Effects of High Temperature and Strong Light Combine Stress on Yield and Quality of Early <i>Indica</i> Rice with Different Amylose Content during Grout Filling

High temperature (HT) accompanied with strong light (SL) often occurs in early indica rice production during grout filling stage in southern China, which accelerates grain ripening. Two indica rice cultivars with different amylose content (Zhongjiazao17, ZJZ17, high amylose content; Xiangzaoxian45, XZX45, low amylose content) were grown under control (CK), HT, and HT+SL conditions during grout filling to determine the effects on grain yield and quality of rice. The results showed that compared with CK, HT and HT+SL significantly reduced the 1000-grain weight and filled grain rate whether in high or low amylose content early indica rice cultivars during grout filling, resulting in a significantly lower grain yield. Meanwhile, HT and HT+SL significantly decreased the milled rice rate, brown rice rate and head rice rate, whereas significantly increased chalky rate and chalky degree; and breakdown decreased and setback, pasting temperature increased in the cultivars, leading to the poor processing, appearance and cooking and eating quality of early indica rice cultivars. Compared with HT, the yield of ZJZ17 was significantly decreased under HT+SL, due to the lower 1000-grain weight. However, the effect of HT+SL on rice quality varied in the cultivars. In general, the yield and rice quality of ZJZ17 were relatively poor under HT+SL. Our results suggested that HT and HT+SL during grout filling had significant damage to the yield and quality of early indica rice cultivars, especially HT+SL, while the high amylose cultivar ZJZ17 showed a higher negative effect under HT+SL.     

Microalgae Improve the Photosynthetic Performance of Rice Seedlings (<i>Oryza sativa</i> L.) under Physiological Conditions and Cadmium Stress

The aim of this study was to assess the impact of the microalgae Chlorella vulgaris on the rice seedlings at physiological conditions and under cadmium (Cd) stress. We examined the effects of C. vulgaris in the nutrient solution on rice seedlings grown hydroponically in the presence and the absence of 150 μM CdCl₂, using the low (77 K) temperature and pulse amplitude modulated (PAM) chlorophyll fluorescence, P700 photooxidation measurements, photochemical activities of both photosystems, kinetic parameters of oxygen evolution, oxidative stress markers (MDA, H₂O₂ and proline), pigment content, growth parameters and Cd accumulation. Data revealed that the application C. vulgaris not only stimulates growth and improves the functions of photosynthetic apparatus under physiological conditions, but also reduces the toxic effect of Cd on rice seedlings. Furthermore, the presence of the green microalgae in the nutrient solution of the rice seedlings during Cd exposure, significantly improved the growth, photochemical activities of both photosystems, the kinetic parameters of the oxygen-evolving reactions, pigment content and decreased lipid peroxidation, H₂O₂ and proline content. Data showed that the alleviation of Cd-induced effects in rice seedlings is a result of the Cd sorption by microalgae, as well as the reduced Cd accumulation in the roots and its translocation from the roots to the shoots.     

A loss‐of‐function allele of OsHMA3 associated with high cadmium accumulation in shoots and grain of Japonica rice cultivars

Excessive cadmium (Cd) accumulation in rice poses a risk to food safety. OsHMA3 plays an important role in restricting Cd translocation from roots to shoots. A non‐functional allele of OsHMA3 has been reported in some Indica rice cultivars with high Cd accumulation, but it is not known if OsHMA3 allelic variation is associated with Cd accumulation in Japonica cultivars. In this study, we identified a Japonica cultivar with consistently high Cd accumulation in shoots and grain in both field and greenhouse experiments. The cultivar possesses an OsHMA3 allele with a predicted amino acid mutation at the 380^th position from Ser to Arg. The haplotype had no Cd transport activity when the gene was expressed in yeast, and the allele did not complement a known nonfunctional allele of OsHMA3 in F₁ test. The allele is present only in temperate Japonica cultivars among diversity panels of 1483 rice cultivars. Different cultivars possessing this allele showed greatly increased root‐to‐shoot Cd translocation and a shift in root Cd speciation from Cd―S to Cd―O bonding determined by synchrotron X‐ray absorption spectroscopy. Our study has identified a new loss‐of‐function allele of OsHMA3 in Japonica rice cultivars leading to high Cd accumulation in shoots and grain.     

Effects of Melatonin on Growth,Physiology and Gene Expression in Rice Seedlings Under Cadmium Stress

Melatonin (MLT) is a hormonal substance found in many organisms and can improve plant stress resistance. In this study, the japonica rice variety Y32 and indica rice variety NJ6 were cultivated in hydroponics under different concentrations of CdCl₂ at the two-leaf stage. The growth, physiological and biochemical responses of the seedlings and the expression of cadmium (Cd)-related genes under exogenous melatonin (MLT) treatment were assessed. The results indicated that Cd stress destroyed the dynamic balance between reactive oxygen species (ROS) production and removal, resulting in ROS accumulation, membrane lipid peroxidation, and impaired growth and development. Following the application of exogenous MLT to rice seedlings, increases in plant biomass including both underground and above-ground areas were observed. MLT also scavenged the inhibition of superoxide dismutase (SOD) and peroxidase (POD) in a concentration dependent manner in response to Cd stress. Catalase (CAT) activity and malondialdehyde (MDA) expression also decreased following MLT treatment. Amongst the six Cd-related genes assessed, five genes were down-regulated and one was up-regulated in response to MLT treatment. Taken together, these data demonstrate that MLT improves the resilience of rice seedlings at the biochemical, physiological, and molecular levels, and diminishes the damage caused by Cd stress.     

Cadmium elevates level of protein, amino acids and alters activity of proteolytic enzymes in germinating rice seeds

When seeds of two rice cvs. Ratna and Jaya were germinated under increasing levels of cadmium nitrate (0, 100 and 500 μM) in the medium, a marked decrease in germination percentage was observed with Cd treatments, as compared to controls. There was more absorbed Cd in embryo axes than in endosperms. More uptake resulted with increasing Cd levels in the growth medium in embryo axes. In both rice cultivars, during a germination period of 0 – 120 h, an increased level of protein as well as free amino acids was noted in Cd treatments. Protease activity in general decreased in both embryo axes as well as endosperms due to Cd treatment. In vitro studies showed an enhancement in protease activity in Cd treatments at low Cd levels (50–100 μM), whereas concentrations above this caused inhibition in enzyme activity. Under 500 μM Cd treatments in vivo there was about 30 to 50 percent decline in leucine aminopeptidase (LAP) activity in endosperms, however, carboxypeptidase activity showed a marked increase in endosperms beyond 24 h under Cd treatments. In embryo axes of germinating seeds there was always a decline in peptidase activities, under the influence of cadmium. The leucine amino peptidase and protease activity were always greater in embryo axes in cv. Ratna than cv. Jaya. However, the carboxypeptidase activity was higher in Jaya when compared to Ratna in endosperms under Cd treatments. The results suggest possible suppression of protease and peptidase activities due to Cd treatments in germinating rice seeds leading to altered levels of protein and amino acids.     

Role of iron plaque in Cd uptake by and translocation within rice (Oryza sativa L.) seedlings grown in solution culture

A hydroponics culture experiment was conducted to investigate the effect of iron plaque on Cd uptake by and translocation within rice seedlings grown under controlled growth chamber conditions. Rice seedlings were pre-cultivated for 43 days and then transferred to nutrient solution containing six levels of Fe (0, 10, 30, 50, 80 and 100 mg L⁻¹) for 6 days to induce different amounts of iron plaque on the root surfaces. Seedlings were then exposed to solution containing three levels of Cd (0, 0.1 and 1.0 mg L⁻¹) for 4 days. In order to differentiate the uptake capability of Cd by roots with or without iron plaque, root tips (white root part without iron plaque) and middle root parts (with iron plaque) of pre-cultivated seedlings treated with 0, 30 and 50 mg L⁻¹ Fe were exposed to ¹⁰⁹Cd for 24 h. Reddish iron plaque gradually became visible on the surface of rice roots but the visual symptoms of the iron plaque on the roots differed among treatments. In general, the reddish color of the iron plaque became darker with increasing Fe supply, and the iron plaque was more homogeneously distributed all along the roots. The Fe concentrations increased significantly with increasing Fe supply regardless of Cd additions. The Cd concentrations in dithionite–citrate–bicarbonate (DCB)-extracts and in shoots and roots were significantly affected by Cd and Fe supply in the nutrient solution. The Cd concentrations increased significantly with increasing Cd supply in the solution and were undetectable when no Cd was added. The Cd concentrations in DCB-extracts with Fe supplied tended to be higher than that at Fe₀ at Cd_0.1, and at Cd_1.0, DCB-Cd with Fe supplied was significantly lower. Cd concentrations in roots and shoots decreased with increasing Fe supply at both Cd additions. The proportion of Cd in DCB-extracts was significantly lower than in roots or shoots. Compared to the control seedlings without Fe supply, the radioactivity of ¹⁰⁹Cd in shoots of seedlings treated with Fe decreased when root tips were exposed to ¹⁰⁹Cd and did not change significantly when middle parts of roots were exposed. Our results suggest that root tissue rather than iron plaque on the root surface is a barrier to Cd uptake and translocation within rice plants, and the uptake and translocation of Cd appear to be related to Fe nutritional levels in the plants.     

Calcium acetate‐induced reduction of cadmium accumulation in Oryza sativa: Expression of auto‐inhibited calcium‐ATPase and cadmium transporters

• Calcium (Ca) signalling has an essential role in regulating plant responses to various abiotic stresses.
• This study applied Ca in various forms (Ca acetate and CaCl₂) and concentrations to reduce cadmium (Cd) concentration in rice and propose a possible mechanism through which Ca acts to control the Cd concentration in rice.
• The results showed that supplementation of Cd‐contaminated soil with Ca acetate reduced the Cd concentration in rice after exposure for 7 days in both hydroponic and soil conditions. The possible involvement of the auto‐inhibited Ca²⁺‐ATPase gene (ACA) might act to control the primary signal of the Cd stress response. The messages from ACA3 and ACA13 tended to up‐regulate the low‐affinity cation transporter (OsLCT1) and down‐regulate Cd uptake and the Cd translocation transporter, including the genes, natural resistance‐associated macrophage protein 5 (Nramp5) and Zn/Cd‐transporting ATPase 2 (HMA2), which resulted in a reduction in the Cd concentration in rice. After cultivation for 120 days, the application of Ca acetate into Cd‐contaminated soil inhibited Cd uptake of rice.
• Increasing the Ca acetate concentration in the soil lowered the Cd concentration in rice shoots and grains. Moreover, Ca acetate maintained rice productivity and quality whereas both aspects decreased under Cd stress.

     

Characterization of Cadmium Binding, Uptake, and Translocation in Intact Seedlings of Bread and Durum Wheat Cultivars

High Cd content in durum wheat (Triticum turgidum L. var durum) grain grown in the United States and Canada presents potential health and economic problems for consumers and growers. In an effort to understand the biological processes that result in excess Cd accumulation, root Cd uptake and xylem translocation to shoots in seedlings of bread wheat (Triticum aestivum L.) and durum wheat cultivars were studied. Whole-plant Cd accumulation was somewhat greater in the bread wheat cultivar, but this was probably because of increased apoplastic Cd binding. Concentration-dependent ¹⁰⁹Cd²⁺-influx kinetics in both cultivars were characterized by smooth, nonsaturating curves that could be dissected into linear and saturable components. The saturable component likely represented carrier-mediated Cd influx across root-cell plasma membranes (Michaelis constant, 20–40 nm; maximum initial velocity, 26–29 nmol g⁻¹ fresh weight h⁻¹), whereas linear Cd uptake represented cell wall binding of ¹⁰⁹Cd. Cd translocation to shoots was greater in the bread wheat cultivar than in the durum cultivar because a larger proportion of root-absorbed Cd moved to shoots. Our results indicate that excess Cd accumulation in durum wheat grain is not correlated with seedling-root influx rates or root-to-shoot translocation, but may be related to phloem-mediated Cd transport to the grain.     

Uptake and partitioning of cadmium by cultivars of peanut (Arachis hypogaea L.)

Cadmium has been found to accumulate in peanut (Arachis hypogaea) kernels to levels exceeding the current maximum permitted concentration in Australia of 0.1 mg kg^-1. Little is known of the mechanisms of Cd uptake into kernels by cultivars of peanut, so the aims of the experiments reported here were to determine if Cd is absorbed directly through the pod wall or via the main root system, and if differences exist between cultivars in this respect. Split-pot soil and sand/nutrient solution experiments were performed with two cultivars of peanut (cv. NC7 and Streeton) known to accumulate Cd to different levels in the kernel. The growth medium was separated into pod and root zones with Cd concentrations in each zone varied. In confirmation of previous field trial results, cv. NC7 had higher concentrations of Cd in kernels, given the same Cd levels in the external medium (solution or soil). Despite total Cd uptake by cv. NC7 being similar to cv. Streeton, cv. NC7 appeared to retain more Cd in the roots and translocate less Cd to shoots. Results from both soil and sand/solution culture indicated that the dominant path of Cd uptake by peanut was via the main root system, with direct pod uptake contributing less than 5% of the total Cd in the kernel. There was little difference between cultivars in this characteristic. This indicates that unlike Ca nutrition of peanuts, agronomic techniques to manage Cd uptake will require modification of soil to the full depth of root exploration, rather than just the surface strata where pods develop. Cadmium concentrations in testa were up to an order of magnitude higher than in the kernel, indicating that blanching of kernels would be effective in reducing Cd in the marketed product. This revised version was published online in June 2006 with corrections to the Cover Date.     

The relation between growth inhibition and secretion level of momilactone B from rice root

Abstract

The growth inhibitory activity of seven rice (Oryza sativa L.) cultivars and the secretion level of momilactone B from these rice cultivars were determined to understand chemical basis of the interaction of rice with other plant species. All rice cultivars inhibited the growth of hypocotyls and roots of lettuce (Lactuca sativa L.) seedlings when the lettuce was grown together with the rice, and showed different range of the inhibitory activity. These results suggest that all rice cultivars may possess allelopathic activity and the activity may be cultivar dependent. Momilactone B, which is a potent growth inhibitor, was found in root exudates of all rice cultivars, and the momilactone B concentration was also cultivar-dependent. The allelopathic activity of each rice cultivar was closely correlated with momilactone B concentration in the root exudates. The present results suggest that rice cultivars possess various allelopathic activities and their allelopathic activity may depend on the secretion level of momilactone B. Therefore, momilactone B may play an important role in rice allelopathy and in the chemical interactions of rice with other plant species.     

Cadmium and lead interactive effects on oxidative stress and antioxidative responses in rice seedlings

Interactive effects of two heavy metal pollutants Cd and Pb in the growth medium were examined on their uptake, production of reactive oxygen species (ROS), induction of oxidative stress and antioxidative defence responses in Indica rice (Oryza sativa L.) seedlings. When rice seedlings in sand culture were exposed to 150 μM Cd (NO₃)₂ or 600 μM Pb (CH₃COO)₂ individually or in combination for 8–16 days, a significant reduction in root/shoot length, fresh weight, relative water content, photosynthetic pigments and increased production of ROS (O₂˙^? and H₂O₂) was observed. Both Cd and Pb were readily taken up by rice roots and localisation of absorbed metals was greater in roots than in shoots. When present together in the growth medium, uptake of both the metals Cd and Pb declined by 25–40 %. Scanning electron microscope (SEM) imaging of leaf stomata revealed that Pb caused more distortion in the shape of guard cells than Cd. Dithizone staining of roots showed localisation of absorbed Cd on root hairs and epidermal cells. Both Cd and Pb caused increased lipid peroxidation, protein carbonylation, decline in protein thiol and increase in non-protein thiol. The level of reduced forms of non-enzymic antioxidants glutathione (GSH) and ascorbate (AsA) and their redox ratios (GSH/AsA) declined, whereas the activities of antioxidative enzymes superoxide dismutase (SOD) and guaiacol peroxidase (GPX) increased in metal treated seedlings compared to controls. In-gel activity staining also revealed increased intensities of SOD and GPX isoforms with metal treatments. Catalase (CAT) activity increased during early days (8 days) of metal exposure and declined by 16 days. Results suggest that oxidative stress is an important component in expression of Cd and Pb toxicities in rice, though uptake of both metals gets reduced considerably when present together in the medium.     

Cadmium toxicity and translocation in rice seedlings are reduced by hydrogen peroxide pretreatment

A hydroponic experiment was carried out to study the role of hydrogen peroxide (H₂O₂) in enhancing tolerance and reducing translocation of cadmium (Cd) in rice seedlings. Plant growth (length and biomass of shoot and root) was significantly repressed by Cd exposure. However, pretreatment with 100 μM H₂O₂ for 1d mitigated Cd stress by inducing enzyme activities for antioxidation (e.g., superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX)) and detoxification (e.g., glutathione S-transferase (GST)) as well as by elevating contents of reduced glutathione (GSH) and ascorbic acid (AsA). As a result, H₂O₂ and malondialdehyde (MDA) content decreased in plants and the seedling growth was less inhibited. On the other hand, H₂O₂ pretreatment decreased Cd concentration in shoots, thus lowered the ratio of Cd concentration in shoots and roots (S/R), indicating that H₂O₂ may affect Cd distribution in rice seedlings. The improved Cd tolerance is partly due to an enhanced antioxidative system that efficiently prevents the accumulation of H₂O₂ during Cd stress. Increased Cd sequestration in rice roots may contribute to the decline of Cd translocation.     

Studies on Metabolic Products of Hypochnus sasakii Shirai

A considerable amount of p-hydroxyphenylacetic acid was isolated from the culture filtrate of Hypochnus sasakii.

p-Hydroxyphenylacetic acid induced wilt of soybean plant and retarded the growth of rice seedlings at concentrations up to 1:20,000. The O₂ uptake in roots decreased in proportion to reduction of dry weight of rice seedlings.     

Aspects of the Fe and Mn nutrition of rice plants

Summary In three water-culture experiments, the effects of variations in pH, N form, and Si- and P level on the uptake and translocation of Fe and Mn, and on the chlorophyll contents of lowland rice were examined.It was found that Mn uptake increased with increasing pH, that it was not affected by variations in N form (NO₃ or NH₄), and that Si has a suppressive effect on Mn uptake. With increasing pH, the translocation of Fe to the shoots was reduced. This pH effect might be indirect, in that Fe translocation is hampered by excessive Mn uptake induced by high pH. Variations in N form and in Si level did not influence Fe uptake and- translocation.A combination of high P-and high Mn levels in solution proved to reduce the translocation of Fe to the rice shoots. Precipitation of Mn phosphate on the roots is likely to occur at high concentrations of both Mn and P in the root medium.A negative correlation was found between chlorophyll content and Mn content of the leaves. The chlorophyll content was not related to the iron content of the leaves. It is likely that chlorosis of rice leaves in an early growth stage can be caused by several combinations of the following factors: 1. high Mn supply, 2. NO₃ nutrition inducing an increase in solution pH favouring a further increase in Mn uptake, 3. absence of Si which exerts a suppressive effect on Mn uptake, and 4. high P supply. These factors can induce chlorosis, with and without exerting a concomitant influence on the uptake and translocation of Fe.     

Flavonoids and Growth Hormones Influence Endophytic Colonization and in Planta Nitrogen Fixation by a Diazotrophic Serratia sp. in Rice

Summary Several endophytic diazotrophs were isolated from cultivars of rice and screened for their diazotrophy by nitrogenase assay and amplification of partial nifH gene. Ability of one of the diazotrophic endophytes, Serratia sp. (isolate EDA2 from cultivar ADT36) to colonize the rice seedlings grown in the presence of flavonoids and growth hormones, under gnotobiotic condition was assessed in cultivar ADT36 using a strain marked with transposon-based egfp and Km ^r . The endophytic colonization was monitored through re-isolation from different parts of rice seedlings in LB+Km plates. Addition of the flavonoids quercetin and diadzein to the growth medium increased the extent of endophytic colonization of the conjugant in rice seedlings by colonizing throughout the plant. Population and in planta nitrogenase activity of Serratia in rice seedlings were significantly increased by addition of flavonoids, quercetin and diadzein, whereas growth hormones, IAA and NAA reduced the efficiency of Serratia. The inoculation of Serratia sp. with flavonoids increased the plant biomass and biochemical constituents of rice seedlings under controlled condition.     

Parameter determination involved in phytotoxicity and transport of cadmium in rice seedlings

Hydroponic experiments were conducted with rice seedlings to determine parameters involved in phytotoxicity and transport of Cadmium (Cd). Results showed that a linear decrease in relative growth rate and water use efficiency was observed in rice seedlings with increasing Cd concentrations. More severe inhibitory effects on both parameters were found at the 4-d treatment. The effective concentrations (EC) were estimated using the Levenberg–Marquardt Algorithm. The EC values obtained from the relative growth rate were always smaller than these from water use efficiency, indicating that the former was more sensitive to change of Cd than the latter. Phyto-transport of Cd was apparent, but the distribution of Cd in different parts of rice seedlings was different and roots were the dominant sink for Cd accumulation (p < 0.05). Although the translocation of Cd into shoots was detectable, more Cd was detected in shoots at the 4-d treatments than that at the 2-d treatments (p < 0.05). The partial correlation analysis suggested that the total accumulation rate of Cd was highly related to the doses of Cd supplied (p < 0.05). In conclusion, Cd is problematic at relatively low concentrations for rice seedlings, and inhibitory effects are highly dependent on the selected response endpoints and the duration of exposure periods.     

Growth and Cadmium Phytoextraction by Swiss Chard,Maize, Rice,Noccaea caerulescens,and Alyssum murale in pH Adjusted Biosolids Amended Soils

Past applications of biosolids to soils at some locations added higher Cd levels than presently permitted. Cadmium phytoextraction would alleviate current land use constraints. Unamended farm soil, and biosolids amended farm and mine soils were obtained from a Fulton Co., IL biosolids management facility. Soils contained 0.16, 22.8, 45.3 mg Cd kg^–1 and 43.1, 482, 812 mg Zn kg^–1 respectively with initial pH 6.0, 6.1, 6.4. In greenhouse studies, Swiss chard (Beta vulgaris var. cicla), a Cd-accumulator maize (inbred B37 Zea mays) and a southern France Cd-hyperaccumulator genotype of Noccaea caerulescens were tested for Cd accumulation and phytoextraction. Soil pH was adjusted from ～5.5–7.0. Additionally 100 rice (Oryza sativa) genotypes and the Ni-hyperaccumulator Alyssum murale were screened for potential phytoextraction use.

Chard suffered phytotoxicity at low pH and accumulated up to 90 mg Cd kg^–1 on the biosolids amended mine soil. The maize inbred accumulated up to 45 mg Cd kg^–1 with only mild phytotoxicity symptoms during early growth at pH > 6.0. N. caerulescens did not exhibit phytotoxicity symptoms at any pH, and accumulated up to 235 mg Cd kg^–1 in 3 months. Reharvested N. caerulescens accumulated up to 900 mg Cd kg^–1 after 10 months. Neither Alyssum nor 90% of rice genotypes survived acceptably.

Both N. caerulescens and B37 maize show promise for Cd phytoextraction in IL and require field evaluation; both plants could be utilized for nearly continuous Cd removal. Other maize inbreds may offer higher Cd phytoextraction at lower pH, and mono-cross hybrids higher shoot biomass yields. Further, maize grown only for biomass Cd maximum removal could be double-cropped.     

H2O2 pretreated rice seedlings specifically reduces arsenate not arsenite: difference in nutrient uptake and antioxidant defense response in a contrasting pair of rice cultivars

The study investigated the reduction in metalloid uptake at equimolar concentrations (~53.3 μM) of As(III) and As(V) in contrasting pair of rice seedlings by pretreating with H₂O₂ (1.0 μM) and SA (1.0 mM). Results obtained from the contrasting pair (arsenic tolerant vs. sensitive) of rice seedlings (cv. Pant Dhan 11 and MTU 7029, respectively) shows that pretreatment of H₂O₂ and H₂O₂ + SA reduces As(V) uptake significantly in both the cultivars, while no reduction in the As(III) uptake. The higher growth inhibition, higher H₂O₂ and TBARS content in sensitive cultivar against As(III) and As(V) treatments along with higher As accumulation (~1.2 mg g⁻¹ dw) than in cv. P11, unravels the fundamental difference in the response between the sensitive and tolerant cultivar. In the H₂O₂ pretreated plants, the translocation of As increased in tolerant cultivar against AsIII, whereas, it decreased in sensitive cultivar both against AsIII and AsV. In both the cultivars translocation of Mn increased in the H₂O₂ pretreated plants against As(III), whereas, the translocation of Cu increased against As(V). In tolerant cultivar the translocation of Fe increased against As(V) with H₂O₂ pretreatment whereas, it decreased in the sensitive cultivar. In both the cultivars, Zn translocation increased against As(III) and decreased against As(V). The higher level of H₂O₂ and SOD (EC 1.15.1.1) activity in sensitive cultivar whereas, higher, APX (EC 1.11.1.11), GR (EC 1.6.4.2) and GST (EC 1.6.4.2) activity in tolerant cultivar, also demonstrated the differential anti-oxidative defence responses between the contrasting rice cultivars.

Electronic supplementary material

The online version of this article (doi:10.1007/s12298-014-0255-1) contains supplementary material, which is available to authorized users.     

Root iron plaque formation and characteristics under N2 flushing and its effects on translocation of Zn and Cd in paddy rice seedlings (Oryza sativa)

Background and Aims

Anoxic conditions are seldom considered in root iron plaque induction of wetland plants in hydroponic experiments, but such conditions are essential for root iron plaque formation in the field. Although ferrous ion availability and root radial oxygen loss capacity are generally taken into account, neglect of anoxic conditions in root iron plaque formation might lead to an under- or over-estimate of their functional effects, such as blocking toxic metal uptake. This study hypothesized that anoxic conditions would influence root iron plaque formation characteristics and translocation of Zn and Cd by rice seedlings.

Methods

A hydroponic culture was used to grow rice seedlings and a non-disruptive approach for blocking air exchange between the atmosphere and the induction solution matrix was applied for root iron plaque formation, namely flushing the headspace of the induction solution with N₂ during root iron plaque induction. Zn and Cd were spiked into the solution after root iron plaque formation, and translocation of both metals was determined.

Key Results

Blocking air exchange between the atmosphere and the nutrient solution by N₂ flushing increased root plaque Fe content by between 11 and 77 % (average 31 %). The N₂ flushing treatment generated root iron plaques with a smoother surface than the non-N₂ flushing treatment, as observed by scanning electron microscopy, but Fe oxyhydroxides coating the rice seedling roots were amorphous. The root iron plaques sequestrated Zn and Cd and the N₂ flushing enhanced this effect by approx. 17 % for Zn and 71 % for Cd, calculated by both single and combined additions of Zn and Cd.

Conclusions

Blocking of oxygen intrusion into the nutrient solution via N₂ flushing enhanced root iron plaque formation and increased Cd and Zn sequestration in the iron plaques of rice seedlings. This study suggests that hydroponic studies that do not consider redox potential in the induction matrices might lead to an under-estimate of metal sequestration by root iron plaques of wetland plants.     

Identification of hot pepper cultivars containing low Cd levels after growing on contaminated soil: uptake and redistribution to the edible plant parts

Aims

This study aimed to screen and identify low-cadmium (Cd) hot pepper (Capsicum annuum L.) cultivars and to clarify the mechanisms of low Cd accumulation in fruits.

Methods

A pot experiment was conducted to investigate the variations of fruit Cd concentration among 30 hot pepper cultivars and to determine the differences in uptake and translocation of Cd between low- and high-Cd cultivars in the control and two Cd treatments.

Results

There are significant differences among the cultivars in their ability to accumulate Cd in fruits. Fruit Cd concentrations are positively and significantly correlated with the translocation of Cd from roots to aboveground parts and the Cd concentrations of leaves and stems. However, no correlation was observed between the fruit’s Cd concentration and the root’s Cd uptake ability.

Conclusions

Two hot pepper cultivars, Yeshengchaotianjiao (No. 16) and Heilameixiaojianjiao (No. 23), were identified as low-Cd cultivars, and two, Jinfuzaohuangjiao (No. 13) and Shuduhong (No. 18), were treated as high-Cd cultivars. The difference in fruit Cd concentrations between low- and high-Cd cultivars is attributable to the difference in Cd translocation from roots to aboveground parts and from leaves and stems to fruits, rather than to the root’s Cd uptake ability.