Browsing by Subject "photoperiod"

Sort by: Order: Results:

Now showing items 1-8 of 8
  • Kurokura, Takeshi; Samad, Samia; Koskela, Elli; Mouhu, Katriina; Hytonen, Timo (2017)
    According to the external coincidence model, photoperiodic flowering occurs when CONSTANS ( CO) mRNA expression coincides with light in the afternoon of long days (LDs), leading to the activation of FLOWERING LOCUS T (FT). CO has evolved in Brassicaceae from other Group Ia CO-like (COL) proteins which do not control photoperiodic flowering in Arabidopsis. COLs in other species have evolved different functions as floral activators or even as repressors. To understand photoperiodic development in the perennial rosaceous model species woodland strawberry, we functionally characterized FvCO, the only Group Ia COL in its genome. We demonstrate that FvCO has a major role in the photoperiodic control of flowering and vegetative reproduction through runners. FvCO is needed to generate a bimodal rhythm of FvFT1 which encodes a floral activator in the LD accession Hawaii-4: a sharp FvCO expression peak at dawn is followed by the FvFT1 morning peak in LDs indicating possible direct regulation, but additional factors that may include FvGI and FvFKF1 are probably needed to schedule the second FvFT1 peak around dusk. These results demonstrate that although FvCO and FvFT1 play major roles in photoperiodic development, the CO-based external coincidence around dusk is not fully applicable to the woodland strawberry.
  • Jokela, Venla; Trevaskis, Ben; Seppanen, Mervi M. (2015)
    Timothy is a perennial forage grass grown commonly in Boreal regions. This study explored the effect of vernalization and photoperiod (PP) on flowering and growth characteristics and how this related to changes in expression of three flowering related genes in accessions from different geographic origin. Large variation was found in accessions in their vernalization and PP responses. In southern accessions vernalization response or requirement was not observed, the heading date remained unchanged, and plants flowered without vernalization. On the contrary, northern types had obligatory requirement for vernalization and long PP, but the tiller elongation did not require vernalization at 16-h PP. Longer vernalization or PP treatments reduced the genotypical differences in flowering. Moreover, the vernalization saturation progressed stepwise from main tiller to lateral tillers, and this process was more synchronized in southern accessions. The expression of PpVRN1 was associated with vernalization while PpVRN3 accumulated at long PP. A crucial role for PpVRN3 in the transition to flowering was supported as in southern accession the transcript accumulated in non-vernalized plants after transfer to 16-h PP, and the apices transformed to generative stage. Differences in vernalization requirements were associated with variation in expression levels of PpVRN1 and PpVRN3, with higher expression levels in southern type. Most divergent transcript accumulation of PpMADS10 was found under different vernalization conditions. These differences between accessions can be translated into agronomic traits, such as the tiller composition of canopy, which affects the forage yield. The southern types, with minimal vernalization response, have fast re-growth ability and rapidly decreasing nutritive value, whereas northern types grow slowly and have better quality. This information can be utilized in breeding for new cultivars for longer growing seasons at high latitudes.
  • Fan, Guangxun; Andres, Javier; Olbricht, Klaus; Koskela, Elli; Hytönen, Timo (2022)
    In perennial fruit and berry crops of the Rosaceae family, flower initiation occurs in late summer or autumn after downregulation of a strong repressor TERMINAL FLOWER1 (TFL1), and flowering and fruiting takes place the following growing season. Rosaceous fruit trees typically form two types of axillary shoots, short flower-bearing shoots called spurs and long shoots that are, respectively, analogous to branch crowns and stolons in strawberry. However, regulation of flowering and shoot architecture differs between species, and environmental and endogenous controlling mechanisms have just started to emerge. In woodland strawberry (Fragaria vesca L.), long days maintain vegetative meristems and promote stolon formation by activating TFL1 and GIBBERELLIN 20-OXIDASE4 (GA20ox4), respectively, while silencing of these factors by short days and cool temperatures induces flowering and branch crown formation. We characterized flowering responses of 14 accessions of seven diploid Fragaria species native to diverse habitats in the northern hemisphere and selected two species with contrasting environmental responses, Fragaria bucharica Losinsk. and Fragaria nilgerrensis Schlecht. ex J. Gay for detailed studies together with Fragaria vesca. Similar to F. vesca, short days at 18 degrees C promoted flowering in F. bucharica, and the species was induced to flower regardless of photoperiod at 11 degrees C after silencing of TFL1. F. nilgerrensis maintained higher TFL1 expression level and likely required cooler temperatures or longer exposure to inductive treatments to flower. We also found that high expression of GA20ox4 was associated with stolon formation in all three species, and its downregulation by short days and cool temperature coincided with branch crown formation in F. vesca and F. nilgerrensis, although the latter did not flower. F. bucharica, in contrast, rarely formed branch crowns, regardless of flowering or GA20ox4 expression level. Our findings highlighted diploid Fragaria species as rich sources of genetic variation controlling flowering and plant architecture, with potential applications in breeding of Rosaceous crops.
  • Bäckström, Hanna (Helsingin yliopisto, 2020)
    The growth and development of barley (Hordeum vulgare L.) is affected by photoperiod and temperature. Photoperiod has various signalling functions affecting reproductive development and its rate. It also affects the rates of leaf area extensions and dry matter production. Increase in photoperiod hastens the plant developmental processes and affects the leaf area and tiller formation. Primary tillers form from axillary buds in the leaf nodes on the main culm and increase the leaf area of the plant. Under favourable conditions, initiated tillers grow to separate culms with grain bearing ears. However, the environmental conditions during the growing season in northern latitudes affect tiller formation. The aims of the experiments were to investigate the effects of photoperiod on barley leaf and tiller development. Other aims were to compare the differences expressed by the two row-types and tillering habits. Seven barley accessions, differing in tillering habit and row-type, were used in the experiments. Three pairs of near-isogenic accessions six-rowed ‘Morex’ and ‘Uniculm Morex’, ‘Kindred’ and ‘Uniculm Kindred’, two-rowed ‘Ingrid’ and ‘3-503’, differing in tillering habit, and two-rowed ‘Saana’ were grown in growth chamber at humidity of 60/70 % and at temperature 18/12 ºC (day/night), in three different photoperiods (15 h, 18 h and 21 h). The leaf length and width were measured from the full-grown leaves. The samples to identify main culm and tillers were taken after the plants reached the 4-leaf-stage. The effects of photoperiod, accession, tillering habit and row-type on the plant, leaf and tiller growth were statistically analysed. Increase in photoperiod hastened the plant development as well as leaf and tiller emergence rates. The leaf size and main culm leaf area decreased as the photoperiod increased. The number of tillers increased as photoperiod increased. The uniculm accessions had larger leaves and a larger main culm leaf area than the conventional tillering accessions. Six-rowed accessions had larger leaves and a larger main culm leaf area than the two-rowed accessions. The two-rowed accessions had a faster tiller emergence rate and a higher tiller number compared to the six-rowed accessions. Photoperiod treatments affected the leaf and tiller growth and development as expected apart from the number of tillers produced in the longest, 21h photoperiod. Differences between the two tillering habits and row-types were also as expected, although some exceptions occurred. Potentials and limitations of uniculm growth habit in agricultural production were also discussed.
  • Koskela, Elli Aurora; Sonsteby, Anita; Flachowsky, Henryk; Heide, Ola Mikal; Hanke, Magda-Viola; Elomaa, Paula; Hytönen, Timo (2016)
    The effects of daylength and temperature on flowering of the cultivated octoploid strawberry (Fragaria x ananassa Duch.) have been studied extensively at the physiological level, but information on the molecular pathways controlling flowering in the species is scarce. The flowering pathway has been studied at the molecular level in the diploid short-day woodland strawberry (F. vesca L.), in which the FLOWERING LOCUS T1 (FvFT1) SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (FvSOC1)-TERMINAL FLOWER1 (FvTFL1) pathway is essential for the correct timing of flowering. In this work, we show by transgenic approach that the silencing of the floral repressor FaTFL1 in the octoploid short-day cultivar 'Elsanta' is sufficient to induce perpetual flowering under long days without direct changes in vegetative reproduction. We also demonstrate that although the genes FaFT1 and FaSOC1 show similar expression patterns in different cultivars, the regulation of FaTFL1 varies widely from cultivar to cultivar and is correlated with floral induction, indicating that the transcription of FaTFL1 occurs at least partially independently of the FaFT1-FaSOC1 module. Our results indicate that changing the expression patterns of FaTFL1 through biotechnological or conventional breeding approaches could result in strawberries with specific flowering and runnering characteristics including new types of everbearing cultivars.
  • Luomajoki, Alpo (Suomen metsätieteellinen seura, 1986)
    A study of 16 tree species showed that, including yearly and latitudinal variation, the tetrad phase was reached from late March to early June in conifers and Populus tremula (correlated with heat sums) and in late July to mid-Aug. in Betulaceae (correlated with daylength). These differences were thought to be associated with seasonal adaptive strategies rather than taxonomic relationships.
  • Mäkelä, Tii (Helsingfors universitet, 2013)
    The aim of this research was to find out the effect of photoperiod and quantity of light on growth and flowering of arctic bramble (Rubus arcticus L.) cv. Mesma. The object was also to find out the effect of light on development of floral organs in apical buds of root suckers. Three 12 week long standard treatments were: LD (long day, 12 h HPS-light + 12 h incandescent light), SD (short day, 12 h HPS-light) and HPS (24 h HPS-light). Additionally, the effect of changing the light conditions was examined in four treatments: SD->LD (6 wk SD-treatment + 6 wk LD-treatment), SD->HPS (6 wk SD-treatment + 6 wk HPS-treatment), HPS->SD (6 wk HPS-treatment + 6 wk SD-treatment) and HPS->LD (6 wk HPS-treatment + 6 wk LD-treatment). In standard treatments the vegetative growth determined as the dry weight of the shoots was increased in HPS and decreased in SD. Elongation of shoot was enhanced by LD and development of new leaves was increased in LD and HPS. The number of flowers was highest in HPS and lowest in SD. The average dry weight of a flower and the number of flowers in relation to vegetative growth were increased in HPS. In SD growth and flowering were suppressed towards the end of the experiment. When plants were moved from SD to HPS or LD, growth and flowering were continued. Growth and flowering were clearly enhanced by continuous HPS light. Cessation of growth and flowering in SD suggests that the plants were becoming dormant. Growth and flowering continued when plants were moved from SD to LD or HPS, which indicates that plants were not fully dormant. The differences between treatments LD and SD were probably a consequence of dormancy induction in SD. Floral initiation in apical buds of root suckers occurred in all three standard treatments regardless of photoperiod or quantity of light.