Non-chilled Control Research Articles

Effect of chilling on the spring emergence of overwintering Eurytoma maslovskii (Eurytomidae: Hymenoptera).

This study investigated the effect of chilling temperature and duration on diapause termination in Eurytoma maslovskii, a major apricot pest in Korea and China. The experimental insects were sampled in mid-autumn. Overwintering larvae were subjected to a temperature range at -16, -4, 2, 9, 13 °C for 12 wk (a temperature of 19 °C was used for nonchilled control), and then exposed to cold temperature (2 °C) for different durations (from 1 to 16, 19, and 22 wk) at different times (20 September and 30 November) to determine adult emergence, prolonged larval diapause, and development rate postchilling. The results demonstrated a strong association between chilling temperature and duration with the emergence of E. maslovskii. It was observed that diapause may be terminated after at least 6 wk in the cold. However, the rate only reached a higher significance after 10 wk or longer duration of chilling. The optimal chilling temperature ranged from 2 to 9 °C. Late autumn chilling (mid-September) did not differ from winter chilling (late November). The postdiapause development rate of E. maslovskii was determined to be affected by the chilling duration and could be described by a 3-parameter probability density Weibull function. These results suggest that winter conditions play a crucial role in the phenology of E. maslovskii in spring.

Investigating the impact of chilling temperature on male Aedes aegypti and Aedes albopictus survival

In genetic control programmes, including the sterile insect technique (SIT), it is crucial to release insects of the highest quality with maximum survival. It is likely that male mosquitoes will follow the trend of other insects in SIT programmes and be stored, transported and eventually released under chilled conditions. The aim of our study was to investigate the impact of different chilling temperatures on male Aedes aegypti and Ae. albopictus survival by exposing them to a range of temperatures for different durations. Ae. aegypti were found to be less sensitive to the impact of chilling, with only 6°C causing a marginal decrease in survival in comparison to non-chilled controls. Conversely, Ae. albopictus displayed a significantly reduced survival at all chilling temperatures even when exposed for a short time. In both species, longer exposure to low temperatures reduced survival. Our results uncovered that Ae. albopictus are more sensitive to chilling, regardless of the temperature, when compared to Ae. aegypti. Such results indicate differences in thermal tolerances between species and the necessity of conducting experiments on a species by species basis when determining temperature limits for any insect destined for release as part of a genetic control programme.

Optimisation of Transplant Age in Combination with Dark-chilling to Enhance the Biological Quality of Broccoli Cultivated in Summer

Under field conditions, crops are exposed simultaneously to more than one environmental stress factor. Controlled abiotic stress applied at the transplant stage can be used as a tool for inducing stress memory, improving stress tolerance after transplanting, and enhancing the nutraceutical value of the yield. The aim of present study was to determine the effect of dark-chilling at 2 °C for 1 and 2 weeks on the tolerance of broccoli seedlings of various ages against adverse conditions in the field and the chemical composition of the inflorescences. Two separate planting programmes were undertaken in the summer. In general, planting delay by about 1 month resulted in an increase in dry weight of about 3%, ascorbic acid (38%), soluble sugars (18%), K (14%), P (13%), Zn (12%), Fe (8%), and Mn (9%) in broccoli inflorescences. Planting of young, 4-week-old seedlings resulted in higher ascorbic acid content in broccoli inflorescences of about 15%, soluble sugars (7%), K (5%), P (6%), Mg (4%), Na (11%), and Zn (3%) in broccoli inflorescences as compared to 10-week-old ones. Chilling of seedlings for two weeks caused an increase in dry weight in broccoli inflorescences of about 6%, ascorbic acid (15%), soluble sugars (12%), K (2%), P (2%), Mg (5%), Zn (3%), Fe (4%), and Mn (6%) as compared to the non-chilled control. The results indicated that the age of the seedlings and dark-chilling influenced the level of chemicals related to taste and biological value of broccoli inflorescences in a complex way. There was no general superiority or interaction of any of the experimental factors affecting all health-related compounds. Dark-chilling can be considered as a practice of broccoli seedling management before transplanting, positively affecting some yield parameters through stress memory induction.

Sequential abiotic stress applied to juvenile eggplant modifies the seedlings parameters, plant ontogeny and yield

The main goal of this study was to evaluate eggplant (Solanum melongena L.) susceptibility to a sequence of stress factors during plant ontogeny based on seedling morphological, biochemical and physiological parameters and the subsequent assessment of yield characteristics. After germination, seedlings at the radical stage were exposed to chilling, heat, osmotic or oxidative stress. Four weeks after development in standard conditions in a greenhouse, the seedlings were again subjected to chilling stress in a growth chamber. A non-chilled Control was implemented. Then, the yield and physiological characteristics were assessed after field cultivation. Generally, stress application after germination resulted in better plant acclimation to chilling at the 4-week-old seedling phase, evaluated on the basis of photosynthetically active pigment contents, chlorophyll fluorescence and some morphological characteristics. The comparable time to reach successive phenological stages by stressed and Control plants in the field suggests that stress pretreatment does not retard eggplant development. These results also confirm the thesis that stress memory can be induced in eggplant by stressor application during the early stages of development.

Use of methanol as cryoprotectant and its effect on sox genes and proteins in chilled zebrafish embryos

Methanol is a widely used cryoprotectant (CPA) in cryopreservation of fish embryos, however little is known about its effect at the molecular level. This study investigated the effect of methanol on sox gene and protein expression in zebrafish embryos (50% epiboly) when they were chilled for 3h and subsequently warmed and cultured to the hatching stages. Initial experiments were carried out to evaluate the chilling tolerance of 50% epiboly embryos which showed no significant differences in hatching rates for up to 6h chilling in methanol (0.2-, 0.5- and 1M). Subsequent experiments in embryos that had been chilled for 3h in 1M methanol and warmed and cultured up to the hatching stages found that sox2 and sox3 gene expression were increased significantly in hatched embryos that had been chilled compared to non-chilled controls. Sox19a gene expression also remained above control levels in the chilled embryos at all developmental stages tested. Whilst stable sox2 protein expression was observed between non-chilled controls and embryos chilled for 3h with or without MeOH, a surge in sox19a protein expression was observed in embryos chilled for 3h in the presence of 1M MeOH compared to non-chilled controls and then returned to control levels by the hatching stage. The protective effect of MeOH was increased with increasing concentrations. Effect of methanol at molecular level during chilling was reported here first time which could add new parameter in selection of cryoprotectant while designing cryopreservation protocol.

Short-term chilled storage of zebrafish (Danio rerio) embryos in cryoprotectant as an alternative to cryopreservation.

As zebrafish embryos have never been cryopreserved, we developed a protocol to store zebrafish embryos (50% epiboly-5.3 hour post fertilization) for up to 18 h at 0°C. Initial experiments to optimize the cryoprotectant (CPA) solution demonstrated improved embryo hatching rate following chilling at 0°C for 18 h with 1 M MeOH+0.1 M sucrose (56 ± 5%) compared with other combinations of methanol (0.2-0.5 M) and sucrose (0.05-0.1 M). This combination of CPAs that protects against chilling injury was further tested to assess its impact on sox gene and protein expression. Significant decreases in sox3 gene expression were observed in hatched embryos that had been chilled for 18 h in 1 M MeOH+0.1 sucrose compared with non-chilled controls, however the expression of both sox2 and sox3 proteins was unaffected. Significant decreases in sox2 protein expression were, however, observed in embryos that had been chilled without CPAs and these embryos also had lower hatching rates than those chilled with the optimal CPA solution. We, therefore, conclude that the CPA combination of 1 M MeOH+0.1 M sucrose facilitates chilled storage of early stage (50% epiboly) zebrafish embryos for up to 18 h without compromising transcriptional response.

Magnetic resonance imaging provides spatial resolution of Chilling Injury in Micro-Tom tomato (Solanum lycopersicum L.) fruit

Magnetic resonance imaging (MRI) was used to monitor internal changes in harvested tomato (Solanum lycopersicum L. cv. Micro-Tom) fruit. Measurements of ethylene evolution, respiration, and ion leakage indicated that the fruit developed chilling injury (CI) after storage at 0°C. Unlike these measurements, MRI provided spatially resolved data. The apparent diffusion coefficient (ADC), which is an indication of water mobility in tissues, was calculated from MRIs of the different parts of the fruit. Storage for 1 or 2 weeks at 0°C caused no difference in the ADCs (D-values) in the pericarp, but it did lead to higher values in the inner tissues i.e., the columella and locular region compared to non-chilled fruit (P<0.05). Changes in inner fruit D-values after 1 and 2 weeks of chilling at 0°C were similar to changes in respiration, ethylene production and ion leakage which increased (P<0.05) compared to the non-chilled controls. Most CI studies of tomato fruit used pericarp tissue. Our data indicate that columella tissue changes occur in response to chilling injury in tomato fruit and suggest that more caution is needed when interpreting data from experiments commonly used to study this phenomenon.

Dark-chilling of Seedlings Affects Initiation and Morphology of Broccoli Inflorescence

The constant supply of broccoli heads for a vegetable market can be kept by the differentiation of sowing time and the age of seedlings. Dark-chilling of young seedlings can also modify the time of transplanting, subsequent plant development, yield and inflorescence quality. The aim of the present study was to analyze the influence of seedling dark-chilling on the inflorescence initiation and the morphological quality of broccoli heads. The experiment was carried out at the University of Agriculture in Krakow (South Poland) in the years 2009 and 2010, with broccoli (Brassica oleracea L. var. italica Plenck) medium late cultivar ‘Monaco’ F1. The examined factors were the age of seedlings (4-, 6-, 8-, and 10-week-old) and dark-chilling (2°C/2 weeks and non-chilled control). Microscopic analysis of the apex sections was performed to determine the time of the inflorescence differentiation in chilled and non-chilled seedlings of different age. Chosen morphological features of the mature heads were also described as depended on age and chilling of seedlings. The inflorescence initiation was observed between 4 and 6 week of the plant ontogeny. Especially 4-week-old seedlings, chilled by two weeks, were more advanced in the generative development in comparison to non-chilled control. Low temperature applied in the seedling stage did not cause the head buttoning. Inflorescences developed by broccoli planted from 4 and 6-week-old seedlings, both chilled and control, were characterized by the best visual quality, determined by a convex head shape, tight branching angle, small and uniform size and regular form of flower buds. Chilling of oldest, 8- and 10-week-old seedlings negatively affected the inflorescence quality, through planed and spread shape of heads and non-uniform shape of flower buds.

Metabolite content of harvested Micro-Tom tomato ( Solanum lycopersicum L.) fruit is altered by chilling and protective heat-shock treatments as shown by GC–MS metabolic profiling

The primary aim of this study was to identify metabolites associated with chilling tolerance that was engendered by a heat-shock treatment of tomato fruit pericarp ( Solanum lycopersicum L. cv. Micro-Tom). Harvested mature-green fruit were immersed in 20 or 40 °C water for 7 min (‘Heat-Shock’) and then stored at 2.5 °C for 0 or 14 d (‘Chilled’). A reduction in chilling injury symptoms (i.e., slow or abnormal ripening, increased ion leakage, and increased respiration following chilling) was used to select this heat-shock treatment as optimal. Using GC–MS (Gas Chromatography–Mass Spectrometry) metabolite profiling, 363 analytes were detected in fruit pericarp of which 65 are identified metabolites. Principal Component Analysis of these data led to distinct groups among the samples based on their treatments; ‘Chilled’ and ‘Chilled + Heat-Shocked’ fruit were markedly different from each other, while the ‘Non-Chilled Control’ and ‘Heat-Shocked’ fruit were similar and grouped closer to the ‘Chilled + Heat-Shocked’ fruit. These results indicate that the heat treatment provided protection from chilling in part by altering levels of fruit metabolites. The levels of arabinose, fructose-6-phosphate, valine and shikimic acid appear to be associated with this heat-shock induced chilling tolerance since their levels were altered in the ‘Chilled’ samples ( p < 0.05), relative to the control and the heat-shocked protected fruit. We also describe the metabolites we identified that could be further studied as being indicative of incipient chilling injury in mature-green tomato fruit.

High Root Temperature Blocks Both Linear and Cyclic Electron Transport in the Dark During Chilling of the Leaves of Rice Seedlings

The most photosynthetically active leaves of rice seedlings were severely damaged when shoots but not roots were chilled (10°C/25°C, respectively), but no such injury was observed when the whole seedling was chilled (10°C/10°C). To elucidate the mechanisms, we compared the photosynthetic characteristics of the seedlings during the dark chilling treatments. Simultaneous analyses of Chl fluorescence and the change in absorbance of P700 showed that electron transport almost disappeared in both PSII and PSI in the 10°C/25°C leaves, whereas the electron transport rate in PSI in the 10°C/10°C leaves was similar to or higher than that in non-chilled control leaves. Light-induced non-photochemical quenching in PSII was inhibited in the 10°C/25°C leaves, occurring at only half the level in the 10°C/10°C leaves, whereas non-light-induced non-photochemical quenching remained high in the 10°C/25°C leaves. The light induction of Chl a fluorescence (OJIP curves) in the 10°C/25°C leaves was similar to that in leaves treated with DCMU. The fluorescence decay after a single turnover saturating flash in the 10°C/25°C leaves was much slower than in the 10°C/10°C leaves. In vivo analyses of the 550-515 nm difference signal indicated decreased formation of a proton gradient across the thylakoid membrane and decreased zeaxanthin formation in the 10°C/25°C leaves. Our results suggest that electron transport was blocked between Q(A) and Q(B) in the dark 10°C/25°C leaves, but without irreversible damage to the components of this system. The consequent light-dependent losses of electron transport, proton gradient formation across the thylakoids and thermal dissipation may therefore be responsible for the visible injury.

Induction of ethylene in avocado fruit in response to chilling stress on tree

Chilling of avocado fruit (Persea americana cv. Arad) in the orchard caused a dramatic induction of fruit ripening and a parallel increase in ethylene biosynthesis and receptor genes' expression during shelf life. In-orchard chilling stress stimulated ethylene and CO(2) production already in fruit attached to the tree, and these reduced thereafter during 20 degrees C storage. In non-chilled control fruit, ethylene and CO(2) production started after 3d at 20 degrees C and exhibited a climacteric peak. In-orchard chilling stress also led to membrane destruction expressed as higher electrical conductivity (EC) in chilling stressed (CS) fruit and accelerated softening compared with control fruit. The increase in ethylene production on the day of harvest in CS fruit was accompanied by high expression of two 1-aminocyclopropane-1-carboxylic aCSd (ACC) synthase genes: PaACS1 and PaACS2, and ACC oxidase PaACO. The initial gene expressions of PaACS1, PaACS2, and PaACO in the CS fruit at the day of harvest was similar to the levels reached by the control fruit after 4d at 20 degrees C. The expression levels of both PaETR and PaERS1 in CS fruit on tree were 25 times higher than the control. In control fruit, expression of ethylene receptor genes was very low at harvest and increased in parallel to the onset of the climacteric ethylene peak. PaCTR1 transcript levels were less affected by chilling stress, and small changes (less than 3-fold) were observed in CS fruit on the day of harvest. Together, our results suggest that ethylene biosynthesis and ethylene response-pathway genes are involved in regulation of ethylene responsiveness in response to in-orchard chilling stress and during ripening.

Effect of heat shock on the chilling sensitivity of trichomes and petioles of African violet (Saintpaulia ionantha).

Chilling at 6 degrees C caused an immediate cessation of protoplasmic streaming in trichomes from African violets (Saintpaulia ionantha), and a slower aggregation of chloroplasts in the cells. Streaming slowly recovered upon warming to 20 degrees C, reaching fairly stable rates after 4, 15, 25 and 35 min for tissue chilled for 2 min and for 2, 14 and 24 h, respectively. The rate of ion leakage from excised petioles into an isotonic 0.2 M mannitol solution increased after 12 h of chilling and reached a maximum after 3 days of chilling. A heat shock at 45 degrees C for 6 min reduced chilling-induced rates of ion leakage from excised 1-cm petiole segments by over 50%, namely to levels near that from non-chilled control tissue. Heat-shock treatments themselves had no effect on the rate of ion leakage from non-chilled petiole segments. Protoplasmic streaming was stopped by 1 min of heat shock at 45 degrees C, but slowly recovered to normal levels after about 30 min Chloroplasts aggregation was prevented by a 1 or 2 min 45 degrees C heat-shock treatment administered 1.5 h before chilling, but heat-shock treatments up to 6 min only slightly delayed the reduction in protoplasmic streaming caused by chilling. Tradescantia virginiana did not exhibit symptoms associated with chilling injury in sensitive species (i.e. cessation of protoplasmic streaming in stamen hairs and increased ion leakage from leaf tissue).

Activity of enzymatic antioxidant defense systems in chilled and heat shocked cucumber seedling radicles

Chilling whole cucumber seedlings that had 10‐mm long radicles for 4 days at 2.5°C significantly inhibited subsequent radicle growth both by increasing the time it took the seedlings to recover from chilling and attain a linear rate of radicle growth, and by decreasing the subsequent rate of linear growth. Exposing cucumber seedlings to 45°C for up to 20 min had no effect on subsequent radicle growth, while longer exposures produced reductions in growth. A heat shock at 45°C for 10 min induced the optimal protection to 4 days of chilling at 2.5°C by reducing chilling inhibition from 60 to 42%. Two hours after being chilled, heat shocked or heat shocked and then chilled, there was no difference in protein content of the apical 1 cm of the seedling radicle among these treatments and the non‐heat shocked, non‐chilled control. Two days after treatment, the protein content was still similar in tissue that had been heat shocked or heat shocked and chilled, while it was significantly reduced in tissue that had been chilled. In general, 2 h after treatment, the activity of the 5 antioxidant enzymes examined in this study [superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (GPX; EC 1.11.1.7) and glutathione reductase (GR; EC 1.6.4.2)] were reduced by chilling and unaffected or increased by heat shock. When heat shock was followed by chilling, there was a consistent effect of the heat shock treatment on preventing the loss of enzyme activity following chilling. This protective effect of the heat shock treatment was even more pronounced after 2 days of recovery at 25°C for SOD, CAT and APX. In contrast, the activity of GR and GPX was substantially higher in chilled tissue than in tissue that had been heat shocked before being chilled. Elevated levels of GR and GPX therefore appear to be correlated with the development of chilling injury, while elevated levels of SOD, CAT and APX appear to be correlated with the development of heat shock‐induced chilling tolerance.

Refrigeration of the Root Zone to Delay Budbreak in Grapes

Grapes grown in West Texas are especially susceptible to freeze damage during spring deacclimation and budbreak. This experiment was undertaken to evaluate whether refrigeration of the root zone would delay budbreak in two grape cultivars, `Chardonnay' and `Cabernet Sauvignon'. The experiment was conducted under greenhouse conditions using 1-year-old grafted plants planted into containers in water bath chillers to cool the root zone. Three root-zone temperatures were maintained: 7.2 °C, 1.7 °C, and a nonchilled control. The experiment followed a randomized split plot, with main plots being temperatures and the sub-plots being genotype, and the experiment was repeated once. Evaluation of budbreak was performed on a daily basis. Other data collected included shoot dry weight and root dry weight with soil, water, and air temperatures recorded using type T thermocouples (copper-constantan) attached to a datalogger. The experiments indicated that budbreak could be delayed in both varieties by the refrigeration of the root zone by an average of 1 to 2 days when comparing the 1.7 °C treatment with the nonchilled control. The refrigerated treatments of `Chardonnay' also tended to show a prolonged budbreak over time. This finding may be significant since `Chardonnay' generally exhibits budbreak relatively early compared to other grape varieties and a prolonged budbreak may allow some buds to escape spring frost injury.

330 Effects of Calcium Salts on Chilling Tolerance in Cucumber Seedling Roots

The effects of calcium salts and concentrations from 25 to 200 mM on the induction of chilling tolerance in cucumber roots were studied using total root growth, electrolyte leakage, lipid peroxidation, and activities of antioxidant enzymes as indicies of chilling injury. Cucumber seeds `Poinsett 76' germinated at 25 °C for 36 h were treated with calcium sulfate, calcium nitrate, and calcium chloride for 2 h at 25 °C. After incubation, treated seedlings were rinsed with distilled H2O and chilled at 2 °C for 72 or 96 h with or without re-warming at 25 °C. Roots of CaSO4-treated cucumber seedlings exhibited less chilling injury at all concentrations, when exposed to 72- or 96-h chilling periods with a 72-h re-warming period as shown by greater root growth compared to the chilled control. Concentrations of CaCl2 and Ca(NO3)2 above 100 mM resulted in significant root growth inhibition. Electrolyte leakage (EL) was significantly reduced by CaSO4 up to 150 mM under chilling conditions and all calcium salt treatments reduced malondialdehyde (MDA) levels in seedling roots up to 150 mM. However, at 150 mM CaSO4 both EL and MDA values of 72 h chilled and re-warmed roots were at their lowest levels compared to the control and other treatments. Both superoxide dismutase and catalase activities of seedling roots decreased under chilling conditions compared to the nonchilled control, although the reduction was less in the presence of CaSO4. Peroxidase and glutathione reductase activities increased under chilling conditions and were generally reduced in the presence of calcium salts compared to the chilled control.

Effect of Chilling on the Gravitropic Response of `Poinsett 76' Cucumber (Cucumis sativus L.) Radicles

Germinating 'Poinsett 76' cucumber (Cucumis sativus) seeds are chilling sensitive, and subsequent radicle elongation is inhibited by exposure to nonfreezing temperatures below 10 degrees C. Reorienting germinated seeds with 5-mm-long radicles from a vertical to a horizontal position induced gravitropic curvature within 2 hours at 10 to 25 degrees C without significantly affecting the rate of radicle elongation. However, neither elongation nor curvature occurred in similar seeds held at 2.5 or 5 degrees C. Chilling seeds with 5-mm-long radicles at 2.5 degrees C for 18 hours significantly reduced the subsequent rate of radicle elongation at 25 degrees C by 47% compared with nonchilled control, while gravitropic curvature was reduced by only 34%. After 36 hours of recovery at 25 degrees C, the difference was even more pronounced; elongation was reduced by 26% while curvature was reduced by only 6%. Clearly, gravitropic curvature was less chilling sensitive than radicle elongation, despite the fact that differential elongation of cells in the radicle are needed to produce curvature. Exposing seeds with 5-mm-long radicles to a heat shock of 45 degrees C for 4 to 10 minutes significantly diminished the chilling-induced reduction in radicle elongation and gravitropic curvature.

771 PB 351 VARIATION IN FLORICULTURAL PERFORMANCE OF `GLORIA' AZALEA AFTER DORMANCY-BREAKING TEMPERATURE TREATMENTS

Commercially-produced, endodormant `Gloria' azaleas were placed into temperature × duration dormancy-breaking treatments at 2 month intervals to characterize seasonal variation in floricultural performance. Given the standard industry practice to break bud dormancy is 6 weeks at 3.5 to 7.2 C, three temperatures (3.5, 7.5, 11.5 C) and four durations (2, 4, 6, 8 weeks), plus a non-chilled control, were used to examine the contribution of each dormancy-breaking factor to subsequent floricultural quality. Treatment-Induced leaf abscission and flowering were quantitated, including days to Initial flowering and 50% flowering. Flowering response of dormant-budded azaleas produced during late spring and early summer (chilled during summer and early fall, respectively) was primarily and positively related to chilling duration, with only a minor influence of chilling temperature. In contrast, flowering of fall-produced endodormant plants (chilled during late fall) was best at 3.5 C, regardless of duration. Across all intervals, control plants averaged a leaf loss rate of 3 to 4 per day, suggesting a steady-state turnover rate. While leaf abscission was higher in all chilling-treated plants, those produced during fall and given the standard (or longer) chilling treatment exhibited about twice the total abscission (averaging as much as 20 leaves per day) as plants produced at other times, resulting in a clear reduction in plant foliar quality.

Effects of Chilling on the Biochemical and Functional Properties of Thylakoid Membranes

The mechanism of chilling resistance was investigated in 4-week-old plants of the chilling-sensitive cultivated tomato, Lycopersicon esculentum Mill. cv H722, and rooted cuttings of its chilling-resistant wild relative, L. hirsutum Humb. and Bonpl., which were chilled for 3 days at 2 degrees C with a 14-hour photoperiod and light intensity of 250 micromoles per square meter per second. This chilling stress reduced the chlorophyll fluorescence ratio, stomatal conductance, and dry matter accumulation more in the sensitive L. esculentum than in the resistant L. hirsutum. Photosynthetic CO(2) uptake at the end of the chilling treatment was reduced more in the resistant L. hirsutum than in L. esculentum, but recovered at a faster rate when the plants were returned to 25 degrees C. The reduction of the spin trap, Tiron, by isolated thylakoids at 750 micromoles per square meter per second light intensity was taken as a relative indication of the tendency for the thylakoids to produce activated oxygen. Thylakoids isolated from the resistant L. hirsutum with or without chilling treatment were essentially similar, whereas those from chilled leaves of L. esculentum reduced more Tiron than the nonchilled controls. Whole chain photosynthetic electron transport was measured on thylakoids isolated from chilled and control leaves of the two species at a range of assay temperatures from 5 to 25 degrees C. In both species, electron transport of the thylakoids from chilled leaves was lower than the controls when measured at 25 degrees C, and electron transport declined as the assay temperature was reduced. However, the temperature sensitivity of thylakoids from chilled L. esculentum was altered such that at all temperatures below 20 degrees C, the rate of electron transport exceeded the control values. In contrast, the thylakoids from chilled L. hirsutum maintained their temperature sensitivity, and the electron transport rates were proportionately reduced at all temperatures. This sublethal chilling stress caused no significant changes in thylakoid galactolipid, phospholipid, or protein levels in either species. Nonchilled thylakoid membranes from L. hirsutum had fourfold higher levels of the fatty acid 16:1, than those from L. esculentum. Chilling caused retailoring of the acyl chains in L. hirsutum but not in L. esculentum. The chilling resistance of L. hirsutum may be related to an ability to reduce the potential for free radical production by close regulation of electron transport within the chloroplast.

Seed Germination of Intermountain Penstemons as Influenced by Stratification and GA3 Treatments

Abstract Propagation of the genus Penstemon for use in landscape horticulture has been handicapped by a lack of understanding of seed dormancy and a practical method for breaking dormancy for numerous species. The extent of dormancy in seeds of 27 wild populations of Penstemon representing 16 Intermountain species was investigated by subjecting seeds to stratification (moist prechilling) of 2 to 16 weeks at 2°C (36°F) and varying concentrations of gibberellic acid (GA3). Germination varied from 0 to 88% for non-treated seeds and from 13 to 100% for seeds treated with 250 ppm GA3. Collections from 10 species required 12 or more weeks of stratification for complete germination. Three species exhibited reduced germination after stratification when compared to the non-chilled control. Gibberellic acid significantly reduced the stratification requirement of seeds for the more dormant species. Concentrations of 150, 250, and 500 ppm GA3 were equally effective in breaking dormancy for most species. The considerable variability in seed dormancy suggests that the most practical solution to penstemon propagation from seed may be the selection of species and ecotypes with minimal dormancy.

Polyamine Titre in Relation to Chill-Sensitivity inPhaseolus sp.

Guye, M. G., Vigh, L. and Wilson, J. M. 1986. Polyamine titre in relation to chill-sensitivity in Phaseolus sp.—J. exp. Bot. 37: 1036-1043. Endogenous levels of the polyamines putrescine, spermidine and spermine were quantified in the primary leaves of five cultivars of bean (Phaseolus sp.) differing in their 'wilting response' to a chilling exposure of 5 °C for 24 h. Levels of polyamines prior to chilling treatment did not appear to be correlated with chill-tolerance as levels in the non-chilled controls were highest in cultivars of medium chill-sensitivity. Plants grown under a vapour saturation deficit (PSD) of 8-4 g m ~ 3 day/6-1 g m ~ 3 night exhibited a mild hardening as compared to plants grown under a VSD of 5-7 g m3 day/4-1 g m ~3 night, as the former showed less wilting on chilling. Hardening at high VSD had the effect of slightly lowering the putrescine content of non-chilled tissue but total polyamine content remained unchanged. However, on chilling, the largest relative increase in polyamine levels, in particular that of putrescine, occurred in hardened plants. There was also a significant relative increase in putrescine titre in response to chilling in non-hardened genotypes of high chill-tolerance, whereas more chill-sensitive genotypes remained unchanged or slightly declined in putrescine content on chilling. Relative changes in putrescine content rather than absolute levels appears to be correlated with chill-tolerance. These results are discussed in view of present knowledge on the adaptive significance of stress-induced changes in polyamines, especially with regard to membrane stability.