BOT 6516 Plant Metabolism

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Jeffery Whitehead
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1 BOT 6516 Plant Metabolism Lecture 19 Nitrate & Sulfur Assimilation Slide sets available at:

Overview of Nitrate Assimilation 16.34 What does Δψ indicate? Where is this cell in the plant?

2 Overview of Nitrate Assimilation What does Δψ indicate? Where is this cell in the plant? What drives uptake? What is the product of GS-GOGAT? What the physical separation of NR and NiR?

Nitrate Uptake 16,35, 16.36 Gene Name AGI Other Names Affinity H, L, D NRT1.1 AT1G12110 NRT1.1, ATNRT1, ATNRT1.

TRANSPORTER, NRT1 Inducible D ATPTR2-B AT2G02040 NITRATE TRANSPORTER 1, NTR1, PTR2-B Inducible H ATNRT2:1

2 AT1G08100 NITRATE TRANSPORTER 2, NRT2, ACH2 Inducible H ATNRT2.3 AT5G60780 None Inducible H? ATNRT2.4 AT5G60770 None Inducible H?

3 Nitrate Uptake 16,35, Gene Name AGI Other Names Affinity H, L, D NRT1.1 AT1G12110 NRT1.1, ATNRT1, ATNRT1.1, B-1, CHL1-1, CHLORATE RESISTANT, CHLORATE RESISTANT 1, CHLORATE/NITRATE TRANSPORTER, NITRATE/CHLORATE TRANSPORTER, NRT1 Inducible D ATPTR2-B AT2G02040 NITRATE TRANSPORTER 1, NTR1, PTR2-B Inducible H ATNRT2:1 AT1G08090 NITRATE TRANSPORTER 1, NRT2, 1AT-ACH1, LATERAL ROOT INITIATION 1, LIN1 Inducible H ATNRT2.2 AT1G08100 NITRATE TRANSPORTER 2, NRT2, ACH2 Inducible H ATNRT2.3 AT5G60780 None Inducible H? ATNRT2.4 AT5G60770 None Inducible H? ATNRT2.5 AT1G12940 None Inducible H? ATNRT2.6 AT3G45060 None Inducible H? ATNRT2.7 AT5G14570 None Inducible H?

4 Nitrate Uptake and Membrane Depolarization What does this depolarization mean?

5 Nitrate Reduction 16.38, NO 3 + NADPH + H + NO 2 + NADP + + H 2 O NADPH + H + e FAD e Heme-Fe e MoCo e NO 3 NO 2 Nitrate Reductase is a mini-electron transport chain!

6 Regulation of NR 16.41, 16.42

7 Regulation of NR Signal Glutamine, nitrogen starvation Light Darkness Circadian Clock Nitrate, sucrose, cytokinin High [CO 2 ], anoxia Oxygen, low [CO 2 ] Effect on NR Down-regulation of transcription Up-regulation of transcription and activity Down-regulation of transcription and activity Modulation of transcription up and down Up-regulation of transcription Up-regulation of activity Down-regulation of activity What are some N:C interactions that influence nitrate assimilation? Why might there be an interaction?

Regulation of NR Simplified scheme for regulation

8 Regulation of NR Simplified scheme for regulation of nitrate reductase activity NR is inactivated by phosphorylation, and activated by dephosphorylation. Lillo, C. et al. J. Exp. Bot : Phosphorylated NR is reactivated by a PP2A protein phosphatase. Copyright restrictions may apply.

9 Nitrite Reductase NO 2 + 6Fdx red + 8H + NH Fdx ox + 2H 2 O NADPH + 2Fdx ox (Fe 3+ 6e ) NADP + + 2Fdx red (Fe 2+ ) + H + Ferredoxin-NADP+ reductase

10 Regulation of NR, Nitrite Production and NO Nitrite is mutagenic. The influence of nitrite-derived compounds in plants has not been much investigated. Reactions between nitrite and a large diversity of organic compounds present in plants is expected to be likely, and produce mutagenic compounds, not so good for us. If nitrate assimilation is not properly co-regulated this could result in the temporary accumulation of nitrite and possibly a higher mutation frequency than desirable in the plant and anything that eats it. In plant evolution, nitrite accumulation is likely to have been eliminated by introducing proper regulation of the pathway; with post-translational inactivation of NR being an important mechanism. Nitric oxide synthase, is responsible for NO formation in mammals. In plants, NO also appears to be synthesized from NO 2 produced by NR. Post-translational modification of NR modulates NO production in plants as the NO production depends on the level of nitrite. NO is also known to be mutagenic in bacteria and leads to the production of peroxynitrite. NO is now known to act as a plant signal molecule, influencing growth and development, and promoting stomatal closing. The accumulation of nitrite can therefore also influence growth and development. NO emission from leaves and roots of N. plumbaginifolia was higher in plants when the post-translational regulation of NR was abolished (Lea et al., 2004). However, NR is not the only source of NO synthesis in plants, as it was very recently shown that Arabidopsis possesses a nitric oxide synthase gene. (Lillo, C. et al. J. Exp. Bot. 2004)

11 Overview of Sulfur Metabolism 16.45, How does sulfate assimilation compare with nitrate assimilation? What can you say about anion transporters? Guess which field was amended with sulfate?

12 Uptake of Sulfate 16.56, 16.57, 1658 What can you tell me about sulfate uptake?

13 Arabidopsis Sulfate Transporters Gene Name AGI Other Names Affinity H, L, D SULTR1;1 AT4G08620? SULTR1;2 AT1G78000 SULFATE TRANSPORTER 1;2 H? SULTR1;3 AT1G22150 H SULTR3;1 AT3G51895 SULFATE TRANSPORTER 1, ATST1? SULTR3;4 AT3G15990? SULTR3;5 AT5G19600? SULTR4;1 AT5G13550? SULTR4;2 AT3G12520? AST91 AT1G23090 SULFATE TRANSPORTER 91? AST77 AT4G02700? AST56 AT1G77990? Sulfate transporter AT2G25680? Sulfate transporter AT1G80310? Why are there more sulfate transporter genes than nitrate transporter genes? Why is the naming and characterization of affinity less complete for sulfate transporters compared to nitrate transporters?

14 Sulfur Assimilation 16.46

15 Glutathione and Phytochelatin Structure 16.47, 16.48

16 Sulfur Containing Compounds 16.49, 16.50, 16.51

17 Sulfur Containing Flavor Compounds Box 16.2

18 Global Sulfur Cycles 16.54, 1655

19 The Reactions of Sulfate Assimilation SO ATP + 8e + 8H + S H 2 O + AMP + PP i SO ATP APS + PP i APS + ATP PAPS + ADP PAPS + Thioredoxin red SO PAP + Thioredoxin ox SO Fdx red S 2 + 6Fdx ox Serine + Acetyl-CoA O-acetylserine + CoAS O-acetylserine + S 2 Cysteine + Acetate

20 Sulfate Assimilation 16.59, 16.60, 16.61, 16.63

21 Sulfur Assimilation Continued 16.64

22 Glutathione Structure and Synthesis 16.66, 16.67

23 Phytochelatin Metabolism and Function 16.68, 16.69, 16.70

Nitrogen Assimilation

Nitrogen Assimilation 1. Introduction and Overview Importance of nitrogen to plant metabolism: often the limiting nutrient in plants (& agriculture) nitrogen can regulates growth processes, due to integration