Alkali grass resists salt stress through high [K+] and an endodermis barrier to Na+.
In order to understand the salt-tolerance mechanism of alkali grass (Puccinellia tenuiflora) compared with wheat (Triticum aestivum L.), [K(+)] and [Na(+)] in roots and shoots in response to salt treatments were examined with ion element analysis and X-ray microanalysis. Both the rapid K(+) and Na(+) influx in response to different NaCl and KCl treatments, and the accumulation of K(+) and Na(+) as the plants acclimated to long-term stress were studied in culture- solution experiments. A higher K(+) uptake under normal and saline conditions was evident in alkali grass compared with that in wheat, and electrophysiological analyses indicated that the different uptake probably resulted from the higher K(+)/Na(+) selectivity of the plasma membrane. When external [K(+)] was high, K(+) uptake and transport from roots to shoots were inhibited by exogenous Cs(+), while TEA (tetraethylammonium) only inhibited K(+) transport from the root to the shoot. K(+) uptake was not influenced by Cs(+) when plants were K(+) starved. It was shown by X-ray microanalysis that high [K(+)] and low [Na(+)] existed in the endodermal cells of alkali grass roots, suggesting this to be the tissue where Cs(+) inhibition occurs. These results suggest that the K(+)/Na(+) selectivity of potassium channels and the existence of an apoplastic barrier, the Casparian bands of the endodermis, lead to the lateral gradient of K(+) and Na(+) across root tissue, resulting not only in high levels of [K(+)] in the shoot but also a large [Na(+)] gradient between the root and the shoot.
Peng
Yan-Hui
YH
Institute of Plant Physiology and Ecology, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 300 Fenglin Road, Shanghai, 200032, PR China.
Zhu
Ya-Fang
YF
Mao
Yong-Qiang
YQ
Wang
Suo-Min
SM
Su
Wei-Ai
WA
Tang
Zhang-Cheng
ZC
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D004707:Endoderm / Q000502:physiology; D007700:Kinetics; D018517:Plant Roots / Q000502:physiology; D018520:Plant Shoots / Q000502:physiology; D006109:Poaceae / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013045:Species Specificity; D014908:Triticum / Q000502:physiology*
D012964:Sodium; D011188:Potassium; D002118:Calcium