Nutrition of Horticultural Crops Exam 3 (Micronutrients) Flashcards
What does ATPase accomplish by expelling hydrogen ions into the soil solution?
reduces the pH of the rhizosphere to make micronutrients more soluble
What type of cationic iron is not immediately available to plants? How have they adapted?
ferric iron (Fe3+) is not immediately available, leading to new strategies to bring the ion across the membrane
What enzyme is used in Strategy I iron acquisition to acquire ferrous iron?
ferric reductase (FCR) reduces Fe3+ in the soil to Fe2+ for cell entry through a protein channel
What are the key components seen in the exudation-centric Strategy II for acquiring iron from the soil?
phytosiderophores (PS)
Phytosiderophores are (1)____________________ compounds expelled by the cell. Predominately comprised of C, H and O, they have a high affinity to (2)___________ iron, which they will complex with. Once they are a (3)__________ phytosiderophore [(4)____________], they re-enter the cell via (5)____________________ in the membrane
(1) low molecular weight
(2) ferric (Fe3+)
(3) loaded
(4) PS–Fe3+
(5) transport proteins
What group of plants typically acquire iron from the soil using Strategy II?
grasses (Poaceae)
What group of plants typically acquire iron from the soil using Strategy I?
broadleaves and angiosperms
(non-Poaceae)
Why are iron ions in the cytoplasm quickly immobilized by chelators?
iron ions in the cytoplasm can cause deleterious redox reactions
What are three common chelators in the plant cell cytoplasm?
(1) citrate
(2) malate
(3) nicotianamine
What causes a low soil pH to make iron ions more available in soils than when the pH is more neutral?
when the soil is neutral or basic, iron is typically present as ferric hydroxide [Fe(OH)3], but the high concentration of H+ at low pH reacts with it to form water and ferric iron
Why do plant cells excrete citrate into the soil at low pH?
citrate is a siderophore and chelator which binds with ferric iron in the soil so that off-target organisms do not acquire it
Once in the cytoplasm, what compounds protects organelles from redox reactions Fe2+ ions may trigger?
malate
What is the amine compound which acts as a chelator for iron and other metals?
nicotianamine (C12H21N3O6)
What is the primary use of iron in plants?
facilitates redox reactions in respiration and photosynthesis
What are two kinds of structures which include iron in the plant cell?
(1) heme groups
(2) iron/sulfur clusters
What is a deficiency in iron most associated with in crops and plants in general?
highly symmetrical interveinal chlorosis
Because it is an immobile plant nutrient, where are iron deficiency symptoms typically present first?
young tissues
(blossoms and young leaves)
What are the four divalent metals (elements which have a +2 charge as a cation)?
(1) copper (Cu2+)
(2) iron (Fe2+)
(3) manganese (Mn2+)
(4) zinc (Zn2+)
What is a consequence of the four divalent metals having the same charge and relatively similar sizes?
Cu2+, Fe2+, Mn2+ and Zn2+ can all move across the same channel protein and can be chelated by low molecular weight organic acids (LMWOAs)
What are the group of enzymes which chelate manganese, copper and zinc cations in the cytoplasm?
superoxide dismutases
What are the classical symptoms of zinc deficiency in plants?
(1) interveinal chlorosis
(2) reduced size of plant organs
How can the symptoms of zinc deficiency be distinguished from those of iron deficiency?
zinc-deficient plants will have smaller leaves and shorter internode spaces
How is chlorosis due to a manganese deficiency different from the chlorosis seen in iron and zinc deficient plants?
interveinal chlorosis caused by having too little manganese is less symmetrical (“mosaic”)
What are three symptoms associated with a deficiency in copper?
(1) interveinal chlorosis
(2) inward curling of leaves
(3) shoot dieback
