Abscisic Acid Accumulation In Roots Research Articles

Physiological and biochemical response analysis of Styrax tonkinensis seedlings to waterlogging stress

Climate change is increasing flooding in provinces of the south of the Yangtze River, posing challenges for promoting Styrax tonkinensis seedlings in these areas. To understand the physiological reasons for this species' intolerance to waterlogging, we observed biochemical parameters in one-year-old S. tonkinensis seedlings during two seasons. For 4 and 12 days in summer and winter experiments, respectively, we subjected seedlings to a pot-in-pot waterlogging treatment. Control groups were established at 0 h and 0 days. We examined indicators related to root vigor, reactive oxygen species (ROS), antioxidant enzymes, fermentative pathways, and more. The results displayed that decreased abscisic acid accumulation in roots inhibited water transport. Increased dehydrogenase and lactate dehydrogenase activity in roots promoted alcohol and lactate fermentation, causing toxic damage and reduced root vigor, impeding water absorption. In leaves, high ROS levels led to lipid peroxidation, exacerbating water loss from continuous transpiration. The high relative electric conductivity and low leaf relative water content indicated water loss, causing leaf wilting and shriveling. Conversely, winter seedlings, devoid of leaves, significantly reduced transpiration, and dormancy delayed root fermentation. With less ROS damage in roots, winter seedlings exhibited greater waterlogging tolerance. In summary, excessive water loss from leaves and inhibited vertical water transport contributed to low summer survival rates, while winter leafless dormancy and reduced ROS damage enhanced tolerance. Our findings provide insights for enhancing waterlogging resistance in S. tonkinensis amidst climate change challenges.

Root ABA Accumulation Delays Lateral Root Emergence in Osmotically Stressed Barley Plants by Decreasing Root Primordial IAA Accumulation

Increased auxin levels in root primordia are important in controlling root branching, while their interaction with abscisic acid (ABA) likely regulates lateral root development in water-deficient plants. The role of ABA accumulation in regulating root branching was investigated using immunolocalization to detect auxin (indoleacetic acid, IAA) and ABA (abscisic acid) in root primordia of the ABA-deficient barley mutant Az34 and its parental genotype (cv. Steptoe) barley plants. Osmotic stress strongly inhibited lateral root branching in Steptoe plants, but hardly affected Az34. Root primordial cells of Steptoe plants had increased immunostaining for ABA but diminished staining for IAA. ABA did not accumulate in root primordia of the Az34, and IAA levels and distribution were unaltered. Treating Az34 plants with exogenous ABA decreased root IAA concentration, while increasing root primordial ABA accumulation and decreasing root primordial IAA concentration. Although ABA treatment of Az34 plants increased the root primordial number, it decreased the number of visible emerged lateral roots. These effects were qualitatively similar to that of osmotic stress on the number of lateral root primordia and emerged lateral roots in Steptoe. Thus ABA accumulation (and its crosstalk with auxin) in root primordia seems important in regulating lateral root branching in response to water stress.

Interactive Effects of Intraspecific Competition and Drought on Stomatal Conductance and Hormone Concentrations in Different Tomato Genotypes

Plant physiological responses to various stresses are characterized by interaction and coupling, while the intrinsic mechanism remains unclear. The effects of intraspecific competition on plant growth, stomatal opening, and hormone concentrations were investigated with three tomato genotypes (WT-wild type, Ailsa Craig; FL-a abscisic acid (ABA) deficient mutant, flacca; NR-a partially ethylene-insensitive genotype) under two water regimes (full irrigation, irrigation amount = daily transpiration; deficit irrigation, 60% of irrigation amount in full irrigation) in this study. Three kinds of competitions were designed, i.e., root and canopy competition, non-root competition, and non-canopy competition, respectively. Intraspecific competition reduced plant leaf area and stomatal conductance (gs) of wild-type tomato, accompanied by ABA accumulation and ethylene evolution. Intraspecific competition-induced decrease in gs was absent in FL and NR, indicating ABA and ethylene involved in plant response to intraspecific competition. As soil water becomes dry, the competition decreased gs by elevating ABA and ethylene accumulations. Under severe drought, the competition-induced decline in gs was covered by the severe drought-induced decrease in gs, as hydraulic signals most probably dominate. The absence of canopy competition insignificantly influenced plant stomatal opening of well-watered tomato, as canopy separation minimized the plant neighbor sensing by ethylene and other signals. Whereas under water deficit condition, the absence of canopy competition significantly reduced ABA accumulation in roots and then stomatal conductance, indicating the belowground neighbor detection signals maybe enhanced by soil drought. The absence of root competition increased ethylene evolution, confirming the importance of ethylene in neighbor detection and plant response to environmental stress.

Leaf Gas Exchange of Tomato Depends on Abscisic Acid and Jasmonic Acid in Response to Neighboring Plants under Different Soil Nitrogen Regimes.

High planting density and nitrogen shortage are two important limiting factors for crop yield. Phytohormones, abscisic acid (ABA), and jasmonic acid (JA), play important roles in plant growth. A pot experiment was conducted to reveal the role of ABA and JA in regulating leaf gas exchange and growth in response to the neighborhood of plants under different nitrogen regimes. The experiment included two factors: two planting densities per pot (a single plant or four competing plants) and two N application levels per pot (1 and 15 mmol·L−1). Compared to when a single plant was grown per pot, neighboring competition decreased stomatal conductance (gs), transpiration (Tr) and net photosynthesis (Pn). Shoot ABA and JA and the shoot-to-root ratio increased in response to neighbors. Both gs and Pn were negatively related to shoot ABA and JA. In addition, N shortage stimulated the accumulation of ABA in roots, especially for competing plants, whereas root JA in competing plants did not increase in N15. Pearson’s correlation coefficient (R2) of gs to ABA and gs to JA was higher in N1 than in N15. As compared to the absolute value of slope of gs to shoot ABA in N15, it increased in N1. Furthermore, the stomatal limitation and non-stomatal limitation of competing plants in N1 were much higher than in other treatments. It was concluded that the accumulations of ABA and JA in shoots play a coordinating role in regulating gs and Pn in response to neighbors; N shortage could intensify the impact of competition on limiting carbon fixation and plant growth directly.

Root Abscisic Acid Contributes to Defending Photoinibition in Jerusalem Artichoke (Helianthus tuberosus L.) under Salt Stress.

The aim of the study was to examine the role of root abscisic acid (ABA) in protecting photosystems and photosynthesis in Jerusalem artichoke against salt stress. Potted plants were pretreated by a specific ABA synthesis inhibitor sodium tungstate and then subjected to salt stress (150 mM NaCl). Tungstate did not directly affect root ABA content and photosynthetic parameters, whereas it inhibited root ABA accumulation and induced a greater decrease in photosynthetic rate under salt stress. The maximal photochemical efficiency of PSII (Fv/Fm) significantly declined in tungstate-pretreated plants under salt stress, suggesting photosystem II (PSII) photoinhibition appeared. PSII photoinhibition did not prevent PSI photoinhibition by restricting electron donation, as the maximal photochemical efficiency of PSI (ΔMR/MR0) was lowered. In line with photoinhibition, elevated H2O2 concentration and lipid peroxidation corroborated salt-induced oxidative stress in tungstate-pretreated plants. Less decrease in ΔMR/MR0 and Fv/Fm indicated that PSII and PSI in non-pretreated plants could maintain better performance than tungstate-pretreated plants under salt stress. Consistently, greater reduction in PSII and PSI reaction center protein abundance confirmed the elevated vulnerability of photosystems to salt stress in tungstate-pretreated plants. Overall, the root ABA signal participated in defending the photosystem’s photoinhibition and protecting photosynthesis in Jerusalem artichoke under salt stress.

Prolonged drying cycles stimulate ABA accumulation in Citrus macrophylla seedlings exposed to partial rootzone drying

Partial rootzone drying (PRD) establishes discrete wet and dry parts of the rootzone (for example using parallel drip lines on either side of the crop row), and alternates them to stimulate root growth and root-to-shoot ABA signalling. To assess whether alternation frequency affects plant physiological responses, Citrus macrophylla Wester seedlings were grown with the root system split between two pots and 5 irrigation treatments applied: Control, PRD-Fixed (where wet and dry parts of the rootzone were not alternated) and three alternate PRD treatments where the wet and dry parts were swapped at 3 (PRD1), 6 (PRD2) and 12 (PRD3) days intervals, to dry the soil to different degrees before alternating the irrigation. Water was equally distributed between both pots in Control plants, whereas only one pot was watered and the other allowed to dry in PRD plants, with all plants receiving the same irrigation volume. After 24 days, soil water content (θv), leaf water potential (Ψleaf), root water potential (Ψroot), abscisic acid (ABA) concentration in roots ([ABA]root), leaves ([ABA]leaf) and shoot xylem sap ([X-ABA]shoot), biomass allocation and leaf area were measured. Higher soil water availability of the dry side (PRD1 and PRD2) had no significant effects on leaf water relations, ABA status and plant biomass allocation. However, increasing the duration of exposure of part of the root system to dry soil (PRD3 and PRD-Fixed) further decreased Ψroot and stimulated root ABA accumulation, while decreasing Ψleaf and increasing [ABA]leaf of PRD3 plants compared to the other treatments. Differences in physiological response between PRD3 and PRD-Fixed plants were attributed to differences in the proportion of root mass exposed to drying soil: PRD3 plants had a lower Ψleaf and a higher [ABA]leaf with a smaller proportion of their root mass in wet soil. Since long drying cycles were required to alter plant biomass allocation and physiological responses in PRD plants, these should be implemented in designing suitable PRD strategies for field application.

Leaf dehydration is needed to induce abscisic acid accumulation in roots of citrus plants

The root system is the main organ involved in the water uptake and it is assumed that it perceives soil dehydration, triggering water stress responses at the entire plant level, including abscisic acid (ABA) accumulation. However, several lines of evidence demonstrate that leaves directly adjust their water status (and induce increases in ABA levels) in response to changes in the evaporative demand. To evaluate the influence of leaf water status on ABA accumulation in roots, the canopy of citrus plants was kept at high humidity while roots were dehydrated. Leaves and roots of completely dehydrated plants increased levels of ABA whereas plants with turgid leaves did not accumulate ABA either in leaves or in roots. Furthermore, in dehydrated roots, the expression of several key genes involved in carotenoid and ABA biosynthetic pathways such as CsβCHX1 and CsNCED1 was strongly affected by the water status of leaves whereas water availability in roots showed a marginal influence. Overall, results confirm that leaves are a relevant source of ABA for roots during dehydration and also demonstrate that leaf-dehydration is required to trigger ABA-induced responses in roots.

Root ABA Accumulation Enhances Rice Seedling Drought Tolerance under Ammonium Supply: Interaction with Aquaporins.

In previous studies, we demonstrated that ammonium nutrition enhances the drought tolerance of rice seedlings compared to nitrate nutrition and contributes to a higher root water uptake ability. It remains unclear why rice seedlings maintain a higher water uptake ability when supplied with ammonium under drought stress. Here, we focused on the effects of nitrogen form and drought stress on root abscisic acid (ABA) concentration and aquaporin expression using hydroponics experiments and stimulating drought stress with 10% PEG6000. Drought stress decreased the leaf photosynthetic rate and stomatal conductivity and increased the leaf temperature of plants supplied with either ammonium or nitrate, but especially under nitrate supply. After 4 h of PEG treatment, the root protoplast water permeability and the expression of root PIP and TIP genes decreased in plants supplied with ammonium or nitrate. After 24 h of PEG treatment, the root hydraulic conductivity, the protoplast water permeability, and the expression of some aquaporin genes increased in plants supplied with ammonium compared to those under non-PEG treatment. Root ABA accumulation was induced by 24 h of PEG treatment, especially in plants supplied with ammonium. The addition of exogenous ABA decreased the expression of PIP and TIP genes under non-PEG treatment but increased the expression of some of them under PEG treatment. We concluded that drought stress induced a down-regulation of aquaporin expression, which appeared earlier than did root ABA accumulation. With continued drought stress, aquaporin expression and activity increased due to root ABA accumulation in plants supplied with ammonium.

Ethylene responses in rice roots and coleoptiles are differentially regulated by a carotenoid isomerase-mediated abscisic acid pathway.

Ethylene and abscisic acid (ABA) act synergistically or antagonistically to regulate plant growth and development. ABA is derived from the carotenoid biosynthesis pathway. Here, we analyzed the interplay among ethylene, carotenoid biogenesis, and ABA in rice (Oryza sativa) using the rice ethylene response mutant mhz5, which displays a reduced ethylene response in roots but an enhanced ethylene response in coleoptiles. We found that MHZ5 encodes a carotenoid isomerase and that the mutation in mhz5 blocks carotenoid biosynthesis, reduces ABA accumulation, and promotes ethylene production in etiolated seedlings. ABA can largely rescue the ethylene response of the mhz5 mutant. Ethylene induces MHZ5 expression, the production of neoxanthin, an ABA biosynthesis precursor, and ABA accumulation in roots. MHZ5 overexpression results in enhanced ethylene sensitivity in roots and reduced ethylene sensitivity in coleoptiles. Mutation or overexpression of MHZ5 also alters the expression of ethylene-responsive genes. Genetic studies revealed that the MHZ5-mediated ABA pathway acts downstream of ethylene signaling to inhibit root growth. The MHZ5-mediated ABA pathway likely acts upstream but negatively regulates ethylene signaling to control coleoptile growth. Our study reveals novel interactions among ethylene, carotenogenesis, and ABA and provides insight into improvements in agronomic traits and adaptive growth through the manipulation of these pathways in rice.

Local root abscisic acid (ABA) accumulation depends on the spatial distribution of soil moisture in potato: implications for ABA signalling under heterogeneous soil drying.

Patterns of root abscisic acid (ABA) accumulation ([ABA]root), root water potential (Ψroot), and root water uptake (RWU), and their impact on xylem sap ABA concentration ([X-ABA]) were measured under vertical partial root-zone drying (VPRD, upper compartment dry, lower compartment wet) and horizontal partial root-zone drying (HPRD, two lateral compartments: one dry, the other wet) of potato (Solanum tuberosum L.). When water was withheld from the dry compartment for 0-10 d, RWU and Ψroot were similarly lower in the dry compartment when soil volumetric water content dropped below 0.22cm(3) cm(-3) for both spatial distributions of soil moisture. However, [ABA]root increased in response to decreasing Ψroot in the dry compartment only for HPRD, resulting in much higher ABA accumulation than in VPRD. The position of the sampled roots (~4cm closer to the surface in the dry compartment of VPRD than in HPRD) might account for this difference, since older (upper) roots may accumulate less ABA in response to decreased Ψroot than younger (deeper) roots. This would explain differences in root ABA accumulation patterns under vertical and horizontal soil moisture gradients reported in the literature. In our experiment, these differences in root ABA accumulation did not influence [X-ABA], since the RWU fraction (and thus ABA export to shoots) from the dry compartment dramatically decreased simultaneously with any increase in [ABA]root. Thus, HPRD might better trigger a long-distance ABA signal than VPRD under conditions allowing simultaneous high [ABA]root and relatively high RWU fraction.

Ethylene-induced inhibition of root growth requires abscisic acid function in rice (Oryza sativa L.) seedlings.

Ethylene and abscisic acid (ABA) have a complicated interplay in many developmental processes. Their interaction in rice is largely unclear. Here, we characterized a rice ethylene-response mutant mhz4, which exhibited reduced ethylene-response in roots but enhanced ethylene-response in coleoptiles of etiolated seedlings. MHZ4 was identified through map-based cloning and encoded a chloroplast-localized membrane protein homologous to Arabidopsis thaliana (Arabidopsis) ABA4, which is responsible for a branch of ABA biosynthesis. MHZ4 mutation reduced ABA level, but promoted ethylene production. Ethylene induced MHZ4 expression and promoted ABA accumulation in roots. MHZ4 overexpression resulted in enhanced and reduced ethylene response in roots and coleoptiles, respectively. In root, MHZ4-dependent ABA pathway acts at or downstream of ethylene receptors and positively regulates root ethylene response. This ethylene-ABA interaction mode is different from that reported in Arabidopsis, where ethylene-mediated root inhibition is independent of ABA function. In coleoptile, MHZ4-dependent ABA pathway acts at or upstream of OsEIN2 to negatively regulate coleoptile ethylene response, possibly by affecting OsEIN2 expression. At mature stage, mhz4 mutation affects branching and adventitious root formation on stem nodes of higher positions, as well as yield-related traits. Together, our findings reveal a novel mode of interplay between ethylene and ABA in control of rice growth and development.

The accumulation and transport of abscisic acid insoybean (Glycine max L.) under aluminum stress

Abscisic acid (ABA) plays an important role in mediating some biotic and abiotic stresses. In the present study, to better understand the relationship of ABA production and Aluminum (Al)-resistance in plants, Al-resistance genotype (Jiyu70) of soybean was adopted to investigate the accumulation and transport of ABA in plants exposed to Al. Results showed that exogenous application of ABA and ABA synthesis inhibitor-fluridone respectively increased and reduced endogenous ABA content in root apices of soybean, and results in the corresponding reduction and aggravation of Al toxicity. Increasing of either Al concentration (0–50 μM) or treatment duration (0–12 h, 30 μM Al) cause a higher inhibition of root elongation and ABA accumulation in root apices of soybean. Al-induced enhancement of endogenous ABA production not only was in roots but also in leaves, whereas La3+ (behaves similarly as Al3+ at the level of cell surface) only increased ABA accumulation in roots. In split-root experiments, Al treatment in two parts of roots (Part A, + Al; Part B, + Al) both decreased root elongation and increased ABA accumulation in root apices of soybean. Whereas when only part A of roots was exposed to Al (Part A, + Al; Part B, -Al), endogenous ABA content in root apices increased in part A but inversely in part B, but root elongation inhibition only was found in part A. Using [3H]-ABA radioisotope technique, it was found that [3H]-ABA can transport at the rate of more than 3.2 cm·min−1 in the whole plants, and this can be accelerated by Al supply. In addition, [3H]-ABA tended to distribute in the root part under Al stress. Together, these results suggest that ABA may play an important role in regulating Al resistance of soybean as an Al-stress signal.

Abscisic acid accumulation in the roots of nutrient-limited plants: Its impact on the differential growth of roots and shoots

We describe the involvement of abscisic acid (ABA) in the control of differential growth of roots and shoots of nutrient limited durum wheat plants. A ten-fold dilution of the optimal concentration of nutrient solution inhibited shoot growth, while root growth remained unchanged, resulting in a decreased shoot/root ratio. Addition of fluridone (inhibitor of ABA synthesis) prevented growth allocation in favour of the roots. This suggests the involvement of ABA in the redirecting of growth in favour of roots under limited nutrient supply. The ABA content was greater in shoots and growing apical root parts of starved plants than in nutrient sufficient plants. Accumulation of ABA in shoots of nutrient deficient plants was linked to a decrease in leaf turgor. Increased flow of ABA in the phloem apparently contributed to the accumulation of ABA in the apical part of the roots. Thus, partitioning of growth between roots and shoots of wheat plants limited in mineral nutrients appears to be modulated by accumulation of ABA in roots. This ABA may originate in the shoots, where its synthesis is stimulated by the loss of leaf turgor.

Microtubule dynamics in relation to osmotic stress-induced ABA accumulation in Zea mays roots

Microtubules play important roles in many physiological processes such as plant responses to drought stress. Abscisic acid (ABA) accumulates significantly in plants in response to drought conditions, which has been considered as a major response for plants to enhance drought tolerance. In this work, the focus was on the possible roles of microtubules in the induction of ABA biosynthesis in the roots of Zea mays when subjected to osmotic stress. The dynamic changes of microtubules in response to the stress were investigated by immunofluorescence staining, enzyme-linked immunosorbent assay, and a pharmacological approach. Disruption and stabilization of microtubules both significantly stimulated ABA accumulation in maize root cells, although this stimulation was markedly lower than that caused by osmotic stress. Cells in which the microtubule stability had been changed did not respond further to osmotic stress in terms of ABA biosynthesis. However, treatment with both a microtubule de-stabilizer and a stabilizer enhanced the sensitivity of cells to osmotic stress in terms of ABA accumulation. It is suggested that both osmotic stress and changes in microtubule dynamics would trigger maize root cells to biosynthesize ABA, and interactions between osmotic stress and microtubule dynamics would have an effect on ABA accumulation in root cells, although the exact mechanism is not clear at present.

Dynamic analysis of ABA accumulation in relation to the rate of ABA catabolism in maize tissues under water deficit

The plant hormone abscisic acid (ABA) accumulates in plant tissues which experience water deficit (stress ABA). This study analysed its accumulation as a function of both synthesis and catabolism in maize tissues. By following the disappearance of the stress ABA when ABA synthesis was blocked by nordihydroguaiaretic acid (NDGA), the rate of the catabolism of stress ABA was determined. When compared with the catabolic rate of baseline (non-stress) ABA, stress ABA showed a catabolic rate >11 times higher. With such an elevated catabolic rate, it is proposed that the xanthophyll precursor pool may not be able to sustain the ABA accumulation, and such a proposition has been substantiated by further experiments where fluridone is used to limit the availability of upstream ABA precursors. When fluridone was used, stress ABA accumulation could only be sustained for a few hours, i.e. approximately 5 h for leaf and 1 h for root tissues. In detached roots, stress ABA accumulation could not be sustained even if fluridone was not used, suggesting that stress ABA accumulation in root systems requires the continuous import of ABA precursors from the shoots. Such an assumption was substantiated by the observation that defoliation or shading significantly reduced ABA accumulation in intact roots. The present study suggests that ABA catabolism is rapid enough to play an important role in the regulation of ABA accumulation.

Leaf Abscission Induced by Ethylene in Water-Stressed Intact Seedlings of Cleopatra Mandarin Requires Previous Abscisic Acid Accumulation in Roots.

The involvement of abscisic acid (ABA) in the process of leaf abscission induced by 1-aminocyclopropane-1-carboxylic acid (ACC) transported from roots to shoots in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings grown under water stress was studied using norflurazon (NF). Water stress induced both ABA (24-fold) and ACC (16-fold) accumulation in roots and arrested xylem flow. Leaf bulk ABA also increased (8-fold), although leaf abscission did not occur. Shortly after rehydration, root ABA and ACC returned to their prestress levels, whereas sharp and transitory increases of ACC (17-fold) and ethylene (10-fold) in leaves and high percentages of abscission (up to 47%) were observed. NF suppressed the ABA and ACC accumulation induced by water stress in roots and the sharp increases of ACC and ethylene observed after rewatering in leaves. NF also reduced leaf abscission (7-10%). These results indicate that water stress induces root ABA accumulation and that this is required for the process of leaf abscission to occur. It was also shown that exogenous ABA increases ACC levels in roots but not in leaves. Collectively, the data suggest that ABA, the primary sensitive signal to water stress, modulates the levels of ethylene, which is the hormonal activator of leaf abscission. This assumption implies that root ACC levels are correlated with root ABA amounts in a dependent way, which eventually links water status to an adequate, protective response such as leaf abscission.

Phenotypic Expression of Wild-Type Tomato and Three Wilty Mutants in Relation to Abscisic Acid Accumulation in Roots and Leaflets of Reciprocal Grafts

Lycopersicon esculentum Mill. cv Rheinlands Ruhm (RR) and cv Moneymaker and the three wilty mutants flacca (flc), sitiens (sit), and sitiens(w) (sit(w)), together with most reciprocal grafts, were grown in pots and in solution culture. Detached leaflets, and control and steam-girdled intact plants, were left turgid or were wilted in air. Detached leaflets and the leaflets and roots of the intact plants were analyzed for their abscisic acid (ABA) content. Turgid RR leaflets contained about 2.9 ng ABA per milligram dry weight. On average, the flc and sit leaflets contained 33 and 11% of this amount, respectively. The lack of ABA approximately correlated with the severity of the mutant phenotype. Mutant roots also contained less ABA than wild-type roots. Wild-type scions on mutant stocks (wild type/mutant) maintained the normal phenotype of ungrafted plants. Mutant scions grafted onto wild-type stocks reverted to a near wild-type phenotype. After the wild-type leaves were excised from solution culture-grown mutant/wild-type plants, the revertive morphology of the mutant scions was maintained, although endogenous ABA levels in the leaflets fell to typical mutant levels and the leaflets became wilty again. When stressed in air, both leaflets and roots of RR plants produced stress-induced ABA, but the mutant leaflets and roots did not. The roots and leaflets of the grafted plants behaved according to their own genotype, with the notable exception of mutant roots grown with wild-type scions. Roots of flc and sit(w) recovered the ability to accumulate stress-induced ABA when grafted with RR scions before the stress was imposed.