Nutrition of Horticultural Crops Exam 3 (Micronutrients)

Question 1

What does ATPase accomplish by expelling hydrogen ions into the soil solution?

Answer 1

reduces the pH of the rhizosphere to make micronutrients more soluble

Question 2

What type of cationic iron is not immediately available to plants? How have they adapted?

Answer 2

ferric iron (Fe3+) is not immediately available, leading to new strategies to bring the ion across the membrane

Question 3

What enzyme is used in Strategy I iron acquisition to acquire ferrous iron?

Answer 3

ferric reductase (FCR) reduces Fe3+ in the soil to Fe2+ for cell entry through a protein channel

Question 4

What are the key components seen in the exudation-centric Strategy II for acquiring iron from the soil?

Answer 4

phytosiderophores (PS)

Question 5

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

Answer 5

(1) low molecular weight
(2) ferric (Fe3+)
(3) loaded
(4) PS–Fe3+
(5) transport proteins

Question 6

What group of plants typically acquire iron from the soil using Strategy II?

Answer 6

grasses (Poaceae)

Question 7

What group of plants typically acquire iron from the soil using Strategy I?

Answer 7

broadleaves and angiosperms
(non-Poaceae)

Question 8

Why are iron ions in the cytoplasm quickly immobilized by chelators?

Answer 8

iron ions in the cytoplasm can cause deleterious redox reactions

Question 9

What are three common chelators in the plant cell cytoplasm?

Answer 9

(1) citrate
(2) malate
(3) nicotianamine

Question 10

What causes a low soil pH to make iron ions more available in soils than when the pH is more neutral?

Answer 10

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

Question 11

Why do plant cells excrete citrate into the soil at low pH?

Answer 11

citrate is a siderophore and chelator which binds with ferric iron in the soil so that off-target organisms do not acquire it

Question 12

Once in the cytoplasm, what compounds protects organelles from redox reactions Fe2+ ions may trigger?

Answer 12

malate

Question 13

What is the amine compound which acts as a chelator for iron and other metals?

Answer 13

nicotianamine (C12H21N3O6)

Question 14

What is the primary use of iron in plants?

Answer 14

facilitates redox reactions in respiration and photosynthesis

Question 15

What are two kinds of structures which include iron in the plant cell?

Answer 15

(1) heme groups
(2) iron/sulfur clusters

Question 16

What is a deficiency in iron most associated with in crops and plants in general?

Answer 16

highly symmetrical interveinal chlorosis

Question 17

Because it is an immobile plant nutrient, where are iron deficiency symptoms typically present first?

Answer 17

young tissues
(blossoms and young leaves)

Question 18

What are the four divalent metals (elements which have a +2 charge as a cation)?

Answer 18

(1) copper (Cu2+)
(2) iron (Fe2+)
(3) manganese (Mn2+)
(4) zinc (Zn2+)

Question 19

What is a consequence of the four divalent metals having the same charge and relatively similar sizes?

Answer 19

Cu2+, Fe2+, Mn2+ and Zn2+ can all move across the same channel protein and can be chelated by low molecular weight organic acids (LMWOAs)

Question 20

What are the group of enzymes which chelate manganese, copper and zinc cations in the cytoplasm?

Answer 20

superoxide dismutases

Question 21

What are the classical symptoms of zinc deficiency in plants?

Answer 21

(1) interveinal chlorosis
(2) reduced size of plant organs

Question 22

How can the symptoms of zinc deficiency be distinguished from those of iron deficiency?

Answer 22

zinc-deficient plants will have smaller leaves and shorter internode spaces

Question 23

How is chlorosis due to a manganese deficiency different from the chlorosis seen in iron and zinc deficient plants?

Answer 23

interveinal chlorosis caused by having too little manganese is less symmetrical (“mosaic”)

Question 24

What are three symptoms associated with a deficiency in copper?

Answer 24

(1) interveinal chlorosis
(2) inward curling of leaves
(3) shoot dieback

Question 25

Why is it not uncommon for deficiencies in multiple divalent ions to be present at the same time in crop plants?

Answer 25

divalent cations are present in the same direction and can be acquired by off target organisms all at once

Question 26

Which cation is least present in crop tissues?

Answer 26

molybdenum

Question 27

Why is a symport mechanism involving ATPase necessary to acquire molybdenum?

Answer 27

molybdenum is brought into the cell as the polyatomic anion molybdate (MoO42-), whose negative charge would otherwise be repelled by the cell membrane

Question 28

What is the main role served by molybdenum once it is in the cell cytoplasm? In what two forms does this usually manifest?

Answer 28

molybdenum is typically a co-factor of enzymes in the cytoplasm, the two common ones being MoCo and FeMoCo

Question 29

What is ironic about how MoCo and FeMoCo facilitate the uptake of nitrogen via their interaction with enzymes at active sites?

Answer 29

molybdenum is the least present nutrient in the plant and nitrogen is the most present

Question 30

Why are molybdenum-deficient plants susceptible to leaf marginal burning?

Answer 30

nitrates can build up in plant leaves since nitrate reductase activity is reduced

Question 31

In what form can boron be acquired by plants via simple diffusion?

Answer 31

boric acid (H3BO3) is a neutral molecule and fairly small, so it is able to pass through the lipid bilayer without a channel protein

Question 32

In what form does boron need to acquired by plants using a symport mechanism?

Answer 32

when boron is present in the soil as borate (H2BO42-), it is repelled by the partially negative charges of the soil membrane

Question 33

What type of soil solution causes boric acid (H3BO3) to react and form borate (H2BO42-)

Answer 33

a soil solution which is slightly more acidic than one which supports boric acid will present boron as borate

Question 34

What are two roles played by borons in plants?

Answer 34

(1) boron is used to crosslink the components of cell walls
(2) boron is included in pollen tube development

Question 35

How does the cell wall linking done by boron differ from the cell wall linking accomplished by calcium?

Answer 35

boron links cellulose microfibrils, while calcium links pectins

Question 36

Without the cell-wall linking boron accomplishes, the cell walls are not sturdy, so deficiencies can manifest as what two symptoms in plants?

Answer 36

(1) poor fruit set
(2) malformation in plant organs

Question 37

What is a consequence of boron being immobile in plant tissues?

Answer 37

the first leaves to appear malformed are the younger ones

Question 38

Why do many commercial fertilizers meant to correct a calcium deficiency or a boron deficiency include both of those elements?

Answer 38

symptoms of a calcium and a boron deficiency are similar in plants