Fundamental parenchyma cells are involved in Na+ and Cl– removal ability in rice leaf sheath

Abstract

Salt sensitivity in rice plants is associated with the accumulated amount of Na+ and Cl– in shoots and, more significantly, in photosynthetic tissues. Therefore, salt removal ability at the leaf sheath level is an important mechanism of salt tolerance. In the present study we attempted to determine whether rice leaf sheaths excluded Cl– as well as Na+, and to identify the tissues that were involved in the removal ability of both ions. In two rice genotypes, salt-tolerant FL478 and -sensitive IR29, leaf sheaths excluded Na+ and Cl– under NaCl treatment as estimated using their sheath:blade ratios. The sheath:blade ratio of Na+ but not of Cl–, was increased by NaCl treatment. Under NaCl treatment, Na+ concentration was higher in the basal leaf sheath, whereas Cl– concentration was higher in the middle and tip parts. At the tissue level, fundamental parenchyma cells of leaf sheaths retained the highest amounts of Na and Cl when treated with high amount of NaCl. These results imply that the leaf sheath potentially functions to remove excess Na+ and Cl– from xylem vessels in different locations along the axis, with the fundamental parenchyma cells of leaf sheaths being involved in over-accumulation of both Na+ and Cl–.

Tissue-specific expression analysis of Na+ and Cl− transporter genes associated with salt removal ability in rice leaf sheath

“…The rice leaf sheath has been found to play an important role in decreasing toxic ion such as Na + and Cl − concentrations in the leaf blade, the major photosynthetic tissue of rice plants [ 1 – 3 ]. The salt removal ability in leaf sheaths consists of salt unloading from xylem and salt sequestration into the leaf sheath cells, which is done by two different inner parts, peripheral and central parts in coordination with each other.…”

“…The salt removal ability in leaf sheaths consists of salt unloading from xylem and salt sequestration into the leaf sheath cells, which is done by two different inner parts, peripheral and central parts in coordination with each other. The leaf sheath unloads Na + and Cl − ions from xylem vessels in the vasculature in the peripheral part, then preferentially transports these ions from the peripheral part to the central part, and sequestering those ions into the fundamental parenchyma cells in the central part [ 3 ]. Additionally, Na + and Cl − were accumulated into different regions of the leaf sheath, Na + in basal part and Cl − in apical part, suggesting that responsive genes for the transport of those ions might be up-regulated in each of these locations in the rice leaf sheath [ 3 ].…”

“…The leaf sheath unloads Na + and Cl − ions from xylem vessels in the vasculature in the peripheral part, then preferentially transports these ions from the peripheral part to the central part, and sequestering those ions into the fundamental parenchyma cells in the central part [ 3 ]. Additionally, Na + and Cl − were accumulated into different regions of the leaf sheath, Na + in basal part and Cl − in apical part, suggesting that responsive genes for the transport of those ions might be up-regulated in each of these locations in the rice leaf sheath [ 3 ]. Therefore, to elucidate the molecular mechanism of salt removal ability in the leaf sheath, it is important to identify which known candidate Na + and Cl − transporter genes are associated with the removal of Na + in the basal part and Cl − in the apical of leaf sheaths, and with salt unloading in the peripheral part and salt sequestration in the central fundamental parenchyma cells, under salinity.…”

“…In this study, we aimed to determine which known candidate Na + or Cl − transporter genes are associated with the salt removal ability in leaf sheaths of rice via general and localized expression analysis. Firstly, we determined the transcript levels of candidate Na + and Cl − transporter genes in the basal (Na + ) and apical (Cl − ) parts of the leaf sheath in the rice genotype FL 478, respectively, where Na + and Cl − were accumulated at the highest level [ 3 ] to identify the genes whose expression levels increase in response to salt stress. Secondly, we compared the transcript levels of candidate Na + and Cl − transporter genes between the peripheral and central regions of the leaf sheath of FL 478 plants grown under saline conditions.…”

“…Secondly, we compared the transcript levels of candidate Na + and Cl − transporter genes between the peripheral and central regions of the leaf sheath of FL 478 plants grown under saline conditions. The peripheral part includes vasculatures, epidermis and peripheral fundamental parenchyma cells [ 3 ]. We hypothesized that Na + or Cl − transporter genes that are highly expressed in the peripheral part may be involved in unloading of these ions in vasculature, or accumulation in the peripheral tissues.…”