Responses of bean plants to root temperatures. IV Translocation of 22Na applied to the leaves

The foliar uptake and subsequent transport in bean plants of 22Na, 32P and 134Cs was studied under controlled environmental conditions but at varying root temperatures. The amounts taken up by the plants, held in the treated areas, distributed in various plant fractions or excreted through the roots were determined for periods of up to 6 days. Uptake of 22Na was found to be slower than that of 134Cs and much faster than that of 32P. Root temperature strongly influenced the rate of entrance of the isotopes with an optimum range between 20 and 25 °C. The penetration was found to be more affected by the root temperature during the pretreatment period than by that during the experimental period itself. The translocation and distribution during the first 6 hours of the experimental periods were also influenced by the pretreatment temperature of the roots. Na and Cs leakage in the solution was found to occur at all temperatures, provided transport had allowed their presence in the root tissues.