In UV‐B Irradiated Rice High Levels of Mn Limits Chloroplasts Injury Triggered by Oxidative Stress

The molecular mechanism to control the oxidative burst exerted by Mn accumulation in rice (Oryza sativa L.) plants, grown in hydroponics containing 0.5, 2 and 8 mg l^–1 Mn and irradiated with a total biological effective UV‐B irradiation of 20.825 kJ m^?2, was investigated in the chloroplasts at the 15th and 21st days after germination. In both experimental periods, Mn accumulation kinetics in the leaves and in the chloroplast lamellae displayed overall increases. Coupled to higher membrane selectivity, superoxide production and acyl lipids peroxidation in the thylakoids decreased, prompting upper rates of the Hill and Mehler reactions. Connected to UV‐B irradiation, higher accumulated Mn in thylakoids was found to be chelated in a 36.5 kDa protein, with Mn/protein ratio of about 1 and high content of Gln, Asp, Glu, Leu and Gly, being its EPR spectrum characteristic of high‐spin Mn(II), in a S = 5/2 ground state. As this protein exhibited enzymatic catalysis of superoxide dismutation, it was concluded that, under UV‐B irradiation, the high internal tolerance of Oryza sativa L. to Mn during the vegetative growth also triggers the synthesis of a manganese protein that mimics superoxide dismutase functioning, therefore furnishing an additional intimate protection against oxidative stress.     

The Physiology and Stability of Leaf Carbon Isotope Discrimination as a Measure of Water‐Use Efficiency in Barley on the Canadian Prairies

Temporal and seasonal water deficit is one of the major factors limiting crop yield on the Canadian prairie. Selection for low carbon isotope discrimination (Δ¹³C) or high water‐use efficiency (WUE) can lead to improved yield in some environments. To understand better the physiology and WUE of barley under drought conditions on the Canadian prairie, 12 barley (Hordeum vulgare L.) genotypes with contrasting levels of leaf Δ¹³C were investigated for performance stability across locations and years in Alberta, Canada. Four of those genotypes (‘CDC Cowboy’, ‘Niobe’, ‘170011’ and ‘Kasota’) were also grown in the greenhouse under well‐watered and water‐deficit conditions to examine genotypic variations in leaf Δ¹³C, WUE, gas exchange parameters and specific leaf area (SLA). The water‐deficit treatment was imposed at the jointing stage for 10 days followed by re‐watering to pre‐deficit level. Genotypic ranking in leaf Δ¹³C was highly consistent, with ‘170011’, ‘CDC Cowboy’ and ‘W89001002003’ being the lowest and ‘Kasota’‘160049’ and ‘H93174006’ being the highest leaf Δ¹³C. Under field and greenhouse (well‐watered) conditions, leaf Δ¹³C was significantly correlated with stomatal conductance (g_s). Water deficit significantly increased WUE, with ‘CDC Cowboy’– a low leaf Δ¹³C genotype with significantly higher WUE and lower percentage decline in assimilation rate (A) and g_s than the other three genotypes (‘Niobe’, ‘170011’ and ‘Kasota’). We conclude that leaf Δ¹³C is a stable trait in the genotypes evaluated. Low leaf Δ¹³C of ‘CDC Cowboy’ was achieved by maintaining a high A and a low g_s, with comparable biomass and grain yield to genotypes showing a high g_s under field conditions; hence, selection for a low leaf Δ¹³C genotype such as ‘CDC Cowboy’ maybe important for maintaining productivity and yield stability under water‐limited conditions on the Canadian prairie.     

Contrasting Water‐Use Efficiency (WUE) Responses of a Potato Mapping Population and Capability of Modified Ball‐Berry Model to Predict Stomatal Conductance and WUE Measured at Different Environmental Conditions

Potatoes (Solanum tuberosum L.) are drought‐sensitive and more efficient water use, while maintaining high yields is required. Here, water‐use efficiency (WUE) of a mapping population comprising 144 clones from a cross between 90‐HAF‐01 (Solanum tuberosum₁) and 90‐HAG‐15 (S. tuberosum₂ × S. sparsipilum) was measured on well‐watered plants under controlled‐environment conditions combining three levels of each of the factors: [CO₂], temperature, light, and relative humidity in growth chambers. The clones were grouped according to their photosynthetic WUE (pWUE) and whole‐plant WUE (wpWUE) during experiments in 2010. Two offspring groups according to pWUE and wpWUE were identified on the basis of experiments conducted in 2010, which in experiments in 2011 again showed significant differences in pWUE (46 %, P < 0.001) and wpWUE (34 %, P < 0.001). The high‐WUE group had a higher net photosynthesis rate (34 %) and dry matter accumulation (55 %, P < 0.001) rather than leaf‐level transpiration rate (?4 %, no significant difference) or whole‐plant water use (16 %). The pWUE correlated negatively to the ratio between leaf‐internal and leaf‐external [CO₂] (R² = ?0.86 in 2010 and R² = ?0.83 in 2011, P < 0.001). The leaf chlorophyll content was lower in the high‐WUE group indicating that the higher net photosynthesis rate was not due to higher leaf‐N status. Less negative value of carbon isotope discrimination (δ¹³C) in the high‐WUE group was only found in 2011. A modified Ball‐Berry model was fitted to measured stomatal conductance (g_s) under the systematically varied environmental conditions to identify parameter differences between the two groups, which could explain their contrasting WUE. Compared to the low‐WUE group, the high‐WUE group showed consistently lower values of the parameter m, which is inversely related to WUE. Differences related specifically to the dependence of g_s on humidity and net photosynthesis rate were only found in 2010. The lower ratio between leaf‐internal and leaf‐external [CO₂] and higher WUE of the high‐WUE group was consistent over a wide range of air vapour pressure deficits from 0.5 to 3.5 kPa. The mapping population was normally distributed with respect to WUE suggesting a multigenic nature of this trait. The WUE groups identified can be further employed for quantitative trait loci (QTL) analysis by use of gene expression studies or genome resequencing. The differences in population WUE indicate a genetic potential for improvement of this trait.     

Acquired Thermo‐Tolerance and Trans‐Generational Heat Stress Response at Flowering in Rice

In rice, pre‐exposure to sublethal treatment followed by harsh lethal treatment is known to improve tolerance of different abiotic stresses at the vegetative stage within and across generations. Our major aim was to test the phenomenon of thermo‐tolerance at flowering across (trans)‐generations and within generation using rice cultivars contrasting for heat stress tolerance at flowering. To test trans‐generational response, plants were exposed to higher temperature at flowering stage and seeds obtained from previous generations were exposed to heat stress during flowering, which recorded significantly lower fertility when exposed to the same degree of stress in their subsequent generations. A pre‐acclimation to moderately high acclimating temperatures imposed over three different durations during the vegetative and initial reproductive stage showed positive response in the tolerant N22, particularly under severe heat stress (40 °C). This finding indicates the possibility of acquiring ameliorative thermo‐tolerant mechanisms at anthesis, restricted to tolerant genetic backgrounds to combat subsequent harsh conditions within the same generation. However, trans‐generational memory was ineffective in mitigating spikelet sterility losses in both tolerant and susceptible backgrounds. Rice is extremely sensitive to heat stress during flowering; hence, similar exercise across other crops of interest needs to be carried out before generalizing conclusions.     

5‐Aminolevulinic Acid Activates Antioxidative Defence System and Seedling Growth in Brassica napus L. under Water‐Deficit Stress

The present study assesses the effects of 5‐aminolevulinic acid (ALA, 0, 0.1, 1 and 10 mg l^?1) on the growth of oilseed rape (Brassica napus L. cv. ZS758) seedlings under water‐deficit stress induced by polyethylene glycol (PEG 6000, 0 and ?0.3 MPa). Water‐deficit stress imposed negative effects on seedling growth by reducing shoot biomass, cotyledon water potential, chlorophyll content and non‐enzymatic antioxidants (glutathione and ascorbic acid) levels. On the other hand, water‐deficit stress enhanced the malondialdehyde (MDA) content, reactive oxygen species (ROS) production, enzymatic antioxidants activities, reduced/oxidized glutathione ratio (GSH/GSSG) and reduced/oxidized ascorbic acid (ASA/DHA) ratio in seedlings. Application of ALA at lower dosages (0.1 and 1 mg l^?1) improved shoot weight and chlorophyll contents, and decreased MDA in rape seedlings, whereas moderately higher dosage of ALA (10 mg l^?1) hampered the growth. The study also indicated that 1 mg l^?1 ALA improved chlorophyll content, but reduced MDA content and ROS production significantly under water‐deficit stress. Lower dosages of ALA (0.1 and 1 mg l^?1) also enhanced GSH/GSSG and ASA/DHA as compared to the seedlings under water‐deficit stress. The antioxidant enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase and superoxide dismutase) enhanced their activities remarkably with 1 mg l^?1 ALA treatment under water‐deficit stress. It was also revealed that 1 mg l^?1 ALA treatment alone induced the expression of APX, CAT and GR substantially and under water‐deficit stress conditions ALA treatment could induce the expression of POD, CAT and GR to a certain degree. These results indicated that 0.1–1 mg l^?1 ALA could enhance the water‐deficit stress tolerance of oilseed seedlings through improving the biomass accumulation, maintaining a relative high ratio of GSH/GSSG and ASA/DHA, enhancing the activities of the specific antioxidant enzymes and inducing the expression of the specific antioxidant enzyme genes.     

Effect of Water‐Deficit Stress on Germination and Early Seedling Growth in Sugar Beet

Sugar beet progeny lines screened for both high water use efficiency and high sugar yield under drought stress conditions in the field were assessed for the rate of seed germination and early seedling growth in water deficit stress, induced by mannitol solutions. Seeds of nine different sugar beet progeny lines were grown in three experimental conditions using filter paper, perlite and water agar as substrate. Three levels of 0.0, 0.2 and 0.3 m mannitol concentrations were applied in each experiment. A factorial design was used with three replications. Germination percentage was determined in all experiments. Seedling growth parameters such as cotyledon fresh weight, cotyledon dry weight, root fresh weight, root dry weight (RDW) and root length (RL) were measured experimentally. Abnormality was only recorded in the filter paper experiment. The results showed that drought stress could be simulated by mannitol solution and significant differences were found between stress levels for seedling characteristics. Distinct genetic variances were found among progeny lines with respect to germination and early seedling growth characteristics, except for cotyledons and RDW. Seedling growth and germination rates severely declined at the highest concentration of mannitol. The rate of abnormality was increased progressively at the germination stage with an increase in mannitol concentration but it was more pronounced in the drought‐susceptible progeny lines. The highest values of relative germination % and relative growth % of RL were obtained for the most tolerant line. In conclusion, seedling characteristics, in addition to other physiological components involved in the seed germination process under specific stress conditions, may be considered for breeding purposes.     

Nitrogen Uptake by Rice (Oryza sativa L.) Exposed to Low Water Temperatures at Different Growth Stages

The responses of nitrogen (N) uptake by rice (Oryza sativa L.) to low water temperatures at different growth stages were examined during a 3‐year field trial in northern Japan. Cool irrigation water was applied at two to three temperature levels (16–25 °C) for 20–34 days during the vegetative stage and then during reproductive growth. We measured the N uptake rate, N content and canopy radiation interception during both growth stages. Exposure to low water temperature during either the vegetative or the reproductive growth stage slowed N uptake, and the magnitude of the decrease differed between the growth stages; the decrease was greater during vegetative growth than during reproductive growth. Consequently, total N uptake at maturity was most strongly reduced by low water temperature during vegetative growth and was not affected by low water temperature during reproductive growth, even though N distribution to the panicle was greatly reduced. The variations in N uptake during the growing season among growth stages and years were explained better by the amount of canopy radiation capture than by the number of degree‐days based on water temperature. This strong dependency on canopy radiation capture improves our understanding of the factors responsible for variations in N uptake under different levels of water temperature, and this knowledge will provide an opportunity to simplify the modelling of N uptake.     

Leaf Carbon Isotope Discrimination as an Accurate Indicator of Water‐Use Efficiency in Sunflower Genotypes Subjected to Five Stable Soil Water Contents

Leaf carbon isotope discrimination (CID) has been suggested as an indirect tool for breeding for water‐use efficiency (WUE) in various crops. This work focused on assessing phenotypic correlations between WUE and leaf CID and analysing genotypic variability in four sunflower genotypes grown in a greenhouse in pots with five different stable levels of soil water content (SWC). We measured WUE at whole plant and leaf (intrinsic) level. At whole plant level, WUE was derived from the ratio of total dry aerial biomass (BM) to cumulative water transpired (CWT). At leaf level, intrinsic WUE was calculated as the ratio of light‐saturated CO₂ assimilation to stomatal conductance (A/g_s) in younger expanded leaves. Significant differences among the four genotypes and the five SWCs were observed for whole plant and leaf WUE and CID. Strong negative correlations were observed between whole plant WUE and CID as well as between intrinsic WUE and CID with decreasing water availability. No relationships appeared between BM production and WUE or CID. Our results can help agronomists and breeders to evaluate sunflower lines with high WUE for adaptation to drought conditions and for reducing water consumption and crop water needs. Leaf CID appears to be a pertinent and valuable trait to select sunflower genotypes with high WUE.     

Photosynthesis and Remobilization of Dry Matter in Wheat as Affected by Progressive Drought Stress at Stem Elongation Stage

With increasingly erratic rainfall patterns particularly in drought‐prone production systems, the capacity of plants to recover productively from drought spells becomes an important feature for yield stability in rainfed agriculture. Consequently, effects of water management at the stem elongation stage on partitioning and remobilization of dry matter, alteration in photosynthesis and water‐use efficiency (WUE), and yield components of wheat plants were studied in a glasshouse pot experiment. The plants were subjected to three soil moisture regimes: well watered during all phenological stages (WW), drought affected during stem elongation and post‐anthesis stages (DD) and drought affected during stem elongation and rewatered at post‐anthesis stage (DW). Total dry weight substantially decreased by both drought treatments. However, DD plants allocated relatively higher assimilates to roots whereas DW plants remobilized them to the grains. Drought applications resulted in a decrease of grain yield and thousand grain weight while reduction was more pronounced in DD treatment. Relative contribution of post‐anthesis photosynthesis to dry matter formation in grain was higher in WW treatment (72.6 %) than DD (68.5 %) and DW (68.2 %) treatments. Photosynthetic rate, gas exchange and transpiration decreased whereas leaf (photosynthetic) and plant level WUE increased with drought applications. However, all these parameters were rapidly and completely reversed by rewatering. Our findings showed that partitioning of dry weight to grain increases with rewatering of wheat plants subjected to drought during stem elongation phase, but the relative contributions of remobilization of stem reserves and post‐anthesis photosynthesis to grain did not change. Moreover, rewatering of plants at booting stage after a drought period lead to full recovery in photosynthesis and WUE, and a significant although partial recovery of yield components, such as grain yield, TGW and harvest index.     

Characterization of Drought‐Tolerance Traits in Nodulated Soya Beans: The Importance of Maintaining Photosynthesis and Shoot Biomass Under Drought‐Induced Limitations on Nitrogen Metabolism

Drought is the single most important factor limiting soya bean (Glycine max L. Merr.) yields in the field. The following study was therefore undertaken to identify phenotypic markers for enhanced drought tolerance in nodulated soya beans. Leaf and nodule parameters were compared in three genotypes: Prima 2000, glyphosate‐resistant A5409RG and Jackson, which had similar shoot biomass and photosynthesis rates at the third trifoliate leaf stage under water‐replete conditions. When water was withheld at the third trifoliate leaf stage, photosynthesis, nodule numbers, nodule biomass and symbiotic nitrogen fixation (SNF) were greatly decreased. Significant cultivar–drought interactions were observed with respect to photosynthesis, which also showed a strong positive correlation with nodule SNF, particularly under drought conditions. Prima leaves had high water‐use efficiencies, and they also maintained high photosynthetic electron transport efficiencies under long‐term drought. Moreover, Prima had the highest shoot biomass under both water‐replete and drought conditions. A‐5409RG was the most drought‐sensitive genotype showing early closure of stomata and rapid inhibition of photosynthesis in response to drought. In addition to classifying the genotypes in relation to drought tolerance, the results demonstrate that the ability to sustain shoot biomass under nitrogen limitation is an important parameter, which can be easily applied in germplasm screening for drought tolerance in soya bean.     

Genotypic Variation of Gas Exchange Parameters and Leaf Stable Carbon and Nitrogen Isotopes in Ten Quinoa Cultivars Grown under Drought

Genotypic variations in leaf gas exchange and grain yield were analysed in 10 highland‐adapted quinoa cultivars grown in the field under drought conditions. Trials took place in an arid mountain region of the Northwest of Argentina (Encalilla, Amaicha del Valle, 22°31′S, 65°59′W). Significant changes in leaf gas exchange and grain yield among cultivars were observed. Our data demonstrate that leaf stomatal conductance to water vapour (g_s) is a major determinant of net CO₂ assimilation (A_n) because quinoa cultivars with inherently higher g_s were capable of keeping higher photosynthesis rate. Aboveground dry mass and grain yield significantly varied among cultivars. Significant variations also occurred in chlorophyll, N and P content, photosynthetic nitrogen‐use efficiency (PNUE), specific leaf area (SLA), intrinsic water‐use efficiency (_iWUE) and carboxylation capacity (A_n/C_i). Many cultivars gave promissory grain yields with values higher than 2000 kg ha^?1, reaching for Sayaña cultivar 3855 kg ha^?1. Overall, these data indicate that cultivars, which showed higher photosynthesis and conductances, were also generally more productive. Carbon isotope discrimination (Δ) was positively correlated with the grain yield and negatively with _iWUE, but δ¹⁵N did not show significant correlations. This study provides a reliable measure of specific responses of quinoa cultivars to drought and it may be valuable in breeding programmes.     

Leaf,canopy and agronomic water‐use efficiency of field‐grown sugar beet in response to potassium fertilization

Potassium (K) fertilization is important to maintain adequate concentrations of plant available K in agricultural soils to achieve best yields and improve crop stress tolerance and water‐use efficiency (WUE). Water‐use efficiency (WUE) can be expressed on various spatiotemporal scales, and it is known that responses of WUE to external stress are not uniform across scales. Multiscale evaluations of the impact of varying K fertilization on the WUE of C₃ crops under field conditions are missing so far. In the present field study, we evaluated effects of K fertilization on WUE of sugar beet (Beta vulgaris L.) on short‐termed leaf‐ (WUE_Leaf) and canopy‐scales (WUE_Canopy) and as the agronomic ratio of white sugar yield (WSY) to in‐season water use (i.e. WUE_WSY). In K‐fertilized plots, WUE_WSY was enhanced by 15.9%. This effect is attributed to increased beet yield and WSY, as no differences in total in‐season water use between fertilized and unfertilized plots were observed. Potassium (K) fertilization significantly enhanced the leaf area index, resulting in a more efficient depletion of soil moisture by roots in K‐fertilized plots. As a consequence, WUE_Leaf was increased due to stomatal adjustment. Potassium (K) improved WUE_Canopy only by tendency. It is concluded that K fertilization improves the WUE of field‐grown sugar beet across scales, but processes that regulate WUE are highly scale dependent.     

High embryo sac fertility and diversity of abnormal embryo sacs detected in autotetraploid indica/japonica hybrids in rice by whole‐mount eosin B‐staining confocal laser scanning microscopy

An eosin B staining procedure for use with confocal microscopy (WE‐CLSM) was used to examine the mature embryo sacs in 24 typical autotetraploid (2n = 4x = 48) indica/japonica hybrids and to compare with their original diploid (2n = 2x = 24) indica/japonica hybrids in rice. Four of the 24 hybrids showed >80% embryo sac fertility, and 13 hybrids over 70%. The average embryo sac fertility of the 24 autotetraploid indica/japonica hybrids was 68.08%, which was 17.33% higher than that in diploid hybrids. When compared with the diploid hybrids, 79.17% of the autotetraploid hybrids had higher embryo sac fertility. A diversity of abnormal embryo sacs occurred in autotetraploid indica/japonica hybrids. Embryo sac abnormalities were similar for both autotetraploid and diploid hybrid, but their frequencies were different. Some novel abnormal types were found in autotetraploid hybrids, such as enlarged egg apparatus. The embryo sac fertilities and frequencies of various abnormalities in autotetraploid hybrids varied with parental genotype and environment. The average seed set of the autotetraploid hybrids were higher than their diploid hybrids in different growing seasons.     

Diversity in daytime and night‐time transpiration dynamics in barley indicates adaptation to drought regimes across the Middle‐East

A challenge to breeding drought‐tolerant barley in the Middle‐East is that precipitation and evaporative demand patterns dictate opposite water use strategies (conservative vs. risk‐taking). To characterize these strategies, we examined high‐resolution, whole‐plant transpiration rate (TR) responses to increasing vapour pressure deficit (VPD) and nocturnal TR (TR_N) dynamics among 25 local barley genotypes, using a novel phenotyping system. These traits were specifically selected because they exist under modalities enabling the expression of both strategies. The genotypes were selected from locations spread across a large aridity gradient represented by temperature and precipitation data spanning 30 years. Here, we uncovered a substantial diversity in TR responses to VPD where slopes of the linear responses correlated negatively with local maximal temperatures, pointing to opposite drought tolerance strategies. Low canopy conductance (low slopes) was associated with higher aridity, likely to enable water‐saving, while higher conductance was associated with wetter areas, likely to enable a more aggressive water use to maximize physiological activity. TR_N was highly diverse and represented up to 15% of maximal daytime TR, pointing to the possibility of increasing water‐saving by reducing TR_N. Furthermore, we detected pre‐dawn variation in TR_N that negatively correlated with local precipitation, indicating that a tighter circadian control is associated with adaptation to drought, consistently with a circadian resonance mechanism. These findings indicate that canopy conductance and TR_N are potentially beneficial to design drought‐tolerant barley germplasm adapted to different drought regimes taking place in the Middle‐East.     

Foliage‐applied sodium nitroprusside and hydrogen peroxide improves resistance against terminal drought in bread wheat

Terminal drought is threatening the wheat productivity worldwide, which is consumed as a staple food by millions across the globe. This study was conducted to examine the influence of foliage‐applied stress signalling molecules hydrogen peroxide (H₂O₂; 50, 100, 150 μm ) and nitric oxide donor sodium nitroprusside (SNP; 50, 100, 150 μm ) on resistance against terminal drought in two bread wheat cultivars Mairaj‐2008 and BARS‐2009. These stress signalling molecules were applied at anthesis stage (BBCH 61); drought was then imposed by maintaining pots at 35% water holding capacity. Terminal drought caused significant reduction in grain yield of both tested bread wheat cultivars; however, foliage application of both stress signalling molecules at either concentration improved the performance of both bread wheat cultivars. Maximum improvement in 100‐grain weight (12.2%), grains per spike (19.7%), water‐use efficiency (WUE; 19.8%), chlorophyll content index (10.7%), total soluble phenolics (21.6%) and free leaf proline (34.3%), and highest reduction in leaf malondialdehyde contents (20.4%) was recorded when H₂O₂ was foliage‐applied at 100 μm . Foliage application of SNP enhanced the grains per spike, 100‐grain weight and grain yield by 14.9%, 11.3% and 20.1%, respectively, than control. The foliage‐applied stress signalling molecules improved the accumulation of soluble phenolics, proline and glycine betaine with simultaneous reduction in malondialdehyde contents, which enabled wheat plants to sustain the biological membranes under stress resulting in better stay green (high chlorophyll contents) under drought. This helped improving the grain number, grain weight, grain yield, WUE and transpiration efficiency. In crux, foliage‐applied H₂O₂ and SNP, at pre‐optimized rate, may be opted to lessen the drought‐induced yield losses in bread wheat in climate change conditions.     

Development of AS‐PCR marker based on a key mutation confirmed by resequencing of Wx‐mp in Milky Princess and its application in japonica soft rice (Oryza sativa L.) breeding

Soft rice with low amylose content (AC) ranging by 5–15% is a unique type with special eating and appearance quality and has become popular in the rice market. We resequenced the Wx‐mp, a key allele from Milky Princess, a Japanese low AC variety, and found that the +473 mutation in exon 4 is the key mutation in both Wx‐mp and its ancestor allele, Wx‐mq from Milky Queen. Based on this functional mutation, an allele‐specific PCR (AS‐PCR) marker was developed and proven in a breeding population derived from a cross between a Chinese late variety Nan Keng 46 (Wx‐mp/Wx‐mp) and an early line Ning 63121(Wx‐b/Wx‐b). Based on the marker‐aided selection by our newly developed AS‐PCR marker for Wx‐mp and the known ST10 marker for Stvb‐i, a total of 12 Wx‐mp homozygotes were selected from 198 F₂ progenies, and four of them were immune to rice stripe virus (RSV) with averagely 11.3 days earlier heading than Nan Keng 46 without significant change in grain yield.     

Growth,Physiological Attributes and Antioxidant Enzyme Activities in Soybean Seedlings Treated With or Without Silicon Under UV‐B Radiation Stress

Silicon (Si) can increase plant defence systems against abiotic and biotic stress, but there is little information on UV‐B radiation stress alleviation by Si for field crops. Using soybean (Glycine max (L.) Mell) seedlings, we determined how Si may mediate UV‐B radiation stress by studying changes in biomass, physiological attributes and antioxidants’ activities. The seedlings were raised with 0, 1.70 and 2.55 mm of Si in the growth chamber under ambient, ambient +2.7 kJ m^?2 day and ambient +5.4 kJ m^?2 day of UV‐B radiation. As expected, plants suffered severe growth limitations under UV‐B radiation, but Si alleviated these limitations through improvements in leaf area (LA) and root‐to‐shoot ratio (R/S). The UV‐B radiation stress reduced the LA by 73.9–94.7%, total dry weight (TDW) by 11.8–36.6% and R/S by 9.2–30.2% but induced the activities of soluble protein by 18.4–21.0%, catalase (CAT) by 22.7–54.2%, superoxide dismutase (SOD) by 31.9–63.1%, and peroxidases (POD) by as much as 162.9–381.6%. Further confirmation of stress alleviations by Si was noted from reductions in these stress signals (antioxidant activities) under UV‐B radiation: CAT decreased significantly by 78.3–79.4%, SOD by 5.3–7.2% and POD by 49.9–61.9% in silicon‐treated UV‐B stressed soybean.