Induction of Frost Hardiness in Stem Cortical Tissues of Cornus stolonifera Michx. by Water Stress: I. Unfrozen Water in Cortical Tissues and Water Status in Plants and Soil

Water supply and day length were varied in cold hardiness studies of red osier dogwood plants (Cornus stolonifera Michx.). The frost killing temperature, the content and freezing of stem cortical tissue water along with soil moisture content and tension were evaluated. Seven days of water stress in long and short day photoperiod regimes caused a rapid decrease in soil moisture content and plant water potential. During the same period, the frost hardiness increased from −3 to −11 C. Further water stress treatment had little effect. Control plants in short days showed only a gradual decrease in plant water potential and only gradually increased in frost hardiness while control plants in long days were unchanged. Freezing studies using nuclear magnetic resonance showed that increased hardiness in water-stressed plants resulted from both an increased tolerance of freezing and an increased avoidance of freezing, the latter resulting from higher solute concentration in the tissue solutions. The short day controls also showed similar changes; however, the changes were smaller over the 21 days of the study.     

Induction of Frost Hardiness in Stem Cortical Tissues of Cornus stolonifera Michx. by Water Stress: II. Biochemical Changes

A decrease of protein, RNAs, and starch, and an increase of sugar were observed in 3-day water-stressed red osier dogwood plants (Cornus stolonifera Michx.) when the frost hardiness increased from −3 to −6 C. As the frost hardiness increased to −11 C after 7 days of treatment, the starch continuously decreased, however, the proteins and RNAs increased with a continuous increase of sugar. Further water stress treatment had little effect on the changes of these chemicals. Control plants in short days showed similar gradual biochemical changes in patterns. From the results of frost hardiness increases, the pattern of biochemical changes, and the mechanism of the increased freezing resistance, it appears that the water stress and short days accomplished essentially the same physiological end(s) in inducing frost hardiness in red-osier dogwood.     

Temperature-driven plasticity in growth cessation and dormancy development in deciduous woody plants: a working hypothesis suggesting how molecular and cellular function is affected by temperature during dormancy induction

The role of temperature during dormancy development is being reconsidered as more research emerges demonstrating that temperature can significantly influence growth cessation and dormancy development in woody plants. However, there are seemingly contradictory responses to warm and low temperature in the literature. This research/review paper aims to address this contradiction. The impact of temperature was examined in four poplar clones and two dogwood ecotypes with contrasting dormancy induction patterns. Under short day (SD) conditions, warm night temperature (WT) strongly accelerated timing of growth cessation leading to greater dormancy development and cold hardiness in poplar hybrids. In contrast, under long day (LD) conditions, low night temperature (LT) can completely bypass the short photoperiod requirement in northern but not southern dogwood ecotypes. These findings are in fact consistent with the literature in which both coniferous and deciduous woody plant species’ growth cessation, bud set or dormancy induction are accelerated by temperature. The contradictions are addressed when photoperiod and ecotypes are taken into account in which the combination of either SD/WT (northern and southern ecotypes) or LD/LT (northern ecotypes only) are separated. Photoperiod insensitive types are driven to growth cessation by LT. Also consistent is the importance of night temperature in regulating these warm and cool temperature responses. However, the physiological basis for these temperature effects remain unclear. Changes in water content, binding and mobility are factors known to be associated with dormancy induction in woody plants. These were measured using non-destructive magnetic resonance micro-imaging (MRMI) in specific regions within lateral buds of poplar under SD/WT dormancing inducing conditions. Under SD/WT, dormancy was associated with restrictions in inter- or intracellular water movement between plant cells that reduces water mobility during dormancy development. Northern ecotypes of dogwood may be more tolerant to photoinhibition under the dormancy inducing LD/LT conditions compared to southern ecotypes. In this paper, we propose the existence of two separate, but temporally connected processes that contribute to dormancy development in some deciduous woody plant: one driven by photoperiod and influenced by moderate temperatures; the other driven by abiotic stresses, such as low temperature in combination with long photoperiods. The molecular changes corresponding to these two related but distinct responses to temperature during dormancy development in woody plants remains an investigative challenge.     

Cold hardiness of rhododendron cultivars grown in different photoperiods and temperatures

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.     

Cold-acclimation of Hibiscus rosa-sinensis L. and Hibiscus syriacus L. in natural and controlled environments

Abstract Seasonal cold-acclimation patterns and the effects of photoperiod and temperature on cold-hardiness of Hibiscus rosa-sinensis L. and Hibiscus syriacus L. were determined. Field-grown H. rosasinensis consistently failed to survive freezing at - 2°C. Two genotypes of field- and container-grown H. syriacus initiated cold-acclimation in mid September, in response to decreasing daylength, and continued to an ultimate midwinter hardiness level of - 27°C in early February. Controlled environment experiments using combinations of short days (SD) and cool day/night temperatures were unable to induce even minimal cold acclimation of H. rosasinensis. In controlled environments, H. syriacus attained a moderate amount of cold tolerance at warm temperatures and long days (LD). Low night temperature combined with LD, warm day produced the same degree of cold-acclimation as the SD treatments. While not essential, SD enhanced H. syriacus cold-acclimation in controlled environments. A - 5°C frost treatment of intact plants did not enhance cold-hardiness of H. syriacus.     

The Influence of Photoperiod and Temperature on the Development of Frost Hardiness in Seedlings of Pinus silvestris and Picea abies

The influence of short days and low temperature on the development of frost hardiness in seedlings of Scots pine (Pinus silvestris L.) and Norway spruce [Picea abies (L.) Karst.], grown for 6 months in glasshouses and climate chambers, was investigated. The degree of hardiness was estimated by freezing the shoots of the seedlings to predetermined temperatures. After 8 weeks in a glasshouse the viability of the seedlings was determined by establishing bud flushing. The most effective climate for the development of frost hardiness was short days (SD) and low temperature (2°C); the next most effective was SD and room temperature (20°C). However, long days (LD) and low temperature also had a marked effect on the development of hardiness. A combination of 3 weeks’treatment with SD and 20°C, and 3 weeks with SD and 2°C gave the same results as 6 weeks with SD and 2°C. The results clearly demonstrate the importance of the photoperiod prior to low temperature for the development of frost hardiness. In conclusion both short days and low temperature induce frost hardiness development. Probably this occurs by initiation of different processes in the two cases. The degree of frost hardiness development appears to depend on the sum of these different processes and on the timing between them.     

Water Relations, Stomatal Behavior, and Root Conductivity of Red Osier Dogwood during Acclimation to Freezing Temperatures

Red osier dogwood (Cornus stolonifera Michx.) was artificially acclimated by exposing plants to 8-hour short days (SD) and low (15/5 C) temperatures for 54 to 63 days. Several factors including transpiration rate, stomatal resistance, and root conductivity were correlated so that the rate of water loss in acclimating plants was higher during the first 30 to 40 days of the acclimation sequence. Six days after transferring plants to SD conditions, the stomatal resistance (r₈) decreased significantly below the r₈ of the 16-hour long day (LD) control plants at the same temperature. Transpiration rate increased by approximately 20 to 30% in the plants transferred to SD. After the initially higher transpiration rate and greater stomatal opening, the stomates closed tightly during the last 2 weeks of acclimation and the transpiration rate of the SD plants dropped to well below the LD control plants. By the end of the acclimation sequence, root conductivity to water uptake was two to three times lower in the SD plants. Leaf xylem water potentials were similar or slightly lower in the plants kept under SD conditions during the first 5 to 7 weeks of the acclimation sequence. During the last 10 to 15 days of acclimation when the stomates closed, SD leaf water potential rose significantly above the plants in the LD conditions. During acclimation, stem water content decreased by 40 to 50%. Changes in tissue hydration can be indirectly related to plant hardiness and may be affected by alteration of stomatal resistance, transpiration rate, and root conductivity during acclimation.     

Interrelations between photoperiod, frost hardiness and sulfhydryl groups in cabbage

Hardening of SD (8 and 12 hrs) and LD (18- and 24-hr photoperiods) cabbage plants in stages at temperatures starting with + 5° and ending with − 3° led to the following changes:

Soluble protein plus nonprotein N showed a net increase only in the SD plants. In both SD and LD plants, it decreased to a minimum toward the end of the first stage of hardening, increased to a maximum in the second stage. The degree of this change was proportional to the photoperiod. These changes were mainly due to the proteins.

As in previous investigations, SH content rose during the first 1 to 2 weeks, but only in the SD plants. This rise was primarily due to the protein fraction. After the first 1 to 2 weeks both SD and LD plants showed a decrease in SH content, most pronouncedly during the second stage of hardening.

Nonprotein SH content was very low and decreased during hardening in both SD and LD plants. Nonprotein SS increased during the first stage of hardening. Total nonprotein SH+2SS rose to a maximum during the first stage of hardening, paralleling both osmotic potential and hardiness. During the second stage the total decreased, in spite of the rise in hardiness. These results held true for both SD and LD plants.

These results are all explainable on the basis of the SHSS theory of frost resistance.

     

Interactions of low temperature, water stress, and short days in the induction of stem frost hardiness in red osier dogwood

The induction of stem frost hardiness by low temperature, water stress, short days, and their combinations in 2- and 4-month-old growing dogwoods (Cornus stolonifera) were investigated. When plants were subjected to more than one factor, the increased hardiness was the sum of the effects of the individual factors involved. No interactions among these factors on hardiness were observed during a 3-week treatment. Results indicate that low temperature, water stress, and short days initially trigger independent frost-hardening mechanisms. Plant ages significantly influenced the change in low temperature-induced frost hardiness, but not the water stress or short day-induced frost hardiness.     

Changing Environmental Effects on Frost Hardiness of Scots Pine During Dehardening

The effects of raised temperature and extended photoperiod onthe dehardening of quiescent and winter-hardy Scots pine saplingswere examined in an open-top-chamber experiment. The saplingswere exposed during winter to natural, square-curve fluctuating(between 1 and 11 °C with a 14 d interval), and constant(6 °C) temperatures with a natural and an extended (17 h)photoperiod. Frost hardiness of needles was determined by controlledfreezing tests and visual damage scoring. The constant 6 °Ctemperature treatment caused a gradual dehardening of needleswhereas under fluctuating temperatures the level of frost hardinessfluctuated. Trees exposed to extended photoperiods were lesshardy than under natural photoperiods after the initiation ofshoot elongation, but before this there were no clear differencesin frost hardiness between different photoperiodic treatments.The results indicate that the frost hardening competence ofScots pine changes during quiescence. Climate change; frost hardiness; hardening competence; photoperiod; Pinus sylvestris, Scots pine; temperature     

Regulation of the loss of frost hardiness in Pinus radiata by photoperiod and temperature

Abstract. In controlled environments, the interactive effects of warm (16: 8°C, day: night) and cool (12: 4°C, day: night) temperatures and long (13.5 h) and short (10 h) photoperiods on the dehardening of seedlings of Pinus radiata D. Don were investigated. In another experiment, the effect of four photoperiods from 9 to 14 h was examined. In a third, dehardening at constant temperatures from 5 to 17°C was followed. There was no evidence for an interaction between photoperiod and temperature. Dehardening was temporarily delayed by photoperiods below about 10 h, but there was no other quantitative effect of photoperiod. At constant temperatures, the rate of dehardening was initially constant but declined as the minimum summer frost hardiness was reached. In the initial phase the rate of dehardening was a linear function of temperature, increasing from 0.05°C day⁻¹ at 8°C to 0.30 °C day⁻¹ at 17°C. Temperature controlled the loss of frost hardiness by regulating the rate of dehardening.     

Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.) needles. I. Seasonal changes in the photosynthetic apparatus and its function

Photosynthetic CO₂ uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO₂ with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state. Received: 3 March 1997 / Accepted: 16 July 1997     

Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca)

Floral induction and development requirements of a range of latitudinal and altitudinal Norwegian populations of the wild strawberry Fragaria vesca L. have been studied in controlled environments. Rooted runner plants were exposed to a range of photoperiods and temperatures for 5 weeks for floral induction and then transferred to long day (LD) at 20°C for flower development. A pronounced interaction of temperature and photoperiod was shown in the control of flowering. At 9°C, flowers were initiated in both short day (SD) and LD conditions, at 15 and 18°C in SD only, whereas no initiation took place at 21°C regardless of daylength conditions. The critical photoperiod for SD floral induction was about 16 h and 14 h at 15 and 18°C, respectively, the induction being incomplete at 18°C. The optimal condition for floral induction was SD at 15°C. A minimum of 4 weeks of exposure to such optimal conditions was required. Although the populations varied significantly in their flowering performance, no clinal relationship was present between latitude of origin and critical photoperiod. Flower development of SD-induced plants was only marginally advanced by LD conditions, while inflorescence elongation and runnering were strongly enhanced by LD at this stage. The main shift in these responses took place at photoperiods between 16 and 17 h. Unlike all other populations studied, a high-latitude population from 70°N ('Alta') had an obligatory vernalization requirement. Although flowering and fruiting in its native Subarctic environment and after overwintering in the field in south Norway, this population did not flower in the laboratory in the absence of vernalization, even with 10 or 15 weeks of exposure to SD at 9°C. Flowering performance in the field likewise indicated a vernalization requirement of this high-latitude population.     

Vegetative growth and frost hardiness of cloudberry (Rubus chamaemorus) as affected by temperature and photoperiod

The effect of photoperiod and temperature on growth and induction and development of frost hardiness in cloudberry ( Rubus chamaemorus L.) was examined in two experiments. The photoperiods were 8, 12 or 24 h and the temperatures were 18, 15, 12, 9, 4, 3, –3 or –4°C depending on the experiment. The level of hardiness was expressed as LT₆₆ or LT₅₀ (the lethal temperature for 66 or 50% of the plant material) for percentage of bud break and for the degree of coloring by triphenyltetrazolium chloride for rhizomes. The vegetative growth was clearly affected by daylength; petiole elongation, leaf growth, shoot dry weight and number of shoots per plant were all reduced under short days compared with long days. However, the photoperiod had no significant effect on hardening of buds or rhizomes. Hardening increased with successively decreasing temperatures. To get the maximum hardiness, plants had to be exposed to freezing temperatures.     

Effects of photoperiod and temperature on sexual recrudescence in the male weakfish,Cynoscion regalis

Synopsis Male weakfish,Cynoscion regalis, were collected in the south-west portion of Delaware Bay from April through August of 1992. Histological examination of testes collected from these specimens was used as a baseline for comparison with laboratory data. Weakfish testes were found to be of the unrestricted, continuous spermatogenic type and spermatogenesis was apparently prenuptial. The effects of photoperiod and temperature on gonadal maturation were studied in the laboratory using fish collected in June and July 1991. These fish were exposed to two months of simulated winter conditions prior to assignment to one of four experimental photoperiod/temperature regimes. The treatments included combinations of long day (LD,15 h light) or short day (SD, 9 h light) and high (HT, 20° C) or low (LT, 13° C) water temperatures. The four treatment groups were LD/HT, LD/LT, SD/HT, SD/LT. The LD/HT group was the only one to mature fully, expressing increased plasma androgen levels, increased gonadosomatic index (GSI) and advanced spermatogenesis, as well as hypertrophy of the sonic muscles, a seasonally expressed secondary sexual characteristic of male weakfish. High temperatures promoted the later stages of spermatogenesis, which were apparently inhibited by low temperatures. The presence of an endogenous annual cycle is suggested by the partial maturation of the testes and sonic muscles in all treatment groups, regardless of photoperiod/temperature regime.     

Effect of photoperiod and temperature on the development of frost hardiness in three Alnus species

The influence of short day and low temperature on cold acclimation of A. crispa (Ait.) Pursh, A. glutinosa (L.) Gaertn. and A. rubra Bong, was investigated. Two clones of each species originating from in vitro propagation were exposed to three daylength/temperature treatments. Periodically plantlets were exposed to controlled freezing temperature in order to evaluate their level of frost hardiness.
Short day (SD) and cold temperature (CT) and long day (LD) and cold temperature (CT) were the most effective treatments for the development of frost hardiness in shoots and roots of the three species tested. Short day (SD) and warm temperature (WT) induced a significant increase in hardiness in shoots of all three species. However, this treatment did not trigger root hardening. A. crispa was found to be the hardiest species followed by A. glutinosa and A. rubra . Intraspecific variation was observed between the two A. glutinosa clones. A glutinosa clone AG8, a Russian provenance, showed a greater freezing resistance than A. glutinosa clone AG2, a German provenance.     

Environmental control of flowering and morphology in the high-arctic Cerastium regelii, and the taxonomic status of C. jenisejense

Cerastium regelii has a distribution confined largely to regions north of 70° N but has retained a strong short-day (SD) response for primary flower induction despite the fact that it will hardly ever experience SD in a non-frozen condition in its natural environment. However, like many other high-latitude short-long-day plants it has also an alterntive long day (LD) pathway for floral initiation at low temperatures (<15°C). Floral primordia which are fully differentiated during SD have an absolute requirement for LD for flower development. The critical photoperiod for this LD response is about 16 h at 18°C and more than 20 h at 9°C. Plant morphology, including key characters for identification of the species, is greatly modified by environment and stage of plant development. At higher temperatures and LD C. regelii develops a striking resemblance to the sub-arctic C. jenisejense . Based on examination of authentic herbarium material it is concluded that the latter is merely a high-temperature morphotype of C. regelii .     

Regulation of Cold Hardiness in Acer negundo

The application of gibberellin to Acer negundo either during or after a short photoperiod strikingly lowered the amount of hardiness obtained after 4 weeks in darkness at 5°. Two growth retardants, B9 and Amo 1618, the latter of which interferes with gibberellin synthesis, brought about hardiness increases under long photoperiods. The naturally occurring inhibitor, dormin, also increased hardiness under the usual inhibiting influence of long photo-periods. Extracts from plants given long or short days had gibberellin-like compounds in largest quantities during LD and lowest quantities under SD, while the inverse was true for the inhibitor.     

Stem-swelling and photosynthate partitioning in stem mustard are regulated by photoperiod and plant hormones

The experiment was conducted to study the relationship between stem-swelling and photoperiod and growth hormones by comparing stem swelling with non-stem-swelling stem mustard (Brassica juncea var. tsatsai) plants about their growth characteristics and levels of endogenous gibberellin and cytokinin under different photoperiods. The results here showed that plant biomass was higher in 12-h photoperiod compared to that in long day (LD) and short day (SD), whereas stem growth was much stronger in LD compared to 12-h photoperiod and SD. Exogenous application of 1.0 mM gibberellic acid (GA₃) accelerated stem elongation in SD, but 8.9 μM benzyladenine (BA) failed. The shape of the swollen stem was also found to be associated with day length: a LD promoted stem elongation, while a 12-h photoperiod made the stem oval swollen. Also, stem was shown to have no sign of swelling in plants in SD with a relatively poor growth. The further studies showed that the largest proportion of ¹⁴C photosynthate was allocated to the swelling stems in stem-swelling plants, but to expanded leaves in non-stem-swelling plants, and endogenous gibberellin A₁ (GA₁) and zeatin + zeatin riboside (ZRs) were higher in LD compared to 12-h photoperiod and SD. These results from this experiment indicate that stem growth and swelling is a physiological process of hormonal control, and the photoperiod possibly exerts its influence by altering the balance between the levels of endogenous gibberellins and cytokinins.     

Photoperiodic and Thermal Regulation of Development and Cold Hardiness in Larvae of the Clover Leaf Weevil, Hypera punctata

Effects of photoperiod and temperature on the development and cold hardiness were investigated in larvae of Hypera punctata. At a relatively low temperature (15°C), the larvae fed less and developed more slowly under a 12L:12D (SD) photoperiod than under a 16L:8D photoperiod (LD). SD larvae had lower gut weight against the whole body weight and lower supercooling point (SCP) than the LD counterparts for the same instar and same body weight. This was because the larval SCP is markedly affected by the quantity of the gut content. Laboratory experiments indicated that the low temperature mortality of this larvae occurred mainly due to freezing irrespective of the photoperiod and temperature, suggesting that the lower lethal temperature (LLT) depends on the supercooling ability of larvae. The SD larvae tended to have a lower SCP and hence a lower LLT than the LD counterparts at 15 or 10°C, unlike at 20°C. Thus, the slower larval development under SD conditions at relatively low temperatures may prevent larvae from reaching the later instar, which have a higher SCP and thus less cold tolerance, during the coldest season. The suppressed feeding activity under SD conditions would lower the SCP, thereby reducing the possibility of lethal tissue freezing. Such a photoperiodic and thermal regulation of the larval development and the supercooling ability appear to represent adaptive mechanisms for winter survival in this beetle.