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Activation of hormonal responses defines the drought acclimation ability of plants and may condition their survival. However, aside ABA, little is known about the possible contribution of other phytohormones, such as jasmonates and salicylates, in the response of CAM plants to water deficit. Here, we aimed to study the physiological mechanisms underlying the stress tolerance of house leek (Sempervivum tectorum L.), a CAM plant adapted to survive harsh environments, to a combination of water deficit and nutrient deprivation. We exposed plants to the combination of these two abiotic stresses by withholding nutrient solution for 10 weeks and monitored their physiological response every two weeks by measuring various stress makers together with the accumulation of stress-related phytohormones and photoprotective molecules, such as tocopherols (vitamin E). Results showed that ABA content increased by 4.2-fold after four weeks of water deficit to keep later constant up to 10 weeks of stress, variations that occurred concomitantly with reductions in the relative leaf water content, which decreased by up to 20% only. The bioactive jasmonate, jasmonoyl-isoleucine was the other stress-related phytohormone that simultaneously increased under stress together with ABA. While contents of salicylic acid and the jasmonoyl-isoleucine precursors, 12-oxo-phytodienoic acid and jasmonic acid decreased with water deficit, those of jasmonoyl-isoleucine increased 3.6-fold at four weeks of stress. The contents of ABA and jasmonoyl-isoleucine correlated positively between them and with the content of α-tocopherol per unit of chlorophyll, thus suggesting a photoprotective activation role. It is concluded that S. tectorum not only withstands a combination of water deficit and nutrient deprivation for 10 weeks without any symptom of damage but also activates effective defense strategies through the simultaneous accumulation of ABA and the bioactive jasmonate form, jasmonoyl-isoleucine., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier GmbH.. All rights reserved.)

A complex network of cellular receptors, RNA targeting pathways, and small-molecule signaling provides robust plant immunity and tolerance to viruses. To maximize their fitness, viruses must evolve control mechanisms to balance host immune evasion and plant-damaging effects. The genus Potyvirus comprises plant viruses characterized by RNA genomes that encode large polyproteins led by the P1 protease. A P1 autoinhibitory domain controls polyprotein processing, the release of a downstream functional RNA-silencing suppressor, and viral replication. Here, we show that P1Pro, a plum pox virus clone that lacks the P1 autoinhibitory domain, triggers complex reprogramming of the host transcriptome and high levels of abscisic acid (ABA) accumulation. A meta-analysis highlighted ABA connections with host pathways known to control RNA stability, turnover, maturation, and translation. Transcriptomic changes triggered by P1Pro infection or ABA showed similarities in host RNA abundance and diversity. Genetic and hormone treatment assays showed that ABA promotes plant resistance to potyviral infection. Finally, quantitative mathematical modeling of viral replication in the presence of defense pathways supported self-control of polyprotein processing kinetics as a viral mechanism that attenuates the magnitude of the host antiviral response. Overall, our findings indicate that ABA is an active player in plant antiviral immunity, which is nonetheless evaded by a self-controlled RNA virus.

Postharvest senescence and associated stresses limit the shelf life and nutritional value of vegetables. Improved understanding of these processes creates options for better management. After harvest, controlled exposure to abiotic stresses and/or exogenous phytohormones can enhance nutraceutical, organoleptic and commercial longevity traits. With leaf senescence, abscisic acid (ABA) contents progressively rise, but the actual biological functions of this hormone through senescence still need to be clarified. Postharvest senescence of detached green cabbage leaves (Brassica oleracea var. capitata) was characterized under cold (4 °C) and room temperature (25 °C) storage conditions. Hormonal profiling of regions of the leaf blade (apical, medial, basal) revealed a decrease in cytokinins contents during the first days under both conditions, while ABA only increased at 25 °C. Treatments with ABA and a partial agonist of ABA (pyrabactin) for 8 days did not lead to significant effects on water and pigment contents, but increased cell integrity and altered 1-aminocyclopropane-1-carboxylic acid (ACC) and cytokinins contents. Transcriptome analysis showed transcriptional regulation of ABA, cytokinin and ethylene metabolism and signalling; proteasome components; senescence regulation; protection of chloroplast functionality and cell homeostasis; and suppression of defence responses (including glucosinolates and phenylpropanoids metabolism). It is concluded that increasing the concentration of ABA (or its partial agonist pyrabactin) from the start of postharvest suppresses senescence of stored leaves, changes the transcriptional regulation of glucosinolates metabolism and down-regulates biotic stress defence mechanisms. These results suggest a potential for manipulating ABA signalling for improving postharvest quality of leafy vegetables stored at ambient temperature., (© 2017 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

Boron (B) is an essential microelement for vascular plant development, but its toxicity is a major problem affecting crop yields in arid and semi-arid areas of the world. In the literature, several genes involved in abscisic acid (ABA) signalling and responses are upregulated in Arabidopsis roots after treatment with excess B. It is known that the AtNCED3 gene, which encodes a crucial enzyme for ABA biosynthesis, plays a key role in the plant response to drought stress. In this study, root AtNCED3 expression and shoot ABA content were rapidly increased in wild-type plants upon B-toxicity treatment. The Arabidopsis ABA-deficient nced3-2 mutant had higher transpiration rate, stomatal conductance and accumulated more B in their shoots than wild-type plants, facts that were associated with the lower levels of ABA in this mutant. However, in wild-type plants, B toxicity caused a significant reduction in stomatal conductance, resulting in a decreased transpiration rate. This response could be a mechanism to limit the transport of excess B from the roots to the leaves under B toxicity. In agreement with the higher transpiration rate of the nced3-2 mutant, this genotype showed an increased leaf B concentration and damage upon exposure to 5 mM B. Under B toxicity, ABA application decreased B accumulation in wild-type and nced3-2 plants. In summary, this work shows that excess B applied to the roots leads to rapid changes in AtNCED3 expression and gas exchange parameters that would contribute to restrain the B entry into the leaves, this effect being mediated by ABA., (© 2016 Scandinavian Plant Physiology Society.)

The relationship between the phytohormones, gibberellin (GA) and abscisic acid (ABA) and light and temperature on seed germination is still not well understood. We aimed to investigate the role of the ABA and GA on seed germination of Vellozia caruncularis, V. intermedia and V. alutacea in response to light/dark conditions on different temperature. Seeds were incubated in GA (GA 3 or GA 4 ) or ABA and their respective biosynthesis inhibitors (paclobutrazol - PAC, and fluridone - FLU) solutions at two contrasting temperatures (25 and 40 °C). Furthermore, endogenous concentrations of active GAs and those of ABA were measured in seeds of V. intermedia and V. alutacea during imbibition/germination. Exogenous ABA inhibited the germination of Vellozia species under all conditions tested. GA, FLU and FLU + GA 3 stimulated germination in the dark at 25 °C (GA 4 being more effective than GA 3 ). PAC reduced seed germination in V. caruncularis and V. alutacea, but did not affect germination of V. intermedia at 40 °C either under light or dark conditions. During imbibition in the dark, levels of active GAs decreased in the seeds of V. intermedia, but were not altered in those of V. alutacea. Incubation at 40 °C decreased ABA levels during imbibition in both V. caruncularis and V. alutacea. We conclude that the seeds of Vellozia species studied here require light or high temperature to germinate and ABA has a major role in the regulation of Vellozia seed germination in response to light and temperature., (© 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Abscisic acid (ABA) is a plant growth regulator with roles in senescence, fruit ripening and environmental stress responses. ABA and pyrabactin (a non-photosensitive ABA agonist) effects on red raspberry (Rubus idaeus L.) fruit development (including ripening) were studied, with a focus on vitamin and antioxidant composition. Application of ABA and/or pyrabactin just after fruit set did not affect the temporal pattern of fruit development and ripening; neither provitamin A (carotenoids) nor vitamin E contents were modified. In contrast, ABA and pyrabactin altered the vitamin C redox state at early stages of fruit development and more than doubled vitamin C contents at the end of fruit ripening. These were partially explained by changes in ascorbate oxidation and recycling. Therefore, ABA and pyrabactin applications may be used to increase vitamin C content of ripe fruits, increasing fruit quality and value. However, treatments containing pyrabactin-combined with ABA or alone-diminished protein content, thus partially limiting its potential applicability., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The hormonal mechanisms involved in palm seed germination are not fully understood. To better understand how germination is regulated in Arecaceae, we used macaw palm (Acrocomia aculeata (Jacq.) Lodd. Ex Mart.) seed as a model. Endogenous hormone concentrations, tocopherol and tocotrienol and lipid peroxidation during germination were studied separately in the embryo and endosperm. Evaluations were performed in dry (D), imbibed (I), germinated (G) and non-germinated (NG) seeds treated (+GA3 ) or not treated (control) with gibberellins (GA). With GA3 treatment, seeds germinated faster and to a higher percentage than control seeds. The +GA3 treatment increased total bioactive GA in the embryo during germination relative to the control. Abscisic acid (ABA) concentrations decreased gradually from D to G in both tissues. Embryos of G seeds had a lower ABA content than NG seeds in both treatments. The GA/ABA ratio in the embryo was significantly higher in G than NG seeds. The +GA3 treatment did not significantly affect the GA/ABA ratio in either treatment. Cytokinin content increased from dry to germinated seeds. Jasmonic acid (JA) increased and 1-aminocyclopropane-1-carboylic acid (ACC) decreased after imbibition. In addition, α-tocopherol and α-tocotrienol decreased, while lipid peroxidation increased in the embryo during germination. We conclude that germination in macaw palm seed involves reductions in ABA content and, consequently, increased GA/ABA in the embryo. Furthermore, the imbibition process generates oxidative stress (as observed by changes in vitamin E and MDA)., (© 2015 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Much effort has been focussed on better understanding the key signals that modulate floral senescence. Although ethylene is one of the most important regulators of floral senescence in several species, Lilium flowers show low sensitivity to ethylene; thus their senescence may be regulated by other hormones. In this study we have examined how (1) endogenous levels of hormones in various floral tissues (outer and inner tepals, androecium and gynoecium) vary throughout flower development, (2) endogenous levels of hormones in such tissues change in cut versus intact flowers at anthesis, and (3) spray applications of abscisic acid and pyrabactin alter flower longevity. Results show that floral tissues behave differently in their hormonal changes during flower development. Cytokinin and auxin levels mostly increased in tepals prior to anthesis and decreased later during senescence. In contrast, levels of abscisic acid increased during senescence, but only in outer tepals and the gynoecium, and during the latest stages. In addition, cut flowers at anthesis differed from intact flowers in the levels of abscisic acid and auxins in outer tepals, salicylic acid in inner tepals, cytokinins, gibberellins and jasmonic acid in the androecium, and abscisic acid and salicylic acid in the gynoecium, thus showing a clear differential response between floral tissues. Furthermore, spray applications of abscisic acid and pyrabactin in combination accelerated the latest stages of tepal senescence, yet only when flower senescence was delayed with Promalin. It is concluded that (1) floral tissues differentially respond in their endogenous variations of hormones during flower development, (2) cut flowers have drastic changes in the hormonal balance not only of outer and inner tepals but also of androecium and gynoecium, and (3) abscisic acid may accelerate the progression of tepal senescence in Lilium.

It is still an unsolved question of fundamental biology if, and how, perennial plants senesce. Here, age- and sex-related changes in phytohormones were tested in Borderea pyrenaica, a small dioecious geophyte relict of the Tertiary with one of the longest lifespan ever recorded for any non-clonal herb (more than 300 years). Biomass allocation, together with levels of cytokinins, auxins and absicisic acid, and other indicators of leaf physiology (chlorophylls, lipid peroxidation and F (v)/F (m) ratio) were measured in juvenile and mature plants, including both males and females of three age classes (up to 50 years, 50-100 years, and over 100 years). Plants maintained intact capacity of their vegetative growth and reproductive potential. Cytokinin levels decreased with age, but only in females. Such sex-related differences, however, were not associated with symptoms of physiological deterioration in leaves, but with an increased reproductive effort in females. It is concluded that B. pyrenaica does not show clear signs of senescence at the organism level. Altered cytokinin levels in females were associated with their reproductive effort, rather than to a degenerative process. The alternate use of five meristematic points in the tuber could explain the extraordinary longevity of this species.

To better understand aging in perennials, age-related changes in the physiology of leaves and flower buds of the Mediterranean shrub, Cistus albidus L. were evaluated. Two groups of different ages (5 and 10 years old), both at advanced developmental stages but of similar size, were compared. Total plant biomass, biomass produced per apical meristem and levels of cytokinins, abscisic acid and jasmonic acid in leaves and flower buds, as well as flower production, were measured. No differences in plant size, vegetative growth rates and levels of phytohormones in leaves were observed between 5- and 10-year-old plants. However, they showed significant differences in flower bud development; the older plants having reduced vigour, with 29.6% of flowers reaching anthesis compared to 52.5% in the younger plants. Furthermore, endogenous concentrations of zeatin and abscisic acid in flower buds at stage I (start of flower organ formation) were 61% and 41%, respectively, smaller in 10- than in 5-year-old plants. At stage II (with all flower organs formed), zeatin and abscisic acid concentrations decreased by ca. 90% and 80%, respectively, but differences between age groups were still evident (60% and 29% for zeatin and abscisic acid, respectively). Jasmonic acid levels in flower buds decreased by 80% from stage I to II, but did not differ between age groups. Despite reductions in flower bud vigour, total number of flowers per individual was not significantly different between age groups, so that an age-related loss in reproductive vigour at the organ level did not lead to a decrease in flower production at the whole plant level.

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.

Compared with our knowledge of senescence in annuals and biennials, little is known about age-related changes in perennials. To get new insights into the mechanisms underlying aging in perennials, we measured oxidative stress markers in leaves and organelles, together with abscisic acid levels in leaves of 2- and 7-year-old Cistus clusii dunal plants grown under Mediterranean field conditions. Recently emerged leaves, which either appeared during autumn or spring, were compared to evaluate the effects of environmental constraints on oxidative stress and abscisic acid accumulation as plants aged. Plant aging led to an enhanced oxidation of ot-tocopherol and ascorbate, increased lipid peroxidation and reduced PSII efficiency in leaves during the more stressful conditions of spring and summer, but not during autumn. Analyses of lipid peroxidation in organelles isolated from the same leaves revealed that oxidative stress occurred both in chloroplasts and mitochondria. Although both plant groups showed similar leaf water and nitrogen contents throughout the study, abscisic acid levels were markedly higher (up to 75%) in 7-year-old plants compared to 2-year-old plants throughout the study. It is concluded that (a) meristematic tissues of C. clusii maintain the capacity to make new leaves with no symptoms of oxidative stress for several years, unless these leaves are exposed to environmental constraints, (b) leaves of oldest plants show higher oxidative stress than those of young plants when exposed to adverse climatic conditions, thus supporting the idea that the oxidative stress associated with aging is due at least partly to extrinsic factors, (c) at the subcellular level, age-induced oxidative stress occurs both in chloroplasts and mitochondria, and (d) even in the absence of environmental stress, newly emerged leaves accumulate higher amounts of ABA as plants age.

Melatonin ( N-acetyl-5methoxytryptamine) is an amphiphilic low-molecular-weight compound found in evolutionary distant living organisms, from bacteria to mammals. It can be synthesized by plants and acts as a potent antioxidant and/or a regulator of plant growth and development. Here, we investigated the role of melatonin in plant response to drought stress and recovery in maize ( Zea mays L.) plants, with an emphasis on its possible photoprotective and antioxidant role and/or signalling function in relation to the stress-related phytohormones, abscisic acid, salicylic acid and jasmonic acid. Results show a positive correlation between endogenous contents of melatonin and photoprotection, as indicated by the maximum efficiency of photosystem II photochemistry ( F v/ F m ratio), which was confirmed further by exogenous application of melatonin during recovery from drought stress. Melatonin applications during drought recovery improved the F v/ F m ratio in maize plants exposed to a subsequent drought stress. Furthermore, endogenous contents of melatonin positively correlated with those of stress-related phytohormones, particularly with those of salicylic acid, although exogenous application of melatonin did not alter the contents of these defence compounds. It is concluded that melatonin can exert a defensive role in maize plants exposed to drought stress, particularly improving the efficiency of photosystem II photochemistry. [ABSTRACT FROM AUTHOR]

Abstract Background Plant hormones play a pivotal role in several physiological processes during a plant's life cycle, from germination to senescence, and the determination of endogenous concentrations of hormones is essential to elucidate the role of a particular hormone in any physiological process. Availability of a sensitive and rapid method to quantify multiple classes of hormones simultaneously will greatly facilitate the investigation of signaling networks in controlling specific developmental pathways and physiological responses. Due to the presence of hormones at very low concentrations in plant tissues (10-9 M to 10-6 M) and their different chemistries, the development of a high-throughput and comprehensive method for the determination of hormones is challenging. Results The present work reports a rapid, specific and sensitive method using ultrahigh-performance liquid chromatography coupled to electrospray ionization tandem spectrometry (UPLC/ESI-MS/MS) to analyze quantitatively the major hormones found in plant tissues within six minutes, including auxins, cytokinins, gibberellins, abscisic acid, 1-amino-cyclopropane-1-carboxyic acid (the ethylene precursor), jasmonic acid and salicylic acid. Sample preparation, extraction procedures and UPLC-MS/MS conditions were optimized for the determination of all plant hormones and are summarized in a schematic extraction diagram for the analysis of small amounts of plant material without time-consuming additional steps such as purification, sample drying or re-suspension. Conclusions This new method is applicable to the analysis of dynamic changes in endogenous concentrations of hormones to study plant developmental processes or plant responses to biotic and abiotic stresses in complex tissues. An example is shown in which a hormone profiling is obtained from leaves of plants exposed to salt stress in the aromatic plant, Rosmarinus officinalis.