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The role of cytosolic potassium and pH in the growth of barley roots

Plant Physiology, ISSN: 0032-0889, Vol: 118, Issue: 3, Page: 957-964
1998
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In an earlier paper we showed that in fully developed barley (Hordeum vulgare L.) root epidermal cells a decrease in cytosolic K was associated with an acidification of the cytosol (D.J. Walker, R.A. Leigh, A.J. Miller [1996] Proc Natl Acad Sci USA 93: 10510-10514). To show that these changes in cytosolic ion concentrations contributed to the decreased growth of K-starved roots, we first measured whether similar changes occurred in cells of the growing zone. Triple-barreled ion-selective microelectrodes were used to measure cytosolic K activity and pH in cells 0.5 to 1.0 mm from the root tip. In plants growing from 7 to 21 d after germination under K-replete conditions, the mean values did not change significantly, with values ranging from 80 to 84 mM for K and 7.3 to 7.4 for pH. However, in K-starved plants (external [K], 2 μM), the mean cytosolic K activity and pH had declined to 44 m and 7.0, respectively, after 14 d. For whole roots, sap osmolality was always lower in K-starved than in K-replete plants, whereas elongation rate and dry matter accumulation were significantly decreased after 14 and 16 d of K starvation. The rate of protein synthesis in root tips did not change for K-replete plants but declined significantly with age in K-starved plants. Butyrate treatment decreased cytosolic pH and diminished the rate of protein synthesis in K-replete roots. Procaine treatment of K-starved roots gave an alkalinization of the cytosol and increased protein synthesis rate. These results show that changes in both cytosolic pH and K can be significant factors in inhibiting protein synthesis and root growth during K deficiency.

Bibliographic Details

Walker, David J.; Black, Colin R.; Miller, Anthony J.

Oxford University Press (OUP)

Biochemistry, Genetics and Molecular Biology; Agricultural and Biological Sciences

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