Red LED Light Improves Pepper (Capsicum annuum L.) Seed Radicle Emergence and Growth through the Modulation of Aquaporins, Hormone Homeostasis, and Metabolite Remobilization.

Red LED light (R LED) is an efficient tool to improve seed germination and plant growth under controlled environments since it is more readily absorbed by photoreceptors' phytochromes compared to other wavelengths of the spectrum. In this work, the effect of R LED on the radicle emergence and growth (Phase III of germination) of pepper seeds was evaluated. Thus, the impact of R LED on water transport through different intrinsic membrane proteins, via aquaporin (AQP) isoforms, was determined. In addition, the remobilization of distinct metabolites such as amino acids, sugars, organic acids, and hormones was analysed. R LED induced a higher germination speed index, regulated by an increased water uptake. PIP2;3 and PIP2;5 aquaporin isoforms were highly expressed and could contribute to a faster and more effective hydration of embryo tissues, leading to a reduction of the germination time. By contrast, TIP1;7, TIP1;8, TIP3;1 and TIP3;2 gene expressions were reduced in R LED-treated seeds, pointing to a lower need for protein remobilization. NIP4;5 and XIP1;1 were also involved in radicle growth but their role needs to be elucidated. In addition, R LED induced changes in amino acids and organic acids as well as sugars. Therefore, an advanced metabolome oriented to a higher energetic metabolism was observed, conditioning better seed germination performance together with a rapid water flux.

Protective effects of cerium oxide nanoparticles in grapevine (Vitis vinifera L.) cv. Flame Seedless under salt stress conditions.

High levels of soil salinity can cause substantial decline in growth and productivity of crops worldwide, thus representing a major threat to global agriculture. In recent years, engineered nanoparticles (NPs) have been deemed as a promising alternative in combating abiotic stress factors, such as salinity. In this context, the present study was designed to explore the potential of cerium oxide nanoparticles (CeO2NPs) in alleviating salt stress in grapevine (Vitis vinifera L. cv. Flame Seedless) cuttings. Specifically, the interaction between CeO2 NPs (25, 50 and 100 mg L-1) and salinity (25 and 75 mM NaCl) was evaluated by assaying an array of agronomic, physiological, analytical and biochemical parameters. Treatments with CeO2 NPs, in general, alleviated the adverse impacts of salt stress (75 mM NaCl) significantly improving relevant agronomic traits of grapevine. CeO2 NPs significantly ameliorated chlorophyll damage under high levels of salinity. Furthermore, the presence of CeO2 NPs attenuated salinity-induced damages in grapevine as indicated by lower levels of proline, MDA and EL; however, H2O2 content was not ameliorated by the presence of CeO2 NPs under salt stress. Additionally, salinity caused substantial increases in enzymatic activities of GP, APX and SOD, compared with control plants. Similar to stress conditions, all concentrations of CeO2 NPs triggered APX activity, while the highest concentration of CeO2 NPs significantly increased GP activity. However, CeO2 NPs did not significantly modify SOD activity. Considering mineral nutrient profile, salinity increased Na and Cl content as well as Na/K ratio, while it decreased K, P and Ca contents. Nevertheless, the presence of CeO2 NPs did not lead to significant alterations in Na, K and P content of salt-stressed plants. Taken together, current findings suggest that CeO2 NPs could be employed as promising salt-stress alleviating agents in grapevine.

Halophytes of the Mediterranean Basin-Underutilized Species with the Potential to Be Nutritious Crops in the Scenario of the Climate Change.

Halophyte plants are adapted to saline environments and represent a novel type of crops given their possible uses at both culinary and industrial levels. In this work, the nutritional quality of different Mediterranean halophyte species, Atriplex halimus, Salicornia fruticosa, and Cakile maritima, was evaluated under conditions of high salinity. For this, plants were grown at different NaCl concentrations (0, 100, 200, and 300 mM) and the contents of proteins, total lipids, polyphenols, and mineral elements were analyzed as well as growth. Of the three species, C. maritima was the most sensitive to salt stress and therefore showed the highest phenolic compounds content. By contrast, whereas salinity increased the amounts of proteins and phenolics with respect to the control in A. halimus and S. fruticosa, it decreased them in C. maritima. Plants of A. halimus accumulated higher amounts of Na+ in their leaves, but the level of this ion, considering human consumption, was below that of other culinary halophyte species. In conclusion, all the results indicate that these three halophyte species grown at high salt levels represent optimal crops for-new foodstuff-production as green salt or spice due to their nutritional potential.

Analysis of physiological traits in the response of Chenopodiaceae, Amaranthaceae, and Brassicaceae plants to salinity stress.

Soil salinity is one of the main factors affecting plant growth. Dissection of plant response to salinity into physiological traits may result a simple approximation than the overall response that may influence many aspects of the plant. In the present study two factors were considered to evaluate the correlation of different physiological variables in the plant response to salinity. The first factor was the species, with four levels (Atriplex halimus, Salicornia fruticosa, Cakile maritima, and Brassica rapa), and the second was the salinity (0, 100, 200, and 300 mM NaCl). Thus, the interrelationships of distinct physiological traits - leaf succulence, minerals (micronutrients and macronutrients), plant water relations (osmotic potential, water potential, and hydraulic conductivity), protein content, catalase, and unsaturated fatty acids - were analyzed by Discriminant Canonical Analysis (DCA). Additional information supplied by the interaction between the variables provided a multivariate response pattern in which the two factors (species x salinity) influenced the relationship between responses rather than affecting a single response. Such analysis allows to establish whether the selected trait was associated to each other for helping to define the best set of parameters in relation to the response of new genotypes to salinity. Thus, plant growth was influenced by leaf succulence adaptation to salt stress whereas it was not determined by water relations. The Na ion prevailed over K as the element with the highest variability in the response to salinity in A. halimus and S. fruticosa, whereas in C. maritima and B. rapa, Ca, S, and P stood out more. Patterns of ion accumulation together with the protein and unsaturated fatty acid ratios could be used in discriminating plant response to salt stress may be positioned in interrelated groups. The results highlight new evidences in the response to salt stress associated to a specific interrelationship of a set of physiological parameters.

Plasma membrane aquaporins mediates vesicle stability in broccoli.

The use of in vitro membrane vesicles is attractive because of possible applications in therapies. Here we aimed to compare the stability and functionality of plasma membrane vesicles extracted from control and salt-treated broccoli. The impact of the amount of aquaporins was related to plasma membrane osmotic water permeability and the stability of protein secondary structure. Here, we describe for first time an increase in plant aquaporins acetylation under high salinity. Higher osmotic water permeability in NaCl vesicles has been related to higher acetylation, upregulation of aquaporins, and a more stable environment to thermal denaturation. Based on our findings, we propose that aquaporins play an important role in vesicle stability.

Effects of seed priming, salinity and methyl jasmonate treatment on bioactive composition of Brassica oleracea var. capitata (white and red varieties) sprouts.

BACKGROUND: Brassica spp. sprouts are rich in nutrients and bioactive compounds, especially glucosinolates and phenolic acid derivatives, and the composition of these young germinating seeds can be altered by several external factors. In this study two cabbage varieties (Brassica oleracea var. capitata, red and white) were studied using seed priming (KCl 50 mmol L-1 ; NaCl 150 mmol L-1 ) and MeJA spraying (25 µmol L-1 ) to elicit the phytochemical content of edible sprouts. RESULTS: The red variety was richer in glucosinolates and phenolic compounds than the white one but not in mineral nutrients. Seed priming enhanced the potassium (K) content and flavonols in both varieties, while the total content of glucosinolates was reduced after seed priming only in the red variety. The white variety responded better than the red one to KCl seed priming, increasing the flavonols (89%). Salinity did not induce any change in the phytochemical content of these two varieties. Elicitation with sprayed MeJA was effective in significantly increasing the content of indolic glucosinolates glucobrassicin (5.7-fold) and neoglucobrassicin (9.7-fold) in the red cultivar. In the white variety, in addition to glucobrassicin (19.4-fold) and neoglucobrassicin (9.4-fold), 4-hydroxyglucobrassicin (2.3-fold) was also enhanced. MeJA also elicited significant amounts of anthocyanins (41%) and chlorogenic acid derivatives (329%) in the white variety. CONCLUSION: KCl seed priming and MeJA elicitation promoted the phytochemical composition of the cabbage varieties, especially in the white variety. The application of NaCl resulted in less efficient elicitation. © 2016 Society of Chemical Industry.

Mutual Interactions between Aquaporins and Membrane Components.

In recent years, a number of studies have been focused on the structural evaluation of protein complexes in order to get mechanistic insights into how proteins communicate at the molecular level within the cell. Specific sites of protein-aquaporin interaction have been evaluated and new forms of regulation of aquaporins described, based on these associations. Heterotetramerizations of aquaporin isoforms are considered as novel regulatory mechanisms for plasma membrane (PIPs) and tonoplast (TIPs) proteins, influencing their intrinsic permeability and trafficking dynamics in the adaptive response to changing environmental conditions. However, protein-protein interaction is an extensive theme that is difficult to tackle and new methodologies are being used to study the physical interactions involved. Bimolecular fluorescence complementation and the identification of cross-linked peptides based on tandem mass spectra, that are complementary to other methodologies such as heterologous expression, co-precipitation assays or confocal fluorescence microscopy, are discussed in this review. The chemical composition and the physical characteristics of the lipid bilayer also influence many aspects of membrane aquaporins, including their functionality. The molecular driving forces stabilizing the positions of the lipids around aquaporins could define their activity, thereby altering the conformational properties. Therefore, an integrative approach to the relevance of the membrane-aquaporin interaction to different processes related to plant cell physiology is provided. Finally, it is described how the interactions between aquaporins and copolymer matrixes or biological compounds offer an opportunity for the functional incorporation of aquaporins into new biotechnological advances.

Plant plasma membrane aquaporins in natural vesicles as potential stabilizers and carriers of glucosinolates.

Their biodegradable nature and ability to target cells make biological vesicles potential nanocarriers for bioactives delivery. In this work, the interaction between proteoliposomes enriched in aquaporins derived from broccoli plants and the glucosinolates was evaluated. The vesicles were stored at different temperatures and their integrity was studied. Determination of glucosinolates, showed that indolic glucosinolates were more sensitive to degradation in aqueous solution than aliphatic glucosinolates. Glucoraphanin was stabilized by leaf and root proteoliposomes at 25°C through their interaction with aquaporins. An extensive hydrogen bond network, including different aquaporin residues, and hydrophobic interactions, as a consequence of the interaction between the linear alkane chain of glucoraphanin and Glu31 and Leu34 protein residues, were established as the main stabilizing elements. Combined our results showed that plasma membrane vesicles from leaf and root tissues of broccoli plants may be considered as suitable carriers for glucosinolate which stabilization can be potentially attributed to aquaporins.

Genotype influences sulfur metabolism in broccoli (Brassica oleracea L.) under elevated CO2 and NaCl stress.

Climatic change predicts elevated salinity in soils as well as increased carbon dioxide dioxide [CO2] in the atmosphere. The present study aims to determine the effect of combined salinity and elevated [CO2] on sulfur (S) metabolism and S-derived phytochemicals in green and purple broccoli (cv. Naxos and cv. Viola, respectively). Elevated [CO2] involved the amelioration of salt stress, especially in cv. Viola, where a lower biomass reduction by salinity was accompanied by higher sodium (Na(+)) and chloride (Cl(-)) compartmentation in the vacuole. Moreover, salinity and elevated [CO2] affected the mineral and glucosinolate contents and the activity of biosynthetic enzymes of S-derived compounds and the degradative enzyme of glucosinolate metabolism, myrosinase, as well as the related amino acids and the antioxidant glutathione (GSH). In cv. Naxos, elevated [CO2] may trigger the antioxidant response to saline stress by means of increased GSH concentration. Also, in cv. Naxos, indolic glucosinolates were more influenced by the NaCl×CO2 interaction whereas in cv. Viola the aliphatic glucosinolates were significantly increased by these conditions. Salinity and elevated [CO2] enhanced the S cellular partitioning and metabolism affecting the myrosinase-glucosinolate system.

New challenges in plant aquaporin biotechnology.

Recent advances concerning genetic manipulation provide new perspectives regarding the improvement of the physiological responses in herbaceous and woody plants to abiotic stresses. The beneficial or negative effects of these manipulations on plant physiology are discussed, underlining the role of aquaporin isoforms as representative markers of water uptake and whole plant water status. Increasing water use efficiency and the promotion of plant water retention seem to be critical goals in the improvement of plant tolerance to abiotic stress. However, newly uncovered mechanisms, such as aquaporin functions and regulation, may be essential for the beneficial effects seen in plants overexpressing aquaporin genes. Under distinct stress conditions, differences in the phenotype of transgenic plants where aquaporins were manipulated need to be analyzed. In the development of nano-technologies for agricultural practices, multiple-walled carbon nanotubes promoted plant germination and cell growth. Their effects on aquaporins need further investigation.

Involvement of a glucosinolate (sinigrin) in the regulation of water transport in Brassica oleracea grown under salt stress.

Members of the Brassicaceae are known for their contents of nutrients and health-promoting phytochemicals, including glucosinolates. The concentrations of these chemopreventive compounds (glucosinolate-degradation products, the bioactive isothiocyanates) may be modified under salinity. In this work, the effect of the aliphatic glucosinolate sinigrin (2-propenyl-glucosinolate) on plant water balance, involving aquaporins, was explored under salt stress. For this purpose, water uptake and its transport through the plasma membrane were determined in plants after NaCl addition, when sinigrin was also supplied. We found higher hydraulic conductance (L0 ) and water permeability (Pf ) and increased abundance of PIP2 aquaporins after the direct administration of sinigrin, showing the ability of the roots to promote cellular water transport across the plasma membrane in spite of the stress conditions imposed. The higher content of the allyl-isothiocyanate and the absence of sinigrin in the plant tissues suggest that the isothiocyanate is related to water balance; in fact, a direct effect of this nitro-sulphate compound on water uptake is proposed. This work provides the first evidence that the addition of a glucosinolate can regulate aquaporins and water transport: this effect and the mechanism(s) involved merit further investigation.

Enhancement of root hydraulic conductivity by methyl jasmonate and the role of calcium and abscisic acid in this process.

The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wild-type plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.

Response of three broccoli cultivars to salt stress, in relation to water status and expression of two leaf aquaporins.

The aim of this study was to compare differences in water relations in the leaves of three broccoli cultivars and differential induction of the expression of PIP2 aquaporin isoforms under salt stress. Although broccoli is known to be moderately tolerant to salinity, scarce information exists about the involvement of leaf aquaporins in its adaptation to salinity. Thus, leaf water relations, leaf cell hydraulic conductivity (Lpc), gas exchange parameters and the PIP2 expression pattern were determined for short- (15 h) and long- (15 days) term NaCl treatments. In the long term, the lower half-time of water exchange in the cells of cv. Naxos, compared with Parthenon and Chronos, and its increased PIP2 abundance may have contributed to its Lpc maintenance. This unmodified Lpc in cv. Naxos under prolonged salinity may have diluted NaCl in the leaves, as suggested by lower Na(+) concentrations in the leaf sap. By contrast, the increase in the half-time of water exchange and the lower PIP2 abundance in cvs. Chronos and Parthenon would have contributed to the reduced Lpc values. In cv. Parthenon, there were no differences between the ε values of control and salt-stressed plants; in consequence, cell turgor was enhanced. Also, the increases in BoPIP2;2 and BoPIP2;3 expression in cv. Chronos for the short-term NaCl treatment suggest that these isoforms are involved in osmotic regulation as downstream factors in this cultivar, in fact, in the short-term, Chronos had a significantly reduced osmotic potential and higher PIP2 isoforms expression.

Differential responses of two broccoli (Brassica oleracea L. var Italica) cultivars to salinity and nutritional quality improvement.

The comparative responses of two broccoli cultivars (Brassica oleracea var. Italica, cv. Parthenon and cv. Naxos) to a 15 d exposure to different NaCl levels were investigated. Salinity led to increased concentrations of Na(+) and Cl(-) ions in both cultivars, a disruption of the endogenous minerals levels in the shoots and roots-that varied with the cultivar and salt concentration-and decreases in the osmotic potential (Ψ(π)), root hydraulic conductance (L(0)), and stomatal conductance (G(s)). The reduced biomass of Naxos at moderate NaCl indicates greater sensitivity to salinity, compared with Parthenon. Parthenon accumulated more soluble sugars, for osmotic adjustment, whereas Naxos accumulated proline, which gave the two cultivars differing nutritional characteristics. The total glucosinolates (GSLs) content was not affected by salinity in Parthenon while it decreased significantly in Naxos as a consequence of the decrease in the indole GSL. However, Naxos accumulated more aliphatic GSLs under salt stress than Parthenon, which confers on this cultivar a greater nutritional value when cultivated under salinity.These results suggest that, at distinct salinity levels, each broccoli cultivar adopts a specific strategy, indicating the crucial role of the genetic background on the organoleptic and nutritional properties that each cultivar acquires.

Natural antioxidants in purple sprouting broccoli under Mediterranean climate.

UNLABELLED: Broccoli, (Brassica oleracea var. Italica), is generally recognized as a nutritive food rich in natural antioxidants, including vitamins and phenolics compounds. Phytochemical composition of 3 different purple sprouting broccoli varieties according with their production cycle: EEP (Extra Early), EP (Early), and LP (Late) were determined. The 3 cultivars tested were grown under the same conditions in an experimental field (SE Spain) where they were not previously cultivated since these cultivars are typical of cold, Northern-European areas. EP variety showed greater growth according to the photosynthetic rate and C assimilation. However, it was not possible to obtain inflorescences for variety LP. The health-promoting compounds (vitamin C, phenolic compounds, and glucosinolates) were higher in purple broccolis than in traditionally grown green broccolis and showed differences according to the variety. With respect to the use of broccoli byproducts as source of antioxidants, any variety would be suitable although the leaves of EP variety seems the richest in total phenolic acids, whereas the amount of anthocyanins was higher in LP variety, followed by EP and EEP varieties. Under our experimental conditions, the levels of glucosinolates were higher in purple broccoli than in green cultivars and also higher than other purple broccolis grown under different climate conditions. Therefore, the results reported data for production of the EEP and EP varieties in the Mediterranean climate with potential to obtain vegetables with improved nutritional quality. PRACTICAL APPLICATION: The results of this study reported data of the health-promoting nutrients and natural antioxidants of EEP, EP, and LP purple sprouting broccoli varieties grown under the Mediterranean climate. The vitamin C, phenolic compounds, and glucosinolates in these purple varieties were higher than in traditionally grown green broccolis and other purple broccolis grown under different climate conditions.

Identification and differential induction of the expression of aquaporins by salinity in broccoli plants.

Plant aquaporins belong to a large superfamily of conserved proteins called the major intrinsic proteins (MIPs). There is limited information about the diversity of MIPs and their water transport capacity in broccoli (Brassica oleracea) plants. In this study, the cDNAs of isoforms of Plasma Membrane Intrinsic Proteins (PIPs), a class of aquaporins, from broccoli roots have been partially sequenced. Thus, sequencing experiments led to the identification of eight PIP1 and three PIP2 genes encoding PIPs in B. oleracea plants. The occurrence of different gene products encoding PIPs suggests that they may play different roles in plants. The screening of their expression as well as the expression of two specific PIP2 isoforms (BoPIP2;2 and BoPIP2;3), in different organs and under different salt-stress conditions in two varieties, has helped to unravel the function and the regulation of PIPs in plants. Thus, a high degree of BoPIP2;3 expression in mature leaves suggests that this BoPIP2;3 isoform plays important roles, not only in root water relations but also in the physiology and development of leaves. In addition, differences between gene and protein patterns led us to consider that mRNA synthesis is inhibited by the accumulation of the corresponding encoded protein. Therefore, transcript levels, protein abundance determination and the integrated hydraulic architecture of the roots must be considered in order to interpret the response of broccoli to salinity.

Changes in plasma membrane lipids, aquaporins and proton pump of broccoli roots, as an adaptation mechanism to salinity.

Salinity stress is known to modify the plasma membrane lipid and protein composition of plant cells. In this work, we determined the effects of salt stress on the lipid composition of broccoli root plasma membrane vesicles and investigated how these changes could affect water transport via aquaporins. Brassica oleracea L. var. Italica plants treated with different levels of NaCl (0, 40 or 80mM) showed significant differences in sterol and fatty acid levels. Salinity increased linoleic (18:2) and linolenic (18:3) acids and stigmasterol, but decreased palmitoleic (16:1) and oleic (18:1) acids and sitosterol. Also, the unsaturation index increased with salinity. Salinity increased the expression of aquaporins of the PIP1 and PIP2 subfamilies and the activity of the plasma membrane H(+)-ATPase. However, there was no effect of NaCl on water permeability (P(f)) values of root plasma membrane vesicles, as determined by stopped-flow light scattering. The counteracting changes in lipid composition and aquaporin expression observed in NaCl-treated plants could allow to maintain the membrane permeability to water and a higher H(+)-ATPase activity, thereby helping to reduce partially the Na(+) concentration in the cytoplasm of the cell while maintaining water uptake via cell-to-cell pathways. We propose that the modification of lipid composition could affect membrane stability and the abundance or activity of plasma membrane proteins such as aquaporins or H(+)-ATPase. This would provide a mechanism for controlling water permeability and for acclimation to salinity stress.

Growing hardier crops for better health: Salinity tolerance and the nutritional value of broccoli.

To evaluate the variations in the nutritional components of a broccoli cultivar under saline stress, two different NaCl concentrations (40 and 80 mM) were assayed. Glucosinolates, phenolic compounds, and ascorbic and dehydroascorbic acids (vitamin C) were analyzed by HPLC, and mineral composition was determined by ICP spectrophotometry. Qualitative differences were observed for several bioactive compounds depending on the plant organ and the intensity of the salt stress. Glucosinolate content showed the most significant increase in the florets; phenolic compounds also increased in the florets, whereas no variation in the vitamin C content was observed as a result of the saline treatments. The mineral composition of the edible parts of the inflorescences remained within the range of the recommended values for human consumption. Overall, the nutritional quality of the edible florets of broccoli was improved under moderate saline stress.

Boric acid and salinity effects on maize roots. Response of aquaporins ZmPIP1 and ZmPIP2, and plasma membrane H+-ATPase, in relation to water and nutrient uptake.

Under saline conditions, an optimal cell water balance, possibly mediated by aquaporins, is important to maintain the whole-plant water status. Furthermore, excessive accumulation of boric acid in the soil solution can be observed in saline soils. In this work, the interaction between salinity and excess boron with respect to the root hydraulic conductance (L(0)), abundance of aquaporins (ZmPIP1 and ZmPIP2), ATPase activity and root sap nutrient content, in the highly boron- and salt-tolerant Zea mays L. cv. amylacea, was evaluated. A downregulation of root ZmPIP1 and ZmPIP2 aquaporin contents were observed in NaCl-treated plants in agreement with the L(0) measurements. However, in the H3BO3-treated plants differences in the ZmPIP1 and ZmPIP2 abundance were observed. The ATPase activity was related directly to the amount of ATPase protein and Na+ concentration in the roots, for which an increase in NaCl- and H3BO3+ NaCl-treated plants was observed with respect to untreated and H3BO3-treated plants. Although nutrient imbalance may result from the effect of salinity or H3BO3 alone, an ameliorative effect was observed when both treatments were applied together. In conclusion, our results suggest that under salt stress, the activity of specific membrane components can be influenced directly by boric acid, regulating the functions of certain aquaporin isoforms and ATPase as possible components of the salinity tolerance mechanism.