The removal of nitrate reductase phosphorylation enhances tolerance to ammonium nitrogen deficiency in rice

Nitrate reductase(NR) is a key enzyme for nitrogen assimilation in plants,and its activity is regulated by posttranslational phosphorylation.To investigate the effects of dephosphorylation of the NIA1 protein on the growth and the physiological and biochemical characteristics of rice under different forms of nitrogen supplies,the phenotypes,nitrogen metabolism and reactive oxygen metabolism were measured in NIA1 phosphorylation site-directed mutant lines(S532 D and S532 A),an Os Nia1 over-expression line(OE) and Kitaake(wild type,WT).Compared with WT and OE,S532 D and S532 A have stronger nitrogen assimilation capacities.When ammonium nitrate served as the nitrogen source,the plant heights,dry weights of shoots and chlorophyll(Chl) contents of S532 D and S532 A were lower than those of the WT and OE,whereas hydrogen peroxide(H_(2)O_(2)),malondialdehyde(MDA) and nitrite contents were higher.When potassium nitrate served as the nitrogen source,the plant heights,dry weights of shoots and Chl contents of S532 D and S532 A were higher than those of the WT and OE,there were no significant differences in the contents of H_(2)O_(2) and MDA in the leaves of the test materials,and the difference in nitrite contents among different lines decreased.When ammonium sulfate served as the nitrogen source,there were no significant differences in the physiological indexes of the test materials,except NR activity.Compared with ammonium nitrate and ammonium sulfate,the content of NH_(4)^(+)-N in the leaves of each plant was lower when potassium nitrate was used as the nitrogen source.The q PCR results showed that Os GS and Os NGS1 were negatively regulated by downstream metabolites,and Os Nrt2.2 was induced by nitrate.In summary,when ammonium nitrate served as the nitrogen source,the weak growth of NIA1 phosphorylation site-directed mutant lines was due to the toxicity caused by the excessive accumulation of nitrite.When potassium nitrate served as the nitrogen source,the assimilation rates of nitrate,nitrite and ammonium salt were accelerated in NIA1 phosphorylation site-directed mutant lines,which could provide more nitrogen nutrition and improve the tolerance of rice to ammonium nitrogen deficiency.These results could provide a possible method to improve the efficiency of nitrogen utilization in rice under low-nitrogen conditions.

藏区不同类型水稻品种产量和稻米品质特性分析

通过对西藏自治区不同类型水稻品种的产量和品质特性进行分析,为雪域高原水稻品种的选择提供依据,更好地推动藏区水稻产业的发展。以14个粳稻和7个籼稻品种为试验材料,以当地品种“芒白(音译)”为对照,采用随机区组设计,于2020年4~10月在西藏自治区察隅县开展高产优质水稻品种的试种试验,考察指标包括产量、产量构成因素、稻米外观品质、蒸煮品质和RVA谱特征值等。结果表明,参试品种中WJ313、赣73优8601、赣宁粳1号和莲香早等12个品种产量达7500 kg/hm^(2)以上,较对照增产75.9%~122.3%,其中粳稻品种在藏区更具增产优势;对产量与产量构成因素进行相关性分析,发现穗实粒数是影响藏区水稻产量的重要构成因子;在供试材料中仅8个品种的整精米率达到国优稻谷标准,除WJ313外其他参试品种的垩白度均达到国优稻谷标准,粳稻中直链淀粉含量达到国优稻谷标准的有8个,籼稻则全部达到国优稻谷标准。综上,藏区种植水稻应在适宜穗数的基础上,主攻大穗,并兼顾结实率与千粒重;优质稻引种应首选整精米率高的水稻品种,同时直链淀粉含量也是藏区粳稻选种的重要指标。

NO对低温胁迫下水稻幼苗生理生化特性的影响

【目的】探究外源NO对低温胁迫下水稻幼苗生理生化特性的影响。【方法】以粳稻品种Kitaake为试验材料,于苗期2叶1心时进行低温胁迫处理,并对叶面喷施不同浓度一氧化氮供体硝普钠(SNP),研究不同浓度的SNP对水稻幼苗耐冷性的影响。【结果】结果表明,低温胁迫下,水稻幼苗株高、鲜质量、干质量均下降,叶片中超氧化物歧化酶(SOD)活性提高,过氧化氢酶(CAT)活性降低,脯氨酸含量降低。叶面喷施SNP可减缓叶绿素的分解,提高SOD活性和脯氨酸(Pro)含量。不同浓度SNP对水稻幼苗的生理生化影响存在差异,50μmol/L SNP处理后,SOD和CAT活性及脯氨酸含量增幅均达到最大值,可溶性蛋白含量也较高。【结论】外源NO可缓解低温胁迫对水稻幼苗生长的抑制。

Reducing phosphorylation of nitrate reductase improves nitrate assimilation in rice

Nitrate reductase(NR) is an important enzyme for nitrate assimilation in plants, and post-translational phosphorylation regulates NR activity. To evaluate the impact of the dephosphorylation of nitrate reductase 1(NIA1) protein on NR activity,nitrogen metabolism and plant growth, NIA1 phosphorylation site directed mutant lines(S532 D and S532 A) and an OsNia1 over-expression line(OE) were constructed, and the phenotype, NIA1 protein and its phosphorylation level, NR activity,nitrate metabolism and reactive oxygen metabolism of the transgenic lines were analysed. Exogenous NIA1 protein was not phosphorylated in S532 D and S532 A mutant lines, and their NR activities, activity states of NR and assimilation efficiencies of NO3–-N were higher than those in Kitaake(WT) and OE. The changes in these physiological and biochemical indexes in the OE line were less than in S532 D and S532 A compared to WT. These results suggest that the removal of transcriptional level control had little effect on nitrogen metabolism, but the removal of post-translational modification had a profound effect on it. With the removal of NIA1 phosphorylation and the improvement in the nitrate assimilation efficiency, the plant height and chlorophyll content of S532 D and S532 A decreased and the hydrogen peroxide and malondialdehyde contents of rice seedlings increased, which may be related to the excessive accumulation of nitrite as an intermediate metabolite. These results indicated that the phosphorylation of NR may be a self-protection mechanism of rice. The reduced phosphorylation level of nitrate reductase improved the assimilation of nitrate, and the increased phosphorylation level reduced the accumulation of nitrite and prevented the toxic effects of reactive oxygen species in rice.

Silencing of Os XDH reveals the role of purine metabolism in dark tolerance in rice seedlings

Xanthine dehydrogenase(XDH) is a crucial enzyme involved in purine metabolism. To evaluate the effect of XDH deficiency on rice growth during dark treatment, wild type(WT) Nipponbare(Oryza sativa L.) and two independent transgenic lines with severe RNAi suppression(xdh3 and xdh4) were used in the present experiment. Under normal growth conditions, chlorophyll levels and biomass were indistinguishable between WT and the two RNAi transgenic lines, but XDH enzyme activity and ureide levels were suppressed in XDH RNAi transgenic lines. When XDH RNAi transgenic lines were subjected to dark treatment, chlorophyll content and biomass were significantly decreased, while O~–· production rate and malonaldehyde(MDA) were significantly increased compared to WT. The spraying test of exogenous allantoin raised chlorophyll content and biomass and reduced O~–· production rate and MDA in WT and both transgenic lines, and it also simultaneously reduced differences between RNAi and WT plants caused by XDH deficiency in growth potential and anti-oxidative capacity under dark treatment. These results suggested that fully functional purine metabolism plays an important role in reducing the sensitivity of rice seedlings to dark stress.