Effect of calcium on transport of cations to the xylem exudate of tobacco

Summary Roots of detopped tobacco plants (Nicotiana tabacum var. Virginia Gold) were exposed to Na, K, and Ca salts or to water, and cation transfer to xylem vessels was measured. In some cases plants had been exposed to Na in addition to regular nutrient solutions before detopping. Calcium in the external medium greatly depressed the transport of Na from the external medium to the xylem vessels and it often stimulated the transfer of K from the external medium to the xylem vessels. The K/Na ratio in the exudate thus was dependent upon the Ca content of the external medium under these conditions. In contrast, externally applied Ca or Ca deficiency had very little effect on the transfer of preaccumulated K and Na from compartments within roots to the xylem vessels. The K/Na ratio in the exudate under these conditions was not related to Ca levels nor to mild Ca deficiency. The ratios decreased with time after detopping regardless of Ca level. Intact plants accumulated more Na than did root systems of detopped plants in a 6-day period.Riverside University of CaliforniaSoil Science and Agricultural Engineering