Mineral Nutrition in Plants II

1. Mineral Nutrition in Plants II Oh Oh, I get by with a little help from my friends. - Ringo Starr et al.

2. Today • Nitrogen Assimilation; • Mychorhizzae; • Questions.

3. Structural Elements, Covalently Bonded IGroup 1: Nutrients that are parts of carbon compounds... • N: amino acids, proteins, nucleic acids, co-enzymes, etc. • forms three covalent bonds, • chains, rings, branches, • one pair unshared electrons for metal coordination, • carbon “substitute”; distorts symmetry in rings and chains, • participates in hydrogen bonding, • metal complexion (see chlorophyll), • Triple bond is extremely stable.

4. History Varro praeceptis adicit equino sit levissium segetes alendi, prata vero graviore quod ex hordeo fiaat multasque gignat herbas…inter omnes autem constat nihil esse utilis lupini segete priusquam siliquetur aratro vel bidentibus versa manipuisve desectae circa radices arborum ac vitium obrutis… - Pliny the Elder (~A.D. 80) Haber-Bosch Reaction

5. Nitrogen Species N2 gas N N Oxidation State Name Nitrogen Gas …as a reactant, is of limited use to most living organisms, …some prokaryotes can break the triple bond and form ammonia, …eukaryotes do not have the enzymes required to perform this task. …plants assimilate nitrate and ammonium, • NO3- and NH4+ .

6. Terrestrial System + Symbiotic Lost: Plant Assimilation Volatilization 100 tg Denitrification 210 tg 1200 tg Leaching 36 tg Sources: Industrial 80 tg Lightning 19 tg Biotic 170 tg

7. Anabaena • - heterocysts: • cells adapted for • nitrogen fixation; • no O2. Free-Living Nitrogen Fixation • Cyanobacteria (blue green algae), • i.e. Anabaena, • Other bacteria, • Anaerobic: maintain anaerobic lifestyles, • Facultative: can switch to anaerobic metabolism, • Aerobic: adapt specific cells for “anaerobic” metabolism.

8. Ammonia and H2 Output. 8 reduced ferredoxins N2 8 protons Nitrogen Fixation is Sensitive to O2 O2 is a good electron acceptor.

9. Oxidation of ammonium yields energy for carbon fixation. Decomposition of complex organic molecules. Sources of Fixed Nitrogen I Fig. 37.9

10. Nitrogen Assimilation I • NO3- can be assimilated in either the root or shoot, • NO3- is absorbed by the root, stored in the vacuole, assimilated, or transported to leaves, • NO3- is reduced to nitrite, • NO2- is reduced to form ammonium, • uses light reactions of photosynthesis for reducing power in leaves, • ferrodoxin reduction by plastid metabolism in roots, • NH4+ (from the soil matrix, or from NO3- reduction) is incorporated into amino acids for use, or for N transport.

11. Nitrate Toxicity • NO3- is not generally toxic to plants and can be readily stored and transported, • It is toxic, in high concentrations, to other organisms, • Methemoglobinemia (“blue baby syndrome”), • liver reduces nitrate to nitrite (or at higher pH, via bacteria in the gut), • nitrite oxidizes iron in hemoglobin, (Fe2+ ---> Fe3+), • renders hemoglobin unable to bind O2, • Nitrosamines, • R2NNO or RNHNO, • Extremely mutagenic and carcinogenic.

12. Ammonia and H2 Output. 8 reduced ferredoxins N2 8 protons 16 ATPs for hydrolysis Nitrogen Fixation Requires Energy …why would bacteria associate with plants

13. Ceanothuscordulatus; Mountain Whitethorn Anabaena Azolla Plant N2 SymbiontsNitrogen Assimilation II • Plants supply reducing power, • Bacteria provide fixed nitrogen, • Alder (trees), Ceanothus (shrub), • Frankia (bacteria), • Sugarcane, • Nostoc (bacteria), • Azolla/Fairy Fern (water fern), • Anaebena, (cyanobacteria)

14. Anabaena Azolla Arrows point to Anabaena strands. Azolla cross section Azolla/Anabaena • Anabaena grows in leaf axes and lacuna.

15. Azolla/Anabaena/Rice/Humans 3. Stomp (or machine smash), 4. Fixed nitrogen is released to soil. 1. Spread Azolla, let grow, 2. Break clumps, drain paddy,

16. shu (soybean) • Chou scholars (~1000 B.C.) More History Soy Root Nodules: result from an infection by Rhizobium.

17. Nitrogen FixationRhizobium symbionts

18. if compatible? Rhizobium Infection I 1. Emerging root hair sends chemical attractants (elicitors), 2. Bacteria respond with a recognition signal, 3. Root hair grows and curls around the bacterial colony, 4. Bacteria proliferate within the curl.

19. Sweet Talk? 3. Flavanoid binds transcription factor (Nod D), complex bids DNA, 4.nod genes are expressed, 5. Nod factor is produced (a molecule with host specificity), 2. Bacterial receptor recognizes signal, and transports it across cell membrane, 6. Nod factor is recognized by the host, in turn activating host genes for proper response. 1. Plant secretes a specific elicitor (flavonoid).

20. Rhizobium Infection II 5. Plant cell wall is degraded, 6. Plant plasma membrane invaginates root hair cell, 7.Infection thread reaches root hair plasma membrane, fuses, 8. Bacteria enter the apoplast.

21. Rhizobium Infection III 9. New infection threads form, 10. Threads form toward “target cells”, 11.Bacteria “bleb” off of the infection thread, into the cytosol, 12. Bacteria are surrounded by a plant membrane.

22. 12. Bacteria are surrounded by a plant membrane. - bacterial induce plant cell division in infected and surrounding cells, - cells in the pericycle begin dividing, (similar to lateral root formation). Nodule Formation 13. Affected pericycle and cortical derived cells continue to divide until the regions fuse. 14. Vasculature forms between the nodule and the plant stele, - nitrogenous compounds are carried to the plant, - nutrients to the bacteria.

23. Nitrogen Assimilation II • Symbiosome, • plant membrane, surrounding… • one or more bacteria, • once inside a symbiosome, bacteria differentiate into bacteroids, • bacteroids may differentiate, • Host Cell Synthesizes, • transport proteins for the symbiosome membrane, • leghemoglobin, an oxygen binding molecule, • N assimilation enzymes.

24. Symbiosomes Figure 37.10

25. Nitrogen Assimilation I vs. II • Cost of symbiosis (to the plant), • unless there is a nitrogen deficit, plants without rhizobium infection generally do better than infected plants, • generally, • high NO32-, no R (best growth), • high NO32-, R (good growth), • low NO32-, R (good growth), • low NO32-, no R (poor growth). I II

26. Eucalyptus Root/Hartig Net MycorrhizaePhosphate Extraction …phosphate (HPO42-) is readily absorbed by roots via a H+ / HPO42- symporter, …however, HPO42- has low solubility and high sorption capacity in soil, • low concentration in the soil (1mM or less), millimolar in root cells, ... Mycorrhizae increase the root surface area, actively transport HPO42-.

27. Absorbtion of Water and Minerals by RootsMycorrhizae ectotropic mycorrhizal fungi • penetrate the intercellular spaces of the root cortex, • surround the root to form a dense fungal sheath. vesicular-arbuscular fungi • penetrate the intercellular spaces of the root cortex, and penetrate cortical cells, • do not break the plant plasma membrane, • hyphae/plant structures form that exchange nutrients.

28. Focus? Chapter 37? • Excretion? • Essential Elements? • Groups 1 - 4, • Phytochelation and Phytoremediation? • Dose Response curves and Nutrient Deficiencies? • Nitrogen and Nitrogen Assimilation, • Nitrate and Ammonium Assimilation, • Nitrogen Symbionts, • Mychorrhizae?