The Effects of Temperature and Photoperiod on the Onset of Summer Dormancy in Poa bulbosa L.

Poa bulbosa L. plants became dormant in long days (16 h), whilein short days (8 h) they remained non-dormant for extended periods.Morphologically, the onset of dormancy was expressed by theformation of a true bulb at the base of every tiller, by thecessation of tillering and leaf emergence and, finally, by thedrying-up of the leaves. Low temperature delayed the onset ofdormancy but did not prevent it. This effect of temperaturemay explain the delayed onset of dormancy observed in naturalpopulations under a cool climate at a hilly habitat, comparedto plants growing under a warmer climate, at a lower, coastal-plainhabitat. Dormancy could be induced under short days by pre-exposureof the plants to a limited number of long days. The responsewas proportional to the number of long days given. The adaptivesignificance of the results for plant survival in a Mediterraneanclimate is discussed. Poa bulbosa L., summer dormancy, photoperiod, temperature, leaf emergence, bulbs, tillers     

Growth and Dormancy in Norway Spruce Ecotypes (Picea abies) I. Interaction of Photoperiod and Temperature

Growth and dormancy as affected by photoperiod and temperature have been studied in Norway spruce ecotypes of different latitudinal and altitudinal origin. First-year seedlings were used. In all ecotypes apical growth cessation and terminal bud formation occurred within 2 weeks after exposure to SD at temperatures of 18 to 24°C. At lower temperatures or at near-critical photoperiods the response was delayed. The critical photoperiod for apical growth cessation varied from 21 hours in ecotype Steinkjer, Norway (64°N) to about 15 hours in ecotype Lankowitz, Austria (47°04′N). High-elevation ecotypes also had longer critical pholoperiods than low-elevation ecotypes from the same latitude. A detectable growth depression resulted from as little as 1 or 2 SDs of 10 hours, and with 4 or more SDs apical growth cessation took place. In contrast to the situation in the shoot, root growth was not affected by photoperiod. Accordingly, the top:root ratio is drastically affected by photoperiod. The critical photoperiod for cambial growth was shorter than that for apical growth in all ecotypes and cambial growth cessation was delayed for several weeks compared with cessation of apical growth. A transition to formation of late-wood tracheids with thick walls and narrow lumens took place upon exposure to SD. The photoperiodic effects were significantly modified by temperature, but the critical photoperiods were only slightly changed by temperature in the range of 12 to 24°C. However, a 10-hour “night” at 4°C caused growth cessation in continuous light in four ecotypes tested. Temperature optimum for apical growth under non-limiting photoperiods (24 hours) was 21°C in all ecotypes, but with little difference among 18,21 and 24°C. The Q₁₀ for apical growth was 3.5 in the temperature range 12 to 18°C. The growth potential as determined in 24-hour photoperiods was not significantly different among the various ecotypes except for one northern eco-type which was clearly inferior to the others. However, the growth of ecotype Steinkjer (64°N) was greatly suppressed even by the long midsummer days at 59°40′N, thus demonstrating the misleading impression one gets of the growth potential of northern ecotypes when they are moved southwards.     

雾灵山草地早熟禾多胚囊和多胚的研究

无融合生殖是指未经炷卵事例而产生后代的特殊生殖方式,它可以分为单倍体无融合生殖和二倍体无融合生殖;对于作物意义更大的是二倍体无融合生殖。多胚囊和多胚现象ＳＨＩ是无融合生殖的表现形式。本文运用石蜡切片法、子房整体透明法研究了雾灵山草地早熟禾（Ｐｏａ ｐｒａｔｅｎｓｉｓ Ｌ．）多胚囊和多胚现象。结果表明,（１）草地早熟禾多胚囊来源有两种：一是自大孢子母细胞,二是来自珠心细胞;（２）草地早熟禾多 来源有     

Effect of Temperature, Photoperiod and Several Growth Substances on the Cold Hardiness of Chrysanthemum morifolium Rhizomes

The effect of 14 combinations of photoperiod, soil and air temperature, and growth substance applications on the cold hardiness of Chrysanthemum morifolium‘Astrid’ rhizomes was evaluated. Both triphenyl tetrazolium chloride and regrowth tests were used to determine the viability of the cold-stressed rhizome tissues. The rhizomes exhibited different degrees of cold hardiness under these environmental conditions. A combination of short photoperiod and low air and soil temperatures induced maximum cold hardiness. Low soil temperature accompanied by long photoperiods and warm aerial temperatures did not induce rhizome hardening, while some hardening in cool soils was evident under either short photoperiods or low aerial temperatures. Warm soils reduced rhizome hardening under the normally inductive short photoperiod-cool aerial conditions. Since the induction of rhizome hardening was dependent on the induction of the aerial organs, the involvement of translocatable hardiness promoters is indicated. Foliar applications of low levels of gibberllic acid (GA₃) or abscisic acid only slightly influenced rhizome hardiness.     

Specific features of early embryogenesis in apomictic Poa pratensis L

We studied the early stages of embryo formation in apomictic Poa partensis L. It was shown that during transition to parthenogenesis, at least at the initial stages of embryogenesis, the algorithm of development of the sexual embryo is preserved. This could be due to the system of genetic control of embryogenesis, common for amphimixis and apomixis. We described asynchrony of developmental processes both within the efflorescence (asynchronous maturation of ovules) and within the ovule and even gametophyte (different timing of induction of apoarchesporic initials and oospores). This feature of pseudogamous apomicts allows them to produce simultaneously both sexual and apomictic progenies.     

Developmental Responses to Temperature and Photoperiod in Ecotypes of Medicago polymorpha L. Collected Along an Environmental Gradient in Central Chile

The phenological development of nine Chilean accessions of Medicagopolymorpha, collected along a north–south aridity gradient,and of two commercial cultivars of the same species, were comparedin 12 sequential outdoor sowings at Cauquenes (35°58'S,72°17'W, elev. 177 m), in the sub-humid Mediterranean climatezone of Chile. A glasshouse experiment was also conducted toevaluate the effect of photoperiod on phenophase timing. Therewas a clear gradient in precocity among the Chilean accessionsin both experiments: accessions MPO-9-88 and MPO-7-88, fromthe arid zone, were the earliest-flowering accessions, whereasMPO-36-88 from the humid Mediterranean zone was the latest.Both experiments revealed significant variation among the Chileanaccessions in the response of flowering time to variation inphotoperiod regime. Differences in days to flowering betweenthe least- (8 h) and the most- (16 h) inductive photoperiodswere lower in precocious accessions from arid and semi-aridzones, than in late-flowering accessions from more humid zones.Rate of progress to flowering, defined as the inverse of timefrom emergence to first flower appearance (1/ f), was relatedto mean diurnal temperature, or to both mean diurnal temperatureand mean photoperiod. In two early-flowering accessions fromthe arid zone, and in the Australian cultivar ‘CircleValley’, 1/ f was affected significantly (P < 0.05)by both temperature and photoperiod. In the remaining accessions,no significant responses to temperatures were detected; 1/ fwas influenced significantly by photoperiod only. Copyright2000 Annals of Botany Company Annual medic, aridity gradient, Medicago polymorpha, flowering time, rate of development     

The Growth and Survival of Severely-shaded Tillers in Lolium perenne L.

The effect of shading a single tiller to below its compensationpoint for a period of 5 weeks in vegetative plants of Loliumperenne L. cv. S23, was studied in two different experimentseach employing two light regimes, one of which was common toboth experiments. In the first experiment tillers in the axils of the first leafwere shaded three weeks from appearance at both 40 and 70 Wm^–2. None of the shaded tillers died and they continuedto produce new leaves and increase in dry weight but at a reducedrate. In the second experiment, tillers with one emerged leafin any leaf axil position were shaded at 70 W m^–2 andin a treatment in which light was reduced to 13 W m^–2after initial growth at 70 W m^–2. As in the first experimentall shaded tillers survived at 70 W m^–2 but in the 70 13 W m^–2 transfer regime all shaded tillers died. In the second experiment shaded tillers in both light regimeswere supplied with ¹⁴C-assimilate by translocation from theremainder of the plant but in the 70 13 W m^–2 the initialsupport was withdrawn within 5 weeks of shading. The results are discussed in terms of the physiological relationshipsbetween the tillers of the grass plant. Lolium perenne L., growth of tillers, survival of tillers, effect of light     

N uptake and growth responses to sub-lethal freezing in the grass Poa pratensis L.

Background and aims

Climate warming has the potential to increase both the exposure and vulnerability of grass roots to frost in temperate regions by reducing snow cover and altering the timing of cold acclimation. Despite a strong research focus on the direct effects of freezing on grass mortality, the direct sub-lethal effects of freezing on grass performance have not been well-characterized. We examined sub-lethal responses of the grass Poa pratensis to variation in the timing, severity, rate and length of freezing.

Methods

We assessed short term root functional responses (¹⁵N uptake) and longer term plant growth responses to freezing administered both under controlled conditions in a refrigerated incubator, and in the field by manipulating snow and litter cover.

Results

In fall and spring, ¹⁵N uptake declined in response to 1?day of freezing down to ?10?°C or to 3?days of freezing at ?5?°C, whereas in winter, ¹⁵N uptake was insensitive to freezing. Long term growth responses were similar, with reduced growth only occurring for grasses frozen for 3?days at ?5?°C in spring, but not for grasses frozen in fall or winter. Snow and litter removal intensified soil freezing over winter, but did not significantly affect plant growth.

Conclusions

Our results demonstrate that while P. pratensis is relatively tolerant to frost damage over winter, it may be vulnerable to sub-lethal frost effects in fall, and particularly in spring. These sub-lethal effects occur at temperatures approximately 15–20?°C warmer than the published LT₅₀ values for this species.     

Effects of Temperature and Photoperiod on Flowering in Chickpeas (Cicer arietinum L.)

Factorial combinations of two photoperiods (12 and 15 h), threeday temperatures (20, 25 and 30 °C) and three night temperatures(10, 15 and 20 °C) were imposed on nodulated plants of ninechickpea genotypes (Cicer arietinum L.) grown in pots in growthcabinets. The times to first appearance of open flowers wererecorded. For all genotypes, the rates of progress towards flowering(the reciprocals of the times taken to flower) were linear functionsof mean temperature. There were no interactions between meantemperature and photoperiod but the longer photoperiod increasedthe rate of progress towards flowering. These effects were independentof both radiation integral (the product of irradiance and photoperiod)and the vegetative stature of the plant. Taken in conjunctionwith evidence from work on other long-day species, it is suggestedthat the photo-thermal response of flowering in chickpeas, overthe range of environments normally experienced by the crop,may be described by the equation: 1/f = a+b     

Effects of Photoperiod, Nitrogen Nutrition and Temperature on Inflorescence Initiation and Development in Onion (Allium cepa L.)

The effects of photoperiod, nitrogen nutrition and temperatureon inflorescence initiation and development in onion cv. Rijnsburgerand cv. Senshyu Semi-globe Yellow were studied in controlledenvironments. Rates of inflorescence initiation were estimatedusing the data for leaf numbers formed prior to flower formationand the rates of leaf initiation. At 9 °C inflorescenceinitiation was accelerated by long photoperiods particularlyfor cv. Rijnsburger where the average time for initiation was86 days in 8 h and 38 days in 20 h photoperiods. Initiationwas as rapid at 12 °C as at 9 °C but was slower at 6°C. A reduction in the nitrate concentration in the nutrientsolution from 0.012 to 0.0018 M greatly accelerated inflorescenceinitiation particularly in photoperiods and temperatures notconducive to rapid initiation. Cv. Senshyu initiated more slowlythan cv. Rijnsburger and was less sensitive to photoperiod andnitrogen level. The development rate of inflorescences afterinitiation was accelerated by long photoperiods and increasesin temperature from 6 to 12 °C but was retarded by the lowernitrogen level. Allium cepa L., onion, flower initiation, inflorescence development, photoperiod, nitrogen nutrition, temperature, vernalization     

Effects of Photoperiod and Temperature on Shoot, Root and Rhizome Growth in ThreeLotus uliginosusSchkuhr Populations

The growth of three populations of greater lotus (Lotus uliginosusSchkuhrsyn.L. pedunculatusCav.) was compared at photoperiods of 10,12 and 14 h at a maximum day/minimum night temperature of 21/16°C and at maximum day/minimum night temperatures of 27/22,21/16, 18/13 and 15/10 °C at a photoperiod of 12 h. Shortdays (10 h) favoured root and rhizome development compared tolong days (14 h). A temperature regime of 15/10 °C restrictedrhizome development compared to the 18/13 and 21/16 °C regimes.Shoot growth was restricted at the highest temperature regime(27/22 °C). The cultivar Sharnae had fewer, but heavier,rhizomes than Grasslands Maku; this may indicate adaptationto the dry summers at its site of origin (Algarve, Portugal).The response of rhizome growth to temperature and photoperiodexplains part of the performance of greater lotus in the fieldat a wide range of latitudes. Grazing management to encouragethe persistence ofL. uliginosusin pasture in temperate environmentsmay include the exclusion of grazing livestock in autumn. Inthe sub-tropics, monitoring of rhizome production in the fieldwould be required before deciding the appropriate time intervalbetween grazing.Copyright 1998 Annals of Botany Company Lotus uliginosus(Schkuhr); greater lotus; temperature; daylength; shoots; roots; rhizomes.     

The Partitioning of Photosynthetically Fixed Carbon in the Leaf Blade and Leaf Sheath of Poa pratensis L.

The partitioning of photosynthetically fixed carbon betweencarbohydrate fractions and the processes of export and storagewere compared in mature leaf blades and sheaths of the grassPoa pratensis L. Most of the fixed carbon was destined for exportfrom the leaf blade with only 1% of the carbon fixed duringthe photoperiod being stored after 24 h. Although most of theassimilates imported to the sheath from the blade were subsequentlyexported, there was some unloading and storage of assimilates.Autoradiography was used to compare the translocation of ¹⁴C-labelledassimilates through non-fed areas of leaf blade and sheath andrevealed that the veins in the sheath showed a greater capacityfor storage of assimilates compared to the leaf blade. Biphasickinetics of sucrose and glucose uptake were observed in segmentsof leaf blade and sheath. Although similar carriers for eachof the sugars appear to exist in the blade and sheath, the rateof uptake via these carriers was significantly lower in thesheath compared to the blade. Assuming that unloading proceedsvia a symplastic pathway, it would appear that the conversionof sucrose to starch in the sheath could be an important meansof regulating unloading and in determining sink strength ofthe sheath. It is concluded that although the net amount ofsugars unloaded in the sheath is small, the storage of assimilatesin the vein network could be an important means of bufferingchanges in sucrose concentration in the translocate during periodsof fluctuating assimilation. Key words: Poa pratensis, autoradiography, sugar uptake, leaf blade, leaf sheath     

Biochemical and molecular markers for investigating the mode of reproduction in the facultative apomict Poa pratensis L.

Isozymes and random amplified polymorphic DNA (RAPD) markers were used for precocious identification of non-maternal plants in progenies of the facultative apomict Poa pratensis. Four progenies obtained from controlled crosses that showed different degrees of apomixis on isozyme analysis of phospho-gluco-isomerases, esterases and peroxidases were chosen for RAPD analysis to generate genomic fingerprints using species-specific primers. At an advanced vegetative stage, a morphological analysis was also performed and characteristics related to growth habit and leaf morphology were observed and recorded. On the basis of the isozyme and RAPD electrophoretic pattern and the morphological appearance, each plant was classified as maternal or aberrant. All three classes of genetic markers employed were able to identify plants that exhibited aberrant traits in the four progenies. Overall, the results of RAPD analysis supported those of isozyme and morphology studies. However, in each progeny, some plants which both isozyme and morphological analyses distinguished as of maternal origin were aberrant according to RAPD analysis. Therefore, the RAPD method proved the most precise screening technique. The greater cost of the molecular approach was offset by its higher accuracy. The use of either three isozyme systems or six primers for PCR amplification seems to be sufficient for reliable estimation of the degree of apomixis. Histological analyses were carried out and the aposporic development of the plant material studied.     

Photoperiod and Temperature Interactions in Growth and Flowering of Strawberry

Growth and flowering of strawberry cultivars were studied in controlled environments. Early cultivars adapted to marginal growing areas in Scandinavia initiated flower buds in all photoperiods including continuous light at temperatures of 12 and 18°C. At 24°C they remained vegetative in photoperiods above 14 or 16 h. The later cultivars ‘Senga Sengana’ and ‘Abundance’ did not initiate flower buds in 24-h photoperiods at any of these temperatures. Their critical photoperiod changed from above 16 h at 12°C to about 14 and 13 h at 18 and 24°C, respectively. It is concluded that at high latitudes temperature is as important as photoperiod in controlling flowering in the strawberry. Stolon formation, petiole elongation, and leaf area growth were stimulated by high temperature and long days, usually with optima at 16 h and 18°C for petiole elongation and 16 h and 24°C for stolon formation. Although growth and flowering responses in general were opposite, the results indicate that they are to some extent independent. The photoperiodic growth responses were mainly of morphogenetic nature. Dry weight of stem and leaves was little influenced by photoperiod when the irradiance was kept constant.     

Inheritance of parthenogenesis in Poa pratensis L.: auxin test and AFLP linkage analyses support monogenic control

 Gametophytic apomixis in Kentucky bluegrass (Poa pratensis L.) involves the parthenogenetic development of unreduced eggs from aposporic embryo sacs. Attempts to transfer the apomictic trait beyond natural sexual barriers require further elucidation of its inheritance. Controlled crosses were made between sexual clones and apomictic genotypes, and the parthenogenetic capacity of (poly)diploid hybrids was ascertained by the auxin test. A bulked segregant analysis with RAPD and AFLP markers was then used to identify a genetic linkage group related to the apomictic mode of reproduction. This approach enabled us to detect both an AFLP marker located 6.6 cM from the gene that putatively controls parthenogenesis and a 15.4-cM genomic window surrounding the target locus. A map of the P. pratensis chromosome region carrying the gene of interest was constructed using additional RAPD and AFLP markers that co-segregated with the parthenogenesis locus. Highly significant linkage between parthenogenesis and a number of AFLP markers that also appeared to belong to a tight linkage block strengthens the hypothesis of monogenic inheritance of this trait. If a single gene is assumed, apomictic polyploid types of P. pratensis would be simplex for a dominant allele that confers parthenogenesis, and this genetic model would be further supported by the bimodal distribution of the degree of parthenogenesis exhibited in the (poly)diploid progenies from sexual x apomictic matings. The molecular tagging of apomixis in P. pratensis is an essential step towards marker-assisted breeding and map-based cloning strategies aimed at investigating and manipulating its mode of reproduction. Received: 13 January 1998 / Accepted: 19 January 1998     

Effects of Temperature and Photoperiod on Winged Beans [Psophocarpus tetragonolobus (L.) D.C.]

The effects of temperature and photoperiod on winged beans werestudied using 15 University of New Guinea (UPS) selections andfive Sri Lanka (SL) selections. They were grown at 25/20 or30/25 °C day/ night temperature at 11 or 14 h photoperiodwith 12 h thermoperiod. Differences in stomatal density wereobserved among selections and between photoperiods. Higher densitiesoccurred at 14 h photoperiod than at 11 h photoperiod. Whenstomatal density was high due to a photoperiod or temperatureeffect, there was a corresponding increase in leaf area andd. wt of plants. Total chlorophyll content at 25/20 °C was higher at 11 hphotoperiod than at 14 h photoperiod in all selections whilethe total chlorophyll content at 30/25 °C varied with thephotoperiod and selection. Leaf area of SL selections was greater than that of UPS selections.Also greater leaf area was observed at 14 h photoperiod thanat 11 h photoperiod, irrespective of the growing temperature. Temperature was as important as photoperiod in controlling floweringof winged beans. All the UPS selections and two SL selectionsflowered at 11 h photoperiod at 25/20 °C but failed to flowerat the same photoperiod at 30/25 °C indicating an interactionbetween temperature and photoperiod. It is likely that wingedbeans have a narrow photoperiodic range, particularly the SLselections. Psophocarpus tetragonolobus (L.) D.C., winged bean, stomatal density, leaf area, flowering, temperature, photoperiod