Some Plant Mechanisms for Improving Uptake of Nutrients

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Some Plant Mechanisms for Improving Uptake of
Nutrients

• Von D. Jolley
• Department of Plant and Animal Sciences
• Brigham Young University
• Provo, Utah

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Barriers to overcome to accumulate micronutrient
metals in seeds
1. Increase micronutrient availability from soil
by modification of root morphology and root
exudates 2. Improve absorption mechanisms by
developing more active and specific ion
transporters/channels 3. Improve translocation
to and accumulation in edible seeds by improving
phloem sap loading, transport and unloading 4.
Improve bioavailability of micronutrient metal in
edible seed by modifying anti-nutrients and
promoters
Modified form Welch and Graham (2004)
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Whole plant processes relevant to Fe transport
and accumulation

• Fe acquisition/uptake phenomena, including the
  release of compounds by roots to chelate or
  solubilize soil Fe
• intracellular/intercellular transport, including
  the involvement of xylem parenchyma
• transpiration rates of vegetative tissues
• storage and remobilization phenomena
• Fe-chelate expression and capacity for phloem Fe
  loading
• phloem transport capacity of photoassimilates
  from a given source region
• communication of shoot Fe status via
  phloem-mobile signal molecules to regulate root
  processes.

Modified fromGrusak, 1999
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Iron Availability in Soil

• Largely unavailable for plant uptake
• Precipitates at high pH
• Decreases in solubility 1000 times per unit
  increase in pH
• Iron deficiency chlorosis common in calcareous
  soils

Lindsay (1974)
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Enhanced Fe uptake mechanisms are divided into
two divisions
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Briat and Lobreaux, 1997
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Strategy 1
Rhizosphere
Free Space
PM
Cytoplasm
chelators
reductants
Fe
Fe
ATP- ase
soil particle
H
H
Citrate
Fe3-Chel
Fe3-Chel
Fe2-Chel
R
IT
Fe2
Chelate
Modified from Marschner et al. (1986)
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Pictures from Terry and Jolley

• Reducing capacity of soybean roots
• Original agar technique (Marschner et al., 1982)
• Fe3-EDTA bathophenanthrolinesulfonate (BPDS)

• Efficient

• Inefficient

• Soybean roots under
• iron-deficiency stress

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Pictures by Terry and Jolley

• Acidification of rhizosphere from soybean roots
• pH indicator - bromocresol purple

• Efficient

• Inefficient

• Soybean roots under
• iron-deficiency stress

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Citrate and Fe In Stem Exudates
0 Fe in Pre Culture
Brown and Tiffin (1965)
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• 17-day old soybean
• Roots in ferricyanide-ferrichloride solution for
  10 hrs

Brown et al. (1961)
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• Under Fe deficiency stress
• T3238Fe - tomato (efficient) takes up more iron
  than T3238fe - tomato (inefficient)

T3238Fe tomato (efficient)
T3238fe tomato (inefficient)
Brown et al. (1971)
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Is the increase in leaf Fe and reduced
chlorosis from enhanced Fe reduction reflected in
seed Fe?

• Grusak (2004) surveyed 481 accessions of pea for
  reductase activity in Fe-sufficient and
  Fe-deficient conditions
• Fe reductase varied 10 fold in Fe-stressed plants
• Fe reductase varied four fold in unstressed
  plants
• No correlation between seed iron concentration
  and root reductase activity was found

Conclusion Other factors of Fe transport and
distribution may be more important in determining
Fe content of seed
Grusak (2004)
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Could these enhanced uptake mechanisms be
important if development of transgenic plants
improve seed Fe contents?
Goto and coworkers (1999) transferred the code
for soybean ferritin gene into rice with these
results
Fe content in rice tissues expressing ferritin
cDNA
Conclusion A three fold increase in Fe in seed
was possible with no effect on vegetative or root
tissues
Goto and et al. (1999)
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Could these enhanced uptake mechanisms be
important if development of transgenic plants
improve seed Fe contents?

• Qu et al. (2004) developed a transgenic rice seed
  by combining
• the cloning of a soybean ferritin gene and a new
  rice endosperm
• specific expression promoter
• Ferritin was five times higher in rice seed
• Fe in rice seed doubled in concentration
• Fe in vegetative organs declined in half compared
  to standard

Conclusion Absorption of Fe might be the
limiting factor for accumulating high Fe in
transgenic rice
Qu et al. (2004)
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AHA2 is a P-type H -ATPpase
AHA2
FRO2
FRO2 is a Fe(III) chelate reductase
IRT1
IRT1 is a Fe(II) transporter
Modified from Schmidt, 2003
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Examples of Molecular Level Control of Strategy I
Plants

• CsHA1 and AHA2 encode the Fe-deficiency induced
  plasma membrane P-type H-ATPase cDNA in cucumber
  and Arabidopsis
• 2. FRO2 encodes the plasma membrane-bound Fe(III)
  chelate reductase
• IRT1 (Iron-regulated transporter) in Arabidopsis
  a member of ZIP family of metal transporters
• Molecular understanding of citrate and
  PEP-carboxylase management in cells exist

Summarized from Abadia et al. (2002) Guerinot
(2000) Santi et al. (2004) Schmidt (2003)
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WF9
ys1
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Briat and Lobreaux, 1997
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Strategy II
Rhizosphere
Free Space
PM
Cytoplasm
X
phyto-
Enzyme
NA
siderophores
Fe
Fe
Nicotianamine
soil particle
Fe
YS1
Fe3PS
Fe3PS
Modified from Marschner et al. (1986) Schmidt
(2003)
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1.2 mg Fe/l in solution
COKER 227 - oat (efficient)
mg Fe3 solubilized/L (phytosiderophore)
TAM 0-312 - oat (inefficient)
Jolley et al. (1989)
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Jolley et al. (1989)
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Takhashi et al. (1999) introduced into rice two
barley genes encoding nicotianamine amino
transferase (NAAT) which catalyzes formation of
deoxymugineic acid (PS)

• Compared to non-transformants the transformed
  rice had
• Higher NAAT activity
• Higher phytosiderophore release
• Four times higher yields
• Fe content of tissues was not measured in this
  study, but the
• potential for Fe increases in seeds could be
  significant

Takhashi et al. (1999)
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Examples of Molecular Level Control in Strategy
II Plants

• NA-synthesis gene encodes for nicotianamine
  synthesis in barley and tomato, ubiquitous in
  plants, but an essential intermediary in
  phytosiderophore biosynthesis
• NAAT-synthesis gene encodes for nicotianamine
  aminotrnasferase, second step in the biosynthesis
  of phytosiderophore and implicated
• in cells associated with long distance transport
  of Fe in xylem
• 3. YS1 (yellow stripe 1) gene encodes membrane
  protein for Fe-phytosiderophore transport
  (identified in Strategy I plants too--YSL genes)

Summarized from Guerinot (2001) Inoue
(2004) Kolke et al. (2004) Schmidt
(2003) Takahashi et al. (1999)
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Summary
Knowledge of Fe-deficiency stress responses
related to increased dissolution, transport and
uptake is well developed and genes controlling
most activities are identified, often in multiple
species This knowledge can be applied to
improve uptake of Fe to vegetative tissues, but
without guarantee to effect seed Fe
content Enhanced Fe nutrition of seed by
infusion of seed storage genes looks promising,
but concomitant improvements in uptake, and
translocation of Fe from roots and in phloem
mobility likely be critical to success