Potato cold hardiness development and abscisic acid. II. De novo synthesis of proteins is required for the increase in free abscisic acid during potato (Solanum commersonii) cold acclimation

During cold acclimation of potato plantlets ( Solanum commersonii Dun, PI 458317), there are two transitory increases in free ABA content corresponding to a three-fold increase on the 2nd day and a five-fold increase on the 6th day (Ryu and Li 1993). During this period, plantlets increased in cold hardiness from −5°C (killing temperature, control grown at 22/18°C, day/night) to −10°C by the 7th day of exposure to 4/2°C (day/night). This increase in free ABA was not found when cycloheximide (CHI), an inhibitor of cytoplasmic protein synthesis, was added to the culture medium 6 h before exposure to low temperatures. Plantlets treated with CHI did not acclimate to cold, maintaining a hardiness level (−5°C) similar to that of the 22/18°C-grown plantlets. When the CHI-treated plantlets were exposed to low temperatures for 3 days, transferred to CHI-free culture medium and grown at low temperatures, the plantlets showed a transitory increase in free ABA 2 days later. This increase was followed by the development of cold hardiness (−8°C). Application of CHI to the culture medium after 3 days of cold acclimation, when the first ABA peak and a partial development of cold hardiness (−8°C) had occurred, blocked the second transitory increase in free ABA and resulted in no further development of cold hardiness. These results suggest that de novo synthesis of proteins is required for these transitory increases in free ABA during cold acclimation of potato plantlets.     

A proposed role for the anaerobic pathway during low-temperature sweetening in tubers of Solanum tuberosum

Survival and growth of temperate zone woody plants under changing seasonal conditions is dependent on proper timing of cold acclimation and development of vegetative dormancy, shortening photoperiod being an important primary signal to induce these adaptive responses. To elucidate the physiological basis for climatic adaptation in trees, we have characterized photoperiodic responses in the latitudinal ecotypes of silver birch ( Betula pendula Roth) exposed to gradually shortening photoperiod under controlled conditions. In all ecotypes, shortening photoperiod triggered growth cessation, cold acclimation and dormancy development, that was accompanied by increases in endogenous abscisic acid (ABA) and decreases in indole-3-acetic acid (IAA). There were distinct differences between the ecotypes in the rates and degrees of these responses. The critical photoperiod and the photoperiodic sensitivity for growth cessation varied with latitudinal origin of the ecotype. The northern ecotype had a longer critical photoperiod and a greater photoperiodic sensitivity than the southern ecotype. Compared with the southern ecotypes, the northern ecotype was more responsive to shortening photoperiod, resulting in earlier cold acclimation, dormancy development, increase in ABA content and decrease in IAA content. However, at the termination of the experiment, all the ecotypes had reached approximately the same level of cold hardiness (−12 to −14°C), ABA content (2.1–2.3 µg g⁻¹ FW) and IAA content (17.2–20.3 ng g⁻¹ FW). In all ecotypes, increase in ABA levels preceded development of bud dormancy and maximum cold hardiness. IAA levels decreased more or less parallel with increasing cold hardiness and dormancy, suggesting a role of IAA in the photoperiodic control of growth, cold acclimation and dormancy development in birch.     

Abscisic acid and mefluidide in the regulation of cold hardiness development in Solanum tuberosum L. potato

Plants of Solanum tuberosum L. potato do not cold acclimate when exposed to low temperature such as 5°C, day/night. When ABA (45 M) was added to the culture medium, stem-cultured plantlets of S. tuberosum, cv. Red Pontiac, either grown at 20°C/15°C, day/night, or at 5°C, increased in cold hardiness from –2°C (killing temperature) to –4.5°C. The increase in cold hardiness could be inhibited in both temperature regimes if cycloheximide (70 M) was added to the culture medium at the inception of ABA treatment. Cycloheximide did not inhibit cold hardiness development, however, when it was added to the culture medium 3 days after ABA treatment.When pot-grown plants were foliar sprayed with mefluidide (50 M), ABA content increased from 10 nmol to 30 nmol g^–1 dry weight and plants increased in cold hardiness from –2°C to about –3.5°C. The increases in free ABA and cold hardiness occurred only in plants grown at 20°C/15°C; neither ABA nor cold hardiness increased in plants grown at 5°C.The results suggest that an increase in ABA and a subsequent de novo synthesis of proteins are required for the development of cold hardiness in S. tuberosum regardless of temperature regime, and that the inability to synthesize ABA at low temperature, rather than protein synthesis, appears to be the reason why S. tuberosum does not cold acclimate.     

The role of ABA in freezing tolerance and cold acclimation in barley

The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley ( Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT₅₀, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT₅₀ and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT₅₀ of leaves of cold‐acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT₅₀ decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.     

Alterations of gene expression in potato (Solanum commersonii) during cold acclimation

Plantlets of Solanum commersonii stem-culture were acclimated at 5°C day/night temperature for 14 days. Cold hardiness increased from – 3.5°C to – 8.6°C. During the course of acclimation, the synthesis of polypeptides was investigated and poly (A⁺) RNA was isolated. Translation products of poly(A⁺) RNA in a rabbit rcticulocyte lysate system were then analyzed. During the 14 days of acclimation, 23 cold-induced polypeptides were identified. Most of them disappeared following 1 day of de-acclimation at a 20/15°C day/night regime. The synthesis of one group of polypeptides is prominent and stable throughout the acclimation period. The other group is transient. The most prominent and stable polypeptides have molecular weights of 21, 22, 31 and 83 kDa.
Acclimation alters translatable mRNA population during the development of cold hardiness. Two mRNAs encoding in vitro translation products at 26 and 27 kDa were identified during the course of acclimation. These proteins may play important roles in the overall programming for the development of cold hardiness in tuber-bearing S. commersonii.     

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.     

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.     

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 .     

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.     

Effect of long-term and rapid cold hardening on the cold torpor temperature of an aphid

Abstract.  The effect of long-term (seasonal) acclimation and rapid cold hardening is investigated on the cold torpor temperature ( CT _min) of adult grain aphids, Sitobion avenae, reared at 20 or 10 °C for more than 6 months before experimentation. Rapid cold hardening is induced by exposing aphids reared at 20 to 0 °C for 3 h and aphids reared at 10 to 0 °C for 30 min (acclimation regimes previously found to induce maximum rapid cold hardening). The effect of cooling aphids from the same rearing regimes from 10 to −10 °C at 1, 0.5 and 0.1 °C min⁻¹ is also investigated. In the 20 °C acclimated population, rapid cold hardening and cooling at 0.1 °C min⁻¹ both produce a significant decrease in CT _min from 1.5 ± 0.3 to –0.9 ± 0.3 and –1.3 ± 0.3 °C, respectively. Rapid cold hardening also results in a significant reduction in CT _min of the population reared at 10 °C from 0.8 ± 0.1 to –0.9 ± 0.2 °C. However, none of the cooling regimes tested reduces the CT _min of the winter-acclimated (10 °C) population. The present study demonstrates that rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles could lower the movement threshold of S. avenae , allowing insects to move and continue feeding at lower temperatures than would otherwise be possible.     

Is tissue culture a viable system with which to examine environmental and hormonal regulation of cold acclimation in woody plants?

In vitro-grown saskatoon berry (Amelanchier alnifolia Nutt.) plantlets were exposed to various hormonal treatments, dormancy-inducing and cold acclimation conditions to determine if this in vitro system would be viable for dormancy/hardiness studies in woody plants. Low temperature induced significant hardiness levels in plantlets to ?27°C after 6 weeks at 4°C but did not approach liquid nitrogen levels of fully hardened, field-grown buds. Control plantlets were consistently killed at ?5°C throughout this period. Significant hardiness was attained under both short and long day/low temperature conditions; however, hardiness was reduced under continuous light or dark treatments. A pre-exposure to the typical short photoperiod regime of woody plants did not significantly increase the rate of acclimation in these plantlets. The presence/absence of phytohormones in the media have a pronounced influence on the ability of plantlets to cold acclimate. Hormone-free media increased hardiness to ?10.5°C after 2 weeks in treatment. Addition of abscisic acid (ABA) increased cold hardiness levels (?12°C) while addition of benzylaminopurine (BAP) to this hormone-free media decreased hardiness to ?5.3°C. A combination of BAP and ABA treatments produced LT₅₀ values intermediate between individual applications of either hormone. Conversely, α-naphthaleneacetic acid (NAA) could not counteract the ABA-induced hardiness. ABA treatments alone were not able to harden plantlets to the extent attained under low temperature acclimation conditions. Further, ABA could not maintain the hardiness levels of cold-acclimating treatments and plantlets de-acclimated to ?9°C in BAP + ABA media. Subculturing in itself significantly elevated cold hardiness in plantlets to ?9°C on BAP + NAA media within 3 days after subculture and thereafter plantlets dehardened to ?5°C. While tissue culture has value in specific cases, caution should be taken when using tissue-cultured plantlets as a system to evaluate environmental regulation of cold acclimation in woody plants, in part, due to the influence of phytohormones in the media.     

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.     

Cold-acclimation induced changes in freezing tolerance and translatable RNA content in Citrus grandis and Poncirus trifoliata

Cold-acclimation-induced changes in freezing tolerance and translatable RNA content were compared in seedlings of a relatively cold sensitive citrus species, Citrus grandis L. Osb. cv. Thong Dee (pummelo), and the cold-hardy citrus relative, Poncirus trifoliata L. Raf. cv. Pomeroy (trifoliate orange). Cold acclimation of pummelo (10 days at 15°C followed by 4 weeks at 10°/5°C, day/night) resulted in a decrease in LT₅₀ from −6 to −8°C, while in trifoliate orange (acclimated for 7 weeks at 5°C), the LT₅₀ decreased from −9 to −18°C. Qualitative changes in the in vitro translation profile, revealed by two-dimensional gel electrophoresis, were observed following cold acclimation in both species. An mRNA for a large polypeptide (ca 160 kDa) was detected following cold acclimation of trifoliate orange. A similar change was not observed in pummelo following cold acclimation.     

Content of low-molecular-weight thiols during the imbibition of Pea seeds

The metabolism of low-molecular-weight thiols was investigated in seeds of Pisum sativum L. cv. Kleine Rheinländerin during imbibition in water for 14 h. The amount of oxidized glutathione (GSSG) decreased from 319 nmol (g dry weight)⁻¹ in dry seeds to 38 nmol (g dry weight)⁻¹ within the first 14 h of imbibition. The decrease may have been due to the reduction of GSSG to reduced glutathione (GSH), catalyzed by the enzyme glutathione reductase (GR; EC 1.6.4.2). The enzyme activity was high in dry seeds [25 nkat (g dry weight)⁻¹] and decreased to 20 nkat (g dry weight)⁻¹ within 14 h of imbibition. The activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) decreased from 100 nkat (g dry weight)⁻¹ in dry seeds to 67 nkat (g dry weight)⁻¹ after 14 h of imbibition. Within 14 h the amount of γ-glutamyl-cysteine (γ-GC) decreased from 135 to 38 nmol (g dry weight)⁻¹, whereas the cysteine content rose from 81 nmol (g dry weight)⁻¹ in dry seeds to a maximum of 170 nmol (g dry weight)⁻¹ after 12 h of imbibition, which may be due to the degradation of γ-GC into cysteine.     

Involvement of abscisic Acid in potato cold acclimation

Upon exposure to 2°C day/night (D/N), leaves of Solanum commersonii (Sc) began acclimating on the 4th day from a −5°C (killing temperature) hardy level to −12°C by the 15th day. Leaves of S. tuberosum L. (St) cv `Red Pontiac' typically failed to acclimate and were always killed at −3°C. Leaves of control (20/15°C, D/N) and treated plants (2°C, D/N) of St showed similar levels of free abscisic acid (ABA) during a 15-day sampling period. In treated Sc plants, however, free ABA contents increased 3-fold on the 4th day and then declined to their initial level thereafter. The increase was not observed in leaves of Sc control plants.

Treated St plants showed a slightly higher content of leaf soluble protein than controls. In Sc, leaves of controls maintained relatively constant soluble proteins, but leaves of treated plants showed a distinct increase. This significant increase was initiated on the 4th day, peaked on the 5th day, and remained at a high level throughout the 15-day sampling period.

Exogenously applied ABA induced frost hardiness in leaves of Sc plants whether plants were grown under a 20°C or 2°C temperature regime. When cycloheximide was added to the medium of stem-cultured plants at the beginning of 2°C acclimation, or at the beginning of the ABA treatment in the 20°C regime, it completely inhibited the development of frost hardiness. However, when cycloheximide was added to plants on the 5th day during 2°C acclimation, the induction of frost hardiness was not inhibited. The role of ABA in triggering protein synthesis needed to induce frost hardiness is discussed.

     

Physiology of diapause and cold hardiness in overwintering pupae of the apple leaf miner Phyllonorycter ringoniella in Japan

Abstract The apple leaf miner Phyllonorycter ringoniella (Matsumura) (Lepidoptera: Gracillariidae) overwinters as a diapausing pupa. The diapause rate reaches 100% in early October. Diapause intensity decreases gradually from early October and diapause terminates in early February. The fresh body weight of diapausing pupae is 1.6 times that of non-diapausing pupae. The main cryoprotectant in P. ringoniella pupae is trehalose. Three stages are distinguishable as indicated by the correlations between diapause intensity, levels of cold hardiness and the trehalose content: diapause induction occurred in October, diapause development from November to December, and post-diapause quiescence from January to April. During diapause induction, the pupae accumulate low levels of trehalose and do not survive exposure to −15 °C. During diapause development, the pupae gradually accumulate more trehalose and show some ability to survive exposure to −15 °C, but not to −20 °C. During post-diapause quiescence, the pupae accumulate relatively more trehalose and cold hardiness fully develops, but decreases quickly in April. The trehalose content in pupae sampled in December is unaffected by acclimation temperatures in the range 0–30 °C, but decreases in pupae sampled in March after acclimation at temperatures from 5 to 15 °C. These results suggest that overwintering pupae of P. ringoniella have the ability to accumulate trehalose and develop a high level of cold hardiness during diapause development.     

Changes in phenolic acids and abscisic acid in sugar pine embryos and megagametophytes during stratification

The phenolic acids and abscisic acid (ABA) of sugar pine ( Pinus lambertiana Dougl.) embryos and megagametophytes, separated by high-pressure liquid chromatography, were analyzed during 90 days stratification of the seeds. The phenolic acids occurred mainly as glycosides. Following hydrolysis, the majority of phenolics present could be identified as common benzoic and ciranamic acid derivatives. Levels of phenolic acids were relatively low in dormant seeds, but increased substantially in the embryos during stratification at 5°C, particularly cinnamic acid, p -coumaric acid, ferulic acid, and one unknown. This active synthesis during stratification did not support an inhibitory function for phenolic acids. During stratification at 5°C, changes in ABA levels in both tissues followed a triphasic pattern, with no loss during the first 30 days, a significant decrease the second 30 days, and a lesser decrease the last 30 days. Loss of ABA from moist seeds at 25°C occurred three times as rapidly, so that by 30 days the ABA level of these seeds was equivalent to that of seeds stratified 90 days at 5°C; however, dormancy was not alleviated at 25°C. Application of exogenous ABA (10⁻⁷ to 10⁻⁴M) to stratified seeds did not significantly reduce germination. Together, the above results did not support a primary role for ABA in the maintenance of dormancy in sugar pines.
A correlated increase in phenylpropanoid metabolism and respiratory capacity with increased germinability during stratification suggests that loss of dormancy may be more closely dependent on increased levels of growth promoters or shifts in metabolic pathways.     

The influence of thermal parameters on the acclimation responses of pinfish Lagodon rhomboides exposed to static and decreasing low temperatures

Pinfish Lagodon rhomboides acclimation rates were determined by modelling changes in critical thermal minimum ( T _{crit min}, ° C) estimates at set intervals following a temperature decrease of 3–4° C. The results showed that pinfish gained a total of 3·7° C of cold tolerance over a range of acclimation temperatures ( T _acc, ° C) from (23–12° C), that cold tolerance increased with exposure time to the reduced temperature at all T _acc, but that the rate of cold tolerance accruement (mean 0·14° C day⁻¹) was independent of T _acc. A highly significant ( P < 0·001) multivariate predictive model was generated that described the acclimation rates and thermal tolerance of pinfish exposed to reduction in water temperature: log₁₀ T _{crit min}= 0·41597 − 0·01704 T _acc+ 0·04320 T _plunge− 0·08376[log₁₀ ( t + 1)], where T _plunge is plunge temperature (° C) and t is the time (days). A comparison of the present data, with acclimation rate data for other species, suggests that factors such as latitude or geographic range may play a more important role than ambient temperature in determining cold acclimation rates in fishes.     

Phosphate transport in potato cuttings: Effect of gibberellic acid and abscisic acid

Apical cuttings of Solanum tuberosum L. cv. Sirtema were used al different stages of development to study long-distance transport of phosphate. The effects of two hormones, gibberellic acid (GA₃) and abscisic acid (ABA), on this process were also investigated. Before tuberization, phosphate (³²P) supplied to a single leaf was transported preferentially in the young and growing parts of the plant: apical bud, young leaves and roots. After tuberization, the tuber became the principal site of phosphate accumulation. GA³ treatment (10⁻⁴ M) of the tuber as well as of the leaves led to reduced transport of ³²P into the tuber. By contrast, treatment of the tuber with ABA (10⁻⁴M) did not change the ³²P distribution within the plant, while foliar spray with ABA greatly increased the transport into the tuber. The opposite effects of the two hormones on phosphate accumulation by tubers are discussed with regard to their opposite effects on the tuberization process.     

Hardening, abscisic acid, proline and freezing resistance in two winter wheat varieties

Two varieties of winter wheat ( Triticum aestivum L.) differing in freezing resistance ("Holme" from Sweden, freezing resistant, and "Amandus" from Germany, less freezing resistant) were hardened for five weeks by gradually reducing the day/night temperature from 20°C/15°C during the first week to 2° C/0° C during the fifth week and the photoperiod from 15 to 9 h. This treatment increased the freezing resistance of both varieties in comparison to unhardened control plants. Hardening caused an increase in osmolarity of cell sap and in the levels of proline and abscisic acid (ABA). Increase in osmolarity preceded the increase in ABA level, and proline levels increased later than ABA levels. Holme had higher values of osmolarity as well as higher levels of ABA and proline. but the differences between the two varieties were significant only for proline. Since the pressure potential remained constant or increased slightly during the hardening period, it is suggested that the accumulation of ABA is due to the hardening process and not to simple water stress caused by cold-induced inhibition of water uptake by the root.
Spraying hardened plants with 10⁻⁴ M ABA 24 h before a freezing test increased freezing resistance in both varieties, but did not obliterate the differences in freezing resistance between the two varieties. Spraying hardened plants with an aqueous proline solution (10%, w/v) was without effect on freezing resistance. It is concluded that the hardening procedure causes an accumulation of ABA in winter wheat leaves and that ABA is involved in the chain of events leading to freezing resistance.