Andrea Andrade

Endogenous jasmonates and octadecanoids in hypersensitive tomato mutants during germination and seedling development in response to abiotic stress

Although jasmonates (JAs) are involved in germination and seedling development, the regulatory mechanism of JAs, and their relation with endogenous level modifications in these processes, is not well understood. We report here the detection of 12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), 11-hydroxyjasmonate (11-OH-JA), 12-hydroxyjasmonate (12-OH-JA) and methyljasmonate (JAME) in unimbibed seeds and seedlings of tomato Lycopersicon esculentum Mill cv. Moneymaker (wild type) and tss1 , tss2 , tos1 mutants. The main compounds in wild-type and tss1 , tss2 , tos1 seeds were the hydroxylate-JAs; 12-OH-JA was the major component in dry seeds of the wild type and in tss2 and tos1 . The amounts of these derivatives were higher in seeds than in seedlings. Changes in JAs during wild-type and tss1 imbibition were analysed in seeds and the imbibition water. In wild-type imbibed seeds, 11-OH-JA content was higher than in tss1 . 12-OH-JA showed a different tendency with respect to 11-OH-JA, with high levels in the wild type at early imbibition. In tss1 , levels of 12-OH-JA rose from 24 to 48 h of imbibition. At 72 h of imbibition, when radicles had emerged, the amounts of both hydroxylates in wild-type and tss1 seeds were minimal. An important release of the hydroxylate forms was observed in the imbibition water. 11-OH-JA decreased in the imbibition water of wild-type seeds at 48 h. On the contrary, a high and sustained liberation of this compound was observed in tss1 after 24 h. 12-OH-JA increased in wild-type as well in tss1 until 24 h. Thereafter, a substantial reduction in the content of this compound was registered. NaCl-treated wild-type seedlings increased their 12-OH-JA, but tss1 seedlings increased their JA in response to salt treatment. In tss2 seedlings, NaCl caused a slight decrease in 11-OH-JA and JAME, whereas tos1 seedlings showed a dramatic OPDA and 12-OH-JA decrease in response to salt treatment. Under salt stress the mutant seedlings showed different patterns of JAs according to their differential hypersensitivity to abiotic stress. The JA-hydroxylate forms found, and the differential accumulation of JAs during germination, imbibition and seedling development, as well as their response to NaCl stress, provide new evidence about the control of many developmental processes by JA.

Drought and salinity alter endogenous hormonal profiles at the seed germination phase

The most critical phase in plant life is seed germination, which is influenced by environmental factors. Drought and salinity are key environmental factors that affect seed germination. Reduction or alterations of germination when seeds are exposed to these factors have been shown to be due to either the adverse effects of water limitation and/or specific ion toxicity on metabolism. Phytohormones are chemical messengers produced within the plant that control its growth and development in response to environmental cues; small fluctuations of phytohormone levels alter the cellular dynamics and, hence, play a central role in regulating plant growth responses to these environmental factors. To integrate current knowledge, the present review focuses on the involvement of endogenous phytohormones in plant adaptative responses to drought and salinity at one of the plants developmental phases.

Early perception of stink bug damage in developing seeds of field-grown soybean induces chemical defences and reduces bug attack.

BACKGROUND Southern green stink bugs (Nezara viridula L.) invade field-grown soybean crops, where they feed on developing seeds and inject phytotoxic saliva, which causes yield reduction. Although leaf responses to herbivory are well studied, no information is available about the regulation of defences in seeds. RESULTS This study demonstrated that mitogen-activated protein kinases MPK3, MPK4 and MPK6 are expressed and activated in developing seeds of field-grown soybean and regulate a defensive response after stink bug damage. Although 10-20 min after stink bug feeding on seeds induced the expression of MPK3, MPK6 and MPK4, only MPK6 was phosphorylated after damage. Herbivory induced an early peak of jasmonic acid (JA) accumulation and ethylene (ET) emission after 3 h in developing seeds, whereas salicylic acid (SA) was also induced early, and at increasing levels up to 72 h after damage. Damaged seeds upregulated defensive genes typically modulated by JA/ET or SA, which in turn reduced the activity of digestive enzymes in the gut of stink bugs. Induced seeds were less preferred by stink bugs. CONCLUSION This study shows that stink bug damage induces seed defences, which is perceived early by MPKs that may activate defence metabolic pathways in developing seeds of field-grown soybean.

Phytohormones and Other Plant Growth Regulators Produced by PGPR: The Genus Azospirillum

One of the first mechanisms proposed to explain the plant growth promotion due to bacterial inoculation has been the nitrogen biological fixation; however, this mechanism has been of less agronomic significance than was initially expected. In counterpart, other mechanisms have been proposed to explain these inoculation effects, such as production of phytohormones and other plant growth regulators. Nowadays, we know that benefic effect of inoculation with rhizobacteria can be correlated with production and metabolism of chemically defined compounds such as auxins, cytokinins, gibberellins, and other plant growth regulators, such as abscisic acid and nitric oxide. In this chapter, we highlight the analytical and biological methods used to identify and quantify the most relevant phytohormones and plant growth regulators produced by Azospirillum sp. and other benefic rhizobacteria.

Production and function of jasmonates in nodulated roots of soybean plants inoculated with Bradyrhizobium japonicum

Little is known regarding production and function of endogenous jasmonates (JAs) in root nodules of soybean plants inoculated with Bradyrhizobium japonicum. We investigated (1) production of jasmonic acid (JA) and 12-oxophytodienoic acid (OPDA) in roots of control and inoculated plants and in isolated nodules; (2) correlations between JAs levels, nodule number, and plant growth during the symbiotic process; and (3) effects of exogenous JA and OPDA on nodule cell number and size. In roots of control plants, JA and OPDA levels reached a maximum at day 18 after inoculation; OPDA level was 1.24 times that of JA. In roots of inoculated plants, OPDA peaked at day 15, whereas JA level did not change appreciably. Shoot dry matter of inoculated plants was higher than that of control at day 21. Chlorophyll a decreased more abruptly in control plants than in inoculated plants, whereas b decreased gradually in both cases. Exogenous JA or OPDA changed number and size of nodule central cells and peripheral cells. Findings from this and previous studies suggest that increased levels of JA and OPDA in control plants are related to senescence induced by nutritional stress. OPDA accumulation in nodulated roots suggests its involvement in “autoregulation of nodulation.”

Differential accumulation of abscisic acid and its catabolites in drought-sensitive and drought-tolerant sunflower seeds

Eleven sunflower (Helianthus annuus L.) inbred lines were evaluated in field and laboratory studies under drought and irrigation. In the field, lines B59, R419 and B67 had reduced seed and oil yield under drought, while no reduction was observed for R432, HAR4 and B71. Lines HA89, R415, R049, RHA274 and R423 presented intermediate responses. In laboratory tests, seeds of line B59 had reduced germination percentages at 200 and 400 mM mannitol, while germination of seeds of lines R432, B71, HAR4, RHA274 and HA89 was reduced only at 400 mM mannitol. Droughtsensitive B59 and drought-tolerant B71 grown under irrigation and drought conditions in the field were selected for hormone assays. Abscisic acid (ABA) and its catabolites in pericarp, embryonic axis and cotyledons of dry and germinated seeds of B59 and B71 were determined. ABA was the major component of the pericarp of dry seeds from B71 and B59 plants grown under drought. The embryonic axis of B71 dry seeds from drought-grown plants also showed high ABA content. The major findings from this study are: (1) the drought-sensitive and -tolerant lines exhibited different ABA and catabolite profiles; (2) water environment during maternal plant growth affected ABA content and the composition of catabolites in mature and germinated seeds; (3) ABA content did not affect germination performance in our conditions; and (4) the dry and germinated seed parts showed different ABA and catabolite profiles.

Tomato mutants sensitive to abiotic stress display different abscisic acid content and metabolism during germination

Laboratorio de Fisiologi´a Vegetal, Departamento de Ciencias Naturales, Facultad de Ciencias Exactas,Fi´sico-Qui´micas y Naturales, Universidad Nacional de Ri´o Cuarto, 5800 Ri´o Cuarto, ArgentinaAbstractWe report the determination of abscisic acid (ABA)and its metabolites, phaseic acid (PA), dihydropha-seic acid (DPA) and ABA glucose ester (ABA-GE),in non-dormant dry and imbibed seeds of tomato(Solanum lycopersicum Mill.) cv. Moneymaker (wildtype), and its tss1, tss2 and tos1 mutants. High ABA indryseedsmayoriginate from ABAaccumulation inthesheath tissue, which was in contact with an ABA-containing medium, the endocarpus. The highestgermination percentages at 72h, observed in tss1and tss2, coincided with minimal ABA content. Wild-type and mutant seeds showed different ABA andcatabolic patterns, and these were correlated withtheir sensitivity to abiotic stress. Whereas dry seedsshowed a high basal ABA, imbibed seeds showedhigher ABA metabolite content, particularly DPA. Thedramatic decrease of ABA following seed imbibitionsuggests an activation of ABA catabolism during theearlystagesofthegerminationprocess.Theobservedvariation of ABA metabolites among dry and imbibedseeds of Solanum lycopersicum cv. Moneymaker andits tss1, tss2 and tos1 mutants shows that ABAmetabolism is differentially regulated in thesegenotypes.Keywords: abiotic stress, abscisic acid, abscisic acidmetabolites, germination, Solanum lycopersicum,tomato mutantsIntroductionSeveral metabolites of abscisic acid (ABA) havebeen isolated from various plant materials. ABAcatabolism proceeds through two major pathways: the‘oxidative pathway’ involving oxidation at differentpositions, and the ‘conjugation pathway’. The path-way used depends on the plant species, develop-mental stage or tissue type. The oxidative pathway,considered the more common in plant catabolism(Nambara and Marion-Poll, 2005), is initiated byhydroxylation at C-8

Metabolomic Approach to Understand Plant Adaptations to Water and Salt Stress

Abstract Plants are sessile organisms unable to escape from regularly changing environmental conditions that affect their growth and development; thus their survival depends upon adaptive responses. These adaptive features have been observed in plants exposed to abiotic stress, including morphophysiological, biochemical, and molecular. Moreover, the regulation of metabolic pathways activated by stresses can be characterized through the profile of metabolites involved in them. Therefore several compounds or metabolites with extraordinarily large chemical complexity play different functions in intricate metabolic networks. Consequently, the complex molecular regulatory system involved in plant response to abiotic stress can be understood through high-throughput “omic” techniques, such as metabolomics. At present, metabolomics is a new tool for increasing our knowledge about specific metabolites playing crucial roles in plant responses to environmental stresses, particularly salinity and drought. In fact, several researchers have reported that plants exposed to salinity or water stress show alterations in certain metabolites, such as primary metabolites (osmolytes, osmoprotectants) and secondary metabolites (defense metabolites). However, not all plant species synthesize all kinds of metabolites; some species accumulate very low quantities of some of these metabolites, whereas some others do not do so at all. Indeed, the flux through a metabolic pathway rather than the accumulation of a specific metabolite per se might contribute to stress tolerance. In addition, alterations in secondary metabolites cannot be inferred only from variations in their primary metabolite precursors but is usually a result of a complex regulatory process. In this chapter, we review the recent progress in the field of metabolomics, including the analytical technologies, highlighting changes in specific metabolites induced by salt and water stress and discussing the meaning of specific and nonspecific responses to these stresses. This approach could lead to new insights into understanding plant water and salt stress adaptations for future application in biotechnology.

Stress Hormone Levels Associated with Drought Tolerance vs. Sensitivity in Sunflower (Helianthus annuus L.)

Six inbred lines (B59, B67, B71, R432, R419, and HAR4) of sunflower (Helianthus annuus L.) were evaluated in field and laboratory experiments under drought vs. irrigation. In field studies, relative seed yield per hectare and oil yield per hectare were reduced under drought in B59, B67, and R419, but not in R432, B71, or HAR4. In lab studies, germination percentage was reduced under 200 and 400 mM mannitol treatment (which simulates drought) for B59 and under 400 mM mannitol for R432, B71, and HAR4. B59 and B71 were used as typical drought-sensitive and drought-tolerant lines, respectively, for subsequent experiments. Levels of the phytohormones jasmonates (JAs), abscisic acid (ABA), and ABA catabolites were evaluated in dry and germinated seeds from B59 and B71 parent plants grown under drought and irrigation. For dry seeds from plants grown under drought, ABA was the major compound accumulated in B71, whereas 12-OH-JA was the major compound in B59. Germinated seeds of both lines, compared to dry seeds, showed increased 12-oxophytodienoic (OPDA) and decreased ABA. Our results indicate that soil moisture conditions under which parent plants grow affect hormonal content of seeds produced, and JAs and ABA levels during germination are variable. F3 seedling families obtained by crossing R432 (drought-tolerant) and A59 (drought-sensitive) lines were assayed for germination percentage and endogenous levels of salicylic acid (SA), JA, and ABA following drought treatment (400 mM mannitol). Germination percentage showed a typical segregation pattern of quantitative inheritance to drought tolerance in the phenological stage of seedling. Levels of SA and ABA under drought compared to control condition increased in F3 tolerant families but decreased in F3 sensitive families. JA levels changed under drought condition, but the direction of change was not consistent within tolerant or sensitive families. Our results provide important information for strategies to maintain or increase yield of sunflower crops under drought conditions.