Endogenous abscisic acid levels are not linked to methyl jasmonate-promoted senescence of detached rice leaves

Both abscisic acid (ABA) and jasmonates are known to promote leaf senescence. Since ABA and jasmonates have both chemical and physiological similarities, we are interested to know whether senescence of detached rice leaves induced by methyl jasmonate (MJ) is mediated through an increase in endogenous ABA levels. In darkness, the endogenous level of ABA in detached rice leaves remained unchanged in the first day of incubation in water and increased about 5 times its initial value in the second day. However, the pattern of senescence, as judged by protein loss, was rapid during the first day. MJ significantly promoted senescence of detached rice leaves. Contrary to our expectation, endogenous ABA levels decreased in MJ-treated detached rice leaves. Similar to the effect of MJ, endogenous ABA levels decreased in detached rice leaves which were induced to senesce by treatment with NH₄Cl. These results suggest that endogenous ABA levels are not linked to MJ-induced senescence of detached rice leaves.     

Drought, abscisic acid and transpiration rate effects on the regulation of PIP aquaporin gene expression and abundance in Phaseolus vulgaris plants

BACKGROUND AND AIMS: Drought causes a decline of root hydraulic conductance, which aside from embolisms, is governed ultimately by aquaporins. Multiple factors probably regulate aquaporin expression, abundance and activity in leaf and root tissues during drought; among these are the leaf transpiration rate, leaf water status, abscisic acid (ABA) and soil water content. Here a study is made of how these factors could influence the response of aquaporin to drought. METHODS: Three plasma membrane intrinsic proteins (PIPs) or aquaporins were cloned from Phaseolus vulgaris plants and their expression was analysed after 4 d of water deprivation and also 1 d after re-watering. The effects of ABA and of methotrexate (MTX), an inhibitor of stomatal opening, on gene expression and protein abundance were also analysed. Protein abundance was examined using antibodies against PIP1 and PIP2 aquaporins. At the same time, root hydraulic conductance (L), transpiration rate, leaf water status and ABA tissue concentration were measured. KEY RESULTS: None of the treatments (drought, ABA or MTX) changed the leaf water status or tissue ABA concentration. The three treatments caused a decline in the transpiration rate and raised PVPIP2;1 gene expression and PIP1 protein abundance in the leaves. In the roots, only the drought treatment raised the expression of the three PIP genes examined, while at the same time diminishing PIP2 protein abundance and L. On the other hand, ABA raised both root PIP1 protein abundance and L. CONCLUSIONS: The rise of PvPIP2;1 gene expression and PIP1 protein abundance in the leaves of P. vulgaris plants subjected to drought was correlated with a decline in the transpiration rate. At the same time, the increase in the expression of the three PIP genes examined caused by drought and the decline of PIP2 protein abundance in the root tissues were not correlated with any of the parameters measured.     

Influence of salinity and abscisic acid on the O2 uptake by N2-fixing nodules of common bean

The effects of NaCl and ABA on the respiration of N₂-fixing nodules were analysed in common bean (Phaseolus vulgaris) inoculated with Rhizobium tropici the reference strain CIAT899. Shoot and nodule growth was more inhibited by NaCl than root growth. The O₂ uptake by nodulated roots at 21 kPa O₂ was significantly inhibited by salinity. Raising pO₂ stimulated nodule respiration more under NaCl treatment than for the control, although it did not compensate totally for the inhibitory effect of NaCl. Short NaCl application was less destructive than long term application. Also, the external application of ABA inhibited nodule respiration, and this inhibition was partly compensated by raising pO₂.     

Row orientation effects on FR/R light ratio, growth and development of field-grown bush bean

Bush bean ( Phaseolus vulgaris L. cv. Tenderette) plants were grown in north-south (N-S) and east-west (E-W) rows under field conditions to test effects of row orientation on reflected far-red (FR) light patterns and on shoot size and edible bean productivity. Soil water and nutrients were adequate. Plants in N-S rows received slightly higher ratios of FR relative to red (R) light, because of heliotropic movement of the leaves. Plants in N-S rows partitioned more dry matter to shoots and edible green beans than those in E-W rows. We conclude that row orientation of broadleaf plants can affect the FR/R light ratio and the phytochrome-mediated regulation of plant development under field conditions.     

A comparison of methods for inoculating bean plants with Elsinoë phaseoli and some factors affecting infection

Bean (Phaseolus vulgaris) leaves were inoculated with a conidial suspension of Elsinoe phaseoli by spraying, by applying a 10 μl drop, by a cotton wool technique or by using a camel hair brush. Spray application resulted in a uniform distribution of lesions over the leaf surface and gave consistent levels of infection between repetitions. Drop application allowed good control of the amount of inoculum applied. Although brush or cotton wool techniques gave high levels of infection it was not possible to control the amount of inoculum. Only immature tissues were susceptible to infection. Five cultivars were inoculated with two isolates and disease was scored on the basis of numbers of lesions and lesion type (scab severity). The small white cvs PAN 181 and Teebus were the most resistant; lesions were small and generally fewer than on the large-seeded red speckled sugar bean cvs Umlazi and Umvoti. The value of the different inoculation techniques in studies on bean scab is discussed.     

Binding of abscisic acid to human LANCL2

The phytohormone abscisic acid (ABA) is the central regulator of abiotic stress in plants and plays important roles during plant growth and development. In animal cells, ABA was shown to be an endogenous hormone, acting as a stress signal and stimulating cell functions involved in inflammatory responses and in insulin release. Recently, we demonstrated that Lanthionine synthetase component C-like protein 2 (LANCL2) is required for ABA binding to the plasmamembrane of granulocytes and for the activation of the signaling pathway triggered by ABA in human granulocytes and in rat insulinoma cells. In order to investigate whether ABA activates LANCL2 via direct interaction, we performed specific binding studies on human LANCL2 recombinant protein using different experimental approaches (saturation binding, scintillation proximity assays, dot blot experiments and affinity chromatography). Altogether, results indicate that human recombinant LANCL2 binds ABA directly and provide the first demonstration of ABA binding to a mammalian ABA receptor.     

Individual and interactive effects of temperature,carbon dioxide and abscisic acid on mung bean (Vigna radiata) plants

We studied the effects of temperature, carbon dioxide and abscisic acid on mung bean (Vigna radiata). Plants were grown under 26/22°C or 32/28°C (16?h?light/8?h?dark) at 400 or 700?μmol?mol^?1 CO₂ and received ABA application of 0 or 100?μl (10?μg) every other day for three weeks, after eight days of initial growth, in growth chambers. We measured 24 parameters. As individual factors, in 16 cases temperature; in 8 cases CO₂; in 9 cases ABA; and as interactive factors, in 4 cases, each of temperature?×?CO₂, and CO₂?×?ABA; and in 2 cases, temperature?×?ABA were significant. Higher temperatures increased growth, aboveground biomass, growth indices, photochemical quenching (qP) and nitrogen balance index (NBI). Elevated CO₂ increased growth and aboveground biomass. ABA decreased growth, belowground biomass, qP and flavonoids; increased shoot/root mass ratio, chlorophyll and NBI; and had little role in regulating temperature–CO₂ effects.

Abbreviations: A_N: net CO₂ assimilation; E: transpiration; F_v/F_m: maximum quantum yield of PSII; g_s: stomatal conductance; LAR: leaf area ratio; LMA: leaf mass per area; LMR: leaf mass ratio;φPSII: effective quantum yield of PSII; qNP: non-photochemical quenching; qP: photochemical quenching; SRMR: shoot to root mass ratio; WUE: water use efficiency     

Effect of zeatin on the growth and indolyl-3-acetic acid and abscisic acid levels in maize roots

Elongation, indolyl-3-acetic acid (IAA) and abscisic acid (ABA) levels, – gas chromatography-mass spectrometry quantification –, in the elongating zone were analysed for maize ( Zea mays L., Cv. LG11) roots immersed in buffer solution with or without zeatin (Z). The effect of Z depends on the initial extension rate of roots. The slower growing roots are more strongly inhibited by Z (10⁻⁷−10₋₅ M ) and they show a greater increase in IAA and ABA content. When compared to the rapidly growing roots, the larger reactivity of the 'slow'ones cannot be attributed to a higher Z uptake as shown when using [¹⁴C]-Z. It is suggested that Z could regulate root elongation by acting on the IAA and/or ABA level. The comparative action of these two hormones is discussed.     

Endogenous levels of free and conjugated forms of auxin, cytokinins and abscisic acid during seed development in Douglas fir

Endogenous levels of free and conjugated forms of three classes of planthormones were quantified at various stages of megagametophyte development inDouglas fir. Megagametophytes were excised weekly from 8–16 weeks pastpollination (WPP), a period encompassing the central cell to the earlymaturation stage of seed development. The hormones indole-3 acetic acid (IAA),indole-3-aspartate (IAAsp), zeatin (Z), zeatin riboside (ZR), isopentenyladenine(iP), isopentenyladenosine (iPA), abscisic acid (ABA) and abscisic acid glucoseester (ABA-GE) were extracted, purified, fractionated by high- performanceliquid chromatography (HPLC), and then quantified using an enzyme-linkedimmunosorbent assay (ELISA) method. Z levels ranged from 0–25ng/g dry weight (DW) and were highest in megagametophytes at thecentral cell stage (8 WPP). During embryogenesis, Z levels peakedduring week 13. In contrast, the ZR conjugate was not detected over the periodstudied. The iP content of megagametophytes increased at 10 and 13WPP, while the iPA concentration increased at 13 WPP.Prior to fertilisation, IAA was highest in megagametophytes at 9WPP. During embryogenesis, the major IAA accumulations occurred at11, 13 and 15 WPP, the concentration ranging from 0–0.43g/g DW. IAAsp concentrations reached their highest level duringembryogenesis at 14 WPP. ABA content increased at 11 and 13WPP, with a concentration range of 0.1–13 g/gDW. In contrast, ABA-GE levels were relatively constant over the 9-weekperiod analyzed. The endogenous levels of plant hormones varied withmegagametophyte development and were associated with morphological changes.     

Effect of morphactin on certain plant growth substances in bean roots

The effect of morphactin (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate) on the content of several plant growth substances in bean roots was determined. Beans (Phaseolus vulgaris L. cv. Spartan) were soaked in aqueous solutions of morphactin, 1 x 10^-4, 1 x 10^-5, and 1 x 10^-6M and grown in moist vermiculite. As controls were used beans grown in water-moistened vermiculite either intact or having the root tips removed (decapped). The roots, morphactin-treated, controls, and the decapped ones were analyzed for indol-3-yl acetic acid (IAA), indol-3-yl acrylic acid (IAcA), indol-3-yl pyruvic acid (IPyA), indol-3-yl lactic acid (1LA), abscisic acid (ABA), gibberellins GA₁, GA₃, GA₄, and GA₉ using gas-liquid chromatographic methods. Morphactin, while affecting the geotropical responses, changed also the growth substance content of roots. IAA, ABA, GA₁, and GA₉ contents decreased, IPyA, IAeA, GA₃, and GA₄ contents were not affected and ILA content increased slightly with increasing dosages of morphactin. Growth substance pattern of decapped roots resembled that of the roots treated with the highest dose, 1 x 10^-4M, of morphactin.     

ADP-ribosyl cyclase and abscisic acid are involved in the seasonal growth and in post-traumatic tissue regeneration of Mediterranean sponges

In previous papers it has been demonstrated that the plant hormone abscisic acid (ABA) is responsible for the stimulation of water filtration and oxygen consumption elicited by a temperature increase in the Mediterranean demosponge Axinella polypoides. The signal transduction pathway triggered by ABA involves activation of ADP-ribosyl cyclase (ADPRC), leading to an increase of the intracellular concentration of cyclic ADP-ribose (cADPR), a universal and potent intracellular calcium mobilizer. These data prompted us to investigate the possible involvement of the ABA/ADPRC/cADPR system in the sponge life cycle and in post-traumatic tissue regeneration of Mediterranean sponges. ADPRC activity was detected in the cell lysate from several common Mediterranean sponge species, including Calcarea and Demospongiae. Specimens were collected monthly over a 2-year period, from January 2002 to April 2004. All species studied showed a peak of ADPRC activity during July and August 2003, concomitant with an anomalous heat wave that struck the whole Mediterranean basin during these months. In the aquarium, during spontaneous tissue regeneration, an increase of the [ABA]_i and of the ADPRC activity over time zero values was consistently observed. In conclusion, these results indicate that an increase of ABA content and of ADPRC activity correlates with the growth and with post-traumatic tissue regeneration in several Mediterranean sponge species, indicating that the ABA/ADPRC/cADPR system is involved in the response to environmental stress in sponges. Determination of ADPRC activity/ABA content may provide a means to assess metabolic activation of sponge populations under conditions of environmental stress.     

Sensitivity of Commelina stomata to abscisic acid

Stomata of Commelina leaves pre-opened by incubation in moist air were found to close within 30 min when supplied with abscisic acid (ABA) via the transpiration stream. Radioactive ABA had similar effects, but allowed the distribution of the compound within the leaf to be measured and correlated with stomatal movements to give estimates of the sensitivity of Commelina stomata. On a whole-leaf basis, less than 163 fmol ABA per mm² leaf area were present at the time of complete stomatal closure. This was close to other published estimates. By taking epidermal ¹⁴C measurements, however, it was possible to increase the accuracy of the estimate on the assumption that only ABA present in the epidermis was physiologically active. Thus, less than 235 amol ABA for stomatal complex were present at complete closure, and statistically significant narrowing of the stomatal aperture had occurred when between 12.6 and 45.4 amol per complex were present. The distribution of ABA within the epidermal tissue after transpiration-stream application was studied using microautoradiography, and the compound appeared to have accumulated within the stomatal complex.Abbreviations ABA abscisic acid - TLC thin-layer chromatography     

Possible effects of pathogen inoculation and salicylic acid pre-treatment on the biochemical changes and proline accumulation in green bean

The effects of pre-treatment of salicylic acid (SA) and pathogen inoculation, Rhizoctonia solani on proline accumulation, and enzymes activities were investigated in green bean leaves and roots. The plants were grown in greenhouse conditions, and were soil drenched with SA treatments, with and without pathogen inoculation. It was observed that the highest level of free proline accumulation in leaves was in Rhizoctonia?+?400?μM SA treatment, followed by Rhizoctonia?+?200?μM SA treatment. When comparing free proline content in leaves and roots, treated with SA and Rhizoctonia?+?SA, to their controls, the accumulation levels in Rhizoctonia?+?400?μM SA treatments were significantly higher than controls. When the enzyme activities with Rhizoctonia?+?SA treatment were compared to their solely applied SA treatments, the levels of β-1,4-glucanase and chitinase activities were lower than SA treatments alone. However, the free proline accumulation in leaves was higher in Rhizoctonia?+?400?μM SA treatment than in sole SA treatments.     

Meristem aging is not responsible for age-related changes in growth and abscisic acid levels in the Mediterranean shrub, Cistus clusii

To obtain new insights into the mechanisms underlying aging in perennials, we measured abscisic acid levels, growth and other stress indicators in leaves of Cistus clusii Dunal plants of different ages grown under Mediterranean field conditions. Recently emerged leaves from 9-year-old plants were compared to those of 1-year-old plants (obtained from cuttings from 9-year-old plants) to evaluate the effects of meristem aging on plant aging. Rooting and successful establishment of the cuttings allowed us to compare the physiology of plants with old meristems, but of different size. Plants obtained from cuttings were rejuvenated, with new leaves displaying a higher leaf area and chlorophyll content, but smaller leaf mass per unit area ratios and endogenous abscisic acid levels than those of 9-year-old plants. A comparative study in 1-, 4- and 9-year-old plants revealed that abscisic acid levels increase during the early stages of plant life (with increases of 90% between 1- and 4-year-old plants), but then remain constant at advanced developmental stages (between 4- and 9-year-old plants). Although leaf biomass was 53% smaller in 9-year-old compared to 4-year-old plants, the dry matter produced per shoot apical meristem was equivalent in both plant groups due to an increased number of leaves per shoot in the former. It is concluded that (i) C. clusii plants maintain the capacity to rejuvenate for several years; (ii) newly emerged leaves accumulate higher amounts of abscisic acid during early stages of plant life, but the levels of this phytohormone later remain constant; and (iii) although plant aging leads to the production of smaller leaves, the amount of biomass produced per shoot apical meristem remains constant at advanced developmental stages.     

Stem pithiness in tomato plants: The effect of water stress and the role of abscisic acid

The pith parenchyma in tomato ( Lycopersicum esculentum ) stems was found to be disrupted in response to water stress (stem pithiness). The process of the degradation starts at the upper part of the stem and proceeds downwards as the stress is prolonged. The damage to the stem tissue was found to be irreversible upon rehydration of the stressed plants. Scanning electron microscopy revealed that the protoplast of the affected cells is disrupted first, followed by degradation of the cell wall.
Application of abscisic acid (ABA) induced pithiness in non-stressed plants and also enhanced the effect of a short period of dehydration. Kinetin, although causing severe wilting, did not induce pithiness. However, when given after a short period of water stress or within the period of stress, kinetin enhanced pithiness development.
In the course of the stress, ABA levels in the upper part of the stem and in the young leaves were higher than the levels found in the lower parts of the plant shoot. The increase in ABA levels was detected before any sign of pithiness.
It is suggested that ABA might be the triggering agent of the cellular degradation process initiated by water stress.     

Cryopreservation of in vitro sugar beet shoot tips using the encapsulation-dehydration technique: influence of abscisic acid and cold acclimation

It has been previously shown that shoot tips of in vitro plantlets of sugar beet (Beta vulgaris L. clone SES1) can be cryopreserved using the encapsulation-dehydration technique (survival rate of 37% after freezing). This article reports the influence of abscisic acid (ABA) and cold acclimation on survival after cryopreservation. When ABA was added to the multiplication medium of the plants, the survival rate of shoot tips after cryopreservation was not increased (45%). After cold acclimation of the plants, their growth pattern differed (plants became apically dominant) and the survival rate of the shoot tips after cryopreservation clearly increased (70% survival and 50% plant regeneration after freezing). This improved protocol was successfully applied to three other clones. Received: 28 October 1996 / Revision received: 28 January 1997 / Accepted: 15 March 1997     

The effect of drought on levels of abscisic acid,cytokinins, gibberellins and ethylene in aeroponically-grown sunflower plants

Abscisic acid (ABA), cytokinins and gibberellin-like substances (GAs) were extracted from the roots and shoots of 17-day-old sunflower seedlings which had been droughted or were unstressed. Plants were grown in an aeroponic chamber which allowed for good control over degree of water stress and easy access to roots. Following methanolic extraction of lyophilized material, cytokinins were separated from the acidic growth-regulators on a cellulose PO₄ cationic exchange column. The cytokinins were analysed by paper chromatography and HPLC and the soybean hypocotyl section assay. Semipurified acidic regulators were chromatographed on SiO₂ columns and HPLC and aliquots assayed with the dwarf rice cv. Tan-ginbozu bioassay for GAs. Fractions known to contain ABA were purified by sequential reverse-phase HPLC of the acid and then of the methyl ester forms followed by quantitation as Me-ABA on GLC-EC. ABA losses were measured by using an internal standard [³H]-ABA). Ethylene production was also monitored in stressed and unstressed seedlings.The effect of drought on GAs and ethylene was minimal. The ABA levels were markedly higher in droughted plants. Stressed roots had 32 times more ABA than controls. The levels of cytokinins in the shoots of droughted plants were about half those in unstressed shoots, and qualitative differences occurred in the roots. Under stress a large peak of activity was present similar to zeatin glucoside which was not present in the unstressed condition. The results are discussed in relation to drought-effects on metabolism.     

Interaction with ethylene: changing views on the role of abscisic acid in root and shoot growth responses to water stress

Shoot and root growth are differentially sensitive to water stress. Interest in the involvement of hormones in regulating these responses has focused on abscisic acid (ABA) because it accumulates in shoot and root tissues under water-limited conditions, and because it usually inhibits growth when applied to well-watered plants. However, the effects of ABA can differ in stressed and non-stressed plants, and it is therefore advantageous to manipulate endogenous ABA levels under water-stressed conditions. Studies utilizing ABA-deficient mutants and inhibitors of ABA synthesis to decrease endogenous ABA levels, and experimental strategies to circumvent variation in plant water status with ABA deficiency, are changing the view of the role of ABA from the traditional idea that the hormone is generally involved in growth inhibition. In particular, studies of several species indicate that an important role of endogenous ABA is to limit ethylene production, and that as a result of this interaction ABA may often function to maintain rather than inhibit shoot and root growth. Despite early speculation that interaction between these hormones may influence many of the effects of water deficit, this topic has received little attention until recently.     

Influence of spectral quality on the growth response of intact bean plants to brassinosteroid, a growth-promoting steroidal lactone. II. Chlorophyll content and partitioning of assimilate

The chlorophyll content and partitioning of assimilate of bean ( Phaseolus vulgaris L. 'Pinto') plants were determined 6 days after treatment of the second internode (I₂ with 5 μg of brassinosteroid (BR), a growth-promoting steroidal lactone. Plants were grown for 6 days under equal levels (90 μmol s^-1 m^-2) of photosynthetic photon flux density (PPFD) provided by cool white fluorescent (CWF) or incandescent (INC) lamps and equal levels of far-red (28 W m^-2, 700–800 nm) radiation provided by the same INC or far-red (FR) fluorescent lamps. Brassinosteroid treatment had no appreciable effect on total biomass production but caused a decrease of 15–20% dry matter distribution in the upper portion of the shoot, a small (4%) but constant increase in dry matter in l₂ and a large (11–16%) increase in dry matter in the lower portion of the shoot (especially I₁). Treatment with BR increased assimilate accumulation in the primary leaves, especially under INC and FR lamps, and reduced dry matter in the trifoliate leaves. BR also caused a 16–21% reduction in total leaf area and even a greater reduction in area of the trifoliate leaves, but significantly increased specific leaf weight of the primary leaves and the first trifoliate leaf and the amount of dry matter in the lateral shoots under all radiation sources. In comparison to controls, BR treatment increased dry matter accumulation in the treated internode 3.3x under CWF and 1.6x under INC or FR. BR treatment also increased chlorophyll content in the primary leaves under all radiation sources and in the trifoliate leaves under CWF and INC lamps. These findings suggest a possible mobilization role of BR and establish the importance of adequate PPFD (and photosynthate) for maximum swelling and splitting response to brassinosteroid.     

Contrasting photo- and thermoperiod-induced changes in abscisic acid and lipid contents in leaves of mungbean seedlings

Seedlings of Phaseolus aureus ROXB were grown under 12/12 h light/dark cycles with the light period at 32.5°C and darkness at 10°C (normal conditions N) or with light at 10°C and darkness at 32.5°C (inverse conditions, I). I-conditions affected the level of chlorophyll and carotenoids (very low), monogalactosyldiacylgycerol (low) and phosphatidylinositol (high) in the leaves. Leaves of I-seedlings showed a sharp and durable decline of relative water content during the low temperature phase. For the N-seedlings, loss of water was restricted to the end of this period. The loss of water was accompanied by visible symptoms of wilting at specific times of day. Although the pigment content remained nearly unchanged, ABA content of leaves of both N-and I-seedlings increased during water stress. Upon return to the warm period, ABA level continued to increase after the leaves had regained turgor, this 'after stress'increase being more pronounced in the leaves of I-seedlings. Exogenous application of ABA induced a slight increase in the content of phospholipids in N- and I-leaves and a decrease in free fatty acids, whereas monogalactosyldiacylglycerol content was significantly reduced in N-leaves after application of ABA. Upon transfer of I-plants to 20°C for 12 h during the light period, pigment and chloroplastic lipid content increased rapidly whereas upon a further exposure to 10°C in light, pigments and especially monogalactosyldiacylglycerol were lost. The control of pigment and lipid metabolism and the role of ABA during chilling stress are discussed.