Effect Of Exogenous Abscisic Acid Research Articles

Foliar spraying exogenous ABA resists chilling stress on adzuki beans (Vigna angularis).

Adzuki bean, an important legume crop, exhibits poor tolerance to low temperatures. To investigate the effect of exogenous abscisic acid (ABA) on the physiological metabolism and yield resistance of adzuki bean under low-temperature stress, we conducted a potted experiment using Longxiaodou 4 (LXD 4) and Tianjinhong (TJH) as test materials and pre-sprayed with exogenous ABA at flowering stage continuously for 5 days with an average of 12°C and an average of 15°C, respectively. We found that, compared with spraying water, foliar spraying exogenous ABA increased the activities of antioxidants and the content of non-enzymatic antioxidants, effectively inhibited the increase of malondialdehyde (MDA), hydrogen peroxide (H2O2) content, O2-· production rate. Exogenous ABA induced the activation of endogenous protective mechanisms by increasing antioxidant enzymes activities such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as elevated levels of non-enzymatic antioxidants including ascorbic acid (ASA) and glutathione (GSH). Moreover, the yield loss of 5.81%-39.84% caused by chilling stress was alleviated by spraying ABA. In conclusion, foliar spraying exogenous ABA can reduce the negative effects of low-temperature stress on the yield of Adzuki beans, which is essential to ensure stable production of Adzuki beans under low-temperature conditions.

Effect of exogenous abscisic acid on improving low-phosphorus (P) response in rice (Oryza sativa L.)

Phosphorus (P) deficiency is a major constraint to rice productivity worldwide. Exogenous application of abscisic acid (ABA) has not been reported to improve rice response toward P-deficiency. Present study analyzed the biochemical response in the shoots and roots of two rice cultivars, CSR10 (low-P tolerant) and Pusa44 (low-P susceptible) at 36, 72 and 216 h after normal P (NP) (10 ppm) (control), low P (LP) (1 ppm), and LP + ABA given to 12-d old seedlings. Results found that biomass and P-uptake reduced in Pusa44 compared to CSR10 under LP but improved significantly under LP + ABA. P-fractionation was utilized efficiently by CSR10 under LP while LP + ABA improved P-fractionation in both cultivars. LP + ABA improved acid phosphatases in both cultivars. Hexose and sucrose levels were depleted while starch hydrolyzed poorly in Pusa44 compared to CSR10 under LP while LP + ABA enhanced starch hydrolysis and levels of sugars in both cultivars. Starch increased at a late stage in the roots of CSR10 under LP while Pusa44 improved it under LP + ABA. Antioxidant capacity was low while H2O2 was high at early stage in Pusa44 compared to CSR10 under LP. LP + ABA improved antioxidant capacity and reduced H2O2 in both cultivars. Results concluded that ABA is a versatile regulator of not only P-acquisition/P-utilization but also carbohydrates and antioxidant activities under P-deficiency, and exogenous ABA improved low-P tolerance in rice.

Dynamic Changes of Phytohormone Concentrations during <i>Prunella vulgaris</i> L. Development and Impact of Rosmarinic Acid Accumulation through Exogenous ABA Application

Background: Plant hormones not only participate in regulating the growth and development process of plants, but also play an important regulatory role in the synthesis of secondary metabolites. Prunella vulgaris L. (P. vulgaris) is a perennial herb that has a long history for use as a kind of medicinal and edible plant. In order to understand the relationship between plant hormones and Prunella vulgaris L. (P. vulgaris) development. Methods: The quantification of indoleacetic acid (IAA), salicylic acid (SA), jasmonates (JAs), abscisic acid (ABA), 1-aminocyclopropane-1-carboxylic acid (ACC) and cytokinins (CKs) of P. vulgaris during development was performed by a liquid chromatography-mass spectrometry (LC-MS). Furthermore, the effect of exogenous ABA on rosmarinic acid (RA) accumulation was verified. Results: Nuts formation was related to the concentrations of IAA, ABA and ACC in the green-fruit stage, and IAA and ABA levels increased rapidly in this stage. High IAA concentrations can promote an increase in ACC. SA, JAs, ethylene (ET) and ABA were related to the defence response of plants to pathogens. SA concentrations increased sharply after the turning stage, while the concentration of JAs, which are antagonistic to SA, was low. The decrease in ABA concentration after this period may be related to the antagonistic effect of IAA or SA. The CKs trans-zeatin (tZ) and trans-zeatin riboside (tZR) promoted the growth and development of early P. vulgaris, and their concentrations decreased in the late period, leading to withering and senescence of P. vulgaris. The CKs cis-zeatin (cZ) and N6-(2-isopentenyl) adenine (iP) were presumed to be present in nuts. After elicitation with 10 μg/mL ABA, an increase of RA content was observed (p < 0.05). Conclusion: This study can provide an improved basis for elucidating the growth and development mechanism of P. vulgaris in the future, as well as a better understand of the effects of ABA application on RA accumulations.

Effect of Exogenous Abscisic Acid (ABA), a Potential Growth Regulator on Physiological Response to Chilling Stress of Adzuki Bean (Vigna angularis) at Flowering Stage

Background: Low temperatures during flowering severely affect crop growth and yield. Methods: This experiment was conducted under potted conditions with LXD 4 and TJH as test materials and pre-sprayed with exogenous ABA at a concentration of 20 mg·L-1 at flowering stage, respectively and then with an average of 15°C condition for 5 days. Result: The results showed that foliar spraying exogenous ABA effectively inhibited the increase of MDA content and relatively significantly improved the photosynthetic parameters such as Gs and Tr and alleviated the loss of yield factors caused by chilling stress. Compared with spraying water, spraying exogenous ABA can significantly increase the yield per pot of LXD 4 by 6.72~17.77% and TJH by 6.41~37.04% under low temperature conditions. In summary, foliar spraying exogenous ABA ameliorated the effects of chilling stress on the physiological characteristics of adzuki bean leaves and improved yield as a result of improved antioxidant defense mechanisms which impeded lipid peroxidation. Thus, we conclude that foliar spraying exogenous ABA could decelerate the damages caused by chilling stress to some extent.

Quality analysis and metabolomic profiling of the effects of exogenous abscisic acid on rabbiteye blueberry.

Blueberry is a characteristic berry fruit shrub of the genus Vaccinium in the Rhododendron family. The fruit is rich in anthocyanins and has a variety of nutritional and health functions. This study aimed to systematically study the effect of exogenous abscisic acid (ABA) application on ripening and metabolites in blueberry fruits. Blueberry fruit ripening was divided into six stages for further analysis. In this study, nontarget metabolomics was performed to demonstrate the effect on metabolite levels. The results showed that 1000 mg/L ABA significantly promoted fruit ripening and increased anthocyanin content. Moreover, exogenous ABA treatment can affect endogenous ABA levels and improve its antioxidant capacity. Important metabolites of the flavonoid pathway were detected, and the results showed that anthocyanin synthesis increased, and some other bioactive metabolite levels decreased. After comprehensive assessments, we believe that 1000 mg/L exogenous ABA application will have positive impacts on blueberry fruit quality and economic benefits.

Priming effect of exogenous ABA on heat stress tolerance in rice seedlings is associated with the upregulation of antioxidative defense capability and heat shock-related genes

Heat stress is a major restrictive factor that suppresses rice production. In this study, we investigated the potential priming effect of exogenous abscisic acid (ABA) on heat tolerance in rice seedlings. Seedlings were pretreated with 10 µM ABA by root-drenched for 24 h and then subjected to heat stress conditions of 40 °C day/35 °C night. ABA pretreatment significantly decreased leaf withering by 2.5–28.5% and chlorophyll loss by 12.8–35.1% induced by heat stress in rice seedlings. ABA pretreatment also mitigated cell injury, as shown by lower malondialdehyde content, relative electrolytic conductivity, and expression of cell death-related genes OsKOD1, OsCP1, and OsNAC4, while expression of OsBI1, a cell death-suppressor gene, was upregulated by ABA pretreatment. Moreover, ABA pretreatment improved antioxidant defense capacity, as shown by an obvious upregulation of ROS-scavenging genes and a decrease in ROS content (O2− and H2O2), and downregulation of the OsRbohs genes. Application of fluridone, an ABA biosynthesis inhibitor, increased membrane injury and the accumulation of ROS under heat stress. Exogenous antioxidants (proanthocyanidins) significantly alleviated leaf withering by decreasing ROS overaccumulation and membrane injury induced by heat stress. In addition, ABA pretreatment significantly superinduced the expression of ABA-responsive genes SalT and OsWsi18, the ABA biosynthesis genes OsNCED3 and OsNCED4, and the heat shock-related genes OsHSP23.7, OsHSP17.7, OsHSF7, and OsHsfA2a. Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing heat stress tolerance of rice seedlings mainly by improving antioxidant defense capacity and heat shock-related genes.

Effect of exogenous abscisic acid on growth, biochemical changes and antioxidant enzyme activities in black gram [Vigna mungo (L.) Hepper] under drought

Drought stress is a significant limitation to the production and yield of black gram [Vigna mungo (L.) Hepper] and abscisic acid plays a subtle role in the biosynthetic pathway during drought stress. The present study examined the morphology, biochemical, relative water content and antioxidant activities of black gram plants treated with various abscisic acid (ABA) levels under drought conditions. The ABA at 50 ppm concentration showed promising recovery of morphological characters compared to other concentrations. The photosynthetic pigments, biochemical constituents, malondialdehyde and antioxidant enzymes (CAT, POD, SOD and APX) were active at 50 ppm. Infrared Spectroscopic (IR) analysis of black gram leaves in a bandwidth ranging from 400 to 4000 cm-1 revealed a change in metabolites under drought stress and exogenous ABA application. The FTIR spectroscopy results warrant that the expression of functional organic compounds in the drought response of black gram can aid in the discovery of new drought-tolerant traits. As a result, ABA-responsive cultivars can cultivate and produce drought-resistant black gram varieties in arid and semi-arid climates.

Effect of Exogenous Abscisic Acid on Sugar Metabolism in Tomato Fruits

Aims: This research explored the effect of exogenous abscisic acid (ABA) treatment on sugar metabolism in tomato fruits, and provided theoretical basis for the regulation of ABA on the growth and development of tomato fruits.
 Study Design: The whole tomato plant was treated by spraying with 50 mg·L-1 ABA. Spraying distilled water was as the control.
 Place and Duration of Study: College of Biological Science and Technology, between February 2019 and March 2020.
 Methodology: The contents of soluble sugar in tomato fruits were measured with HPLC (High performance liquid chromatography). The enzyme extraction and activities were followed the biochemical method.
 Results: Exogenous ABA treatment reduced the weight and transverse meridians of the fruit at the ripening stage, but increased the contents of fructose, glucose and sucrose in the fruit. At the same time, it also increased the activities of acid invertase, neutral invertase, and sucrose phosphate synthase at the ripening stage.
 Conclusions: Exogenous ABA treatment was beneficial to the accumulation of sugar in tomato fruit and improved tomato quality. Therefore, it could be applied to tomato production.

Effect of exogenous abscisic acid (ABA) on the morphology, phytohormones, and related gene expression of developing lateral roots in ‘Qingzhen 1’ apple plants

Effect of exogenous abscisic acid (ABA) on the morphology, phytohormones, and related gene expression of developing lateral roots in ‘Qingzhen 1’ apple plants

Concentrations-dependent effect of exogenous abscisic acid on photosynthesis, growth and phenolic content of Dracocephalum moldavica L. under drought stress

Main ConclusionThe drought conditions and the application of ABA reduce the photosynthetic activity, and the processes related to the transpiration of Dracocephalum moldavica L. At the same time, the plant increases the production of phenolic compounds and essential oil as a response to stress conditions.In the semi-arid regions, drought stress is the most important environmental limitations for crop production. Abscisic acid (ABA) plays a crucial role in the reactions of plants towards environmental stress such as drought. Field experiments for two consecutive years in 2016 and 2017 were conducted to evaluate the effect of three watering regimes (well-watered, moderate and severe drought) and five exogenous ABA concentrations (0, 5, 10, 20 and 40 μM) on growth, photosynthesis, total phenolic and essential oil content of Dracocephalum moldavica L. Without ABA application, the highest photosynthetic rate (6.1 μmol CO2 m−2 s−1) was obtained under well-watered condition and, moderate and severe drought stress decreased photosynthesis rate by 26.39% and 34.43%, respectively. Some growth parameters such as stem height, leaf area, leaf dry weight and biological yield were also reduced by drought stress. ABA application showed a decreasing trend in photosynthesis rate and mentioned plant growth parameters under all moisture regimes. The highest seed yield (1243.56 kg ha−1) was obtained under well-watered condition without ABA application. Increasing ABA concentration decreased seed yield in all moisture regimes. The highest total phenolic content (8.9 mg g−1 FW) and essential oil yield (20.58 kg ha−1) were obtained from 20 and 5 μM ABA concentration, respectively, under moderate drought stress.

Foliar application of abscisic acid mitigates cadmium stress and increases food safety of cadmium-sensitive lettuce (Lactuca sativa L.) genotype.

Cadmium (Cd2 +) is among the toxic non-essential heavy metals that adversely affect plants metabolic processes and the safety of produce. However, plant hormones can improve plant’s tolerance to various stresses. This study investigated the effect of exogenous abscisic acid (ABA) on the biochemical and physiological processes and food safety of cadmium (Cd2 +)-sensitive lettuce genotype (Lüsu). Seedlings were subjected to five treatments: [(i) Control (untreated plants), (ii) 100 µM CdCl2, (iii) 100 µM CdCl2+10 µg L−1 ABA (iv) 10 µg L−1 ABA, and (v) 0.01 g L−1 ABA-inhibitor (fluridone)] for fourteen days in hydroponic system. The 100 µM CdCl2 increased the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA), decreased photosynthesis and plant biomass. Moreover, it decreased the contents of essential nutrients (except copper) in the leaves but increased the contents of toxic Cd2 + in the leaves and roots of the plants. Foliar application of fluridone (0.01 g L−1) also caused oxidative stress by increasing the contents of H2O2 and MDA. It also decreased the contents of nutrient elements in the leaves of the plants. However, exogenous ABA (10 µg L−1) mitigated the Cd2 +-induced stress, increased antioxidant enzymes activities, photosynthesis and plant biomass under CdCl2 treatment. Remarkably, exogenous ABA increased the contents of essential nutrient elements but decreased the Cd2 + content in leaves under the CdCl2 treatment. Our results have demonstrated that foliar application of ABA mitigates Cd2 + stress and increases the nutritional quality and food safety of Cd2 +-sensitive lettuce genotype under CdCl2 treatment.

Exogenous Abscisic Acid Alleviates Harmful Effect of Salt and Alkali Stresses on Wheat Seedlings.

Exogenous hormones play an important role in plant growth regulation and stress tolerance. However, little is known about the effect of exogenous abscisic acid (ABA) on wheat seedlings under salt and alkali stresses. Here, a pot experiment of saline and alkaline stresses (0 and 100 mmol/L) in which ABA water solution (0, 50 and 100 μmol/L) was sprayed on wheat seedlings was conducted to study the alleviative effectiveness of ABA on salt and alkali stresses. After spraying ABA (50 μmol·L−1), shoot biomass increased 19.0% and 26.7%, respectively. The Na+ content in shoots reduced from 15-fold and 61.5-fold to 10-fold and 37.3-fold in salt and alkali stresses, compared to controls. In addition, proline and organic acid synthesis in shoots also reduced significantly, but the soluble sugar content increased under alkali stress. A high concentration of ABA (100 μmol·L−1) had no significant effects on biomass and ion content in wheat seedlings under both stresses. In conclusion, foliar application of ABA with moderate concentration could effectively accelerate shoot growth of salt-induced wheat seedlings by adjusting the levels of ions and organic solutes.

Вплив екзогенної абсцизової кислоти на морфометричні показники ростових процесів озимої пшениці та спельти за дії гіпертермії

Вплив екзогенної абсцизової кислоти на морфометричні показники ростових процесів озимої пшениці та спельти за дії гіпертермії

Effect of Exogenous Abscisic Acid (ABA), Gibberellic Acid (GA3) and Cluster Thinning on Yield of some Grape Cultivars

Experiment was carried out throughout two successive seasons of 2016 and 2017 on Flame Seedless, Ruby Seedless and Thompson Seedless grapevines grown at the Experimental Orchard of Assiut University, Faculty of Agriculture. The aim of this study was to assess the impacts of abscisic acid (ABA), cluster thinning and their combinations with GA3 on yield weight of three important grape cultivars grown under hot region. Data revealed that, the application of abscisic acid (ABA) increased yield weight (kg/vine), while cluster thinning decreased it. During the 1st season of study (2016), all individual ABA treatments and ABA at 400 ppm combined with GA3 at 10 ppm significantly increased yield weight (kg/vine) comparing with the control treatment. As a result of ABA treatments at 200, 400 and 600 ppm and ABA at 400 ppm plus GA3 at 10 ppm, the yield was increased by 15.5%, 10.5%, 9.8% and 9.2%, respectively. During the 2nd season of study (2017), only ABA at 600 ppm treatment significantly surpassed the control treatment with an increment percentage of 20.5%. The rest of treatments either had no effect or reduced the yield weight comparing with the control. On the other side, cluster thinning by removing 30% of the total clusters that the vine bearing significantly reduced the yield weight (kg/vine) during the two studied seasons. As a result of such treatment, the yield was reduced by 37.2% and 39.2% in 2016 and 2017 seasons, respectively.

Salt tolerance in apple seedlings is affected by exogenous ABA application

Salinity imposes stress on plant tissues that can lead to water deficits or ion-specific stresses resulting from altered ion ratios. The effect of exogenous ABA on 'Fuji' apple seedlings exposed to sodium chloride (NaCl) was analyzed by measuring parameters such as water potential, stomata aperture, sodium (Na+) concentration, endogenous abscisic acid (ABA), and total polyamines as well as genes related to their metabolism. The results show that damage to the leaf surface such as sunburn, yellowing and hardening of the leaves became more prominent compared to untreated controls (no ABA or NaCl) as treatment progressed. Regarding endogenous ABA levels, there was a significant difference at 5 days between the ABA+NaCl and NaCl groups. At the end of the treatment, the NaCl group showed higher levels of chlorophyll when compared to the untreated control and ABA+NaCl group. The stomata of the groups under stress showed recovery at the end of the treatment; however, the ABA+NaCl group response more closely resembled the status of the untreated, non-stressed control. Water potential levels dropped and stomata closure was apparent at 5 days for groups under stress; however, while the ABA+NaCl group displayed recovery as treatment continued, the NaCl group remained low even when the plants had recovered from the initial shock. Total polyamine levels were higher for the ABA+NaCl group after ABA application and then decreased with time, whereas that for the NaCl group was higher after stress began, peaking at 5 and 10 days. Taken together, ABA, PA and gene activations suggest that the early response to stress induced by ABA might have helped the seedlings overcome it more efficiently.

Effect of exogenous abscisic acid on morphology, growth and nutrient uptake of rice (Oryza sativa) roots under simulated acid rain stress.

Application of proper ABA can improve acid tolerance of rice roots by balancing endogenous hormones and promoting nutrient uptake. Abscisic acid (ABA) has an important signaling role in enhancing plant tolerance to environmental stress. To alleviate the inhibition on plant growth and productivity caused by acid rain, it is crucial to clarify the regulating mechanism of ABA on adaptation of plants to acid rain. Here, we studied the effects of exogenously applied ABA on nutrients uptake of rice roots under simulated acid rain (SAR) stress from physiological, biochemical and molecular aspects. Compared to the single SAR treatment (pH 4.5 or 3.5), exogenous 10μM ABA alleviated the SAR-induced inhibition of root growth by balancing endogenous hormones (abscisic acid, indole-3-acetic acid, gibberellic acid and zeatin), promoting nutrient uptake (nitrate, P, K and Mg) in rice roots, and increasing the activity of the plasma membrane H+-ATPase by up-regulating expression levels of genes (OSA2, OSA4, OSA9 and OSA10). However, exogenous 100μM ABA exacerbated the SAR-caused inhibition of root growth by disrupting the balance of endogenous hormones, and inhibiting nutrient uptake (nitrate, P, K, Ca and Mg) through decreasing the activity of the plasma membrane H+-ATPase. These results indicate that proper concentration of exogenous ABA could enhance tolerance of rice roots to SAR stress by promoting nutrients uptake and balancing endogenous hormones.

Proteomics analysis to understand the ABA stimulation of wound suberization in kiwifruit

Quick suberin-based healing after wounding played a protective role for plant to prevent further damage. In this study, the stimulative effect of exogenous abscisic acid (ABA) on wound suberization in postharvest kiwifruit was evaluated through suberin staining with toluidine blue O as well as the determination of suberin phenolics and aliphatics in wound tissue. Furthermore, to reveal the regulatory involvement of ABA in wound suberization, comparative quantitative proteomics and transcriptomics analyses based on iTRAQ and qRT-PCR technique were performed. In proteomics levels, a total of 95 protein species consistently showed differential abundance between ABA and control, including 29 down-regulated and 66 up-regulated protein species. The Kyoto Encyclopedia of Genes and Genomes (KEGG) with protein-protein interaction analyses revealed that ABA mainly affected the antioxidant system, phenylpropanoid metabolism and lipid metabolism associated with wound suberization. Based on the data of proteomics analysis, the differential expressions of genes encoding 11 selected protein species were confirmed by qRT-PCR analyses. GSH-Px, MDHAR, SOD, APX, POD, PAL, CCR, PPO, CYP86B1, DGGT and KCS11 were likely to be the key enzymes that involved the response of ABA to stimulate wound suberization by mediating the antioxidant system, phenylpropanoid metabolism and lipid metabolism. Biological significanceKiwifruit is susceptible to physical injury causing postharvest deterioration during harvest, transportation and storage. Therefore, quick healing is important for maintaining the postharvest quality of injured fruit. This work elucidated the potential role of ABA and the proteomic mechanism of its regulation in wound suberization of postharvest kiwifruit.

Exogenous abscisic acid promotes the nitrogen use efficiency of Brassica napus by increasing nitrogen remobilization in the leaves

ABSTRACTThe effect of exogenous abscisic acid (ABA) on the nitrogen use efficiency (NUE) of Brassica napus was studied by pot experiments using ABA (1 mg L−1) daubed on the leaves at the early siliquing stage. The results showed that activities of proteases and glutamine synthetase (GS) were significantly promoted by the ABA treatment, which increased the capacity of degradation of foliar proteins and biosynthesis of glutamine (N-transport compounds), both of which promote decreased N in leaves of the ABA treatment. L-glutamine, other free amino acids, and soluble sugar content in the phloem sap of the ABA treatment were significantly higher than those of the control. A 15N label trial showed that more 15N was distributed from leaves to the grain by the ABA treatment, which resulted in a significantly higher NUE in the ABA treatment relative to the control.

Formation of adaptive reactions in Arabidopsis thaliana wild-type and mutant jin1 plants under action of abscisic acid and salt stress

To elucidate the possible role of the transcription factor (TRF) JIN1/MYC2 in implementation of stress-protective effects of abscisic acid (ABA), the effect of exogenous ABA on the state of stomata and the activity of antioxidant enzymes and proline content under salt stress conditions in Arabidopsis thaliana plants of wild type (Col-0) and jin1 mutants with impaired jasmonate signaling was investigated. Treatment of leaves’ epidermis with ABA (10 or 100 μM) caused the closing of stomata in Col-0 plants but has hardly any influence on stomatal aperture in jin1 mutants. Salt stress (200 mM NaCl exposure for 24 h) caused a reduction of the water content in the plant leaves of both genotypes. Addition of 10 μM ABA into the growing medium contributed to a maintaining of normal hydration in wild-type but not in jin1 plants under salt stress. ABA treatment caused an almost twofold increase in proline content in the leaves of plants of both genotypes under normal conditions. Pretreatment with phytohormone contributed to enhancing the proline content in wild-type plants at salt stress and had a less significant effect on its amount in jin1 plants. Treatment with ABA under physiologically normal conditions increased the catalase activity in wild-type plants. Both genotypes under ABA influence showed increased activity of superoxide dismutase (SOD). Under salt stress conditions, higher activity of SOD, catalase, and guaiacol peroxidase was observed in ABA-treated wild-type plants but not in jin1 mutants. A conclusion about the participation of TRF JIN1/MYC2 in the formation of certain ABA-induced physiological responses of Arabidopsis plants was made.

Decrease of mesophyll conductance to CO2 is a possible mechanism of abscisic acid influence on photosynthesis in seedlings of pea and wheat

Treatment of plants by phytohormones is a perspective method of regulation of the plant stress resistance and productivity. However, the mechanisms of phytohormone effects on physiological processes require investigations. The aim of this work was the analysis of the influence of exogenous abscisic acid (ABA) on photosynthesis in seedlings of pea and wheat, and in particular, an estimation of the involvement of the mesophyll conductance to CO2 in the realization of the ABA effects. A standard system for recording of photosynthetic parameters and a system for intracellular measurements of electrical activity were used in the experiments. It was shown that the effect of exogenous ABA on photosynthesis was most prominent 1 day after spraying of a plant. A detailed analysis of photosynthetic processes showed that ABA decreased photosynthetic assimilation of CO2 and increased cyclic electron flow in plants under study; these processes were interconnected. A decrease of the mesophyll conductance to CO2 was probably a mechanism of the decrease in the photosynthetic assimilation of CO2, because ABA did not significantly influence water conductance of a leaf and parameters of the CO2 fixation in Calvin–Benson cycle. It is likely that the decrease of the mesophyll conductance to CO2 was related with a decrease of the plasma membrane conductance to carbon dioxide. Inactivation of H+-ATP-ase and changes in extracellular pH can be a mechanism of this decrease. A decrease of the metabolic component of the electrical resting potential after the ABA treatment testifies in favor of this possibility.