Role of Cation and Anion Uptake in Salt-stimulated Elongation of Lettuce Hypocotyl Sections

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Abstract
The role of cation and anion uptake in salt-stimulated growth of light-grown, GA3-treated lettuce (Lactuca sativa L.) hypocotyl sections was investigated. Potassium chloride (10 mM) causes a 2-fold increase in the growth rate of GA3-treated hypocotyl sections without affecting the growth rate of sections incubated in the absence of GA3. Salt uptake is the same in both treatments and the uptake of cation and anion is stoichiometric during the first 24 h under all incubation conditions. The importance of the anion for cation uptake is demonstrated in experiments with benzenesulfonate- and iminodiacetate2-. When K+ and Na+ are supplied only as the benzenesulfonate and iminodiacetate salts, growth and cation uptake are markedly reduced compared to KCl and NaCl. Calculation of the osmotic potential of salt-treated sections based on measurement of K+ and Cl- uptake suggests that the observed increase in tissue osmolality is a result of salt uptake. Similarly, uptake of ions can account for the shift in water potential when sections are incubated in 10 mM KCl. Apparently the change in growth rate of light-grown, GA3-treated sections caused by the addition of KCl or NaCl to the incubation medium results solely from decreased water potential of the tissue due to ion uptake.