Increase In Soluble Sugars Research Articles

VviRafS5 Is a Raffinose Synthase Involved in Cold Acclimation in Grapevine Woody Tissues.

The accumulation of raffinose family oligosaccharides (RFOs) is a hallmark of plant response to different abiotic stresses, including cold. The synthesis of galactinol, by galactinol synthases (GolS), and raffinose, by raffinose synthases (RafS), are fundamental for stress-induced accumulation of RFOs, but the role of these enzymes in the cold response of grapevine (Vitis vinifera L.) woody tissues is still unclear. To address this gap in the literature, 1-year-lignified grapevine canes were incubated at 4°C for 7 and 14 days and tissues were analyzed for sugar content and gene expression. Results showed that, in parallel to starch breakdown, there was an increase in soluble sugars, including sucrose, glucose, fructose, raffinose, and stachyose. Remarkably, abscisic acid (ABA) levels increased during cold acclimation, which correlated with the increased expression of the key ABA-synthesis genes VviNCED2 and VviNCED3. Expression analysis of the VviGolS and VviRafS family allowed the identification of VviRafS5 as a key player in grapevine cold response. The overexpression of VviRafS5 in Saccharomyces cerevisiae allowed the biochemical characterization of the encoded protein as a raffinose synthase with a size of ~87 kDa. In grapevine cultured cells, VviRafS5 was upregulated by cold and ABA but not by heat and salt stresses. Our results suggest that ABA accumulation in woody tissues during cold acclimation upregulates VivRafS5 leading to raffinose synthesis.

Exploring the significance of photosynthetic activity and carbohydrate metabolism in peel tissues during banana fruit ripening

Starch synthesis and degradation in banana pulp have been extensively characterized. However, no literature studies are currently available on these processes in the peel, except concerning the presence of starch granules. Thus, this work explored the potential connection between photosynthetic activity and starch accumulation in banana peel. Bananas, cultivar Nanicão, were analyzed at different development and ripening stages. The chlorophyll a fluorescence values for green banana peels indicated that the photosystems were active before fruit ripening, concomitant to starch accumulation. During banana ripening, accumulated starch is degraded concomitantly with an increase in soluble sugars, such as those occurring in the pulp. For comparison, the peel and pulp starch granules were characterized during the fruit ripening. The results showed that the peel starch granules presented higher amylose contents than the pulp, and SEM images exhibited similar patterns of granules, shapes, and sizes. As ripening advanced, starch granules from the peel appeared to undergo different degradation steps, and the appearance of starch fragments of different sizes indicated an apparent weakness, probably due to the low structural complexity of their components, amylose and amylopectin.

Different Temperature Regimes Influenced the Quality of Broccoli Seedlings, Which Caused a Change in the Chemical Composition of Mature Heads

Exposure of vegetable seedlings to lowered temperature affects their growth and the content of certain chemical constituents. Chilling activates defensive mechanisms against stress and leads to acclimatization which increases plant ability to withstand harsh field conditions. Thus, seedlings subjected to low-temperature treatment had altered metabolic pathways, and these changes can persist until harvest. We therefore assessed: (i) the direct response of broccoli seedlings to 1 week or 2 weeks at lowered temperatures (6 °C, 10 °C, 14 °C, and 18 °C—control); and (ii) the long-term effects of the latter treatments on phytochemical components level in mature heads of broccoli cultivated in the field. Chilling stress decreased seedling shoot and root fresh and dry weights, plant height, number of leaves, leaf area, leaf perimeter, and leaf width. The most spectacular reductions in these parameters were observed at 6 °C and 10 °C. Longer exposure to lowered temperature resulted in greater reduction in the values of morphological traits. Chilling led to reduction in L-ascorbic acid content in broccoli seedlings, while a 6 °C temperature caused an increase in soluble sugars. The highest content of dry weight, soluble sugars, and L-ascorbic acid were observed in the heads of plants exposed to 14 °C; however, the content of dry weight (at 10 °C) and L-ascorbic acid (at 6 °C and 10 °C) also increased in broccoli heads in comparison with the control. Longer chilling (for 2 weeks) generally increased the content of these constituents in mature broccoli. Lower temperature (6–14 °C) applied at seedling stage increased P and Zn contents in broccoli heads in comparison to the control, whereas plants treated with 10 °C had more K, Fe, and, together with 6 °C treatment, Cu. The lowest temperature applied to the seedlings (6 °C) caused an increase in Mn content, while no effects of seedling chilling was noted for Ca levels. Significant linear correlations were noted and regression models were developed for the content of dry weight, soluble sugars, and L-ascorbic acid in the broccoli heads based on the chosen seedling parameters. The results show that the effect of lowered temperature to which the seedlings were subjected persists also in the further stages of plant ontogenesis, causing permanent changes in the chemical composition of mature broccoli heads.

Effects of Cold Treatments on Seedling Emergence and Growth of Lilium davidii var. unicolor Bulblets

For Lilium davidii var. unicolor bulblets produced by scale propagation, the effects of cold treatments on the sprouting and development of bulblets were studied. The results showed that 5 °C was a more suitable temperature than 2 or 10 °C. Bulblets treated at 5 °C for 3 weeks presented the best uniformity of seedling emergence, and the sprouting rate was 100%. Moreover, the largest bulbs were observed in this treatment after a growing season. It was found that long storage at low temperatures is unfavorable for bulb development. The weight and circumference of bulbs from bulblets that were cold-treated for more than 5 weeks were significantly less than those treated for 1 to 4 weeks. During the first 4 weeks of cold storage, the starch content of bulblets decreased significantly, coinciding with an increase in soluble sugars. The starch and soluble sugar contents in bulblets stored at 2 and 5 °C changed faster than those in bulblets stored at 10 °C. However, the effect of temperature on carbohydrates diminished gradually as the storage time increased. Long storage of bulblets at low temperatures is not good for subsequent growth and development. The results of this study provide important information for accelerating the scale propagation of L. davidii var. unicolor and maximizing bulb yield.

The Brachypodium distachyon cold-acclimated plasma membrane proteome is primed for stress resistance.

In order to survive subzero temperatures, some plants undergo cold acclimation (CA) where low, nonfreezing temperatures, and/or shortened day lengths allow cold-hardening and survival during subsequent freeze events. Central to this response is the plasma membrane (PM), where low temperature is perceived and cellular homeostasis must be preserved by maintaining membrane integrity. Here, we present the first PM proteome of cold-acclimated Brachypodium distachyon, a model species for the study of monocot crops. A time-course experiment investigated CA-induced changes in the proteome following two-phase partitioning PM enrichment and label-free quantification by nano-liquid chromatography-mass spectrophotometry. Two days of CA were sufficient for membrane protection as well as an initial increase in sugar levels and coincided with a significant change in the abundance of 154 proteins. Prolonged CA resulted in further increases in soluble sugars and abundance changes in more than 680 proteins, suggesting both a necessary early response to low-temperature treatment, as well as a sustained CA response elicited over several days. A meta-analysis revealed that the identified PM proteins have known roles in low-temperature tolerance, metabolism, transport, and pathogen defense as well as drought, osmotic stress, and salt resistance suggesting crosstalk between stress responses, such that CA may prime plants for other abiotic and biotic stresses. The PM proteins identified here present keys to an understanding of cold tolerance in monocot crops and the hope of addressing economic losses associated with modern climate-mediated increases in frost events.

Are the well-fed less thirsty? Effects of drought and salinity on New Zealand mangroves

AbstractDespite a large number of studies examining the effects of abiotic stress factors on plants, the mechanistic explanations of drought-induced tree mortality remain inconclusive and even less is known about how multiple stressors interact. The role of non-structural carbohydrates (NSCs) in preventing or postponing drought mortality is gaining attention. Here, we tested the role of NSCs in mitigating the effects of drought and salinity in New Zealand mangroves, Avicennia marina subsp. australasica. We experimentally manipulated plant NSC levels, prior to subjecting them to combinations of drought and salinity. Plant growth and survival rates were 2- and 3-fold higher in the high-NSC (H-NSC) group than in the low-NSC (L-NSC) group under high salinity and drought conditions, respectively. After 12 weeks under high salinity–high drought conditions, the H-NSC group showed higher stem hydraulic conductivity (281 ± 50 mmol cm−1 s−1 MPa−1) compared with the L-NSC group (134 ± 40 mmol cm−1 s−1 MPa−1). Although starch levels remained relatively constant, we found a 20% increase in soluble sugars in the stems of H-NSC group under high drought and high salinity in week 8 compared with week 12. Our results suggest (i) an important role of NSCs in mitigating the effects of low soil water potential caused by drought and salinity, and (ii) sink-limited growth under conditions of combined salinity and drought.

When vegetation indicates reproduction: The affinity between leaf morphology and flowering commitment in the lily meristem.

At the reproductive stage, lily plants bear two morphological types of mature leaves, one at the lower and one at the upper part of the stem. At the vegetative stage, all the leaves are similar to each other and to the reproductive plant's lower leaves. This heterophylly has not yet been explored. In this study, we show that it is not a result of the plant's age but rather an outcome of floral induction. The induction appears as an on-going process, during which the meristem still produces leaves but progressively becomes committed to reproduction. This intermediate period lasts until the ultimate switch to flower primordia occurs. The leaves produced during floral induction, termed here as "inductive," appear at the upper part of the stem. Besides their typical higher stomata density, these leaves have a poly-layered palisade mesophyll, whose cells exhibit a unique morphology and contain more chlorophyll than leaves of vegetative plants. These leaves display higher carbon assimilation, soluble sugar production, and chloroplast-lipid accumulation. Accordingly, genes associated with stomata, chloroplast, and photosynthesis are upregulated in these leaves. Our results were obtained when floral induction was achieved either by vernalization or photoperiod signals, ruling out a mere environmental effect. We suggest that lily plants prepare themselves for the high-energy-demanding bloom by producing leaves with enhanced photosynthetic capacity, leading to an increase in soluble sugars. These novel findings introduce an adjacent affinity between photosynthesis and flowering and provide a nondestructive tool for identifying the plant's developmental stage-vegetative or reproductive.

Morpho-Physiological, Biochemical, and Genetic Responses to Salinity in Medicago truncatula.

We used an integrated morpho-physiological, biochemical, and genetic approach to investigate the salt responses of four lines (TN1.11, TN6.18, JA17, and A10) of Medicago truncatula. Results showed that TN1.11 exhibited a high tolerance to salinity, compared with the other lines, recording a salinity induced an increase in soluble sugars and soluble proteins, a slight decrease in malondialdehyde (MDA) accumulation, and less reduction in plant biomass. TN6.18 was the most susceptible to salinity as it showed less plant weight, had elevated levels of MDA, and lower levels of soluble sugars and soluble proteins under salt stress. As transcription factors of the APETALA2/ethylene responsive factor (AP2/ERF) family play important roles in plant growth, development, and responses to biotic and abiotic stresses, we performed a functional characterization of MtERF1 gene. Real-time PCR analysis revealed that MtERF1 is mainly expressed in roots and is inducible by NaCl and low temperature. Additionally, under salt stress, a greater increase in the expression of MtERF1 was found in TN1.11 plants than that in TN6.18. Therefore, the MtERF1 pattern of expression may provide a useful marker for discriminating among lines of M. truncatula and can be used as a tool in breeding programs aiming at obtaining Medicago lines with improved salt tolerance.

Unravelling resilience mechanisms in forests: role of non-structural carbohydrates in responding to extreme weather events.

Extreme weather events are increasing in frequency and intensity due to global climate change. We hypothesized that tree carbon reserves are crucial for resilience of beech, buffering the source-sink imbalance due to late frosts and summer droughts, and that different components of non-structural carbohydrates (NSCs) play specific roles in coping with stressful situations. To assess the compound effects on mature trees of two extreme weather events, first a late frost in spring 2016 and then a drought in summer 2017, we monitored the phenology, radial growth and the dynamics of starch and soluble sugars in a Mediterranean beech forest. A growth reduction of 85% was observed after the spring late frost, yet not after the drought event. We observed a strong impact of late frost on starch, which also affected its dynamic at the beginning of the subsequent vegetative season. In 2017, the increase of soluble sugars, associated with starch hydrolysis, played a crucial role in coping with the severe summer drought. Non-structural carbohydrates helped to counteract the negative effects of both events, supporting plant survival and buffering source-sink imbalances under stressful conditions. Our findings indicate a strong trade-off between growth and NSC storage in trees. Overall, our results highlight the key role of NSCs on beech trees, response to extreme weather events, confirming the resilience of this species to highly stressful events. These insights are useful for assessing how forests may respond to the potential impacts of climate change on ecosystem processes in the Mediterranean area.

Salt tolerance of Calotropis procera begins with immediate regulation of aquaporin activity in the root system.

The online version contains supplementary material available at 10.1007/s12298-021-00957-9.

Effect of vernalisation on the diurnal changes in fatty acid profile and nutrient composition of chicory in response to defoliation frequency

ABSTRACT The effect of defoliation frequency and severity on FA and nutrient composition of forage chicory (Cichorium intybus L.) before and after vernalisation were compared. Before vernalisation, the FA and nutrient components exhibited little variation with defoliation frequency and severity irrespective of the time of day. After vernalisation, total FA more than halved compared with pre vernalisation levels (52.2 versus 19.2 mg/g DM). Concentrations of total FA and polyunsaturated FA: linoleic and linolenic declined by 63%, 50%, and 74%, respectively. Furthermore, extending the defoliation frequency from 300 to 600 growing degree-days after vernalisation caused a decline of 28% of linoleic, 40% of linolenic and 33% of total FA concentrations. Diurnal fluctuations were detected for linoleic and oleic acids after vernalisation (P < 0.01). In terms of nutrient composition, vernalisation decreased CP, digestibility and ME, while fibre contents increased. Between morning and afternoon, there were general declines in CP and fibre contents as well as increases in soluble sugars the herbage regardless of vernalisation. Overall, the feeding value and the concentration of FA were greater on chicory herbage managed under shorter regrowth intervals than that under longer regrowth intervals, which is likely to favour animal production and the concentration of the desirable FA in ruminant products.

Responses of AG1 and AG2 QTL introgression lines and seed pre-treatment on growth and physiological processes during anaerobic germination of rice under flooding

Rice seeds germinating in flooded soils encounter hypoxia or even anoxia leading to poor seed germination and crop establishment. Introgression of AG1 and AG2 QTLs associated with tolerance of flooding during germination, together with seed pre-treatment via hydro-priming or presoaking can enhance germination and seedling growth in anaerobic soils. This study assessed the performance of elite lines incorporating AG1, AG2 and their combination when directly seeded in flooded soils using dry seeds. The QTLs were in the background of two popular varieties PSB Rc82 and Ciherang-Sub1, evaluated along with the donors Kho Hlan On (AG1) and Ma-Zhan Red (AG2) and recipient parents PSB Rc82 and Ciherang-Sub1. In one set of experiments conducted in the greenhouse, seedling emergence, growth, and carbohydrate mobilization from seeds were assessed. Metabolites associated with reactive oxygen species (ROS) scavenging including malondialdehyde (MDA) as a measure of lipid peroxidation, ascorbate, total phenolic concentration (TPC), and activities of ROS scavenging enzymes were quantified in seeds germinating under control (saturated) and flooded (10 cm) soils. In another set of experiments conducted in a natural field with 3–5 cm flooding depths, control and pretreated seeds of Ciherang-Sub1 introgression lines and checks were used. Flooding reduced seedling emergence of all genotypes, though emergence of AG1 + AG2 introgression lines was greater than the other AG lines. Soluble sugars increased, while starch concentration decreased gradually under flooding especially in the tolerant checks and in AG1 + AG2 introgression lines. Less lipid peroxidation and higher α-amylase activity, higher ascorbate (RAsA) and TPC were observed in the tolerant checks and in the AG1 + AG2 introgression lines. Lipid peroxidation correlated negatively with ascorbate, TPC, and with ROS scavengers. Seed hydro-priming or pre-soaking increased emergence by 7–10% over that of dry seeds. Introgression of AG2 and AG1 + AG2 QTLs with seed pretreatment showed 101–153% higher emergence over dry seeds of intolerant genotypes in the field. Lines carrying AG1 + AG2 QTLs showed higher α-amylase activity, leading to rapid starch degradation and increase in soluble sugars, ascorbate, and TPC, together leading to higher germination and seedling growth in flooded soils. Seed hydro-priming or pre-soaking for 24 h also improved traits associated with flooding tolerance. Combining tolerance with seed management could therefore, improve crop establishment in flooded soils and encourage large-scale adoption of direct seeded rice system.

SH1-dependent maize seed development and starch synthesis via modulating carbohydrate flow and osmotic potential balance

BackgroundAs the main form of photoassimilates transported from vegetative tissues to the reproductive organs, sucrose and its degradation products are crucial for cell fate determination and development of maize kernels. Despite the relevance of sucrose synthase SH1 (shrunken 1)-mediated release of hexoses for kernel development, the underlying physiological and molecular mechanisms are not yet well understood in maize (Zea mays).ResultsHere, we identified a new allelic mutant of SH1 generated by EMS mutagenesis, designated as sh1*. The mutation of SH1 caused more than 90% loss of sucrose synthase activity in sh1* endosperm, which resulted in a significant reduction in starch contents while a dramatic increase in soluble sugars. As a result, an extremely high osmolality in endosperm cells of sh1* was generated, which caused kernel swelling and affected the seed development. Quantitative measurement of phosphorylated sugars showed that Glc-1-P in endosperm of sh1* (17 μg g− 1 FW) was only 5.2% of that of wild-type (326 μg g− 1 FW). As a direct source of starch synthesis, the decrease of Glc-1-P may cause a significant reduction in carbohydrates that flow to starch synthesis, ultimately contributing to the defects in starch granule development and reduction of starch content.ConclusionsOur results demonstrated that SH1-mediated sucrose degradation is critical for maize kernel development and starch synthesis by regulating the flow of carbohydrates and maintaining the balance of osmotic potential.

Effects of foliar application of graphene oxide on cadmium uptake by lettuce

Although graphene oxide (GO) has been widely used to enhance soil quality and crop yield, there is currently little information regarding the effects of foliar application of GO on cadmium (Cd) toxicity to plants. In this study, we investigated the response to GO in lettuce cultivated under Cd stress in hydroponic conditions. Lettuce was grown from seeds in a nutrient solution supplemented with 2 mg/L Cd and the leaves were sprayed with 0, 30, and 60 mg/L GO. The results indicated that application of 30 mg/L GO significantly increased the total length, surface area, average diameter, and hair number of lettuce roots, and effectively alleviated the negative effects of Cd on root growth. Furthermore, foliar application of 30 mg/L GO, but not 60 mg/L GO, significantly improved the quality of lettuce, including reduction in Cd accumulation in leaves and roots and increase in soluble sugar, protein, and vitamin C content. Transmission electron microscopy revealed that GO nanoparticles, which entered the leaves and were subsequently transported to the roots via the vascular system (phloem), reduced the damaging effect of Cd on cellular organelles, including the cell wall and membrane, chloroplasts, and starch granules. The effect may be attributed to the absorption of GO by lettuce cells, where it fixed Cd2+, thus reducing Cd2+ bioavailability, or to the improvement of Cd tolerance through regulation of lettuce metabolic pathways. Gaussian simulation analysis revealed that Cd caused significant changes in the GO molecule, resulting in detachment of an epoxy group from the GO carbon ring and breakage of OH bonds in hydroxyl groups, whereupon the oxygen freed from the OH bond formed a new bond with Cd. Collectively, these results indicate that foliar application of 30 mg/L GO can enhance the tolerance of lettuce to Cd, promote plant growth, and improve nutritional quality.

Abscisic Acid and Glycine Betaine Mediated Tolerance Mechanisms under Drought Stress and Recovery in Axonopus compressus: A New Insight

Changing climatic scenarios affect plant growth and consequences are more malicious in drought conditions. This study was performed for better understanding of tolerance mechanisms under prevailing drought stress and succeeding recovery in Axonopus compressus by exogenously applied abscisic acid (ABA) and glycine betaine (GB). Three A. compressus accessions (A-38, A-58 and A-59) were subjected to well-watered (100% field capacity) and drought (40% field capacity) conditions. Two weeks later, plants were recovered from drought by re-watering. Water (control), GB, ABA and their combination were foliar applied on plants under drought twice a week until recovery. Drought stress decreased photosynthetic pigments and increased reactive oxygen species, lipid peroxidation, osmolytes and antioxidants in all accessions of A. compressus. Nonetheless, exogenous ABA and GB alone or in combination improved drought tolerance in all accessions which was maintained even after recovery. Maximum decrease in hydrogen peroxide and malondialdehyde, and increase in soluble sugars, proteins, proline, phenolics and chlorophyll contents, and superoxide dismutase, catalase, peroxidase and ascorbate peroxidase activity was recorded when GB was applied alone under drought. Order of improvement in drought tolerance among accessions was A-58 > A-59 > A-38. In conclusion, improved drought tolerance mechanisms by ABA and GB in A. compressus were retained even after recovery.

Overexpression of NtSnRK2.2 enhances salt tolerance in Nicotiana tabacum by regulating carbohydrate metabolism and lateral root development.

SnRK2 is a plant-specific protein kinase family implicated in environmental stress tolerance. Individual SnRK2 genes have acquired distinct regulatory properties in response to various environmental stresses. In this study, NtSnRK2.2, a SnRK2 subclass II member in Nicotiana tabacum L., was cloned and characterised. Sequence alignment analysis showed that SnRK2.2 exhibits widespread sequence differences across Nicotiana species. The tissue expression pattern of NtSnRK2.2 showed a root-predominant expression. To investigate its biological function, NtSnRK2.2 was overexpressed in tobacco, which subsequently resulted in increased soluble sugars and more lateral roots under a normal condition. A salt-stress tolerance assay showed that NtSnRK2.2-overexpressing plants exhibited enhanced salt tolerance, which was further confirmed based on its better root architecture and increase in soluble sugars, thereby implying that NtSnRK2.2 is a multifunctional regulatory factor in plants. Together, our results indicated the possible role played by NtSnRK2.2 in maintaining metabolic homeostasis via the regulation of carbohydrate metabolism in response to environmental stress.

Salt response of the freshwater microalga Scenedesmus obliquus (Turp.) Kutz is modulated by the algal growth phase

Growth and biochemical responses of the coenobial green alga Scenedesmus obliquus to salinity stress were monitored across different phases of growth. The alga was cultured on BG11 growth medium and subjected to 0, 30, 100, and 200 mmol/L NaCl for a period of 20 d, during which algal cultures were harvested at 4-d intervals. The salinity-induced inhibition of algal growth was accompanied with prolongation of timing of the different growth phases. The sharp and progressive salinity-induced inhibition of algal growth rate during the early phase of growth points to salt shock but moderation of inhibition at the subsequent stages of growth means algal acclimation to salinity. The concentrations of chlorophylls a and b, soluble sugars, proteins as well as those of K+ and Na+ in the alga exhibited peaks at the initiation of the exponential phase of growth, with increasing magnitude in proportion to the increase in the level of salinity. Nevertheless, whereas soluble sugars of the alga peaked at initiation of the exponential phase, starch concentration progressively increased with culture age, reaching saturation towards the stationary phase. Whereas the salinity-induced increase in soluble sugars was most evident at the early stages of growth the reverse was true for starch. The present results point to fast acclimation of S. obliquus to salt stress post a brief salt shock, utilizing soluble sugars, K+ and Na+ for osmotic adjustment. Increasing salinity from 0 to 200 mmol/L NaCl led to progressive increase in soluble sugars, proteins, K + and Na + concentrations of the algal cells, particularly at the early stages of growth. However, the salinity-induced increase in chlorophyll concentration approached a limit at 100 mmol/L NaCl whereas that in starch concentration was more evident at the later stages of growth.

Responses of morphological, physiological, and biochemical characteristics of maize (Zea mays L.) seedlings to atrazine stress.

Atrazine is a synthetic herbicide applied to control broadleaf weeds in different crops. In many parts of the world, atrazine is mainly applied for controlling weeds in maize fields. However, studies on the possible adverse effects of atrazine on maize crop can hardly be found in literature. The present study was therefore conducted to evaluate the effect of atrazine on different characteristics of maize seedlings including germination, growth, chlorophyll contents, soluble sugars, proteins and proline levels, ions accumulation, cell viability, and cell injury. In addition, the effects of atrazine on reactive oxygen species (ROS) accumulation and antioxidant enzymes activities in maize seedlings were estimated. It was found that at high concentration, atrazine slightly but significantly inhibited seed germination and growth of maize seedlings. Light-harvesting pigments (chlorophylls a and b, and total carotenoids) exhibited a higher sensitivity to atrazine and were negatively impacted by atrazine at doses above 50 ppm. Atrazine caused an increase in soluble sugars at all tested doses and decrease in soluble proteins at the highest tested dose. Exposure of maize seedlings to atrazine resulted in an increased cell injury and decreased cell viability. Atrazine did not affect the concentration of Na+, K+, and Ca2+ ions in maize seedlings to any greater extent; however, some minor changes were observed in some cases. An increase in the stress marker, proline, was found upon exposure to atrazine. The observed effects of atrazine in maize seedlings can be attributed to oxidative stress as revealed by an increase in H2O2 content and higher activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) enzymes in atrazine-treated seedlings. The present investigation concludes that atrazine has the potential to adversely affect germination and growth of maize seedlings by inducing oxidative stress that causes increased cell injury and decreased cell viability as well as impairs the concentration of light-harvesting pigments.

Critical Periods and Changes Involved in Hemerocallis lilioasphodelus Floral Transition

Hemerocallis is a valuable commercial perennial with prominent flowers. In this study, a wild variety of Hemerocallis lilioasphodelus L. cv. Licheng 7 (H. lilioasphodelus, LC7) from China was chosen as the experimental material due to its stable flowering trait in cultivation. Three main conclusions were obtained. Our observations revealed that the transition from vegetative to reproductive growth had a strong relationship with shoot apical meristem (SAM) fasciation, and the process was outlined in four morphological transitional stages. In addition, we detected a temporary increase in soluble sugar in the shoot tip, which was suggested to be a physiological indicator of inflorescence primordium initiation. In addition, the full-length sequences of two phosphatidylethanolamine-binding protein (PEBP) family genes from the wild species LC7 were cloned. From quantitative RT-PCR (qRT-PCR) and correlation analyses, we elucidated that the two PEBP family genes were correlated with some SAM morphological traits and involved in the regulation of the floral transition of the wild species LC7. To the best of our knowledge, this study provided a precious resource investigation of critical periods in the floral transition of H. lilioasphodelus, which will be recommended for regulation of the flowering time in perennials in the future.

Selenium impedes cadmium and arsenic toxicity in potato by modulating carbohydrate and nitrogen metabolism

Past studies have already determined that selenium (Se) is very effective in alleviating cell oxidative damage caused by various abiotic stresses in plants. Past studies have also indicated other physiological pathways by which Se may benefit plants. In order to better understand the full array of potential applications for Se in agriculture, this study investigated the influence of Se on carbohydrate and nitrogen (N) metabolism in potato plants (Solanum tuberosum L. cv. Sante) grown under cadmium (Cd) and/or arsenic (As) toxicity. Potato plants were grown in a growth chamber and fertigated with Hoagland nutrient solution with or without Se (9 μM). After 48-d of growth under Cd (40 μM) and/or As (40 μM) stress, carbohydrate and N metabolism in leaves, roots and stolons were measured. For carbohydrate metabolism, various sugars—i.e., sucrose, starch, glucose, fructose, and total soluble sugar contents (TSSC)—and the activities of enzymes associated with sucrose metabolism and glycolysis—i.e., acid invertase (AI), neutral invertase (NI), sucrose-synthetase (SS), sucrose phosphatesynthetase (SPS), fructokinase (FK), hexokinase (HK), phosphofructokinase (PFK), and pyruvatekinase (PK)—were measured. For N metabolism, NO3−, NO2− and NH4+ contents along with the enzymatic activities of nitrate reductase (NRA), nitrite reductase (NiRA), glutamine-synthetase (GS), and glutamate-synthetase (GOGAT) were measured. Overall, Cd and/or As treatments had reduced plant growth relative to those plants grown without heavy metal toxicity, due to hindered photosynthesis and alterations in N metabolism and glycolysis. Regarding N metabolism, heavy metal toxicity caused a reduction in NO3− and NO2− content and NRA and NiRA enzymatic activity and enhanced NH4+ content and GDH activity in leaves, roots and stolons. Regarding glycolysis, the activity of enzymes of glycolysis—i.e., FK, HK, PFK, and PK—were also reduced. In the C metabolism study, plants combatted Cd and As toxicity naturally by an adaptation mechanism which caused an increase in soluble sugars (fructose, glucose, sucrose) by increasing NI, SS and SSP enzymatic activity. Supplementation with Se in the Cd and/or As treatments in the carbohydrate and N metabolism studies improved plant growth. Selenium supplementation in the Cd and As treatments decreased Cd and/or As content in the plant tissue and alleviating the Cd- and/or As-induced toxicity by enhancing the C-metabolism adaptation mechanism. Applying Se to Cd and As treatments also decreased nitrogen losses by hindering Cd- and As-induced changes in the N-metabolism. Se also limited Cd and As accumulation in the plant tissue by the antagonistic effect between Cd/Se and As/Se in the roots. The results of this study indicate that in the presence of Cd and/or As. soil toxicity, Se may be a powerful tool for promoting plant growth.