Abscisic Acids Research Articles

Expression of an A20/AN1 Stress-Associated Protein from Aeluropus littoralis in Rice Deregulates Stress-Related Genes

The AlSAP gene, which has been isolated from the C4 halophyte grass Aeluropus littoralis, a member of the stress-associated protein gene family. Like other members of this family, AlSAP contains A20 and AN1 zinc-finger domains, and its transcription is induced by abiotic stresses such as salinity, drought, and temperature as well as by several hormones, including abscisic and salicylic acids. Additionally, AlSAP overexpression in rice has been demonstrated to enhance cold and drought stress tolerance. In the present study, we investigated the transcriptional deregulation of stress-related genes following ectopic expression of the AlSAP gene in two transgenic rice lines, namely, RN4 and RN5. Compared with control plants, a total of 1734 and 3650 annotated genes were found to be differentially expressed in the leaves and roots of the RN4 and RN5 lines, respectively. AlSAP transcript accumulation primed the expression of abiotic-stress-related genes involved in transcription, signaling, protein degradation, and hormonal homeostasis in rice plants grown under unstressed conditions. We hypothesized that this priming underlies the enhanced tolerance to abiotic stresses previously reported in AlSAP rice lines. Notably, AlSAP also induces transcript accumulation of genes known to be major negative regulators of pathogen response in rice. Consistently, our results showed that abiotic stress-tolerant AlSAP rice lines also exhibit enhanced susceptibility to rice blast fungus Magnaporthe oryzae.

Differential defense responses of tropical grasses to Mahanarva spectabilis (Hemiptera: Cercopidae) infestation.

The spittlebugs Mahanarva spectabilis economically challenges cattle production of neotropical regions, due to its voracious feeding on tropical grasses. Here, we evaluated biochemical responses of the interaction between M. spectabilis and the widely cultivated tropical grasses Brachiaria spp. (i.e., brizantha and decumbens) and elephant grasses (cvs. Roxo de Botucatu and Pioneiro), regarding lipoxygenases, protease inhibitors, phytohormones, and proteolytic activities in the midgut of M. spectabilis. The M. spectabilis-infested grasses increased lipoxygenases activity, except for cv. Pioneiro. The levels of the phytohormones jasmonic and abscisic acids were similarly low in all genotypes and increased under herbivory. Furthermore, salicylic acid concentration was constitutively higher in Brachiaria sp., increasing only in spittlebug-infested B. decumbens. M. spectabilis infestations did not induce increases of protease inhibitors in any forage grass type. The trypsin activity remained unaltered, and the total proteolytic activity increased only in B. decumbens-fed insects. Our findings revealed that most forage grasses exposed to spittlebugs activate the lipoxygenases pathway, resulting in increased abscisic and jasmonic acids. However, greater amounts of these hormones do not induce protease inhibitory activity in response to spittlebug attack. This knowledge certainly helps to guide future projects aiming at reducing the impact of spittlebugs on forage production.

Chromatin-Level Differences Elucidate Potential Determinants of Contrasting Levels of Cold Sensitivity in Maize Lines

Maize is a subtropical, cold-sensitive species. However, some varieties of this species have the potential to withstand long-term low temperatures, even at the seedling stage. The molecular basis of this phenomenon has not been determined. In a chromatin-level study, we compared the cold-stress reaction of seedlings of two maize inbred lines showing contrasting levels of cold sensitivity. The cold-tolerant line was selected based on field data and previous physiological and transcriptomic level studies. The first condition of gene expression—chromatin accessibility—was assessed by formaldehyde-aided isolation of regulatory elements method and DNA sequencing. Potentially expressed genes and cis-regulatory sequences open for interaction with transcription factors have been defined. The results of this study suggest that during cold stress, the tolerant maize line shifted resources from growth to defense. This shift was shown by potential hormone-level events—degradation of growth-promoting gibberellins and synthesis of jasmonic and abscisic acids. This finding is congruent with the xeromorphic morphology of seedlings of the cold-tolerant line and their ability to regrow when stress ceases. It is a common reaction of cold-tolerant maize lines. Moreover, in the cold-tolerant line, several genes from the low-temperature signaling pathways were potentially expressed. Additionally, numerous stress-response AP2/EREBP-binding cis-motifs were accessible in the cold-tolerant line. Differently in the cold-sensitive B73 line, MADS-binding cis-motifs were the most abundant. Development of the photosynthetic apparatus is crucial for the survival of maize seedlings at low temperature. Our results suggest efficient photosynthesis in seedlings of the cold-tolerant line, as was described earlier in physiological-level analyses.

Effects of plant growth regulators on growth, flowering, fruiting and fruit yield of cucumber (Cucumis sativus L.): A review

This review provides a comprehensive overview of the basic and applied aspects of different plant growth regulators in the regulation of growth and development of cucumber plants. The study is completely based on the use of secondary sources of data; related journals, government institutes, and relevant reports. Foliar application of PGRs has been shown to change the physiological and developmental processes, including plant vegetative growth, sex expression, yield, and yield components in cucumber. There are basically two types of growth regulators; plant growth promoters such as auxin, gibberellins, cytokinins, maleic hydrazide, ethephon, etc. and plant growth inhibitors such as ethylene, abscisic acids, dormins, etc. The combined use of auxins and gibberellins result in increased secondary growth. Maleic hydrazide (MH) along with Ethephon at 100 ppm each increases the number of nodes and primary branches. Ethrel at 300-400 ppm retards the secondary development and increase femaleness, and at 200-300 ppm make fruit surface smooth. Silver nitrate (AgNO3) at 400 ppm enhances the maleness in cucumber. Application of Ethephon at 300 ppm reduces the harvesting time of the fruit. Salicylic acid (at 2 doses of 0.07 mm/l + 0.18 mm/l) increases chlorophyll content and its exogenous application increases the fruit yield. Maleic Hydrazide (MH) alone at 100 ppm increases the femaleness, inhibits apical growth at 50-100 ppm, and increases fruit size at 200 ppm. Therefore, various auxin [indole-3-acetic acid (IAA), NAA], auxin transport inhibitor (TIBA), cytokinins (KIN), gibberellin [gibberellic acid (GA3)], ABA, ethylene [(2-chloroethylphosphonic acid (ethrel; ethephon; CEPA)] and growth retardant (MH) have been applied to control the vegetative growth and to maximize yield of cucumber. Numerous obstacles have hindered the quality cucumber production in Nepal; like environmental stresses, biotic and abiotic constraints, pest and disease outbreaks, and many others. The use of exogenous plant growth regulators has been crucial to Nepali cucumber producers as plant growth regulators has hasty effect on vegetative as well as the quality yield of plants. This study aims to reveal the suitable concentrations for the applications of growth regulators so that the use of such regulators is environmentally and toxicologically safe for both plants and the consumers.

A Lipidomic Analysis of Leaves of Esca-Affected Grapevine Suggests a Role for Galactolipids in the Defense Response and Appearance of Foliar Symptoms.

Both qualitative and quantitative changes occur in the lipid composition of Vitis vinifera L. tissues, which may compromise the defense response against Esca complex disease, a widespread and damaging trunk disease. In this study, a lipidomic analysis of grapevine leaves is conducted to assess how lipid membrane remodeling relates to the emergence and progression of Esca foliar symptoms. In total, 208 molecular species (including lipids, four hormones, and some other compounds of the metabolism of lipids) were detected. Lipid species were readily assigned to the classes fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, and prenol lipids. Using different clustering analyses, distinct metabolic pathways stimulated at different stages of disease development were characterized. These analyses revealed consistent changes in the abundance of 13 galactolipids and two diacylglycerolipids. Overall, the observations indicated an increment in the levels of these lipid species in leaves of asymptomatic vines and a progressive drop with increasing foliar symptom severity in symptomatic vines. Five fatty acids also appear to exert a central role in the etiopathogenesis of Esca complex disease because of their accumulation in leaves of asymptomatic vines, namely, heptadecanoic, linoleic, γ-linolenic, arachidonic, and stearic acids. Symptomatic leaves were characterized by high levels of all lipid classes, except for galactolipids, lyso-galactolipids, and compounds relevant to the biosynthesis of chlorophylls and carotenoids, that exhibited decreased levels. The data also suggested a jasmonic acid-associated signaling mechanism activation upon the invasion of woods by Esca-associated fungi, compared with abscisic and salicylic acids. Further research is required for validation of these results with additional molecular analyses using more vine cultivars.

Morphogenesis, pigment content, phytohormones and productivity of eggplants under the action of gibberellin and tebuconazole

Regulation of growth and development of cultivated plants in order to optimize the production process is one of the main objectives of modern plant physiology. Both activators and growth inhibitors are used for this purpose. The effect of foliar treatment with 0.005% solution of gibberellic acid and 0.025% solution of antigibberellic preparation of tebuconazole on the morphogenesis, leaf structure, photosynthetic pigment content, balance of phytohormones and eggplant productivity cv. Diamond variety was investigated. The treatment with the preparations was carried out in the budding phase. The vegetation experiment was laid under soil and sand culture in vessels of a ten-liter capacity. The morphometric parameters were determined every 10 days, the mesostructure was studied in the leaves of the middle tier in the phase of fruit formation, chlorophyll content was measured in the raw material by spect­rophotometric method. Analytical determination of phytohormones (indole-3-acetic acid, gibberellic, abscisic acids and cytokinins – zeatin, zeatin-O-glucoside, zeatinriboside, isopentenyladenine and isopentenyladenosine) was performed by high performance liquid chromatography. Under the action of gibberellic acid, plant height increased significantly, and it decreased after its treatment with tebuconazole. The stimulator and inhibitor increased the number of leaves per plant, the weight of the leaf dry matter, the area of the individual leaf blade and the area of leaves per plant. Both preparations increased the weight of the raw material of the stems and roots, as well as the mass of dry matter of the whole plant. Under the action of tebuconazole, the content of chlorophylls in the leaves increased, while under the action of gibberellic acid it decreased. After treatment with gibberellic acid and tebuconazole, the thickness of the leaf blade increased due to chlorenchyma thickening. In the variant with gibberellic acid, the thickness of upper and lower epidermis increased, and in the variant with tebuconazole, these parameters decreased. Both growth regulators increased the volume of cells of the columnar parenchyma. The contet of endogenous gibberellic, indole-3-acetic and abscisic acids of the stems and especially in the leaves increased with the treatment of exogenous gibberellic acid, whereas after the application of tebuconazole the gibberellic and indole-3-acetic acid content of the stems decreased significantly and practically decreased to traces. Instead, the amount of abscisic acid increased. After treatment with exogenous gibberellic acid, the pool of cytokinins in the leaves significantly decreased. The inactive isoforms of the hormone zeatin-O-glucoside and isopentenyladenosine dominated in the stems. The effect of tebuconazole decreased the pool of cytokinins in the stems and increased in the leaves. In general, due to the multidirectional action, growth regulators positively influenced the elements of eggplant productivity. More effective was the retardant – tebuconazole. Therefore, the anatomic-morphological and structural-functional rearrangements in eggplants under the effects of exogenous gibberellic acid and tebuconazole are due to changes in the balance and distribution of endogenous hormones. Increased photosynthetic activity, stimulation of growth processes of some organs of the plant and inhibition of others enlarged the biological productivity of the culture.

Endogenous Phytohormones of Fern Polystichum aculeatum (L.) Roth Gametophytes at Different Stages of Morphogenesis in vitro Culture

The content of indole-3-acetic (IAA), gibberellic (GA3), abscisic acids (ABA), and cytokinins—zeatin (Z), zeatin glucoside (ZG), zeatin riboside (ZP), isopentenyladenin (iР), and isopentenyladenosine (iРА)—was determined using the method of high-performance liquid chromatography in fern Polystichum aculeatum gametophytes at different stages of morphogenesis in vitro culture. It was shown that, at the stage of spatulate prothallium development, gametophytes contained significant amounts of GA3 and IAA, while the content of ABA and cytokinins was low. The inactive ZG and active iP were dominant. At the stage of cordiform thallus formation, the level of GA3 increased by 1.6, IAA by 2.4, and ABA by 1.7 times. The content of inactive iPA increased twice, significantly increased the level of active ZR and iP. At the development stage of sporophyte on the surface of gametophyte thallus, the levels of IAA, ABA, and GA3 decreased. The accumulation of inactive ZG and decrease in the content of active zeatin and zeatin riboside were documented. At all stages of gametophytes’ morphogenesis, GA3 was dominant, and its highest content was detected during the development of archegonia and antheridia. The pattern of gibberellic acid and zeatin riboside accumulation has shown the key role of these hormones in the regulation of growth processes and the development of reproductive structures of P. aculeatum gametophytes.

Post-Anoxia in Plants: Reasons, Consequences, and Possible Mechanisms

One of the adverse factors affecting plants is oxygen deficiency, which develops as a result of excessive waterlogging and flooding. In a natural habitat, following a period of oxygen deficiency, aerobic conditions are usually restored, resulting in exposure of plants to post-anoxic oxidation conditions. The endogenous reduced metabolites and soil toxins accumulated during oxygen deficiency begin to be oxidized by atmospheric oxygen, which leads to the generation of reactive oxygen species (ROS) and the development of damage that can cause the death of a plant even if it has survived anoxic conditions. Recent studies discussed in the review indicate that the main mechanisms of adaptation to the post-anoxic period are mainly the biosynthesis of antioxidants and the effective operation of antioxidant system, the activation of alternative oxidase and detoxification of anaerobic metabolites. Ethylene-dependent transcription factors ERF-VII, which are also involved in the regulation of adaptation directly to oxygen deficiency, as well as phytohormones, such as jasmonic and abscisic acids, play an important role in ensuring the regulation of adaptation to post-anoxic conditions. Post-anoxia should not be considered as an independent stressor, since it represents a complex effect (the effects of anoxia, oxidative stress, and desiccation together contribute to the development of damage), and adaptation mechanisms and their regulation have many common elements with adaptation to oxygen deficiency.

Induction of morphogenesis in the callus culture of Lavandula angustifolia Mill.

The influence of the nutrient medium hormonal composition on the induction of calluso- and morphogenesis in Lavandula angustifolia Mill., as well as the content of some endogenous hormones (indolylacetic acid, cytokinins, abscisic acid) in morphogenic and non-morphogenic calli, were studied. The leaf explants were isolated from obtained in vitro plants of the Stepnaya and Vdala cultivars. In primary calli with a frequency of 5.7-11.6%, buds and shoots were formed on different Murashige and Skoog (MS) culture media supplemented with 6-benzylaminopurine, thidiazuron, kinetin, and gibberellic acid. In the callus of the first passage in both cultivars, the induction of morphogenesis was observed with the greatest frequency (39.5-43.2%) on the MS medium with the addition of 1.0 mg/l 6-benzylaminopurine and 1.0 mg/l kinetin. Morphogenic calli of the Vdala cultivar were characterized by a higher content of cytokinins, but a lower content of indolylacetic and abscisic acids compared with non-morphogenic ones.

Involvement of homocastasterone, salicylic and abscisic acids in the regulation of drought and freezing tolerance in doubled haploid lines of winter barley

Ten doubled haploid (DH) lines of winter barley with an increased range of freezing/drought tolerance were used to identify phytohormones involved in plant stress acclimation. Cold hardening and drought stress were applied at the most critical stages of plant development on young seedlings and heading plants, respectively. The level of the phytohormones was significantly higher at heading, more than 5-fold in respect of salicylic acid (SA) and total brassinosteroids (BRs) and 1.7-fold in the case of abscisic acid (ABA). Moreover, the spectrum of detectable BRs increased from one—homocastasterone (HCS)—found in seedlings to four BRs identified in heading plants [HCS, castasterone (CS), teasterone and dolicholide], with the last one detected for the first time in cereal species. To some extent freezing tolerance seems to be determined by native hormonal status as control seedlings of tolerant DH lines contained 1.4- and 2.3-fold lower amount of ABA and HCS and 2.3-fold higher amount of SA in comparison to freezing-sensitive ones. Such dependency was not observed in heading plants as significant variation in CS content was the only detected difference. Under stress treatments, tolerant DH lines accumulated significantly lower (75–81%) amount of ABA, which probably reflected lower stress intensity resulting from another defence strategy. In contrast, stress-induced significant almost 2-fold increase in HCS/CS and 2–3-fold decrease in SA content specific for tolerant DH lines of barley suggest the involvement of these molecules in freezing/drought defence. Detected correlations suggest their interaction with nonspecific peroxidase and low molecular weight antioxidants.

Induced resistance by jasmonic and abscisic acids and Nesidiocoris tenuis feeding on Solanum lycopersicum against Trialeurodes vaporariorum

In the present study, resistance to Trialeurodes vaporariorum (Westwood) was induced in tomato plants using foliar and root application of jasmonic acid (JA) and abscisic acid (ABA) alone or in combination with infection with Nesidiocoris tenuis (Reuter). This induced resistance significantly prolonged development and reduced the survival of immature stages of T. vaporariorum, and reduced the longevity and fecundity of adults. Treating plants with both hormones (JA or ABA) and N. tenuis resulted in greater magnitude in the delay of growth and development in comparison to single treatments. This reduction in T. vaporariorum performance is due to enhanced activity of plant enzymes and increased phenolic content following treatment. Our results show that JA, ABA as well as prior mirid phytophagy induce systemic defenses in tomato plants that have a negative effect on the performance of T. vaporariorum. Taken together, our findings suggest that these physiological changes underlie the induction of resistance to whitefly in tomato plants.

Physiological characterization and thylakoid ultrastructure analysis in super high-yield hybrid rice leaves under drought stress

Rice serves for more than a third of the world's population. However, drought stress (DS) affects its growth and yield. In order to understand plant drought adaptability, we explored the physiological and thylakoid ultrastructural alteration in super high-yield hybrid rice Liangyoupeijiu (LYPJ) under DS. Results showed that DS altered the thylakoid ultrastructure; twisted and fractured stroma thylakoids and more starch granules in chloroplast of LYPJ were present. Also, DS lowered chlorophyll and carotenoid contents in LYPJ after 7 d. DS reduced the proportion of unsaturated fatty acids in thylakoid membranes and increased the content of linoleic and abscisic acids (ABA) and osmotic substances such as calcium and potassium in LYPJ. Based on these results, we concluded that although DS severely affected normal growth, plants employed various strategies, such as changing their membrane lipid fluidity, increasing endogenous ABA and osmotic substance contents and stabilizing the grana thylakoids, in order to adapt to drought stress.

Endogenous phytohormone profiles in Pteris fern species differing in arsenic accumulating ability

Physiological and biochemical processes in plants are regulated by phytohormones. Phytohormone profiles are unknown in the fern family Pteridaceae. In this work, we analysed phytohormones in fronds and roots of three Pteris fern varieties with differing abilities in arsenic (As) accumulation. The ferns (hyperaccumulating P. cretica var. Albo-lineata and var. Parkerii, and non-hyperaccumulating P. straminea) were cultivated in a pot experiment with low contaminated soil (Astotal 16 mg kg−1, Aswater soluble 0.15 mg kg−1) for 185 days and harvested four times during growth. Phytohormone profiles were determined using high-performance liquid chromatography coupled to a hybrid triple quadrupole/linear ion trap mass spectrometer. We found twenty-five phytohormones and their structural and functional analogues (including growth and stress hormones) at detectable levels in fronds and roots. Interactions between growth hormones promoted the growth of ferns in the absence of environmental stress. Cytokinins of cis-zeatin type affected biomass yield, especially in the non-hyperaccumulator P. straminea. Phytohormone correlations between fern fronds and roots indicate a significant role for xylem-phloem transport and highlight the importance of transport in stress response. We observed similarities in phytohormone correlation profiles in the hyperaccumulators P. cretica var. Albo-lineata and var. Parkerii. In P. cretica var. Albo-lineata, interaction between jasmonic and abscisic acids was demonstrated, representing significant feedback of the defence response against oxidative stress by As. On the other hand, we did not find significant correlation among stress phytohormones in P. straminea. Profiling of growth and stress hormones in ferns confirms that they have specific phenotypic regulation. Hormonal regulations in the hyperaccumulator P. cretica var. Albo-lineata significantly differed from the non-hyperaccumulator P. straminea. A greater number of phytohormone correlations in the two hyperaccumulators suggests they use biosynthesised phytohormones more effectively.

Somatic Embryogenesis in Wheat and Barley Calli in vitro Is Determined by the Level of Indoleacetic and Abscisic Acids

The effect of a number of phytohormones (IAA, ABA, and cytokinines) on the induction of in vitro somatic embryogenesis in callus cultures of wheat, cultivar Bashkirskaya 26, barley, cultivar Steptoe, and its ABA-deficient mutant AZ34 has been studied. It was shown that the ability or inability for somatic embryogenesis in callus tissue of both wheat and barley is determined by the IAA : ABA ratio. However, the level of cytokinines was similar in both embryogenic and nonembryogenic calli of each object studied. The analysis of callus tissue of the ABA-deficient mutant AZ34 revealed the stimulating role of ABA not only in the induction of somatic embryogenesis but also in the formation of normal embryos.

SEED CAROTENOID DEFICIENT Functions in Isoprenoid Biosynthesis via the Plastid MEP Pathway.

Plastid isoprenoids, a diverse group of compounds that includes carotenoids, chlorophylls, tocopherols, and multiple hormones, are essential for plant growth and development. Here, we identified and characterized SEED CAROTENOID DEFICIENT (SCD), which encodes an enzyme that functions in the biosynthesis of plastid isoprenoids in maize (Zea mays). SCD converts 2C-methyl-d-erytrithol 2,4-cyclodiphosphate to 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate in the penultimate step of the methylerythritol phosphate (MEP) pathway. In scd mutants, plant growth and development are impaired and the levels of MEP-derived isoprenoids, such as carotenoids, chlorophylls, and tocopherols, as well as abscisic and gibberellic acids, are reduced in leaves and seeds. This scd metabolic alteration varies among plant tissues and under different light conditions. RNA-sequencing of the scd mutant and wild type identified a limited number of differentially expressed genes in the MEP pathway, although isoprenoid levels were significantly reduced in scd seeds and dark-grown leaves. Furthermore, SCD-overexpressing transgenic lines showed little or no differences in isoprenoid levels, indicating that SCD may be subject to posttranslational regulation or not represent a rate-limiting step in the MEP pathway. These results enhance our understanding of the transcriptomic and metabolic regulatory roles of enzymes in the MEP pathway and of their effects on downstream isoprenoid pathways in various plant tissues and under different light conditions.

The Role of Phytohormones in the Regulation of the Tolerance of Wheat, Rye, and Triticale Seeds to the Effect of Elevated Temperatures during Germination

The dynamics of changes in the content of phytohormones, abscisic (ABA), and indole-3-acidic (IAA) acids at early stages of the germination of wheat, rye, and triticale (a hybrid of wheat and rye) seeds at a normal temperature (22°C) and during short heat shock (40°C) was studied. In dry wheat and triticale germs, free and conjugate indole-3-acidic and abscisic acids were present, although conjugates prevailed. The effect of elevated temperatures on germs at different stages of swelling and germination induced rapid changes in the levels of hormones. Changes in the ratio of these acids in wheat and triticale germs exposed to short heat shock were revealed. These changes may be associated with self-regulation and hormone transition to an inactive state. The dependence of growth processes on the IAA/ABA ratio during a short heat shock was indicated. The processes preceding seedling emergence and active growth were shown to differ in temperature sensitivity.

Accumulation of Indolyl-3-Acetic and Abscisic Acids by “Hairy” Roots of Artemisia vulgaris

High-performance liquid chromatography–mass spectrometry has been used to study the character of the accumulation and balance of endogenous indolyl-3-acetic (IAA) and abscisic (ABA) acids in the “hairy” roots of Artemisia vulgaris obtained by transformation with Agrobacterium rhizogenes agropine strain A4. The free IAA content was significantly higher than the level of the conjugated form of the hormone. The highest amount of the active IAA form (554.4 ± 27.7 ng/g fresh weight) was detected in line no. 2. The free form of ABA predominated in the roots of control samples, where its level was significantly higher than in the transformed lines. The “hairy” roots accumulated a conjugated form of ABA, and the highest content of this compound amounted to 459.6 ± 23.0 ng/g of fresh weight (in line no. 4). The architecture of the transformed roots was marked by significant branching and lateral root formation; active accumulation of biomass was detected. The results obtained demonstrate changes in the endogenous phytohormone balance in the “hairy” A. vulgaris roots, namely, a trend to predomination of the free IAA form and a significant decrease of the ABA content.

Control of Fusarium wilt in wheat seedlings by grain priming with defensin-like protein

The exogenous application of natural plant resistance inducer is a new interesting way for disease management. From this point of view, this study investigated the effect of wheat grain priming with defensin on the resistance of the grown plants against the Fusarium wilt. The results showed that priming enhanced the antioxidant system represented in antioxidant enzymes (superoxide dismutase, polyphenol oxidase, soluble and cell wall-bound peroxidase) and non-enzymatic antioxidant compounds (proline, free soluble and cell wall-bound phenols) in the plants. This results in decreasing the H2O2 content and lipid peroxidation in these plants, which protects plants from the oxidative stress. Defensin priming not only improved the antioxidant system but also improved the hydrolysis processes. Under infection, the protease activity in the primed plants decreased compared to its highly significant increase in the non-primed group. Defensin priming also increased the activity of the phosphatases and amylase which increased the soluble phosphate and sugar. This served the high metabolic activity of the defensin-primed plants. The highly significant decrease in the shikimic acid content in the defensin-primed group ensured its high metabolic activity. All these changes are initiated by the regulation of defense signal molecules such as jasmonic and abscisic acids. This helped the plants grown from defensin-primed grains to overcome the Fusarium infection.

Core features of the hormonal status in in vitro grown potato plants

ABSTRACTSome time ago, potato transformants expressing Agrobacterium-derived auxin synthesis gene tms1 were generated. These tms1-transgenic plants, showing enhanced productivity, were studied for their hormonal status, turnover and responses in comparison with control plants. For this purpose, contents of phytohormones belonging to six different classes (auxins, cytokinins, gibberellins, abscisic, jasmonic and salicylic acids) were determined by a sensitive UPLC-MS/MS method in tubers and shoots of in vitro grown plants. To date, this study represents the most comprehensive analysis of the potato hormonal system. On the basis of obtained results, several new generalizations concerning potato hormonal status were drawn. Overall, these data can serve as a framework for forthcoming integrative studies of the hormonal system in potato plants.

Silicon Improves Chilling Tolerance During Early Growth of Maize by Effects on Micronutrient Homeostasis and Hormonal Balances.

Low soil temperature in spring is a major constraint for the cultivation of tropical and subtropical crops in temperate climates, associated with inhibition of root growth and activity, affecting early growth and frequently plant performance and final yield. This study was initiated to investigate the physiological base of cold-protective effects induced by supplementation with silicon (Si), widely recommended as a stress-protective mineral nutrient. Maize was used as a cold-sensitive model plant, exposed to chilling stress and low root-zone temperature (RZT) during early growth in a lab to field approach. In a pot experiment, 2–weeks exposure of maize seedlings to low RZT of 12–14°C, induced leaf chlorosis and necrosis, inhibition of shoot and root growth and micronutrient limitation (particularly Zn and Mn). These phenotypes were mitigated by seed treatments with the respective micronutrients, but surprisingly, also by Si application. Both, silicon and micronutrient treatments were associated with increased activity of superoxide dismutase in shoot and roots (as a key enzyme for detoxification of reactive oxygen species, depending on Zn and Mn as cofactors), increased tissue concentrations of phenolics, proline, and antioxidants, but reduced levels of H2O2. These findings suggest that mitigation of oxidative stress is a major effect of Zn, Mn, and Si applied as cold stress protectants. In a soil–free culture system without external nutrient supply, Si significantly reduced large leaching losses of Zn and Mn from germinating seeds exposed to low-temperature stress. Silicon also increased the translocation of micronutrient seed reserves to the growing seedling, especially the Zn shoot translocation. In later stages of seedling development (10 days after sowing), cold stress reduced the root and shoot contents of important hormonal growth regulators (indole acetic acid, gibberellic acid, zeatin). Silicon restored the hormonal balances to a level comparable with non-stressed plants and stimulated the production of hormones involved in stress adaptation (abscisic, salicylic, and jasmonic acids). Beneficial effects of Si seed treatments on seedling establishment and the nutritional status of Zn and Mn were also measured for a field-grown silage maize, exposed to chilling stress by early sowing. This translated into increased final biomass yield.