Mefluidide protection of severely chilled crop plants

Mefluidide, the common name of N-(2,4-dimethyl-5-[([trifluoromethyl] sulfonyl)amino]phenyl)acetamide, is capable of protecting chilling sensitive plants such as cucumber (Cucumis sativus L.) and corn (Zea mays L.) from chilling injury. The applied concentrations that protect plants from stress are species specific. Applied above a threshold concentration, it has no protective effect. Regardless of its immediate potential for agriculture, it appears at least to be a powerful tool for the biologist in the study of the protection from temperature stress mechanism.     

Patterns of Assimilate Production and Translocation in Muskmelon (Cucumis melo L.) : II. Low Temperature Effects

Muskmelon (Cucumis melo L.) plants were exposed to a 10°C chilling treatment for 72 hours, which induced leaf chilling injury symptoms (wilting, appearance of water-soaked areas, necrosis). Chilling caused an accumulation of starch, sucrose, hexoses (glucose and fructose), and certain amino acids (glutamate, aspartate, and citrulline) in source leaf tissues, but no accumulation of stachyose or other galactosyl-oligosaccharides occurred. Chilling also caused a general increase in sugar (stachyose, raffinose, sucrose) and amino acid content of the phloem sap, although rates of phloem transport were apparently reduced. Pretreatment of the leaves with a 20-milligram per liter abscisic acid (ABA) spray before chilling prevented the appearance of chilling injury symptoms. ABA pretreatment had little or no affect on sugar accumulation in leaf tissues but greatly reduced or eliminated the chilling-induced amino acid accumulation. Higher levels of aspartate and particularly of arginine were found in phloem saps from ABA-pretreated plants. The data indicate that changes in leaf metabolism caused by environmental stresses such as chilling may change the composition of cucurbit phloem sap. This raises the possibility that some of the deleterious effects of stress on sink tissues may, in part, be due to alterations in the nature of the assimilate supply.     

Stomatal behaviour and leaf water potential of chilled and water-stressed Solanum melongena, as influenced by growth history

Abstract Leaf diffusion resistance and leaf water potential of intact Solanum melongena plants were measured during a period of chilling at 6 °C. Two pretreatments, consisting of a period of water stress or a foliar spraying of abscisic acid (ABA), were imposed upon the plants prior to chilling. The control plants did not receive a pretreatment. In addition to intact plant studies, stomatal responses to water loss and exogenous abscisic acid were investigated using excised leaves, and the influence of the pretreatment observed. Chilled, control plants wilted slowly and maintained open stomata despite a decline in leaf water potential to –2.2 MPa after 2 d of chilling. In contrast plants that had been water stressed or had been sprayed with abscisic acid, prior to chilling, did not wilt and maintained a higher leaf water potential and a greater leaf diffusion resistance. In plants that had not received a pretreatment, abscisic acid caused stomatal closure at 35 °C, but at 6°C it did not influence stomatal aperture. The two pretreatments greatly increased stomatal sensitivity to both exogenous ABA and water stress, at both temperatures. Stomatal response to water loss from excised leaves was greatly reduced at 6°C. These results are discussed in relation to low temperature effects on stomata and the influence of preconditioning upon plant water relations.     

Cloning and characterisation of a pepper aquaporin,CaAQP, which reduces chilling stress in transgenic tobacco plants

Ubiquitous cell membrane proteins called aquaporins are members of major intrinsic proteins (MIPs), which control the specific transport of water molecules across cell membranes. A pepper aquaporin gene (CaAQP), which exhibits the structural features of tonoplast intrinsic proteins of the MIP subfamily, was isolated from the leaves of chilling-treated seedlings of pepper (Capsicum annuum L.) cv. P70. Assays indicated high levels of expression in young seeds, green fruits and flower buds and low levels of expression in the stems, leaves and roots of pepper. The expression patterns were strongly and rapidly induced by HgCl₂, low temperature, abscisic acid, fluridone and osmotic stresses. The responsiveness of pepper seedlings pretreated with abscisic acid at low temperatures demonstrated up-regulation of CaAQP by chilling, which is potentially involved in ABA signalling. Our results indicated that overexpression of CaAQP decreased chilling stress in transgenic plants, likely by increasing the stomatal aperture under stress, increasing the rate of membrane damage during the recovery stage, thereby affecting the intercellular CO₂ concentration with lower stomatal conductance and transpiration rates. VIGS of CaAQP in pepper plants caused significant growth retardation. These results suggested that CaAQP played a crucial role in the plant response to abiotic stresses.     

Abscisic Acid and stomatal regulation

The closure of stomata by abscisic acid was examined in several species of plants through measurements of CO₂ and H₂O exchange by the leaf. The onset of closure was very rapid, beginning at 3 minutes from the time of abscisic acid application to the cut base of the leaf of corn, or at 8 or 9 minutes for bean, Rumex and sugarbeet; rose leaves were relatively slow at 32 minutes. The timing and the concentration of abscisic acid needed to cause closure were related to the amounts of endogenous abscisic acid in the leaf. Closure was obtained in bean leaves with 8.9 picomoles/cm². (+)-Abscisic acid had approximately twice the activity of the racemic material. The methyl ester of abscisic acid was inactive, and trans-abscisic acid was likewise inactive. The effects of stress on levels of endogenous abscisic acid, and the ability of very small amounts of abscisic acid to cause rapid closure suggests that stomatal control is a regulatory function of this hormone.     

Quantitation of Chill-Induced Release of a Tubulin-Like Factor and Its Prevention by Abscisic Acid in Gossypium hirsutum L

The degree of tubulin polymerization in cotton (Gossypium hirsutum L. cv Acala) cotyledonary tissue was estimated by radioimmunoassay which measured the amount of a tubulin-like factor. It was assumed that the release of this tubulin-like factor indicated depolymerization of microtubules. Exposure to chilling resulted in complete release of the tubulin-like factor. Pretreatment with abscisic acid in the light almost completely prevented the chill-induced release of the tubulin-like factor. Addition of colchicine during the chilling period accelerated the release of the tubulin-like factor. Pretreatment with abscisic acid greatly reduced this effect of colchicine. It is concluded that the destruction of the microtubular network is involved in the development of chilling injury in cotton. Abscisic acid apparently decreased chilling injury by stabilization of the microtubular network.     

CbCBF from Capsella bursa-pastoris enhances cold tolerance and restrains growth in Nicotiana tabacum by antagonizing with gibberellin and affecting cell cycle signaling

Plant cells respond to cold stress via a regulatory mechanism leading to enhanced cold acclimation accompanied by growth retardation. The C-repeat binding factor (CBF) signaling pathway is essential for cold response of flowering plants. Our previously study documented a novel CBF-like gene from the cold-tolerant Capsella bursa-pastoris named CbCBF, which was responsive to chilling temperatures. Here, we show that CbCBF expression is obviously responsive to chilling, freezing, abscisic acid, gibberellic acid (GA), indoleacetic acid or methyl jasmonate treatments and that the CbCBF:GFP fusion protein was localized to the nucleus. In addition, CbCBF overexpression conferred to the cold-sensitive tobacco plants enhanced tolerance to chilling and freezing, as well as dwarfism and delayed flowering. The leaf cells of CbCBF overexpression tobacco lines attained smaller sizes and underwent delayed cell division with reduced expression of cyclin D genes. The dwarfism of CbCBF transformants can be partially restored by GA application. Consistently, CbCBF overexpression reduced the bioactive gibberellin contents and disturbed the expression of gibberellin metabolic genes in tobacco. Meanwhile, cold induced CbCBF expression and cold tolerance in C. bursa-pastoris are reduced by GA. We conclude that CbCBF confers cold resistance and growth inhibition to tobacco cells by interacting with gibberellin and cell cycle pathways, likely through activation of downstream target genes.     

Altitude variation in chilling tolerance among natural populations of <Emphasis Type="Italic">Elymus nutans</Emphasis> in the Tibetan Plateau

Low temperatures limit plant growth, development, and reproductive success. A series of complex adaptive responses in plants evolved to withstand this environmental challenge. Here, eight accessions of Elymus nutans, which originated in Tibet at altitudes between 3720 and 5012 m above sea level, were used to identify heritable adaptations to chilling stress. Dynamic responses of phytohormone, sugar, and gene expression levels related to chilling tolerance were analyzed. During the initial stage of chilling stress (0–24 h), some high-altitude E. nutans accessions exhibited rapid increases in abscisic acid (ABA), jasmonic acid (JA), and zeatin content. This coordinated with decreases in the levels of auxin (IAA), salicylic acid (SA), gibberellins (GA), and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). EnCBF9 and EnCBF14 expression in the high-altitude accessions, Baqing, Xainza, Damxung, and Ali, increased within 1 h of chilling exposure, while chilling induction of EnCOR14a was detected after 3 h of chilling stress. Accessions from high altitudes displayed an increased sucrose and raffinose accumulation and a reduced degradation of chlorophyll under chilling stress. After 24–120 h of chilling exposure, plant adaptation to the chilling treatment was associated with a lower accumulation of ABA and moderate rise of zeatin, IAA, GA, ACC, SA, and JA. EnCBF9, EnCBF14, and EnCOR14a genes were down-regulated during the late stage of chilling stress. Taken together, the dynamic responses of phytohormones and sugars, and the higher expression of the EnCBFs and EnCOR genes play critical roles in the acclimation to chilling in high-altitude accessions of E. nutans, thereby allowing them to achieve higher chilling tolerance.     

Relationship of cold acclimation,total phenolic content and antioxidant capacity with chilling tolerance in petunia (Petunia × hybrida)

Extracts from Petunia × hybrida plants, which had been subjected to cold pretreatment to induce chilling tolerance, were analyzed for specific phenolic acids, such as gentisic acid, and assessed for their antioxidant capacity by their ability to reduce (decolorize) the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt radical (ABTS^*). Gentisic acid was induced in significant quantities by the third week of cold acclimation and levels remained constant up to the fourth week. Cold acclimation induced accumulation of total phenolics, which was positively related to antioxidant capacity. Petunia plants recovered from chilling injury following 3 weeks of cold pretreatment with an increase in total phenolics, which suggested some form of antioxidant protection. However, antioxidant capacity was only moderately related to chilling tolerance, which indicated that factors other than total phenolics may play a role in the chilling tolerance in petunia. These data suggest that the 5 °C cold pretreatment may have initially caused injury that impeded acclimation at the outset, and that subsequent phenolic metabolism was related to protective functions in petunia.     

Abscisic Acid Content and Stomatal Sensitivity to CO(2) in Leaves of Xanthium strumarium L. after Pretreatments in Warm and Cold Growth Chambers

The degree of stomatal sensitivity to CO₂ was positively correlated with the content of abscisic acid of leaves of Xanthium strumarium grown in a greenhouse and then transferred for 24 hours or more to a cold (5/10 C, night/day) or a warm growth chamber (20/23 C). This correlation did not exist in plants kept in the greehouse continuously (high abscisic acid, no CO₂ sensitivity), nor in plants transferred from the cold to the warm chamber (low abscisic acid, high CO₂ sensitivity). The abscisic acid content of leaves was correlated with water content only within narrow limits, if at all. At equal water contents, prechilled leaves contained more abscisic acid than leaves of plants pretreated in the warm chamber. There appear to be at least two compartments for abscisic acid in the leaf.     

Relationship between Proline and Abscisic Acid in the Induction of Chilling Tolerance in Maize Suspension-Cultured Cells

Both proline and abscisic acid (ABA) induce chilling tolerance in chilling-sensitive plants. However, the relationship between proline and ABA in the induction of chilling tolerance is unclear. We compared the time course of the increase in chilling tolerance induced by proline and ABA, and the time course of the uptake of both into the cultured cells of maize (Zea mays L. cv Black Mexican Sweet) at 28[deg]C. The plateau of proline-induced chilling tolerance preceded by 12 h the plateau of ABA-induced chilling tolerance. The uptake of exogenous ABA into the cells reached a plateau in 1 h, whereas the uptake of exogenous proline gradually increased throughout the 24-h culture period. Although the proline content in ABA-treated cells was 2-fold higher than in untreated cells at the end of the 24-h ABA treatment at 28[deg]C, the correlation between the endogenous free proline content and the chilling tolerance in the ABA-treated cells was insignificant. Isobutyric acid treatment, which resulted in a larger accumulation of proline in the cells than ABA treatment, did not increase chilling tolerance. The induction of chilling tolerance by proline and ABA appeared to be additive. Cycloheximide inhibited ABA-induced chilling tolerance, but it did not inhibit proline-induced chilling tolerance. Newly synthesized proteins accumulate in ABA-treated cells at 28[deg]C while the chilling tolerance is developing (Z. Xin and P.H. Li [1993] Plant Physiol 101: 277-284), but none of these proteins were observed in the proline-treated cells. Results suggest that proline and ABA induce chilling tolerance in maize cultured cells by different mechanisms.     

A water potential threshold for the increase of abscisic Acid in leaves

A relationship between abscisic acid concentration and leaf water status is reported. Water potentials were measured in leaves of Ambrosia artemisiifolia L. and Ambrosia trifida L. throughout a period of dehydration of intact plants. Tissues from the same leaves were analyzed for abscisic acid. For both species, abscisic acid began to increase in a critical water potential range (−10 to −12 atmospheres). These data suggest a threshold water potential that stimulates abscisic acid synthesis. The data support the hypothesis that a small change in water potential could affect stomatal resistance to water loss by means of a very sensitive chemical feedback control mechanism.     

The level of phytohormones in monoecious and gynoecious cucumbers as affected by photoperiod and ethephon

The endogenous levels of auxin, gibberellin, and inhibitors were followed in monoecious and gynoecious cucumber (Cucumis sativus L.) plants, and in plants treated with the ethylene-releasing compound Ethephon (2-chloroethyl phosphonic acid). Higher auxin inhibitor and lower gibberellin levels were associated with female tendency. The endogenous level of gibberellin and auxin decreased in Ethephon-treated plants. Application of Ethephon induced a rise in abscisic acid. Root application of abscisic acid promoted female tendency of gynoecious cucumbers grown under conditions which increase maleness. High CO₂ levels, which are known to antagonize ethylene, increased maleness of gynoecious cucumbers. The possibility of interrelationship between gibberellin, auxin, ethylene, and abscisic acid on sex expression are discussed.     

Chilling injury in cotton (Gossypium hirsutum L.) Prevention by abscisic acid

Cotton (Gossypium hirsutum L.) intact seedlings and isolatedcotyledonary discs were exposed to chilling (4?C) under humidconditions which prevented dehydration. The damage resultingfrom chilling was estimated by means of electrolyte leakageand survival in whole seedlings and by the electrolyte leakageand necrotic areas in isolated cotyledonary discs. Also, theeffect of chilling on membrane phospholipids and cellular reducedglutathione was determined. Within the first two and three daysof chilling, there was a marked reduction in the reduced glutathioneand membrane phospholipid levels without electrolyte loss andnecrosis. This reduction was completely prevented by pretreatmentwith abscisic acid. Prolonging the chilling period resultedin decreased survival in whole seedlings and in progressiveincrease in electrolyte leakage and necrosis in isolated cotyledonarydiscs. Pretreatment with abscisic acid prior to chilling almostcompletely prevented this chilling injury when exposure to 4?Cwas less than 5 days. Even with longer chilling periods, theabscisic acid pretreatment greatly reduced the damage. ³Incumbent of the Seagram Chair in Plant Science. (Received July 21, 1979; )     

Periodicity of response to abscisic acid in lateral buds of willow (Salix viminalis L.)

Aseptically cultured lateral buds of Salix viminalis L. collected from field-grown trees exhibited a clear periodicity in their ability to respond to exogenous abscisic acid (ABA). Buds were kept unopened by ABA only when the plants were dormant or entering dormancy. Short days alone did not induce bud dormancy in potted plants but ABA treatment following exposure to an 8-h photoperiod prevented bud opening although ABA treatment of buds from long-day plants did not. Naturally dormant buds taken from shoots of field-grown trees and cultured in the presence of ABA opened following a chilling treatment. In no cases were the induction and breaking of dormancy and response to ABA correlated with endogenous ABA levels in the buds.Abbreviations ABA abscisic acid - GA₃ gibberellic acid - HPLC high-performance liquid chromatography - LD long day - MeABA methyl ABA - PAR photosynthetically active radiation - SD short day     

Conversion of 5-(1,2-epoxy-2,6,6-trimethylcyclohexyl) -3-methylpenta-cis-2-trans-4-dienoic acid into abscisic acid in plants

(±)-5-(1,2-Epoxy-2,6,6-trimethylcyclohexyl) -3-methyl[2-¹⁴C]penta-cis-2-trans-4-dienoic acid is converted into abscisic acid by tomato fruit in 1.8% yield (or 3.6% of one enantiomer if only one is utilized) and 15% of the abscisic acid is derived from the precursor. The 2-trans-isomer is not converted. The amounts of [2-³H]mevalonate incorporated into abscisic acid have shown that the 40-times higher concentration of (+)-abscisic acid in wilted wheat leaves in comparison with unwilted ones reported by Wright & Hiron (1969) arises by synthesis. The conversion of (±)-5-(1,2-epoxy-2,6,6-trimethylcyclohexyl) -3-methyl-[2-¹⁴C]penta-cis-2-trans-4-dienoic acid into abscisic acid by wheat leaves is also affected in the same way by wilting and it is concluded from this that the epoxide or a closely related compound derived from it is on the biosynthetic pathway leading to abscisic acid. The oxygen of the epoxy group was shown, by ¹⁸O-labelling, to become the oxygen of the tertiary hydroxyl group of abscisic acid.     

Light Moderates the Induction of Phosphoenolpyruvate Carboxylase by NaCl and Abscisic Acid in Mesembryanthemum crystallinum

In Mesembryanthemum crystallinum, phosphoenolpyruvate carboxylase is synthesized de novo in response to osmotic stress, as part of the switch from C₃-photosynthesis to Crassulacean acid metabolism. To better understand the environmental signals involved in this pathway, we have investigated the effects of light on the induced expression of phosphoenolpyruvate carboxylase mRNA and protein in response to stress by 400 millimolar NaCl or 10 micromolar abscisic acid in hydroponically grown plants. When plants were grown in high-intensity fluorescent or incandescent light (850 microeinsteins per square meter per second), NaCl and abscisic acid induced approximately an eightfold accumulation of phosphoenolpyruvate carboxylase mRNA when compared to untreated controls. Levels of phosphoenolpyruvate carboxylase protein were high in these abscisic acid- and NaCl-treated plants, and detectable in the unstressed control. Growth in high-intensity incandescent (red) light resulted in approximately twofold higher levels of phosphoenolpyruvate carboxylase mRNA in the untreated plants when compared to control plants grown in high-intensity fluorescent light. In low light (300 microeinsteins per square meter per second fluorescent), only NaCl induced mRNA levels significantly above the untreated controls. Low light grown abscisic acid- and NaCl-treated plants contained a small amount of phosphoenolpyruvate carboxylase protein, whereas the (untreated) control plants did not contain detectable amounts of phosphoenolpyruvate carboxylase. Environmental stimuli, such as light and osmotic stress, exert a combined effect on gene expression in this facultative halophyte.     

Effects of Abscisic Acid Application on Photosynthesis and Photochemistry of Stylosanthes guianensis under Chilling Stress

In our previous study, it was found that abscisic acid (ABA) improved the chilling resistance of Stylosanthes guianensis. In order to determine the effects of ABA on photosynthesis and photochemistry of S. guianensis, an experiment was conducted under controlled condition to determine the effects of exogenous ABA on stomatal conductance (g_s), transpiration (E), photosynthetic rate (A) and chlorophyll a fluorescence of this pasture legume. The results showed that ABA treatment reduced A, g_s, and E under both chilling (8 °C) and control temperature (28 °C). A of the ABA treated plants returned to a high rate, while that of the water-treated plants remained low when plants were rewarmed after chilling treatment. ABA-treated plants had higher maximum photochemical efficiency (F_v/F_m), non-photochemical quenching (NPQ), quantum efficiency of PS II photochemistry (Φ_{ps ii}) than water-treated ones during chilling. Although the biomass of S. guianensis was reduced by ABA under control temperature, ABA-treated plants had higher biomass than water-treated ones after 7 days of recovery.