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Holding harvested asparagus spears at non-freezing temperatures below 2.5 °C induces chilling injury (CI), a physiological disorder that reduces quality and shelf life. CI can be quantified by subjective visual parameters, or by objective measurements of the increased rate of ion leakage from excised tissue into an isotonic bathing solution. The rate of ion leakage from apical (2–3 cm), middle (9–10 cm), and basal (15–16 cm) segments excised from 18-cm asparagus spears increased after 7 days of chilling at 2.5 °C. The increase continued and was similar for middle and basal segments after 14 days of chilling, but more pronounced from apical segments. Various heat-shock treatments (i.e., combinations of temperature and duration) decreased the chilling-induced increase in ion leakage from these 1-cm stem segments. Although the chilling tolerance of all spear segments was increased by specific heat-shock treatments, the optimal temperature and duration of exposure varied among the segments; some treatments that were effective in segments from one location were either ineffective or damaging to segments from another location. As the apical half of the whole spear is the predominant culinary portion and contains the most chilling sensitive tissue, heat-shock treatments that would increase the chilling tolerance of the upper half of whole spears were selected for further study. These heat-shock treatments were applied to freshly harvested whole 18-cm asparagus spears that were chilled at 2.5 °C for 14 days. Two treatment combinations (i.e., 45 °C for 4.0 ± 0.6 minutes or 50 °C for 2.9 ± 0.8 minutes) were identified that maintained the highest level of quality and significantly reduced the rate of chilling-induced ion leakage.

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. © 2014 Elsevier B.V.

Cold soil and air temperatures reduce germination, seedling growth, and stand establishment of manyimportant agronomicand horticultural crops. Chilling tolerance of many seeds is lost as they germinate and grow into young seedlings. Cucumber (Cucumis sativus cv. Poinsett 76) seedling radicles lose chilling tolerance as they emerge and elongate. Chillingat2.5Cfor72hreducedsubsequentelongationat25Cby12,41, and 77% for 1-, 10-, and 20-mm-long radicles, respectively. Radicle elongation followed an exponential decline with increasing mannitol concentration (r 2 . 0.9) for radicles initially 1 or 10 mm in length. Chilling1-mmradicles treatedfor 24h in 0.3or0.6Mmannitolinhibited elongation 90 or 40%, respectively. During mannitol treatment, 0.3 and 0.6 M treated radicles increased 12.5 and 0.7 mm in length. Chilling 10-mm radicles treated for 24 h in 0.3 or 0.6 M mannitol inhibited elongation 99 or 33%, respectively. During mannitol treatment, 0.3 and 0.6 M treated radicles increased 23.8 and 1.1 mm in length. The percentage inhibition of chilling-induced radicle elongation was related totheinitialradiclelengthwhenchilledbyacurveoftheformCL 5Co3 (1 2 e 2KL ) that describes many biological reactions where the rate of change is constant and proportional to the amount of reactants present. The increase in chilling-induced inhibition of radicle elongation with increasing radicle length was consistent with the progressive loss of protective compounds, possibly through dilution as the tissue expanded in volume during radicle elongation.

11 pages, 8 figures., In plant tissue, a wound signal is produced at the site of injury and propagates or migrates into adjacent tissue where it induces increased phenylalanine ammonia lyase (PAL, EC 4.3.1.5) activity and phenylpropanoid metabolism. We used excised mid-rib leaf tissue from Romaine lettuce (Lactuca sativa L., Longifolia) as a model system to examine the involvement of components of the phospholipid-signaling pathway in wound-induced phenolic metabolism. Exposure to 1-butanol vapors or solutions inhibited wound-induced increase in PAL activity and phenolic metabolism. Phospholipases D (EC 3.1.4.4), an enzyme involved in the phospholipid-signaling pathway is specifically inhibited by 1-butanol. Re-wounding tissue, in which an effective 1-butanol concentration had declined below active levels by evaporation, did not elicit the normal wound response. It appears the 1-butanol-treated tissue developed resistance to wound-induced increases in phenylpropanoid metabolism that persisted even when active levels of 1-butanol were no longer present. However, a metabolic product of 1-butanol, rather than 1-butanol itself, may be the active compound eliciting persistence resistance. Inhibiting a subsequent enzyme in the phospholipid-signaling pathway, lipoxygenase (LOX; EC 1.13.11.12) with 1-phenyl-3-pyrazolidinone (1P3P) or reducing the product of LOX activity with diethyldithio-carbamic acid (DIECA) also inhibited wound-induced PAL activity and phenolic accumulation. The effectiveness of 1-butanol, DIECA, and 1P3P declined as the beginning of the 1-h immersion period was delayed from 0 to 4 h after excision. This decline in effectiveness is consistent with involvement of the inhibitors in the production or propagation of a wound signal. The wound signal in lettuce moves into adjacent tissue at 0.5 cm h−1, so delaying application would allow the signal to move into and induce the wound response in adjacent tissue before the delayed application inhibited synthesis of the signal. Salicylic acid (SA) inhibits allene oxide synthase (AOS, EC 4.2.1.92), another enzyme in the phospholipid-signaling pathway. Exposure to 1 or 10 mM SA for 60 min reduced wound-induced phenolic accumulation by 26 or 56%, respectively. However, 1 mM SA lost its effectiveness if applied 3 h after excision, while 10 mM SA remained effective even when applied 4 h after excision. At 1 mM, SA may be perturbing the wound signal through inhibition of AOS, while at 10 mM it appears to have some generally inhibitory effect on subsequent phenolic metabolism. These data further implicate the phospholipid-signaling pathway in the generation of a wound signal that induces phenolic metabolism in wounded leaf tissue.

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 degrees 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.

Wounding lettuce (Lactuca sativa L., var. Longifolia) leaves induced an eight-fold increase in the activity of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), and the subsequent accumulation of phenolic compounds and tissue browning at 10degreesC. PAL is a key enzyme in the synthesis of phenolic compounds. A PAL cDNA was previously isolated by reverse-transcription PCR using total RNA from wounded lettuce leaves. RNA gel blots showed that maximum accumulation of both PAL mRNA and PAL enzyme activity occurred 24 h after wounding. A 2-min heat shock at 45degreesC administered within 5 min of wounding delayed the wound-induced increase in PAL activity, but did not delay the increase in wound-induced PAL mRNA. Changes in the content of PAL protein were also followed by immunoblot using anti-PAL antibody raised against the bacterially expressed protein from the cDNA. Immunoblots showed that the level of PAL protein in wounded lettuce tissue was significantly reduced by the heat shock treatment. These data suggest that heat shock reduces the rise in wound-induced PAL enzyme activity by reducing the translation of wound-induced PAL mRNA, or by increasing the turnover of the induced PAL protein.

Phenylalanine ammonia-lyase (PAL) catalyses the first step controlling the rate of phenylpropanoid metabolism. Wounding is a ubiquitous stress in nature and in the harvesting and preparation of fruits and vegetables that induces an increase in PAL activity, an accumulation of phenolic compounds and subsequent tissue browning. A wound-inducible PAL gene (LsPAL1) was isolated from Romaine lettuce by RT-PCR. The putative protein encoded by LsPAL1 is similar to predictive polypeptides sequences for other PALs. The kinetics of PAL mRNA accumulation is similar to those of induced PAL enzyme activity, with enzyme activity following mRNA accumulation by 12 h. Wound-induced PAL transcripts accumulated in cells close to the wound sites. Tissue printing showed that PAL mRNA was associated with tissue next to the epidermis and vascular bundles. A heterologous PAL protein was expressed in E. coli and was found to show significant PAL activity.

Exposure to a chilling temperature of 2.5 degrees C for 96 h inhibited the subsequent growth of cucumber seedling radicles at 25 degrees C by 92%. Exposing seedling with 5 +/- 1 mm long radicles to acetaldehyde vapour (275 micro l l(-1)) or to an aqueous ethanol solution (0.6 M) for 2 h, or to 45 degrees 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 [(35)S]-methionine) by about 70%. In contrast, treatment for 2 h with an aqueous arsenite solution (100 micro M) had no effect on chilling sensitivity or the incorporation of [(35)S]-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.

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 45degreesC 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 (R-2 > 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 45degreesC 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.

Ethylene production was measured from excised 10-mm apical and subapical root segments from 50 cultivars in 19 species of 7 families. Monocotyledonous species tended to have much lower rates of ethylene production than dicotyledonous species. Ethylene production was generally higher in apical root segments than in subapical segments within 1 h of wounding. However, cultivars of Cucumis melo, C. sativus, Helianthus annuus, Hibiscus esculentus, and Zea mays had higher rates of ethylene production from subapical segments. In apical root segments, Phaseolus aureus cv. Berken had the highest ethylene production rate (76.7 etal g(-1) h(-1)), while Zea mays cv. Silver Queen had the lowest rate (0.6 etal g(-1) h(-1)). In subapical root segments, Cucumis sativus cv. Armenian had the highest rate (55.7 etal g(-1) h(-1)), while Zea mays cv. Silver Queen again had the lowest rate (0.6 etal g(-1) h(-1)). The many different responses in magnitude and kinetics of wound-induced ethylene production among the species, cultivars and tissues should provide interesting and useful systems with which to study wound responses and induced ethylene production.

The chilling tolerance of cucumber seedling radicles was influenced by their relative levels of vigour. Radicles of high-vigour seedlings grew to 20 mm in length in 36 h at 25 ° C, whereas it took 60 h for low-vigour seedling radicles to reach that length. Chilling at 2·5 ° ° ° C for 48 h inhibited the subsequent growth of high- and low-vigour seedlings by 39 and 68%, respectively. The 2,3,5-triphenyltetrazolium chloride (TTC) viability index, and α , α -diphenyl- β -picrylhydrazyl (DPPH)-radical scavenging activity were higher in high than low-vigour radicles. Higher ascorbate peroxidase (APX) and catalase (CAT) enzyme activity, DPPH-radical scavenging activity, and recovery of CAT activity after chilling in high-vigour radicles corresponded with their higher level of chilling tolerance in comparison with low-vigour radicles. In contrast, elevated levels of superoxide dismutase, glutathione reductase and guaiacol peroxidase appear to be correlated with chilling injury since they only showed substantial increases in activity in the more chillingsensitive low-vigour radicles after chilling. Manipulation of APX, CAT, and/or DPPH activity could produce plants with superior and persistent chilling tolerance.

Wounds and injuries incurred during preparation of fresh-cut lettuce (Lactuca sativa L.) stimulate phenolic metabolism, which leads to tissue browning. Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5.) is the first committed enzyme in the phenylpropanoid pathway and regulates its overall activity. Maximum activity of wound-induced PAL occurred sooner as the storage temperature increased from 0 to 25 °C, but the maximums were lower. A heat shock at 50 °C for 90 seconds protected fresh-cut lettuce tissue against browning, helped retain greenness, and decreased subsequent production of phenolics when applied either after or before wounding. Browning was reduced when the heat shock was applied up to 36 hours after wounding, while the maximum effect occurs around 6 hours before cutting. Like the heat-shock treatment, the protein synthesis inhibitor cycloheximide reduced wound-induced PAL activity, but it did not prevent tissue browning. When cycloheximide was applied in combination with heat-shock treatments, browning did not occur. Heat shocks may control tissue browning by more than just interfering with protein synthesis.

Seeds of cotton (Gossypium hirsutum L.), kenaf (Hibiscus cannabinus L.), okra [Abelmoschus esculentus (L.) Moench. `Clemson Spineless' (syn. Hibiscus esculentus L.)], rice (Oryza sativa L.), and wheat (Triticum sativum (L.) Lam.) were germinated and grown at 25 °C until their radicles reached 10 mm in length. They were then exposed to chilling temperatures for 0 to 5 days followed by 3 days at 25 °C. Radicle length was measured periodically and inhibition of elongation was used as an indicator of the severity of chilling injury. Exposure to chilling reduced radicle elongation in all species except chilling insensitive wheat. When seedlings were heat-shocked at 45 °C for 1 to 12 min before being chilled, radicles of the chilling sensitive okra, kenaf, cotton, and rice seedlings elongated more than seedlings not heat-shocked before chilling. The method of heat-shock application and the stringency (i.e., time× temperature) of the heat-shock and chilling treatments all affected the response of the tissue. In comparison to nonheat-shocked wheat seedlings, the radicles of chilling insensitive wheat seedlings did not elongate more than seedlings in which the heat shocks were applied before chilling. A brief heat shock ameliorates chilling injury in these chilling sensitive species.

An in vitro assay was used to determine the effect of AA and pH on the enzymatic and nonenzymatic production of ethylene (C2H4) from ACC. We were interested in the effect of AA on C2H4 production from ACC because aldehydes, primarily AA, can accumulate in tissue as the result of ripening, storage under modified atmospheres, packaging, and stress. Using crude extracts of ACC oxidase from tomato (Lycopersicon esculentum Mill. `Castlemart') and apple (Malus ×domestica Borkh. `Golden delicious'), C2H4 production from ACC was shown to increase in response to an increase in pH above 7.2 and inclusion of 0.2 to 2 mm AA. Nonenzymatic C2H4 production from ACC also increased linearly with increasing AA concentrations in all the buffers tested. Removal of ascorbate or O2 suppressed AA-induced nonenzymatic C2H4 production. Nonenzymatic AA-induced production of C2H4 from ACC appeared to be an ascorbate dependent oxidation, which was augmented by O2 and was sensitive to minor pH fluctuation. The nonenzymatic AA-stimulated conversion of AEC to 1-butene lacked stereospecificity. Formaldehyde and propionaldehyde also stimulated C2H4 production from ACC. These data indicate that ACC oxidase assays or C2H4 measurements assessing physiological status can be seriously affected by the presence of aldehydes, such as AA. Chemical names used: AA, acetaldehyde; ACC, 1-aminocyclopropane-1-carboxylic acid; AEC, 1-amino-2-ethylcyclopropanecarboxylic acid; ADH, alcohol dehydrogenase; EtOH, ethanol.

Wounding during minimal processing of lettuce (Lactuca sativa, L.) induces alterations in phenolic metabolism that promote browning and the loss of quality. The activity of phenylalanine ammonia-lyase (PAL; the first committed enzyme in phenylpropanoid metabolism) and the concentration of phenolic compounds (e.g., chlorogenic acid, dicaffeoyl tartaric acid, and isochlorogenic acid) increase in excised iceberg lettuce midrib segments after wounding. The effect of short heat-shock treatments on browning and phenolic metabolism in excised midrib segments of iceberg lettuce was studied. As the heat-shock temperature increased from 20 to 70 °C, there was a decrease in the subsequent increase in PAL activity and the accumulation of phenolic compounds in excised midrib segments. Treatments of 45 °C for 120 s, 50 °C for 60 s, or 55 °C for 30 s significantly reduced the increase in PAL activity and subsequent browning seen in control tissue after wounding. Exposure to 45 °C for 480 s, 50 °C for 60 s, or 55 °C for 45 s prevented PAL activity from rising above initial levels. Phenolic compounds remained at initial levels for 3 days in excised midribs exposed to 50 °C for 90 s or to 55 °C for 60 s. However, 55 °C damaged the tissue, as indicated by a* and L* Hunter color values. The synthesis of chlorogenic acid, dicaffeoyl tartaric acid, and isochlorogenic acid was greatly reduced by these heat-shock treatments. These treatments also decreased polyphenol oxidase activity and, to a lesser extent, peroxidase activity.

`Castlemart' tomato (Lycopersicon esculentum Mill.) pericarp discs were used to study the physiological effects of acetaldehyde and ethanol on fruit ripening. Short-term exposure of discs from mature-green fruit to acetaldehyde vapors on a fresh mass basis (≤500 μg·g-1) or ethanol vapors (≤3 mg·g-1) promoted ripening, while higher concentrations inhibited ripening. Discs from mature-green fruit absorbed greater amounts of ethanol and produced significantly higher concentrations of acetaldehyde than discs from breaker fruit. Ripening was promoted by ethanol when the discs were unable to retain or produce a certain level of acetaldehyde. Inhibition of ripening by 4 hours of exposure to ethanol (6 mg·g-1) was almost completely abolished by hypobaric treatments (18 kPa for 24 hours). However, acetaldehyde-induced ripening inhibition (2 days exposure to 180 μg·g-1) was only slightly reduced by vacuum. Concentrations of acetaldehyde and ethanol that inhibited ripening reduced C2H4 production, whereas lower concentrations of acetaldehyde and ethanol that promoted ripening increased C2H4 production. Application of 4-methylpyrazole, an alcohol dehydrogenase inhibitor, enhanced acetaldehyde-induced ripening inhibition and reduced ethanol-induced ripening inhibition or promotion at all concentrations of acetaldehyde and ethanol tested. The inhibition or promotion of ripening of excised tomato pericarp discs by ethanol and acetaldehyde depended on initial fruit maturity, applied volatile concentration, and duration of exposure.

The phenolic composition of whole heads and excised midrib sections of iceberg, butter leaf, and romaine lettuce (Lactuca sativa L.) was followed at 5 and 10 °C during the first 3 days after wounding or during continuous exposure to 10 μL·L-1 ethylene in air. After 3 days of storage at 5 and 10 °C, only 5-caffeoylquinic acid (chlorogenic acid), 3,5-dicaffeoylquinic acid (isochlorogenic acid), caffeoyltartaric acid, and dicaffeoyltartaric acid were detected in wounded lettuce midribs. Of these four compounds, chlorogenic acid accumulated to the highest level in all three lettuce types. The content of caffeic acid derivatives increased 3- and 6-fold after 72 hours of storage at 5 and 10 °C, respectively. The synthesis of caffeoyltartaric acid was not induced by wounding in iceberg lettuce, while chlorogenic acid increased 5-fold at 5 °C and 10-fold at 10 °C. Similar relative phenolic compositions were detected in the three lettuce types studied, although at different concentrations. Changes observed in the content of individual phenolic compounds during the first 3 days of ethylene exposure seemed to follow the same pattern observed during wound induction of the synthesis of phenolic compounds. Chlorogenic acid increased 5-fold and isochlorogenic acid increased 10-fold, while the content of caffeoyltartaric derivatives were not significantly altered by ethylene treatment. Isochlorogenic acid, which was only present in low amounts in the control, was synthesized in the later steps of wound and ethylene induction. Similar kinetics for the induction of phenolic compounds were observed in the three lettuce types studied, suggesting that the mechanisms by which wounding induces phenylpropanoid synthesis are common for the different lettuce types.

Inhibition of tomato (Lycopersicon esculentum Mill.) fruit ripening by exogenously applied ethanol was shown to be caused by elevated endogenous levels of acetaldehyde (AA). Exposure of excised pericarp discs of mature-green tomato fruit to ethanol or AA vapors produced elevated levels of both compounds in the tissue, but only the levels of AA were associated with ripening inhibition. Ripening inhibition was dependent on both the applied concentration and the duration of exposure. Discs treated with inhibitory levels of AA had levels of ethanol that were elevated but below that associated with inhibition of ripening. The in vivo activity of alcohol dehydrogenase was inhibited 40 to 60% by 4-methylpyrazole (4-MP), a competitive inhibitor of this enzyme. The inhibitory effect of ethanol on ripening was reduced by the simultaneous application of 4-MP. Tissue treated with 4-MP plus AA vapors had higher endogenous levels of AA and ripening was inhibited longer than in tissue without 4-MP. The tissue AA level resulting from ethanol or AA application appears to be the critical determinant of ripening inhibition.

Germinating `Poinsett 76' cucumber (Cucumis sativus) seeds are chilling sensitive, and subsequent radicle elongation is inhibited by exposure to nonfreezing temperatures below 10 °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 °C without significantly affecting the rate of radicle elongation. However, neither elongation nor curvature occurred in similar seeds held at 2.5 or 5 °C. Chilling seeds with 5-mm-long radicles at 2.5 °C for 18 hours significantly reduced the subsequent rate of radicle elongation at 25 °C by 47% compared with nonchilled control, while gravitropic curvature was reduced by only 34%. After 36 hours of recovery at 25 °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 °C for 4 to 10 minutes significantly diminished the chilling-induced reduction in radicle elongation and gravitropic curvature.

Chilling sensitivity increased as the radicle of germinating corn (Zea mays L. `Jubilee' hybrid), cucumber (Cucumis sativus L. `Poinsett 76'), mung bean (Phaseolus aureus Roxb. `Berkin'), and tomato (Lycopersicon esculentum Mill. `Rio Grande') seeds increased in length from 1 to 7 mm. In contrast, radicles of germinating okra (Hibiscus esculentus L. `Clemson' spineless) seeds exhibited similar levels of chilling sensitivity at all radicle lengths. The degree of chilling sensitivity varied among the species in relation to time required to elicit a significant response and the magnitude of the elicited response. Based on subsequent radicle elongation, okra and cucumber were the most sensitive species to chilling at 2.5C for 96 h; tomato and corn were relatively less sensitive, and mung bean was the least sensitive. This pattern of sensitivities changed when other criteria were used to evaluate chilling sensitivity. The development of lateral roots decreased with prolonged chilling in all species, except for corn in which the apical tip remained viable even after 192 h of chilling. Heat shock (0 to 10 min at 45C) induced chilling tolerance in all species, except okra. In okra, neither increasing the heat shock temperature nor decreasing the severity of chilling (i.e., temperature and duration of exposure) resulted in a significant reduction in chilling injury. The differential induction of heat shock proteins in okra and the other species is discussed.

This study was undertaken to determine if endogenous IAA content and axillary bud development correlate with phenylalanine ammonia-lyase (PAL) induction and russet spotting (RS) susceptibility among RS susceptible and resistant cultivars of Iceberg lettuce (Lactuca sativa L.). Final levels of ethylene-induced PAL activity and RS development were highly correlated among cultivars, field conditions, and harvest dates. Harvested Iceberg lettuce midribs contained relatively low amounts of free IAA (maximum of 5.2 ng·g-1 fresh weight). There was poor correlation between free IAA content in lettuce leaf midribs and final RS development among all cultivars, growing conditions, and harvest dates. Axillary bud development, as measured by the number of visible buds per head, bud weight, or bud length, were not significantly correlated with final RS development or midrib IAA content. Cultivars with higher initial free IAA content lost much of their IAA after 8 days storage at 5C in air ± ethylene.

The density of excised 2-cm celery (Apium graveolens L.) petiole segments was highly correlated with a subjective evaluation of pithiness. Loss of density and the appearance of pithiness was stimulated by lengthening the duration of storage, raising the storage temperatures above 0C, and excising petiole segments. Segments excised from the upper two- thirds of the petiole lost less density during storage than segments excised from the bottom third of the petiole. Segments with initial high densities lost slightly less density during storage at 5C for 5 weeks than segments that were initially less dense. The extent of pithiness development varied significantly among six cultivars held at 5C for 2 weeks. Treating whole petioles with 1 µM abscisic acid for 4 days significantly increased density loss. Exposing petiole segments to up to 100 µl·liter -1 ethylene in humidified air for up to 2 weeks at 5C did not significantly change density over air controls. The loss of density and the development of pithiness in lightly processed celery petioles could be reduced by selecting resistant cultivars, monitoring water stress during growth, using only segments excised from the upper two-thirds of the petiole, and selecting segments with initial high densities. Air spaces that form in the cortex of many plant tissues such as celery petioles, corn roots, tomato stems, and roots of wetland species are collectively called aerenchyma. Aerenchyma develops through the lysis of parenchymatou s cells of the cortex and is stimulated by a variety of stresses, such as deficiencies in water, oxygen, and minerals, and is thought to enhance oxygen transport within the plant since it is associated with the tolerance of some crops to anaerobic soils (Drew et al., 1979). When aerenchyma forms in tomato stems and celery petioles, it is often referred to as pithiness. Pithiness is characterized by the appearance of whitish regions and air spaces within the tissue, and is a major source of quality loss and decreased shelf life in celery. Several climatic and storage factors have been associated with the development of pithiness in field-grown celery plants, in harvested stalks and processed petioles. Abscisic acid (ABA) may have a role in aerenchyma development since an increase in endogenous levels of ABA followed water stress and the develop- ment of aerenchyma (Livne and Vaadia, 1972). Water stress during growth favors development of pithiness in celery (Aloni and Pressman, 1979). They found that the level of free ABA in water stressed celery increased before the onset of pithiness and was related to the development of pithiness in celery petioles. Withholding water increased the level of ABA 7-fold after 24 h, with a rapid increase in pithiness occurring after 3 days. Also, exogenously applied ABA induced pithiness in detached petioles, with the degree of pithiness increasing with ABA concentration. They hypothesized that ABA production induced by water stress stimulated the development of pithiness. Aloni and Pressman (198 1) subsequently investigated the relationship between water stress in the field and ABA content on the development of pithiness in tomato stems. The degree of pithiness was greater in drought- stressed plants treated with 20 µ M ABA than in water-stresse d plants alone. Nonstressed plants treated with ABA exhibited more pithiness than controls, but less than water-stressed plants. Aloni

A proposed mechanism of white discoloration development on peeled carrots included both physical and physiological responses to wounding. The physical response is a color change due to reversible surface dehydration. This study was performed at 2.5 and 10°C using a mode1 system controlling relative humidity, at 33, 75 or 98%, and a commercial system with low-density polyethylene (LDPE) plastic film bags. The rate of surface discoloration increased with decreasing RH. When excess surface moisture was left on peeled carrots, rates of white development decreased sharply at all RH compared with a dewetted control. The same effects were observed on peeled carrots stored in LDPE bags. Carrots partially regained their original color when water-dipped, due to reversal of the physical response component.

Excised mung bean (Vigna radiata L.) hypocotyl sections were exposed to 40 °C for up to 4 h in the presence or absence of 50 μM cycloheximide (CHX) before being held at a non-chilling (20°C) or chilling (2.5°C) temperature. Mung bean hypocotyl tissue is chilling sensitive, and the rate of solute leakage is highly correlated with the extent of chilling injury. A 3 heat shock at 40°C reduced chilling-induced solute leakage by up to 40%, but leakage was similar to non-heat-shocked hypocotyls when CHX was present. Specific proteins were labelled when hypocotyls were exposed to [ 35 S] methionine during the last hour of heat shock. The nine most intense bands on the autoradiographs of SDS-PAGE gels of extracted protein corresponded to molecular weights of 114, 79, 73, 70, 60, 56, 51, 46, and 18 kDa. The 18 kDa band reached a maximum after 1 h at 40 °C and then rapidly decreased in intensity as the heat shock continued, becoming undetectable at 4 h. The four most intense bands after 3 h at 40°C corresponded to molecular weights of 79, 70, 51, and 46 kDa. The synthesis of these four hsps was markedly reduced when the hypocotyl sections were exposed to CHX during heat shock. During chilling for 6 d, the levels of hsps 79 and 70 remained significantly higher in tissue that was heat shocked prior to chilling than in tissue that was not heat shocked. In contrast, the levels of hsps 51 and 46 were similar in both heat-shocked and control tissues. Heat-shock-induced chilling tolerance was lost between 6 and 9 d of storage at 2.5°C; this loss coincided with the decay of hsps 79 and 70 to control levels. These results suggest that heat shock induces an increase in both chilling tolerance and the de novo synthesis of specific heat shock proteins; namely hsps 79 and 70. This is the first report showing a relationship between heat-shock-induced chilling tolerance and specific heat-shock-induced proteins.

Unlike horticulturally mature fruit of 'Dasher II' and 'Poinsett 76' cucumbers (Cucumis sativus L.), two cultivars that differ significantly in their level of chilling tolerance, imbibing and germinating seeds of these two cultivars responded similarly to chilling temperatures (e.g., increases in fresh weight, time to radicle emergence, and root growth). 'Dasher II' and 'Poinsett 76' seeds were imbibed and germinated at 10 to 30C, and seeds germinated at 25C for 24 h were chilled at 2.5C for various durations. In comparison, seeds from an aged lot of 'Poinsett 76' seed (1989) responded very differently from the 1992 seed lots in all experiments. The chilling tolerance level of germinating 'Poinsett 76' seed varied with the seedling age as measured by resumption of root growth. Our results suggest that some factor that confers chilling tolerance is gradually lost during the early stages of germination following imbibition. Uniform germination and seedling establishment is crucial for the commercial growth of many agricultural crops. Species that originated in the tropics or subtropics are especially sensitive to chilling (i.e., physiological injury caused by exposure to nonfreez- ing temperatures below ≈10C) that often occurs under early season temperate conditions (Bennett et al., 1992; Bradow, 1990; Christiansen, 1968; Harrington and Kihara, 1960; Herner, 1990; Nelson and Sharples, 1980; Pollock and Toole, 1966; Sachs, 1977). Although low soil temperatures can be avoided in commer- cial practice by delaying planting, there is an economic incentive to achieve early season harvest or extend the growing season by planting under less than ideal conditions early in the season. The delay in planting to await more favorable temperature conditions can be compensated for by using transplants, but transplants of chilling sensitive crops are also susceptible to injury when exposed to chilling temperatures during production or after planting.

Freshly harvested asparagus (Asparagus officinalis L.) spears were exposed to an anaerobic N2 atmosphere for 0, 2, 4, or 6 hours at 2.5 or 20C and then returned to 2.5C. Carbon dioxide production was measured each day, starting 3 days before and ending 11 days after the treatment. Significant increases in CO2 production relative to 0-hour controls were found within 1 day of treatment at 20C and were directly proportional to the duration of the anaerobic exposure. At 2.5C, CO2 production relative to the 0-hour control was stimulated by the 2- and 4-hour treatments and depressed by the 6-hour treatment, with the relative rate of production inversely proportional to the duration of the anaerobic treatment. A decrease in CO2 production occurred 7 days after N2 treatment, regardless of temperature. A sensory panel evaluated effects of treatments on appearance quality 7 and 15 days after treatment and on taste quality 4 days after treatment. Judges could not detect any significant differences between anaerobic treatments and control. No significant difference was found in the percent of decayed asparagus among treatments as detected by visual evaluation 6 days after treatment. It appears that exposure to an anaerobic N2 atmosphere for up to 6 hours was not detrimental to the storability or quality of harvested asparagus spears. These results indicate that cooling with vaporized liquid N2, during which an anaerobic atmosphere could be produced before the spears were significantly cooled, would not reduce subsequent quality or storability.

Cucumber (Cucumis sativus L. cv. Poinsett 76) seedlings with fully expanded cotyledons, and excised cotyledons, first true leaves, hypocotyl segments and fruit mesocarp discs were exposed to vapours from a series of aqueous alcohol solutions of 0 to 320 mM methanol, ethanol, n-propanol, n-butanol, and n-pentanol during chilling at 2.5 o C for 5 d. Certain concentrations of each alcohol reduced subsequent chilling-induced ion leakage from the cotyledons and leaves. Exposure of cotyledons to certain methanol or ethanol solutions also reduced chilling-induced ethylene production, but not carbon dioxide production. In contrast, exposing cucumber seedlings with fully expanded cotyledons to the same series of alcohol concentrations that resulted in reduced chilling-induced ion leakage and ethylene production of excised cotyledons actually increased chilling injury of the seedlings

High pressures and anaesthetics were used to study chilling injury in plants. Changes in membrane fluidity at low but nonfreezing temperatures are thought to be involved in cgilling injury-a physiological disorder of many economically important plants, e.g. banana, cotton, cucumber, maize, rice, sorghum, and tomato. High-pressure helium and nitrogen atmospheres of 12 MPa increased the severity of chilling injury (i.e. rate of ion leakage) in excised cucumber cotyledon discs, cucumber hypocotyl segments and tomato pericarp discs, and also increased the threshold temperature at which chilling occurred by 2 o to 6 o C. Exposure to vapours of the anaesthetics halothane and methoxyflurane reduced chilling injury in cucumber cotyledon di cucumber hypocotyl segments and tomato pericarp discs

A burst in respiration coincident with fruit ripening has been used for over half-a-century to classify harvested fruit such as apples, bananas, melons, and tomatoes as climacteric. In contrast, respiration slowly declines in harvested non-climacteric fruit such as citrus and strawberries. Autocatalytic ethylene production was later recognized as accompanying the ripening of climacteric fruit. We developed a procedure to insert sterile ports in netted muskmelon (Cucumis melo var. Reticulatus Naud.) fruit to allow repetitive sampling of internal gases in both attached and detached fruit as they ripened. Detached fruit produced the characteristic climacteric pattern of carbon dioxide and ethylene production as they ripened

The physiological responses associated with chilling of horticultural ly mature cucumber (Cucumis sativus L.) fruit were examined using 13 lines that differ in chilling sensitivity. The low correlation coefficient between pitting and decay suggested that these two early manifestations of chilling injury are not significantly related. Likewise, fruit pitting and decay were not highly correlated with the tolerance of seedlings to chilling, suggesting that fruit and seedlings of the same line may have dissimilar sensitivity to chilling temperatures. Exudates from fruit cut in half transversely were collected on filter paper. The amount of exudate showed a significant correlation with pitting, decay, and percent ion leakage after 10 days of chilling. The fresh and dry weight of the exudates from fruit kept for 8 days at 12.5C ranged from 141- to 346-mg fresh weight and from 15 to 47-mg dry weight, respectively. Cucumber lines that were more sensitive to chilling had watery exudate, as indicated by their lower dry weight and percent solids. The conductivity of exudates from sensitive lines was higher (60 µsiemen/cm) than from chilling resistant lines (30 µsiemen/cm). Chilling-induced ethylene production was higher in sensitive than in resistant lines, and chilling caused a greater loss of ethylene forming enzyme activity in resistant lines than from chilling sensitive lines. Chilling injury is an economically important postharvest problem that reduces the overall quality and marketability of many harvested fruits and vegetables indigenous to the tropics and subtropics (Couey, 1982; Lyons, 1973; Saltveit and Mor- ris, 1990). Sensitivity to chilling injury varies among species of Passiflora (Patterson et al., 1976) and Lycopersicon (Paull, 1981), among cultivars of avocados (Persea americana Mill.; Hatton et al., 1965), cucumbers (Jasim and Marr, 1989), pa- payas (Carica papaya L. ; Chen and Paull, 1986), tomatoes (Lycopersicon esculentum Mill.; Burgis, 1970; King and Ludford, 1983), and watermelons (Citrullus lunatus L.; Risse et al., 1990). Chilled cucumbers exhibit reduced shelf life characterized by accelerated water loss, surface pitting, and increased sus- ceptibility to disease (Eaks and Morris, 1956, 1957; Ryall and Lipton, 1979). A significant increase in solute leakage was observed from mesocarp tissue excised from cucumbers exposed to chilling temperatures (Cabrera and Saltveit, 1990; Tatsumi and Murata, 1978; Tatsumi et al., 1981). Jasim and Marr (1989) observed that leakage of Mg+ and K+ was greater in sensitive than in resistant cultivars of cucumbers after 20 days at 4.4C. Surface pitting developed on 'Poinsett 76' fruit that were exposed to 2.5C for > 3 days (Cabrera and Saltveit, 1990). Similar results were observed by Jasim and Marr (1989) in resistant cultivars, (e.g., 'Dasher II' and 'Universal'), but not in sensitive cultivars, (e.g., 'Monarch' and 'Sweet Slice'), which showed slight pitting after the fruit were exposed to 4.4C for 3 days. The objectives of this present study were to characterize the physiological responses of fruit from various cucumber cultivars to chilling temperatures, and to correlate these changes with subjective evaluations of chilling injury in those fruit.

Tomato fruit (Lycopersicon esculentum Mill., cv. Castelmart) were harvested at various degrees of ripeness and exposed to ethanol vapor at 0, 2, or 4, ml·kg-1 in a 20-liter jar for 0, 2, 4, or 6 hours at 20C. Ripening was measured as changes in subjective color and in firmness and production of CO2 and ethylene. The soluble solids concentration (percent), titratable acidity (percent), and pH were measured at the end of the storage period when the fruit were red-ripe. Ethanol's inhibition of ripening was not confined to mature-green fruit, but also inhibited reddening of breaker, turning, and pink fruits. Storage of mature-green fruit at 20, 15, or 12C after treatment with 0 or 2 ml ethanol/kg at 20C prolonged the delay in ripening for 5, 6, and 7 days, respectively, compared with controls. There was no reduction in the quality of these fruit when they were red-ripe, even though there was an 11-day difference between the time the 20C control and the 12C-treated fruit became red-ripe. An informal panel did not detect any differences in flavor between these control and ethanol-treated fruit that were red-ripe. Increasing the duration of exposure to ethanol vapors from 2 to 6 hours had a pronounced effect on ethylene and CO2 production, but it did not significantly prolong the inhibition of ripening of mature-green fruit nor did it change their rate of softening during ripening. Increasing the temperature during exposure increased the effectiveness of ethanol, with the same level of inhibition produced by 6 hours at 20C, 4 hours at 25C, or 2 hours at 30C. Postharvest use of ethanol vapor to retard ripening may be a useful technique to extend the market life of tomato fruit.

Etiolated pea (Pisum sativum cv Alaska) seedlings growing against a horizontal barrier in the soil will assume a horizontal orientation and continue to grow for prolonged periods of time. With removal of the barrier or after seedlings grow out from underneath the obstruction, seedlings immediately return to normal vertical growth. Ethylene production increased several hours after the seedlings began to grow horizontally and not at the first contact with a barrier. Increases in ethylene production from horizontally growing seedlings were associated with decreased rates of elongation and increased stem diameter. The data suggest that increased ethylene production does not play a mediating role in the horizontal growth of pea seedlings when obstructed during emergence. We conclude that seedlings follow a path of least resistance when they grow against a barrier in the soil.

Additional index words. CO2, climacteric, color, C zH4, firmness, respiration, soluble solids "Abstract. External color, length, diameter, fresh weight, C0 2 production, internal C2HA concentration, flesh firm- ness, soluble solids concentration (SSC), flesh color, and seed cavity diameter were measured during fruit growth and maturation of seven melon cultivars (Cucumis melo L., Inodorus Group, Naud. CV. 'Amarelo', 'Golden Beauty Casaba', 'Honey Dew', 'Honey Loupe', 'Juan Canary', 'Paceco', and 'Santa Claus Casaba') of known age. There was no increase in C0 2 production either during ripening (e.g., loss of firmness and increased SSC) or with increasing C2H4 levels in fruit from any of the seven cultivars. There was a significant decline in respiration only at the second sampling date, which ranged from 14 to 18 days after anthesis. Respiration measured 1 week later was substantially higher and was followed by a general decline. This post 14- to 18-day rise in respiration was not a climacteric since it occurred well in advance of other ripening characteristics, e.g., loss of firmness, increase in SSC, or rise in internal C2H4. The increase in internal C2H4. coincided with or followed attainment of full fruit size, while flesh softening and the rapid rise in SSC preceded the rise in internal C 2H4, concentration. Respiration declined from 67 to 18 ml CO 2/ kg per hour by day 43 in all cultivars, except 'Honey Dew' and 'Honey Loupe'. Respiration in 'Honey Loupe' remained above 23 ml CO2/kg per hour and showed a rise to 32 ml/kg per hour on day 53. Respiration in 'Honey Dew' did not fall below 18 ml CO2/kg per hour until day 53. As with internal C 2H4 levels, there was no correlation between changes in and any marked change in the other signs of ripening that were measured. Morphological and physiological changes during fruit growth, maturation, and ripening of many melon cultivars have not been studied extensively, even in countries where the fruit are grown commercially and are very popular. Many diverse types of mel- ons are marketed; they differ in shape, external and internal color, surface netting, sweetness, flavor, and storability. While muskmelons have long been popular in the United States, ca- sabas are only now becoming as popular with American con- sumers as they are with consumers in other countries. The best flavor for melons depends on sweetness and on various volatile compounds that are not yet fully identified (Ya

Symptoms of chilling injury were reduced by intermittently warming cucumber fruit (Cucumis sativus L. cv. Poinsett 76) from 2.5 to 12.5C for 18 hr every 3 days. Fruit continuously held at 2.5C for 13 days developed severe pitting and decay after 6 days at 20C, while fruit continuously held at 12.5C or intermittently warmed showed no pitting or decay during subsequent holding at 20C. The increased rate of C2H4 production during the first warming period, from 12 nl·(kg·hr)-1 at 2.5C to 201 nl·(kg·hr)-1 at 12.5C, was significantly greater than that during the second or third warming periods, i.e., 53 to 98 and 53 to 55 nl C2H4/(kg·hr), respectively. Respiration increased 3-fold during the initial warming period, but only 2-fold during subsequent warming periods. Leakage of cellular ions from excised disks of mesocarp tissue was around 6% and 10% of the total ion content of the tissue for control and intermittently warmed fruit, respectively, but increased to 17% for fruit that were continuously held at 2.5C for 10 days. After 320 hr (three cycles) of chilling and warming, chilled fruit showed significantIy lower ethylene-forming enzyme activity than the control or intermittently warmed fruit. Fruit held at 12.5C contained 0.09 to 0.34 nmol·g-1 of ACC. ACC levels were 6.23 nmol·g-1 in fruit exposed to 2.5C for 320 hr. In contrast, intermittently warmed fruit only showed 30% and 27% increases in ACC content during the first and second warming periods, respectively. Periodic warming appears to allow chilled fruit to acclimate to subsequent periods of chilling. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).

9 pages, 7 figures., A wound signal originates at the site of injury in lettuce (Lactuca sativa L.) leaf tissue and propagates into adjacent tissue where it induces a number of physiological responses which include increased phenolic metabolism with the de novo synthesis of phenylalanine ammonia lyase (PAL, EC 4.3.1.5), the synthesis and accumulation of soluble phenolic compounds (e.g., chlorogenic acid), and subsequent tissue browning. Exposing excised mid-rib leaf tissue to vapors (20 μmol/(g FW)) or aqueous solutions (100 mM) of n-alcohols inhibited this wound-induced tissue browning by 40 and 60%, respectively. Effectiveness of the alcohol increased linearly from ethanol to the 7-carbon heptanol, and then was lost for the longer n-alcohols 1-octanol and 1-nonanol. The 2- and 3-isomers of the effective alcohols did not significantly reduce wound-induced phenolic accumulation at optimal 1-alcohol concentrations, but significant reductions did occur at much higher concentrations (100 μmol/(g FW)) of the 2-, and 3-isomers. The active n-alcohols were maximally effective when applied during the first 2 h after excision, and were ineffective if applied 6 h after excision. Phospholipase D (PLD) and its products linolenic acid (LA) and phosphatidic acid (PA) are thought to initiate the oxylipin pathway that culminates in the production of jasmonic acid, and PLD is specifically inhibited by 1-butanol, but not by 2-, or 3-butanol. These results suggest that PLD, LA, PA, and the oxylipin pathway may be involved in producing the wound signal responsible for increased wound-induced PAL activity, phenolic accumulation and browning in fresh-cut lettuce leaf tissue.

10 pages, 11 figures., Wounding, as during excision and preparation of lettuce (Lactuca sativa L.) leaf tissue for salads, induces the synthesis and accumulation of phenolic compounds that participate in subsequent reactions that cause tissue browning. Exposure of excised 5-mm mid-rib segments of romaine lettuce leaf tissue to vapors of mono-carboxylic acids or aqueous solutions of mono-carboxylic acids or their salts inhibited wound-induced phenolic accumulation (WIPA) and subsequent tissue browning. The decline in phenolic content followed a quadratic curve with increasing concentration, reaching a maximum inhibition after 60 min of 74 ± 8% for 50 mM sodium acetate (2 carbons, C2) and 91 ± 4% for 20 mM sodium decanoate (capric acid, C10). Respiration (i.e. carbon dioxide production) was unaffected by concentrations of formic, acetic, or propionic acids that reduced wound-induced phenolic content or that increase ion leakage from the tissue into an isotonic mannitol solution. However, WIPA was suppressed up to 70% at concentrations (20 mM acetate) that did not increase ion leakage over that of water controls. Various acetate salts (i.e. ammonium, calcium, magnesium, and sodium) all produced the same level of inhibition. The effectiveness of the compounds increased with increasing number of carbons in the molecule from 1 to 10, and was unaffected by whether the carbons were a straight chain or branched or whether the treatment was delayed by up to 6 h. The effectiveness of butyrate (C4) in reducing WIPA (27% reduction at 20 mM) was less than that predicted from the response of the two adjacent mono-carboxylates similarly applied: propionate (C3) (62%) and valerate (C5) (73%). It appears that, unlike the n-alcohols, mono-carboxylates are not interfering with the synthesis or propagation of a wound signal but are interfering with subsequent steps in the production and accumulation of wound-induced phenolic compounds.

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).

Sugar peas (Pisum sativum var. saccharatum cv. Manoa Sugar) were stored for 14 or 21 days under controlled atmospheres (CA) of 21% or 2.4% O2, plus 0%, 2.6%, or 4.7% CO2 at 10 or 1C. Changes in appearance, weight, and in the concentrations of chlorophyll, total soluble sugars, insoluble solids, and soluble protein were evaluated before and after storage. After 14 days of storage at 10C there were minor changes in all indicators of quality under the various storage conditions, but the appearance of sugar peas was better under CA than under 21% O2. When quality was evaluated after 21 days, however, storage under CA at 10C was not as beneficial as storage in 21% O2, at 1C. Holding peas in 2.4% O2, for up to 3 weeks at l0C, a higher than recommended storage temperature, maintained better quality than 21% O2. Increasing the CO, concentration from 0% to 2.6% or 4.7% had no adverse effects on quality and had a beneficial effect in some treatments. Compared with storage in 21% O2, the appearance of the peas was better, the concentrations of chlorophyll and soluble sugar were maintained at higher levels, and the insoluble solids were decreased in all atmospheres with 2.4% O2. Appearance and concentrations of chlorophyll, soluble sugars, and proteins were maintained at 1C regardless of treatments.

A method is described for the rapid determination of the anaerobic compensation point (ACP) of plant tissue, i.e., the O2 concentration at which CO2 production is minimum. The rate of CO2 production is measured from tissue exposed to an exponentially declining O2 concentration produced by a flow of N2 into a dilution bottle initially containing air. Too rapid a rate of O2 decline produces abnormal data because of the time required for the tissue to respond to changes in O2 concentration. The ACP is easily determined from a plot of CO2 production vs. O2 concentration. Rates of CO2 production and ACPS calculated using the exponentially declining system are similar to those calculated from traditional methods of continuously holding tissue under various O2 concentrations.

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 degrees C for 6 hours followed by 4 days at 2.5 or 12.5 degrees C. Ion leakage, a qualitative indicator of chilling injury, increased after 2 to 3 day exposure to 2.5 degrees C, but not to 12.5 degrees C, a nonchilling temperature. Exposure to 37 degrees C before chilling significantly reduced the rate of ion leakage by about 60% compared to tissue exposed to 12.5 degrees C before chilling, but slightly increased leakage compared to tissue exposed to 12.5 or 37 degrees C and held at the nonchilling temperature of 12.5 degrees C. There was no relationship between abscisic acid content following exposure to 12.5 or 37 degrees 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 degrees 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 degrees C.

Heat-shock induced chilling tolerance in excised discs of tomato fruit pericarp tissue significantly alter the kinetics of chilling-induced ion leakage from the discs into an aqueous isotonic mannitol solution. Pericarp discs were excised from mature-green tomato fruit, trimmed of locular material to 5-mm thickness, held overnight (ca. 16 h) at 20 °C and then subjected to various heat-shock (45 °C) treatments before being chilled at 2.5 °C for up to 30 days. Two discs were immersed in 20 mL of 0.3 m mannitol in a 50-mL plastic centrifuge tube and the conductivity of the aqueous solution periodically measured. The tube was capped and frozen at -20 °C. Total conductivity was measured once the tube had warmed to 20 °C with shaking. The percent ion leakage was calculated as the percent of total, and subjected to an analysis to partition rates of leakage into symplastic and apoplastic components. The symplastic component was not affected by the heat-shock treatment, while the apoplastic component showed reductions consistent with reduced chilling-induced damage to the cellular membrane. The protective heat-shock treatments also significantly increased the tissues resistance to fungal infection.

The wounds and injuries incurred during minimal processing of lettuce stimulates phenolic metabolism, which leads to tissue browning. Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5.) is the first committed enzyme in the phenylpropanoid pathway and regulates its overall activity. The maximum activity of wound-induced PAL occurs sooner as the temperature increases from 0 to 25 °C, but the maximums are lower. A heat shock at 50 °C for 90 s protects minimally processed lettuce tissue against browning, helps to retain greenness, and decreases the production of phenolics when applied either after or before wounding. Browning is reduced when the heat shock is applied up to 36 h after wounding, while the maximum effect occurs around 6 h before cutting. Like the heat-shock treatment, a number of protein synthesis inhibitors (e.g., chloramphenicol, cycloheximide, emetine, and puromycin) reduced wound-induced PAL activity, but they did not prevent browning itself. These inhibitors seemed to cause chemical damage that promoted tissue browning. When cycloheximide was applied in combination with heat-shock treatments browning did not occur. Heat shocks appear to control tissue browning by more than just interfering with protein synthesis.

Chilling 10-mm cucumber (Cucumis sativus L. `Poinsett 76') radicles at 2.5 °C reduced their subsequent growth during 3 days at 25 °C. The reduction in radicle growth was linear for 1 to 3 days of chilling but then increased substantially until subsequent radicle growth was all but eliminated by 6 days of chilling. Heat shocks of 40 °C applied for 4 to 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, which brought the response in line with the responses of the non-heat-shocked seeds chilled for 1 to 3 days. Eight-minute heat shocks applied before 5 days of chilling resulted in a 45% inhibition of subsequent growth, compared to 82% for chilled non-heat-shocked controls. Heat shocks applied before 3 days of chilling did not result in a significant increase in subsequent growth compared to the non-heat-shocked controls chilled for 3 days. Heat shocks were only able to protect that part of radicle growth that was in excess of the linear decrease in radicle growth. There appears to be two effects of chilling on radicle growth. The first is linear and cannot be affected by heat shocks. The second is much more severe and can be prevented by heat shocks. Seeds were selected for three categories of vigor according to the rate at which their radicles grew to 10 mm. Seeds classified with different vigors neither responded significantly differently to 3 days exposure to 2.5 °C nor did they respond differently to chilling stress following application of heat shocks.

Changes in phenolic metabolism are induced by minimally processing, which ultimately leads to the browning of lettuce tissue. Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5.) is greatly influenced by storage temperature. Evaluation of PAL activity at temperatures going from 0 to 25 °C showed that peaks occurred sooner at higher temperatures but at lower levels. Heat-shock treatments (50 °C, 90 s) have a protective effect against browning, help to retain greenness of tissue, and decrease the production of phenolics when applied either after or before wounding. To achieve a considerable, beneficial effect from hot water treatments applied after wounding these should not be delayed more than 36 h. The best results for heat-shock treatments before wounding occurred when applied at ≈12 h before cutting the tissue. Although cycloheximide did reduce PAL activity in a similar pattern as heat-shock treatments, it did not prevent browning itself. Cycloheximide seems to cause some sort of chemical damage that promotes the browning of lettuce tissue. When cycloheximide was applied in combination with heat-shock treatments browning did not occur.

Crops with origins in tropics and subtropics undergo physiological injury when subjected to nonfreezing temperatures below 12°C. Application of heat and chemical shocks to tissue prior to chilling induces chilling tolerance. This study was undertaken to investigate the effects of low oxygen and high carbon dioxide atmospheres on subsequent chilling tolerance. Cucumber seedlings (Cucumis sativus L., cv. Poinsett 76) with radicles 8 to 12 mm long were subjected to 0% to 21% oxygen and/or 0% to 20% CO2 atmospheres for 0 to 72 hr at 2.5 or 15°C. After chilling, they were placed at 25°C for three additional days. Radicle growth was used to assess chilling injury. Modification of the individual germination plates was necessary to ensure seedling exposure to the desired atmospheres. Chilling injury was reduced by exposure to oxygen levels below 1% and to carbon dioxide levels above 5%. Effects of brief exposures were small in comparison to prolonged exposures during chilling. Seed to seed variability was high and obscured some results. The effects of the various atmospheres were greater with the less vigorous seedlings.

The cessation of protoplasmic streaming is one of the first observable effects of chilling in sensitive plant tissue. If the lack of protoplasmic streaming contributes to the development of chilling injury, then impeding protoplasmic streaming at the chilling threshold temperature should induce chilling injury symptoms in tissue that would normally not exhibit symptoms at that temperature. A centrifuge was constructed to subject entire germinating cucumber (Cucumis sativus L., cv. Poinsett 76) seeds to centrifugal forces of up to 20 xg at 2.5, 10 and 12.5°C. Subjecting cucumber seeds with 5-mm-long radicles to high centrifugal forces (18 xg) at a marginal chilling temperature of 10°C for up to 3 days had no significant effect on subsequent radicle elongation of the entire population. In one experiment, spun seedlings were 7.4 ± 0.52 cm long, while the controls were 6.1 ± 4.3 cm long after 48 hr at 25°C. When analyzed by individual seed, the spinning treatments had no effect on high-vigor seedlings, while an 18 xg treatment significantly improved subsequent radicle elongation of low vigor seedlings. The effect of increased centrifugal forces on the respiration, metabolism and chilling sensitivity of cucumber seedlings will be discussed.

Fruit processing treatments, such as osmotic dehydration, washing, aqueous dips and coatings applications, and even microbial adhesion, depend critically on the surface energy of surfaces. Knowledge of these values can be used as reference targets for treatment formulations when complete wetting is necessary. Unripened and ripened tomato cultivars, `Ace' and `Castlemart', and bell pepper cultivars `California Wonder' and `Garden Sunshine' were characterized by color, firmness, and soluble solids, and evaluated for their surface energy. Calculated surface energy was obtained using Fowkes' equation by measuring contact angles of a series of pure surfactants of different HLB values on the fruit surface and by comparing with a reference paraffin surface of 25.5 dynes/cm. Results indicated that surface energies were similar between both types of fruits, while there were differences between maturity stages for tomato fruits. Surface energy in all cases was lower than 30 dynes/cm, indicating the hydrophobic nature of the epicuticular surface of the fruits tested.

Mechanical wounding and exposure to ethylene induces an increase in phenylpropanoid metabolism in lettuce and an increase in the concentration of several soluble phenolic compounds that are easily oxidized to brown substances by polyphenol oxidase. To study the early response of lettuce to wounding and ethylene, leaves of iceberg, butter leaf, and Romaine lettuces were either wounded or exposed to ethylene at 10 μL·L–1 in flows of humidified air at 5 or 10°C. Soluble phenolic compounds were extracted at intervals up to 72 hours and were analyzed by HPLC. After 72 hours, wounded leaves of all three lettuce types showed elevated levels of caffeoyl tartaric acid, Chlorogenic acid, dicaffeoyl tartanc acid, and 3,5-dicaffcoyl quinic acid at both temperatures. In contrast, there were no significant increases in soluble phenolic compounds in iceberg lettuce exposed to ethylene at 10°C. At 5°C for iceberg, and at both temperatures for the other two types, there was the same pattern for ethylene treated and wounded leaf tissue. The kinetics of wound and ethylene-induced phenolic metabolism are different and will be discussed in relation to phenolics produced and browning susceptibility.