18th International Symposium on Iron Nutrition and Interaction in Plants
Madrid – May 30-June 3 2016
THE REGULATORY MECHANISM OF IRON AND METABOLIC ADAPTATION IN LEAVES OF IRONDEFICIENCY TOLERANT CULTIVARS OF BARLEY
Kyoko Higuchi*, Tomomi Ogawa, Chiyo Kawamura, Rei Obata, Tomoe Fujisaku, Akihiro Saito
Tokyo University of Agriculture, Japan
*[email protected]
Plants with tolerance to Fe deficiencies do not always have more Fe in their mesophyll cells under low Fe
conditions. We have proposed at least three Fe-saving mechanisms in barley plants: remodeling of the major
light-harvesting antenna proteins [1, 2], allocation of Fe in mesophyll cells [3], and recycling of assimilates [4,
5]. In this presentation, we will discuss two topics: preferential allocation of Fe to photosystem I (PSI) and the
“energy valve” SnRK1 kinase complex.
We aimed to clarify how Fe is effectively allocated within chloroplasts, which have a high demand for Fe. We
fractionated the contents of chloroplasts and thylakoids from the Fe-deficiency tolerant barley cultivar
Ehimehadaka No.1 and Fe-deficiency susceptible cultivar Kairyo-ohgara and measured the Fe, protein, and
chlorophyll concentrations in each fraction. Proportions of Fe in the thylakoids and PSI decreased in each
cultivar under Fe-deficient conditions, but Ehimehadaka No.1 preferentially distributed Fe to the thylakoids
and PSI compared to that in Kairyo-ohgara. Conversely, the proportion of stromal Fe was increased by Fe
deficiency in Kairyo-ohgara. Concurrently, swollen grana-like thylakoids were observed in Ehimehadaka
No.1, but grana-like structure was no longer found in Kairyo-ohgara. Maintenance of grana-like thylakoids,
supported by the supply of Fe to PSI, may be an important factor for adaptation to Fe deficiency. The
efficiency of the insertion of Fe-S clusters into PSI should be elucidated in the future.
Besides Fe, chloroplasts are composed of a large amount of protein; however, organic matter is scarce when
the assimilation rate is reduced by Fe deficiency. Thus, newly emerged chlorotic leaves are heterotrophic,
and older leaves simultaneously conduct photosynthesis, catabolism, and translocation of C and N to
chlorotic leaves in Fe-deficient barley. We have focused on SnRK1 (AMPK in animals; SNF in yeast), which
promotes catabolism and suppresses anabolism under stress conditions generally. mRNA accumulation, in
vitro activity, and in vivo activity of SnRK1 increased in chlorotic leaves of Ehimehadaka No.1, but not in
chlorotic leaves of Shirohadaka, an Fe-deficiency susceptible cultivar. The balance of energy metabolism
may contribute to the slow but steady growth of new leaves under the Fe-deficient condition. In our future
studies, we plan to identify the kinase and regulatory subunits of the SnRK1 complex, which function under
Fe-deficient conditions.
Barley, Fe-deficiency tolerant cultivar, Photosystem I, SnRK1
[1] Saito et al. 2010 Plant Cell Physiol 51: 2013-2030, [2] Saito et al. 2014 FEBS Lett 588: 2042-2048, [3]
Mikami et al. 2011 Plant Physiol Biochem 49: 513-519, [4] Higuchi et al. 2011 Soil Sci Plant Nutr 57: 233-247,
[5] Higuchi et al. 2014 Physiol Plant 151: 313-322
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