Exogenous Proline Research Articles

RmZAT10, a novel Cys2/His2 zinc finger transcription factor of Rosa multiflora, functions in cold tolerance through modulation of proline biosynthesis and ROS homeostasis

The Cys2/His2-type (C2H2) zinc finger transcription factor (TF) consists of a significant gene family that has an effect on development process regulation and a wide range of stress responses, whereas the roles and regulatory pathways of the majority of C2H2-type zinc finger TFs remain unclear. Here, we characterized a C2H2-type zinc finger TF ( RmZAT10 ) from Rosa multiflora . RmZAT10 was mainly expressed in leaves and located in the nucleus. RmZAT10 was rapidly up-regulated during dehydration, cold as well as ABA treatment, with the maximal induction under cold stress. RmZAT10 overexpression facilitated the cold tolerance of tobacco, while gene silencing caused by virus-induced gene silencing (VIGS) of RmZAT10 within R.multiflora led to elevated cold sensitivity. Transgenic tobacco accumulated a larger amount of proline, consistent with elevated the expression level of P5CS (Δ -1-pyrroline-5-carboxylate synthetase ). Nevertheless, the VIGS plant achieved the opposing trend. The treatment using 24-epi-brassinolide caused transgenic tobacco plants more sensitive to cold, while exogenous proline partially restored cold tolerance of the VIGS plants. In addition, RmZAT10 could bind specifically to and activate the promoter of RmP5CS. The above results revealed the role played by RmZAT10 in cold tolerance through the modulation of proline biosynthesis and ROS homeostasis. • RmZAT10 is induced by cold, dehydration and ABA treatments, especially prominent under cold stress. • RmZAT10 overexpression enhanced the cold tolerance in tobacco, while VIGS of RmZAT10 increased cold susceptibility. • RmZAT10 played a role in cold tolerance through the modulation of proline biosynthesis and ROS homeostasis.

Contribution of Exogenous Proline to Abiotic Stresses Tolerance in Plants: A Review.

Abiotic stresses are the major environmental factors that play a significant role in decreasing plant yield and production potential by influencing physiological, biochemical, and molecular processes. Abiotic stresses and global population growth have prompted scientists to use beneficial strategies to ensure food security. The use of organic compounds to improve tolerance to abiotic stresses has been considered for many years. For example, the application of potential external osmotic protective compounds such as proline is one of the approaches to counteract the adverse effects of abiotic stresses on plants. Proline level increases in plants in response to environmental stress. Proline accumulation is not just a signal of tension. Rather, according to research discussed in this article, this biomolecule improves plant resistance to abiotic stress by rising photosynthesis, enzymatic and non-enzymatic antioxidant activity, regulating osmolyte concentration, and sodium and potassium homeostasis. In this review, we discuss the biosynthesis, sensing, signaling, and transport of proline and its role in the development of various plant tissues, including seeds, floral components, and vegetative tissues. Further, the impacts of exogenous proline utilization under various non-living stresses such as drought, salinity, high and low temperatures, and heavy metals have been extensively studied. Numerous various studies have shown that exogenous proline can improve plant growth, yield, and stress tolerance under adverse environmental factors.

The Effect of Exogenous Proline and Glycine Betaine on Phyto-biochemical Responses of Salt-stressed Basil Plants

The Effect of Exogenous Proline and Glycine Betaine on Phyto-biochemical Responses of Salt-stressed Basil Plants

Exogenous Proline Alleviated Low Temperature Stress in Maize Embryos by Optimizing Seed Germination, Inner Proline Metabolism, Respiratory Metabolism and a Hormone Regulation Mechanism

Proline (Pro) is not only an important osmotic adjustment substance, but it also plays an important role in regulating plant abiotic stress resistance. The maize varieties, Xinxin 2 (low temperature insensitive) and Damin 3307 (low temperature sensitive), were chosen as materials, setting a normal temperature for germination (22 °C/10 °C, 9d), low temperature germination (4 °C/4 °C, 5d) and normal temperature recovery (22 °C/10 °C, 4d), combined with a proline (15 mmol·L−1) soaking treatment, to reveal the seed germination and regulation mechanism in maize embryos. The results showed that proline significantly improved the germination potential, germination rate, germination index and vigor index of seeds under low temperature stress, increasing the length of the coleoptile and radicle, increasing the dry and fresh weight of young buds (coleoptile + radicle), and increasing the activity of α-amylase. Proline enhanced the activities of Δ1-pyrroline-5-carboxylic acid synthetase (P5CS) and ornithine aminotransferase (OAT) in maize embryos under low temperature stress, enhanced the proline synthesis pathways, and further enhanced proline accumulation. Proline induced the activity of proline dehydrogenase (ProDH) in the early stage of low temperature stress and stress relief. Under low temperature stress, the activities of hexokinase (HXK), phosphofructokinase (PFK), pyruvate kinase (PK), isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) and glucose-6-phosphate dehydrogenase (G-6-PDH and 6-P-GDH) in maize embryos were decreased, resulting in a decrease in the glycolysis (EMP) pathway, tricarboxylic acid (TCA) cycle and pentose phosphate pathway (PPP). Proline alleviated the inhibition of key enzyme activities of the EMP pathway, TCA cycle and PPP of maize embryos under low temperature stress, increased the activities of cytochrome oxidase (COX) and alternative oxidase (AOX), increased the ATP content, alleviated the inhibition of low temperature stress on main cytochrome pathway activity (ρVcyt), while further increasing the total respiratory activity (Vt) and the actual operational activity of the alternative pathway (ρValt) during seed germination at the initial stage of low temperature stress, as well as improving the inhibition of the Vt and ρValt in the middle and late stages of low temperature stress. Under low temperature stress, the content of abscisic acid (ABA) increased significantly, while gibberellin (GA), auxin (IAA) and zeatin nucleoside (ZR) decreased significantly. Proline alleviated the decrease in IAA, ZR and GA contents in maize embryos under low temperature stress, reduced the increase in the ABA content, and reduced the inhibition of low temperature on seed germination.

Exogenous proline mitigates toxic effects of cadmium via the decrease of cadmium accumulation and reestablishment of redox homeostasis in Brassica juncea

BackgroundAs a vital osmoticum, proline has an important role in enhancing the tolerance of plants to environmental stress. It is unclear whether the application of exogenous proline can improve the tolerance of Brassica juncea to cadmium (Cd).ResultsThis study investigated the effects of different concentrations of proline (20, 40, 60, 80, and 100 mg/L) under Cd stress at different times (0 d, 2 d, and 7 d) on the growth and physiology of B. juncea. Treatment with exogenous proline not only increased the content of proline in B. juncea but also alleviated Cd-induced seedling growth inhibition via the maintenance of higher photosynthetic pigment content and cell viability and a decrease in the content of Cd. Moreover, it increased the activities of antioxidant enzymes and the glutathione/glutathione disulfide ratio to reduce the accumulation of reactive oxygen species. Compared with other concentrations, 60 mg/L of exogenous proline was the most effective at mitigating Cd toxicity in B. juncea.ConclusionsExogenous proline treatment enhanced the tolerance to Cd via a decrease in Cd accumulation and reestablishment of the redox homeostasis in B. juncea.

Mathematical quantification of interactive complexity of transcription factors involved in proline-mediated regulative strategies in Oryza sativa under chromium stress

Involvement of transcription factor (TFs) in governing genes at transcription or post transcription level is known to have affirmative impact on plant physiological and morphological development, especially during environmental abuse. Application of exogenous proline (Pro) is one among the effective approaches to strengthen plant resistance against stresses. However, Pro-mediated regulative strategies of TFs in responses to the chromium (Cr) in rice plants through the gene interaction network are still not clear. In the current study, Pro-mediated interactive complexity of various TFs (i.e., MYB, NAC, WRKY, bHLH, and bZIP) under hexavalent chromium [Cr(VI)] was investigated using Agilent 4 × 44 K rice gene chip and gene interactive probability model (GIPM). Results showed that exogenous Pro had a negligible effect on Cr uptake in rice plants, while a small positive response in biomass accretion of rice seedlings was observed under Cr(VI)+Pro treatments which was to certain extend greater than single Cr(VI) treatments. Rice microarray analysis showed that Cr(VI) significantly (p < 0.05) repressed the expression of TFs in the rice roots and shoots, while the application of exogenous Pro significantly (p < 0.05) up-regulated the expression levels of some TFs in rice tissues. Mathematical modularization indicated that Pro-mediated interaction between MYB and NAC carried more weightage than other TFs in rice roots and shoots under Cr(VI) stress. Overall, our study provides convincing evidence to confirm a positive role of exogenous Pro on reducing the negative impact exerted by Cr(VI) on rice plants through regulating expression and interaction of different TFs.

Alternate gene expression profiling of monoterpenes in Hymenocrater longiflorus as a novel pharmaceutical plant under water deficit

Hymenocrater longiflorus (surahalala) is a wild plant species with potential pharmaceutical and ornamental interest. To date, the genomics of this plant is unknown and the gene expression profiling of the genes related to its metabolite has never been studied before. In order to study the responses of in vitro-grown surahalala plants to abiotic stresses and the differential expression of the genes related to its essential oils under exogenous proline application; three levels of PEG600 (0, 10, and 20%) and five levels of proline (0, 5, 10, 15, and 20 µm) were combined in the culture media. Thus, water deficit increased oxidants levels and decreased fresh weight of surahalala tissues, whereas addition of proline up to 15 µm was able to relatively compensate the negative effect of water deficit. Contrarily, high proline level (20 µm) had a negative effect on surahalala plants probably due to the stress simulation (nutrition) under high proline concentration. In addition, the best combination for achieving highest essential oils content was 10 µm proline plus 10% PEG. The expressional profiling of the genes TPS27, L3H, TPS2, TPS1, OMT and GDH3 were successfully carried out and their involvement in 1,8-cineole, carvone, α-pinene, thymol, estragole and β-Citronellol biosynthesis, respectively, was verified. In addition, our results indicated that these genes could also be involved in the synthesis of other metabolites under water deficit condition.

Physiological responses of resistant and susceptible pepper plants to exogenous proline application under Phytophthora capsici stress

Phytophthora capsici Leon. is the main pathogen that limits the production of peppers. In this study, the effects of 1 and 10 mM proline (Pro), prior to exposure of resistant (CM-334) and susceptible (SD-8) pepper seedlings to P. capsici, on some physiological parameters were investigated. A lower Pro concentration (1 mM) was found to be more effective than 10 mM Pro in increasing the stress tolerance of the CM-334 cultivar. Namely, in CM-334 cultivar, the highest chlorophyll a, chlorophyll b, carotenoid, glucose and fructose content and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity percentage were detected on the seventh day after application of 1 mM Pro + P. capsici, while the lowest malondialdehyde (MDA) amount was measured on the third day in the same treatment. The highest ferric reducing antioxidant power (FRAP) increase was determined on the seventh day in the 10 mM Pro + P. capsici application. The effects of the same Pro treatments on the SD-8 cultivar somewhat differed; the highest amounts of chlorophyll a, chlorophyll b, anthocyanins, fructose, total protein and endogenous Pro were detected on the seventh day in the 1 mM Pro + P. capsici application, while the lowest MDA amount was measured on the third day after the 10 mM Pro + P. capsici application, the highest DPPH % and FRAP values were detected on the seventh day with 10 mM Pro + P. capsici application. Although some differences were detected between the cultivars, Pro application against the P. capsici stress in general resulted in a positive effect on photosynthetic pigments, soluble carbohydrates and antioxidant capacity in pepper. The exogenous application of Pro helped the non-resistant cultivar to overcome the stress.

Effect of different concentration of exogenous proline applications on cadmium accumulation and mineral nutrition (K, Mg, Na and Ca) of common wheat (Triticum aestivum)

The present study investigates the role of exogenously applied proline on cadmium (Cd) accumulation in common wheat (Triticum aestivum L.) tissues. Seedlings were subjected for 4 days to different exogenous proline levels (0, 1, 10, and 20 mM) under Cd stress (1000 μM of Cd(NO3)2·4H2O). The concentration of Cd, Ca, Mg, and K was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Exogenous proline caused significant changes in the growth of wheat cultivar under Cd stress. In addition, the growth of wheat under Cd stress increased by the addition of 1 mM proline. According to the analysis results, Cd accumulation in wheat seedlings showed that the increment of exogenous proline treatments (except Cd+Pr1) in the water resulted in a decrease of Cd content in roots and shoots. Under Cd treatment (not applied proline), the contents of Ca, K, Mg, and Na decreased in roots by 22.1, 70, 17.7, and 10.1% and in shoots by 29.6, 32.2, 19.1, and 5.3%, respectively. Nevertheless, K content decreased in roots and shoots under all Cd and exogenous proline treatments.

Exogenous proline treatment inhibiting enzymatic browning of fresh-cut potatoes during cold storage

Fresh-cut potato slices are prone to browning, resulting in a severely reduced commodity value. Hence, a safe and effective method to inhibit the browning of fresh-cut potatoes is urgently needed. In this study, we investigated the effect of pre-treatment with a proline solution on browning, polyphenol oxidase (PPO) activity, total phenol content, antioxidant activity, and free amino acid content of fresh-cut potatoes. The results showed that pre-treatment with 90 mmol L−1 proline for 1 h at 30 °C reduced browning and surface dehydration, improved the overall visual aspect, and extended the shelf-life of potato slices to 4 d at 2−4 °C. The PPO activity and total phenol content in pre-treated potato tubers and slices were lower than control and water treatment. The superoxide dismutase (SOD), catalase (CAT) activities, the percentage inhibition of 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and 2,20-zo-bis-3-ethylben zothiazoline-6-sulfonic acid (ABTS), and the Fe2+ reduction capacity had increased compared with control and water treatment. Compared with control and water treatment, the tyrosine, aspartic acid, glutamic acid, serine, glycine, histidine, and valine content were reduced, whereas proline, histidine, and valine had increased. Mechanistically, pre-treatment with proline inhibited the browning of fresh-cut potatoes by reducing PPO activity, total phenolic content, and the content of several amino acids, while inducing the accumulation of intrinsic proline content and increasing the antioxidant capacity of fresh-cut potatoes.

Exogenously Applied Proline Modulates Drought Tolerance in Maize (Zea mays L)

Improving drought stress tolerance in maize is essential to increase its production and yield worldwide. Thus, the present study was conducted to investigate the improvement of drought tolerance in maize (Zea mays L.) by exogenous application of proline (25 and 50mM) on two maize varieties. Maize plants were subjected to drought stress at various phases of plant growth under pot culture conditions and proline was applied as foliar spray. Water deficit stress caused a significant decrease (by approximately 25%) in growth and yield of both maize varieties by decreasing plant height, cob length, dry root weight, grains per cob and 100-grain weight. Water deficit stress also decreased chlorophyll and intercellular proline contents, and antioxidant enzyme activities viz. catalase (CAT), guaiacol peroxidase (POX) and ascorbate peroxidase (APX). Exogenous application of proline (50 mM) was found to be more effective in increasing growth and yield of both varieties. These increases were positively associated with increased levels (by at least 15%) of chlorophyll and intracellular proline, and enhanced activities of CAT, POX and APX enzymes in both varieties. Interaction effects of exogenous proline and water deficit stress were significant in aspects of higher growth and yields and enhanced levels of chlorophyll, intracellular proline and antioxidant enzyme activities. Therefore, it is concluded that foliar application of proline improves drought tolerance by modulating chlorophyll and intracellular proline contents, and antioxidant enzyme activities.

Exogenous proline triggered internal tolerance mechanism in trifoliate orange (Poncirus trifoliata) acclimated to boron-deficiency

Boron (B)-deficiency is one of the main factors limiting plant growth. Here, we assessed the effects of exogenous proline on mitigating B-deficiency of trifoliate orange seedlings in a hydroponic experiment. The results showed that B-deficiency-induced higher oxidative stress and deleterious to seedling growth. Exogenous proline application enhanced the proline accumulation in leaf and root, especially in root, and attenuated B-deficiency-induced root malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents, which had a positive effects on the growth-related parameters in terms of plant height and root length. Moreover, exogenous proline addition promoted the accumulation of B in root and the formation of pectin and cellulose in root cell wall during B-deficiency. Proline metabolic pathway-related enzymes (pyrroline-5-carboxylic acid synthetase (P5CS), pyrroline-5-carboxylic acid reductase (P5CR), and ornithine transaminase (OAT)) in conjunction with correlation analysis showed that all synthetases in proline metabolism pathway have negative regulation on proline synthesis, yet only OAT activity showed a positive correlation with proline, accompanied by higher OAT expression in root under the conditions of exogenous proline applied with B-deficiency. Collectively, exogenous proline stimulated glutamate and ornithine pathways to promote proline biosynthesis in leaf, whereas only ornithine pathway as a dominant role in proline biosynthesis in root under B-deficiency. And the accumulation of root proline promoted the distribution of B in root, which stimulated the antioxidant defense system to attenuate the oxidative damage of root, and then reduced the thickness of cell wall, thus rescues B-deficiency-induced inhibition on root elongation.

Exogenous proline alters the leaf ionomic profiles of transgenic and wild-type tobacco plants under water deficit

Water deficit can reduce the absorption, accumulation, partition, and use of nutrients in plants. To mitigate the effects of this stress, plants produce osmolytes, such as proline, which may assist in preventing nutrient deficiencies under water deficiency. Therefore, the objective of this work was to evaluate the effects of exogenous proline application on the ionomic profile of wild-type and genetically modified tobacco (Nicotiana tabacum L.) overproducing proline under water deficit conditions. For this, the exogenous proline application in transgenic tobacco plants with constitutive expression of a mutated heterologous delta-1-pyrroline-5-carboxylate synthase enzyme (VaP5CSF129A) with reduced feedback inhibition and wild-type was studied. Water supply was suspended three days after foliar applications of 10 mM proline and the mineral elements content were determined in leaves nine days after the suspension of irrigation. Hierarchical clustering showed a clear differentiation between groups of plants with or without exogenous proline application, demonstrating that this treatment affected the ionomic profile of tobacco plants more than the water regime. The absorption and translocation mechanisms that were probably affected by the higher amount of proline allowed the separation the mineral elements into five groups by multivariate analysis. Notably, potassium was the nutrient present in the greatest content in tobacco leaves. In general, micronutrients were detected in larger amounts in transgenic plants, with the exception of iron possibly due to the competition with copper. Thus, the data suggest that proline might act, directly, or indirectly as a mitigator of nutritional deficiencies caused by water deficiency in tobacco, if applied prior to the onset of the water deficit conditions.

Is proline the quintessential sentinel of plants? A case study of postharvest flower senescence in Dianthus chinensis L.

The present investigation primarily focussed on evaluating the efficacy of exogenous proline on the flower longevity of Dianthus chinensis L. Floral buds were harvested atthe paint brush stage (i.e., a day prior to anthesis) and divided into 6 sets, with one set of buds (i.e., control) held in distilled water and rest of the 5 sets were supplemented with various concentrations of proline, viz., 10mM, 20mM, 30mM, 40mM and 50mM. The application of proline at 40mM concentration proved out to be most effective in improvingthe longevity of the flowers by about 4days as compared to the control. The ameliorated longevity coincided with enhanced floral diameter, fresh mass, dry mass and water content. The flowers with delayed senescence also maintained higher soluble proteins, sugars and phenols. The results suggest that exogenous proline effectively alleviates oxidative stress in the petal tissue, as evident by a relatively lower maloendialdehyde content, which is manifested in the form of reduced lipid peroxidation (LPO). Reduced LPO was commensurate with increased membrane stability, quantified by membrane stability index. Moreover, the flowers with improved longevity exhibiteda decline in lipoxygenase activity and significant augmentation of antioxidant enzymes superoxide dismutase, catalase and ascorbate peroxidase.

Ameliorative Effects of Exogenous Proline on Photosynthetic Attributes, Nutrients Uptake, and Oxidative Stresses under Cadmium in Pigeon Pea (Cajanus cajan L.).

Proline plays a significant role in the plant response to stress conditions. However, its role in alleviating metal-induced stresses remains elusive. We conducted an experiment to evaluate the ameliorative role of exogenous proline on cadmium-induced inhibitory effects in pigeon pea subjected to different Cd treatments (4 and 8 mg/mL). Cadmium treatments reduced photosynthetic attributes, decreased chlorophyll contents, disturbed nutrient uptake, and affected growth traits. The elevated activity of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), in association with relatively high contents of hydrogen peroxide, thiobarbituric acid reactive substances, electrolyte leakage, and endogenous proline, was measured. Exogenous proline application (3 and 6 mM) alleviated cadmium-induced oxidative damage. Exogenous proline increased antioxidant enzyme activities and improved photosynthetic attributes, nutrient uptake (Mg2+, Ca2+, K+), and growth parameters in cadmium-stressed pigeon pea plants. Our results reveal that proline supplementation can comprehensively alleviate the harmful effects of cadmium on pigeon pea plants.

Regulation of Osmotic Balance and Increased Antioxidant Activities under Heat Stress in Abelmoschus esculentus L. Triggered by Exogenous Proline Application

Keeping in view the yield losses instigated by heat stress in several crops, we carried out an experiment to explore the curative effect of exogenous applications of proline on the morpho-physiological, biochemical, and water-related attributes of okra genotypes under high-temperature stress (controlled conditions). Four contrasting genotypes C1, C2, C3, and C4 heat tolerant and heat sensitive genotypes were selected from a diverse panel of okra genotypes (n = 100) to examine plant responses to high-temperature stress and exogenous application of proline. Four-week-old seedlings were subjected to heat stress by gradually increasing the temperature of a growth chamber from 28/22 °C to 45/35 °C (day/night) and sprayed with an optimized proline concentration 2.5 mM. The experiment consisted of a factorial arrangement of treatments in a completely randomized design. The results showed that there were maximum increases in shoot length (32.7%), root length (58.9%), and shoot fresh (85.7%). The quantities of leaves per plant were increased by 52.9%, 123.6%, 82.5%, and 62.2% in C1, C2, C3, and C4 after proline application. On the other hand, only root fresh weight decreased in all genotypes after proline application by 23.1%, 20%, 266.7%, and 280.8% (C1, C2, C3, C4). A lower leaf temperature of 27.72 °C, minimum transpiration of 3.29 mmol m−2 s−1, maximum photosynthesis of 3.91 μmol m−2 s−1, and a maximum water use efficiency of 1.20 μmol CO2 mmol H2O were recorded in the genotypes C2, C1, C3, and C4, respectively. The highest enzymatic activity of superoxide dismutase, peroxidase and catalase were 14.88, 0.31, and 0.15 U mg-protein in C2, C1, and C3, respectively. Maximum leaf proline, glycinebetaine, total free amino acids, and chlorophyll content 3.46 mg g−1, 4.02 mg g−1, 3.46 mg g−1, and 46.89 (in C2), respectively, due to foliar applications of proline. Another important finding was that heat tolerance in okra was highly linked highly linked to genotypes’ genetic potential, having more water use efficiency, enzymatic activities, and physio-biochemical attributes under the foliar applications of proline.

Cyanobacteria-Derived Proline Increases Stress Tolerance in Arabidopsis thaliana Root Hairs by Suppressing Programmed Cell Death.

Nitrogen-fixing heterocystous cyanobacteria are used as biofertilizer inoculants for stimulating plant growth but can also alleviate plant stress by exometabolite secretion. However, only a small number of studies have focused on elucidating the identity of said bioactives because of the wide array of exuded compounds. Here, we used the root hair assay (RHA) as a rapid programmed cell death (PCD) screening tool for characterizing the bioactivity of cyanobacteria Nostoc muscorum conditioned medium (CM) on Arabidopsis thaliana root hair stress tolerance. We found that heat-stressed A. thaliana pre-treated with N. muscorum CM fractions exhibited significantly lower root hair PCD levels compared to untreated seedlings. Treatment with CM increased stress tolerance by suppressing PCD in root hairs but not necrosis, indicating the bioactive compound was specifically modulating the PCD pathway and not a general stress response. Based on documented N. muscorum exometabolites, we identified the stress-responsive proline as a compound of interest and strong evidence from the ninhydrin assay and HPLC indicate that proline is present in N. muscorum CM. To establish whether proline was capable of suppressing PCD, we conducted proline supplementation experiments. Our results showed that exogenous proline had a similar effect on root hairs as N. muscorum CM treatment, with comparable PCD suppression levels and insignificant necrosis changes. To verify proline as one of the biologically active compounds in N. muscorum CM, we used three mutant A. thaliana lines with proline transporter mutations (lht1, aap1 and atprot1-1::atprot2-3::atprot3-2). Compared with the wild-type seedlings, PCD-suppression in lht1and aap1 mutants was significantly reduced when supplied with low proline (1–5 μM) levels. Similarly, pre-treatment with N. muscorum CM resulted in elevated PCD levels in all three mutant lines compared to wild-type seedlings. Our results show that plant uptake of cyanobacteria-derived proline alters their root hair PCD sensitivity threshold. This offers evidence of a novel biofertilizer mechanism for reducing stress-induced PCD levels, independent of the existing mechanisms documented in the literature.

ENHANCING SALT TOLERANCE OF WHEAT PLANT (TRITICUM AESTIVUM L.) BY APPLICATION OF PROLINE, ASCORBIC ACID, ARGININE, GLUTAMINE AND GLUTATHIONE

Salinity is becoming nowadays one of the major abiotic stress issues worldwide. Wheat is considered as moderately salt tolerant crop and is adversely affected in response to the salt stress in terms of growth and yield. Pot experiment was conducted to determine the effect of exogenous proline, ascorbic acid, arginine, glutamine and glutathione application on some growth and biochemical parameters of wheat grown under salt stress conditions. The experiment was conducted under field conditions of wheat (Triticum aestivum L.) cultivar sakha 93. Three replicates, five grains per replicate were sown directly in plastic pots. Wheat plants were treated with 100 mg/l proline, 88 mg/l ascorbic acid, 100 mg/l arginine, 10 mg/l glutamine and 50 mg/l glutathione. Salinity treatments were established by adding 6000, 8000 and 10000 mg/l of sea salt. The results obtained from this experiment revealed that growth parameters such as shoot length, root weight andgrain weight, in addition tobiochemical compounds such as chlorophyll, starch, fiber, ash and fat were affected by both salt and treatments. These parameters were decreased in response to salinity stress compared to untreated plants. The decrement in the growth parameters andbiochemical compounds were found to be increased with increasing salt concentrations, particularly at 6000 mg/l, 8000 mg/l and 10000 mg/l respectively. The selected compounds mitigate the negative effects of salt stress and improved growth parameters and biochemical compounds compared with control plants under different salinity level. Key words: abiotic stress, salt stress, salinity tolerance and wheat plant. Salinity is becoming nowadays one of the major abiotic stress issues worldwide. Wheat is considered as moderately salt tolerant crop and is adversely affected in response to the salt stress in terms of growth and yield. Pot experiment was conducted to determine the effect of exogenous proline, ascorbic acid, arginine, glutamine and glutathione application on some growth and biochemical parameters of wheat grown under salt stress conditions. The experiment was conducted under field conditions of wheat (Triticum aestivum L.) cultivar sakha 93. Three replicates, five grains per replicate were sown directly in plastic pots. Wheat plants were treated with 100 mg/l proline, 88 mg/l ascorbic acid, 100 mg/l arginine, 10 mg/l glutamine and 50 mg/l glutathione. Salinity treatments were established by adding 6000, 8000 and 10000 mg/l of sea salt. The results obtained from this experiment revealed that growth parameters such as shoot length, root weight andgrain weight, in addition tobiochemical compounds such as chlorophyll, starch, fiber, ash and fat were affected by both salt and treatments. These parameters were decreased in response to salinity stress compared to untreated plants. The decrement in the growth parameters andbiochemical compounds were found to be increased with increasing salt concentrations, particularly at 6000 mg/l, 8000 mg/l and 10000 mg/l respectively. The selected compounds mitigate the negative effects of salt stress and improved growth parameters and biochemical compounds compared with control plants under different salinity level.

Exogenous proline enhances antioxidant enzyme activities but does not mitigate growth inhibition by selenate stress in tobacco BY-2 cells

Selenium (Se) causes oxidative damage to plants. Proline is accumulated as a compatible solute in plants under stress conditions and mitigates stresses. Selenate at 250µM increased cell death and inhibited the growth of tobacco BY-2 cells while exogenous proline at 10mM did not mitigate the inhibition by selenate. Selenate increased accumulation of Se and ROS and activities of antioxidant enzymes but not lipid peroxidation in the BY-2 cells. Proline increased Se accumulation and antioxidant enzyme activities but not either ROS accumulation or lipid peroxidation in the selenate-stressed cells. Glutathione (GSH) rather than ascorbic acid (AsA) mitigated the growth inhibition although both reduced the accumulation of ROS induced by selenate. These results indicate that proline increases both antioxidant enzyme activities and Se accumulation, which overall fails to ameliorate the growth inhibition by selenate and that the growth inhibition is not accounted for only by ROS accumulation. Abbreviations: APX: ascorbate peroxidase; AsA: ascorbic acid; BY-2: Bright Yellow-2; CAT: catalase; DAI: days after inoculation; DW: dry weight; FW: fresh weight; GSH: glutathione; ROS: reactive oxygen species.

Exogenous proline induces regulation in 2-acetyl-1-pyrroline (2-AP) biosynthesis and quality characters in fragrant rice (Oryza sativa L.)

Proline is one of the precursors of the biosynthesis of 2-acetyl-1-pyrroline (2-AP) which is the key and characteristic volatile component of fragrant rice aroma. In order to study the effects of exogenous proline on 2-AP biosynthesis and other grain quality attributes in fragrant rice, two indica fragrant rice cultivars, “Meixiangzhan-2” and “Xiangyaxiangzhan”, and one japonica fragrant rice, “Yunjingyou”, were used in present study. At initial heading stage, proline solutions at 0 (CK), 0.10 (Pro1), 0.20 (Pro2) and 0.50 (Pro3) g L-1 were applied as foliar spray solution to fragrant rice plants. Compared with CK, Pro1, Pro2 and Pro3 treatments significantly increased the grain 2-AP content. The significant up-regulation effects due to proline treatments were observed in the contents of proline, △1-pyrrolidine-5-carboxylic acid (P5C) and △1-pyrroline which involved in 2-AP formation. Exogenous proline application also significantly decreased the grain γ-aminobutyric acid (GABA) content. Furthermore, proline treatments enhanced the activity of proline dehydrogenase (ProDH) as well as transcript level of gene PRODH. On the other hand, the transcript level of gene BADH2 and activity of betaine aldehyde dehydrogenase (BADH) decreased under proline treatments. Proline treatments (Pro2 and Pro3) also increased the grain protein content by 3.57–6.51%. Moreover, 32.03–34.25% lower chalky rice rate and 30.80–48.88% lower chalkiness were recorded in proline treatments (Pro2 and Pro3) for both Meixiangzhan and Xiangyaxiangzhan whilst for Yunjingyou, foliar application of proline had no significant effect on chalky rice rate and chalkiness. There was no remarkable difference observed in grain milled quality (brown rice rate, milled rice rate and head rice rate) and amylose content between CK and proline treatments. In conclusion, exogenous proline enhanced the 2-AP biosynthesis and promoted some grain quality characters of fragrant rice.