Abstract. Ammonium sulfate, ammonium carbonate or ammonia gas inhibited water uptake in sugar beet roots whenever the pH was sufficiently high to cause the production of ammonia. When ammonia was removed by aeration, inhibition of the water uptake by roots was rapidly reversed. ATP at 0.2 mm appeared to either wholly or partially prevent the ammon,ia-induced inhibition of water uptake by roots. ATP may be involved in maintaining the structure of water pathways through the root. In roots lacking epidermis, ammonia did not inhibit water uptake by the roots. This may indicate that the site of the inhibition lies within the root epidermis.During a previou,s study we observed that sugar beets grown in the greenhouse or out-of-doors in a nutrient solution (pH 7.6-8.0) using ammonium suilfate as the ni,trogen source wilited severely on h,o,t summer days. Sugar beets ireceiving poitassium nlitraite as a nitrogen soturce sthowed little, if any, wiliting. On ciloudy days or ait night, no difference in wiilting wa's observed between the treatments. lit appeared that amimonia may have been interfering with the movement of water thrrotugh the sugar beeit plant.Several investigators have reported that respiration inhibitor's anid/o,r un!oouplers such as cyanide (2,3,15,16,17,19), aziide (2,13, 19), 2,4-dinitrophen,ol (16), fluoiride (2), i'odoacetate (2), arrsenate (2), phenylurethiane (2), and lack of oxygen (15,20) decrease the movement oif w,alter int'o or oult of coleolptille segmenits, root segments 'or initact roots. Ammonia (NH3) and/or undi ssocia'ted ammonium hydroxide, hereinafter called ammonia, mlay also act as respi,ration inhibitors. AlItschuil et al. (1) showed that treating cotton seed wiitih ammonia inhibited respiration in boith mature and immature seeds. V:nes and Wedd:n,g (24,26) found that ammon.a inhbted resp.rat.on in excised bar'ey roots, garclen bee't di,skq, leaf d.sks of sp:nach antd sugiar beets and garden beet root m:toc'hondr.a. They fouiind that the degree o,f inh'b tion was related to pH, since pH controls the amount of ammon:a present in solutitons contan:ng ammon um ion's (NH,').
