Nitrogen

• Carnivorous Plants

  • Native to east coast of U.S. (North + South Carolina)
  • Autotrophs, live in nutrient-poor areas so they eat animals
  • Found in water-logged areas, bogs, sometimes anaerobic areas
  • Sundews (drosera) have modified leaves containing sticky hairs that trap insects, have these in BC
• Epiphytes

  • Grow on leaves or branches of another tree
  • Not parasitic but use host for support and access to sunlight
  • Absorb water + nutrients from rain water and dust particles
  • Some collect water + organic debris in leaves that form “tanks”
  • Nutrients absorbed through leaves
• Parasitic Plants

  • Infects or attaches onto host, robs it of nutrients/water, harms host + reduces the host’s fitness
  • Dodder grows on host stem, haustoria penetrates the host vascular system
  • Most parasitic plants are photosynthetic and use haustoria to extract water and ions from the xylem of the host plant
  • Ghost plant doesn’t produce any chlorophyll so roots steal sugars from trees and fungal mycorrhizae are connected to
• Nutritional Adaptations

  • Not the most common
  • 99 % of plants are autotrophs, photosynthesize, makes their own sugars
  • 95 % of vascular plants acquire nutrients from soil
  • 80 % of vascular plants obtain soil nutrients from mycorrhizal fungi
  • Some plants parasitize other plants to get nutrients, some appear to live on air, some catch and digest insects
• Nitrogen Fixation

  • Conversion of atmospheric N2 into usable, organic form
  • Certain bacteria + archaea absorb N2 and covert it to ammonia, nitrites, or nitrates
  • Bacteria - free-living Azotobacter, Rhodospirillum, symbiotic Rhizobium
  • Archaea - methanogenic archaea
  • Nitrogenase complex (enzymes + cofactors)
• Nitrogen Introduction

  • Nitrogen makes up 1-5% of the dry matter of a plant, the most abundant macronutrient
  • Nitrogen often limiting nutrient for plant growth
  • Used for amino acids/proteins (includes enzymes), nucleic acids (DNA, RNA (nitrogenous base)), and chlorophyll
  • Bulk of atmosphere is nitrogen (70-80%)
  • Atmospheric nitrogen (N2) isn’t able to be used by plants (unreactive, much energy required to break triple bond)
  • Plants absorb N from soil, ammonium (positive source) or nitrate ions (negative source)
• Nitrogenase Complex

  • Right side has larger component, left has smaller component
  • Right side - responsible for fixing atmospheric nitrogen - N2 gas into NH3
  • Left side - responsible for providing source of electrons to drive right side reactions
  • Considerable energy from ATP (turns into ADP)
  • Used by ferredoxin, reduces Fe3 in the smaller protein
  • Electrons passed over to MoFe2 (cofactor)
  • Electrons used by Mo-Fe-S protein which is a catalyst for the reaction, reduces N2 into nitrate
• Symbiotic Bacteria

  • Roots of a pea plant (or any other legume, all high in protein because of rhizobia) has nodules full of nitrogen-fixing rhizobia on them (this is normal)
  • Nodules are pink because they contain leghemoglobin, oxygen-binding molecule similar to hemoglobin (chemical bonds between Fe and O2 reflect light)
  • Leghemoglobin protects nitrogenase by binding O2 - oxygen highly electronegative, wants to pull electrons which can interfere with reactions in the plant, including important nitrogenase reaction
• Symbiotic Bacteria Process (Part 1)

  • Root hairs release flavonoids, attract rhizobia
  • Rhizobia in environment contact flavonoids, make Nod factors (nodule factors)
• Symbiotic Bacteria Process (Part 2)

  • Bacteria reproduce so they get high abundance and move into plant cell through an “infection thread” - extension of the root hair plasma membrane
  • Infection thread buds off, forming membrane-bound clusters of rhizobia
• Symbiotic Bacteria Process (Part 3)

  • Nod factors bind signalling proteins on root hair membrane, cause cascade of events signalling within the plant that causes expression of DNA to cause formation of nodules
  • Each legume species produces different flavonoids and each rhizobium species responds with one or more unique Nod factors
  • Bacteria stay with plant because they receive sugars from photosynthesis and protection from predators