Effect of Lanthanum on Ion Absorption in Corn Roots

Abstract

Short term (10 min) influx of "6Rb-labeled potassium into corn (Zea mays L. WF9 X M14) root segments was inhibited by La (NO3) (3,12,14,19,20,27,32,35, 41), it forms deposits (above pH 7.2) which can be viewed with the electron microscope, and it has chemical properties resembling those of Ca2. Because of this, La+ has been used to define extracellular space in both animals (12,19,20,32) and plants (3,14,27,35, 41), as well as to study the role of Ca2+ in a number of animal (13,19,34,38) and plant (18,29,30,36) processes.During investigations of the apoplastic continuum in plants it was reported that La3`inhibited salt gland function of several halophytic species (3) and K+ influx in corn roots (27). In this paper, the effect of La3`on ion transport in corn roots is further characterized. The results show that La3`inhibits K+ absorption only over short influx periods and the inhibition is of a competitive nature. Ca2+ has similar effects on K+ absorption in corn. This similarity between La3`and Ca2+ and the observation that La3`does not seem to penetrate the plasma membrane of corn roots (27) indicates that Ca2+ may also influence ion transport without entering cells. MATERIALS AND METHODSPlant Material. Corn seeds (Zea mays L., WF9 X M14) were placed embryo down in glass dishes on paper towels saturated IThis work was supported in part by Grant GB-8199 from the National Science Foundation. with 0.1 mm CaCl., and were allowed to germinate at 26 C for 4 days in the dark (23). Additional 0.1 mm CaC12 was added after 3 days to maintain saturation of the paper towels. The primary roots (6-8 cm in length) were excised, rinsed three times in cold distilled H20, and cut into 2-cm sections on paper towels saturated with cold (3 C) distilled H20. Batches of 16 sections (a random selection of 4 apical and 12 basal, about 250 mg fresh weight) were used for absorption measurements unless otherwise stated.Primary roots were separated into cortex and stele by excising the apical 1 cm, pinching the basal portion of the root between the thumb nail and forefinger to break the cortex, and removing the cortex with a smooth pulling motion. Electron micrographs of glutaraldehyde-fixed, uranyl-and lead-stained (27) samples of isolated cortex and stele showed the break to occur in radial walls of endodermal cells at the Casparian strip (Fig. 1). Endodermal cells were completely destroyed by the procedure with no apparent damage to cortical or stelar parenchyma cells. Others have separated cortex and stele from roots of corn (1,5,15,21,39,40) and pea (25) using somewhat different techniques and also found the break to occur at the endodermis.Separated stele, cortex, and whole roots (with apical 1 cm removed) were cut into 2 cm-sections, and batches of 16 to 20 sections were collected and used for absorption studies.Absorption Measurements. Root sections were incubated with aeration at 30 C in 35 ml of 0.25 mm KCl labeled with s6Rb (for a justification of using 'Rb as a tracer for K+ see references listed in 10, 11, 26) or 3Cl,...

Cerium negatively impacts the nutritional status in rapeseed

“…An observed increase of P in maize roots and a relative decrease in shoots was also observed by Diatloff et al (2008), in treatments with relatively low Ce concentrations in nutrient solutions. However, in the same experiment, the P status was not affected in mungbean, which could be due to a lower demand for P. Nagahashi et al (1974) and Leonard et al (1975), hypothesised a non-metabolic apoplastic precipitation of La with P in roots and suggested that this is the reason why La does not cross the endodermis. However, our data suggest that Ce precipitation can also occur not just in the apoplast, but probably also inside the cells, because we desorbed the roots in appropriate cleansing solution and we tested the plants in a P-free nutrient solution.…”

“…P will precipitate Ce even in the solution, as demonstrated by our observation that the EC 50 for root growth in a complete half-strength Hoagland's is N640 μM, in comparison with 4.2 μM in a half-strength Hoagland's without P and Fe-EDTA. Thus the contrasting observations by Nagahashi et al (1974) and Leonard et al (1975) could simply be due to presence of P (0.25 mM) in the test solutions, so there was no chance for La to enter the root cells, let alone to pass the endodermis. However, further confirmation would be required with TEM-EDAX analysis to see if there are any CePO 4 precipitates inside root cells.…”

Role of Calcium in Serine Transport into Tobacco Cells

“…9) indicates that the net transport of Ca2+ is small relative to Ca2+/Ca2+ exchange. (3,18) and animals (2). K+ was less effective in replacing surface-bound Ca24, as indicated by the total 'Ca2+ and the difference between water and CaCl2 at 10-min values.…”

Reactions of Corn Root Tissue to Calcium

“…Leonard et al (20) found La`as well as Ca2+ to produce the initial inhibition and later promotion of K+(86Rb) influx, but unlike Elzam and Hodges (8) found competitive kinetics over the first 10 min of influx. On the basis of the impermeability of L3+, they concluded that the inhibition and later promotion of K+ influx arise from reaction of Ca2+ and La3+ in the apoplast, including the external surface of the plasmalemma.…”