PLANT MINERAL NUTRITION 
     I. Criteria of essentiality (DI Arnon & PR                                                  Stout, 1939) 

          A. The element must be essential for                 normal growth or reproduction, which                 can not proceed without it. 
          B. The element cannot be replaced by                 another element. 
          C. The requirement must be direct, that                 is not the result of some indirect                 effect such as relieving toxicity                 caused by some other substance. 

     II. Essential elements for normal plant          growth:
 
     C HOPKNS CaFe Mg Na Cl . 
                                 (Mighty good)
                                       (Not always) (Clean) 

     CuMn CoZn MoB(y)!
 
          C = Carbon = Major structural component                   of organic molecules 
          H = Hydrogen = Major structural                   component of organic molecules 
          O = Oxygen = Major structural                   component of organic molecules,                   final electron acceptor in Oxidative                   Phosphorylation 
          P = Phosphorus = Important structural                  component of nucleic acids,                  phospholipids, coenzymes 
          K = Potassium = Important cofactor of                  some enzymes, stomatal opening,                  membrane potentials, osmotic                  balance 

          N = Nitrogen = Important structural                  component of nucleic acids,                   proteins, chlorophyll, some                  phytohormones 
          S = Sulfer = Important structural                  component of some amino acids,                  forms disulfide bridges that are                  important to enzyme activity 
          Ca = Calcium = Important structural                 component of middle lamella,                 cofactor for some enzymes, involved                 in membrane transport phenomenon,                 forms crystals of toxic waste                 products 
          Fe = Iron = Site of catalytic reaction in                 may redox enzymes, essential for                 formation of chlorophyll 
          Mg = Magnesium = Involved in                 stabilization of ribosome particles,                 cofactor for many enxymes, structural                 component of chlorophyll 
          Na = Sodium = Benificial to Halophytes                 (Mangrove, Atriplex, etc) 

          Cl = Chlorine = Involved in photolysis of                water in photosynthesis 
          Cu = Copper = site of catalytic reaction                 for some enzymes 
          Mn = Manganese = Resiratory enzyme                 cofactor, involved in photolysis of                 water, required for auxin synthesis 
          Co = Cobalt = Structural component of                 vitamin B12, necessary for nitrogen                 fixation 
          Zn = Zinc = Involved in auxin synthesis,                 enzyme cofactor 
          Mo = Molybdenum = Involved in reduction                  of nitrates 
          B = Boron = Involved in translocation and                absorption of sugar, interacts with Ca                flux 

     III.  Commercial Fertilizers sold as
            %N, %P, %K 

          eg. 20‑10‑5 = 20%N, 10%P, 5%K 

          Good Soils = 25% Air, 25% Water,
                                2% Organics, 48% Mineral 

          Mineral particles (‑) bind elements with +            charges (Ca++) but not elements with
          ‑ charges (PO ‑ 4) 

          Recent estimates indicate 70% of all            Nitrogen within Nitrogen cycle on Earth            is currently contributed by human            activity! 

     I. Soils 
          A. Important reservoirs for water,                 organic matter, and elements. 

     II. Pathway of soil solution (Water +                                                      Elements) 

          A. Flow of solution is from Soil ‑> Roots                 ‑> Stems ‑> Leaves ‑> Atmosphere 

          B. Initial absorption in roots 
               1. Most readily available in spaces                     between soil particles 
               2. Roots and associated Root Hairs                     grow into these spaces 
               3. Passive uptake into cell wall Active                     uptake into cytoplasm of root hairs                     & epidermis 
               4. Passive movement in cell walls of                     cortex Passive/active movement in                     cytoplasm of cortex

               5. Casparean Strip of Endodermis                     prevents passive movement into                     central xylem, confers active                     selective uptake into cytoplasm by                     Endodermis 
               6. Casparean Strip of Endodermis                     prevents passive backflow of water                     from central Xylem to Cortex,                     Diffusion Gradient favors net flow                     of water into central Xylem =
                   Root Pressure (up to 30‑45 psi) 

          C. Transpiration occurs in xylem 
               1. Primary xylem in roots ‑>                     Secondary xylem in roots ‑>                     Secondary xylem in stems ‑>                     Primary xylem in stems ‑>
                   Midvein in leaves ‑> 
                   Lateral veins in leaves ‑> 
                   Minor veins in leaves ‑>                     Intercellular space in Mesophyll of                     leaves ‑>
                   Stomatal Pores associated with                     Guard Cells 
               2. Cohesion‑Tension Theory 
                   (H. Dixon, early 1900's) 

                    a. Concentration of water vapor                          inside leaves greater than in                          atmosphere so concentration                          gradient favors flow of water                          vapor to atmosphere =                          Transpiration = evaporation of                          water from leaves and stems 
                    b. Transpiration puts water in                          xylem in a state of tension 
                    c. Continuous tension on water                          column pulls it upward from                          roots to leaves 
                    d. Cohesive nature of polar water                          molecules strong enough to                          resist rupturing of liquid water                          column in xylem but not strong                          enough to resist phase change                          and diffusion into mesophyll air                          spaces 

               3. Dynamics of water flow 
                    a. Cuticle and wax of stem/leaf                          epidermis prevents excessive                          water loss in primary plant body 
                    b. Suberin in cork cells prevents                          excessive water loss in                          secondary plant body 
                    c. Flow of water in xylem follows                          Poiseiulles Law = Flow is                          proportional to fourth power of                          xylem element radius 
                    d. Probability of rupture of water                          column is proportional to xylem                          element radius 
                    e. C3 and C4 Plants can regulate                          transpiration by changes in size                          of stomatal pores which is                          related to turgor pressure of                          guard cells and photosynthetic                          activity 
                    f. CAM Plants open stomatal pores                         at night and close them during                         the day to minimize loss of water 

                    g. Current hypothesis is that                          stomata aperture Regulated by                             Potassium flux in and out of                          Guard Cells 
                    h. We haven't a clue in regard to                          water dynamics in Secondary                               Plant Bodies ‑ What, if anything,                          regulates water loss from                          TreeTrunks??

TRANSPORT OF SUGARS AND WATER =                           PHLOEM TRANSLOCATION 

     I. Primary sugar translocated is Sucrose =                                            Glucose + Fructose 

          A. From leaves that are actively                photosynthesizing 
          B. From storage tissue (primarily                parenchyma and collenchyma) 
          C. From organs about to abscise 

     II. Translocation occurs in Phloem 
          A. Bidirectional ‑ From Sink to Source                      Tissues 
          B. Source Storage/Mesophyll Tissue ‑>                      Sieve Tubes (Follows Pathways in                        Primary and Secondary Phloem ‑>                       Sink Storage/Growing Tissue 
          C. Sieve Tubes consisting of Sieve Tube                  Elements conduct sugar + water 
          D. Companion Cells (Specialized                                Parenchyma) provide energy for                 active loading & unloading 

          E. Pressure‑Flow Hypothesis
                             (E. Munch, 1927) 
               1. Sucrose actively loaded into sieve                     tube elements at Source Tissue 
               2. Water moves into STE by osmosis                     in response to increase in sucrose                     concentration 
               3. Hydrostatic pressure increases in                     STE as water moves in 
               4. Bulk flow of water and sucrose                     driven by hydrostatic pressure                     within ST toward Sink Tissue 
               5. Sucrose actively unloaded from                     STE into Sink Tissue 
               6. Water moves out of STE by osmosis                     into Sink Tissue 
               7. Translocation continues as long as                     pressure is maintained by active                     loading and unloading of sucrose                     and osmosis of water 

If you are interested in learning more about Plant Nutrition and Transport consider enrolling in Plant Physiology (BOT 351) offered Every Spring Semester