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It is well known that plants can grow under space conditions, however, perturbations of many biological phenomena have been highlighted due to the effect of altered gravity and its possible interaction with other factors (e.g., CO2 , ion radiation, etc. Our aim was to test whether elevated CO2 could provide 'protection' to Gynura bicolor against the damaging effects of simulated microgravity (SM) on photosynthesis, ion uptake and antioxidant activity. As compared to G. bicolor grown in ambient CO2 with no SM (ACO2 ), growth and yield of the plants increased under elevated ambient CO2 with no SM (ECO2 ) and decreased under ACO2 +SM, whereas there was no significant effect on ECO2 +SM. Reductions in the content of Chl a, carotenoids and Chl a+b were 17.9%, 20.7% and 17.9% under ACO2 +SM, respectively, but under ECO2 there was a significant effect on all photosynthetic pigments except Chl b, compared to ACO2 . Photosynthesis was improved under ECO2 with SM and such an improvement was associated with improved water use efficiency and instantaneous carboxylation efficiency. Furthermore, SM caused a reduction in ion absorption rate, except for Ca(2+) , while ECO2 increased the uptake rate. Finally, the activity of SOD, POD and the content of MDA and H2 O2 were enhanced under SM treatments and were highest in ACO2 +SM. In contrast, T-AOC activity and GSH content significantly declined in ACO2 +SM compared to other treatments. These results suggest that ACO2 is not sufficient to counteract SM impact, but the increase is usually caused by improvement in CO2 nutrition in ECO2 +SM in comparison with ACO2 +SM., (© 2016 German Botanical Society and The Royal Botanical Society of the Netherlands.)

The effect of saline stress on physiological and morphological parameters in Callistemon citrinus plants was studied to evaluate their adaptability to irrigation with saline water. C. citrinus plants, grown under greenhouse conditions, were subjected to two irrigation treatments lasting 56 weeks: control (0.8 dS·m(-1)) and saline (4 dS·m(-1)). The use of saline water in C. citrinus plants decreased aerial growth, increased the root/shoot ratio and improved the root system (increased root diameter and root density), but flowering and leaf colour were not affected. Salinity caused a decrease in stomatal conductance and evapotranspiration, which may prevent toxic levels being reached in the shoot. Net photosynthesis was reduced in plants subjected to salinity, although this response was evident much later than the decrease in stomatal conductance. Stem water potential was a good indicator of salt stress in C. citrinus. The relative salt tolerance of Callistemon was related to storage of higher levels of Na+ and Cl- in the roots compared with the leaves, especially in the case of Na+, which could have helped to maintain the quality of plants. The results show that saline water (around 4 dS·m(-1)) could be used for growing C. citrinus commercially. However, the cumulative effect of irrigating with saline water for 11 months was a decrease in photosynthesis and intrinsic water use efficiency, meaning that the interaction of the salinity level and the time of exposure to the salt stress should be considered important in this species., (© 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Purpose: Developing a practical strategy for both remediating and utilizing Cd-contaminated soils is important, particularly in areas with limited soil resources. Here, Erigeron breviscapus, a plant material used for extracting scutellarin, was selected for a pot experiment to evaluate utilization and remediation potential of heavily Cd-contaminated soil. Methods: We established five treatments, comprising a no-Cd added control (CK) and 0.01% Cd addition with four amounts of lime (0, 5, 15 and 20 g·kg−1 for CdL0, CdL5, CdL15 and CdL20, respectively). Systematic analysis of E. breviscapus physiological and biochemical characteristics, Cd-accumulation capacity, and active ingredients content were performed to thoroughly assess the application effectiveness and ecological restoration potential of lime in managing heavily Cd-contaminated soils. Results: Compared with CdL0, lime application (CdL5, CdL15 and CdL20) reduced soil available Cd and plant shoot-Cd concentrations by 19.2–29.4% and 29.3–36.3%, respectively, due to decreased bioconcentration factor. Soil-Cd concentrations after harvesting E. breviscapus was decreased by 11.8–31.7% with lime application compared with that before cultivation. In the CdL0 treatment, biomass and scutellarin content of E. breviscapus decreased compared to those of the CK. However, plant biomass and scutellarin content increased with CdL15 and CdL20 compared to CdL0. Structural equation modeling indicated that lime application reduced plant Cd uptake via regulating soil-Cd speciation, thereby alleviating damage caused by Cd to photosynthesis, antioxidant system, and Mg acquisition, ultimately increasing biomass and scutellarin content of E. breviscapus. Conclusions: In summary, growing E. breviscapus after lime application is a feasible method for remediating and utilizing heavily Cd-contaminated soil. [ABSTRACT FROM AUTHOR]

Salinity is one of the primary abiotic stresses that seriously hampers plant quality and productivity. It is feasible to reduce or reverse the negative effects of salt through the supplementation of silicon (Si) and aspartic acid (Asp). However, the question of how exogenous Si and Asp induce salt tolerance in celery remains incipient. Thus, this study was performed to determine the synergistic effects of Si and Asp on the alleviation of salt stress in celery. To this end, the celery plants were cultivated in a controlled regime (light for 14 h at 22 °C; darkness for 10 h at 16 °C) and treated with one of five treatments (CK, 100 mM NaCl, 100 mM NaCl + 75 mg/L Si, 100 mM NaCl + 100 mg/L Asp, and 100 mM NaCl + 75 mg/L Si + 100 mg/L Asp). Results showed that solely NaCl-treated celery plants developed salt toxicity, as characterized by decreased growth, declined photosynthetic ability, disturbed nutritious status and internal ion balance, and a boosted antioxidant defense system (Improved antioxidant enzymes and reduced ROS accumulation). In contrast, these adverse effects of NaCl were ameliorated by the additions of Si and Asp, regardless of Si, Asp, or both. Moreover, the mitigatory impacts of the co-application of Si and Asp on salt stress were more pronounced compared to when one of them was solely applied. Collectively, exogenous Si and Asp alleviate the degree of salt stress and thereby improve the salt tolerance of celery. [ABSTRACT FROM AUTHOR]

Basil (Ocimum basilicum L.) contains abundant nutrients and is considered an economically important edible vegetable. The optimal nutrient levels will increase the productivity and basil quality. However, prominent research on basil regarding the diagnostic nutrient deficiency standard and the corresponding nutrient uptake is still scarce. To this end, the basil plants were hydroponically cultured and subjected to one of 14 nutrient solution treatments, corresponding to the omission of a single nutrient element (designated as -N, -P, -K, -Ca, -Mg, -NH4+, -NO3−, -S, -Fe, -Mn, -B, -Zn, -Mo, and -Cu) and a complete nutrient solution (CS) as the control. The most common nutrient deficiency symptoms were chlorosis, stunted roots and growth, and even leaf necrosis and abscission, in particular of -N, -P, -NO3−, and -Fe. We also found that basil is a NH4+-sensitive species. The photosynthetic capacity (photosynthesis pigments, Fv/Fm ratio, and greenness index) was disturbed to varying degrees when a single nutrient was omitted from the nutrient solution. Additionally, the omission of a specific single nutrient confers significant differences in the tissue nutrients, regardless of the macronutrients and micronutrients considered. Concomitantly, multivariate analysis suggested the correlations among certain important nutrients were distinctly different under different treatments (correlation analysis); the influences of different nutrient deficiencies on the tissue nutrient concentrations showed similarity (principal component analysis). Collectively, the growth, physiological, and biochemical changes studied in this trial not only improved our knowledge for diagnosing nutrient deficiency symptoms for practical cultivation but also provided a comprehensive understanding of the internal nutrient associations in basil. [ABSTRACT FROM AUTHOR]

Salinity is one of the primary abiotic stresses that seriously hampers plant quality and productivity. It is feasible to reduce or reverse the negative effects of salt through the supplementation of silicon (Si) and aspartic acid (Asp). However, the question of how exogenous Si and Asp induce salt tolerance in celery remains incipient. Thus, this study was performed to determine the synergistic effects of Si and Asp on the alleviation of salt stress in celery. To this end, the celery plants were cultivated in a controlled regime (light for 14 h at 22 °C; darkness for 10 h at 16 °C) and treated with one of five treatments (CK, 100 mM NaCl, 100 mM NaCl + 75 mg/L Si, 100 mM NaCl + 100 mg/L Asp, and 100 mM NaCl + 75 mg/L Si + 100 mg/L Asp). Results showed that solely NaCl-treated celery plants developed salt toxicity, as characterized by decreased growth, declined photosynthetic ability, disturbed nutritious status and internal ion balance, and a boosted antioxidant defense system (Improved antioxidant enzymes and reduced ROS accumulation). In contrast, these adverse effects of NaCl were ameliorated by the additions of Si and Asp, regardless of Si, Asp, or both. Moreover, the mitigatory impacts of the co-application of Si and Asp on salt stress were more pronounced compared to when one of them was solely applied. Collectively, exogenous Si and Asp alleviate the degree of salt stress and thereby improve the salt tolerance of celery.

Water scarcity is a major problem for crop production around the world including Southwestern United States and growers are increasingly using groundwater for agriculture in Southern New Mexico. Most of the groundwater in New Mexico is brackish and continuous long-term use could lead to salt accumulation in the soil. Reverse osmosis (RO) can desalinate brackish groundwater (BGW), however, environmentally safe disposal of RO concentrate is costly. This greenhouse study evaluated the effects of BGW and RO concentrate at various growth stages of two chile pepper cultivars, NuMex Joe E. Parker and NuMex Sandia Select. Five salinity treatments were applied to plants, three of them used saline waters of 0.6 (control), 4.0 (BGW), and 8.0 dS/m (RO) throughout the growing season, whereas the other two changed waters of 4.0 and 8.0 dS/m to waters of 2.0 and 6.0 dS/m from the beginning of the flowering stage. Number of flowers, days to flowering, relative plant heights, relative fresh biomass, fruit yields, photosynthetic rate (Pn), stomatal conductivity (gS), and actual evapotranspiration (ETa) significantly decreased with increasing irrigation water salinity levels. Concentrations of Mg2+, Na+, and Cl− in plants increased with increasing water salinity levels. Changing to irrigation with reduced salinity waters of 2.0 and 6.0 dS/m at the flowering stage initiated reproductive development more rapidly and alleviated the adverse influence of salinity on the number of flowers of chile pepper, plant height, Pn, as well as fresh shoot and fruit weight than that with continuous irrigation with electrical conductivity (EC) of 4.0 dS/m and 8.0 dS/m beyond the flowering stage. Irrigation that practices a change from high salinity to lower salinity at the flowering stage can optimize the use of saline irrigation water for growing chile peppers.

It is well known that plants can grow under space conditions, however, perturbations of many biological phenomena have been highlighted due to the effect of altered gravity and its possible interaction with other factors ( e.g., CO2, ion radiation, etc. Our aim was to test whether elevated CO2 could provide 'protection' to Gynura bicolor against the damaging effects of simulated microgravity ( SM) on photosynthesis, ion uptake and antioxidant activity. As compared to G. bicolor grown in ambient CO2 with no SM ( ACO2), growth and yield of the plants increased under elevated ambient CO2 with no SM ( ECO2) and decreased under ACO2+ SM, whereas there was no significant effect on ECO2+ SM. Reductions in the content of Chl a, carotenoids and Chl a+b were 17.9%, 20.7% and 17.9% under ACO2+ SM, respectively, but under ECO2 there was a significant effect on all photosynthetic pigments except Chl b, compared to ACO2. Photosynthesis was improved under ECO2 with SM and such an improvement was associated with improved water use efficiency and instantaneous carboxylation efficiency. Furthermore, SM caused a reduction in ion absorption rate, except for Ca2+, while ECO2 increased the uptake rate. Finally, the activity of SOD, POD and the content of MDA and H2O2 were enhanced under SM treatments and were highest in ACO2+ SM. In contrast, T- AOC activity and GSH content significantly declined in ACO2+ SM compared to other treatments. These results suggest that ACO2 is not sufficient to counteract SM impact, but the increase is usually caused by improvement in CO2 nutrition in ECO2+ SM in comparison with ACO2+ SM. [ABSTRACT FROM AUTHOR]

This study evaluated the capacity of high relative humidity associated with K + supply in mitigating harmful effects caused by salt stress on physiological parameters of Jatropha curcas plants. The plants were subjected to four different treatments (K0Na0, K0Na1, K1Na0 and K1Na1) and two different levels of humidity, low (40%) and high (80%), in chamber growth conditions. The plants’ growth was higher under conditions of high relative humidity when compared to low humidity in all the treatments studied. The CO 2 assimilation rate, transpiration and stomatal conductance were stimulated by high humidity independently of treatments of K + and Na + . The Na + concentration in the shoots was more elevated in plants treated with NaCl when compared to NaCl-free plants. On the other hand, the shoots’ K + concentration was highly stimulated in the presence of K + ions, especially in combination with high relative humidity (RH). The shoots’ Na + transport rate was strongly stimulated by a combination of 50 mM NaCl + 40% RH when compared to high humidity. Conversely, the shoots’ K + transport was significantly higher in plants when they were supplied with K + and exposed to high relative humidity. In the roots, the transport rate of Na + presented a similar pattern to that found in the shoot. However, surprisingly, K + transport rate was increased in plants supplied with K + and 40% RH in NaCl absence. The plants exposed to low relative humidity showed lower K + /Na + ratios than plants exposed to 80% RH both in shoots and roots. In addition, the shoots and roots selectivity (K,Na) was strongly stimulated in plants exposed to high humidity when compared to low humidity. In conclusion, the combined effects of high relative humidity and a supply of K + were able to improve the growth, the leaf gas exchange and ionic homeostasis of J. curcas plants. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to assess varietal differences of quinoa's tolerance to salinity and to investigate physiological mechanisms conferring these differences. Methods: Production of biomass in fourteen varieties grown under saline conditions was analysed in a pot experiment. For two contrasting varieties, the Danish variety Titicaca and the Bolivian variety Utusaya gas exchange, chlorophyll content index (CCI), fluorescence and ion relations were studied. Results: Responses to salinity differed greatly among the varieties; least affected were two varieties from the Bolivian altiplano and a variety from Peru. Titicaca and Utusaya both had substantially increased K+ concentrations in the leaf sap. But, Utusaya was much more efficient in restricting xylem Na+ loading. Xylem Na+ and K+ loading were found to be uncoupled. Utusaya maintained a relatively high stomatal conductance resulting in an only 25% NaCl-induced reduction in net CO assimilation compared to a 67% reduction in salt treated Titicaca plants. Maximum photochemical efficiency of PSII was not affected by salinity. Conclusion: In addition to maintaining high gas exchange, tolerant varieties better control xylem Na+ loading. To what extent this control is related to radial root Na+ uptake or to the activity of Na+/H+-exchangers at the xylem parenchyma boundary remains to be studied. [ABSTRACT FROM AUTHOR]

To understand the mechanisms of salt tolerance in a halophyte, sea aster (Aster tripolium L.), we studied the changes of water relation and the factors of photosynthetic limitation under water stress and 300 mM NaCl stress. The contents of Na+ and Cl- were highest in NaCl-stressed leaves. Leaf osmotic potentials (Ψs) were decreased by both stress treatments, whereas leaf turgor pressure (Ψt) was maintained under NaCl stress. Decrease in Ψs without any loss of ψt accounted for osmotic adjustment using Na+ and Cl- accumulated under NaCl stress. Stress treatments affected photosynthesis, and stomatal limitation was higher under water stress than under NaCl stress. Additionally, maximum CO2 fixation rate and O2 evolution rate decreased only under water stress, indicating irreversible damage to photosynthetic systems, mainly by dehydration. Water stress severely affected the water relation and photosynthetic capacity. On the other hand, turgid leaves under NaCl stress have dehydration tolerance due to maintenance of Ψt and photosynthetic activity. These results show that sea aster might not suffer from tissue dehydration in highly salinized environments. We conclude that the adaptation of sea aster to salinity may be accomplished by osmotic adjustment using accumulated Na+ and Cl-, and that this plant has typical halophyte characteristics, but not drought tolerance. [ABSTRACT FROM AUTHOR]

Gametophytes of Onoclea sensiblis L. were grown under various light and media‐ion conditions to gain a better understanding of the source/sink relationships between photosynthetic and ion‐absorbing cells. There was a clear interdependency between green cell and rhizoid functions, such that the growth and development of the rhizoids was completely dependent on the internal delivery of photosynthates from green cells, and conversion of the one‐dimensional filament into the two‐dimensional prothallus required monovalent cations that could only be provided by rhizoid uptake. The need for monovalent cations was related to osmotic demands of dividing and expanding cells; prothallial development was blocked by monovalent cation deficiency, and the system resorted to Na+ uptake to support cell expansion when K+ was absent. Surgical excisions of filament cells further demonstrated the high degree of coordinated growth between the light‐absorbing and ion‐absorbing regions. It was also learned that excised sub‐apical cells of the protonemata, like the intensively studied apical cell, were capable of remodelling remnants of the filament into a normal prothallus. [ABSTRACT FROM PUBLISHER]

Glucose is recognized as signaling molecule that regulates growth and development of plants under various environmental cues, but their effect in regulation of copper induced toxicity in plants is not yet investigated. This study revealed the effect of exogenously sourced glucose on Cucumber plants exposed to increasing concentration of copper. Glucose mediated response on growth performance, photosynthetic efficiency, antioxidant enzymes, oxidative stress markers, ion uptake were analyzed in the presence and absence of copper. Glucose alone and in combination with lower concentration of copper improved the growth, photosynthetic performance, and antioxidant capacity of cucumber plants. However, higher concentrations of copper alone showed oxidative damage through increased electrolyte leakage, H 2 O 2 accumulation, lipid peroxidation and reduced uptake of macronutrients. Application of glucose to copper-stressed plants enhanced activities of Rubisco, antioxidant enzymes, proline accumulation and maintained copper level in aerial parts of plants. These enhanced activities of antioxidant enzymes, proline accumulation, uptake of NPK and maintained equilibrium of copper in plants, leading to detoxification of copper stress in cucumber plants. This study provides an understanding that exogenous application of glucose can be employed as vital biochemical approach in alleviating copper-induced toxicity and could be utilized as phytoremediation technique for removal of excess transition metal from polluted soil. [Display omitted] • Lower concentration of Cu improved growth and photosynthetic efficiency whereas, higher concentration induced toxicity. • Cu toxicity imbalances the ROS and antioxidant system with increased lipid peroxidation, and H 2 O 2 content. • Glucose act as signaling molecule that improved growth, water relation and photosynthetic efficiency. • Glucose treatment to the Cu-stressed plants recovered the damage through enhanced antioxidant system. [ABSTRACT FROM AUTHOR]