raised in Q. ilex at 15 °C and decreased inboth species at 30 °C. Quercus coccifera, Quercus ilex, oak, temperature, water stress, anthocyanin, chlorophyll, carotenoids     

Effects of temperature and salinity on the growth of the red tide flagellates Heterocapsa circularisquama (Dinophyceae) and Chattonella verruculosa (Raphidophyceae)

Growth responses of the red tide flagellates, Heterocapsa circularisquama(Dinophyceae) and Chattonella verruculosa (Raphidophyceae),were examined with 36 different combinations of temperature(5–30°C) and salinity (10–35 PSU). Heterocapsacircularisquama did not grow at or below a temperature of 10°C.The maximum growth rate of H.circularisquama (1.3 divisionsday^–1) was obtained with a combination of 30°C and30 PSU. In contrast, C. verruculosa did not grow at 10 PSU andat temperatures of 25°C or more. The maximum growth rateof C. verruculosa (1.74 divisions day^–1) was obtainedwith a combination of 15°C and 25 PSU. A significant temperature-salinityinteraction on growth was found by factorial analysis. Basedon the physiological characteristics obtained in the presentstudy, these novel flagellates have a potential for future outbreaksof red tides in pre viously unaffected waters.     

Effect of Temperature on the Activity of Carboxylases in Tropical and Temperate Gramineae

Temperate Gramineae show maximal net photosynthesis at 20–5°C, whereas tropical Gramineae have maxima between 30 and35 °C. Moreover, it has been suggested that different carboxylationreactions are involved in the two groups. The present studyof the temperature dependance of in vitro ribulose-1,5- diphosphate(RuDP), and phosphopyruvate (PEP) carboxylases indicates thatthe two enzymes have clearly marked differences in temperaturesensitivity. RuDP carboxylase, present in the temperate andtropical species studied, showed maximal activity around 20–5°C except in Zea. By contrast, PEP carboxylase activityin all species was maximal between 30 and 35 °C. The dataimply that activity and temperature sensitivity of the relevantcarboxylase enzymes may well be a significant limiting factorin leaf photosynthesis, even at light saturation.     

Effects of Temperature on the In vivo Assay of Nitrate Reductase in some C3 and C4Species

Nitrate reductase (NR) activity was measuredin vivo in differentcrop species at 25–60 °C. Highest NR activity wasobserved at 40 °C in pigeon pea, cowpea, sunflower, sesameand sorghum, 45 °C in maize and 50 °C in bajra. At higherincubation temperatures NR activity declined in all species.In mung bean the optimum incubation temperature varied withthe season. In the summer crop of mung beans, NR activity wasmaximum at 50 °C while in the rainy season crop 30 °Cwas the optimum incubation temperature. NR in sesame was relativelyheat-tolerant. The results indicate that 30 °C is not theoptimum incubation temperature for all crop species. Nitrate reductase, temperature, in vivo assay     

Germination of Tagetes minuta L. I. Temperature Effects

Initial studies have indicated that Tagetes minuta achenes haveboth a temperature and a light requirement for germination.Temperatures tested were 10, 20, 25, 30 and 35 °C. Germinationwas optimal at 25 °C under white light conditions. Underthese conditions 100 per cent of achenes germinated within 7days of imbibition. There was no germination at 10 or 35 °Ceither in the light or in the dark. Achenes imbibed and incubatedat 35 °C for 4 days showed no visible signs of germinationbut on transfer to 25 °C, 100 per cent of these achenesgerminated within 24 h. Furthermore, achenes given this hightemperature (35 °C) treatment could be dried at 25 °C,re-imbibed at 25 °C and again 100 per cent of achenes germinatedwithin 24 h of re-imbibition. This rapid germination responsefollowing removal from the high temperature regime could alsobe induced by transfer to temperatures of 20 °C or 20 °C(16 h) alternating with 10 °C (8 h). Tagetes minuta L., weed seeds, germination, temperature, light     

Growth of Trifolium subterraneum L. Selected for Sparse and Abundant Nodulation as Affected by Root Temperature and Rhizobium Strain

Root temperature greatly affected plant growth whether or notplants depended on symbiotic nitrogen fixation. The two plantselections responded differently to the three strains of Rhizobiumand this response was differentially affected by root temperature. Plant yield was significantly decreased by each fall of 4 °Cin temperature from 19 to 7 °C by amounts that dependedboth on the host and Rhizobium strain. Symbiosis with strainTA1, originally isolated from a cold environment, was most tolerantof a root temperature of 11 °C; TA1 produced as much ormore plant material of the abundantly nodulating host in 40days growth at 7 and 11 °C as did the uninoculated plantsgiven KNO³. Root temperature affected the number, rate of formation, anddistribution of nodules on the root system. At 7 °C fewernodules formed than between 11 and 19 °C. At 7 °C nodulesdid not form on secondary roots by 40 days but at 11 °Cthe secondary roots nodulated rapidly between 30 and 40 days.Nodule formation at 19 °C was almost completed at 20 days,when secondary root nodules accounted for 60 per cent of thetotal. Within the range 15 to 19 °C, at which the originalselections for sparse and abundant nodulation were made, plantsnodulated true to selection, but not at 11 °C. At 7 and11 °C plants nodulated with TA1 yielded more with increasingnumber of nodules.     

A Mathematical Model to Utilize the Logistic Function in Germination and Seedling Growth

Several models have been proposed to describe germination rates,but most are limited in statistical analysis and biologicalmeaning of indices. Therefore, a mathematical model is proposedto utilize the logistic function. The function was defined asan overall response including time, temperature, and the interactionbetween time and temperature. Cumulative germination percentagesover time were used to develop the model. Germination tests were conducted on indiangrass (Sorghastrumnutans (L.) Nash) strain ‘IG-2C-F1’, at constanttemperatures of 9, 12, 15, 20, 25, and 30 °C. The functionfitted the observed data over six temperatures at r² = 0.99.Time to reach 10% of final germination (Gt₁₀) increased from2.5 d at 30 °C to 44.0 d at 9 °C, and Gt₅₀ (time toreach 50% of final germination) increased from 3.6 d at 30 °Cto 53.8 d at 9 °C. True germination rate (% d^–1) foreach temperature was maximum at Gt₅₀. A linear model of 1/Gt₅₀versus temperature was used to estimate the base temperatureof 8.3 °C for germination. An Arrhenius plot indicated achange occurred between 20 °C and 25 °C for temperatureresponse of germination. Published data on hypocotyl growthof Cucumis melo L. were recalculated using the model. Absolutegrowth rates showed a temperature response similar to the publishedweighted-mean elongation rates. Base temperature for hypocotylgrowth of C. melo was estimated as 8.8 °C. The proposedmodel proved to be useful in calculating and interpreting germinationand growth kinetics. Key words: Indiangrass, Sorghastrum nutans (L.) Nash, Germination rate, Threshold temperature, Arrhenius plot, Growth rate, Cucumis melo L     

Seed Germination of a Halophytic Grass Aeluropus lagopoides

Aeluropus lagopoides(Linn.) Trin. Ex Thw. (Poaceae) is a perennialgrass distributed from coastal Sindh and Balochistan to salineflats of Punjab, Pakistan. Seeds collected from an inland populationofA. lagopoides located on the University of Karachi campuswere germinated under various levels of salinity (0, 100, 200,300, 400 and 500 m M NaCl) and temperature regimes (10/20, 15/25,20/30 and 25/35 °C) in a 12 h dark/12 h light photoperiod.Highest germination was obtained under non-saline conditions,and an increase in NaCl concentration progressively inhibitedgermination. Inhibition of germination was greater at coolertemperatures (10/20 °C) when no seed germinated above aconcentration of 300 m M NaCl. The germination response at moderatetemperatures (20/30 °C) was optimal, with 30% of seeds germinatingin 500 m M NaCl. The rate of germination decreased as salinityincreased. Germination rate was highest at 20/30 °C andlowest at 10/20 °C. Seeds were transferred from salt solutionsto distilled water after 20 d and those from high salinitiesrecovered quickly at warmer temperatures with an optimal responseat 20/30 °C. Copyright 2001 Annals of Botany Company Aeluropus lagopoides, germination, halophyte, Karachi, salinity, temperature     

Effects of intracellular acidification and varied temperature on force, stiffness, and speed of shortening in frog muscle fibers

This study aimed to establish whether the temperature-dependent effect of acidification on maximum force observed in mammalian muscles also applies to frog muscle. Measurements of force, stiffness, and unloaded velocity of shortening in intact single muscle fibers from the anterior tibialis muscle of Rana temporaria were performed between 0 and 22°C during fused tetani in H₂CO₃-CO₂-buffered Ringer solution with pH adjusted to 7.0 and 6.3, respectively. The force-to-stiffness ratio increased as a rectilinear function of temperature between 0 and 20°C at pH 7.0. Lowering the pH to 6.3 reduced the tetanic force by 13.5 ± 1.2 and 11.5 ± 1.4% at 2.8 and 20.5°C, respectively, with only a minor reduction in fiber stiffness. The maximum speed of shortening was decreased by lowered pH by 12.9 ± 1.5 and 7.8 ± 1.1% at low and high temperature, respectively. Acidification increased the time to reach 70% of maximum force by 18.0% at 2°C; the same pH change performed at 20°C in the same fibers reduced the rise time by 24.1%. The same increase in the rate of rise of force at high temperature was also found at normal pH after the fibers were fatigued by frequent stimulation. It is concluded that, in frog muscle, the force-depressant effect of acidification does not vary significantly with temperature. By contrast, acidification affects the onset of activation in a manner that is critically dependent on temperature. muscle contraction; pH     

Response to Temperature in a Stand of Pearl Millet: 10. PARTITION OF ASSIMILATE

Effects of temperature on partition of assimilate between leaves,stems and panicles of pearl millet are analysed in terms ofa duration (t_w) over which a structure increased in weight,and a partition factor (p)—the fraction of new dry matterallocated to the structure during t_w. The value of tw was, forall structures, inversely proportional to temperature abovea base of 10 °C and below an optimum of 28 to 30 °C.For stems and panicles, the value of p was, with one exception,little affected by temperature. The dry weight of these structureswas, therefore, proportional to t_w, and decreased with risein temperature. (The exception was panicles at the lowest temperature,19 °C, for which p was reduced by 40% because few grainswere set.) For leaves, however, p increased with rise in temperature,counteracting the effect on t_w, such that dry weight changedlittle with temperature. The optimum temperature for reproductiveyield was 22 °C, but the proportion of the total dry matterallocated to reproductive structures changed little between22 °C and 31 °C. Key words: Pearl millet, temperature, thermal time, partitioning     

An Investigation of the Influence of Constant and Alternating Temperature on the Germination of Cassava Seed using a Two-dimensional Temperature Gradient Plate

The germination of cassava seed in response to various constantand alternating temperature regimes within the range 19–40°C was investigated using a two-dimensional temperaturegradient plate. It was found that almost all seeds were incapableof germination unless the temperature for part of the day exceeded30 °C and the mean temperature was at least 24 °C. However,dormant seeds required environments where the temperature forpart of the day exceeded 36 °C, the mean temperature wasat least 33 °C, and the amplitude of the diurnal temperaturealteration was within the range 3–18 °C. Providingthese conditions were met, the times spent at the upper andlower temperatures within a diurnal cycle were not critical.Hermetic storage of the seed for 77 days at 40 °C with 7.9per cent moisture content did not influence the pattern of germinationin response to constant and alternating temperatures. It issuggested that an alternating temperature regime of 30 °Cfor 8 h/38 °C for 16 h applied for a minimum of 21 daysis appropriate for cassava seed viability tests. Manihot esculenta Crantz, cassava, germination, dormancy, temperature     

Thermodormancy Release of Celery Seed by Gibberellins, 6-Benzylaminopurine, and Ethephon Applied in Organic Solvent to Dry Seeds

The emergence of celery (Apium graveolens L. cv. Utah 52–70)seeds was promoted by growth regulators when exposed to hightemperatures during the germination period. The growth regulatorswere applied to dry seeds prior to sowing, by means of the organicsolvent dichloromethane (DCM). A mixture of gibberellins A₄and A₇ (GA_4/7) strongly enhanced emergence at a high day-timetemperature of 35°C alternating with night temperaturesof 20°C and 25°C; however, emergence was very poor whenthe night temperature was raised to 30°C. Under the latterregime, only mixtures of GA_4/7 with 6-benzylaminopurine (BA)or with 2-chlorophosphonic acid (ethephon) promoted seed emergence.However, BA and ethephon applied separately or in combinationwere much less effective in enhancing seed emergence withoutthe addition of GA_4/7, under all the temperature regimes.     

Temperature-dependent consumption and gut-residence time in the opossum shrimp Mysis relicta

Maximum daily consumption was estimated for Mysis relicta fedad libitum rations of Daphnia pulex at 4,10,15 and 18°C.Gut-residence time was also evaluated for M.relicta fed clado-ceranprey at 4, 10 and 157deg;C. Mean daily consumption (g dry weightof Daphnia g^–1 dry weight of Mysis day^–1) rangedfrom 6% at 4%C to 12% at 10°. At 18°C, Mysis feedingrate declined to 9% day1. Mean, weight-adjusted consumptionrates exhibited a ‘dome-shaped’ response in relationto water temperature. Consumption rate was highest at 10°Cand lowest at 4°C. Estimated Q₁₀ was more sensitive from4 to 10°C (Q₁₀= 3) than from 10 to 15°C (Q₁₀=1.2). Gut-residencetime for Mysis was inversely related to water temperature, implyingthat evacuation rate increases linearly with water temperature.Feeding and gut-evacuation rates become disassociated at watertemperatures >10°C. As water temperature increased above1°C, relative evacuation rate increased, whereas feedingrate declined. It is postulated that at higher water temperatures,disassociated feeding and gut-evacuation rates reduce the scopefor growth of vertically migrating Mysis and impose a physiologicalconstraint that isolates Mysis from warm, epilimnetic waterduring thermal stratification. ¹Present address: Center for Aquatic Ecology, Illinois NaturalHistory Survey, Sam Parr Biological Station, 6401 Meacham Road,Kinmundy, IL 62854, USA