Prior temperature exposure affects subsequent chilling sensitivity

The chilling sensitivity of small discs or segments of tissue excised from chillingsensitive species was significantly altered by prior temperature exposure subsequent to holding the tissue at chilling temperatures as measured by a number of physiological processes sensitive to chilling. This temperature conditioning was reversible by an additional temperature exposure before chilling, and mature-green and red-ripe tomato tissue exhibit similar chilling sensitivities. Exposing pericarp discs excised from tomato fruit (Lycopersicon esculentum Mill. cv. Castelmart), a chilling-sensitive species, to temperatures from 0 to 37°C for 6 h before chilling the discs at 2.5°C for 4 days significantly altered the rate of ion leakage from the discs, but had no effect on the rate of ion leakage before chilling and only a minimal effect on discs held at a non-chilling temperature of 12°C. Exposing chillingsensitive tissue to temperatures below that required to induce heat-shock proteins but above 20°C significantly increased chilling sensitivity as compared to tissue exposed to temperatures between 10 and 20°C. Rates of ion leakage after 4 days of chilling at 2.5°C were higher from fruit and vegetative tissue of chilling-sensitive species (Cucumis sativus L. cv. Poinsett 76, and Cucurbita pepo L. cv. Young Beauty) that were previously exposed for 6 h to 32°C than from similar tissue exposed to 12°C. Exposure to 32 and 12°C had no effect on the rate of ion leakage from fruit tissue of chilling tolerant species (Malus domestica Borkh. cv. Golden Delicious, Pyrus communis L. cv. Bartlett). Ethylene and CO₂ production were higher and lycopene synthesis was lower in chilled tomato pericarp discs that were previously exposed for 6 h to 32°C than the values from tissue exposed to 12°C for 6 h before chilling. Increased chilling sensitivity induced by a 6 h exposure to 32°C could be reversed by subsequent exposure to 12°C for 6 h.     

Reduced chilling tolerance in elongating cucumber seedling radicles is related to their reduced antioxidant enzyme and DPPH-radical scavenging activity

Cucumber seedling radicles become more chilling sensitive as they elongate. Chilling seedlings with radicles 20 mm long for 48 h at 2.5°C inhibited subsequent growth by 36%, while it reduced the growth of 70 mm-long radicles by 63%. Although the growth rate of non-chilled cucumber radicles at 25°C is constant from 20 to 80 mm, tissue viability [i.e. reduction of TTC (2,3,5-triphenyltetrazolium chloride) to formazan] and DPPH ( α,α -diphenyl- β -picrylhydrazyl) radical scavenging activity of apical tissue declines as radicles elongate from 20 to 80 mm in length. TTC reduction, DPPH-radical scavenging activity and protein content of apical tissue were higher in 20 than in 70 mm radicles immediately after chilling and after an additional 48 h of growth at 25°C. Catalase (CAT; EC 1.11.1.6) and ascorbate peroxidase (APX; EC 1.11.1.11) activity was higher in the apical tissue of 20 than in 70 mm radicles before chilling. Immediately after chilling and after an additional 48 h at 25°C, superoxide dismutase (SOD; EC 1.15.1.1), glutathione reductase (GR; EC 1.6.4.2), and guaiacol peroxidase (GPX; EC 1.11.1.7) activity increased more rapidly in 70 mm radicles than in 20 mm radicles (SOD, GR, and GPX activity in 70 mm radicles was 1.5-, 1.9- and 8.6-fold higher, respectively, than in 20 mm radicles). However, APX and CAT activity in 20 mm radicles were always higher than in 70 mm radicles. Growth after chilling enhanced the activity of all antioxidant enzymes compared to that found in non-chilled tissue; however, CAT activity in 70 mm radicles did not recover to levels found in non-chilled tissue. Higher levels of CAT, APX and DPPH-radical scavenging activity are correlated with higher chilling tolerance of 20 mm-long cucumber radicles compared to 70 mm-long radicles.     

Effect of acetaldehyde, arsenite, ethanol, and heat shock on protein synthesis and chilling sensitivity of cucumber radicles

Exposure to a chilling temperature of 2.5°C for 96 h inhibited the subsequent growth of cucumber seedling radicles at 25°C by 92%. Exposing seedling with 5 ± 1 mm long radicles to acetaldehyde vapour (275 µl l⁻¹) or to an aqueous ethanol solution (0.6  M ) for 2 h, or to 45°C for 10 min before chilling, increased chilling tolerance so that the chilling treatment reduced growth by only 47, 39 or 36%, respectively. All of these effective treatments induced the synthesis of a number of proteins, and suppressed de novo protein synthesis (i.e. the incorporation of [³⁵S]-methionine) by about 70%. In contrast, treatment for 2 h with an aqueous arsenite solution (100 µ M ) had no effect on chilling sensitivity or the incorporation of [³⁵S]-methionine, yet it induced the synthesis of a complement of proteins that were similar to that induced by the effective heat-shock treatment. A unique protein or set of proteins may be responsible for heat-shock-induced chilling tolerance, but none was detected. The ability of various abiotic stresses to suppress protein synthesis may be more important in increasing tolerance to chilling injury than their ability to induce the synthesis of specific proteins.     

Effects of supraoptimal temperatures on the myxomycete Phyrasum polycephalum

Summary The effects of heat shock on the protoplasmic streaming, respiration and leakage of plasmodial constituents absorbing at 260 nm (products of nucleic acid metabolism), 280 nm (products of protein metabolism), and 415 nm (the yellow pigments of the plasmodia) were studied in plasmodia of the myxomycete Physarum polycephalum.Plasmodia grown on a semidefined medium displayed a lower primary thermoresistance of the protoplasmic streaming, and had a lower Q ₁₀ coefficient of the heat injury of this function compared to those grown on rolled oats. They are able to repair thermal injuries during heating. The primary thermoresistance of the protoplasmic streaming is not changed during the mitotic cycle.A 10 min heating at 32°C lowers the rate of protoplasmic streaming and results in a leakage of plasmodial pigments. After a 10 min exposure at 37–38°C the protoplasmic streaming is stopped, the respiration reduced, and products of nucleic acid metabolism are detectable in the heating fluid. Leakage of protein metabolits was observed after 10 min heatshocks at 41°C. A heating of the plasmodia to 47–50°C caused the highest level of leaked substances and the complete cessation of respiration.In contrast to higher plants, the respiration and leakage of the pigments are thermolabile indicators of the condition of Physarum polycephalum plasmodia.     

Exposure to alcohol vapours reduces chilling-induced injury of excised cucumber cotyledons, but not of seedlings or excised hypocotyl segments

Cucumber (Cucumis sativus L. cv. Poinsett 76) seedlings withfully expanded cotyledons, and excised cotyledons, first trueleaves, hypocotyl segments and fruit mesocarp discs were exposedto vapours from a series of aqueous alcohol solutions of 0 to320 mM methanol, ethanol, n-propanol, n-butanol, and n-pentanolduring chilling at 2.5C for 5 d. Certain concentrations ofeach alcohol reduced subsequent chilling-induced ion leakagefrom the cotyledons and leaves. Exposure of cotyledons to certainmethanol or ethanol solutions also reduced chilling-inducedethylene production, but not carbon dioxide production. In contrast,exposing cucumber seedlings with fully expanded cotyledons tothe same series of alcohol concentrations that resulted in reducedchilling-induced ion leakage and ethylene production of excisedcotyledons actually increased chilling injury of the seedlings.The hypocotyl region directly below the cotyledons was the siteof chilling-induced injury and contained the most chilling-sensitivehypocotyl tissue. Exposing hypocotyl segments excised from thissensitive region to alcohol solutions did not significantlyreduce chilling-inducedion leakage. Exposing excised cucumbercotyledons or hypocotyl segments to equivalent osmotic nonvolatilesolutions of mannitol and glycerol at 2.5C or to alcohol solutionsat 12.5C had no significant effect on the rate of ion leakage.For the series of alcohols used, the relationship between thelog of the alcohol concentration that minimized chilling-inducedion leakage from cucumber cotyledon discs held at 2.5C for5 d and the log of the partition coefficient of the alcoholinto olive oil or the log of the molecular weight of the alcoholswas highly significant. The same concentrations of alcoholsthat reduced chilling-inducedion leakage also reduced stomatalaperture as measured as decreased porosity of excised cotyledons.The correlation between reduced chilling injury and stomatalconductance of cotyledons exposed to a series of ethanol solutionswas highly significant. It appears that alcohols may reducechilling injury of cucumber cotyledons by inducing stomata closure.Sufficient endogenously synthesized ethanol accumulated in discsheld in N2 at 10C for 1 d to confer tolerance to chilling at2.5C for 5 d. Key words: Anaerobic, Cucumis sativus, ethanol, ion leakage, stomatal conductance     

Chilling tolerance of cucumber (Cucumis sativus) seedling radicles is affected by radicle length, seedling vigor, and induced osmotic- and heat-shock proteins

Cucumber seedling radicles decrease in chilling tolerance as they increase in length or decrease in vigor. The protein content of the apical 5 mm of the radicle decreased with decreases in chilling tolerance ( R ² = 0.92). This general reduction in protein content was reflected in a decrease of six dehydrin-like proteins with apparent molecular weights of 13.0, 15.0, 16.8, 23.0, 26.8, and 33.5 kDa. The disappearance of naturally occurring dehydrin-like proteins in cucumber seedling radicles as they elongate or lose vigor was correlated with a loss of chilling tolerance. Exposure to an osmotic (0.6 M mannitol) or heat (2 min at 45°C) stress enhanced chilling tolerance. The osmotic-shock treatment induced both chilling tolerance and the appearance or strengthening of dehydrin-like proteins previously present in radicles. The heat-shock treatment also induced high levels of chilling tolerance and protein(s) that reacted with a 23 and 70 kDa antibody. However, these heat-shock protein (HSPs) did not cross react with the probe for dehydrin-like proteins. When organized into high, medium, and low chilling tolerance groups, radicle that were chilling tolerant contained either the 13.0 and 16.8 kDa dehydrin-like proteins, or the 15.0 and 23.0 kDa dehydrin-like proteins, or the 23 or 70 kDa HSP.     

Heat shock increases chilling tolerance of mung bean hypocotyl tissue

The effects of heat shock on the chilling tolerance of mung bean [Vigna radiata (L.) Wilczek] seedling tissue were studied by using two measurements of chilling injury: increased 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity and solute leakage. ACC oxidase activity (measured as ACC-induced ethylene production) of freshly excised mung bean hypocotyl segments was highly dependent on the temperature at which the seedlings were grown. However, this highly temperature-dependent level of ACC oxidase activity was probably a wound response since it was almost entirely eliminated by incubating the excised segments at 20°C for 3 h. In contrast, heating of excised segments to 40°C for up to 4 h resulted in a time-dependent increase in ACC oxidase activity which was sensitive to cycloheximide, indicating rapid protein synthesis during the heat treatment. ACC oxidase activity fell sharply during subsequent chilling at 2. 5°C. After 3 days of chilling, all treated segments, regardless of their initial ACC oxidase activity, showed a decline to the same low activity level and ACC oxidase activity continued to fall slowly for up to 9 days at 2. 5°C. Hypocotyl segments excised from seedlings held at 15°C showed no change in solute leakage, but leakage increased rapidly when seedlings were either chilled at 2. 5°C or heated to 32°C (just below the heat shock temperature). Chill-induced leakage from non-heat-shocked segments increased steadily with chilling duration and was unaffected by cycloheximide concentration up to day 6. Within the elevated rate of leakage on day 9, however, leakage was lower from segments exposed to 10 and 50 μM cycloheximide. Solute leakage was markedly reduced for up to 9 days when segments were heat shocked at 40°C for 3 or 4 h with or without 10 M cycloheximide, but the presence of 50 μM cycloheximide caused an initial doubling of solute leakage and a 3-fold increase after 3 days of chilling. Cycloheximide prevented formation of heat shock protection against chilling from the start at 50 μM and after 9 days at 10 μM. These results indicate that the protection afforded by heat shock against chilling damage is quantitative and probably involves protein synthesis.     

Chilling-induced potassium leakage of cultured citrus cells

Callus of 'Marsh' grapefruit ( Citrus paradisi Macf.) albedo tissue was used to investigate the effect of preconditioning temperature on the rate of chilling - stimulated K⁺ leakage. Callus grew most rapidly at 30°C and attained a weight of about 1 g after 30 days. The rate of K.⁺ leakage from nonchilled callus tissue decreased as temperature decreased from 20 to 7.5°C, but no measurable change in rate was observed between 7.5 and 0°C. When calli were held for 40 days at 0¹ 2.5 or 5°C, K⁺ leakage increased 200%, 60% or 0%) respectively. Holding callus for 5 days at 10 or 15°C prior to chilling for 40 days at 0°C prevented the increase in K⁺ leakage observed in callus receiving no preconditioning treatment. Preconditioning at 7.5 and 20°C was less effective in reducing chilling - induced leakage. Preconditioning at 10°C for 5, 2 or 1 day reduced chilling – induced leakage after 40 days at 0°C by 50%, 33% and 15%. respectively.     

Wound-induced PAL activity is suppressed by heat-shock treatments that induce the synthesis of heat-shock proteins

Wounding lettuce leaves induces the de novo synthesis of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), the accumulation of phenolic compounds, and subsequent tissue browning. A brief heat-shock at 45°C reduces the rise in wound-induced PAL, the accumulation of phenolic compounds, and tissue browning. The activity of PAL measured 24 h after wounding and the content of phenolic compounds (absorbance of methanol extract at 320 nm) measured 48 h after wounding was highly correlated (R² > 0.90) in tissue developing the normal wound response and in tissue subjected to 0–180 s of heat-shock after wounding. The synthesis of a unique set of proteins called heat-shock proteins (hsps) is induced by these heat-shock treatments. Western-blot analyses of proteins isolated from wounded and heat-shocked Iceberg and Romaine lettuce mid-rib leaf tissue was done using antibodies against hsp 23. Only those heat-shock treatments that were effective at inducing the synthesis of hsp 23 were effective in reducing the activity of PAL induced by wounding and the subsequent accumulation of phenolic compounds. Hsps induced in non-wounded, whole leaves by exposure to 45°C for 150 s did not significantly interact with PAL previously synthesized in non-heat-shocked wounded leaves to limit its activity. The preferential synthesis of hsps over that of wound-induced PAL, rather than the presence of hsps, may be responsible for the ability of a heat-shock treatment to reduce the wound-induced increase in PAL activity. Our results support this novel concept, and the possibility that heat-shock treatments can have significant physiological effects on the response of the tissue to other stresses, not because of the specific genes they induce or repress, or the products they cause to be synthesized, but by their secondary action of influencing the synthesis of other proteins (e.g. PAL) by the suppression of non-hsps protein synthesis.     

Changes of polyamines and ethylene in cucumber seedlings in response to chilling stress

Cucumber ( Cucumis sativus L. cv. Victory) seedlings were exposed to chilling at 5°C and endogenous levels of polyamines and 1-aminocyclopropane-1-carboxylic acid (ACC) were measured after chilling and after warming at 20°C. The level of spermidine was higher in the chilled seedlings than in the non-chilled seedlings. Treatment with a plant bioregulator, (2RS,3RS)-1-(4-cholorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol), reduced the chilling injury and the levels of spermidine in the chilled seedlings. The levels of ACC and production of ethylene showed sharp increases after warming following exposure to chilling. These increases were suppressed by the application of aminooxyacetic acid (AOA). However, AOA treatment did not reduce chilling injury or affect the levels of polyamines in the tissue. These data indicate that the increase in ACC and ethylene is a response of the tissue to the chilling exposure and is not a cause of the injury. The data also suggest that the syntheses of polyamines and ethylene are not competitive with each other even under chilling stress conditions.     

Monitoring chilling injury: A comparison of chlorophyll fluorescence measurements, post-chilling growth and visible symptoms of injury in Zea mays

Changes in chlorophyll fluorescence emission from maize ( Zea mays L. cv. Northern Belle) seedlings chilled at 1.5°C in the dark for 3–30 h were compared with the ability of plants to resume growth in the immediate post-chilling period and with the development of visible symptoms of injury to the leaves. During chilling, the maximal rate of increase of the induced chlorophyll fluorescence rise. F_R, was measured on secondary leaf tissue. F_R decreased exponentially, at approximately the same rate in plants grown and chilled in hydroponic pots, in leaves detached from similar plants and in plants that were removed from the hydroponic pots and laid on wet filter paper adjacent to the detached leaves. The half-fall time for F_R in the 3 treatments was 7.8 ± 1.3 h, 8.6 ± 0.6 h and 8.8 ± 1.0 h, respectively. Following seedling removal from 1.5°C and return to 25/15°C, relative growth rates were determined from daily measurements of plant fresh weight gain. Compared with non-chilled seedlings, plants chilled for 3 h and longer showed depressed rates of growth. Inhibition of growth in the immediate post-chilling period (0–27 h) was linearly related to the duration of the chilling period and had a high positive correlation with the decrease in chlorophyll fluorescence (linearly related to log F_R) sustained during the chilling exposure. Visible symptoms of chilling injury developed during the post-chilling period on seedlings chilled for longer than 3 h. The decrease in log F_R during chilling was also linearly correlated with the severity of visual symptoms of chilling injury expressed in the post-chilling period. It is concluded that the extent of chilling injury in maize can be rapidly and non-destructively assessed from measurements of chlorophyll fluorescence.     

Heat resistance of 2 types of protoplasmic movement in Physarum polycephalum plasmodia]

The thermostabilities of the "unordered" and shuttle protoplasmic streamings in myxomycete Physarum polycephalum plasmodia was studied. A comparison of these thermostabilities has revealed that the cessation of the former streaming occurs at temperatures higher than those required for arresting the shuttle streaming. The difference between the two types of protoplasmic streamings is better seen in the rate of repair of protoplasmic streaming halted by a 10 minutes heating at 38-41 degrees C. For example, the unordered streaming is restored 2 minutes after heating plasmodia at 39 degrees for 10 min., while the shuttle streaming is resumed in 24 minutes. It is supposed that the two protoplasmic streamings are independent to an appreciable extent, and that the shuttle streaming, being more complex and coordinated, has appeared in the evolution at later stages than the unordered one. The higher heat sensitivity of the shuttle streaming substantiates a view of the lower stability to injury in regulatory mechanisms if compared to the stability of motile mechanisms.     

Temperature and chemical shocks induce chilling tolerance in germinating Cucumis sativus (cv. Poinsett 76) seeds

Roots of 24-h-old germinated cucumber ( Cucumis sativus cv. Poinsett 76) seeds were subjected to thermal and chemical stresses, equilibrated at 25°C for 2 h and chilled at 2.5°C for 96 h. The germinated seeds were then held at 25°C for 72 h after they were chilled and the elongation of the primary root was used as a measure of chilling tolerance. Control roots elongated from an initial length of 0.2 cm to a final length of 6.3 cm at the end of 72 h. while chilled roots elongated to a final length of only 0.4 to 0.6 cm. Exposure to 0.4 M ethanol for 4 h or to 40°C for 1 h induced substantial chilling tolerance and the roots had a final length of 4.1 and 3.1 cm. respectively. Exposure to 7.5°C for 3 h conferred less chilling tolerance (elongation to 1.4 cm). while exposure to other chemicals (i.e. aqueous solutions of Ca(NO₃)₂, mannitol. methanol and NaCl) produced less, though still significant increases in chilling tolerance. A more severe chilling treatment of 144 h at 2.5°C was required to consistently induce elevated rates of ion leakage. Only the heat and the ethanol shock treatments significantly reduced chilling-induced ion leakage. Inclusion of the protein synthesis inhibitor cycloheximide negated the protective effects of these shock treatments. It appears that de novo protein synthesis is required for induction of chilling tolerance by a variety of chemical and thermal shock treatments.     

Geographical variation in Japan in egg development of the mayfly, Ephoron shigae (Ephemeroptera: Polymitarcyidae)

1. The effect of temperature on embryonic development was compared in four populations, two bisexual and two unisexual, of Ephoron shigae , including one each near the northern and southern periphery of the species range in Japan.
2. Eggs from every population were chilled at 4, 8 or 12 °C for diapause development after 50 days at 20 °C for pre-diapause development (experiment I). Some eggs hatched during chilling at 8 °C or 12 °C, whereas no eggs hatched at 4 °C. The rate of hatching in a given condition of chilling was higher for the eggs from warmer winter environments.
3. Chilling at 4 or 8 °C effectively facilitated diapause development. Chilling at 12 °C was, in general, not so effective, but relatively effective for the eggs from warmer winter environments.
4. Eggs were incubated at 8, 12, 15 or 20 °C after chilling at 4 °C to examine the effect of temperature on post-diapause development (experiment II). The eggs incubated at higher temperature after chilling hatched quicker and more synchronously and had higher hatching success.
5. The relationship between temperature and the days required for hatching after chilling was well described by the power function. There was no significant difference in the slope of the regression lines (i.e. temperature dependency) among local populations. However, a longer time was required for hatching at a given temperature for the population from the colder winter environment.
6. There was no detectable difference in the observed intraspecific variations between unisexual and bisexual populations.     

Effect of chilling, heat shock, and vigor on the growth of cucumber (Cucumis sativus) radicles

Chilling at 2.5°C reduced the subsequent growth of cucumber ( Cucumis sativus L.) radicles at 25°C. The reduction in radicle growth was linear for 1–3 days of chilling at ≈10% per day of treatment, but then it increased in a non-linear pattern until subsequent radicle growth was all but eliminated by 6 days of chilling. A heat shock of 40°C for 4–12 min increased chilling tolerance such that 4 days of chilling caused only a 36% decrease in radicle growth, compared to 66% for seedlings not heat shocked. Heat shocks were only able to protect that part of radicle growth that was in excess of the linear decrease in radicle growth projected from 0–3 days. There appear to be two effects of chilling on radicle growth. The first inhibition of subsequent growth was linear and was not affected by heat shocks. The second inhibition was much more severe; it appeared after 3 days of chilling and could be prevented by heat shock. Seeds classified with different levels of vigor (i.e., different initial rates of growth) did not respond significantly different to chilling stresses following heat-shock treatments.     

Effect of temperature conditioning on chilling injury of cucumber cotyledons: possible role of abscisic Acid and heat shock proteins

Endogenous abscisic acid levels and induced heat shock proteins were measured in tissue exposed for 6 hours to temperatures that reduced their subsequent chilling sensitivity. One-centimeter discs excised from fully expanded cotyledons of 11-day-old seedlings of cucumber (Cucumis sativus L., cv Poinsett 76) were exposed to 12.5 or 37°C for 6 hours followed by 4 days at 2.5 or 12.5°C. Ion leakage, a qualitative indicator of chilling injury, increased after 2 to 3 day exposure to 2.5°C, but not to 12.5°C, a nonchilling temperature. Exposure to 37°C before chilling significantly reduced the rate of ion leakage by about 60% compared to tissue exposed to 12.5°C before chilling, but slightly increased leakage compared to tissue exposed to 12.5 or 37°C and held at the nonchilling temperature of 12.5°C. There was no relationship between abscisic acid content following exposure to 12.5 or 37°C and chilling tolerance. Five heat shock proteins, with apparent molecular mass of 25, 38, 50, 70, and 80 kilodaltons, were induced by exposure to 37 or 42°C for 6 hours, and their appearance coincided with increased chilling resistance. Heat shock treatments reduced the synthesis of three proteins with apparent molecular mass of 14, 17, and 43 kilodaltons. Induction of heat shock proteins could be a possible cause of reduced chilling injury in tissue exposed to 37 or 42°C.     

Net CO2 output by CAM plants in the light: the role of leaf conductance

Triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-l-(l,2,4-triazol-l-yl)-2-butanone] is a triazoie fungicide which protects bean ( Phaseolus vulgaris L. cv. Spring Green) plants from heat and chilling injury. When the plants were exposed to heat shock by dipping the shoots in hot (50°C) distilled water for 2 min or exposing the plants to cold (1°C) for 8 h the primary leaves showed visual symptoms of injury 2 days after treatment and thereafter there was a progressive decline in chlorophyll and an increase in electrolyte leakage indicative of a loss of membrane integrity. There was a loss of metabolic (respiratory) activity in the root meristems when the roots were dipped in hot (48°C) water. All these symptoms of heat and chilling injury in the controls were either delayed or prevented by root application of triadimefon.     

An <i>in Vitro</i> Approach to Investigate the Role of Abscisic Acid in Alleviating the Negative Effects of Chilling Stress on Banana Shoots

Banana is a tropical crop cultivated in warm places. Chilling stress in Egypt is making banana crops less productive. Abscisic acid (ABA), a key plant hormone, regulates metabolic and physiological processes and protects plants from a variety of stresses. In vitro growing banana shoots were pre-treated with ABA at four concentrations (0, 25, 50, and 100 mM) and chilled at 5°C for 24 h, followed by a six-day recovery period at 25°C. By comparing ABA treatments to both positive and negative controls, physiological and biochemical changes were investigated. Chilling stress (5°C) caused a considerable increase in lipid peroxidation and ion leakage and reduced photosynthetic pigments in cold-treated plantlets. Increasing the concentration of ABA to 100 µM enhanced the response to chilling stress. ABA had a major effect on mitigating chilling injury in banana shoots by keeping cell membranes stable and lowering the amount of ion leakage and lipid peroxidation. Also, ABA significantly maintained the photosynthetic pigment concentration of banana shoots; accumulated higher amounts of total soluble carbohydrates and proline; and increased DPPH radical scavenging activity. Furthermore, ABA treatment enhanced cold tolerance in chilling-stressed banana shoots through the regulation of antioxidant enzyme activity. Overall, the results show that ABA is a good choice for protecting banana shoots from the damage caused by chilling stress.     

Effect of chilling and subsequent storage at 20°C on electrolyte leakage and phospholipid fatty acid composition of tomato pericarp

Mature green tomato fruit ( Lycopersicon esculentum cv. Caruso) were stored at 1°C or 20°C and analyzed on day 0, 18 and 22 for electrolyte leakage, ripening-associated changes in pigmentation and phospholipid fatty acid composition. Chilled fruit were also analyzed 4 days after they were returned to 20°C. Fruit did not ripen significantly during chilling and subsequent storage at 20°C, and showed visible chilling injury symptoms only at 20°C. Electrolyte leakage increased in control and chilled fruit, indicating enhanced membrane permeability during both ripening and chilling. Returning the fruit to ambient temperature gave an apparent decrease in electrolyte leakage. Phospholipid and linolenic acid content and double bond index decreased during ripening at 20°C. The small changes in phospholipid fatty acid composition during chilling cannot account for the enhanced membrane permeability. The significant decrease in percentage of linolenic acid and in double bond index in the total lipids, but not in the phospholipids, upon returning the fruit to 20°C suggests loss of galactolipid polyunsaturated fatty acids     

Enhancing effects of heat shock and gibberellic acid on the thermotolerance in etiolated Vigna radiata. I. Physiological aspects on thermotolerance

The effect of heat shock on the thermotolerance of etiolated mung bean seedlings ( Vigna radiata L. cv. Wilczek) and the effects of gibberellic acid (GA) were studied. The potentially lethal temperature of etiolated mung bean seedlings was 45°C. But, when seedlings were pretreated with a heat-shock period at 40°C for 1 h before incubation at 45°C, they become thermotolerant and survived the 45°C treatment. The addition of actinomycin D or cycloheximide during the heat-shock period decreased the subsequent thermotolerance of the seedlings. Depending upon the time of its application, GA appeared to have multiple effects: (1) when applied during the 40°C heat-shock period, GA enhanced the heat-shock effect; (2) when applied during the 45°C potentially lethal temperature period, GA enhanced the subsequent growth of hypocotyls. This suggests that GA makes the seedlings tolerant to the potentially lethal temperature; (3) when GA was applied during a following 25°C growth period to seedlings which had been exposed first to 40°C and then 45°C, it promoted growth, suggesting that GA enhanced the restoration of the seedlings from high temperature damage. The role of GA and heat shock in the acquisition of thermotolerance in etiolated mung bean seedlings are discussed.