Nitrogen assimilation in crops (I)

1. Nitrogen assimilation in crops (I) March 7, 2012

2. Talk outline: • N cycling and nitrogen use efficiency (NUE) in crops. • Nitrogen fixation and nitrate assimilation pathway in crops. (agronomic view) • uptake, translocation, assimilation, partition, remobilization . • 3. The regulation of nitrogen fixation in crops. • Nitrate reductase, nitrite reductase, glutamine synthase etc. • (NR, NiR, GS/GOGAT,GDH, AspAT, AS) • 4. Journey of nitrate from soil to plant) (botanical view) • Travelling ( soil to plant, within plant and within cell) • transporter (Nrt1, CCL1), sensor, signal transducer (Nla: nitrogen limitation adaption) • 5. Cytokinin as an internal sensing signal for root availability to Nitrogen. • 6. How can we raise up the NUE of crops? • genotype with different NUE (agronomic view) • nitrogen (fertilizer) management practice (SSNM: site specific nutrient management) • genetic engineering (botanical view)

3. http://cctr.net.cn/index_xx1.asp?xxmc=%BB%AA%D6%D0%C5%A9%D2%B5%B4%F3%D1%A7&imageField.x=20&imageField.y=8http://cctr.net.cn/index_xx1.asp?xxmc=%BB%AA%D6%D0%C5%A9%D2%B5%B4%F3%D1%A7&imageField.x=20&imageField.y=8 (华中农业大学精品课程) • http://nhjy.hzau.edu.cn/kech/zwzp/jxlx/ShowArticle.asp?ArticleID=446 • 水稻氮素養管理技術 Real-time nutrient management SSNM (site-specific nutrient management) http://nhjy.hzau.edu.cn/news/news_4.asp(彭少兵) http://zwx.hzau.edu.cn/article.php?act=view&id=198&cid=52 paper: Improving nitrogen fertilization in rice by site-specific N management. A review. Agron. Sustain. Dev. 30 (2010) 649–656. • Crop physiology research at IRRI: Exit seminar of Shaobing Peng http://www.youtube.com/watch?v=lpecLYsracQ (Two decades of crop physiology research on irrigated rice at IRRI) • 合理化施肥

8. Important nitrogenous compounds in crops Nitrogen is a component of many important organic compounds ranging from proteins to nucleic acids. It is also a constituent of compounds like chlorophyll and alkaloids.

9. Introduction: • In 1971/1972, the quantity of N use whole world is • 80 Mt, however; the amount of N use increases to 140 Mt in 1995 (around 175%). • 2. It was estimated the total N inputs of the world’s cropland is about 169 Mt. Out of this total N, 46% is added as inorganic fertilizers, 20% by biological N fixation from legumes and other N-fixing microorganisms, 12% by atmospheric deposition, 11% by animal manure, and 7% by crop residues. • 3. Crop response to applied N and use efficiency are important criteria for evaluating crop N requirements for maximal economic yield. Recovery of N in crop plants is usually less than 50% worldwide.

11. 4. Low recovery of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, denitrification, and plant canopy. 5. The major part of N is added to soil through inorganic fertilizers. Other sources of N addition to soil are biological fixation, precipitation, gases adsorption, and organic manures (farmyard manures, green manures, and crop residues.) The main transformations of N in soil- plant systems include fixation, mineralization (ammonification), nitrification, and immobilization. 6. Nitrogen is a highly mobile nutrient in plants; hence its deficiency usually causes premature senescence, reduce yield and first occurs in the older leaves.

12. Sources and fates of nitrogen in plants and the environment (Nitrogen cycle)

15. Form of nitrogen change in environment Mineralization Ammonification Nitrification Urea hydrolysis Denitrification NH3 volatization Denitrification Nitrogen stabilizers (e.g., nitrapyrin, DCD [dicyandiamide], NBPT [n-butylthiophosphoric triamide]) inhibit nitrification or urease activity, thereby slowing the conversion of the fertilizer to nitrate

17. Economic view Agronomic view Physiological view Environmental view: right rate, right time, and right place

19. Nitrogen uptake and use efficiency • The nitrogen use efficiency (NUE) can be defined as the maximum economic yield produced per unit of N applied, absorbed, or utilized by the plant to produce grain and straw. • The determination of NUE in crop plants is an important approach to evaluate the fate of applied chemical fertilizers and their role in improving crop yields. • Higher N rates can decrease crops NUE indicated that crops were unable to absorb N when applied in excess because their absorption mechanisms might have been saturated.

21. Possible ways to increase NUE in crops: (a) traditional breeding and marker-assisted selection. (b) genetic engineering of Nitrate assimilation pathway. (C) transfer nitrogen fixation genes into crops. (d) Interaction between photosynthesis and N assimilation.

28. Journal of Experimental Botany, Vol. 62, No. 4, pp. 1349–1359, 2011

29. How the nitrate was absorbed and transported in crops or plants??? • Travelling from the soil to plant roots ----- Nitrate transporters (Nitrate sensors) (HATS and LATS) • Travelling within the plant • Traveling in the cell

38. Nitrate assimilation Nitrogen assimilation

41. MoCo NO3- NO2-

42. Structure of nitrite reductase (NiR) from plants

43. Nitrogenase complex and nodule formation in pea

44. Regulation of nitrate reductase (NR) gene expression

47. The GS/GOGAT cycle is the principle nitrogen assimilation pathway in plants

48. Different isoforms Homo- or heterooctamer Cytosolic GS1 (1-4) Primary ammonina Assimilation in roots Plastid GS2 (1) Leaves, primary Ammonia and photorespiration ammonina assimilation Plastid localized Fdx-GOGAT Leaves (95-97%) NADPH-GOGAT NADH-GOGAT roots

49. GS inhibitors (the glutamate analogs) GOGAT inhibitor: azaserine (a glutamine analog)