Some Effects of Humidity on the Translocation of 2,4,5-T in Bean Plants

Abstract

The effect of humidity on the rate and direction of translocation of stem-injected (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in bean (Phaseolus vulgaris L., var. Stringless Green-pod) seedlings was determined. A total of 0.75 μg of 14C-labeled 2,4,5-T was injected into the stem with a 1-μl syringe pipette. Translocation was determined by assaying the nutrient solution and plant parts for 14C. High relative humidities enhanced downward translocation to roots and nutrient solutions. About 41% of the applied 2,4,5-T was found in the nutrient solution after 2 days' treatment at about 95% relative humidity while only 23% was found when treatment was conducted at 20% relative humidity. Low humidity during treatment caused much more 2,4,5-T to be translocated upward to the primary leaves and young shoots of the seedlings and this effect was more pronounced in plants which were grown in low humidity prior to treatment. The results confirm the conclusions of others and show that the increased basipetal phloem transport of herbicides in plants under high humidity is not due to an effect on penetration of herbicides in leaf tissue.