Chilling Period Research Articles

Optimal Low Temperature and Chilling Period for Both Summer and Winter Diapause Development in Pieris melete: Based on a Similar Mechanism

The cabbage butterfly, Pieris melete hibernates and aestivates as a diapausing pupa. We present evidence that the optimum of low temperature and optimal chilling periods for both summer and winter diapause development are based on a similar mechanism. Summer or winter diapausing pupae were exposed to different low temperatures of 1, 5, 10 or 15°C for different chilling periods (ranging from 30 to 120 d) or chilling treatments started at different stages of diapause, and were then transferred to 20°C, LD12.5∶11.5 to terminate diapause. Chilling temperature and duration had a significant effect on the development of aestivating and hibernating pupae. The durations of diapause for both aestivating and hibernating pupae were significantly shorter when they were exposed to low temperatures of 1, 5 or 10°C for 50 or 60 days, suggesting that the optimum chilling temperatures for diapause development were between 1 and 10°C and the required optimal chilling period was about 50–60 days. Eighty days of chilling was efficient for the completion of both summer and winter diapause. When chilling periods were ≥90 days, the durations of summer and winter diapause were significantly lengthened; however, the adult emergence was more synchronous. The adaptive significance of a similar mechanism on summer and winter diapause development is discussed.

Meat quality of swine supplemented with ractopamine under commercial conditions in Brazil1

Commercial crossbred barrows and gilts (n = 340) were used to study the effects of different dietary inclusions of ractopamine hydrochloride (RAC) on quality of LM and semimembranosus muscle (SM). Pigs were blocked by BW (107.3 ± 0.76 kg) and allotted to gender-specific pens (10 to 12 pigs/pen), and within blocks, pens of barrows or gilts (10 pens/treatment) were randomly assigned to 1 of 3 dietary RAC inclusions (0, 5, or 10 mg/kg) fed during the last 28 d before slaughter. Initial (45-min) and ultimate (24-h) pH and temperature were measured in LM and SM. Visual and instrumental [lightness (L*), redness (a*), and yellowness (b*) values] color as well as drip loss percentages were measured in both muscles after the 24-h chilling period at 1 to 4 °C. The LM was also evaluated for marbling, and samples of the LM were used to measure intramuscular fat (IMF) content, cooking losses, and Warner-Bratzler shear force (WBSF). Pork quality characteristics of the LM (P ≥ 0.227) and SM (P ≥ 0.082) did not differ between barrows and gilts. Furthermore, neither pH nor temperature of the LM (P ≥ 0.164) or SM (P ≥ 0.284) was affected by feeding pigs RAC. The LM from pigs fed 10 mg/kg of RAC received lesser (P = 0.032) subjective color scores than LM from pigs fed 0 and 5 mg/kg of RAC, and LM from pigs fed 10 mg/kg of RAC was less (P = 0.037) red than LM from pigs fed 0 mg/kg of RAC. In addition, SM from pigs fed 10 mg/kg of RAC had lesser (P ≤ 0.015) a* and b* values than pork from control-fed pigs; however, L* values for LM and SM were not (P ≥ 0.081) affected by dietary RAC. Drip loss percentages of the LM were similar (P = 0.815) among RAC treatments, but the SM from RAC-fed pigs had smaller (P = 0.020) drip loss percentages than SM from pigs fed 0 mg/kg of RAC. Marbling scores and IMF content of the LM did not (P ≥ 0.133) differ among RAC treatments; however, WBSF values were greater (P = 0.005) for LM chops from pigs fed 10 mg/kg than chops from pigs fed 0 and 5 mg/kg of RAC. Even though feeding barrows and gilts 10 mg/kg of dietary RAC reduced (P = 0.050) cooking losses of LM chops compared with feeding 5 mg/kg of RAC, including 10 mg/kg of RAC in the diet of finishing pigs reduced pork tenderness. Therefore, results from this study support the recommendation that including 5 mg/kg of RAC in finishing diets should improve live pig performance without detrimental effects on fresh pork quality and cooked pork palatability.

Drought-induced chilling tolerance in cucumber involves membrane stabilisation improved by antioxidant system

We assessed changes in ultrastructure, membrane lipid peroxidation and antioxidant systems for cucumbner seedlings subjected to low temperature stress (day/night temperature of 8 o C /5 o C) that had been either pre-treated with 10% PEG for 2 days or not. We found extensive cell structure damage in the non-treated seedlings, whereas the seedlings pretreated with PEG to simulate drought remained essentially undamaged, except for slight damage to plasma membrane lipids and alveolation in the mitochondria. Low temperature stress increased electrolyte leakage, MDA levels and H2O2; decreased the activities of SOD, CAT and APX, and AsA and GSH content. An increase in POD activity was observed in the PEG-pretreated seedlings during the chilling period, while non-treated seedlings showed an increase in POD activity only in the early days of chilling stress. PEG pre-treatment diminished the level of lipid peroxidation caused by chilling compared to the non-treated seedlings, possibly due to a decrease in electrolyte leakage and MDA content. Furthermore, PEG pre-treatment increased the activities of SOD, POD, CAT and APX and AsA and GSH content in the chilling-stressed seedlings. These results suggest that PEG pre-treatment stimulates the adaptation of cucumber to low temperature. This could be due to stabilisation of the cell structure, alleviation of lipid peroxidation as a result of the increased activity of antioxidant enzymes and contents of antioxidant metabolites.

Identification of chilling and heat requirements of cherry trees—a statistical approach

Most trees from temperate climates require the accumulation of winter chill and subsequent heat during their dormant phase to resume growth and initiate flowering in the following spring. Global warming could reduce chill and hence hamper the cultivation of high-chill species such as cherries. Yet determining chilling and heat requirements requires large-scale controlled-forcing experiments, and estimates are thus often unavailable. Where long-term phenology datasets exist, partial least squares (PLS) regression can be used as an alternative, to determine climatic requirements statistically. Bloom dates of cherry cv. ‘Schneiders späte Knorpelkirsche’ trees in Klein-Altendorf, Germany, from 24 growing seasons were correlated with 11-day running means of daily mean temperature. Based on the output of the PLS regression, five candidate chilling periods ranging in length from 17 to 102 days, and one forcing phase of 66 days were delineated. Among three common chill models used to quantify chill, the Dynamic Model showed the lowest variation in chill, indicating that it may be more accurate than the Utah and Chilling Hours Models. Based on the longest candidate chilling phase with the earliest starting date, cv. ‘Schneiders späte Knorpelkirsche’ cherries at Bonn exhibited a chilling requirement of 68.6 ± 5.7 chill portions (or 1,375 ± 178 chilling hours or 1,410 ± 238 Utah chill units) and a heat requirement of 3,473 ± 1,236 growing degree hours. Closer investigation of the distinct chilling phases detected by PLS regression could contribute to our understanding of dormancy processes and thus help fruit and nut growers identify suitable tree cultivars for a future in which static climatic conditions can no longer be assumed. All procedures used in this study were bundled in an R package (‘chillR’) and are provided as Supplementary materials. The procedure was also applied to leaf emergence dates of walnut (cv. ‘Payne’) at Davis, California.Electronic supplementary materialThe online version of this article (doi:10.1007/s00484-012-0594-y) contains supplementary material, which is available to authorized users.

Kualitas Fisik Daging Sapi Peranakan Simmental dengan Perlakuan Stimulasi Listrik dan Lama Pelayuan yang Berbeda

This research was conducted to observe the influence of electric stimulation and chilling period on meat of Simmental cross. This experiment used factorial design with 5 blocks. The first factor was electric stimulation (with and without electric stimulation), the second factor was chilling period (0, 12 and 24 hours). Around 7.5 kg Simmental cross meat (Tricep brachii) from 5 head were used on this research. The observed variables were pH, cooking loss and tenderness. The results showed that there was no interaction of electric stimulation and chilling period (up to 24 hours) on all of observed variables. Electric stimulation treatment was significant improved tenderness of Simmental cross beef but it was not significant on pH and cooking loss. There was significant influenced of chilling period on pH, cooking loss and tenderness of Simmental cross beef.

EFFECTS OF SOAKING TEMPERATURE, STRATIFICATION, POTASSIUM NITRATE AND GIBBERELLIC ACID ON SEED GERMINATION OF LOQUAT TREES

The present study was carried out to increase loquat seed germination with treatments consisting of two soaking temperatures (24 ± 2°C and 38 ± 2°C), chemical agents [control, 0.5% potassium nitrate (KNO3) and 250 mgL−1 gibberellic acid (GA3) each for 20 h], and different moist chilling (MC) periods (1, 2, 3 and 4 weeks under 4–5°C). Compared with 24 ± 2°C, soaking at 38 ± 2°C reduced germination%, mean daily germination (MDG), and mean germination time (MGT), plumule and radicle lengths. Germination percentage, days to 50% emergence, fresh weight and lateral root numbers significantly reduced as MC period increased. KNO3 and GA3 had no significant effect on germination percentage, MDG, MGT and lateral root numbers. KNO3 reduced days to 50% emergence and radicle length, but increased fresh weight compared with control and GA3. Finally, our results suggest the soaking at 24 ± 2°C followed by 0.5% KNO3 each for 20 h plus 1 week of MC or soaking at 24 ± 2°C followed by 250 mgL−1 GA3 each for 20 h plus 2 week of MC.

Influence of Cool Storage before Freezing on the Quality of Frozen–Thawed Semen Samples in Dogs

The aim of this study was to determinate the semen quality of frozen-thawed samples that were chilled for up to 2 days before freezing. The ejaculates (n = 18) from six dogs were collected, pooled and divided into six aliquots. The first aliquot (C, control) was frozen in liquid nitrogen using a conventional protocol to reach a final concentration of 100 × 10(6) spermatozoa/ml, 20% egg yolk and 5% glycerol. The remaining five aliquots were diluted with a chilled extender (Tris-glucose and 20% egg yolk) and cooled at 4 °C as follows: R1, the semen was cooled for 1 h; R6, the semen was cooled for 6 h; R12, the semen was cooled for 12 h; R24, the semen was cooled for 24 h and R48, the semen was cooled for 48 h. After the chilling period, a second extender was added (Tris-glucose, 20% egg yolk, 10% glycerol and Equex at 1%) to reach a final composition similar to aliquot C, and then, the semen samples (R1, R6, R12, R24 and R48) were frozen in liquid nitrogen. The post-thaw sperm quality was assessed in 30 straws from each experimental group. After freezing-thawing, the total sperm motility (approximately 60-70%) in the semen chilled for up to 48 h did not show any differences from the samples frozen by the conventional cryopreservation method (63.2%). No significant differences were detected in the percentages of abnormal sperm cells among the fresh semen, the control group and the frozen samples after the different cooling times. Finally, the post-thaw percentages of damaged acrosomes showed a very uniform distribution, with mean values ranging between 7% and 10.5%. The results clearly demonstrated that cooling the semen up to 48 h before freezing did not produce a decrease in the semen quality when was compared with semen frozen by a traditional procedure.

Chilling-Dependent Release of Seed and Bud Dormancy in Peach Associates to Common Changes in Gene Expression

Reproductive meristems and embryos display dormancy mechanisms in specialized structures named respectively buds and seeds that arrest the growth of perennial plants until environmental conditions are optimal for survival. Dormancy shows common physiological features in buds and seeds. A genotype-specific period of chilling is usually required to release dormancy by molecular mechanisms that are still poorly understood. In order to find common transcriptional pathways associated to dormancy release, we analyzed the chilling-dependent expression in embryos of certain genes that were previously found related to dormancy in flower buds of peach. We propose the presence of short and long-term dormancy events affecting respectively the germination rate and seedling development by independent mechanisms. Short periods of chilling seem to improve germination in an abscisic acid-dependent manner, whereas the positive effect of longer cold treatments on physiological dwarfing coincides with the accumulation of phenylpropanoids in the seed.

Uncertainties in terrestrial carbon budgets related to spring phenology

In temperate regions, the budburst date of deciduous trees is mainly regulated by temperature variation, but the exact nature of the temperature dependence has been a matter of debate. One hypothesis is that budburst date depends purely on the accumulation of warm temperature; a competing hypothesis states that exposure to cold temperatures is also important for budburst. In this study, variability in budburst is evaluated using 15 years of budburst data for 17 tree species at Harvard Forest. We compare two budburst hypotheses through reversible jump Markov chain Monte Carlo. We then investigate how uncertainties in budburst date mapped onto uncertainties in ecosystem carbon using the Geophysical Fluid Dynamics Laboratory's LM3 land model. For 15 of 17 species, we find that more complicated budburst models that account for a chilling period are favored over simpler models that do not include such dependence. LM3 simulations show that the choice of budburst model induces differences in the timing of carbon uptake commencement of ∼11 days, in the magnitude of April–May carbon uptake of ∼1.03 g C m−2day−1, and in total ecosystem carbon stocks of ∼2 kg C m−2. While the choice of whether to include a chilling period in the budburst model strongly contributes to this variability, another important factor is how the species‐dependent field data gets mapped onto LM3's single deciduous plant functional type (PFT). We conclude budburst timing has a strong impact on simulated CO2fluxes, and uncertainty in the fluxes can be substantially reduced by improving the model's representation of PFT diversity.

EFFECT OF CHILLING AND TWO PGRS ON SEED DORMANCY OF QARE-QAT BERRY (VACCINIUM ARCTOSTAPHYLOS L.)

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Berries: From Genomics to Sustainable Production, Quality and Health EFFECT OF CHILLING AND TWO PGRS ON SEED DORMANCY OF QARE-QAT BERRY (VACCINIUM ARCTOSTAPHYLOS L.)

Garlic physiological characteristics from harvest to sprouting in response to low temperature

Garlic is a perennial vegetable crop which belongs to liliaceae family and propagated by bulbs. Garlic sprouting depends on air temperature and its storage period. This study was conducted to investigate physiological trait variations from sprouting to harvest of garlic cv. White Gorgan stored in low temperature (4°C). Toward this end, variations of chlorophyll, carotenoid, carbohydrates, as well as the activity of Amylase and Invertase enzymes were measured before and after chilling treatment for 15 and 30 days. Obtained results showed a significant difference among measured traits (p < 0.01). Chlorophyll a, chlorophyll b, chlorophyll ab, carotenoid, glucose, and activity of Amylase and Invertase enzymes were increased in response to increment of chilling period which reached their highest values after 30 days. Sucrose and starch had the highest contents in the beginning of experiment and reached to their lowest value after chilling treatment (p < 0.01). Results of correlation analysis indicates negative correlation of all chlorophyll types with total sugar, sucrose and starch, while all chlorophyll types had positive correlation with glucose, a-amylase, b-amylase and Invertase. Increment of chilling treatment is followed by a-amylase and b-amylase increment as well as decreased starch content of Bulblets. Starch content showed a negative correlation with a-amylase and b-amylase. Also sucrose content was negatively correlated with invertase (p < 0.01). In conclusion, storage of garlic cv. White Gorgan in 4°C for 30 days had the best sprouting result. Key words: Garlic, sprouting, chilling, carbohydrate, enzyme.

Laboratory survival of Drosophila suzukii under simulated winter conditions of the Pacific Northwest and seasonal field trapping in five primary regions of small and stone fruit production in the United States

Drosophila suzukii was first found in Oregon in August 2009. The threat of this pest to regional small and stone fruit production industries led to investigations on its overwintering capabilities in fruit-growing regions in the Pacific Northwest. Knowledge of its cold tolerance will help in the development of computer models to forecast seasonal population growth and decline. Of 1500 adults or pupae, 22 (1.4%) individuals survived the 84 day experimental chilling period. Most (86%) of the survivors were subjected to 10 °C temperature treatments. Survival decreased significantly at lower temperature treatments. Freezing temporarily increased the mortality rate but did not significantly affect overall mortality over the trial period. Flies that emerged from pupae are estimated to survive for up to 103-105 days at 10 °C and for shorter periods at lower temperatures. Field trapping in five fruit production areas has demonstrated overwintering survival in California and Oregon, but lower survival is predicted in Eastern Washington and Michigan. The experiments reported here indicate that long-term survival of D. suzukii is unlikely at temperatures below 10 °C. Field data from five climatic regions indicated extended low initial D. suzukii field presence in 2010 in all regions except California, where field presence was recorded earlier.

Mechanism of seed dormancy and its relationship to bud dormancy in Persian walnut

Stratification, chilling, and heat requirements for both seeds and buds of five Persian walnut genotypes were compared. In experiments carried out between November 2006 and March 2008, 1-year-old twigs were collected after leaf-fall, placed in plastic bags, and kept at 4 ± 1 °C to provide chilling periods ranging from 400 to 1500 h. After chilling, twigs were transferred to a greenhouse for determination of chilling requirement and the number of growing degree hours (°C) needed for bud break. For germination experiments, mature seeds were stratified at 4 ± 1 °C for treatment periods ranging from 0 to 8 weeks and then grown in a greenhouse under natural conditions. Germination rate and time to radicle emergence were recorded weekly and seedling heights were recorded after 2 months growth. Results indicated genotypes could be classified into three dormancy groups based on their chilling and heat requirements: low (‘Ronde de Montignac’ and ‘Serr’), medium (‘Z 53’), and high (‘Lara’ and ‘Z 63’) dormancy. Stratification for 6–8 weeks was most appropriate to overcome walnut seed dormancy, to obtain the best germination percentage and germination rate, and to prevent physiological dwarfing. A relationship between the chilling and heat requirements for bud-break and the stratification requirement for germination of seeds was observed and data showed that the nutshell is a mechanical barrier to germination in walnut seeds with intermediate physiological dormancy.

Chilling-induced oxidative stress and polyamines regulatory role in two wheat varieties

Fifteen-day-old seedlings of two wheat varieties (Side 1 & Gimmiza 7) were randomly separated into three equal groups to investigate the effect of chilling stress on their antioxidant defense system. Moreover, the possible role of polyamines (PAs) pretreatment during alleviating chilling injuries. The first group was kept in a green house at 21/15°C (day/night) and 10: 14h light/dark (−ve control). Second seedlings group were chilled at 5°C for 6 or 9 hours (+ve control). The Seedlings of the third group were divided into three sub-groups and sprayed with 0.5, 1.0 and 2.0mM spermidine (Spd). After 12 hours of polyamine pre-treatments, the seedlings were incubated at 5°C for 6 or 9 hours. At the end of the chilling period, the treated plants were transferred to the pre-experimental conditions in the greenhouse where they recovered for 10 days. Chilling stress induced a significant increase of lipid peroxidation, membrane leakage and hydrogen peroxide level, while Spd treatments resulted in a significant decrease. In addition, endogenous PA level increased in response to chilling stress. Activities of catalase, peroxidase and ascorbate peroxidase declined after the exposure to chilling whereas glutathione and free ascorbate increased. Spd treatments alleviated the injury caused by chilling stress by preventing the decrease in the activity of the antioxidant enzymes. It can be concluded that the stress protection caused by spermidine treatment probably contributes to the enhancement of the activity of the free-radical scavenging systems. Moreover, it was clear that the Sids-1 cultivar was more tolerant to chilling stress than Gemmieza-7cultivar.

Photothermal control of the reproductive cycle in temperate fishes

AbstractTemperate fish species are annual spawners and mainly rely on annually cycling cues (temperature and photoperiod) to synchronise the three main phases of their reproductive cycle, that is, induction (initiation of oogenesis), vitellogenesis and the final stages (including maturation, ovulation and oviposition). This review synthesises how these three phases are controlled by specific temperature and photoperiod variations. The direction of the changes (i.e. decrease or increase) is the most important factor, although the amplitude, rates and timing of variations should also be considered to improve/optimise the quality of reproduction in aquaculture. In addition, we tentatively classified temperate fish species sharing similar temperature and/or photoperiod variation requirements for reproduction into three general functional groups. The first group (salmonids) is induced by increasing photoperiod. Vitellogenesis and the final stages are synchronised by decreasing photoperiod. The second group (percids, moronids and gadids) is induced by decreasing both temperature and photoperiod. A chilling period allows vitellogenesis. Increasing temperatures synchronise the final stages. The third group (cyprinids) is induced by decreasing either photoperiod or temperature. Vitellogenesis is faster at warm temperatures. The final stages require an increase in either photoperiod or temperature. This classification may help future research on the control of reproduction in newly cultured fish species.

Responses of Antioxidant Enzymes to Chilling Stress in Tobacco Seedlings

Chilling is one of the major abiotic stresses limiting yield and quality of many important crops. For better understanding of chilling stress responses in tobacco ( Nicotiana tabacum), growth rate and antioxidant enzymes of seedlings in 2 tobacco cultivars, viz., MSk326 (chilling sensitive variety) and Honghuadajinyuan (HHDJY, chilling tolerant variety) at chilling temperature (5÷C) were studied. The results showed that the relative growth rate in chilling period to that in recovery period was significantly higher in roots than that in shoots for both cultivars, suggesting that shoots growth was more easily affected by chilling stress. Chilling stress increased peroxidase (POD) activity and reduced superoxide dismutase (SOD) activity in shoots of HHDJY, and catalase (CAT) activity was little affected. In the roots of HHDJY, chilling stress increased SOD and CAT activities, and had little effect on POD activity. For MSk326, chilling treatment increased SOD activity in shoots and declined CAT activity in roots. MDA concentration in both varieties was increased under the chilling stress, while it was decreased after seedlings were recovered growth for 4 d at normal temperature (25÷C). It showed that tobacco seedlings might have the capacity of recovering from chilling injury for a short term. The relationship between the growth rate and antioxidant enzyme activity was analyzed by stepwise regression. It was found that there was a close relationship between relative growth rate of tobacco seedlings and CAT activity under chilling stress condition and regression equations containing CAT could be used in predicting seedling growth rate of tobacco under chilling stress condition.

Chilling relieves corm dormancy in Calopogon tuberosus (Orchidaceae) from geographically distant populations

Many plant species require a chilling period to commence regrowth from overwintering structures such as buds, corms, tubers, and rhizomes. While the effects of chilling have been thoroughly studied in a horticultural context, little information exists regarding the relationship between ecotypic differentiation and chilling requirements. Effects of chilling storage organs on shoot emergence of widespread orchid species has not been examined, and ecotypic differentiation in the Orchidaceae has also received little attention. The effects of chilling on corm dormancy in Calopogon tuberosus, a widespread orchid of eastern North America, were studied. Seeds were collected from south Florida, north central Florida, South Carolina, and Michigan, and germinated in vitro to produce plants. After 20 weeks in vitro culture, corms were removed from seedlings and chilled for 0, 2, 4, 6, and 8 weeks. Corms were subsequently planted in a soilless potting mix and placed under ex vitro conditions in an environmental growth chamber. Shoot emergence was monitored bi-weekly for 16 weeks, and shoot length, leaf number, leaf width, root number, root length, and corm diameter were measured after 16 weeks. Longer chilling periods broke corm dormancy more effectively than shorter chilling treatments regardless of population. Shoots of all populations sprouted rapidly on corms after 6 and 8 weeks chilling. In addition, a higher percentage of shoots sprouted on corms after 8 weeks chilling. After 16 weeks, north central Florida and South Carolina plantlets were larger than Michigan and south Florida plantlets. Differing chilling requirements among C. tuberosus populations may reflect ecotypic differentiation resulting from varying environmental conditions at each site.

A proteomic approach to decipher chilling response from cold acclimation in pea (Pisum sativum L.)

Two pea lines (Pisum sativum L.) with contrasted behaviours towards chilling and subsequent frost were studied by a proteomic approach to better understand cold acclimation. Following a chilling period, the Champagne line becomes tolerant to frost whereas Terese remains sensitive. Variance analysis allowed to select 260 statistically variable spots with 68 identified proteins (35 in leaves, 18 in stems, and 15 in roots). These proteins were shared out in proteins related to chilling response or cold acclimation. The better adaptation of Champagne to chilling might be related to a higher content in proteins involved in photosynthesis and in defence mechanisms. Moreover Champagne might prevent freezing damage particularly thanks to a higher constitutive expression of housekeeping proteins related to Terese. After three days of subsequent frost, proteomes of previously chilled plants also showed significant differences compared to unchilled plants. Out of 112 statistically variable spots (44 in leaves, 38 in stems, and 30 in roots), 32 proteins were identified. These proteins were related to frost response or frost resistance. It seems that Champagne could resist to frost with the reorientation of the energy metabolism.

Limitations for prolonged chilled storage of zebrafish (Danio rerio) embryos

Chilled storage of zebrafish embryos is possible for up to 33 h at 8 °C without a loss in viability. In the present study, higher chilling temperatures in the range of 10–16 °C were tested to extend the storage periods to 65 h. It was also investigated whether prevention of microbiological growth with antibiotics and iodine, and stabilization of the quality of the storage solution by regular changes and constant aeration had an effect on the embryo and larvae viability. At incubation temperatures of 10 and 12 °C, the embryo development was completely arrested; at 14 and 16 °C, it proceeded slowly. At 10 °C, the percentage of embryos developing to the long-pec stage was significantly lower than those at 12, 14 and 16 °C and in the control. At 10 and 12 °C, the percentage of embryos developing to the long-pec stage decreased with increasing chilling period, while it remained constant at 14 and 16 °C. All chilling treatments resulted in low hatching rates <25% and many larvae showed malformations. Supplementation of storage solutions with antibiotics and iodine had no effect on the embryo and larvae viability, similar to regular solution changes and constant aeration.

Isolation and Identification of an Anti-Bolting Compound, Hexadecatrienoic Acid Monoglyceride, Responsible for Inhibition of Bolting and Maintenance of the Leaf Rosette in Radish Plants

Generally, the bolting (stem elongation from rosette plants) of winter annuals is believed to be induced by an increase in the levels of gibberellin that occurs after a certain period of chilling (vernalization), and a deficiency of gibberellin allows the plant to maintain a rosette style. Lack of direct evidence proving the above assumption in radish plants (Raphanus sativus L.) encouraged us to assume the presence of an anti-bolting compound actively maintaining the rosette habit through inhibition of bolting. Anti-bolting activity was detected in an extract of rosette shoots of radish plants by an assay using seedlings cultured in vitro. The causal compound that strongly inhibited bolting was isolated and identified as alpha-(7Z,10Z,13Z)-hexadecatrienoic acid monoglyceride (16:3 monoglyceride). This compound did not inhibit leaf production at the apical meristem, indicating that it merely inhibits growth at the internode. The compound disappeared completely after vernalization, and bolting occurred thereafter. The results suggest that the release from inhibition by 16:3 monoglyceride induces the initiation of bolting. The possible mechanism by which the compound exerts the activity is discussed.