Chapter 36: Plant Nutrition

36.1 Nutritional Requirements of Plants

• Biologists define an essential nutrient as an element or compound at is required for normal growth and reproduction means that the plant cannot complete its life cycle without it. 
  • ==Essential nutrients cannot be synthesized by the organism.==
• Plants need relatively large quantities of certain elements in the soil; these elements are called macronutrients. 
  • ==Some of them are major components of nucleic acids, proteins, and phospholipids, all of which are plentiful in plants.==
• Among the macronutrients, nitrogen (N), phosphorus (P), and potassium (K) are particularly important because they often act as limiting nutrients, meaning their availability limits plant growth.
  • ==If N, P, and/or K are added in appropriate quantities to the soil as fertilizer, plant growth usually increases.==
  • This outcome explains why the leading ingredients in virtually every commercial fertilizer are N, P, and K.
• In contrast to macronutrients, plants require micronutrients in small quantities. 
• These elements represent mobile nutrients-meaning ey are readily transported from older leaves to younger leaves when they are in short supply-so older leaves deteriorate first when these elements are scarce.
• Immobile nutrients such as iron or calcium, in contrast, stay tied up in older leaves. 
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6.2 Soil: A dynamic Mixture of Living and Nonliving Components

• The ability to diagnose nutrient deficiencies is based largely on studies involving hydroponic grow systems. 

  • ==Hydroponic growth takes place in liquid cultures, without soil, so researchers can precisely control the availability of each nutrient.==

• This decaying organic matter is called humus. 

• Techniques that maintain long-term soil quality and productivity are the basis of sustainable agriculture and sustainable forestry.

• The loss of nutrients via the movement of water through soil is called leaching. 

•  The presence of protons in soil water can cause the release of cations that are bound to soil particles.

  • The process responsible is called cation exchange. 
  • ==Cation exchange occurs when protons or other soluble cations bind to negative charges on soil particles and cause bound cations.==

36.3 Nutrient Uptake 

• Most nutrient uptake occurs just above the growing root tip, in the region called the zone of maturation.
• These transport proteins cannot import the ions that the plant needs completely on their own. 
  • They often function together with other proteins, specifically proton pumps, or H+-ATPases. 
  • ==Proton pumps aids in the absorption of certain ions by establishing a relatively high concentration of protons on the outside of root epidermal cells.==
• One mechanism for coping with toxic concentrations of metals involves small proteins called metallothioneins, and short peptides called phytochelatins that are synthesized by special enzymes.
• A second mechanism for actively neutralizing specific toxins involves transport proteins located in the tonoplast-the membrane surrounding the large central vacuole. 
  • ==Proteins in the tonoplast membrane allow plants to actively remove toxic substances from the cytosol and store them in the vacuole.==
• A transport protein that functions as an antiporter then uses this gradient to move sodium ions into the vacuole.
  • ==The antiporter accomplishes this by carrying sodium ions into the vacuole as protons diffuse out of the vacuole.==
  • ==As a result, sodium ions are transported against their concentration gradient.== 

36.4 Nitrogen Fixation

•  Leghemoglobin is related to the hemoglobin at carries oxygen in your blood.
  • Like hemoglobin, leghemoglobin binds oxygen.
  • ==Leghemoglobin is important because nitrogenase is poisoned by the presence of oxygen.==
• When rhizobia contact the flavonoids, the bacteria respond by producing sugar-containing molecules called Nod factors.
  • ==Nod factors, in turn, bind to signaling proteins on the membrane surface of root hairs.== 

36.5 Nutritional Adaptations of Plants

• Some parasitic plants are non- hotosynthetic and obtain all of their nutrition by tapping into the vascular tissue of the host individual they are heterotrophs, organisms that obtain food by consuming other organisms. 
• Carnivorous plants trap insects and other animals, kill them, and then digest the prey to absorb their nutrients.