Chilling Resistance as Affected by Stressing Environments and Abscisic Acid

282

127

ABSTlRACTThe effect of abscisic acid (ABA) on the cold hardiness of cell suspension was investigted. Cell (2,(15)(16)(17). Because of the involvement of ABA in many environmental stresses, ABA has been proposed as a common mediator for plant stress response (5). However, the role of ABA in the adaptation of plants to freezing stress is not clear. Irving and Lamphear (13) were among the first to suggest that ABA may be involved in the cold hardening process.Two lines of evidence support the involvement of ABA in plant cold hardening. First, an increase in the endogenous level of ABA has been observed when plants are exposed to low temperature (2,5,(14)(15)(16). Second, exogenous applications of ABA have been shown to increase the cold hardiness in certain plants (2,3,15,16). However, attempts to increase cold hardiness by exogenous applications of ABA have not always been successful (6, 9). In these studies ABA was applied either as a foliar spray (6) or through the roots in a hydroponics solution (10). The failure ofexogenously added ABA to increase cold hardiness in these studies may be due to the lack of uptake, or microbial and enzymic degradation. (20), and by regrowth.The procedures for measuring TTC reduction was essentially the same as that described by Towill and Mazur (18) with the following modifications: thawed cells (0.2 g fresh weight) were incubated in 3 ml TTC solution (0.08% TTC in 0.05 M sodium phosphate buffer, pH 7.4) for 18 h at 20°C in the dark. After TTC incubation, the cells were rinsed with 3 ml distilled H20 and the reduced TTC extracted with 5 ml of 95% ethanol. TTC reduction was determined by measuring A at 485 nm. Freezing injury is expressed as the percentage ofdecrease in TTC reduction as compared to a nonfrozen control. The temperature which resulted in a 50% decrease TTC reduction is defined as the 50% killing temperature (LT50).Viability as determined by regrowth was conducted under sterile conditions. Following the freeze test, cell aggregates approximately 1 mm in diameter were transferred to 0.7% agar containing the appropriate medium. After I month at 20°C in the dark, the growth of the callus was determined.

“…Cell (2,(15)(16)(17). Because of the involvement of ABA in many environmental stresses, ABA has been proposed as a common mediator for plant stress response (5).…”

Section: Abstlractmentioning

confidence: 99%

mentioning

confidence: 99%

Abscisic Acid-Induced Freezing Resistance in Cultured Plant Cells

Chen

Gusta²

1983

282

127

“…Exposure to 370C before chilling significantly reduced the rate of ion leakage by about 60% compared to tissue exposed to 12.50C before chilling, but slightly increased leakage compared to tissue exposed to 12.5 to chilling significantly reduced the chilling-induced increase in ion leakage, possibly by reducing the effects of chillinginduced water stress or the direct effect of low temperature (20). Rikin et al (19) showed that exogenous application of ABA and pretreatments with physiological stresses, which increased the endogenous level of ABA, increased the tolerance of tissue to subsequent chilling. Stressful temperatures can alter the internal water status and thereby ABA production (25), or they can directly affect ABA levels (4).…”

Section: Introductionmentioning

confidence: 99%

“…Rikin et al (19) showed that exogenous application of ABA and pretreatments with physiological stresses, which increased the endogenous level of ABA, increased the tolerance of tissue to subsequent chilling. Stressful temperatures can alter the internal water status and thereby ABA production (25), or they can directly affect ABA levels (4).…”

mentioning

confidence: 99%

Effect of Temperature Conditioning on Chilling Injury of Cucumber Cotyledons

Lafuente¹,

Belver²,

Guye³

et al. 1991

129

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. Onecentimeter 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 370C for 6 hours followed by 4 days at 2.5 or 12.50C. Ion leakage, a qualitative indicator of chilling injury, increased after 2 to 3 day exposure to 2.50C, but not to 12.50C, a nonchilling temperature. Exposure to 370C before chilling significantly reduced the rate of ion leakage by about 60% compared to tissue exposed to 12.50C before chilling, but slightly increased leakage compared to tissue exposed to 12.5 to chilling significantly reduced the chilling-induced increase in ion leakage, possibly by reducing the effects of chillinginduced water stress or the direct effect of low temperature (20). Rikin et al. (19) showed that exogenous application of ABA and pretreatments with physiological stresses, which increased the endogenous level of ABA, increased the tolerance of tissue to subsequent chilling. Stressful temperatures can alter the internal water status and thereby ABA production (25), or they can directly affect ABA levels (4). However, this conclusion was questioned by Eamus and Wilson (6) who showed that increased levels of endogenous ABA did not accumulate if leaves of Phaseolus vulgaris were chilled in a water-saturated atmosphere.Thermal stress also induces the synthesis of specific HSPs4 in a wide range of plants (1,3,10), and reduces the synthesis of some normally expressed proteins (1). The physiological basis by which these proteins confer thermal tolerance is still unclear, although their synthesis and accumulation appears to provide thermal tolerance, and their selective localization appears to be linked to the expression of this tolerance (10). Lin et al. (13) found that the synthesis of HSPs prevented heat shock-induced leakage from cell. However, the possible relationship between the induction of HSPs and the effect of temperature conditioning on the susceptibility of the tissue to chilling injury was not investigated. HSPs can also be synthesized in response to water stress and ABA (8, 10).We undertook to study the effect of prior temperature exposure on the susceptibility of cucumber plants to chilling injury and to determine the physiological basis for the observed changes. Since ABA may have a beneficial effect on reducing chilling injury, and ABA, water stress, and thermal stress elicit HSPs which reduce heat shock-induced ion leakage, we evaluated changes in ABA levels and induction of HSPs after exposure to temperatures in a water saturated atmosphere. This was done to determine the possible role of endogenous ABA and HSPs in increasing the chilling tolerance to plants previously subjected to various temperatures.The connection between ABA levels and HSPs was also studied.

“…Exogenously applied as well as endogenously produced ABA hardened plants to exposure to low temperatures (18,19). ABA is known to cause stomatal closure (16,20) and has been reported to alter root permeability to water (5,(7)(8)(9)13).…”

Section: Introductionmentioning

confidence: 99%

Penetration of Soybean Root Systems by Abscisic Acid Isomers

Markhart¹

1982

The penetration of soybean (Glycine max L. cv. Ransom) root systems by exogenously applied isomers of abscisic acid was monitored by measuring the concentration of the chemical in the xylem exudate of root systems exposed to a three bar hydrostatic pressure difference. The cis-trans isomer penetrated more readily than the trans-trans isomer, however, up to 6 hours was needed to reach steady-state values. Exogenous abscisic acid also decreased volume flux through the root system and increased total carbon dioxide efflux from the vessel containing the root system.Recent evidence indicates an important role of ABA2 in plant resistance to environmental stress (13, 19). Exogenously applied as well as endogenously produced ABA hardened plants to exposure to low temperatures (18,19). ABA is known to cause stomatal closure (16,20) and has been reported to alter root permeability to water (5,(7)(8)(9)13). In experiments where ABA is added to the irrigation water (18), it is often unclear whether the hormone acts on the root or is transported to the shoot and directly effects the stomata.Despite the potential importance of exogenously applied plant growth regulators, there is a paucity of information on the uptake and transport of hormones to sites of action. The experiments presented here investigate the penetration of soybean root systems by ABA geometric isomers. This information is essential to understanding the mechanism of action of ABA and to the future use of exogenous ABA to ameleorate plant damage due to environmental stress. Additionally, a convenient accurate method of general use for measuring the transport of these compounds through root systems is described. MATERIALS AND METHODSSoybean (Glycine max L. cv. Ransom) plants were grown hydroponically in 3-L plastic pots containing half-strength Hoagland solution for 20 to 40 days in controlled environment chambers at the Duke University Phytotron as described previously (14 Twenty 1d aliquots were analyzed directly with an Altex Model 310 high performance liquid chromatograph with a UV (254 nm) detector for the presence of ABA. Separation of the two geometric isomers was achieved with a solvent system of methanol:H20: acetic acid (40:60: 1), a LiChrosorb RP-18 column, and a flow rate of 1 ml/min. Standard curves of peak height versus concentration were linear between 10-6 and l0-4 M and were used to determine exudate ABA concentration. The ABA concentration of the ambient solution was also monitored during the experiment. The exudate ABA concentration expressed as a fraction of the ambient concentration was used as a relative measure of the penetration of the isomers.Exudation Rates. Exudation rates were measured as the volume of exudate flowing from the cut stem per unit time. Rates are expressed on a whole root basis.Respiration. Root respiration was monitored by measuring the CO2 concentration of the gas passing through the pressure vessel with an IR gas analyzer operated in the absolute mode. Rates were expressed as a percent of the rate at the time...