Effects of High Humidity on Translocation of Foliar-Applied Labeled Compounds in Plants Part: I

Very little is known about the effects of humidity and water balance on absorption and translocation of foliar-applied materials. Palmquist (11) reported that when a scraped leaf of a water-stressed plant was immersed in fluorescein solution, the solution moved rapidly through and out of the leaf via the xylem. Colwell (5) found that when a solution containing p32 was applied in small amounts covering 10 to 15 % of the leaf area, phosphorus was not moved out of the treated leaf in the xylem. When, however, a larger volume of the same solution was applied which covered 40 to 60 % of the leaf area, phosphorus moved out of the treated leaf via xylem of the ringed petiole. Went and Carter (14) found that uptake of sucrose by tomato leaves was indepenc1ent of humidity levels. Other workers reported that high humidity increased the absorption of foliarapplied urea, 2,4-D, and maleic hydrazide (Volk & McAuliff, 13; Zukel et al., 16; Pallas, 10). It has been reported also that plants might absorb water from humid air through the leaves by a reversal of the normal transpiration stream, a process termed "negative transpiration" (Stone et al., 12; Breazeale et al., 2, 3). Preliminary experiments on translocation of foliarapplied, C14-labeled 2,4-D, amino-triazole and urea, indicated that translocation of these compounds was greatly increased under high humidity conditions. A more detailed investigation was, therefore, desired.