This paper deals with the effect of calcium binding in the cell wall on the measured 45Ca influx in Chara corallina Klein ex Will. esk. R.D. Wood. Calcium in the cell wall was in the range 687–1197 (μmol · m−2 compared to the sap which contained only 144–256 μmol · m−2. In dilute culture solutions the calcium content of the cell wall was relatively independent of external calcium at concentrations above about 0.1 mol · m−3. The half-times for exchange of calcium from 45Ca-labelled cell walls varied from 45 min at 0.05 mol · m−3 to less than 2 min at 2 mol · m−3. The effectiveness of other cations in displacing calcium from cell walls was in the order La > Zn > Co > Ni > Mg. Rinsing of 45Ca-labelled cell walls in 2 mol · m−3 LaCl3 for 20 min removed more than 99% of the bound 45Ca. However, the residual 45Ca activity in isolated cell walls following La3+ rinsing was similar to that in whole cells. It is concluded that in whole cells 45Ca influx cannot normally be distinguished from extracellular binding of calcium. Methods are described for the measurement of 45Ca fluxes in charophyte cells by isolation of intracellular 45Ca after the uptake period using techniques which avoid contamination from the large amount of tracer bound in the cell wall. At an external calcium concentration of 1 mol · m−3, the plasmalemma influx was approx. 0.2 nmol · m−2 · s−1 of which about half entered the vacuole and half was effluxed back into the external solution. The cytoplasm filled with calcium with a half-time of 40–50 min with an ‘apparent’ pool size of 50 mmol · m−3. After 2 h the net flux to the cell was almost the same as the vacuolar flux. The fluxes reported are an order of magnitude lower than previously reported calcium fluxes in plants.

Measurement of calcium fluxes in plants using 45Ca

Theoretical and experimental studies on freezing point depression and vapor pressure deficit as methods to measure osmotic pressure of aqueous polyethylene glycol and bovine serum albumin solutions.

Rapid calcium exchange for protons and potassium in cell walls of Chara

Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but there appears to be no published study of their failure properties. The mechanical strength of single large internode cell walls (up to 2 mm diameter and 100 mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets of cell wall, which were then notched and fractured under tension. Tensile tests, using a range of notch sizes, were conducted on cell walls of varying age and maturity to establish their notch sensitivity and to investigate the propagation of cracks in plant cell walls. The thickness and stiffness of the walls increased with age whereas their strength was little affected. The strength of unnotched walls was estimated as 47 ± 13 MPa, comparable to that of some grasses but an order of magnitude higher than that published for model bacterial cellulose composite walls. The strength was notch-sensitive and the critical stress intensity factor K
1c was estimated to be 0.63 ± 0.19 MNm−3/2, comparable to published values for grasses.

https://www.jstor.org/stable/pdfplus/23386151.pdf

Fracture mechanics of the cell wall of Chara corallina.

The responses of the freshwater macroalga Nitellopsis obtusa to heavy metal (HM) salts of Hg, Cd, Co, Cu, Cr, and Ni were assessed at different levels: whole-cell mortality (96-h LC(50)), in vivo cell membrane (45-min depolarization of resting potential, EC(50)), and enzyme in plasma membrane preparations (K+, Mg2+-specific H+-ATPase inhibition, IC(50)). To measure ATPase activity, a novel procedure for isolation of plasma membrane-enriched vesicles from charophyte cells was developed. The short-term ATPase inhibition assay (IC(50) from 6.0 x 10(-7) to 4.6 x 10(-4) M) was slightly more sensitive than the cell mortality test (LC(50) from 1.1 x 10(-6) to 2.6 x 10(-3) M), and the electrophysiological test with the end point of 45-min depolarization of resting potential was characterized by less sensitivity for HMs (EC(50) from 1.1 x 10(-4) to 2.2 x 10(-2) M). The variability of IC(50) values assessed for HMs in the ATPase assays was close to that of LC(50) values in the mortality tests (CVs from 33.5 to 83.5 and from 12.4% to 57.7%, respectively), whereas the EC(50) values in the electrophysiological tests were characterized by CVs generally below 30%. All three end points identified two separate HM groups according to their toxicity to N. obtusa: Co, Ni, and Cr comprised a group of less toxic metals, whereas Hg, Cu, and Cd comprised a group of more toxic metals. However, the adverse effects within each group were discriminated differently. For example, the maximum difference between the highest and lowest LC(50) for the group of less toxic metals in the long-term mortality test was approximately 60% of the response range, whereas the corresponding difference in IC(50) values in the ATPase assay was 30%. In contrast, the LC(50) values of the more toxic metals occupied only 10% of the response range, whereas the IC(50) values were spread over 70%. Further investigation should be done of the underlying mechanism or mechanisms responsible for the observed differences in the dynamic range of a particular end point of the groups of toxicants of varying strength.

Response of the charophyte Nitellopsis obtusa to heavy metals at the cellular, cell membrane, and enzyme levels.

. Survival and death of Chara internodal cells were investigated in one of the alkali metal salts KCl, some of the alkali earth metal salts CaCl2, Ca(NO3)2, MgCl2, Mg(NO3)2, SrCl2, Sr(NO3)2, BaCl2 and Ba(NO3)2, potassium phosphate pH buffer solution (pH 7.0), Tris-maleate pH buffer solution (pH 7.0), HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid)-KOH (pH 7.0) pH buffer solution, calcium buffer solutions, and deionized water. Most of the internodal cells died within a day or a few days in KCl, MgCl2, Mg(NO3)2, BaCl2 and Ba(NO3)2 solutions of higher concentrations, calcium buffer solutions of pCa 6.0, 10.0 mol m-3 potassium phosphate pH buffer solution and 10.0 mol m-3 Trismaleate pH buffer solution. However, all of the internodal cells survived more than 10 d in deionized water, 80.0 mol m-3 CaCl2, 80.0 mol m-3 Ca(NO3)2, 80.0 mol m-3 SrCl2, 80.0 mol m-3 Sr(NO3)2 calcium buffer solutions of pCa 4.0 and pCa 5.0, and 10.0 mol m-3 HEPES-KOH (pH 7.0) pH buffer solution. Addition of Ca2+ or Sr2+ to K+, Mg2+ and Ba2+ salt solutions increased the survival rates of the internodal cells. Calcium release from the internodal cell wall was measured in deionized water, KCl, NaCl, MgCl2, CaCl2, SrCl2 and BaCl2 solutions. Except in deionized water and CaCl2 solution, most of the calcium binding to the cell wall was released within one or a few hours in respective electrolyte solutions. Thus, survival and death of the internodal cells in the electrolyte solutions tested were interpreted in terms of the calcium release from the cell wall and the cell membrane, and intrinsic ability of Sr2+ to maintain the cell membrane normal.

T. Adachi

Papers

Survival and death of Chara internodal cells in electrolyte solutions and calcium release from the cell wall