ABA and gibberellin-like substances during prehardening,cold acclimation,de- and reacclimation of oilseed rape

Previously published results showed that high relative reduction state of PSII (PSII excitation pressure) during both early seedling growth (prehardening) as well as cold deacclimation caused significant changes in growth pattern. The differences in elongation growth rate were related to the cold acclimation of photosynthetic apparatus and to frost resistance. To study changes in the hormonal balance connected with alterations in elongation growth rate observed during prehardening and deacclimation under different PSII excitation pressure (modulated by day-temperatures), endogenous concentration of ABA, GA₃ and GA-like substances (GAs) were analysed. Analyses were also performed during cold acclimation and reacclimation of plants characterized by different elongation growth rate triggered by prehardening or deacclimation under different day-temperatures. Growth under high PSII excitation pressure (prehardening) resulted in a significant increase in ABA and a considerable decrease in GAs contents. On the other hand, different ABA content played almost no role in controlling growth rate during cold deacclimation and subsequent reacclimation, when the induction of elongation growth was connected with the changes in concentration of GAs including GA₃. The possible role of ABA and GAs in controlling prehardening, cold acclimation and deacclimation is discussed.     

Cold deacclimation mechanisms and reacclimation potential in flower buds of blackcurrant (Ribes nigrum)

As a consequence of global climate change, cold acclimation and deacclimation cycles are becoming increasingly frequent during winter in temperate regions. However, little is known about plant deacclimation and in particular reacclimation mechanisms, although deacclimation resistance and the ability to reacclimate may have wide‐ranging consequences regarding plant productivity in a changing climate. Here, we report time‐dependent responses of freezing tolerance, respiration rates, metabolite contents (high‐resolution magic angle spinning NMR) and fatty acid levels (gas chromatography) in flower buds of two ecodormant Ribes nigrum cultivars exposed to three different deacclimation temperatures followed by a reacclimation treatment at 4°C. The data reveal that despite differences in the progression of deacclimation, the capacity of blackcurrant flower buds to reharden in late winter is virtually non‐existing, implying that increasingly irregular temperature patterns is critical for blackcurrant fruit yield. The early phase of deacclimation is associated with a transient increase in respiration and decreasing contents of amino acids, tricarboxylic acid (TCA) cycle intermediates and sugars, indicating an increased need for carbon sources and respiratory energy production for the activation of growth. Decreasing sugar levels may additionally cause loss of freezing tolerance. Deacclimation also involves desaturation of membrane lipids, which likely also contributes to decreased freezing tolerance but may also reflect biosynthesis of signaling molecules stimulating growth and floral organ differentiation. These data provide new insights into the under‐researched deacclimation mechanisms and the ability of blackcurrant to reacclimate following different advancements of deacclimation and contribute to our understanding of plant responses to increasingly irregular temperature patterns.     

Regulation of frost resistance during cold de-acclimation and re-acclimation in oilseed rape. A possible role of PSII redox state

A possible role of photosynthetic apparatus during cold de-acclimation was studied in oilseed rape ( Brassica napus var. oleifera ). Plants of spring (Star) and winter (Górczañski) cultivars were cold acclimated at + 5°C, and de-acclimated during 4 weeks at combinations of + 12 and + 20°C operating in the light or/and dark, with a 12-h photoperiod. Evidence is presented that the photosynthetic apparatus may be involved in temperature perception during de-acclimation. De-acclimation was faster under a 20/12°C (day/night) treatment than under the reverse 12/20°C (day/night). De-acclimation rate was constant when the day temperature was constant, irrespective of the night temperature both under cold day temperature regimes (12/20, 12/12°C (day/night) and warm-day treatments (20/12, 20/20°C (day/night). The fast decrease in frost resistance observed under warm-day de-acclimation was always accompanied by an acceleration of elongation growth. In the spring cultivar, elongation growth increased starting from the second week of de-acclimation, regardless of temperature conditions. Once elongation growth had commenced during de-acclimation, it continued throughout the period necessary for re-acclimation to low temperature. Re-acclimation to the initial freezing tolerance level was only possible when plant elongation was reduced. In addition re-acclimation of the photosynthetic apparatus to low temperature was impossible in fast growing plants. A possible relationship between PSII, growth rate and frost resistance during cold acclimation and de-acclimation is discussed.     

Characteristics of Cold Acclimation and Deacclimation in Tuber-bearing Solanum Species

The effect of temperatures on cold acclimation and deacclimation in foliage tissues was studied in Solanum commersonii (Oka 4583), a tuber-bearing potato. The threshold temperature for cold acclimation was about 12 C. In a temperature range of 2 to 12 C, the increase in hardiness was dependent on the acclimating temperature; the lower the acclimating temperature, the more hardiness achieved. A day/night temperature of 2 C, regardless of photoperiod, appeared to the optimum acclimating temperature for the Solanum species studied. A subfreezing temperature hardened plants less effectively. The maximum level of hardiness could be reached after 15 days of cold acclimation. However, it took only 1 day to deacclimate the hardened plants to a preacclimation level when plants were subjected to a warm regime from cold. The degree of deacclimation was dependent on the temperature of the warm regime.     

Simulating the influence of vernalization, photoperiod and optimum temperature on wheat developmental rates

Background and Aims

Accurately representing development is essential for applying crop simulations to investigate the effects of climate, genotypes or crop management. Development in wheat (Triticum aestivum, T. durum) is primarily driven by temperature, but affected by vernalization and photoperiod, and is often simulated by reducing thermal-time accumulation using vernalization or photoperiod factors or limiting accumulation when a lower optimum temperature (T_optl) is exceeded. In this study T_optl and methods for representing effects of vernalization and photoperiod on anthesis were examined using a range of planting dates and genotypes.

Methods

An examination was made of T_optl values of 15, 20, 25 and 50 °C, and either the most limiting or the multiplicative value of the vernalization and photoperiod development rate factors for simulating anthesis. Field data were from replicated trials at Ludhiana, Punjab, India with July through to December planting dates and seven cultivars varying in vernalization response.

Key Results

Simulations of anthesis were similar for T_optl values of 20, 25 and 50 °C, but a T_optl of 15 °C resulted in a consistent bias towards predicting anthesis late for early planting dates. Results for T_optl above 15 °C may have occurred because mean temperatures rarely exceeded 20 °C before anthesis for many planting dates. For cultivars having a strong vernalization response, anthesis was more accurately simulated when vernalization and photoperiod factors were multiplied rather than using the most limiting of the two factors.

Conclusions

Setting T_optl to a high value (30 °C) and multiplying the vernalization and photoperiod factors resulted in accurately simulating anthesis for a wide range of planting dates and genotypes. However, for environments where average temperatures exceed 20 °C for much of the pre-anthesis period, a lower T_optl (23 °C) might be appropriate. These results highlight the value of testing a model over a wide range of environments.Key words: Wheat, Triticum aestivum, T. durum, air temperature, thermal time, shoot apex, phenology, growth stages, anthesis, flowering     

Daily variations in the influence of noradrenaline on preferred ambient temperature of the Siberian hamster

Daily variations in sensitivity to noradrenaline (NA) and the activation of nonshivering thermogenesis (NST) are important for survival under a potentially wide range of environmental conditions. However, little is known regarding the ability of the Siberian hamster and other species to activate NST in the day and night when they may be subjected to marked variations in environmental temperature. In this study, the effects of acclimation temperature and time of day on the behavioral thermoregulatory response to NA injections in Siberian hamsters (Phodopus sungorus) was investigated. Hamsters were acclimated for 4 weeks to 23 degrees C and a L:D 12:12 h photoperiod. After acclimation, preferred ambient temperatures (PT(a)) in saline- and NA-injected animals were measured continuously in the temperature gradient system. NA (0.6 mg/kg; s.c.) was given every 4 h while PT(a) was monitored. After NA injections there was a rapid drop in PT(a), decreasing to approximately 15 degrees C within 10-20 min after each NA injection. Following 4 weeks of acclimation to 10 degrees C and a L:D 8:16 h photoperiod, the same hamsters were re-tested in the temperature gradient system. Cold acclimation led to an accentuation in the behavioral response with a decrease in PT(a) of approximately 10 degrees C. The maximal decrease in preferred ambient temperatures was recorded during the light phase of the day and during the second part of the night. Lowering of PT(a) after NA allows for rapid dissipation of the heat from NST. Overall, the behavioral response reflects the daily changes in brown adipose tissue sensitivity to NA and thus capacity for NST.     

Day and night temperature responses in Arabidopsis: effects on gibberellin and auxin content,cell size,morphology and flowering time

The effect of 16 different day (DT) and night (NT) temperature combinations (DT and NT 12, 17, 22 and 27 degrees C) on rosette leaf growth, flower stem elongation and flowering time in Arabidopsis thaliana Ler was investigated. Final leaf length decreased with increasing NT due to a combination of reduced elongation period and reduced elongation rate. Final stem length increased with increasing DT due to increased elongation rate, and decreased with increasing NT due to a decrease in elongation period. Under NT 27 degrees C, however, stem elongation rate increased greatly, resulting in the same final stem length as under NT 12 degrees C. The transition to flowering was accelerated by increasing NT. A linear regression analysis was performed to clarify the relationship between final leaf length, final stem length and flowering time with DIF (DT minus NT) and/or ADT (average daily temperature). For all three variables, the effect of DIF depended on ADT and vice versa. The relationship of final stem length with DIF also depended on the temperature range. Increased cell volume in flower stems developing at DT/NT 22/12 degrees C gave rise to longer and thicker stems compared with stems developing at DT/NT 12/22 degrees C. GC-MS analysis (gas chromatography-mass spectrometry) showed that the endogenous level of IAA was 56 % higher in stems grown under DT/NT 22/12 degrees C compared with DT/NT 12/22 degrees C. Of the 12 gibberellins analysed, however, only the level of non-bioactive GA29 was affected by the temperature treatment.     

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye ( Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16- or 24-h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24-h photoperiod in 20°C plants and at a 16-h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.     

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.     

Photoperiod and root-zone temperature: Interacting effects on growth and mineral nutrients of maize

Factorial effects of photoperiod (6, 12 and 18 h) and root-zone temperatures (9, 15 and 21°C) on the growth and mineral nutrient concentration and partitioning in maize (Zea mays L.) were investigated. Strong interactions were observed between photoperiod and root-zone temperature on the growth and concentration of numerous mineral elements in the plant tops and roots. For example, a threefold increase in photoperiod (from 6 to 18 h) did not affect the growth of tops or roots if the root-zone temperature was 9°C but increased them each by eightfold if the root-zone temperature was 21°C. On the other hand, raising the root-zone temperature from 9 to 21°C increased the growth of tops and root each by ca. threefold when plants were grown with 6 h of light. At 18 h photoperiod, however, plant growth was increased 20- to 30-fold by the same rise in the root-zone temperature. The concentrations of different mineral elements in the roots and tops were affected quite differently by the interacting effects of photoperiod and root-zone temperature. In general, increasing the photoperiod at a given root-zone temperature decreased the concentrations of elements while increasing the root-zone temperature at a given photoperiod increased the concentrations of most elements in both roots and tops. The exceptions were K and B which reacted opposite to each other: K concentration in both tops and roots was relatively insensitive to photoperiod but very sensitive to root-zone temperature and the reverse was true for boron. The relative insensitivity of plant growth to increased day length as long as the roots are subjected to suboptimal (low) soil temperatures may have survival significance and point to the predominant role of root temperature over that of day length in the early growth of maize. A possible mechanism by which photoperiod and root-zone temperature might interactively alter the nutrient uptake by the roots is discussed.     

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.     

EFFECTS OF PHOTOPERIOD AND VERNALIZATION ON THE NUMBER OF LEAVES AT FLOWERING IN 32 ARABIDOPSIS THALIANA (BRASSICACEAE) ECOTYPES

The extent of natural variation among wild type Arabidopsis thaliana L. Heynh for response to environmental stimuli that affect flowering is poorly documented. The effects of photoperiod and vernalization on the number of rosette leaves at the time of anthesis was measured for 32 Arabidopsis ecotypes. All ecotypes were vernalized 24 days at 4 C under continuous illumination. Vernalized and nonvernalized plants were transplanted into 8- (short-day) and 20-hour (long-day) photoperiods in controlled environment growth chambers. Two ecotypes failed to flower after 110 days. Mean leaf number was less for all ecotypes under long day compared to short day. Sixteen ecotypes responded to vernalization; eight had reduced leaf number regardless of photoperiod, and eight had reduced leaf number only under short day. Two ecotypes required vernalization to flower in this study. For three ecotypes, vernalization and short day resulted in a reduction in leaf number whereas vernalization and long day resulted in increased leaf number. Documentation of the effects and interactions of photoperiod and vernalization across many ecotypes provides a broader range of described natural variation for genetic and physiologic study.     

Cytological observation of two environmental genic male-sterile lines of rice.

We report here two environmental genic male-sterilities (EGMS) in rice. These two EGMS rice lines, thermo-sensitive genic male-sterility (TGMS) and photoperiod-sensitive genic male-sterility (PGMS), are controlled by temperature and photoperiod, respectively, in determining their male-sterility. Male-sterility of the TGMS and PGMS was found to be induced when they were grown at 32 degrees C/26 degrees C (day/night) with 14 h daylight, while they were fertile at 26 degrees C/20 degrees C (day/night) with 10 h daylight in a growth chamber. We also examined their anther structures under a light microscope. The light microscopic observation revealed that the EGMS lines showed a complete pollen abortion at the sterile growth condition while they produced normal fertile pollens at the fertile growth condition.     

The influence of thermoperiod on cucumber growth and development

We studied the influence of gradient temperature regimes on various parameters of the formation of above-the-ground and underground organs of cucumber plants, such as rate of leaf appearance, rate of growth, duration of growth and length of leaves, and the rate of growth of above-the-ground organs and roots. The plants were grown under the controlled conditions: at different combinations of day and night temperature, illumination 100 Wt/m2, and 12 h photoperiod. The comparison of constant and fluctuating diurnal temperature regimes has shown that in the optimal area for all studied indices, the highest values were recorded at the constant daily temperature (25 degrees C for all growth indices of above-the-ground organs and 20 degrees C for growth of roots), while all gradient regimes either did not affect, or exerted inhibitory effects on the plant. The main acting fluctuating temperatures, that exerted stimulating effects, combined low hardening (15 degrees C) and optimal temperatures (25 degrees C), which was earlier described for animals. The 15/35 and 35/15 degrees C combinations were unambiguously inhibitory, since both temperatures are hardening for the cucumber. A lesser stimulating effect of the developmental rate in a plant, as compared to poikilothermic animals, could be due to a greater autonomy of plant ontogenesis because of autotrophy and, correspondingly, a greater degree of homeostasis. The mechanisms accounting for the reactions to temperature gradients are similar in different groups of ectotherms.     

Influence of photoperiod and temperature on reproductive mode in the Brine shrimp, Artemia franciscana

Brine shrimp, Artemia, exhibit two modes of reproduction: oviparity (diapause cyst production) and ovoviviparity (live larvae release). Environmental conditions determining these developmental routes are poorly understood, so we investigated the effects of photoperiod and temperature on reproductive mode. Nauplii of A. franciscana were hatched from cysts produced in the Great Salt Lake, Utah, and raised in 2% natural sea salt water under photoperiods of 24, 14, 12, or 10 h at 28 degrees or 20 degrees C. Mating pairs of mature shrimp were isolated and reared continuously under those conditions. The mode of reproduction shown by each pair was determined daily throughout their life span, and found to be greatly affected by photoperiod, and less influenced by temperature. The relative degree of oviparity increased as the photoperiod became shorter at both temperatures. In contrast, the degree of ovoviviparity was higher as the photoperiod became longer at both temperatures. The critical photoperiod appears to be between 12 and 14 h. For all photoperiods examined, the degree of oviparity was higher at 28 degrees C than at 20 degrees C, whereas the degree of ovoviviparity was greater at 20 degrees C than at 28 degrees C.     

Temperature during the day, but not during the night, controls flowering of Phalaenopsis orchids

Phalaenopsis orchids are among the most valuable potted flowering crops commercially produced throughout the world because of their long flower life and ease of crop scheduling to meet specific market dates. During commercial production, Phalaenopsis are usually grown at an air temperature > or =28 degrees C to inhibit flower initiation, and a cooler night than day temperature regimen (e.g. 25/20 degrees C day/night) is used to induce flowering. However, the specific effect of day and night temperature on flower initiation has not been well described, and the reported requirement for a diurnal temperature fluctuation to elicit flowering is unclear. Two Phalaenopsis clones were grown in glass greenhouse compartments with constant temperature set points of 14, 17, 20, 23, 26, or 29 degrees C and fluctuating day/night (12 h/12 h) temperatures of 20/14, 23/17, 26/14, 26/20, 29/17, or 29/23 degrees C. The photoperiod was 12 h, and the maximum irradiance was controlled to < or =150 micromol m(-2) s(-1). After 20 weeks, > or =80% of plants of both clones had a visible inflorescence when grown at constant 14, 17, 20, or 23 degrees C and at fluctuating day/night temperatures of 20/14 degrees C or 23/17 degrees C. None of the plants were reproductive within 20 weeks when grown at a constant 29 degrees C or at 29/17 degrees C or 29/23 degrees C day/night temperature regimens. The number of inflorescences per plant and the number of flower buds on the first inflorescence were greatest when the average daily temperature was 14 degrees C or 17 degrees C. These results indicate that a day/night fluctuation in temperature is not required for inflorescence initiation in these two Phalaenopsis clones. Furthermore, the inhibition of flowering when the day temperature was 29 degrees C and the night temperature was 17 degrees C or 23 degrees C suggests that a warm day temperature inhibits flower initiation in Phalaenopsis.     

Effects of photoperiod and temperature on diapause induction and termination in the swallowtail,Sericinus montelus

Abstract Sericinus montelus overwinters as diapausing pupae. In the present study, the effects of photoperiod and temperature on diapause induction and termination of diapause are investigated. The results obtained demonstrate that high temperature can reverse the effect of short day‐lengths on diapause induction. Under an LD 12 : 12 h photoperiod, all pupae enter diapause at 15, 20 and 25 °C, whereas all pupae develop without diapause at 35 °C. No pupae enter diapause under an LD 14 : 10 h photoperiod when the temperature is above 20 °C. Photoperiodic response curves obtained at 25 and 30 °C indicate that S. montelus is a long‐day species and the critical day‐length is approximately 13 h at 25 °C. At 25 °C, the duration of diapause is shortest when the diapausing pupae are maintained under an LD 16 : 8 h photoperiod and increases under LD 14 : 10 h and LD 12 : 12 h photoperiods. Under an LD 16 : 8 h photoperiod, the duration of diapause is shortest when the diapausing pupae are maintained at 25 °C, followed by 20 and 30 °C, and then at 15 °C. These results suggest that a moderate temperature favours diapause development under a diapause‐averting photoperiod in this species. The duration of diapause induced by an LD 12 : 12 h photoperiod is significantly longer at 25 °C than those at 15, 20 and 30 °C, and is shortest at 15 °C. At 25 °C, the duration of diapause induced by LD 6 : 18, LD 12 : 12 and LD 13 : 11 h photoperiods is similar and longer than 90 days. Thus, the diapause‐inducing conditions may affect diapause intensity and a photoperiod close to the critical day‐length has significant influence on diapause intensity in S. montelus.     

Effect and interaction of temperature and photoperiod on growth and partitioning in three groundnut (Arachis hypogaea L.) genotypes1

Effect of temperature and photoperiod and their interaction on plant growth and partitioning of dry matter to pods was examined in three selected groundnut genotypes viz., TMV 2, NC Ac 17090 and VA 81B. The genotypes were grown in six walk-in growth chambers which were programmed to simulate three temperature regimes (22/18°C, 26/22°C and 30/26°C day/night) each under long (12 h) and short (9 h) photoperiods. The plant growth rates and partitioning of dry matter to pods were estimated on a thermal time basis. Plant growth rate (PLGR) was significantly influenced by temperature, photoperiod and genotype, whereas pod growth rate (PDGR) was influenced primarily by temperature and genotype. The interaction of genotype with photoperiod and with temperature was significant for both PLGR and PDGR. For example, at the 22/18°C temperature regime, VA 81B had a high PDGR, while NC Ac 17090 did not even initiate pod growth. The partitioning of dry matter to pods (Pf) was also significantly influenced by photoperiod, temperature and genotype, and significant interactions were found. Photoperiod did not significantly affect Pf under the low temperature regime, but at higher temperatures, partitioning to pods was significantly greater under short days. Pf of VA 81B was relatively insensitive to photoperiod compared with the other two genotypes. The study provided evidence of genotypic variability for photoperiod × temperature interactions which could influence adaptation of groundnut genotypes to new environments.     

Thermoperiodic stem elongation involves transcriptional regulation of gibberellin deactivation in pea

The physiological basis of thermoperiodic stem elongation is as yet poorly understood. Thermoperiodic control of gibberellin (GA) metabolism has been suggested as an underlying mechanism. We have investigated the influence of different day and night temperature combinations on GA levels, and diurnal steady-state expression of genes involved in GA biosynthesis (LS, LH, NA, PSGA20ox1, and PsGA3ox1) and GA deactivation (PsGA2ox1 and PsGA2ox2), and related this to diurnal stem elongation in pea (Pisum sativum L. cv Torsdag). The plants were grown under a 12-h light period with an average temperature of 17 degrees C. A day temperature/night temperature combination of 13 degrees C/21 degrees C reduced stem elongation after 12 d by 30% as compared to 21 degrees C/13 degrees C. This was correlated with a 55% reduction of GA1. Although plant height correlated with GA1 content, there was no correlation between diurnal growth rhythms and GA1 content. NA, PsGA20ox1, and PsGA2ox2 showed diurnal rhythms of expression. PsGA2ox2 was up-regulated in 13 degrees C/21 degrees C (compared to 21 degrees C/13 degrees C), at certain time points, by up to 19-fold. Relative to PsGA2ox2, the expression of LS, LH, NA, PSGA20ox1, PsGA3ox1, and PsGA2ox1 was not or only slightly affected by the different temperature treatments. The sln mutant having a nonfunctional PsGA2ox1 gene product showed the same relative stem elongation response to temperature as the wild type. This supports the importance of PsGA2ox2 in mediating thermoperiodic stem elongation responses in pea. We present evidence for an important role of GA catabolism in thermoperiodic effect on stem elongation and conclude that PsGA2ox2 is the main mediator of this effect in pea.     

Low temperature limits photoperiod control of smolting in atlantic salmon through endocrine mechanisms

We have examined the interaction of photoperiod and temperature in regulating the parr-smolt transformation and its endocrine control. Atlantic salmon juveniles were reared at a constant temperature of 10 degrees C or ambient temperature (2 degrees C from January to April followed by seasonal increase) under simulated natural day length. At 10 degrees C, an increase in day length [16 h of light and 8 h of darkness (LD 16:8)] in February accelerated increases in gill Na(+)-K(+)-ATPase activity, whereas fish at ambient temperature did not respond to increased day length. Increases in gill Na(+)-K(+)-ATPase activity under both photoperiods occurred later at ambient temperature than at 10 degrees C. Plasma growth hormone (GH), insulin-like growth factor, and thyroxine increased within 7 days of increased day length at 10 degrees C and remained elevated for 5-9 wk; the same photoperiod treatment at 2 degrees C resulted in much smaller increases of shorter duration. Plasma cortisol increased transiently 3 and 5 wk after LD 16:8 at 10 degrees C and ambient temperature, respectively. Plasma thyroxine was consistently higher at ambient temperature than at 10 degrees C. Plasma triiodothyronine was initially higher at 10 degrees C than at ambient temperature, and there was no response to LD 16:8 under either temperature regimen. There was a strong correlation between gill Na(+)-K(+)-ATPase activity and plasma GH; correlations were weaker with other hormones. The results provide evidence that low temperature limits the physiological response to increased day length and that GH, insulin-like growth factor I, cortisol, and thyroid hormones mediate the environmental control of the parr-smolt transformation.