Chilled Seedlings Research Articles

Exogenous hydrogen peroxide induces chilling tolerance in Phalaenopsis seedlings through glutathione-related antioxidant system

Phalaenopsis is the most economically important flower crops wildly but hardly tolerated to low-temperature stress. Hydrogen peroxide (H2O2), a reactive oxygen species was participated in many chilling-response processes. In this study, the efficiency and mechanism of chilling tolerance induced by transient oxidative shock with H2O2 pretreatment were investigated. Phalaenopsis seedlings demonstrated chilling injury when the ambient temperature was at 6°C or lower. Transient oxidative shock by pretreatment with 50 mM H2O2 induced chilling tolerance. This pretreatment reduced the leaf electrolyte leakage (EL) from 64.1% to 28.3% of plants cultivated at 6°C for 6 days. Increasing the frequency of H2O2 pretreatment from 1 to 3 times strengthened the protective efficiency; however, an H2O2 concentration of ≥100 mM caused abnormal leaf morphology such as curl and necrosis. Time-course analysis findings indicated that chilled seedlings pretreated with H2O2 had lower EL and malondialdehyde (MDA) content but higher chlorophyll content and better photosynthetic performance, including a higher assimilation rate, maximum quantum yield of photosynthetic system II (Fv/Fm), quantum yield of electron transport (ɸPSII), photochemical quenching (qP), and electron transport rates. The results also demonstrated that pretreatment with 50 mM exogenous H2O2 did not alter the endogenous H2O2 level only a minor elevation of approximately 2 μmol•g−1 was noted. Under low temperature suffering, activity of catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were increased with fluctuant changes, but CAT and APX inhibited in the low level by H2O2 pretreatments. In addition, the significantly high GR activity was reduced the glutathione-to-oxidized glutathione ratio, with peaks occurring at 4-8 h and on day 2 during chilling. Taken together, the findings indicate that exogenous H2O2 induced chilling tolerance in Phalaenopsis seedlings, and the process may be involved the glutathione-related oxidant defense system.

Controlled drought stress affects the chilling-hardening capacity of tomato seedlings as indicated by changes in phenol metabolisms, antioxidant enzymes activity, osmolytes concentration and abscisic acid accumulation

Abstract To elucidate the physiological, biochemical and hormonal mechanisms of chilling stress mitigated by drought pretreatment, tomato seedlings (Lycopersicon esculentum cv. C.H Falat) were pretreated by 0, 10 and 20% Polyethylene glycol (PEG) for 7 days followed by subjecting to chilling stress at 3 °C for 6 days and 6 h per day. Results showed that PEG-induced drought improved growth rate of tomato seedling subjected to chilling stress and enhanced their antioxidant enzyme activity, abscisic acid (ABA), anthocyanin accumulation, potassium (K+) and proline content compared with the control (0% PEG) at the end of chilling stress period. PEG pretreatment provided significant protection against chilling stress and reduced poly phenol oxidase (PPO) activity, electrolyte leakage (EL) and H2O2 content in root and leaf of chilled seedlings. Moreover, when PEG pretreatment was applied with chilling stress, we observed an alleviation in the growth impeding and a decrease in chilling symptoms as compared to control seedlings. The highest chilling tolerance was induced by application 20% of PEG. In general, the results indicate that PEG-induced drought, by altering in some tolerant responses, could be effectively used to protect tomato’s seedling from the adverse effects of low temperatures stress.

Exogenous spray application of 24-epibrassinolide induced changes in photosynthesis and anti-oxidant defences against chilling stress in eggplant (Solanum melongena L.) seedlings

SummaryBrassinosteroids (BRs) have been implicated in the responses of plants to various environmental stresses.To explore the mechanism(s) of BRs in the tolerance of plants to low temperatures, 24-epibrassinolide (EBR)-induced changes in chlorophyll concentrations, gas exchange parameters, chlorophyll fluorescence, and anti-oxidant defence systems in eggplant (Solanum melongena L.) were studied under chilling stress conditions. Seedlings were exposed to 10°C/5°C (day/night) chilling temperatures for 8 d, with or without a single spray of 0.1 ?M EBR applied 24 h beforehand.The EBR treatment partially overcame the inhibition of growth caused by 8 d of chilling stress.The application of EBR to chilled seedlings had a significant effect on photosynthesis, as reflected by increases in the concentrations of chlorophyll a, chlorophyll b, and total chlorophyll, the net photosynthetic rate (Pn), stomatal conductance (gs), the quantum efficiency of PSII (Fv/Fm), the efficiency of the excitation capture of open PSII centres (Fv'/Fm'), the quantum yield of PSII (_PSII), and the photochemical quenching coefficient (qP). Moreover, pre-treatment with EBR alleviated chilling-induced oxidative damage, as shown by significantly lower concentrations of reactive oxygen species and reduced membrane lipid peroxidation. EBR also caused increases in the activities of superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, and in the concentrations of ascorbic acid, reduced glutathione, and proline in seedlings grown under chilling stress. These results suggest that the protective role of EBR against chilling stress in eggplant may be associated with an increased photosynthetic capacity and an improved anti-oxidant defence system throughout the 8 d chilling period.

Antioxidant enzymes and isoflavonoids in chilled soybean (Glycine max (L.) Merr.) seedlings

Changes of activity antioxidant enzymes and of levels of isoflavonoids were studied in the roots and hypocotyls of the etiolated soybean (Glycine max (L.) Merr. var. Essor) seedlings, submitted to cold. Prolonged exposure to 1 degrees C inhibited hypocotyl and root elongation and limited their growth after seedlings were transferred to 25 degrees C. Roots were more sensitive to chilling than hypocotyls. At 1 degrees C a gradual increase in MDA concentration in roots but not in hypocotyls was observed. An increase in catalase (CAT, EC 1.11.1.6) and superoxide dismutase (SOD, EC 1.15.1.1) activity in hypocotyls was observed both at 1 degrees C and after transfer of plants to 25 degrees C. In roots, CAT activity increased after 4 days of chilling, while SOD activity only after rewarming. L-Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) activity decreased in roots of chilled seedlings, but did not change in hypocotyls until activity increased after transfer to 25 degrees C. The content of genistein and daidzein increased after 24 h of treatment by low temperature and then decreased with prolonged chilling in hypocotyls and remained high in roots. However, it should be noted that genistin level (genistein glucoside) in chilled hypocotyls is 10 times higher than in roots, despite falling tendency. The role of antioxidant enzymes and isoflavonoids in preventing chilling injury in hypocotyls and roots of soybean seedlings is discussed.

Chilling responses of maize (Zea mays L.) seedlings: root hydraulic conductance, abscisic acid, and stomatal conductance.

Maize seedling water relations and abscisic acid (ABA) levels were measured over 24 h of root chilling (5.5 degrees C). At 2.5 h into chilling, leaf ABA levels increased by 40x and stomatal conductance (g(s)) decreased to 20% compared with prechill levels. Despite a rapid g(s) response to root chilling, leaf water potential (Psi(L)) of chilled seedlings decreased to -2.2 MPa resulting in a complete loss of turgor potential (psi(p)). Ineffective g(s) control early in chilling resulted from decreased root hydraulic conductance (L(r)) due to increased water viscosity and factor(s) intrinsic to the roots. After 24 h chilling, Psi(L) and psi(p) of chilled seedlings recovered to control levels due to stomatal control of transpiration and increased L(r). The impact of the temporal changes in g(s) and L(r) on maize seedling water relations during chilling was analysed using a simple, quantitative hydraulic model. It was determined that g(s) is critical to stabilizing Psi(L) at non-lethal levels in chilled seedlings at 2.5 h and 24 h chilling. However, there was also a significant contribution due to increased L(r) at 24 h chilling so that psi(p) increased to control levels. As a first step in determining the factor(s) responsible for the increase in L(r), cDNA microarrays were used to quantify the transcript levels of eight aquaporins obtained from mature root tissue at 24 h chilling. None of these were significantly up-regulated, suggesting that the increase in L(r) was not due to regulation of these aquaporins at the transcriptional level.

Effect of Salicylic Acid on Growth and Chilling Tolerance of Cucumber Seedlings

The present study was undertaken to investigate the effect of low temperature and salicylic acid(SA) on the chilling tolerance of acclimated and nonacclimated cucumber(Cucurmis sativus L.) seedlings. The acclimation phenomenon was characterized in chilling-sensitive cucumber seedlings and found to have a significant effect on the survival and shoot dry weights. The injuries experienced by the acclimated seedlings in the third leaf stage were on average smaller by half than those experienced by the nonacclimated seedlings. Chilling also caused a large increase in the free proline levels, regardless of the acclimation status. Exogenous treatment with SA(0.5mM) resulted in improved growth and survival of the nonacclimated chilled seedlings, indicating that SA induced chilling tolerance and SA and acclimation had common effects. The application of cycloheximide in the presence of SA restored the acclimation-induced chilling tolerance. The elevated proline level observed in the cold-treated and SA-treated plants was more pronounced in the light than in the dark at a chilled temperature, indicating that endogenous proline may play a role in chilling tolerance by stabilizing the water status in response to chilling. From these results it is suggested that SA provided protection against low-temperature stress by increasing the proline accumulation, and pre-treatment with SA may induce antioxidant enzymes leading to increased chilling tolerance.

24-epibrassinolide and abscisic acid protect cucumber seedlings from chilling injury

SummaryA study investigated the ameliorative effects of the chill-induced inhibition of photosynthesis in cucumber by brassinolides and abscisic acid. Cucumber (Cucumis sativus L) seedlings at the three-leaf stage were sprayed with 24-epibrassinolide (EBS) and abscisic acid (ABA) at different concentrations. After chilling at 8°C, 4°C and 2°C for 3 d, the seedlings were allowed to recover under normal conditions. ABA and EBS pretreatments significantly alleviated chilling injury, increased the maximal photochemical efficiency (Fv/Fm) and net photosynthetic rate (Pn) of the chilled seedlings. Pn and apparent quantum yield of photosynthesis (QY) for seedlings chilled at 4°C declined to 40% and 39% of those for unchilled seedlings respectively, Pn and QY values for those pretreated with ABA and EBS, however, remained almost unchanged compared with those of unchilled seedlings.

The Effect of Short Warm Breaks during Chilling on Photosynthesis and the Activity of Antioxidant Enzymes in Plants Sensitive to Chilling

The effect of short warm breaks (from 15 min to 5 h) during chilling of three chilling‐sensitive species (tomato, maize and soybean) was investigated. Injuries, intensity of net photosynthesis and antioxidant enzyme activity were measured. Throughout chilling treatment, plants were warmed by transferring them during the last few hours of the light phase from chilling temperature (5 °C for tomato and maize, 2 °C for soybean) to 20 °C. After warming, seedlings were moved back to chilling conditions. Warm breaks of 5 h almost entirely prevented the appearance of injuries, as measured by changes in leakage of electrolytes and tissue water content, during 12 days of chilling. Even a 15‐min warm break ensured a significant decrease in injuries in chilled maize seedlings compared to continuously chilled seedlings. Inhibition of gas exchange and fluorescence in seedlings of two maize genotypes differing in chilling resistance was, to a small extent, prevented by 1‐h warm breaks, while 4‐h warm breaks reduced inhibition significantly. The length of the warm break (1 or 4 h) had no influence on changes in SOD activity compared to continuously chilled plants, but warm breaks of 4 h produced a significant increase in CAT activity. The possible influence of an alternative pathway in preventing injuries is discussed.

Effects of Exposure to Short Periods of Suboptimal Temperature during Chill (5 °C) on Gas Exchange and Chlorophyll Fluorescence in Maize Seedlings (Zea Mays L.)

The effect of various periods of exposure to suboptimal temperature (‘warm breaks’– WB: 14 °C for 4 h, 1 h and 0 h – control in 24 h cycles) during chilling (5 °C) of maize seedlings on the photosynthesis, the photochemical efficiency of photosystem II (Fv/Fm) and on the injuries of the cell membranes of leaves and water content in plants was compared. The measurements were conducted after 1, 3, 7 and 12 chill cycles. It was found that WB of either length distinctly diminished the chill‐induced inhibition of net photosynthesis and the decrease of photochemical efficiency of PSII. The protective effect on WB on these parameters was observed shortly after completion of chilling of the plant as well as an after‐effect. Daily warming up of the plants also reduced the leakage of electrolytes and diminished the water deficit of the chilled seedlings. The protective effect of WB on the measured parameters of the plants was greater in the chill‐sensitive genotype than in the chill‐tolerant one, especially when plants were warmed up for 4 h. The results obtained are an indication that short periods of warm weather during cold spring may diminish the injuries of the photosynthetic apparatus, as well as reduce the disturbance of water status of seedlings, contributing in this way to better condition of maize crops.

The Fatty Acid Composition of Phosphatidylglycerol and Sulfoquinovosyldiacylglycerol of Zea mays Genotypes Differing in Chilling Susceptibility

Summary The content and fatty acid composition of four major chloroplast lipids, monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylglycerol and sulfoquinovosyldiacylglycerol, have been measured in the intact leaves of maize inbred lines differing in chilling susceptibility. Visual assessment of chilling injury symptoms during post-chilling recovery of seedlings indicated that both lines CM 7 and Co 151 were more chilling susceptible than lines S 215 and EP l, exhibiting greater chilling tolerance. Fatty acid composition of chloroplast polar lipids was very similar and some small deviation in the content of individual fatty acids did not affect uniformity of the general pattern. In all four lines of maize the content of height-temperature melting fraction of phosphatidylglycerol (htm-PG) and double bond index of polar lipids were equal, while fatty acid composition of polar lipids was very similar despite of small deviations in the content of individual fatty acid. Although the level of the high-temperature melting fraction of sulfoquinovosyldiacylglycerol (htm-SQDG) was lower in CS and CT lines Co 151 and S 215, respectively, than in CS and CT lines CM 7 and EP 1, respectively, this difference could not be related to their chilling sensitivity. All of these data do not support the concepts that the level of htm-PG alone or in combination with low-temperature-melting lipid would differentiate the chilling sensitivity of maize inbred lines. It is likely that some other factors are responsible for differential injury symptoms observed in chilled maize seedlings upon recovery. Discrepancies between the level of htm-PG and chilling sensitivity in several other species as well as various effects of acclimation on the level of htm-PG and temperature of phase transition are discussed.

Does Ethanol-induced Chilling Tolerance Affect the Antioxidant Systems of Cucumber Seedling Roots?

Previous experiments have shown that chilling-stressed cucumber seedlings treated with ethanol have greater chilling tolerance when compared to untreated seedlings. This chilling tolerance persists for a limited time (2-4 h) and, once lost, chilling tolerance can be re-induced by a second ethanol treatment. In all cases, greater chilling tolerance was measured as an increase in root growth and a decrease in lipid peroxidation and electrolyte leakage. This study was undertaken to determine whether antioxidant systems, which may help plants survive some environmental stresses, are affected by ethanol and/or chilling treatments. The relative activities of glutathione reductase (GR) and peroxidase (POX) of chilled and/or ethanol-treated seedlings were compared. GR activity was suppressed by the combination of any ethanol treatment and chilling when compared to the control. Upon re-warming, all ethanol treated groups exhibited higher GR activity than before chilling. POX activity was affected by the chill plus re-warming treatment in which a significant increase was seen in all treatment groups. Any group treated with ethanol had a lower POX activity than the control. POX activity stains, using non-denaturing PAGE, showed the appearance of three new bands in all treatment groups after the chill and rewarming. The increased intensity of the stain in the re-warmed groups supports the enzyme activity data mentioned above. Since ethanol treatment generally suppressed the enzyme activity after chilling, ethanol's possible role as a scavenger of reactive oxygen species will be discussed.

Physiological and biochemical changes related to methyl jasmonate‐induced chilling tolerance of rice (Oryza sativa L.) seedlings

ABSTRACTPhysiological and biochemical changes related to methyl jasmonate (MeJA)‐induced chilling tolerance of rice (Oryza sativa L. cv. Taichung Native 1) seedlings were investigated. Treatment of whole plants with 10 mmol m−3 MeJA for 48 h before chilling (5 °C) was optimal for the induction of chilling tolerance. MeJA greatly improved the survival ratio of chilled seedlings and ameliorated chilling injury such as demolition of membrane structure (estimated by electrolyte leakage). MeJA also prevented water loss in chilled seedlings by reducing the opening of stomata and decreasing the root bleeding rate. Putrescine and spermine levels in shoots increased but spermidine levels decreased on exposure to MeJA. In roots, putrescine levels also increased and spermidine levels increased transiently on exposure to MeJA. Activities of arginine decarboxylase (ADC; EC 4.1.1.19) and S‐adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in both shoots and roots increased on exposure to MeJA, while the activity of ornithine decarboxylase (ODC; EC 4.1.1.17) remained unchanged. The MeJA‐induced putrescine increase was inhibited by 50 mmol m−3α‐difluoromethylarginine (DFMA), an irreversible inhibitor of ADC, but not by 50 mmol m−3α‐difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. The effect of MeJA on the induction of chilling tolerance was also reduced by 50 mmol m−3 DFMA. The effects of DFMA were partly prevented by 1 mol m−3 putrescine. This indicates that putrescine accumulation is required for the induction of chilling tolerance of rice seedlings by MeJA.

Differential Gene Expression in Chilling-Acclimated Maize Seedlings and Evidence for the Involvement of Abscisic Acid in Chilling Tolerance.

An acclimation phenomenon was characterized in seedlings of chilling-sensitive maize (Zea mays L.) inbred G50 (Pioneer). Seedlings were germinated at 27[deg]C for 3 d and then exposed to chilling treatments of 4, 5, or 6[deg]C for 2, 4, 7, or 10 d in darkness. Damage symptoms in the more severe treatments included a waterlogged appearance and a discoloration of the tissue. The symptoms were most obvious in the mesocotyl. After a 10-d grow-out period in the greenhouse, moderately damaged seedlings exhibited chlorotic areas, an occasional disruption in leaf expansion, and a constriction of the mesocotyl. Growth and survival were improved by first exposing seedlings to a 14[deg]C acclimation treatment for 3 d before applying the chilling treatment. After chilling at 5[deg]C for 7 d, 79% of the acclimated seedlings survived, whereas only 22% of the nonacclimated seedlings survived. Differences in gene expression between acclimated and control seedlings were investigated using subtraction and differential screening techniques. Transcripts corresponding to three genes, car333, car30, and car757 (chilling acclimation responsive), were present in higher levels in seedlings after acclimation. Sequence analysis identified car333 as cat3, which encodes maize mitochondrial catalase isozyme 3. Characterization of these three clones revealed that all corresponding transcripts were elevated in acclimated seedlings in a manner that depended on the organ, i.e. coleoptile, mesocotyl, or root. Although transcripts were elevated in all three organs in response to acclimation, car30 was most abundant in the coleoptile and root, whereas cat3 and car757 were most abundant in the coleoptile and mesocotyl. Catalase activity followed the same general trend as cat3 transcript levels. Exogenous treatment with abscisic acid (ABA) resulted in an improvement in growth and survival of nonacclimated, chilled seedlings. Inhibition of ABA biosynthesis with fluridone abolished acclimation-induced chilling tolerance, and exogenous application of ABA to fluridone-treated seedlings restored chilling tolerance. Exogenous ABA treatment also resulted in increases in cat3, car30, and car757 transcript levels and catalase activity in the same organ-specific manner as in acclimated seedlings. These results indicate that ABA synthesis is essential for chilling tolerance. However, measurement of ABA levels in mesocotyls during acclimation and chilling revealed only a marginal increase during acclimation and a dramatic increase during chilling, regardless of whether or not seedlings were acclimated. Thus, although ABA may be required for chilling tolerance, we have no conclusive evidence that the acclimation process is mediated by ABA.

Growth cessation and bud dormancy in relation to ABA level in seedlings and coppice shoots of Betula pubescens as affected by a short photoperiod, water stress and chilling

Seedlings and coppice shoots of Betula pubescens Ehrh. were grown under controlled conditions designed to simulate the annual growth cycle, and a water stress was introduced during the short day (SD). Alleviation of hud dormancy after increasing periods at chilling temperatures was tested under long day (LD) conditions. Abscisic acid (ABA) was analysed in leaf and bud samples by gas chromatography‐mass spectrometry using [2H4]ABA as the internal standard. Elongation growth of coppice shoots was faster than that of seedlings under both LD and SD conditions, while the final growth cessation occurred in a similar manner and was not affected by water stress, which significantly reduced growth rate in both plant types. Bud dormancy gradually decreased with increasing length of chilling, starting from the basal parts of the plant axis. Water stress did not retard hudhurst. but rather improved it in the chilled coppice shoots and in the non‐chilled and partially chilled seedlings. Water content of buds was higher in coppice shoots than in seedlings, but after exposure to SD. it gradually decreased to 45% in both plant types and was not affected by water stress or chilling. The ABA level in both leaves and buds increased during SD treatment and was” enhanced by water stress. No clear differences in bud ABA level were found between the seedlings and coppice shoots under SD conditions, although coppice shoots had less ABA during the preceding LD conditions. There was, in general, no clear effect of chilling on bud ABA level. Budbursl in chilled, single‐node cuttings was inhibited by external ABA treatment, which raised the internal ABA levels 10 to 150 times above normal. The observed correlation between ABA level and water content in buds during induction of dormancy under SD and water stress conditions indicates a possible role for ABA in the regulation of dormancy.

Net CO(2) assimilation of cacao seedlings following dark chilling.

Overnight exposure of cacao (Theobroma cacao L.) seedlings to chilling temperatures between 4.7 and 15.8 degrees C reduced net CO(2) assimilation rate (A) and stomatal conductance to water vapor (g(s)), with temperatures below 10 degrees C causing severe inhibition. Net CO(2) assimilation rates of chilled seedlings recovered to those of nonchilled plants within 7 days. No differences in daytime intercellular CO(2) concentration (c(i)) with overnight temperature were observed on the first day after the chilling treatment, which indicates that the reduction in photosynthesis was not caused by the reduction in stomatal conductance. However, c(i) of chilled plants was much less than that of nonchilled plants on the second day after treatment, which suggests that chilling caused a change in stomatal response to CO(2) concentration. Even 7 days after treatment, when A had recovered to control values, g(s) of chilled leaves was only approximately 70% that of controls. Chilling did not inhibit A through an effect on leaf water potential, which was higher in chilled plants than in unchilled plants.

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.

Effect of temperature and light on ACC and MACC in chilled cucumber seedlings

The levels of the ethylene precursor, 1 -aminocyclopropane-1 -carboxylic acid (ACC) and its conjugate, 1 -(malonyl-amino)-cyclopropane-1 -carboxylic acid (MACC) in cucumber ( Cucumis sativus L.) seedlings at 20°C were higher after exposure to 5°C than after exposure to non-chilling temperatures. The chilled seedlings recovered from chilling-induced wilting after 24 h of warming at 20°C following 1 or 2 days of exposure to 5°C, whereas those exposed to 5°C for 3 days did not recover. Levels of ACC showed a corresponding increase and decrease as the seedlings were chilled and then recovered from the injury. However, MACC content remained elevated even after seedlings had recovered from chilling injury. The susceptibility of seedlings to chilling injury was affected not only by temperature, but also by light intensity. Seedlings exposed to chilling temperature at 5°C under higher photosynthetic photon flux density (PPFD) showed greater chilling injury than those exposed to the same temperature under lower PPFD. ACC and MACC levels, however, were comparable in different PPFD. These data suggested that the stimulation of ACC and MACC is a response to chilling stress, but their endogenous levels may not reflect the severity of chilling injury.

A STUDY ON THE RELATION OF COLD ACCLIMATION AND HARDINESS TO MINERAL NUTRITIONAL AND BIOCHEMICAL FLUCTUATIONS OF THREE AGRICULTURAL FORMS OF BRASSICA OLERACEA L.

The relation of cold acclimation and hardiness with total RNA and DNA, free amino acid nitrogen and soluble protein in various plants has long been known. In this study, this relation has been investigated on non-dormant cabbage. The agricultural aim of our study is to establish the hardy cabbage cultivar, to evaluate the biochemical parameters to be used in improvement studies and to obtain the yield in winter with the applications to inc- rease the hardiness. The effect of cold on three agricultural forras of white head cabbage has been investi­ gated in different development stages. For this purpose, they were planted in different seasons and sampled during seedling and headed phases. While three cultivars planted in June froze, those planted in October did not freeze, chilled onIy. The increases of total RNA and DNA contents during the cold acclimation and har­ diness have been accepted as related with this fact. The increases of total RNA and DNA contents in the headed samples of cultivars are related to cold acclimation and hardiness. Except for the chilled samples of one cultivar, there is a relationship with the content of total RNA in the chilled samples of two cultivars. There is no relationship with the content of total DNA in the chilled samples of seedlings of three cultivars. It has been found out that the changes of free amino acid content showed differences in the cultivars. As for in the headed cultivar, the increase in the free amino acid content is related to cold acclimation and hardiness stages being different than the other cultivars. The free amino acid nitrogen has decreased in the samples of chilled seedlings of the cultivars.

Variation in Sensitivity of Coleus Seedlings to Chilling Injury1

Abstract Four seedlings derived from 3 cultivars of Coleus Χ hybridus Voss and C. blumei Benth were injured when exposed to 5°C for 24, 32, or 48 hours. An exposure of 32 hours or longer increased the foliar damage of chilled seedlings. In the case of ‘Harlequin’ and ‘Weimar Buckley’ seedlings, chilling injury was apparent during or immediately following the 24, 32, and 48 hours chilling exposure. One selection of ‘Red Rainbow’ displayed no symptoms of chilling injury following the 24-hour treatment, and only minor injury after 32- and 48-hour exposure. The other selection was only slightly more sensitive following these treatments. Seven days after a 48-hour exposure at 5°, 100% of the terminal buds of ‘Red Rainbow’ and ‘Weimar Buckley’ seedlings were dead, but no damage was evident on terminal buds of ‘Harlequin’ seedlings. No apparent injury was observed in any seedlings when exposed to 10° for as long as 48 hours.

Effects of Chemical Protectants against Chilling Injury of Young Cucumber Seedlings

Abstract Chilling of 8-day-old cucumber (Cucumis sativus L.) seedlings for 48 hours at 2°C caused reversible damage; chilled seedlings collapsed but regained turgor within 6 hours at 25°. Hypocotyl segments from chilled seedlings exhibited increased solute leakage, ethylene production, and O2 uptake after transfer to 25°. Pretreatment of seedlings with 10−4m abscisic acid generally reduced symptoms of damage but did not prevent chilling injury. Pretreatment with 10−3m CaCl2 was generally ineffective, and pretreatment with 10−3m ascorbate generally intensified symptoms of injury. Oxygen uptake increased during the first 6 hours at 25° but returned to the level of unchilled seedlings within 24 hours. Chilled tissue was sensitive to 2,4-dinitrophenol during this period, although sensitivity was less than in controls during the first 12 hours after chilling. Unchilled tissue was insensitive to SHAM, but O2 uptake was inhibited by SHAM during the respiratory burst following chilling. Tissue was no longer SHAM-sensitive after 24 hours at 25°, by which time the respiratory burst had subsided. Thus, the alternative respiratory pathway was apparently operating only during the time of the respiratory burst, when the seedlings were recovering from chilling injury.