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After pollination outdoors, individual bilberry plants from two Northern and two Southern clones were studied for climatic effects on berry yield and quality in a controlled phytotrone experiment at 12 and 18 °C. At each temperature, the following light treatments were tested: (1) 12 h natural light, (2) 24 h natural light, and (3) 24 h natural light plus red light. The first experimental year there was no difference in yield between temperatures; however, the second experimental year the berry yields was significantly higher at 18 °C. Berry ripening was faster in the Northern than in the Southern clones at 12 °C. Northern clones also showed significantly higher contents of total anthocyanins, all measured anthocyanin derivatives, total phenolics, malic acid and sucrose. Metabolic profiling revealed higher levels of flavanols, hydroxycinnamic acids, quinic acid and carbohydrates at 12 °C.

Vegis has put forward the theory that the range of growth-promoting temperatures changes during the induction and the release of dormancy. We have tested the response of buds of Betula pubescens Ehrh. and B. pendula Roth. on temperature during the induction and release of dormancy. Betula seedlings were exposed to dormancy-inducing high-temperature and short-day conditions and subsequently to dormancy-releasing chilling conditions in darkness. To monitor the dormancy status of the seedlings, subsets of them were transferred to five forcing temperatures and their budburst was observed. The results show that the expression of dormancy was temperature dependent, so that the minimum temperature for 100% budburst rose during the induction and dropped during the release of dormancy. These responses may explain previous contradictions between experimental and modelling studies, but that needs to be verified with more extensive experiments, some of which are identified in this study. The results provide further evidence for the concept of gradual change in bud dormancy. They also suggest that global change studies modelling budburst phenology should address the changing expression of bud dormancy.

In greenhouse production of a number of flowering plant species, a short diurnal temperature drop in the morning is commonly used to reduce stem elongation. Earlier studies of pea (Pisum sativum) exposed to different combinations of day and night temperature, indicate that light, temperature, and gibberellin (GA) interact in the control of stem elongation. However, the mechanisms behind the effects of short-term temperature drops and differential sensitivity depending on the timing of the drop treatment have not been reported. Here, the involvement of GA metabolism in this has been investigated by exposing pea to short-term temperature drops in light or darkness. A 2 h temperature drop from 21 degrees C to 13 degrees C in the middle of the light period rapidly reduced the rate of stem elongation temporarily by 55% and increased mRNA levels of the GA-deactivation gene PsGA2ox2 by 2-fold within 30 min and up to 4-fold within 1.5 h. GA(1) levels were reduced by 36% after a 3-4 h time lag. A temperature drop in the night reduced stem elongation by 27%, but had no effect on transcript levels of PsGA2ox2. Instead, steady-state expression of the GA-biosynthesis genes NA, PsGA20ox1, and PsGA3ox1 was slightly stimulated, but there was no effect on GA(1) level. In conclusion, the effect of a temperature drop on GA metabolism in pea is qualitatively different in light and dark. Light is required for deactivation of GA(1) resulting from increased expression of PsGA2ox2. This suggests that GA-metabolism is a component in the short-term adaptation to changes in ambient temperature and putatively in low temperature-light stress responses.

ABSTRACT In tree species native to temperate and boreal regions, the activity-dormancy cycle is an important adaptive trait both for survival and growth. We discuss recent research on mechanisms controlling the overlapping developmental processes that define the activity-dormancy cycle, including cessation of apical growth, bud development, induction, maintenance and release of dormancy, and bud burst. The cycle involves an extensive reconfiguration of metabolism. Environmental control of the activity-dormancy cycle is based on perception of photoperiodic and temperature signals, reflecting adaptation to prevailing climatic conditions. Several molecular actors for control of growth cessation have been identified, with the CO/FT regulatory network and circadian clock having important coordinating roles in control of growth and dormancy. Other candidate regulators of bud set, dormancy and bud burst have been identified, such as dormancy-associated MADS-box factors, but their exact roles remain to be discovered. Epigenetic mechanisms also appear to factor in control of the activity-dormancy cycle. Despite evidence for gibberellins as negative regulators in growth cessation, and ABA and ethylene in bud formation, understanding of the roles that plant growth regulators play in controlling the activity-dormancy cycle is still very fragmentary. Finally, some of the challenges for further research in bud dormancy are discussed. [ABSTRACT FROM AUTHOR]

The effects of time of tiller emergence on panicle formation and other flowering characteristics were studied in single plants of Scandinavian varieties of Bromus inermis , Festuca pratensis , Dactylis glomerata and Lolium perenne exposed to primary induction at 4°C/LD (24 h), 9°C/SD (10 h) or 15°C/SD. The need for primary induction varied from a predominantly SD requirement in Bromus inermis and Dactylis glomerata to a predominantly low temperature (vernalization) requirement in Lolium perenne and an almost pure low temperature requirement in Festuca pratensis . Although tillers emerging before or during primary induction had the highest chance of becoming reproductive in all species, up to 22%, 15% and 27% of the tillers emerging after termination of primary induction, and thus without direct exposure to SD, became reproductive in Bromus inermis , Dactylis glomerata and Lolium perenne, respectively. In an additional experiment with SD induction at 12°C, detillering during secondary induction increased the flowering capacity of non-directly exposed tillers from 17 to 41 in Bromus inermis . These results are discussed in the light of different hypotheses regarding control of flowering in temperate grasses. It is concluded that indirect induction, i.e. the transmission of flowering induction stimuli from mother to daughter tillers, is more likely after SD induction than after low temperature vernalization. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the influence of temperature applied during short day-induced budset on induction of dormancy in six ecotypes of Betula pubescens Ehrh. and two ecotypes of Betula pendula Roth. Seedlings were grown in a phytotron at constant temperatures of 9-21°C under a 12 h photoperiod (SD) during dormancy induction. Induction of dormancy was monitored by following bud flushing and shoot growth after transfer to long photoperiod conditions (24 h) at 18°C. Chilling requirement was studied in seedlings exposed to 10 weeks of SD. In both species induction of bud dormancy developed most rapidly at 15-18°C, and both 9-12°C and 21°C delayed the induction of dormancy. Raising the temperature (from 9 to 21°C) applied during induction of dormancy significantly increased the chilling requirement. These responses were noted for all ecotypes tested, but in general the northern ecotypes entered dormancy more quickly than the southern ones. No such trend was recorded for chilling requirement, although a B. pubescens ecotype from Iceland and another from the coast of northern Norway appeared to require a longer chilling treatment than the other ecotypes. In conclusion, induction and depth of bud dormancy in birch are significantly affected by temperature conditions and these effects may explain some of the annual variation in dormancy and chilling requirement observed in nature. [ABSTRACT FROM AUTHOR]

Two rhododendron cultivars, ‘Pohjola's Daughter’ and ‘Helsinki University’, were grown at +15 and +24°C, each combined with a photoperiod of 14 h (short day, SD) or 20 h (long day, LD). After a 112-day growing season, they were subjected to a hardening regime of fortnightly decreasing temperature (+9, +5, +1 and -2°C) and a 12-h photoperiod, except that part of the plants grown in LD had LD also at +9 and +5°C. At -2°C, all plants were in darkness. Controlled freezing tests of the leaves were performed before each change in temperature. The injury was evaluated visually and by electrolyte leakage (EL) tests. The observations on the visual assessment were analysed with logit models, and the EL data with non-linear sigmoid functions. The visually scored 50% damage (VD50) correlated better with the EL tests than 10 or 90% damage. Photoperiod and temperature during the growing season affected the cold hardiness of both cultivars, but they differed in their responses. ‘Pohjola's Daughter’ benefited from SD as well as from high temperature, while ‘Helsinki University’ attained better hardiness at a cool growing season temperature and was less sensitive to photoperiod. [ABSTRACT FROM AUTHOR]

Flower bud initiation in seedlings and vegetatively propagated plants of Salix pentandra from different locations has been studied under controlled conditions. In mature plants flower bud formation was induced by 2-chloroethyltrimethylammoniumchloride (CCC) and by short day treatment. The effect of CCC was antagonized by GA3. The critical photoperiod for flower bud formation was about 18 h for a southern clone (from 49°48′N), but cuttings of a northern ecotype (from 69°39′N) formed flower buds even at 24 h photoperiod. Generally, flower bud formation occurred simultaneously with apical growth cessation. However, apical growth cessation was not a prerequisite for floral initiation and flower buds were also found in elongating plants. Seedlings up to 60 days old did not form flower buds in growth chamber studies. The length of the juvenile phase has not been studied in detail, but cuttings taken from seedlings approximately 20 cm high and 60 days old were able to develop flower buds when treated with CCC. A gradual transition from the juvenile to the mature phase was obtained by repeated pruning of seedlings grown at 18°C and 24 h photoperiod. [ABSTRACT FROM AUTHOR]

Apical growth cessation as affected by photoperiod and temperature has been studied in seedlings of two latitudinal ecotypes of Salix and Betula. The critical photoperiod for apical growth cessation at constant temperatures of 15 and 21°C was about 22 h for a northern (69°39'N) and about 15-16 h for a southern (59°40'N) ecotype of Salix pentandra. Fluctuating day/night temperatures (21°C/9°C, 15°C/6°C) induced apical growth cessation in northern ecotypes even at 24-h photoperiod. Disagreements in critical photoperiods found in various studies are discussed. [ABSTRACT FROM AUTHOR]

Low temperature and long day regimes applied during seed development and maturation of red beet (Beta vulgaris var. rubra L.) increased the proportion of empty seed balls and reduced the germination ability of normally developed seeds. Low seed development temperatures also greatly increased the bolting susceptibility of seedlings grown at low temperatures or temperatures which are marginal for bolting, but were not able to bring about bolting under conditions which are not themselves inductive to flowering. In a field experiment a significant reduction of the root tuber yield was associated with these effects. [ABSTRACT FROM AUTHOR]

To study a possible adaptation of the symbiosis between white clover (Trifolium repens L..) and Rhizobium leguminosarum biovar trifolii with regard to light and temperature at northern latitudes, local seed populations of white clover and isolates of R. leguminosarum biovar trifolii from 3 different latitudes in Norway, 58° 48'N, 67° 20'N and 69° 22'N, were used. The commercial cultivar Undrom was used as a reference plant. The experiments were done at 18 and 9°C under controlled conditions in a phytotron during the natural growing season at 69° 39'N. Growth of the plants was evaluated by number and size of leaves, dry matter production and total Ncontent. At 18°C the white clover plants were harvested twice while at 9°C there was only one growth period. The results from first harvest at 18°C and total growth at 9°C, showed that white clover populations from northern Norway had a lower growth potential than the population from the south and cv. Undrom. This difference was not apparent in the second growth period at 18°C. Growth of the plants from seeds to first harvest was enhanced by mineral nitrogen compared to plants dependent on Rhizobium only. However, after a second growth period dry weight and total nitrogen content of the plants with nitrogen fixation were comparable to the plants receiving mineral nitrogen. Statistical analysis showed that the most important factor for the variation in dry matter production was the plant population. Within the populations at 9°C and at first harvest at 18°C, there were no significant differences in dry matter production with different Rhizobium inoculum. In the second growth period at 18°C, different inoculum gave significantly different amount of dry matter within a population. The results showed a significant interaction between plant population and Rhizobium inoculum, and the results indicated that plants from the north gave higher yield when nodulated by Rhizobium from the north than from the south. [ABSTRACT FROM AUTHOR]

Effects of photoperiod and temperature on frost resistance of seedling populations and clones of white clover (Trifolium repens L.) originating from various latitudes (58°48'-69°54'N) and altitudes (up to 1 100 m above sea level) were studied in a phytotron. Low-temperature-induced cold acclimation in all populations was significantly stimulated by short photoperiod and low temperature. The highest levels of host resistance were found in the northernmost seedling populations and in clones from northern coastal locations. [ABSTRACT FROM AUTHOR]

Gibberellin (GA) is believed to be involved in thermoperiodic stem elongation. With this in mind, we studied the correlation between gibberellin A1 (GA1) levels and stem elongation affected by alternating day (DT) and night temperature (NT) in 5 genotypes of Pisum sativum differing in their degree of dwarfism. The endogenous GA content in the tissue of two of the genotypes was determined by combined gas chromatography and mass spectrometry. The wild genotype developed 40 to 50% shorter stems and internodes under a low DT and high NT combination (negative difference [DIF] between DT and NT, DT/NT 15.5/21.5 or 14/24°C) than under the opposite regime of high DT and low NT (positive DIF, DT/NT 22.5/16.5 or 24/14°C). The GA biosynthetic mutants ls and le, and the auxin and brassinosteroid mutant lkb responded in a similar way, but not as strongly as the wild type. The stem length of the GA-insensitive slender mutant (la crys) was reduced by only 8% under negative compared to positive DIF. In the wild type endogenous GA levels decreased by 60% from positive to negative DIF in the upper part of the stem. Further, there was a corresponding decrease in the levels of precursors to GA1, i.e. GA53, GA44, GA19 and GA20, while 2β-hydroxylated GA20 and GA1, GA29 and GA8, respectively, were unaffected by DIF. A similar increase in the ratios of GA29 to GA20 and GA8 to GA1 from positive to negative DIF was seen in the stem tissue of the le mutant as in the wild type. The temperature regimes affected the levels of GA1 and its precursors in combined leaf and petiole samples and in the shoot tip in a similar manner as in the stem tissue. However, the different temperature regimes did not affect the ratio of GA8/GA1 in the shoot tip. The results indicate that altered stem elongation of the pea plants in response to diurnal temperature alternations may be mediated by changes in endogenous levels of GA1. The GA1 levels may be controlled by an effect of DIF on both biosynthetic and inactivation steps. [ABSTRACT FROM AUTHOR]

Effects of mineral nitrogen (2, 4, 6 and 8 mM NH4NO3) and nodulation with Rhizobium on frost hardiness in seedlings of white clover (Trifolium repens) have been studied. Seedlings of a population from Bodø (67°N lat.) were grown in Leonard jars under controlled conditions in a phytotron. For induction of frost hardening, plants were first exposed to 12 h photoperiod conditions for 2 weeks at 18°C, then for 2 weeks at 6°C and finally for 2 weeks at 0.5°C. Frost hardiness after treatments at 6 and 0.5°C was significantly enhanced by increasing nitrogen supply and was positively correlated with total nitrogen content of the stolons. Frost hardiness of nodulated plants correlated to the tissue nitrogen concentration. Content of soluble proteins in stolons decreased during hardening at 6°C but did not change during treatment at 0.5°C. There were minor changes in total amount of free amino acids during hardening. Both absolute and relative amounts of praline and arginine increased, and those of asparagine decreased during hardening. Absolute amounts of all free amino acids increased with increasing nitrogen supply, but the changes during hardening were similar in all treatments. There was a significant increase in the content of soluble carbohydrates during hardening. However, this increase was inversely related to nitrogen supply. [ABSTRACT FROM AUTHOR]

The aim of the experiments was to study the effects of gibberellic acid (GA3) on the germination of Calluna vulgaris L, Ledum palustre L. and Rhododendron lapponicum (L.,) Wahlenb. seeds under different environmental conditions. Under continuous light from white fluorescense tubes (3000 lux), untreated seeds of Calluna were partly dormant at all temperatures studied (9, 15, 21, 27, 27/9, 8/16 hours). Percentage of dormant seeds increased, however, with decreasing temperature, and it varied also from seed lot to seed lot. Untreated seeds of Ledum were dormant in light at 9° and 15° but not at higher temperatures. Untreated seeds of Rhododendron were completely dormant in light at temperatures from 13° to 24°C. Seeds of all species were completely dormant in darkness both at 15° and 27°C. GA3 stimulated greatly the germination of all species under all studied environmental conditions. The used concentrations (0.2-3.2 mM) gave nearly 100 % germination in most cases. At 9°C the dormancy in some seed lots of Calluna and Ledum was only partly broken by the used concentrations of GA3. [ABSTRACT FROM AUTHOR]

Effect of gibberellic acid (GA3) on leaf sheath elongation in a normal (cv. Møystad) and a gibberellin (GA)-insensitive (c. Siete Cerros) genotype of wheat (Triticum aestivum L.) were studied at 18 and 12°C under short (SD, 12 h) or long (LD, 24 h) photoperiod. Leaf sheath length in cv. Møystad was signficantly increased by exogenous GA3 both under SD and LD. LD alone stimulated leaf sheath elongation and the combined effect of LD and GA3 was additive, and there was no statistically signficant interaction between photoperiod and GA3 under any conditions. However, there was a highly significant stimulation of leaf sheath elongation by LD in cv. Siete Cerros as well. These results indicate that stimulation of elongation growth in wheat leaves by LD is not mediated by gibberellin. [ABSTRACT FROM AUTHOR]