Diurnal cycles of leaf extension in unsalinized and salinized Beta vulgaris
Abstract. Continuous high resolution measurement of sugar beet leaf extension over 5 d in growth chambers showed average leaf extension rates (LER) in darkness to be from three to six times those in light for plants growing in non-salinized media. The changes in LER in light-dark transitions occurred within seconds, a response which was more rapid than stomatal opening or closing. When the growth medium was salinized to 100 mol m−3 NaCl, LER's were reduced by about 50% in darkness and 90% in light, markedly increasing the ratio of dark to light LER. 
 
A 2-d episode of root-zone salinity imposed midway through a 5-d period of measurement decreased LER and produced higher leaf temperatures. LER and diurnal leaf temperature patterns reverted to their pre-salinized levels when root-zone salinity was removed. Thus, the effects of short episodes of high sodium chloride in the growth medium appear to be reversible, suggesting a water stress mechanism of growth reduction rather than toxicity effects of salt.