Leaf ABA Research Articles

Identification of QTL for drought responses in maize and their use in testing causal relationships between traits

A difficulty in identifying traits that help crop plants maintain their yield under droughted conditions is distinguishing between those traits that contribute to yield stability under drought and traits that do not affect yield. With the development of molecular markers for many crops it is now possible to identify major quantitative trait loci (QTL) regulating specific drought responses. By comparing the coincidence of such QTL for specific traits it is possible to test much more precisely than before whether a particular constitutive or adaptive response to drought stress is likely to be of significance in improving drought resistance. We have used this approach to identify QTL for ABA content and other traits likely to be important in determining drought response in maize. Eighty-four RFLP markers were mapped in an F2 population of 81 plants from a cross between parents, Polj17 (drought resistant) and F-2 (drought sensitive), that differ markedly in many constitutive and adaptive responses to drought stress. In a soil glasshouse experiment, from which water was withheld for 3 weeks after anthesis, flowering time, stomatal conductance, tissue ABA contents, leaf water relations parameters and fluorescence characteristics, root pulling force, and nodal root number were measured. The minimum number and location of genes having major effects on the traits were determined and possible causal relationships amongst them tested. Comparing the coincidence of QTL for ABA content and stomatal conductance showed that xylem ABA content was more likely to have had a regulatory effect on the stomatal conductance of those plants than the whole leaf ABA content. However, both xylem and leaf ABA contents were significantly associated with root characteristics, suggesting that the rooting behaviour (either constitutive or adaptive) was important in regulating stress responses, particularly in determining xylem ABA contents. We also found that Fm (a measure of the activity of photosynthetic reaction centres) was positively associated with chlorophyll concentration per unit area. Different methods for comparing QTL are presented and discussed.

Drought and Salt Tolerance are not Necessarily Linked:A Study on Wheat Varieties Differing in Drought Tolerance under Consecutive Water and Salinity Stresses

Summary Hydroponically-grown seedlings of two bread-wheat ( Triticum aestivum L.) varieties (Kobomugi:drought tolerant, Regina: drought and salt sensitive) were evaluated for drought (PEG 4000) and salt (NaCl) tolerance under controlled environmental conditions. Changes in net photosynthesis (A), stomatal conductance (g s ), specific leaf area (SLA), abscisic acid content (ABA), and water content of shoots (W s ) and roots (W r ) were measured. Osmotic pressures of the culture solutions were 0.25 [11 % PEG(1)] and 1.0 MPa [21 % PEG(2)]. After the 7 days of exposure, control and PEG treated plants were transferred to equi-osmolal [i.e. with PEG(1) and PEG(2)] NaCl culture solutions. Throughout the PEG induced drought stress, the leaves of Kobomugi exhibited lower stomatal conductance (g s ) and higher leaf ABA content than those of Regina. However, net photosynthesis (A) was similar for both varieties. Thus, Kobomugi possessed a higher water use efficiency (WUE) than Regina. Following the transfer of the plants from control to saline culture solution g s A, WUE, SLA, W s and W r in Kobomugi were not significantly different from those in Regina. Based on these results Kobomugi can be considered as susceptible as Regina for high salinity. Transfer from PEG(2) to equi-osmolal NaCl(2) nutrient solution resulted in a steady increase in both A and g s in Regina, though in Kobomugi both A and g s declined dramatically after an initial increase. So, as a consequence of the consecutive occurrence of water and salt stresses the drought tolerant Kobomugi was more retarded than the drought sensitive Regina. The possible disadvantage of a genotype only possessing the traits that enable it to be a ≪water saver≫ without any obvious ability to cope with the toxic effect of ions, when water limitation is followed with salinity imposed stresses, is discussed.

Changes in cell ultrastructure and endogenous abscisic acid and indole-3-actic acid concentrations in Fatsia japonica leaves under polyethylene glycol-induced water stress

Ultrastructural alterations in epidermal and mesophyll cells as well as variations in bulk leaf endogenous ABA and IAA concentrations were studied in PEG-treated plants of Fatsia japonica Decne & Plank. Under stress induced by PEG vesicles containing fibrous material and electron-dense bodies associated with plasma membranes were observed. Cytochemical examination indicated that electron-dense bodies corresponded to lipids and the fibrous material of the vesicles were polysaccharides. Chloroplasts, mitochondria, nuclei and Golgi apparatus also showed modifications. A strong relationship was found between increasing PEG-induced water stress, increasing endogenous ABA and ultrastructural changes. In relation with leaf ontogeny and ABA concentration a higher ABA level was observed in younger than in older leaves. The differences in the endogenous concentrations of indole-3-acetic acid are unclear, except after 7 days of PEG-treatment. The increase in the endogenous abscisic acid concentration could be related with the ultrastructural changes.

Effects of water stress on cellular ultrastructure and on concentrations of endogenous abscisic acid and indole-3-acetic acid in Fatsia japonica leaves

Ultrastructural alterations in mesophyll cells as well as variations in bulk leaf endogenous ABA and IAA concentrations were studied in water-stressed field-grown plants of Fatsia japonica. Under water deficit cellular membranes were modified and an increase in vesicles was observed. The main damage to the chloroplasts included thylakoid swelling and disruption of the chloroplast envelope. Concomitant variations in abscisic acid and indole-3-acetic acid were observed. Despite the expected increased in endogenous ABA concentration in relation to water stress, after the highest concentration of ABA, observed at predawn in severely stressed plants (29-1), there was a sharp decline from 2768 pmol g fw−1 to 145 pmol g fw−1; thus in severely stressed plants ABA levels were not related to changes in bulk leaf ABA contents. Water stress did not influence the concentrations of indole-3-acetic acid, although the increase in the endogenous abscisic acid concentration could be related with the ultrastructural changes.

ABA AND STOMATAL RESPONSES IN TEPARY AND COMMON BEAN

Tepary beans (Phaseolus acutifolius Gray) are more drought tolerant and have stomata that are more sensitive to low leaf water potentials (ψ w) than common beans (P. vulgaris L.). This study was designed to examine the role of ABA in controlling stomatal behaviour in these species. Comparison of the bulk leaf ABA content does not explain why tepary stomata are more sensitive to low leaf ψ w compared to common bean (at -1.4 MPa ABA content increased 40-fold in common bean and 25-fold in tepary). We hypothesize that the greater sensitivity of tepary stomata to low leaf ψ w is related to a higher concentration of ABA in the xylem sap, and/or to a greater sensitivity of tepary stomata to ABA. Xylem sap of well-watered and water stressed plants is analyzed to determine the concentration of ABA, and whether ABA is a putative candidate serving as a chemical root signal in response to water stress in Phaseolus. To test stomatal sensitivity to ABA, epidermal strips and detached leaves are exposed to a range of ABA concentrations. The relationship between stomatal aperture and different ABA concentrations is discussed.

ABA AS A ROOT SIGNAL IN GRAPEVINES UNDER WATER STRESS

ABA implication in root signals of water stress has been suggested by several authors. To verify this hypothesis in grapevines, this experiment has been carried out. One-year-old own rooted cuttings of grapevine cultivar Cabernet Sauvignon were exposed to water stress. After three months of growth, water was completely withdrawn for nine days, till the plants reached the wilting point. The plants were then rewatered. During the whole period, root hydraulic conductivity was measured with a pressure bomb; xylem sap samples were collected, as well as leaf and root samples. ABA concentration in these samples was measured using Radio Immuno Assay with DBPA1, a monoclonal antibody for ABA. The concentration of xylem sap ABA was 68.2 mg m-3 at the start of the experiment. After eight days of stress it was 1863.6 mg m-3, 27 × higher. On the ninth day the plants were rewatered, and the xylem sap ABA decreased at 100.2 mg m-3, keeping this level for eight more days. Leaf ABA showed high levels of this inhibitor, with a peak in correspondence with the maximum stress. A similar behaviour was attained by roots. In grapevine, ABA seems to be involved in a water stress root signal directed to the canopy.

Xylem ABA controls the stomatal conductance of field‐grown maize subjected to soil compaction or soil drying

ABSTRACTStomatal conductance of individual leaves was measured in a maize field, together with leaf water potential, leaf turgor, xylem ABA concentration and leaf ABA concentration in the same leaves. Stomatal conductance showed a tight relationship with xylem ABA, but not with the current leaf water status or with the concentration of ABA in the bulk leaf. The relationship between stomatal conductance and xylem [ABA] was common for variations in xylem [ABA] linked to the decline with time of the soil water reserve, to simultaneous differences between plants grown on compacted, non‐compacted and irrigated soil, and to plant‐to‐plant variability. Therefore, this relationship is unlikely to be fortuitous or due to synchronous variations. These results suggest that increased concentration of ABA in the xylem sap in response to stress can control the gas exchange of plants under field conditions.

Influence of defruiting on the abscisic acid and indole-3-acetic acid contents of cotton leaves

A field experiment was conducted to test the hypothesis that young cotton ( Gossypium hirsutum L.) fruits (bolls) serve as sinks for ABA, or that they are a source of IAA for subtending leaves. Cotton was grown in eight four-row plots in Phoenix during the summer of 1989 and irrigated about every two weeks. In one test, flowers at anthesis were removed on 22 and 29 June and on 7 and 14 July from the first node of fruiting branches of one center row, but not the other row, in each of four replications. Subtending leaves were harvested seven days after deflowering for ABA and IAA analyses. Removal of one flower per plant had no consistent effect on the concentrations of ABA and IAA in the subtending leaf. In another test, all flowers and bolls were removed from all plants of one center row, but not the other row, of four replications on 30 June and 5 and 13 July. Uppermost fully expanded mainstem leaves were harvested from the same plots on 20, 25, and 27 July, and on 9 August (7, 12, 14, and 27 days after final defruiting) for ABA and IAA analyses. Removal of all fruits apparently caused a slight increase in ABA concentration in mainstem leaves, but the effect disappeared with time after defruiting. The ability of leaves to accumulate ABA apparently decreased slightly as boll load increased. Complete fruit removal did not, however, affect the IAA content of leaves.

Photosynthesis and Leaf Water, Carbohydrate, and Hormone Status during Rooting of Stem Cuttings of Acer rubrum

Leaf water status, carbohydrate levels, net photosynthesis, stomatal conductance, ABA, dihydrozeatin riboside (DHZR), and trans-zeatin riboside (ZR) levels were determined in a greenhouse during rooting of stem cuttings of Acer rubrum L. `Red Sunset' taken on 3 Sept. 1987 and 28 May 1988. Leaf water status deteriorated before rooting and improved after root emergence. Leaf carbohydrate concentrations (glucose, sucrose, total soluble sugars, and total carbohydrates) increased until rooting and decreased after rooting, while changes in starch concentrations were trendless. ABA levels increased after insertion of cuttings into the rooting medium, but decreased before rooting. No correlation between timing of rooting and concentrations of the cytokinins ZR or DHZR was observed. Photosynthetic rates during rooting were higher for the Sept. 1987 cuttings and did not decrease to the compensation point as did those for May 1988 cuttings. Low photosynthetic rates and stomatal conductance of the cuttings during rooting were associated with water stress. The relationship between photosynthetic rates of such cuttings and cytokinin (CK) or ABA content was unclear. Chemical names used: [S-(Z,E]-5-(1-hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexen-1-yl)-3-methyl-2, 4-pentadienoic acid (abscisic acid, ABA); 2-methyl-4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin, Z).

The Influence of Leaf Water Status and ABA on Leaf Growth and Stomata of Phaseolus Seedlings with Hypoxic Roots

The Influence of Leaf Water Status and ABA on Leaf Growth and Stomata of Phaseolus Seedlings with Hypoxic Roots

Drought‐stress‐induced polypeptide accumulation in tomato leaves

Abstract. Tomato (Lycopersicon esculentum Mill ev. Ailsa Craig) leaf polypeptides, radiolabelled with L‐[36S] methionine during drought stress, were separated by two‐dimensional polyacrylamide gel electrophoresis. Three sets of polypeptides were distinguished: those that decreased, increased or transiently increased in response to drought stress. Three sets of polypeptides also could be distinguished during recovery from drought stress: those that increased, decreased rapidly or decreased slowly and could still be detected after 6 h of recovery. The set of polypeptides that decreased during drought stress was the same set that increased during recovery and those that increased during stress, decreased during recovery. The leaf ABA concentration increased rapidly in response to drought stress and decreased rapidly during recovery from drought stress, returning to the nonstress level after 6 h of rehydration. There was a correlation between the accumulation of some of the drought‐induced polypeptides and the pattern of ABA accumulation during stress and recovery from stress.

Changes in the concentration of ABA in xylem sap as a function of changing soil water status can account for changes in leaf conductance and growth

Abstract. Maize seedlings (Zea mays L. John Innes F1 hybrid) were grown in a greenhouse in l‐m‐long tubes of soil. When the plants were well established, water was withheld from half of the tubes. Control plants were watered every day during the 20‐d experimental period. The soil drying treatment resulted in a substantial restriction of stomatal conductance and a limitation in shoot growth, even though there was no detectable difference in the water relations of watered and unwatered plants. From day 7 of the soil drying treatment, xylem ABA concentrations (measured using the sap exuded from detopped plants) were substantially increased in unwatered plants compared to values recorded with sap from plants watered every day. Measurements of water potential through the profile of unwatered soil suggest that xylem ABA concentrations reflects the extent of soil drying. Leaf ABA content was a much less sensitive indicator of the effect of soil drying and during the whole of experimental period there was no significant difference between ABA concentration in leaves of well watered and unwatered plants. In a second set of experiments, ABA was fed to part of the roots of potted maize plants to manipulate xylem ABA concentration. These manipulations suggested that the increases in ABA concentration in xylem sap, which resulted from soil drying, were adequate to explain the observed variation in stomatal conductance and might also explain the restriction in leaf growth rate. These results are discussed in the light of recent work which suggests that stomatal responses to soil drying are partly attributable to an as‐yet unidentified inhibitor of stomatal opening.

Sequential response of whole plant water relations to prolonged soil drying and the involvement of xylem sap ABA in the regulation of stomatal behaviour of sunflower plants

SUMMARYSunflower plants (Helianihus animus cv. Tall Single Yellow} were grown in the greenhouse in drain pipes (100 mm inside diameter and 1 m long) rilled with John Innes No. 2 compost. When the fifth leaf had emerged, half of the plants were left unwatered for 6 days, rewatered for 2 days and then not watered for another 12 days. Measurements of water relations and abaxial stomatal conductance were made at each leaf position at regular intervals during the experimental period. Estimates were also made of soil water potentials along the soil profile and of ABA concentrations in xylem sap and leaves.Soil drying led to some reduction in stomatal conductance alter only 3 days but leaf turgors were not reduced until day 13 (6 days after rewatering). When the water relations of leaves did change, older leases became substantially dehydrated while high turgors were recorded in younger leaves. Leaf ABA content measured on the third youngest leaf hardly changed over the first 13 days of the experiment, despite substantial soil drying, while xylem ABA concentrations changed very significantly and dynamically as soil water status varied, even when there was no effect of soil drying on leaf water relations. We argue that the highest ABA concentrations in the xylem, found as a result of substantial soil drying, arise from synthesis in both the roots and the older leaves, and act to delay the development of water deficit in younger leases.In other experiments ABA solutions were watered on to the root systems of sunflower plants to increase ABA concentrations in xylem sap. The stomatal response to applied ABA was quantitatively very similar to that to ABA generated as a result of soil drying. There was a log‐linear relationship between the reduction of leaf conductance and the increase of ABA concentration m xylem sap.

The Use of14C-Ethane Diol as a Quantitative Tracer for the Transpirational Volume Flow of Water and an Investigation of the Effects of Salinity upon Transpiration, Net Sodium Accumulation and Endogenous ABA in Individual Leaves ofOryza sativaL.

Oryza sativa L. (rice) seedlings growing in saline conditions exhibit pronounced gradients in leaf sodium concentration which is always higher in the older leaves than the younger ones. Individual leaf transpiration rates have been investigated to discover whether movement of sodium in the transpiration stream is able to explain these profiles from leaf to leaf. The use of 14C labelled ethane diol to estimate transpiration was evaluated by direct comparison with values obtained by gas exchange measurements. Ethane diol uptake was linearly related to the transpirational volume flow and accurately predicted leaf to leaf gradients in transpiration rate in saline and non-saline conditions. 14C-ethane diol and 22NaCl were used to compare the fluxes of water and sodium into different leaves. The youngest leaf showed the highest transpiration rate but the lowest Na accumulation in saline conditions; conversely, the older leaves showed the lower transpiration rates but the greater accumulation of Na. The apparent concentration of Na in the xylem stream was 44 times lower into the younger leaf 4 than into the older leaf 1. Exposure to NaCl (50 mol m−3) for 24 h elicited an increase in endogenous ABA in the oldest leaf only, but no significant changes occurred in the younger leaves.

Evidence of a Role for Abscisic Acid in Mediating Stomatal Closure Induced by Obstructing Translocation from Leaves of Pearl Millet (Pennisetum americanum[L.] Leeke)

Application of a heat girdle near the base of the lamina of the 5th, fully expanded leaf of 15-day-old plants of P. americanum cv. BJ 104 decreased solute potential, increased leaf DM content and decreased stomatal conductance and the rate of CO2 assimilation. Total water potential was unaffected while turgor potential increased. Leaf ABA content increased 5- to 6-fold within 1 h of girdling, then declined rapidly before increasing again at a slower rate. Girdled leaves were exposed to 14 h of continuous light or continuous darkness followed by a brief light treatment; girdling reduced conductance equally following darkness or light, but solute accumulation occurred only in the light. ABA accumulated in girdled leaves in both darkness and light. There was no increase in intercellular CO2 conc. following girdling. It was concluded that the decreased conductance after girdling was probably mediated by the increase in ABA content

An Association between Flowering and Reduced Stomatal Sensitivity to Water Stress in Pearl Millet [Pennisetum americanum (L.) Leeke

In field studies carried out at ICRISAT, India, in 1980 and 1982, stomatal closure at midday in water stressed plants of two genotypes (BJ104 and line 112) prior to flowering was associated with higher leaf ABA levels than those found in flowering plants. Differences in ABA levels between flowering and preflowering plants were small or absent in Serere 39 and B282, which had lower leaf water potentials when sampled than BJ104 and line 112

Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Effects of Drought Conditioning on Abscisic Acid Accumulation in the Leaf and Stomatal Response

The effects of a period of water stress (drought conditioning) on responses to a second (challenge) stress were examined in young vegetative rice (Oryza sativa L.) plants. Drought conditioning did not affect the rate of subsequent stress development, nor, in a first experiment, did it influence relations between turgor (ψp) and total (ψ) leaf water potential. However, conditioning did extend the range of ψp over which stomata remained open and significantly reduced the amount of ABA which accumulated in the leaf at a given ψp. The change in stomatal behaviour (stomatal adjustment) was quantitatively accounted for by the change in leaf ABA accumulation. The reduction in ABA accumulation due to conditioning did not involve a change in the potential capacity to produce ABA, as ABA accumulation in partially dehydrated detached leaves was not reduced by conditioning. It is suggested that effects of conditioning on leaf ABA content in the intact plant involve changes in the rate of ABA export from the leaf.

Leaf stomatal resistance, ethylene evolution and ABA levels as influenced by (2-chloroethyl) phosphonic acid

The effect on stomatal resistance of ethylene released from ethephon sprays has been studied in 8 species of plants. Ethephon always increased stomatal resistance, but in some species only slightly. In olive and peach, increased stomatal resistance in treated plants was associated with more abscisic acid in the leaf tissues.