Cold hardiness and water relations parameters in Rhododendron cv. Catawbiense Boursault subjected to drought episodes

We determined whether increase in cold hardiness of Rhododendron cv. Catawbiense Boursault induced by water stress was correlated with changes in tissue water relations. Water content of the growing medium was either maintained near field capacity for the duration of the study or plants were subjected to drought episodes at different times between 15 July and 19 February. Watering during a drought episode was delayed until soil water content decreased below 0.4 m³ m⁻³ then watering was resumed at a level to maintain soil water content between 0.3 and 0.4 m³ m⁻³. Cold hardiness was evaluated in the laboratory with freeze tolerance tests on detached leaves. Water relations parameters were determined using pressure-volume analysis. Exposure to drought episodes increased cold hardiness during the cold acclimation stage in late summer and fall but not during the winter. When water-stressed plants were re-watered to field capacity, the previous gain in cold hardiness gradually disappeared. Water relations parameters correlating with seasonal changes of cold hardiness included dry matter content (r =−0.67). apoplastic water content (r =−0.60), and water potential at the turgor loss point (r = 0.40). Changes of cold hardiness in water-stressed plants in reference to well-watered plants were correlated with changes of all water relations parameters, except for osmotic potential at full turgor (r = 0.13). It is proposed that water stress reduced the hydration of cell walls, thereby increasing their rigidity. Increased rigidity of cell walls could result in a development of greater negative turgor pressures at subfreezing temperatures and therefore increased resistance to freeze dehydration.     

THE COMBINED EFFECTS OF LOW TEMPERATURE AND SO2+NO2 POLLUTION ON THE NEW SEASON'S GROWTH AND WATER RELATIONS OF PICEA SITCHENSIS

Picea sitchensis (Bong.) Carr. seedlings were exposed to SO₂, NO₂ and SO₂+ NO₂ during dormancy in controlled environments, and were taken to night temperatures of 4, 0, −5, −10 and −15 °C in a freezer. Conditions in the freezer were carefully monitored during the low–temperature treatments. In two experiments, different photoenvironments and temperature regimes were imposed prior to the cold treatments, and different effects were observed. In the first, only limited frost hardiness was achieved and night temperatures of −15 °C were lethal. Temperatures of −5 and − 10 °C led to poor survival of lateral buds, particularly in plants exposed to 45 ppb SO₂. The poor bud break in plants exposed to SO₂ and to − 5 °C resulted in a loss of the effectiveness of this temperature as a chill requirement. Pressure-volume analysis showed that the shoots of plants exposed to NO₂ had greater elasticity (lower elastic moduli, e), so that loss of turgor occurred at lower relative water contents. In contrast, a hardening period (2 weeks in night/day temperatures of 3/10 °C and 8 h days at 50 μmol m⁻² s⁻¹ PAR) gave decreased elasticity and lower solute potentials of spruce shoots. In the second experiment, exposure to 30 ppb SO₂ and SO₂+ NO₂ led to slight, but consistent, increases in frost injury to the needles of plants frozen to − 5 and − 10 °C. The results suggest that the main interaction of low temperatures and winter pollutants may be on bud survival rather than on needle damage, but that effects are subtle, only occurring with certain combinations of pollutant dose and cold treatment.     

Intracellular resistance correlates with initial stage of frost hardening in willow (Salix viminalis)

Distributed model parameters of shoots of five clones of willow ( Salix viminalis ) were examined with electrical impedance analysis at the end of the growing season and with cold acclimation. The parameters were compared with regard to frost hardiness, linoleic (18:2) and linolenic (18:3) fatty acids, unsaturation/saturation ratio of fatty acids and dry weight content. The intracellular resistance (r_i) correlated best with changes in frost hardiness. The value of r_i rose from 1–2 Ω m in non-hardened to about 12 Ω m in hardened samples. In the initial stages of frost hardening, a linear relationship was found between r_i and frost hardiness and levels of 18:2 fatty acid, and an inverse relationship between r_i and levels of 18:3 fatty acid. The unsaturation/saturation ratio of fatty acids rose fairly rapidly in the initial stage of hardening. The dry weight content increased stepwise during the experimental period, and less steadily than r_i. In addition, equivalent circuit parameters changed in the prehardening phase, and were probably connected with cell differentiation and lignification. Frost hardiness by the visual method and by extracellular resistance, determined after controlled freezing tests, correlated well in the initial stages of hardening until about − 10°C but deviated upon further hardening.     

The electrical impedance spectroscopy of Scots pine needles during cold acclimation

The electrical impedance spectroscopy (EIS) was applied to current-year needles of Scots pine ( Pinus sylvestris L.) in an 8-year provenance field trial in central Finland during frost hardening. The EIS analysis of the needles using a Model-A equivalent circuit indicated a sequence of events in the needles during their cold acclimation. Some of the EIS-parameters referred to maturation phenomena occurring during the pre-hardening phase at the end of the growing season, and some parameters displayed a clear coincidence with the frost hardening itself. Significant differences between provenances were found in several of the Model-A parameters. Extracellular resistance (r_e) and β -coefficient decreased in all provenances in the pre-hardening phase in August and until mid-September. In the same phase, both the intracellular resistance (r_i) and the cell membrane time constant (τ_m) first increased and then decreased. According to τ_m, r_e and β there was a clear gradation between provenances in the pre-hardening phase. From the end of September significant differences were found in the intracellular resistance between provenances, corresponding with the differences in their hardening pattern. The dry weight (DW) content of needles increased during the study period but no clear differences were found between the provenances.     

Cold hardening of raspberry plants in vitro is enhanced by increasing sucrose in the culture medium

The influence of exogenously applied sucrose on cold hardening of raspberry ( Rubus idaeus L.) in vitro was examined. Raspberry plants (cv. Preussen) were cultured on Murashige-Skoog (MS) media with different levels (1, 3, 5 and 7%) of sucrose and subjected to low-temperature acclimation (3/−3°C day/night temperature, 8-h photoperiod) for 14 days. Cold hardiness (LT₅₀ in controlled freezing), shoot moisture content, osmolality and the amounts of sucrose, glucose and fructose were determined. Exogenously applied sucrose was taken up by plants, but the uptake corresponded to less than 10% of total sugar reserves in the culture. Cold hardiness was primarily affected by acclimation treatment, but sucrose increased cold hardiness of nonacclimated plants and significantly enhanced the effect of acclimation treatment, 5% sucrose in the culture medium being optimal for cold hardening. LT₅₀ values ranged between −4.1 and −7.1°C for nonacclimated, and between −14.2 and −20.7°C for cold-acclimated shoots. Shoot moisture content was inversely related to medium sucrose level and declined only slightly during cold acclimation. After cold acclimation, plant osmolality predicted hardiness better than shoot moisture content. Plant osmolality and sugar content were increased by increasing the medium sucrose level and, to a greater extent, by cold acclimation. Sucrose, glucose and fructose accumulated during hardening. Sucrose was the predominant sugar, and the rate of sucrose accumulation during cold acclimation was independent of the medium sucrose level or the initial plant sucrose content. A close correlation between cold hardiness and total sugars, sucrose, glucose and fructose was established. These results suggest that sugars have more than a purely osmotic effect in protecting acclimated raspberry plants from cold.     

Ecophysiological analysis of two arctic sedges under reduced root temperatures

Shoot physiological activity in arctic vascular plants may be controlled by low soil temperatures. While leaves may be exposed to moderate temperatures during the growing season, root temperatures often remain near freezing. In this study, two tundra sedges, Eriophorum vaginatum and Carex bigellowii , were subjected to reduced soil temperatures, and photosynthetic parameters (light saturated photosynthesis A _max, variable to maximal fluorescence and F _v/ F _m stomatal conductance) and abscisic acid concentrations were determined. Stomatal conductance and A _max for both E. vaginatum and C. bigellowii strongly decreased with declining soil temperatures. Decreasing soil temperature, however, impacted F _v/ F _m to a much lesser degree. Root and leaf ABA concentrations increased with decreasing root temperature. These observations support the contention that soil temperature is a significant photosynthetic driving factor in arctic sedges exposed to variable root and shoot temperatures. Because these two species comprise approximately 30% of the vascular ground cover of wet tussock tundra, the soil temperature responses of these sedges potentially scale up to significant effects on ecosystem carbon exchange.     

Differences in cold hardiness,carbohydrates, dehydrins and related gene expressions under an experimental deacclimation and reacclimation in Prunus persica

To boost our understanding of a recent outbreak of freezing injury, we sought to confirm distinctive features between the shoot tissues of the peach (Prunus persica) cultivars Daewol and Kiraranokiwami by mimicking unseasonable changes of temperatures that occur in the early spring through repeated deacclimation and reacclimation treatments. Patterns of cold hardiness declined dramatically during the deacclimation and rose during the reacclimation in both cultivars. Our results indicated that ‘Daewol’ possessed higher capacity in response to repeated deacclimation and reacclimation treatments than ‘Kiraranokiwami’. ‘Daewol’ showed more sensitive changes in the carbohydrates in response to warm and low temperatures compared with ‘Kiraranokiwami’. ‘Daewol’ indicated almost similar repeated down‐ and up‐patterns in soluble sugar content in response to repeated deacclimation and reacclimation, whereas it indicated repeated up‐ and down‐patterns in starch content. However, ‘Kiraranokiwami’ showed a progressive increase in the soluble sugar content and a progressive decrease in starch content. Notably, patterns of accumulation of a 60‐kDa dehydrin protein encoded by the PpDhn1 gene were confirmed through western blotting and paralleled fluctuations of cold hardiness in both cultivars. Expression of this dehydrin was weak in both cultivars during deacclimation but its band intensity increased during reacclimation. Changes in related genes (β‐amylase, PpDhn1, PpDhn2 and PpDhn3) were positively correlated with changes in cold hardiness throughout the experiment. Our results indicate that recent repeated warm periods may cause premature deacclimation in the early spring, and that more cold‐tolerant cultivar may be more resilient to freezing injury caused by unstable temperature conditions.     

Lipid composition of pine needle chloroplasts and apple bark tissue as affected by growth temperature and daylength changes. 2. Glycolipids, neutral lipids and chlorophyll

Glycolipids, neutral lipids and chlorophyll of chloroplasts of pine needles ( Pinus sylvestris L.) and apple bark tissue ( Malus sylvestris Mill. cv Golden Delicious) were determined in a series of experiments in which growth temperature and daylength were changed. Trees were exposed to 0 and 20°C and to daylength conditions of 9 and 14 h. All 16 possible combinations were studied by transfer of the trees from the original condition to each of the other conditions. There was no direct relation between cold hardiness and glycolipid composition in apple bark and pine chloroplasts, when temperature and/or daylength were changed. Glycolipid and neutral lipid composition seemed to be strongly determined by the sequence of the imposed sets of daylength and temperature, and the effects of these factors on lipids strongly differed from that on cold hardiness. When the treatments were given in seasonal order, the corresponding changes in chloroplast glycolipids matched those reported in the literature for needles collected in the forest the year around. Glycolipid synthesis could well be under phytochrome control.     

Effect of nitrogen supply on frost resistance, nitrogen metabolism and carbohydrate content in white clover (Trifolium repens)

Effects of mineral nitrogen (2, 4, 6 and 8 m M 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 proline 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.     

中华通草蛉成虫抗寒能力季节性变化

中华通草蛉（Chrysoperla sinica）成虫在自然条件下抗寒能力的季节性变化研究表明,雌、雄成虫的抗寒能力均呈现出季节性的变化趋势,即随着冬季低温的到来,其抗寒能力逐渐增强,冬季过后又随气温的回升,其抗寒力逐渐减弱.雌、雄成虫的体内含水量、过冷却点（SCP）和结冰点（FP）均随气温的降低而降低,升高而升高,但体内总脂肪的含量却随气温的降低而升高,升高而降低.越冬代在越冬的前期和中期,雌、雄成虫体内的含水量和SCP均显著低于生长季节的其它各代,越冬代后期的含水量和SCP与生长季节其它各代没有显著差异.经回归分析发现,雌、雄成虫体内含水量与SCP之间均存在极显著负相关关系（p＜0.01）;越冬代成虫（特别是越冬前期）的体内总脂肪含量显著高于其它时期,并且雌成虫体内的总脂肪含量与SCP之间呈显著正相关（p＜0.05）,雄成虫体内总脂肪含量与SCP之间没有显著相关性（p＞0.05）.在一年的不同世代中,雌、雄成虫体内含水量只是在越冬前期有显著差异,SCP和体内总脂肪含量却在越冬后期有显著差异.     

Effects of climatic warming on cold hardiness of some northern woody plants assessed from simulation experiments

Effects of climatic warming on cold hardiness were investigated for some northern woody plants. In the first experiment, seedlings of Norway spruce ( Picea abies [L.] Karst.), Scots pine ( Pinus sylvestris L.) and lodgepole pine ( Pinus contorta Dougl. var. latifolia Engelm.) were exposed to naturally fluctuating temperatures averaging −6°C (ambient) and 0°C (elevated) for 16 weeks in midwinter before they were thawed and re-saturated with water. In lodgepole pine, needle sugar concentrations had decreased by 15%, and the temperature needed to induce 10% injury to needles in terms of electrolyte leakage had increased by 6°C following treatment to elevated as compared with control temperatures. In contrast, Norway spruce and Scots pine showed no effects. The lack of an effect for Scots pine was ascribed to seedlings containing unusually large energy reserves that buffered respiratory expenditure of sugars. A strong, linear relationship between levels of cold hardiness, assessed by the electrolyte leakage method, and sugars was found when combining data from this and previous, similar experiments. In the second experiment, the evergreen dwarf shrub Empetrum hermaphroditum Hagerup was analysed for leaf cold hardiness, using the electrolyte leakage method, and sugar concentrations in late spring and late autumn during the third year of a warming experiment in a subarctic dwarf shrub community. The objective was to test the hypothesis that warming in the growing season alters hardening/dehardening cycles by increasing soil nitrogen mineralization and plant growth. Data found, however, suggested that cold hardening/dehardening cycles were unaffected by warming.     

Differential cold hardiness in adults and nymphs of the peach-potato aphid Myzus persicae

The LT₅₀ (lethal temperature) of first instar and adult stages of the peach-potato aphid Myzus persicae was lowered following long term acclimation at low temperatures.
First instars consistently showed greater cold hardiness than adult stages at each acclimation temperature, with the differential increasing as the temperature was lowered. When maintained at 5°C (the lowest acclimation regime) nymphs and adults had dLT₅₀8.3°C and 4.7°C respectively lower than those for non-acclimated individuals.
When 10°C acclimated adults were returned to 20°C, the acclimation effect was retained in full for 6 days but complete deacclimation occurred by day 10. In contrast the LT₅₀ of their progeny increased gradually from the first day of adult deacclimation towards the level of the unacclimated control over a period of 10 days.
A change in cold hardiness was observed in first instars according to their position in the birth sequence. The LT₅₀ of first-born nymphs (day 1 of reproduction) from 20°C parents was - 15.9°C rising to - 8.3°C by day 4 and remaining at this level until the end of the reproductive period.
The differential mortality between nymphs and adults observed in the laboratory was supported by the results of a field experiment. Adult aphids kept in clip-cages on a crop of oilseed rape showed greater mortality compared with those introduced as nymphs when the minimum temperature fell below -4°C for the first time in winter. At - 10°C mortality of aphids introduced as adults approached 100% whereas more than 50% of those introduced as nymphs were still alive at this temperature.     

The Joensuu dasotrons: A new facility for studying shoot,root, and soil processes

A new, controlled, environment facility for growing trees was built at Joensuu, Finland, between 1996 and 1998. It consists of four large rooms called dasotrons, with four large root pots in each. Each room is a separate unit, with independent control of air and soil temperature, air humidity and light. The environmental variables can be controlled to simulate conditions ranging from tropical to boreal. The controller set-points can be programmed locally or through a central control system running on a PC. The floor area and height of the rooms allows us to grow small trees (up to 3.7 m height) for several growing seasons. In each dasotron, there are four cylindrical pots with a removable upper section. There are access holes in the walls of the pots for the installation of sensors and minirhizotron tubes. Each pot has a drain, with valves, at the bottom to enable the removal of excess water or the collection of percolate samples. The operation of the facility was tested during one simulated annual growing cycle. During this test period, the dasotrons worked reliably and no systematic differences were found in the environmental conditions or in the growth of Norway spruce seedlings between the dasotrons. This new facility will enable diverse physiological and ecophysiological studies to be carried out on the responses of trees to their below- and above-ground environment.     

Geographical variation in egg cold hardiness: a study on the adaptation strategies of the migratory locust Locusta migratoria L.

Abstract. 1. For many species of insect, cold hardiness is an important trait that enables a population to develop in the next season and to extend its range. To elucidate the role of cold hardiness of the migratory locust Locusta migratoria L. in its outbreak and distribution areas, egg cold hardiness was examined in locusts derived from four locations from latitude 18°23'N to latitude 41°10'N in eastern China.
2. The supercooling points of eggs from different geographic populations did not differ significantly for the first development stage, with an average ± SE of −24.5 ± 0.51 °C, or for the second stage, −22.06 ± 0.68 °C, however there was a significant difference for the embryonic development phase among the four geographical populations. The egg supercooling point increased gradually from neonatal egg to old egg; eggs prior to hatching always had a much higher supercooling point.
3. Comparisons of the cold hardiness of four populations were carried out by validating the close correlation between latitude and the effects of cold on hatching, low lethal temperature (Ltemp₅₀), and low lethal time (Ltime₅₀). There were significant differences among the four populations; the northern population was more cold hardy than the southern population, and the two mid-latitude populations were intermediately cold hardy.
4. The cold hardiness of all populations was enhanced to various degrees by short-term cold acclimation at 0 °C and 5 °C. For most populations, a 2-day acclimation period seemed to be optimal.     

Effects of elevated CO2-grown loblolly pine needles on the growth, consumption, development, and pupal weight of red-headed pine sawfly larvae reared within open-topped chambers

Seedlings of loblolly pine, Pinus taeda , were grown in open-topped chambers under four levels of CO₂: two ambient and two elevated. Larvae of the red-headed pine sawfly, Neodiprion lecontei , were reared from early instar to pupation, primarily on branches within chambers. Larval growth and mortality were assessed and leaf phytochemistry samples of immature and mature leaves collected weekly. Mature leaves grown under elevated CO₂ had significant reductions in leaf nitrogen and increases in non-structural carbohydrate contents, resulting in foliage being a poorer food source for larvae, i.e. higher carbohydrate:nitrogen ratio. Nutritional constituents of immature needles were unaffected by seedling CO₂ treatment. Volatile mono- and sesquiterpenes were unrelated to plant CO₂ treatments for either leaf age class. Larval consumption of immature needles significantly increased on seedlings grown under CO₂ enrichment, while mature needle consumption was not different between the treatments. The average weight gain per larva significantly declined in late instar larvae consuming elevated CO₂-grown needles. In spite of this reduced growth, neither the days to pupation nor pupal weights were different among the CO₂ treatments. This study suggests that enriched CO₂-induced alterations in pine needle phytochemistry can affect red-headed pine sawfly performance. However, compensatory measures by larvae, such as choosing to consume more nutritious immature needles, apparently helps offset enriched CO₂-induced reductions in the leaf quality of mature needles.     

The Relationship of Carbohydrates to Cold Acclimation of Hedera helix L. cv. Thorndale

While both the total sugar content and cold hardiness greatly increased during artificial cold acclimation, no direct parallelism was demonstrated. In fact, plants hardened in the dark exhibited an increase in hardiness during the period when the total sugar content declined, furthermore, while there was evidence for an accumulation of sugars (especially sucrose) incorporation of ¹⁴C indicated that all of the isolated fractions were in a dynamic state. Dehardening, paralleled by a large increase in the starch content, was more rapid in the light than in the dark. Furthermore, in stems the sugar content increased after 3 days of dehardening but declined after 7 days. This increase may represent the release of sugars from a previously unextractable form such as a glycoprotein complex. Starvation experiments indicate that photosynthates produced during the cold acclimation period are preferentially used during cold acclimation rather than reserve carbohydrates. This was also indicated by the smaller amount of starch hydrolysis in plants hardened in the light. Thus, while there appears to be a role for carbohydrates in the cold acclimation process, the lack of parallelism between sugar content and hardiness may be interpreted as indicating 1) cold acclimation is not merely an accumulation of sugars or an osmotic effect per se, and 2) under normal conditions, the level of carbohydrates is not limiting the rate or degree of cold acclimation.     

Does the removal of snowpack and the consequent changes in soil frost affect the physiology of Norway spruce needles?

Climate change may cause a decrease in snow cover in northern latitudes. This, on the other hand, may result in more severe soil frost even in areas where it is not common at present, and may lead to increased stress on the tree canopy. We studied the effects of snow removal and consequent changes in soil frost and water content on the physiology of Norway spruce (Picea abies [L.] Karst.) needles and implications on root biomass. The study was conducted at a 47-year-old Norway spruce stand in eastern Finland during the two winters of 2005/06 and 2006/07. The treatments in three replicates were: (i) natural snow accumulation and melting (CTRL), (ii) artificial snow removal during the winter (OPEN), and (iii) the same as OPEN, but the ground was insulated in early spring to delay soil thawing (FROST). In spite of the deeper soil frost in the OPEN than in the CTRL treatment, soil warming in spring occurred at the same time, whereas soil warming in the FROST was delayed by 2 and 1.5 months in 2006 and 2007, respectively. The soil water content was affected by snow manipulations, being at a lower level in the OPEN and FROST than CTRL in spring and early summer. The physiological measurements of the needles (e.g. starch, carbon and nitrogen content and apoplastic electrical resistance) showed differences between soil frost treatments. The differences were mostly seen between the CTRL and FROST, but also in the case of the starch content in early spring 2007 between the CTRL and OPEN. The needle responses in the FROST were more evident after the colder winter of 2006. The physiological changes seemed to be related to the soil temperature and water content in the early growing season rather than to the wintertime soil temperature. No difference was found in the fine root (diameter < 2 mm) biomass between the treatments assessed in 2007. In the future, conditions similar to the OPEN treatment may be more common than at present in areas experiencing a thick snow cover. The present experiment took place over the course of two years. It is possible that whenever thin snow cover occurs yearly, the reduced starch content during the early spring may be reflected in the tree growth itself as a result of reduced energy reserves.     

Lipid composition of pine needle chloroplasts and apple bark tissue as affected by growth temperature and daylength changes. 1. Phospholipids

Phospholipid (PL) and fatty acid composition of chloroplasts of pine needles ( Pinus sylvestris L.) and apple bark tissue ( Malus sylvestris Mill. cv. Golden Delicious) was determined in a series of experiments in which growth temperature and daylength were changed. Trees were exposed to 0 and 20°C and to daylength conditions of 9 and 14 h. All 16 possible combinations were investigated by transfer of the trees from the original condition to each of the other conditions. There was no direct relation between cold hardiness and PL composition in apple bark and pine chloroplasts, when temperature and/or daylength were changed. PL composition seemed to be strongly determined by the sequence of the imposed sets of daylength and temperature. The effect of these environmental factors on PL composition strongly differed from that for cold hardiness. The correlation between the levels of PL (and phosphatidylcholine) and cold hardiness, as reported in the literature, was also evident in this experiment, when treatments, presenting the normal seasonal order, were compared. It seems that the yearly cycle of temperature and daylength is important in determining the PL composition of apple bark and pine chloroplasts.     

Epidermal transpiration, ultrastructural characteristics and net photosynthesis of white spruce somatic seedlings in response to in vitro acclimatization

Mortality of transplanted somatic seedlings at the stage of acclimatization is often high and likely due to rapid change in environmental conditions. To investigate the potential of in vitro acclimatization of somatic seedlings before soil transfer, somatic seedlings of white spruce ( Picea glauca [Moench] Voss) were germinated on a liquid medium supplemented with sucrose. After 6 weeks in germination, sucrose was omitted from the medium for a supplementary 6 weeks at which time somatic seedlings were acclimatized in vitro in their germination tubes before transfer to soil. In vitro acclimatization of somatic seedlings was realized by transferring the test tubes containing the germinated somatic seedlings to the greenhouse for 9 days. During this period, the culture tube lids of acclimatized somatic seedlings were lifted progressively increasing air exchange between the tube and the greenhouse whereas, for non-acclimatized somatic seedlings the culture tubes were maintained closed during in vitro acclimatization. In vitro acclimatized somatic seedlings had higher asymptotic net photosynthesis ( P _n) at light saturation than non-acclimatized seedlings (6 versus 4.5 µmol m⁻² s⁻¹). At the end of the in vitro acclimatization period, a lower rate of epidermal transpiration was also observed for acclimatized somatic seedlings (3.85 versus 4.75% h⁻¹). Microscopic observations showed that starch granules were more abundant in needles of acclimatized somatic seedlings than in non-acclimatized somatic seedlings, probably as a result of their greater photosynthetic capacity. Needles from acclimatized somatic seedlings also showed more epicuticular wax projections than needles from non-acclimatized somatic seedlings. These structural changes may help somatic seedlings to restrict epidermal water loss and stomatal aperture.     

Changes in protein synthesis and translatable messenger RNA populations associated with ABA-induced cold hardiness in potato (Solatium commersonii)

Plantlets of Solanum commersonii Dun, PI 458317 stem-culture were treated with abscisic acid (ABA) (3.78 to 113.5 μ M ) at a 20°/15°C day/night temperature regime for 14 days. Cold hardiness increased from—3.3°C to—8.4°C (killing temperature) after 7 days of ABA treatment and remained at this level thereafter. During the course of treatment (14 days), the synthesis of polypeptides was investigated and poly(A⁺)-RNA was isolated. Translation products of poly(A⁺)-RNA in a rabbit reticulocyte lysate system were then analyzed by 2-D polyacrylamide gel electropho-resis. During the 14 days of ABA treatment, 30 ABA-induced polypeptides were identified. The synthesis of one group of polypeptides was stable and prominent throughout the treatment period. The other group was transient. The most prominent and stable polypeptides had molecular weights of 21 (pi 6.0, 6.3), 22 (pI 6.0, 6.3), 31 (pi 4.5) and 83 (pi 5.4, 5.5, 5.6) ItDa. About one-third of the new polypeptides appeared after cold hardiness reached a maximum (after 7 days of ABA treatments.
ABA treatment alters translatable mRNA populations during the development of cold hardiness. Several mRNAs, encoding in vitro translation products at 26 (pi 6.0, 6.3, 6.4), and 27 (pi 6.0, 6.3, 6.4), 40 (pi 6.4) and 50 (pi 4.5) kDa were identified during course of the ABA treatment. These proteins may play important roles for the development of cold hardiness in tuber-bearing S. commersonii .