Calcium Activation of Orthophosphate Absorption by Barley Roots

Abstract. Magnesium contents of soybean (Glycine max) roots increase and the K and Ca contents decrease with increased MgCl., ooncentrations in ambient solutions. The Mg uptake is inhibited when both Ca and K are present in the solution, but not by K or Ca alone.Chloride uptake, which is very low from the MgCl, solution, is greatly enhanced by the presence of K. The selectivity against Mg imparted by K +-Ca appears to be at an external barrier for cation uptake as shown by its dependence on the presence of Ca in the external solution. experiment. It was more convenient to adjust the root to solution ratios based upon previous experience such that the final pH valuies would be in the range of 5.1 to 5.5.At the end of the experimental period, the roots were rinsed, transferred to beakers, and heated in a muffle oven to 4800 for 2 hr. The ash was dissolved in 20 ml of 0.1 H1NO, and 10 % acetic acid solution anld reserved for analysis.Chloride analysis of plant roots after the above dry-ashing procedure was compared with the analysis after several hot water extractions. The Cl-value was the same for both procedures. However, Cl will be lost if the ash is maintained at 4800 for more than 8 hr. Selection *of the 2-hr period was made on the basis of complete ashing and no Cl-loss. WVe did not attempt to relate Cl-loss more precisely to the ashing period.Intact Planits. Lots of 5 dark-germinated seeds were placed on gauze in a holder with their roots extending into a 0.2 mni CaSO4 solution. These lots wkNere grow^n on a 15-hr day at 270 for 7 days when the first trifoliolate leaf w7as expanding. At this time, the 5 plants had protduced about 2 g of roots and 3 to 4 g wet weight of shoots. The lots were transferred after rinsinig to experimental solutions as desired. Roots and shoots were separated at the end of the experimental period and prepared for analysis as described for excised roots.

“…The maximum Ca24 effect near 1 meq/liter (Fig. 3) was also observed in excised barley roots for the uptake of K' (5,8), S02-4 (ii), and P03-4 (12). (Fig.…”

Section: Methodsmentioning

confidence: 90%

“…The evidence points to the necessity for Ca24 in the external solution to maximize this ion: preference (5, -;.9, 12) 18), although the presence of external Ca24 does not prevent Ca24 loss from the root (13). Anioni uptake can also be maximized by addition of Ca24 to the external solution (12,13,14 (Fig. 3).…”

Section: Methodsmentioning

confidence: 99%

Magnesium Uptake by Soybeans

Leggett

Gilbert

1969

“…One of these reactions, which dominates at low external phosphate concentration, appears highly dependent on Ca (15) and is possibly located in the outer plasma me,mlbrane of the cytoplasm. It may be liniked to NADH and possibly involves combination of ADP with Pi at the membrane surface, movement through the membrane, and release at the inner surface of Pi.…”

Section: Discussionmentioning

confidence: 99%

“…Kinetic studies 'have lead to the postulation of a number of rather precise relationships with respect to the mechanism of phosphate uptake by excised barley roots (10,14,15). Most significant has been the interpretation that 2 apparent sites or mechanisms of P absorption are involved.…”

mentioning

confidence: 99%

Effects of Temperature on Orthophosphate Absorption by Excised Corn Roots

Carter¹,

Lathwell²

1967

Summary. The uptake of orthophosphate (32P) by excised corn roots, Zea mays L.was studied using roots grown on 0.2 mm CaSiO4. Nine concentrations of KH2PO4 from 1 to 256 /uM were used at temperatures of 200, 300, and, 400. Enzyme kinetic analysis was applied to the data obtained. Two apparent mechanisms (sites) o,f phosphate uptake were observed, 1 dominating at high P concentrations and 1 at low P concentrations. A Km of 1.36 X 10-4 and; a Vmax of 177 X 10-9 moles per gram of roots per hour at 300 was calculated for the mechanism dominating at high P concentrations. Similar calctlations gave a Km of 6.09 X 10-6 and-a Vmax of 162 X 10-9 moles per gram of roots per ihour at 300 for the mechanism dominating at low P concentrations. The Qlo for both mechanisms was approximately 2. Calculation of thermodynamic values from the data gave AF of -5200 cal, AH of -950 to -1400 cal, and a enthalpy of activation (A) of 10,300 to 13,800 cal per mole for the mechanism dominating at high P concentrations. Similar calculations from the data for the mechanism dominating at low P concentrations gave a AF of -7300 cal, AH of -10,700 to -8200 cal, and a A of 9300 to 18,900 cal per mole. If the dual mechanism interpretation of this kind of data adequately describes this system, then both mechanisms of P absorption by corn roots involve chemical reactions.Kinetic studies 'have lead to the postulation of a number of rather precise relationships with respect to the mechanism of phosphate uptake by excised barley roots (10, 14, 15). Most significant has been the interpretation that 2 apparent sites or mechanisms of P absorption are involved. The dual mechanism data have been initerpreted to imply separate sites for the absorption of the 2 phosphate ionic species, H2PO,9). Likewise, the enhancement of Ca2+ on P uptake is an important observation. The effect of temperature on absorption of orthophosphate by excised corn roots from solutions of a wide range of phosphate concentrations was examined to test the hypothesis that the apparent dual mechanism of phosphate uptake may be due to the combined action of physical and metabolic components. Enzyme kinetic analysis was applied to the data obtained and certain thermodynamic values were calculated. Materials and MethodsSeeds of Zea mays L, var. OH10 X 51A X B8, supplied by the Department of Plant Breeding, Cornell University, were placed on pa-per towelling covering a 1.5 cm layer of acid washed sand in 33 X 22 cm pyrex baking dishes. The sand was moistened with 0.2 mnm CaSO4. Dishes were covered with saran wrap (punctured for aeration) and placed in an incubator in the dark at 230 for 90 to 95 hours.Roots (approximately 6.5 cm long) were cut off adjacent to the seed, blotted dry, and weighed into ,lots of approximately 1 gram for each treatment.They were then placed into 500 ml wide mouthed jars containing 0.2 mm CaSO4 and aeration tubes. The jars were placed in a temperature controlled water bath and allowed to come to equilibrium for 30 minutes. The CaSO4 solution was removed by suctio...

“…The 'Viets effect' is especially pronoun-ed with K (4,9,14,20). Rb+ (5,17,18,19), Br- (20), Cl-(3, 15), SO042 (11) and P043- (12,17,18). Scditim and lithiulm absorptioni, on the other hand, are drastically curtailed 1!…”

mentioning

confidence: 99%

Calcium Inhibition of Potassium Absorption in Corn Roots

Elzam

Hodges

1967

Sumimiiary. Calcium (or miagnesium) sulfate or chloride was found to inhibit energy dependent ipotassium transport in excised corn roots. This Ca"t inhibition of K' transport was most pronounced during the initial phases of transport. As the absoription periods vere tengthened the effect of Ca 2 gradually changed from an inhibition to a typical promotion (after about 30-45 mins) of K' transport. Kinetic anaiysis indicated the inhibition to be of a non-competitive nature.Identical experiments with excised barley roots showed that CaS,O4 had no effect on K' absorption whereas CaCl9 had a typical stimulatory effect on K+ absorption. Kinetic (4,9,14,20). Rb+ (5,17,18,19), , Cl-(3, 15), SO042 (11) and P043-(12,17, 18). Scditim and lithiulm absorptioni, on the other hand, are drastically curtailed 1! Ca24 (4, 5,10, 16). However, the g'enerallx-prometive effects of (a21 on1 mononovalent cation absorpt on. plus the finding that Ca'2 appears to be essent-al for maintaining the integrity of the se'ectixe ion tranisport mechanisms (4). as well as the fact that (a2+ is necessary for the maintenance of cellular miemnbranes (13)