Comparison on cellular mechanisms of iron and cadmium accumulation in rice: prospects for cultivating Fe-rich but Cd-free rice
Gao et al. Rice
Comparison on cellular mechanisms of iron and cadmium accumulation in rice: prospects for cultivating Fe-rich but Cd-free rice
Lei Gao 0 1 3 4
Jiadong Chang 0 1 3 4
Ruijie Chen 0 1 3 4
Hubo Li 0 1 3 4
Hongfei Lu 0 1 3 4
Longxing Tao 2
Jie Xiong 0 1 3 4
0 Zhejinag Province Key Laboratory of Plant Secondary Metabolism and Regulation , Hangzhou 310018 , People's Republic of China
1 College of Life Sciences, Zhejiang Sci-Tech University , Hangzhou 310018 , People's Republic of China
2 State Key Laboratory of Rice Biology, China National Rice Research Institute , Hangzhou 310006 , People's Republic of China
3 Zhejinag Province Key Laboratory of Plant Secondary Metabolism and Regulation , Hangzhou 310018 , People's Republic of China
4 College of Life Sciences, Zhejiang Sci-Tech University , Hangzhou 310018 , People's Republic of China
Iron (Fe) is essential for rice growth and humans consuming as their staple food but is often deficient because of insoluble Fe(III) in soil for rice growth and limited assimilation for human bodies, while cadmium (Cd) is nonessential and toxic for rice growth and humans if accumulating at high levels. Over-accumulated Cd can cause damage to human bodies. Selecting and breeding Fe-rich but Cd-free rice cultivars are ambitious, challenging and meaningful tasks for researchers. Although evidences show that the mechanisms of Fe/Cd uptake and accumulation in rice are common to some extent as a result of similar entry routes within rice, an increasing number of researchers have discovered distinct mechanisms between Fe/Cd uptake and accumulation in rice. This comprehensive review systematically elaborates and compares cellular mechanisms of Fe/Cd uptake and accumulation in rice, respectively. Mechanisms for maintaining Fe homeostasis and Cd detoxicification are also elucidated. Then, effects of different fertilizer management on Fe/Cd accumulation in rice are discussed. Finally, this review enumerates various approaches for reducing grain Cd accumulation and enhancing Fe content in rice. In summary, understanding of discrepant cellular mechanisms of Fe/Cd accumulation in rice provides guidance for cultivating Fe-fortified rice and has paved the way to develop rice that are tolerant to Cd stress, aiming at breeding Fe-rich but Cd-free rice.
Iron; Cadmium; Biofortification; Mugineic acid; Phytosiderophores; Phytochelatins; Harvestplus; Fertilizer management
Review
Metal elements, such as Fe, Zn, Mn and Cu, are
essential for living organisms and present as ions. Although
there are abundant metal elements in the earth’s crust,
these ions, particularly Fe, are sparingly soluble under
aerobic conditions in high pH or calcareous soils and
are not bioavailable to plants
(Takahashi et al. 2003)
. As
a result, Fe deficiency is a widespread agricultural
problem that causes plants growth retardation and restricts
sources of nutrition from plants (e.g., rice, maize and
barley)
(Mori 1999; Kobayashi et al. 2010)
. In response
to Fe deficiency, higher plants have developed two
strategies for acquiring Fe from the rhizosphere
(Conte and
Walker, 2011; Kobayashi and Nishizawa, 2012)
. The
application of strategy I is non-graminaceous plants, which
includes the reduction of Fe(III) to soluble Fe(II) by
activating membrane-bound Fe(III)-chelate reductases,
followed by uptake of the reduced Fe(II) into cytoplasm
via Fe(II) transporters
(Cheng et al. 2007)
. Strategy II is
employed only by graminaceous plants, such as rice.
Roots can secrete phytosiderophores (PSs) that belongs
to the muginneic acid (MA) family to rhizosphere and
chelate Fe(III), followed by uptake of Fe(III)-PS
complexes via specific plasma membrane transporters
(Conte
and Walker, 2011)
. Rice utilizes strategy II to acquire Fe
from rhizosphere and also possesses strategy I-like
system that can take in Fe(II) directly
(Cheng et al.
2007)
. In spite of rice can apply specific strategies to
acquire Fe, these mechanisms have limited accessibility to
resource-poor people faced with Fe deficiency from
certain areas of the world. To deal with limited Fe and
improve human Fe nutritional status, biofortifying rice
with enhanced Fe absorption will be an effective method
for populations consuming rice as their staple food.
Cd is a toxic heavy metal and accumulation of Cd in
rice grains poses a latent health problem to human. Cd
in human body can lead to chronic toxicity. The
outbreak of “Itai-Itai disease” in the mid-20th century in
Japan is due to consumption of Cd-contaminated rice
(Uraguchi et al. 2011)
. A person with “Itai-Itai” has
symptoms of weakness and softening of the bones
(Horiguchi et al. 2010). Cd enters into environment, such
as soil and river mainly through industrial activities or
fertilizers
(Bolan et al. 2003)
. As a mobile and soluble metal,
Cd causes crops yield reduction and does harm to human
health even at low concentrations
(Choppala et al. 2014)
.
The primary effects on plants caused (...truncated)