Higher Net Photosynthetic Rate Research Articles

Physiological characteristics, dry matter, and active component accumulation patterns of Changium smyrnioides in response to a light intensity gradient

Context: Changium smyrnioides Wolff (Apiaceae) is an endangered medicinal plant with numerous pharmacological uses. Objective: To investigate the effect of light intensity levels on the growth and accumulation of secondary metabolites of C. smyrnioides, cultivated seedlings were subjected to different relative light intensities via sun-shading. Materials and methods: Changium smyrnioides seedlings were subjected to five irradiance treatments (100, 60.54, 44.84, 31.39, and 10.56% sunlight) in glasshouse for 9 months. Enzymatic and non-enzymatic antioxidants with spectrophotometric method, photosynthetic parameters with Li-6400XT, dry matter accumulation and active component contents in the root with spectrophotometric and HPLC method were analyzed. Results: With an increase in relative light intensity levels, activities of enzymatic and non-enzymatic antioxidants, and malondialdehyde (MDA) contents were increased overall, while net photosynthetic rate (Pn) and dry matter accumulation patter first increased and then declined. The highest net photosynthetic rate (30.68 μmol/m2·s) and dry root weight (5.07 g) were achieved under 60.54% sunlight. Lower relative light intensity levels stimulated the accumulation levels of bioactive compounds in the roots so that the highest contents of mannitol (1.35%) and choline (405.58 μg/g) were recorded under 31.39% sunlight, and the highest polysaccharide content (10.80%) were achieved under 44.84% sunlight. With a decrease in the relative light intensity levels, the water-soluble component content increased first and then decreased. Discussion and conclusion: The results revealed that 31.39–60.54% sunlight serve as appropriate relative light intensity conditions for cultivated C. smyrnioides.

Effects of Light Intensity on the Growth, Photosynthetic Characteristics, and Flavonoid Content of Epimedium pseudowushanense B.L.Guo.

Epimedium pseudowushanense B.L.Guo is used in traditional medicine as an aphrodisiac and to strengthen muscles and bones. Several recent reports have shown that flavonoids from Epimedium also significantly affect the treatment of breast cancer, liver cancer, and leukemia. However, few studies have examined the medicinal-ingredient yield of Epimedium, a light-demanding shade herb, under different light intensities. To investigate the effects of light intensity on medicinal-ingredient yields, Epimedium was exposed to five levels of light intensity until harvest time. Leaf dry biomass under L4 was the highest among different light treatments. L4 was also associated with the highest net photosynthetic rate. Quantification of epimedin A, epimedin B, epimedin C, and icariin showed that L3 produced the highest amount of epimedin C, and that flavonoid content responded to light levels differently. Results indicated that L3 and L4 were the optimal light levels for medicinal-ingredient yield.

Grain Shape as a Predictor of Salt Tolerance in Sunflower

To determine whether sunflower (Helianthus annuus L.) grain shape should be considered as a predictor of salt tolerance, seeds of three grain shapes, namely long seeds (DC6009 and RH3146 with a width‐length ratio [WLR] of 0.39), long ovate seeds (SH909 and 135 with a WLR of 0.49) and broadly ovoid seeds (RH118 with a WLR of 0.61) were exposed to 0, 1000, and 2000 mg L−1 NaCl for 30 d. Increases in the WLR increased the 100‐seed weight and kernel/hull rate (KHR) but decreased the water absorption rate (WAR). A level of 2000 mg L−1 NaCl delayed the seed mean germination time (MGT), reduced the germination percentage (GP) and germination index (GI) and caused shorter root length (RL). A level of 1000 mg L−1 NaCl improved the GP and GI compared with the no NaCl‐stressed control with the exception of the long ovate seeds. RL decreased with increasing NaCl levels, and plants with broadly ovoid seeds had longer roots than those with other shapes. The activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) were lower in the NaCl‐stressed plants than the controls. The malondialdehyde (MDA) contents increased with the NaCl levels in all cultivars. The broadly ovoid seeds exhibited the greatest enzyme activities and the highest net photosynthetic rate (Pn) at both NaCl levels. Based on emergence, early seedling growth and physiological characteristics, the long ovate seeds had a higher salt tolerance than those of the other two shapes, followed by those with long seeds. Low dose of NaCl generally improved the germination of most cultivars. Broadly ovoid seeds exhibited the greatest enzyme activities at both NaCl levels and grain shapes. Sunflowers with long‐ovate seeds perform better when subjected to slightly salinized land.

A Natural Light/Dark Cycle Regulation of Carbon-Nitrogen Metabolism and Gene Expression in Rice Shoots.

Light and temperature are two particularly important environmental cues for plant survival. Carbon and nitrogen are two essential macronutrients required for plant growth and development, and cellular carbon and nitrogen metabolism must be tightly coordinated. In order to understand how the natural light/dark cycle regulates carbon and nitrogen metabolism in rice plants, we analyzed the photosynthesis, key carbon-nitrogen metabolites, and enzyme activities, and differentially expressed genes and miRNAs involved in the carbon and nitrogen metabolic pathway in rice shoots at the following times: 2:00, 6:00, 10:00, 14:00, 18:00, and 22:00. Our results indicated that more CO2 was fixed into carbohydrates by a high net photosynthetic rate, respiratory rate, and stomatal conductance in the daytime. Although high levels of the nitrate reductase activity, free ammonium and carbohydrates were exhibited in the daytime, the protein synthesis was not significantly facilitated by the light and temperature. In mRNA sequencing, the carbon and nitrogen metabolism-related differentially expressed genes were obtained, which could be divided into eight groups: photosynthesis, TCA cycle, sugar transport, sugar metabolism, nitrogen transport, nitrogen reduction, amino acid metabolism, and nitrogen regulation. Additionally, a total of 78,306 alternative splicing events have been identified, which primarily belong to alternative 5′ donor sites, alternative 3′ acceptor sites, intron retention, and exon skipping. In sRNA sequencing, four carbon and nitrogen metabolism-related miRNAs (osa-miR1440b, osa-miR2876-5p, osa-miR1877 and osa-miR5799) were determined to be regulated by natural light/dark cycle. The expression level analysis showed that the four carbon and nitrogen metabolism-related miRNAs negatively regulated their target genes. These results may provide a good strategy to study how natural light/dark cycle regulates carbon and nitrogen metabolism to ensure plant growth and development.

Effects of fertilization on the growth, photosynthesis, and biomass accumulation in juvenile plants of three coffee (Coffea arabica L.) cultivars

We carried out a field experiment in order to study effects of fertilization in juvenile plants of three coffee (Coffea arabica) cultivars in Yunnan, SW China. Fertilization treatments included a control without fertilizer (CK), combinations of three NPK fertilization rates [high fertilization (FH), medium fertilization (FM), and low fertilization (FL) with 135, 90, and 45 g per plant per year, respectively], and at two N:P2O5:K2O ratios (R1, 1:0.5:0.8; R2, 1:0.8:0.5). The growth in juvenile plants was not altered by fertilization, with two clear growth peaks being observed in both the height and stem growth rates (RGRs) throughout a year. Both FM and FH resulted in significantly higher RGRs in both height and stem diameter compared to FL and CK in all three cultivars. At the same fertilization rate, the leaf area, branch number, longest branch length, internode number, and biomass of R2 were higher than those of R1, and P significantly affected the root biomass and root to shoot ratio. Compared to the FL treatment, both FM and FH treatments resulted in higher net photosynthetic rates and stomatal conductance across seasons, and in higher intrinsic water-use efficiency during the dry season and at the middle of the wet season. Photosynthetic nitrogen-use efficiency at R2 was higher than that at R1, but no significant differences were observed between the different fertilization rates. Among the three coffee cultivars, Caturra exhibited the highest height, stem diameter, longest branch length, and internode number. Our results indicated that the optimal N:P2O5:K2O ratio was 1:0.8:0.5 for the juvenile growth of coffee plants. Both FM and FH could help optimize the growth and photosynthetic rate of coffee plants, but FM is suitable for the ecological friendly agriculture and economic sustainability at coffee plantations.

Effects of light intensity on leaf photosynthetic characteristics, chloroplast structure, and alkaloid content of Mahonia bodinieri (Gagnep.) Laferr.

The variation of light intensity has obvious effects on leaf external morphology, internal anatomy, and physiological characteristics; it even induces changes in secondary metabolite production. The effects of different irradiance levels on biomass, gas exchange parameters, and photosynthetic pigment contents in Mahonia bodinieri (Gagnep.) Laferr. were analyzed here. Combined analyses of physiology, cytology, and HPLC were used to study the differences in leaf morphology, structure, physiological characters, and alkaloid content in response to different irradiances. The results indicated that the highest foliar biomass was observed under I 50 (50 % of full sunlight) followed by I 30 (30 % of full sunlight), the highest net photosynthetic rate, stomatal conductance, transpiration rate values were observed under I 30 followed by I 50, and lower values occurred in I 10 (10 % of full sunlight) and I 100 (full sunlight). With increased light intensity, total leaf area and the contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and chlorophyll (Chl a+b) per unit leaf area were clearly reduced, whereas leaf mass per area, carotenoid content, leaf thickness, thickness of palisade and spongy parenchyma, and stomatal density were all significantly increased. Electron microscopic observation revealed that the number of grana, stroma lamellae and the number of starch grains in chloroplasts were decreased, the number of plastoglobuli was increased when irradiance levels increased. The estimated total yield of alkaloids in a single plant was higher under I 30 and I 50 than under I 10 or I 100 as a result of the higher biomass of the plants. Therefore, I 30 and I 50 were not only beneficial to increase biomass, but also suitable for the synthesis and accumulation of the major secondary metabolites (alkaloids). Our findings provide valuable data for the determination and regulation of irradiance levels during artificial cultivation of M. bodinieri.

Leaf photosynthetic performance related to higher radiation use efficiency and grain yield in hybrid rice

Yield potential of hybrid rice has been increased by approximately 10% through breeding super hybrid rice. It is well documented that the yield superiority of super hybrid rice is related to higher radiation use efficiency (RUE). However, limited information is available on the factors that contribute to the higher RUE in super hybrid rice. In this study, field and pot experiments were conducted in 2012–2014 to compare yield attributes, RUE and leaf photosynthetic traits between a super hybrid rice cultivar Y-liangyou 087 and an ordinary hybrid rice cultivar Teyou 838. In the field experiments, Y-liangyou 087 produced 11% higher grain yield than Teyou 838. Total biomass was higher in Y-liangyou 087 than in Teyou 838, whereas the difference in harvest index was not significant. The difference in intercepted radiation was insignificant between Y-liangyou 087 and Teyou 838, while RUE was 14% higher in Y-liangyou 087 than in Teyou 838. Y-liangyou 087 had higher net photosynthetic rate than Teyou 838, especially at the late growth stages (heading and milking). In the pot experiment, higher net photosynthetic rate was also observed in Y-liangyou 087 than in Teyou 838. There were no significant differences in stomatal conductance and intercellular CO2 concentration between Y-liangyou 087 and Teyou 838. Y-liangyou 087 had higher chlorophyll a content and equal chlorophyll b content than Teyou 838. Efficiency of excitation capture by open photosystem II (Fv/Fm) and quantum yield of photosystem II (ΦPSII) were higher in Y-liangyou 087 than in Teyou 838, while the difference in photochemical quenching coefficient was insignificant. Y-liangyou 087 had higher Rubisco content than Teyou 838. These results suggest that higher RUE and grain yield can be achieved by improving leaf photosynthetic traits including chlorophyll a content, Fv/Fm, ΦPSII and Rubisco content in hybrid rice.

Photosynthesis enhanced oxidative stress tolerance in high-yield rice varieties (Oryza sativa var. japonica L.) in the field.

The objective of this study was to understand varietal differences in photosynthetic characteristics, chlorophyll fluorescence, antioxidant capability, and yield of japonica rice varieties. Nanjing 44, Oryza sativa var. japonica (average yield of 12.7 t/ha), Nanjing 46, and Nanjing 5055 (average yields of 11.3 and 11.5 t/ha) were included as "super" and high-yield varieties, respectively, whereas Wuyunjing 7 (average yield of 10.2 t/ha) was included as a control variety. These varieties were grown under field conditions in Jiangsu Province, China, in 2010-2012. Different organs (panicle, grain, etc.) were measured, before and after flowering, to identify differences of dry matter accumulation and transformation properties. Photosynthesis, the chlorophyll content, and antioxidant enzyme activities of the flag leaf in the days after flowering (DAF) were also investigated. The results showed that, compared with the other three rice varieties, Nanjing 44 had the highest plant dry weight and number of grains per panicle. It also had a relatively high net flag leaf photosynthetic rate and showed the least inhibition of photosynthesis at noon in DAF, which probably explains the higher yield in this variety. Furthermore, Nanjing 44 also had the highest stem export and conversion rate from stem to grain, exhibiting a strong ability to convert and distribute photosynthetic products. After DAF 42, Nanjing 44 still maintained a high-soluble protein content and a high antioxidant ability in the leaves to clear peroxidation products, which could protect the photosynthetic apparatus of the flag leaves, and maintain the grain-filling activity for longer. The high-yield capability of Nanjing 44 was attributed to its photosynthetic advantages in the leaves during the late developmental stage.

Water Use Efficiency in Cucumis sativus L. in Response to Daily Short-Term Temperature Drop

This study investigates the effect of daily short-term (2 h) low temperature treatment (12 °C) (DROP) on photosynthetic water use efficiency (WUE) at leaf level of cucumber plants. The DROP treatment caused an increase of WUE in the leaves treated by DROP during their early growth (D1), but not in leaves which were already mature during the treatment (D2). The WUE increase in D1 compared to D2 leaves was due to higher net photosynthetic rate at low temperature or lower transpiration rate at common temperature. The elongation of the DROP treatment from early growth stage until full maturation of leaves did not lead to an additional increase in WUE compared to the leaves treated by DROP only during their early growth.

Photosynthetic traits of Siebold's beech seedlings in changing light conditions by removal of shading trees under elevated CO₂.

The purpose of this study was to obtain basic information on acclimation capacity of photosynthesis in Siebold's beech seedlings to increasing light intensity under future elevated CO2 conditions. We monitored leaf photosynthetic traits of these seedlings in changing light conditions (before removal of shade trees, the year after removal of shade trees and after acclimation to open conditions) in a 10-year free air CO2 enrichment experiment in northern Japan. Elevated CO2 did not affect photosynthetic traits such as leaf mass per area, nitrogen content and biochemical photosynthetic capacity of chloroplasts (i.e. maximum rate of carboxylation and maximum rate of electron transport) before removal of the shade trees and after acclimation to open conditions; in fact, a higher net photosynthetic rate was maintained under elevated CO2 . However, in the year after removal of the shade trees, there was no increase in photosynthesis rate under elevated CO2 conditions. This was not due to photoinhibition. In ambient CO2 conditions, leaf mass per area and nitrogen content were higher in the year after removal of shade trees than before, whereas there was no increase under elevated CO2 conditions. These results indicate that elevated CO2 delays the acclimation of photosynthetic traits of Siebold's beech seedlings to increasing light intensity.

Changes in plant growth and photosynthetic performance of Zizania latifolia exposed to different phosphorus concentrations under hydroponic condition

The effects of phosphate concentration on plant growth and photosynthetic performance were examined in leaves of Zizania latifolia. Plants were grown for four weeks in a solution containing 0, 0.16, 0.64, and 2.56 mM orthophosphate. The results showed that the highest net photosynthetic rate (P N) was achieved at 0.64 mM orthophosphate, which corresponded to the maximum content of organic phosphorus in leaves. Low phosphorus (low-P) content in the culture solution inhibited plant growth, affecting plant height, leaf length, leaf number, tiller number, and fresh mass of leaf, sheath, culm, root, and total plant. In addition, we observed that low-P (0.16 mM) did not hinder the growth of roots but increased the root:shoot ratio, and significantly decreased the chlorophyll content, P N, stomatal conductance, and transpiration rate, but increased the intercellular CO2 concentration. Additionally, low-P significantly decreased the maximum carboxylation rate of Rubisco, the maximum rate of ribulose-1,5-bisphosphate regeneration, the effective quantum yield of PSII photochemistry, photochemical quenching coefficient, and electron transport rate, but increased the nonphotochemical quenching. However, the maximal quantum yield of PSII photochemistry was not significantly affected by low-P. High phosphorus (2.56 mM) caused only a slight decrease in gas-exchange parameters. Therefore, the decrease in growth of P-deficient Z. latifolia plants could be attributed to the lowered photosynthetic rate.

Assessment of the role of silicon in the Cu-tolerance of the C4 grass Spartina densiflora

An experiment was designed to investigate the effect of silicon supply (0 and 500μM) on Spartina densiflora plants grown at two copper (Cu) concentrations: 0 and 15mM. Growth parameters together with total concentrations of calcium, Cu, potassium, magnesium, manganese, sodium and nitrogen were determined in roots and leaves. Photosynthetic traits were followed by measurement of leaf gas exchange, efficiency of PSII biochemistry, total content of photosynthetic pigments and concentration and carbamylation of Rubisco sites concentration ([Rubisco]). Respiration and oxygen isotope fractionation were measured in roots to study the in vivo activities of cytochrome oxidase (COX) and alternative oxidase (AOX) pathways, as well as AOX capacity. The results confirm that Si supply improves growth of S. densiflora under Cu stress. Improved growth was associated with higher net photosynthetic rate. Beneficial effect of Si on S. densiflora photosynthetic apparatus was associated with a reduction of the Cu impact on active Rubisco sites, as well as on the photochemical apparatus and chlorophyll concentration. Moreover, ameliorative effects of Si were associated with the avoidance of Cu translocation from roots to leaves. Finally in vivo activities of COX and AOX pathways were strongly inhibited in Cu-treated plants, and this reduction was not mitigated by Si-treatment.Therefore, Si appears to play an important role in Cu-tolerance of S. densiflora, not by avoiding its uptake by roots, but via some mechanism to avoid Cu translocation from roots to leaves, resulting in a general reduction of Cu-induced deleterious effects on the leaf photosynthetic apparatus.

Impact of arbuscular mycorrhizal fungi on the growth, water status, and photosynthesis of hybrid poplar under drought stress and recovery

Poplars (Populus spp.) are widely used in the pulp and paper industry and as bioenergy resources. Poplars require a large amount of water for biomass accumulation and lack of water is a limiting factor for poplar growth. Arbuscular mycorrhizal (AM) fungi have been previously reported to afford some plant species with greater resistance to drought stress. However, the effects of AM fungi on hybrid poplar under drought stress and recovery have not been studied. The main aim of this study was to evaluate the effects of the AM fungus, Rhizophagus irregularis, on the growth, water status, chlorophyll (Chl) content and fluorescence, and photosynthesis of poplar seedlings. The experiment was divided into three stages. At each stage of the experiment, the seedlings were subjected to a different watering regime: well-watered (prior stress), drought, and then rewatering (recovery). Measurements were taken at the end of each stage of the experiment. The results showed that mycorrhizal plants had a higher net photosynthetic rate and Chl fluorescence compared with nonmycorrhizal plants, regardless of the stage. Mycorrhizal and nonmycorrhizal plants showed different responses to drought stress: mycorrhizal plants showed better water-use efficiency and water uptake under drought stress conditions. In general, the poplar seedlings that formed the AM symbiosis with R. irregularis showed enhanced growth and reduced loss of biomass during the drought stress compared with the nonmycorrhizal seedlings.

Responses of Plant Community Composition and Eco-Physiological Characteristics of Dominant Species to Different Soil Hydrologic Regimes in Alpine Marsh Wetlands on Qinghai–Tibetan Plateau, China

Shifts in soil water content affect seasonal wetland plant communities worldwide, but little is known about the responses and influences of plant communities to soil water content on Qinghai–Tibetan Plateau. To determine the relationship between soil water content and plant community structure in seasonally wet alpine marshes, we investigated plant community structures at different soil water content amounts in the field station at sampling sites. We selected and determined eco-physiological characteristics of species belonging to three different functional types (sedges, grasses, forbs) exposed to the same soil water regimes as characteristics in field station and under experimental flooding conditions in controlled treatments on pots plants. The field investigation indicated that decreased soil moisture (from 57 to 43 % m3 m−3) during the growing season was significantly associated with reductions in aboveground biomass, average plant height, and species richness. A shift in dominant plant species within the communities from sedges and grasses to some forbs accompanied the decrease in soil moisture. The controlled treatments demonstrated that the sedge and grass species had higher net photosynthetic rates and higher instantaneous water-use efficiencies than the forb species in the studied communities. The results indicate that shifts in wetland plant community structure and function are the result of longer dry periods and more intense rainfall events. This positive feedback suggests that changes in plant community composition could intensify soil drought conditions in seasonally wet alpine marshes in the future.

Carbon and nitrogen metabolism in arbuscular mycorrhizal maize plants under low-temperature stress

Effects of the arbuscular mycorrhizal (AM) fungus Glomus tortuosum on carbon (C) and nitrogen (N) metabolism of Zea mays L. grown under low-temperature stress was investigated. Maize plants inoculated or not inoculated with AM fungus were grown in a growth chamber at 25°C for 4 weeks and subsequently subjected to two temperature treatments (15°C, low temperature; 25°C, ambient control) for 2 weeks. Low-temperature stress significantly decreased AM colonisation, plant height and biomass. Total N content and activities of glutamate oxaloacetate transaminase and glutamate pyruvate transaminase of AM plants were higher than those of non-AM plants. AM plants had a higher net photosynthetic rate (Pn) than non-AM plants, although low temperature inhibited the Pn. Compared with non-AM plants, AM plants exhibited higher leaf soluble sugars, reducing sugars, root sucrose and fructose contents, and sucrose phosphate synthase and amylase activities at low temperature. Moreover, low-temperature stress increased the C : N ratio in the leaves of maize plants, and AM colonisation decreased the root C : N ratio. These results suggested a difference in the C and N metabolism of maize plants at ambient and low temperature regimes. AM symbiosis modulated C metabolic enzymes, thereby inducing an accumulation of soluble sugars, which may have contributed to an increased tolerance to low temperature, and therefore higher Pn in maize plants.

Dynamics of Vegetative and Reproductive Growth Patterns in Pigeonpea (Cajanus cajan L.) Grown Under Elevated CO2

Pigeonpea (Cajanus cajan (L.) Millspaugh; Fabaceae) is an important food legume crop of equatorial and semi-arid parts of the world. Our two years consecutive study on a short duration cultivar of pigeonpea (ICPL 15011) grown under enriched CO2 conditions (open top chambers; 550μmolmol-1) showed significantly high net photosynthetic rates (A’) and foliar carbohydrate content (36% and 43% respectively) which further manifested in dry biomass at harvest, with an increment of 29% over the ambient plants. Also, in vivo carboxylation efficiency was increased by 24.6% suggesting the absence of Rubisco limitation. Chlorophyll a fluorescence measurements, as indicated by Fv/Fm and Fv’/Fm’ ratios, justified enhanced photosystem II efficiency. Mass and number of nodules exhibited prodigious accretion in elevated CO2 grown plants showing 58% increase in nodule mass ratio (NMR) which directly correlated with A’. Stem and root anatomy showed an increase in the number and diameter of xylem vessels in high CO2 grown plants. An increased phloem cross sectional area in high CO2 grown pigeonpea suggested better mobility of sugars from leaf to root and subsequently to a greater sink capacity in the form of root nodules. Ultrastructure of nodule revealed the distribution of bacterial colonies in the infected zone of nodule. Further, growth under high CO2 extended life cycle of Pigeonpea with delayed flowering and pod setting by nine days. The results demonstrated a developmental reprogramming in pigeonpea due to lack of photosynthetic acclimation and increased carbohydrate - nitrogen reserves which were associated with varied vegetative and reproductive growth patterns under elevated CO2. Our study clearly suggest that the predicted future elevated CO2 atmosphere favour pigeonpea to sequester more atmospheric CO2 and N2 resulting better economic yields under natural habitats.

Duration of freezing necessary to damage the leaves of Fallopia japonica (Houtt.) Ronse Decraene

AbstractFallopia japonica (Houtt.) Ronse Decraene is an invasive plant species that introduces economic, social, and environmental stresses. After observing frost damage to F. japonica plants in the field, we exposed leaves of F. japonica and a native species (Acer saccharum Marshall) to freezing temperatures in the laboratory and compared their net photosynthetic rate to that of fresh leaves. In both species, the net photosynthetic rate of leaves frozen for 0.5 h or for 1 h were not significantly different from each other but were both significantly less than that of fresh leaves. Fresh leaves of F. japonica had a higher net photosynthetic rate than those of A. saccharum, but the relationship was reversed in all freezing treatments. Frozen leaves of F. japonica contained microscopically visible frost lenses, which revealed the mechanism of the damage. These results quantify how quickly F. japonica is damaged by freezing conditions and suggest that minimum vernal temperatures may limit its range expansion.

Physiological efficiencies in mini-core peanut germplasm accessions during summer season

In the present study, the physiological efficiencies of 181 mini-core peanut accessions (genotypes) were evaluated according to variability in their physiological performance in the field during summer (2012). Genotypes were categorized into groups of high, medium, and low physiological activity. Thirty-four genotypes showed high net photosynthetic rate (P N > 33 μmol m−2 s−1), 28 genotypes exhibited high stomatal conductance (g s > 0.54 mmol m−2 s−1), 33 genotypes manifested high transpiration rate (E > 11.8 mmol m−2 s−1), 30 genotypes performed with high water-use efficiency (WUE > 3.8), 30 genotypes reached high chlorophyll SPAD values (SCMR > 40), and 35 genotypes showed high maximum quantum yield of PSII (Fv/Fm > 0.86). In addition, few genotypes showed high values for multiple physiological traits. A total of 54 genotypes exhibited higher values in two, 20 genotypes showed a high value in three, and in eight genotypes, high values occurred in four different physiological traits. Interestingly, only two genotypes, NRCG 14493 and 14507, showed high values for five different traits. Positive correlation was observed between g s and P N, E, and g s, and between P N and Fv/Fm, while WUE and E showed a negative correlation. The genotypes with high P N, g s, and WUE coupled with high SCMR and Fv/Fm could be used in peanut crop improvement programme for yield enhancement as well as stress tolerance.

Effects of supplementary potassium nitrate on growth and gas-exchange characteristics of salt-stressed citrus seedlings

We investigated the effects of supplementary KNO3 and NaCl on one-year-old, potted Valencia orange (Citrus sinensis) scions grafted on Iranian mandarin Bakraii [Citrus reticulate × Citrus limetta] (Valencia/Bakraii) and Carrizo citrange [C. sinensis × Poncirus trifoliata] (Valencia/Carrizo) rootstocks. After watering plants for 60 days with 50 mM NaCl, the lowest reduction in dry mass, stomatal conductance, and chlorophyll (Chl) content was found in Valencia/Bakraii. Bakraii accumulated more Cl− and Na+ in roots and transferred less to Valencia leaves compared with Carrizo rootstock. Moreover, higher net photosynthetic rate was found in Valencia/Bakraii than those on Carrizo rootstock. NaCl caused a decrease in the maximal efficiency of PSII photochemistry (Fv/Fm) and effective quantum yield (ΦPSII) but elevated coefficient of nonphotochemical quenching. Salinity reduced Ca2+, Mg2+, and total N contents, and increased Na+/K+ ratio in leaves and roots of both grafting combinations. Salinity increased K+ and proline content in leaves and decreased K+ concentrations in roots of both grafting combinations. In salinized plants, nitrate supplementation (10 mM KNO3) reduced leaf abscission, Cl−, Na+, Na+/K+, and Ca2+ concentrations in leaves and roots of both combinations. K+ and N concentrations and proline increased in leaves of the nitrate-supplemented salinized plants. Supplementary nitrate increased leaf number and area, stem elongation, Chl content, Fv/Fm, and ΦPSII and stimulated photosynthetic activity. Thus, nitrate ameliorated the deleterious effects of NaCl stress and stimulated the plant metabolism and growth. It can be used as a vital treatment under such condition.

Regulation of some salt defense-related genes in relation to physiological and biochemical changes in three sugarcane genotypes subjected to salt stress.

Sugarcane (Saccharum officinale L.; Poaceae) is a sugar-producing plant widely grown in tropic. Being a glycophytic species, it is very sensitive to salt stress, and salinity severely reduces growth rate and cane yield. The studies investigating the regulation of salt defense metabolite-related genes in relation to final biochemical products in both susceptible and tolerant genotypes of sugarcane are largely lacking. We therefore investigated the expression levels of sugarcane shaggy-like kinase (SuSK), sucrose transporter (SUT), proline biosynthesis (pyrolline-5-carboxylate synthetase; P5CS), ion homeostasis (NHX1), and catalase (CAT2) mRNAs, and contents of Na(+), soluble sugar, and free proline in three sugarcane genotypes (A19 mutant, K88-92, and K92-80) when subjected to salt stress (200mM NaCl). The relative expression levels of salt defense-related genes in salt-stressed plantlets of sugarcane cv. K88-92 were upregulated in relation to salt exposure times when compared with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as housekeeping gene. In addition, final biochemical products, i.e., low Na(+), sucrose enrichment, and free proline accumulation, were evidently demonstrated in salt-stressed plantlets. Chlorophyll b, total chlorophyll, total carotenoid concentrations, and maximum quantum yield of PSII (F v/F m) in positive check (K88-92) were maintained under salt stress, leading to high net photosynthetic rate (P n) and growth retention (root length, fresh weight, and leaf area). In contrast, photosynthetic abilities in negative check, K92-80, and A19 mutant lines grown under salt stress declined significantly in comparison to control, leading to a reduction in P n and an inhibition of overall growth characters. The study concludes that the genetic background of sugarcane cv. K88-92 may further be exploited to play a key role as parental clone for sugarcane breeding program for salt-tolerant purposes.