EFFECT OF PCMBS AND EPTC ON MINERAL NUTRIENT-UPTAKE AND TRANSLOCATION IN WHEAT

Evaluations of the influence of EPTC on mineral ion root uptake and translocation to the foliage were undertaken. Root uptake was measured in wheat (Triticum aestivum L. cv Holley) was grown in 0.5 Hoagland complete mineral nutrient solution. Timed (< 4h) accumulation studies were undertaken in the presence of: a) p-chloromercuribenzenesulfonic acid (PCMBS) which does not penetrate through membranes but does inhibit sulfhydryl groups (SH), and b) dithiothreitol (DTT) which is membrane permeable and protects SH from PCMBS. Mg, Ca, K, Fe, and Mn accumulations were decreased by PCMBS and the partial inhibition was reversed by DTT. Calcium root accumulation data were explicable as two modes of Ca entry into roots and one involved a SH containing enzyme. Ion translocation to the foliage was evaluated in nutrient solutions containing sub-lethal concentrations of S-ethyldipropylthiocarbamate (EPTC) (0, 0.625, 0.125, 0.25, or 0.5 mg/L), EPTC did not act as a general sulfhydryl group inhibitor. Shoot dry weight per pot decreased as EPTC concentration increased. Total water utilization (mL/pot) decreased and transpiration (mLg DW) increased as EPTC concentration increased. Stomatal aperture (mu) increased as EPTC concentration increased. Water use (ml/pot) was linearly correlated with dry weight (mg/pot). Shoot total ion contents (i.e., P, K, Ca, Mg, and Cu) decreased as EPTC concentration increased and absorption and translocation of P, Ca, Mg, and Cu ions were correlated to total water utilization or transpiration [mL/g DW]. Thus, the altered concentration of these ions in EPTC-treated wheat shoots is explicable as the results of an influence by EPTC on stomatal physiology.