Application of ferrous sulfate alleviates negative impact of cadmium in rice(Oryza sativa L.)

Soil contamination with toxic heavy metals[such as cadmium(Cd)]is becoming a serious global problem due to rapid development of social economy.Iron(Fe),being an important element,has been found effective in enhancing plant tolerance against biotic and abiotic stresses.The present study investigated the extent to which different levels of Ferrous sulphate(FeSO_(4))modulated the Cd tolerance of rice(Oryza sativa L.),when maintained in artificially Cd spiked regimes.A pot experiment was conducted under controlled conditions for 146 days,by using natural soil,mixed with different levels of CdCl_(2)[0(no Cd),0.5 and 1 mg/kg]together with the exogenous application of FeSO_(4) at[0(no Fe),1.5 and 3 mg/kg]levels to monitor different growth,gaseous exchange characteristics,oxidative stress,antioxidative responses,minerals accumulation,organic acid exudation patterns of O.sativa.Our results depicted that addition of Cd to the soil significantly(P<0.05)decreased plant growth and biomass,gaseous exchange parameters,mineral uptake by the plants,sugars(soluble,reducing,and non-reducing sugar)and altered the ultrastructure of chloroplasts,plastoglobuli,mitochondria,and many other cellular organelles in Cd-stressed O.sativa compared to those plants which were grown without the addition of Cd in the soil.However,Cd toxicity boosted the production of reactive oxygen species(ROS)by increasing the contents of malondialdehyde(MDA),which is the indication of oxidative stress in O.sativa and was also manifested by hydrogen peroxide(H_(2)O_(2))contents and electrolyte leakage to the membrane bounded organelles.Although,activities of various antioxidative enzymes like superoxidase dismutase(SOD),peroxidase(POD),catalase(CAT)and ascorbate peroxidase(APX)and non-enzymatic antioxidants like phenolics,flavonoid,ascorbic acid,anthocyanin and proline contents increased up to a Cd level of 0.5 mg/kg in the soil but were significantly diminished at the highest Cd level of 1 mg/kg in the soil compared to those plants which were grown without the addition of Cd in the soil.The negative impacts of Cd injury were reduced by the application of FeSO_(4) which increased plant growth and biomass,improved photosynthetic apparatus,antioxidant enzymes,minerals uptake together with diminished exudation of organic acids as well as oxidative stress indicators in roots and shoots of O.sativa by decreasing Cd retention in different plant parts.These results shed light on the effectiveness of FeSO_(4) in improving the growth and upregulation of antioxidant enzyme activities of O.sativa in response to Cd stress.However,further studies at field levels are required to explore the mechanisms of FeSO_(4)-mediated reduction of the toxicity of not only Cd,but possibly also other heavy metals in plants.

A transcription factor STOP1-centered pathway coordinates ammonium and phosphate acquisition in Arabidopsis

Phosphorus(P)is an indispensable macronutrient required for plant growth and development.Natural phosphate(Pi)reserves are finite,and a better understanding of Pi utilization by crops is therefore vital for worldwide food security.Ammonium has long been known to enhance Pi acquisition efficiency in agriculture;however,the molecular mechanisms coordinating Pi nutrition and ammonium remains unclear.Here,we reveal that ammonium is a novel initiator that stimulates the accumulation of a key regulatory protein,STOP1,in the nuclei of Arabidopsis root cells under Pi deficiency.We show that Pi deficiency promotes ammonium uptake mediated by AMT1 transporters and causes rapid acidification of the root surface.Rhizosphere acidification-triggered STOP1 accumulation activates the excretion of organic acids,which help to solubilize Pi from insoluble iron or calcium phosphates.Ammonium uptake by AMT1 transporters is downregulated by a CIPK23 protein kinase whose expression is directly modulated by STOP1 when ammonium reaches toxic levels.Taken together,we have identified a STOP1-centered regulatory network that links external ammonium with efficient Pi acquisition from insoluble phosphate sources.These findings provide a framework for developing possible strategies to improve crop production by enhancing the utilization of non-bioavailable nutrients in soil.

Effects of low pH and aluminum stresses on common beans (Phaseolus vulgaris) differing in low-phosphorus and photoperiod responses

Using common beans differing greatly in the response to photoperiod and low-phosphorus(P)stress,we investigated their responses to acidity and aluminum(Al)toxicity and the relationship between Al tolerance and organic acid exudation under Al or low P stress.A genotype Ginshi was found to be sensitive to low pH treatment.When exposed to pH 4.5,serious curvature in the root tips of cv.Ginshi was observed;however,it was completely corrected by the application of 5 or 10μmol/L AlCl 3;increasing calcium(Ca)could ameliorate Al toxicity,but it could not correct root curvature at pH 4.5.Common beans showed significant differences in both root growth and Al tolerance,and the varieties from the Andes were more tolerant to Al toxicity than those from the Mesoamerican origin.In the presence of 50μmol/L AlCl 3,all the common bean genotypes exuded citrate,and a significant difference in the amounts of citrate was observed among genotypes.The genotypes originated in the Mesoamerica tended to release more citrate than other origins in the presence of Al.The P-inefficient genotype DOR364 exuded more citrate than the P-efficient genotype G19833 in the presence of 50μmol/L AlCl 3,whereas no organic acids were detected in root exudates under low-P stress.A reduction of citrate exudation in the DOR364,but a slight increase of citrate exudation in the G19833,was observed under Al stress after they were exposed to 6-d P starvation.These results suggest that different low-P or Al tolerance in common beans might not be associated with organic acid exudation.