Proline Accumulation Research Articles

Comprehensive Analysis of GH3 Gene Family in Potato and Functional Characterization of StGH3.3 under Drought Stress.

As an important hormone response gene, Gretchen Hagen 3 (GH3) maintains hormonal homeostasis by conjugating excess auxin with amino acids during plant stress-related signaling pathways. GH3 genes have been characterized in many plant species, but they are rarely reported in potato. Here, 19 StGH3 genes were isolated and characterized. Phylogenetic analysis indicated that StGH3s were divided into two categories (group I and group III). Analyses of gene structure and motif composition showed that the members of a specific StGH3 subfamily are relatively conserved. Collinearity analysis of StGH3 genes in potato and other plants laid a foundation for further exploring the evolutionary characteristics of the StGH3 genes. Promoter analysis showed that most StGH3 promoters contained hormone and abiotic stress response elements. Multiple transcriptome studies indicated that some StGH3 genes were responsive to ABA, water deficits, and salt treatments. Moreover, qRT-PCR analysis indicated that StGH3 genes could be induced by phytohormones (ABA, SA, and MeJA) and abiotic stresses (water deficit, high salt, and low temperature), although with different patterns. Furthermore, transgenic tobacco with transient overexpression of the StGH3.3 gene showed positive regulation in response to water deficits by increasing proline accumulation and reducing the leaf water loss rate. These results suggested that StGH3 genes may be involved in the response to abiotic stress through hormonal signal pathways. Overall, this study provides useful insights into the evolution and function of StGH3s and lays a foundation for further study on the molecular mechanisms of StGH3s in the regulation of potato drought resistance.

Melatonin mobilizes the metabolism of sugars, ascorbic acid and amino acids to cope with chilling injury in postharvest pear fruit

Chilling injury manifesting as internal browning is an irreversible physiological disorder in cold-stored ‘Yali’ pear fruit, which seriously restricts postharvest handling and commercialization of pear fruit. This study investigated the impact of melatonin (MN) treatment on chilling injury and the metabolism of sugars, ascorbic acid (AsA), proline, and γ-aminobutyric acid (GABA) during chilling injury development in ‘Yali’ pears. The findings revealed that MN-treated pear fruit exhibited considerably improved tolerance to chilling stress compared with untreated control fruit. MN application augmented proline accumulation, likely owing to increased activities and transcriptional concentrations of Δ1-pyrroline-5-carboxylate synthase and ornithine-δ-aminotransferase as well as diminished activity and transcriptional level of proline dehydrogenase. MN immersion increased enzyme activities and gene expression related to the GABA shunt pathway, leading to increased GABA concentrations in cold-stored pear fruit. Furthermore, MN treatment elevated AsA concentrations in the fruit, exerting protective effects against cell membrane damage and mitigating oxidative stress damage caused by chilling. Compared with the control group, MN-treated fruit exhibited reduced neutral invertase enzyme activity and gene expression. Additionally, MN treatment increased both sucrose-phosphate synthase and sucrose synthase activities and gene expression in pear fruit. These observations indicated that the enhanced chilling tolerance of ‘Yali’ pear fruit following MN treatment may be associated with the regulation of proline, GABA, AsA, and soluble sugars metabolism.

Unveiling novel insights into haloarchaea (Halolamina pelagica CDK2) for alleviation of drought stress in wheat.

Plant growth promoting microorganisms have various implications for plant growth and drought stress alleviation; however, the roles of archaea have not been explored in detail. Herein, present study was aimed for elucidating potential of haloarchaea (Halolamina pelagica CDK2) on plant growth under drought stress. Results showed that haloarchaea inoculated wheat plants exhibited significant improvement in total chlorophyll (100%) and relative water content (30.66%) compared to the uninoculated water-stressed control (30% FC). The total root length (2.20-fold), projected area (1.60-fold), surface area (1.52-fold), number of root tips (3.03-fold), number of forks (2.76-fold) and number of links (1.45-fold) were significantly higher in the inoculated plants than in the uninoculated water stressed control. Additionally, the haloarchaea inoculation resulted in increased sugar (1.50-fold), protein (2.40-fold) and activity of antioxidant enzymes such as superoxide dismutase (1.93- fold), ascorbate peroxidase (1.58-fold), catalase (2.30-fold), peroxidase (1.77-fold) and glutathione reductase (4.70-fold), while reducing the accumulation of proline (46.45%), glycine betaine (35.36%), lipid peroxidation (50%), peroxide and superoxide radicals in wheat leaves under water stress. Furthermore, the inoculation of haloarchaea significantly enhanced the expression of stress-responsive genes (DHN, DREB, L15, and TaABA-8OH) and wheat vegetative growth under drought stress over the uninoculated water stressed control. These results provide novel insights into the plant-archaea interaction for plant growth and stress tolerance in wheat and pave the way for future research in this area.

Rhizoactinobacteria Enhance Growth and Antioxidant Activity in Thai Jasmine Rice (Oryza sativa) KDML105 Seedlings under Salt Stress.

Salinity is one of the most devastating abiotic stresses hampering the growth and production of rice. Nine indole-3-acetic acid (IAA)-producing salt-tolerant plant-growth-promoting rhizobacteria (ST-PGPR) were inoculated into Thai jasmine rice (Oryza sativa L.) variety Khao Dawk Mali 105 (KDML105) seedlings grown under different concentrations of NaCl (0, 50, 100, and 150 mM). The ST-PGPR strains significantly promoted the growth parameters, chlorophyll content, nutrient uptake (N, P, K, Ca, and Mg), antioxidant activity, and proline accumulation in the seedlings under both normal and saline conditions compared to the respective controls. The K+/Na+ ratio of the inoculated seedlings was much higher than that of the controls, indicating greater salt tolerance. The most salt-tolerant and IAA-producing strain, Sinomonas sp. ORF15-23, yielded the highest values for all the parameters, particularly at 50 mM NaCl. The percentage increases in these parameters relative to the controls ranged from >90% to 306%. Therefore, Sinomonas sp. ORF15-23 was considered a promising ST-PGPR to be developed as a bioinoculant for enhancing the growth, salt tolerance, and aroma of KDML105 rice in salt-affected areas. Environmentally friendly technologies such as ST-PGPR bioinoculants could also support the sustainability of KDML105 geographical indication (GI) products. However, the efficiency of Sinomonas sp. ORF15-23 should be evaluated under field conditions for its effect on rice nutrient uptake and growth, including the 2AP level.

Does Sodium Nitroprusside Alleviate Water Deficit Stress in Impatiens walleriana Shoots Grown In Vitro?

Impatiens walleriana is a decorative horticultural plant species. Commercial production requires that the plants be brought to market, often accompanied by reduced water content during transport. Drought significantly affects metabolic processes in plants. The effects of polyethylene glycol (PEG)-induced water deficit on shoots of I. walleriana were investigated using different mechanisms at the biochemical level. In addition, the potential water deficit-ameliorating effect of sodium nitroprusside (SNP) was tested. Shoots of I. walleriana were initially grown on MS media supplemented with SNP (50, 100 and 250 μM). After pre-treatments, shoots were further transferred to media supplemented with PEG8000 (3%) and/or SNP (50, 100 and 250 μM). Water deficit conditions increased proline, photosynthetic pigments, malondialdehyde (MDA), H2O2, total phenolic content and antioxidant activity. In addition, PEG-induced water deficit increased superoxide dismutase (SOD) and peroxidase (POX) activities but decreased catalase (CAT) activity. SNP did not significantly affect photosynthetic pigments and total phenolic content but increased proline accumulation, MDA and H2O2 content, especially when applied simultaneously with PEG. Moreover, none of the investigated SNP pretreatments significantly altered the activities of SOD, POX, and CAT in I. walleriana. The results indicate that exogenous application of SNP effectively alleviated water deficit stress in shoots of I. walleriana grown in vitro.

Proline, Cysteine and Branched-Chain Amino Acids in Abiotic Stress Response of Land Plants and Microalgae.

Proteinogenic amino acids are the building blocks of protein, and plants synthesize all of them. In addition to their importance in plant growth and development, growing evidence underlines the central role played by amino acids and their derivatives in regulating several pathways involved in biotic and abiotic stress responses. In the present review, we illustrate (i) the role of amino acids as an energy source capable of replacing sugars as electron donors to the mitochondrial electron transport chain and (ii) the role of amino acids as precursors of osmolytes as well as (iii) precursors of secondary metabolites. Among the amino acids involved in drought stress response, proline and cysteine play a special role. Besides the large proline accumulation occurring in response to drought stress, proline can export reducing equivalents to sink tissues and organs, and the production of H2S deriving from the metabolism of cysteine can mediate post-translational modifications that target protein cysteines themselves. Although our general understanding of microalgae stress physiology is still fragmentary, a general overview of how unicellular photosynthetic organisms deal with salt stress is also provided because of the growing interest in microalgae in applied sciences.

The Effect of One-Year Seed Spaceflight Storage on Yield, Biochemical and Mineral Characteristics of Mature Leafy Vegetables Belonging to Brassicaceae, Apiaceae and Asteraceae Families

Spaceflight is known to produce genetic changes in seeds, usually accelerating aging, though species and varietal differences have been poorly investigated. Comparisons were carried out in terms of yield, biochemical characteristics and mineral composition between mature plants grown from seeds subjected to a one-year spaceflight, belonging to Brassicaceae (Brassica juncea and Eruca sativa), Apiaceae (Anethus graveolens, and Coriandrum sativum), and Asteraceae (Lactuca sativa, six cultivars) families, and non-treated control. Among the studied species, only Brassica juncea and Eruca sativa demonstrated a growth stimulation effect caused by seed spaceflight, while significant growth inhibition was recorded in Apiaceae plants and three cultivars of Lactuca sativa L. No differences in the total antioxidant activity (AOA), polyphenol and ascorbic acid content were detected between ‘space-treated’ and control plants. On the contrary, significant decrease in proline accumulation and increase in malonic dialdehyde and photosynthetic pigments levels were shown by Brassicaceae species. The effect of long-term seed spaceflight on the mineral composition of mature plants was reflected in the inhibition of accumulation of all 24 elements analyzed in Apiaceae plants, except for Se, whose concentration was higher in all ‘space-treated’ plants compared to the control. Spaceflight seed storage increased V levels in lettuce and decreased Na accumulation in all the investigated species. The results reveal species-dependent changes in the accumulation of macro-, micro- and toxic elements in Apiaceae, Brassicacea, and Asteraceae representatives due to spaceflight seed storage. The detected differences in plant elemental composition between ‘space’ treatment and control partly explain the corresponding yield gap and suggest a relationship between mineral status and adaptability. The highest beneficial effect of spaceflight seed storage on yield was recorded in Eruca sativa cultivar, Rusalochka.

Fungal Elicitation Enhances Vincristine and Vinblastine Yield in the Embryogenic Tissues of Catharanthus roseus.

Fungal elicitation could improve the secondary metabolite contents of in vitro cultures. Herein, we report the effect of Fusarium oxysporum on vinblastine and vincristine alkaloid yields in Catharanthus roseus embryos. The study revealed increased yields of vinblastine and vincristine in Catharanthus tissues. Different concentrations, i.e., 0.05% (T1), 0.15% (T2), 0.25% (T3), and 0.35% (T4), of an F. oxysporum extract were applied to a solid MS medium in addition to a control (T0). Embryogenic calli were formed from the hypocotyl explants of germinating seedlings, and the tissues were exposed to Fusarium extract elicitation. The administration of the F. oxysporum extract improved the growth of the callus biomass, which later differentiated into embryos, and the maximum induction of somatic embryos was noted T2 concentration (102.69/callus mass). A biochemical analysis revealed extra accumulations of sugar, protein, and proline in the fungus-elicitated cultivating tissues. The somatic embryos germinated into plantlets on full-strength MS medium supplemented with 2.24 µM of BA. The germination rate of the embryos and the shoot and root lengths of the embryos were high at low doses of the Fusarium treatment. The yields of vinblastine and vincristine were measured in different treated tissues via high-pressure thin-layer chromatography (HPTLC). The yield of vinblastine was high in mature (45-day old) embryos (1.229 µg g-1 dry weight), which were further enriched (1.267 µg g-1 dry weight) via the F. oxysporum-elicitated treatment, especially at the T2 concentration. Compared to vinblastine, the vincristine content was low, with a maximum of 0.307 µg g-1 dry weight following the addition of the F. oxysporum treatment. The highest and increased yields of vinblastine and vincristine, 7.88 and 15.50%, were noted in F. oxysporum-amended tissues. The maturated and germinating somatic embryos had high levels of SOD activity, and upon the addition of the fungal extracts, the enzyme's activity was further elevated, indicating that the tissues experienced cellular stress which yielded increased levels of vinblastine and vincristine following the T2/T1 treatments. The improvement in the yields of these alkaloids could augment cancer healthcare treatments, making them easy, accessible, and inexpensive.

Mathematical Estimation of Endogenous Proline as a Bioindicator to Regulate the Stress of Trivalent Chromium on Rice Plants Grown in Different Nitrogenous Conditions.

The accumulation of proline impacts the defense mechanisms of plants against the harmful effects of adverse environmental conditions; however, its concentration in plants is associated with the metabolism of N. Therefore, the effects of exogenous organic [glutamate (Glu)/arginine (Arg)] and inorganic [nitrate (NO3-)/ammonium (NH4+)] N on the accumulation of proline (Pro) in rice plants under trivalent chromium [Cr(III)] stress were studied through using the mass balance matrix model (MBMM). Application of 'NH4+' showed the largest contribution to the Pro content in rice shoots under different concentrations of Cr(III), followed by 'NO3-', 'Arg', and 'Glu' applications. On the other hand, 'Arg' application displayed the largest contribution to the Pro content in roots under Cr(III) stress, followed by 'NH4+', 'Glu', and 'NO3-' applications. The combined application of 'NH4++Arg' showed the greatest contribution to the Pro content in both roots and shoots of Cr(III)-treated rice seedlings, while the application of 'NO3-+Glu' showed the least contribution to the Pro content in rice seedlings. The current study indicated that the endogenous level of Pro in rice seedlings is quite sensitive to Cr(III) stress under different N sources, and the mathematical modeling showed a reliable result while estimating the relationship between Pro content and N source application.

Expression analysis of transcription factor (CBF/DREB) gene and biochemical response of Cannabis sativa to cadmium toxicity and foliar application of molybdenum

Plants respond to heavy metals stress by the activation of stress responsive genes to establish biochemical defense mechanisms against the stress. We have investigated the molecular and biochemical response of Cannabis sativa to cadmium (Cd) stress in the presence of molybdenum (Mo) foliar treatments. For this purpose, C. sativa plants were allowed to grow in pots containing Cd polluted soil, for two month duration. Aqueous solutions of ammonium molybdate pentahydrate (0.5, 1.0 and 2.0 ppm) were foliarly sprayed on the plants, at two weeks intervals. Various parameters were inter-correlated i.e., Plant biomass, Cd phyto-accumulation, transcript level/expression of CBF/DREB genes, concentrations of free proline, polyphenolics, and chlorophyll contents. Phenolic compounds were analyzed by High Performance Liquid Chromatography Diode Array Detector (HPLC-DAD) and Cd contents were analyzed by Atomic Absorption Spectrophotometer. Biomass and chlorophyll contents decreased while the concentrations of free proline and polyphenolics increased under Cd stress. Dry biomass of the all the plant parts (roots (1.87 ± 0.22 g), stem (3.28 ± 0.39 g) and leaves (3.54 ± 0.87 g) and free proline in roots (69.00 ± 8.28 µg/g) and leaves (40.56 ± 4.87 µg/g) were most significantly increased with foliar spray of 2.00 ppm Mo. Nineteen (19) different polyphenolic compounds were identified and quantified in leaves and most of them were highly increased in concentration under Cd stress. The highest concentration was noted in Caffeoyl tyramine (1111 µg/g) in plants treated with 2.00 ppm Mo. Transcript level of CBF/DREB genes in control plants were less as compared to Mo treated plants, where a high increase in transcript level of these genes were found. Expression of CBF /DREB genes showed significant positive correlations with Cd accumulation (R2= 0.751) and concentrations of free proline (R2 = 0.62) and polyphenolics (R2 = 0.65) in leaves. The results suggested that Mo increased the expression of CBF/DREB genes and subsequently the concentration of phenolic compounds and free proline to combat plant against the toxicity of high concentration of Cd on plants.

Proline concentrations in seedlings of woody plants change with drought stress duration and are mediated by seed characteristics: a meta-analysis

Proline accumulation represents one of mechanisms used by plants to prevent the adverse consequences of water stress. The effects of increased proline levels in response to drought differ among species. Trees are exposed to the long-term effects of climate change. The reproductive success of species in a specific environment depends on the functional trait of tree seeds. We conducted a meta-analysis to evaluate the effects of drought stress on the proline concentrations in seedling leaf tissues of woody plant species and their relationships to drought duration, seed mass, seed category and coniferous/deciduous classification. Drought duration exhibited a nonlinear effect on proline accumulations. The drought effect on proline accumulations is greater for deciduous than for coniferous species and is higher for orthodox seed species than for recalcitrant. The seedlings of large-seeded species showed greater effect sizes than those of small-seeded species. Our results suggest that there is an optimum level at which proline accumulations under the influence of drought are the highest. A link between seed functional traits, as well as the coniferous/deciduous classification, and proline concentrations in tree seedlings during water stress were determined for the first time. Proline may help to identify high-quality seeds of trees used for reforestation.

Twice-split phosphorus application alleviates low-temperature impacts on wheat by improved spikelet development and setting

Extreme low-temperature incidents have become more frequent and severe as climate change intensifies. In Huang-Huai-Hai wheat growing area of China, the late spring coldness occurring at the jointing-booting stage (the anther interval stage) has resulted in significant yield losses of winter wheat. This study attempts to develop an economical, feasible, and efficient cultivation technique for improving the low-temperature (LT) resistance of wheat by exploring the effects of twice-split phosphorus application (TSPA) on wheat antioxidant characteristics and carbon and nitrogen metabolism physiology under LT treatment at the anther interval stage using Yannong 19 as the experimental material. The treatments consisted of traditional phosphorus application and TSPA, followed by a –4°C LT treatment and natural temperature (NT) control at the anther interval stage. Our analyses showed that, compared with the traditional application, the TSPA increased the net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) of leaves and reduced the intercellular carbon dioxide concentration (Ci). The activity of carbon and nitrogen metabolism enzymes in the young wheat spikes was also increased by the TSPA, which promoted the accumulation of soluble sugar (SS), sucrose (SUC), soluble protein (SP), and proline (Pro) in young wheat spike and reduced the toxicity of malondialdehyde (MDA). Due to the improved organic nutrition for reproductive development, the young wheat spikes exhibited enhanced LT resistance, which reduced the sterile spikelet number (SSN) per spike by 11.8% and increased the spikelet setting rate (SSR) and final yield by 6.0 and 8.4%, respectively, compared to the traditional application. The positive effects of split phosphorus application became more pronounced when the LT treatment was prolonged.

Metabolic and transcriptomic profiling during wheat seed development under progressive drought conditions

Globally, bread wheat (Triticum aestivum) is one of the most important staple foods; when exposed to drought, wheat yields decline. Although much research has been performed to generate higher yield wheat cultivars, there have been few studies on improving end-product quality under drought stress, even though wheat is processed into flour to produce so many foods, such as bread, noodles, pancakes, cakes, and cookies. Recently, wheat cultivation has been affected by severe drought caused by global climate change. In previous studies, seed shrinkage was observed in wheat exposed to continuous drought stress during seed development. In this study, we investigated how progressive drought stress affected seed development by metabolomic and transcriptomic analyses. Metabolite profiling revealed the drought-sensitive line reduced accumulation of proline and sugar compared with the water-saving, drought-tolerant transgenic line overexpressing the abscisic acid receptor TaPYL4 under drought conditions in spikelets with developing seeds. Meanwhile, the expressions of genes involved in translation, starch biosynthesis, and proline and arginine biosynthesis was downregulated in the drought-sensitive line. These findings suggest that seed shrinkage, exemplifying a deficiency in endosperm, arose from the hindered biosynthesis of crucial components including seed storage proteins, starch, amino acids, and sugars, ultimately leading to their inadequate accumulation within spikelets. Water-saving drought tolerant traits of wheat would aid in supporting seed formation under drought conditions.

Hydrogen sulfide counteract copper induced inhibition of photosynthetic performance through altered proline metabolism and enhanced antioxidants in Cucumis sativus

It has been recently discovered that hydrogen sulfide (H2S) is a gaseous substance responsible for controlling the growth and metabolism of plants. The present study was designed to explore the ameliorative effect of H2S on Cucumis sativus plants under increasing levels of copper. This study revealed that varying concentrations of H2S improved seed germination in a concentration-dependent manner. Furthermore, exogenous application of H2S to copper stressed plants accelerated photosynthetic performance, antioxidant system, proline accumulation, and maintained copper uptake that was reflected in improved growth parameters. In addition to this, H2S also curbed oxidative stress by lowering lipid peroxidation, H2O2 content, and electrolyte leakage. H2S enhanced activities of the antioxidant system, and proline metabolism leading to decontamination of cucumber plants under lethal dose of copper. This work offers an understanding that exogenously sourced H2S could be engaged as a significant biochemical approach in alleviating copper-induced toxicity in cucumber plants.

Vermicompost Improves Tomato Yield and Quality by Promoting Carbohydrate Transport to Fruit under Salt Stress

To explore the effect of vermicompost on the yield and quality of tomato cultivated in salty soil, we investigated the soil chemical properties, the yield, vitamin C, organic acid, soluble solids, and nitrate of fruit, photosynthesis, and carbohydrates of plants grown under various salt levels applied with the application of either commercial chemical fertilizers, cow manure, or vermicompost. Results showed that the tomato yield was not increased from the chemical fertilizer application, while there was an increase from the cow manure and vermicompost (increased 31.7% and 65.2%, respectively) under salt stress. Compared to no salt stress, the contents of vitamin C, organic acid, soluble solids, and nitrate increased 26.55%, 40.59%, 46.31%, and 35.08%, respectively, under salt stress (2 g NaCl·kg−1 soil). Compared with the Control, the application of chemical fertilizers failed to improve the sugar/acid ratio but increased nitrate content, while cow manure and vermicompost improved the sugar/acid ratio by 42.0% and 73.1%, respectively. Particularly, vermicompost increased vitamin C and reduced nitrate to the greatest extent among the different fertilizer treatments. The decrease in sodium (Na+) in the roots and leaves, increase in carbohydrates in fruit, and photosynthetic efficiency of leaves imply an amendment effect of vermicompost on salt stress. Moreover, vermicompost also facilitated the transit of carbohydrates from leaves to fruits by increasing the accumulation of nitrogen, phosphate, and potassium in fruits, leaves, and roots, while decreasing proline and soluble protein accumulation in leaves and roots. In conclusion, vermicompost could alleviate the adverse effect of salt stress and improve tomato yield and fruit quality by improving the photosynthetic capacity and promoting carbohydrate transport to fruit. The findings give a new perspective on the beneficial effect of vermicompost on tomato yield and quality.

Responses of salicylic acid encapsulation on growth, photosynthetic attributes and ROS scavenging system in Lactuca sativa exposed to polycyclic aromatic hydrocarbon pollution

Salicylic acid (SA) is a phytohormone that plays a key role in the regulation of the defense response against environmental variables in plants, and it provides increased yield and stress tolerance when exogenously applied to plants as a growth regulator. The role of SA-mediated signals in abiotic stress tolerance varies according to the species, stressor, application method, and dose. This study investigated the effects of salicylic acid (SA, 0.1 mg ml−1) or β-cyclodextrin encapsulated salicylic acid (e-SA, 0.1 mg ml−1) treatments on growth parameters, gas exchange, photosynthesis efficiency, and antioxidant capacity in lettuce seedlings exposed to polycyclic aromatic hydrocarbon pollution. Fluorene (FLN, 100 mg L−1) contamination resulted in a 27% growth rate and a 14% water content reduction in lettuce leaves. Significant suppressions of stomatal conductance, carbon assimilation, and PSII photochemistry were detected in plants under stress. FLN + SA and FLN + e-SA treatments regulated plant-water relations by stimulating proline accumulation and relieving stomatal limitations. As indicated by the high Fv/Fm ratio, photosynthesis efficiency was recovered in FLN + SA and FLN + e-SA group plants. FLN stress caused high oxidative stress in lettuce leaves and increased lipid peroxidation level by 40%. However, especially e-SA application to plants under stress, increased SOD activity by 3-fold and CAT activity by 80% and was successful in preventing H2O2 accumulation and lipid peroxidation. Both SA and e-SA treatments partially activated the AsA-GSH cycle. As a result, direct SA application was effective in mitigating stress-induced physiological limitations with high SA accumulation in the tissues, while encapsulated SA treatment was more effective in regulating photosynthetic and biochemical reactions, alleviating oxidative damage by activating the antioxidant defense, and promoting growth under stress with moderate SA accumulation.

Role of Humic Acid on Inducing Salt Tolerance of Ivy Geranium (Pelargonium peltatum L.) Plants

Saline water is used in floriculture as an alternative to freshwater in arid regions such as Saudi Arabia (SA). However, salt stress considerably accelerates serious physio-biochemical changes associated with a decline in plant establishment. Recently, humic acid (HA) foliar spraying has induced plant stress tolerance in the era of climate change; however, its precise roles in the floriculture industry within saline conditions are not yet well documented. A factorial pot experiment throughout the 2022/2023 season was conducted in the Nursery of Sustainability and Environmental Developmental Department, King Saud University, Riyadh, SA, to evaluate the potential effects of HA (0, 500, 1000 and 2000 mg/L) on growth, flowering and some physiological characteristics of Ivy geranium (Pelargoniumpeltatum) plants irrigated with saline water (230 “control”, 2000 and 4000 mg/L NaCl). Irrigation with saline water markedly inhibited plant growth, flowering attributes, the chlorophyll index, as well as macro and micro-nutrient levels, but increased the content of iron, sodium and proline in plant shoots relative to plants irrigated with non-salinized water. However, HA mainly at 1000 mg/L significantly improved plant growth, flowering capacity, nutrient status, proline accumulation and chlorophyll index under salinized or non-salinized irrigation water. Additionally, spraying of HA concentrations (500, 1000 and 2000 mg/L) under normal or salinity conditions significantly increased shoot sodium content relative to non-treated plants under such salinity levels. Our findings highlight the significance of HA concentrations (500, 1000 and 2000 mg/L) in improving the salt tolerance of Ivy geranium. Within the scarcity of irrigation water, it is recommended to irrigate Ivy geranium with saline water up to 4000 mg/L NaCl associated with spraying HA concentrations in special 1000 mg/L.

Loss of attachment promotes proline accumulation and excretion in cancer cells.

Previous studies have revealed a role for proline metabolism in supporting cancer development and metastasis. In this study, we show that many cancer cells respond to loss of attachment by accumulating and secreting proline. Detached cells display reduced proliferation accompanied by a general decrease in overall protein production and de novo amino acid synthesis compared to attached cells. However, proline synthesis was maintained under detached conditions. Furthermore, while overall proline incorporation into proteins was lower in detached cells compared to other amino acids, there was an increased production of the proline-rich protein collagen. The increased excretion of proline from detached cells was also shown to be used by macrophages, an abundant and important component of the tumor microenvironment. Our study suggests that detachment induced accumulation and secretion of proline may contribute to tumor progression by supporting increased production of extracellular matrix and providing proline to surrounding stromal cells.

Proline Metabolism Process and Antioxidant Potential of Lycium ruthenicum Murr. in Response to NaCl Treatments.

Salinity influences the level of antioxidants and proline content, which are both involved in the regulation of stress responses in plants. To examine the interplay between the antioxidant system and proline metabolism in plant stress acclimation, explants of Lycium ruthenicum were subjected to NaCl treatments, and the growth characteristics, antioxidant enzyme activities, proline accumulation, and metabolic enzyme content were analyzed. The results revealed that NaCl concentrations between 50 to 150 mM have a positive effect on the growth of L. ruthenicum explants. Increasing NaCl concentrations elevated the activities of superoxide dismutase (SOD) and catalase (CAT), while hydrogen peroxide (H2O2) content was inhibited, suggesting that the elevated antioxidants play a central protective role in superoxide anion (O2•-) and H2O2 scavenging processes in response to NaCl treatments. Also, high proline levels also protect antioxidant enzyme machinery, thus protecting the plants from oxidative damage and enhancing osmotic adjustment. Increasing levels of pyrroline-5-carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR), and ornithine-δ-aminotransferase (δ-OAT) were observed, resulting in elevated level of proline. In addition, the expression levels of LrP5CS1, -2, -3, LrOAT-1, and -2 were promoted in NaCl treatments. According to the combined analysis of metabolic enzyme activities and their relative expression, it is confirmed that the glutamate (Glu) pathway is activated in L. ruthenicum faced with different levels of NaCl concentrations. However, Glu supplied by δ-OAT is fed back into the main pathway for proline metabolism.

ABA-dependent suberization and aquaporin activity in rice (Oryza sativa L.) root under different water potentials.

Drought is one of the most stressful environments limiting crop growth and yield throughout the world. Therefore, most efforts have been made to document drought-derived genetic and physiological responses and to find better ways to improve drought tolerance. The interaction among them is unclear and/or less investigated. Therefore, the current study is to find a clue of metabolic connectivity among them in rice root experiencing different levels of drought condition. We selected 19 genes directly involved in abscisic acid (ABA) metabolism (6), suberization (6), and aquaporins (AQPs) activity (7) and analyzed the relatively quantitative gene expression using qRT-PCR from rice roots. In addition, we also analyzed proline, chlorophyll, and fatty acids and observed cross-sectional root structure (aerenchyma) and suberin lamella deposition in the endodermis. All drought conditions resulted in an obvious development of aerenchyma and two- to fourfold greater accumulation of proline. The limited water supply (-1.0 and -1.5 MPa) significantly increased gene expression (ABA metabolism, suberization, and AQPs) and developed greater layer of suberin lamella in root endodermis. In addition, the ratio of the unsaturated to the saturated fatty acids was increased, which could be considered as an adjusted cell permeability. Interestingly, these metabolic adaptations were an exception with a severe drought condition (hygroscopic coefficient, -3.1 MPa). Accordingly, we concluded that the drought-tolerant mechanism in rice roots is sophisticatedly regulated until permanent wilting point (-1.5 MPa), and ABA metabolism, suberization, and AQPs activity might be independent and/or concurrent process as a survival strategy against drought.