Abstract
Summary The influence of lead ions (10 −5 m Pb(NO 3 ) 2 ) upon the water conductivity of plant roots (“WDK” in this paper) was investigated by the method of root pressure exudation measurement (according to O’L eary ) of aeroponically grown beans. The basic phoenomenon was verified as a significant decrease of “WDK” in lead-treated bean roots. The normal “WDK” of the control plants shows a distinct circadian rhythm having a minimum 1 h after the beginning of darkness and a maximum after the fifth light hour. Both the 2 cardinal points are influenced by temperature conditions of growing. The phytochrome dependence of “WDK” was tested by darkening and short day experiments. There is some evidence that lead accumulation in the roots endodermis and the endodermal region causes a stop of symplastical water transport leaving only the small amount of the apoplastical transport. This is suggested by the whole-day quenching of lead influenced “WDK” to the minimum level of normal circadian rhythm. In Fig. 4 we propose an improved method of plant application to the root pressure chamber.
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