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1.
Sensitivity of Stomata to Abscisic Acid (An Effect of the Mesophyll)   总被引:16,自引:3,他引:13       下载免费PDF全文
Trejo CL  Davies WJ  Ruiz L 《Plant physiology》1993,102(2):497-502
The effects of added abscisic acid (ABA) on the stomatal behavior of Commelina communis L. were tested using three different systems. ABA was applied to isolated epidermis or to leaf pieces incubated in the light in bathing solutions perfused with CO2-free air. ABA was also fed to detached leaves in a transpiration bioassay. The apparent sensitivity of stomata to ABA was highly dependent on the method used to feed ABA. Stomata of isolated epidermis were apparently most sensitive to ABA, such that a concentration of 1 [mu]M caused almost complete stomatal closure. When pieces of whole leaves were floated on solutions of ABA of the same concentration, the stomata were almost completely open. The same concentration of ABA fed through the midrib of transpiring detached leaves caused an intermediate response. These differences in stomatal sensitivity to added ABA were found to be a function of differences in the ABA concentration in the epidermes. Comparison of the three application systems suggested that, when leaf pieces were incubated in ABA or fed with ABA through the midrib, accumulation of ABA in the epidermes was limited by the presence of the mesophyll. Even bare mesophyll incubated in ABA solution did not accumulate ABA. Accumulation of radioactivity by leaf pieces floated on [3H]ABA confirmed ABA uptake in this system. Experiments with tetcyclacis, an inhibitor of phaseic acid formation, suggested that rapid metabolism of ABA in mesophyll can have a controlling influence on ABA concentration in both the mesophyll and the epidermis. Inhibition of ABA catabolism with tetcyclacis allows ABA accumulation and increases the apparent sensitivity of stomata to applied ABA. The results are discussed in the context of an important role for ABA metabolism in the regulation of stomatal behavior.  相似文献   

2.
Inherent differences in the responses of stomata on abaxialand adaxial epidermal surfaces of leaves of Commelina communishave previously been suggested to be due to differences in theconcentrations of apoplastic Ca. Adaxial stomata have also beenreported to be more sensitive than abaxial stomata to appliedabscisic acid (ABA). The aims of these experiments were to determinethe validity of these conclusions and to see if xylem sap Cahas a role in determining the response of stomata to ABA. It can be shown from measurements of relative stomatal resistance(determined with a viscous flow porometer) and stomatal conductancethat stomata were more open in plants grown on 8-0 mol m–3Ca, than with those grown on 2-0 mol m–3 Ca. When attachedleaves were fed with ABA via the transpiration stream neitherthe extent nor the rate with which conductance declined wasdependent on Ca nutrition. The extent of Ca accumulation within both epidermes was relatedto the concentration of Ca in the rhizosphere and in the xylemsap. It did not, however, appear to reflect the apparent differencesin the flux of the transpiration stream between the two epidermes.Plants growing at the lower Ca concentration accumulated proportionallymore epidermal Ca relative to Ca in xylem sap. The evidencepresented suggests that Ca movement from the xylem to the epidermiscannot be simply described by a mass flow model, and that thedistribution of Ca is not an adequate explanation of the differencesin the behaviour of adaxial and abaxial stomata. The potentialrole for changes in xylem sap Ca to act as a regulator of stomatalbehaviour are discussed. Key words: Abscisic acid, calcium, Commelina communis L., stomatal conductance  相似文献   

3.
To evaluate whether abscisic acid (ABA) in the xylem sap playsan important role in controlling stomatal aperture of field-grownPrunus persica trees under drought conditions, stomatal conductance(g) and xylem ABA concentrations were monitored both in irrigatedand non-irrigated trees, on two consecutive summer days (threetimes a day). Stomata1 conductance of non-irrigated trees hada morning maximum and declined afterwards. The changes in gduring the day, rather than resulting from variations in theconcentrations of ABA in the xylem sap or the delivery rateof this compound to the leaves, were associated with changesin the relationship between g and xylem ABA. The stomata ofwater-stressed trees opened during the first hours of the day,despite the occurrence of a high concentration of ABA in thexylem sap. However, stomatal responsiveness to ABA in the xylemwas enhanced throughout the day. As a result, a tight inverserelationship between g and the logarithm of xylem ABA concentrationwas found both at midday and in the afternoon. A similar relationshipbetween g and ABA was found when exogenous ABA was fed to leavesdetached from well-watered trees. These results indicate thatABA derived from the xylem may account for the differences ing observed between field-grown peach trees growing with differentsoil water availabilities. Several possible explanations forthe apparent low stomatal sensitivity to xylem ABA in the morning,are discussed, such as high leaf water potential, low temperatureand high cytokinin activity. Key words: Prunus persica L., stomata, xylem ABA, water deficits, root-to-shoot communication  相似文献   

4.
Commelina communis stomata closed within 1 h of transferring intact plants from 27 degrees C to 7 degrees C, whereas tobacco (Nicotiana rustica) stomata did not until the leaves wilted. Abscisic acid (ABA) did not mediate cold-induced C. communis stomatal closure: At low temperatures, bulk leaf ABA did not increase; ABA did not preferentially accumulate in the epidermis; its flux into detached leaves was lower; its release from isolated epidermis was not greater; and stomata in epidermal strips were less sensitive to exogenous ABA. Stomata of both species in epidermal strips on large volumes of cold KCl failed to close unless calcium was supplied. Therefore, the following cannot be triggers for cold-induced stomatal closure in C. communis: direct effects of temperature on guard or epidermal cells, long-distance signals, and effects of temperature on photosynthesis. Low temperature increased stomatal sensitivity to external CaCl(2) by 50% in C. communis but only by 20% in tobacco. C. communis stomata were 300- to 1,000-fold more sensitive to calcium at low temperature than tobacco stomata, but tobacco epidermis only released 13.6-fold more calcium into bathing solutions than C. communis. Stomata in C. communis epidermis incubated on ever-decreasing volumes of cold calcium-free KCl closed on the lowest volume (0.2 cm(3)) because the epidermal apoplast contained enough calcium to mediate closure if this was not over diluted. We propose that the basis of cold-induced stomatal closure exhibited by intact C. communis leaves is increased apoplastic calcium uptake by guard cells. Such responses do not occur in chill-sensitive tobacco leaves.  相似文献   

5.
Some Effects of Abscisic Acid and Water Stress on Stomata of Vicia faba L.   总被引:2,自引:0,他引:2  
Vicia faba seedlings grown under a plastic tent in the laboratorywere either watered well throughout their growth period or weresubjected to a water stress treatment for several days priorto an experimental treatment. The effects of a further waterstress treatment or an application of an aqueous solution ofabscisic acid (ABA) on the stomata of these plants were determined.Stomata of previously water-stressed plants proved to be moresensitive than stomata of well watered plants to ABA appliedthrough the petiole via the transpiration stream and sprayedonto leaf surfaces. Stomata of previously water-stressed plantsclosed more rapidly and to a greater degree than stomata ofwell watered plants. The hormone had only a small effect whenapplied directly to epidermal fragments removed from both groupsof plants. Stomata of plants which had received a water stresspretreatment were less sensitive to a subsequent period of waterstress than were stomata of previously well watered plants.It is proposed that stomatal adaptation to water stress maybe related to changes in the hormonal balance of the plant.  相似文献   

6.
Differences in maximum leaf conductance in grapevine plants growing in soils with contrasting water availabilities during mid-summer in Portugal could be accounted for by differences in the concentration of ABA in xylem sap. This conclusion is reinforced by the observation that the relationship between leaf conductance and endogenous ABA concentration can be mimicked by the application of exogenous ABA to leaves detached from irrigated plants. During the day, leaf conductance decreased after a morning peak, even when the leaves remained in a constant environment at a moderate temperature and leaf-to-air vapour pressure difference. This decline in leaf conductance was not a consequence of an increase in the xylem ABA concentration or the rate of delivery of this compound by the transpiratory stream. The afternoon depression in leaf conductance was associated with an apparent limitation in stomatal opening potential, which persisted even when detached leaves were fed with water and rehydrated. The reason for this inhibition has still to be identified.  相似文献   

7.
We have studied the stomatal response in relation to the xylem-derived abscisic acid (ABA) accumulation in sunflower leaves. When ABA was introduced into detached leaves of the sunflower through xylem flux, stomatal conductance was regulated, water flux was changed as a result and at the same time the xylem-derived ABA was metabolised in the leaves. We computed the xylem-derived ABA accumulation in the leaves as a function of time by taking into account the variation of ABA flux into the leaves (the product of water flux and ABA concentration) and a continuing ABA metabolism. We found that ABA accumulation was rapid during an initial lag phase, much slowed down during the decreasing phase of stomatal conductance, but still substantial when stomatal conductance reached a new stable state. The results show a poor link between the kinetics of ABA-induced stomatal closure and the xylem-derived ABA accumulation. Xylem-derived ABA was metabolised rapidly in the leaves. Tetcyclacis, as an inhibitor, substantially inhibited this process. Two hours after ABA was fed into a leaf, about 70% of the fed ABA was metabolised, but when tetcyclacis was added into the feeding solution, less than 30% of ABA was metabolised, even after 24 h of incubation. The inhibition of ABA metabolism by tetcyclacis did not lead to more stomatal closure, which was still concentration-dependent. Since the accumulation of xylem-derived ABA was enhanced substantially by the presence of tetcyclacis, these results strongly indicate that stomata mainly respond to the prevailing ABA concentration in the xylem stream, rather than to the accumulated amount of xylem-derived ABA in the leaves.  相似文献   

8.
Drought increased the pH of Commelina communis xylem sap from 6.1 to 6.7. Conductances of transpiring leaves were 50% lower in pH 7.0 than in pH 6.0 buffers, but bulk leaf abscisic acid (ABA) concentration and shoot water status were unaffected by pH. Stomatal apertures of isolated abaxial epidermis incubated on simple buffers increased with external pH, so in vivo this must be overridden by alternative pH effects. Reductions in leaf transpiration rate at pH 7.0 were dependent on the presence of 10-8 mol dm-3 ABA in the xylem stream. We inferred that at pH 7.0 leaf apoplastic ABA concentrations increased: pH did not affect distributions of ABA among leaf tissues, but isolated epidermis and mesophyll tissue took up more 3H-ABA from pH 6.0 than from pH 7.0 buffers. The apoplastic ABA increase at pH 7.0 may result from reduced symplastic sequestration. A portion of 3H-ABA uptake by the epidermis was saturable at pH 6.0 but not at pH 7.0. An ABA uptake carrier may contribute to ABA sequestration by the leaf symplast of well-watered plants, and its inactivity at pH 7.0 may favor apoplastic ABA accumulation in draughted plants. Effects of external pH on stomatal apertures in the isolated epidermis indicate that published data supporting a role for internal guard cell ABA receptors should be reassessed.  相似文献   

9.
Two tropical tree species, Acacia confusa and Leucaena leucocephala, were used to study the relationships among stomatal conductance, xylem ABA concentration and leaf water potential during a soil drying and rewatering cycle. Stomatal conductance of both A. confusa and L. leucocephala steadily decreased with the decreases in soil water content and pre-dawn leaf water potential. Upon rewatering, soil water content and pre-dawn leaf water potential rapidly returned to the control levels, whereas the reopening of stomata showed an obvious lag time. The length of this lag time was highly dependent not only upon the degree of water stress but also on plant species. The more severe the water stress, the longer the lag time. When A. confusa and L. leucocephala plants were exposed to the same degree of water stress (around –2.0 MPa in pre-dawn leaf water potential), the stomata of A. confusa reopened to the control level 6 days after rewatering. However, it took L. leucocephala about 14 days to reopen fully. A very similar response of leaf photosynthesis to soil water deficit was also observed for both species. Soil drying resulted in a significant increase in leaf and xylem ABA concentrations in both species. The more severe the water stress, the higher the leaf and xylem ABA concentrations. Both leaf ABA and xylem ABA returned to the control level following relief from water deficit and preceded the full recovery of stomata, suggesting that the lag phase of stomatal reopening was not controlled by leaf and/or xylem ABA. In contrast to drying the whole root system, drying half of the root system did not change the leaf water relations, but caused a significant increase in xylem ABA concentration, which could fully explain the decrease of stomatal conductance. After rewatering, the stomatal conductance of plants in which half of the roots were dried recovered more rapidly than those of whole-root dried plants, indicating that the leaf water deficit that occurred during the drying period was related to the post-stress stomatal inhibition. These results indicated that the decrease in stomatal conductance caused by water deficit was closely related to the increase in xylem ABA, but xylem ABA could not fully explain the reopening of stomata after relief of water stress, neither did the leaf ABA. Some unknown physiological and/or morphological processes in the guard cells may be related to the recovery process.  相似文献   

10.
研究了周期性土壤干旱期间气孔对木质部ABA响应的灵敏度的变化以及叶片水势对灵敏度的影响。实验结果证明了木质部ABA浓度是反映根系周围土壤水分状况的一个指标的结论。土壤周期性干旱不影响木质部ABA浓度对土壤水分状况的依赖关系,但显著地提高了气孔对木质部ABA 响应的灵敏度。根据对实测数据的数学模拟结果显示,引起气孔导度下降50% 所需的木质部ABA浓度从第一轮土壤干旱的750 nmol/L降至第二轮土壤干旱的550 nmol/L。分根实验的结果表明,叶片水分亏缺显著提高了气孔对木质部ABA 的响应的灵敏程度,全根干旱中引起气孔导度下降50 % 所需的木质部ABA 浓度比半根干旱的小2 ~4 倍。这表明,气孔对木质部ABA响应的灵敏度不是一个固定的特性,可随植物生长环境及许多其他因素的变化而表现出很大的差异  相似文献   

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