Hormonal Regulation of Organic and Phosphoric Acid Release by Barley Aleurone Layers and Scutella

The release of acid from the aleurone layer and scutellum of barley (Hordeum vulgare L. cv Himalaya) was investigated. Aleurone layers isolated from mature barley grains acidify the external medium by releasing organic and phosphoric acids. Gibberellic acid and abscisic acid stimulate acid release 2-fold over control tissue incubated in 10 mM CACl2. Gibberellic acid causes medium acidification by stimulating the release of phosphoric and citric acids, whereas abscisic acid stimulates the release of malic acid. The accumulation of these acids in the incubation medium buffers the medium against changes in pH, particularly between pH 4 and 5. The amounts of amino acids that accumulate in the medium are low (2-12 nmol/layer) compared to other organic and phosphoric acids (100-500 nmol/layer). The scutellum does not play a major role in medium acidification but participates in the uptake of organic acids. The organic acid composition of the starchy endosperm changes after 3 d of imbibition; malic, succinic, and lactic acids decrease, whereas citric and phosphoric acids remain unchanged or increase. These results indicate that during postgerminative growth, the acidity of the starchy endosperm is maintained by acid production by the aleurone layer.     

The degradation of malic acid by high density cell suspensions of Leuconostoc oenos

Washed cell suspensions of Leuconostoc oenos catalysed the degradation of L-malic acid to L-lactic acid. Cell suspensions of 10₁₀ cfu ml_-1 degraded 90–95% of the malic acid in a buffer assay system and in wine within 30 min. A reaction time of 6 h was needed to obtain the same extent of degradation with suspensions of 10₉ cfu ml_-1. With a reaction period of 6 h and an initial malic acid concentration of 3 g 1_-1, reaction variables of pH 2.5-4.0, temperature 10–30°C, ethanol up to 15%, and L-lactic acid up to 4 g 1_-1 did not decrease the degradation of malic acid to below 90–95%. Total SO₂ at 100 mg 1_-1 decreased the degradation of malic acid to 80%. The degradation (%) of malic acid was decreased when the concentration of malic acid was decreased below 2 g 1_-1. The results indicate the prospect of using high densities of Leuc. oenos cells in membrane bioreactor systems for the rapid, continuous, deacidification of wine.     

Metabolism of CO2 by leaves of different photosynthetic types of Neurachne species

Following a series of continuous exposures to ¹⁴CO₂ for different lengths of time, leaves from Neurachne munroi (C₄), N. minor (C₃-C₄) and N. tenuifolia (C₃| were estimated to assimilate 100%, 9% and 2–4%, respectively, of atmospheric CO₂ by the C₄ pathway. The percentage of ¹⁴C-label appearing in malate and aspartate in leaves of N. minor progressively increased with longer exposure times indicating that a significant proportion of its C₄ acids are formed as secondary products. In ¹⁴CO₂/¹²CO₂ pulse/chase experiments, the ¹⁴C-label in leaves of N. munroi was rapidly transferred from C₄ acids to sugar monophosphates plus sugar diphosphates, and finally to sucrose. In leaves of N. minor, the ¹⁴C-label was slowly metabolized from the C-4 carboxyl of malate and asparate (apparent half-time = 250 s), and the formation of C₄ acids as secondary products was again evident. ¹⁴C-label in serine/glycine accumulated to comparable magnitudes in both N. minor and in N. tenuifolia, but there was an initial lag phase in the accumulation of label in N. minor. C₄ photosynthesis is apparently of minimal importance in reducing photorespiration in N. minor, but leaf anatomical specializations and a possible compartmentation of photorespiratory metabolism may be of considerable importance.     

Transport in C4 mesophyll chloroplasts. Characterization of the pyruvate carrier

1. Evidence is presented for high rates of carrier-mediated uptake of pyruvate into the stroma of intact mesophyll chloroplasts of the C₄ plant Digitaria sanguinalis, but not the chloroplasts of the C₃ plant Spinacea oleracea. Uptake of pyruvate in the dark with the C₄ mesophyll chloroplasts was followed using two techniques: uptake of [¹⁴C]pyruvate as determined by silicon oil centrifugal filtration and uptake as indicated by absorbance changes at 535 nm (shrinkage/swelling) after addition of 0.1 M pyruvate salts.

2. Uptake of the pyruvate anion by an electrogenic carrier is suggested to be the major mode of transport. Chloroplast swelling was observed in potassium pyruvate plus valinomycin and uptake of [¹⁴C]pyruvate was inhibited by membrane-permeant anions. Valinomycin reduced uptake in the absence of external potassium and the inhibition could be reversed by addition of external potassium.

3. Uptake of pyruvic acid (or a pyruvate ⁻/OH⁻ antiport) is ruled unlikely since [¹⁴C]pyruvate uptake was relatively independent of the pH gradient across the envelope and addition of pyruvate to chloroplasts did not result in an alkalization of the medium. The low rate of swelling observed in ammonium pyruvate may be due to non-mediated permeation of pyruvic acid, which is possible only at high pyruvate concentrations.

4. The concentration of pyruvate in the stroma increased with external concentration over the range tested (up to 40 mM) but the concentration ratio (internal/external) was always less than one. The steady-state concentration of [¹⁴C]pyruvate in the stroma was dependent on the ionic strength of the medium, with saturation at roughly I = 0.04 M, while accumulation of the membrane-permeant cation tetraphenylmethylphosphonium decreased with increasing ionic strength. This suggests that ionic strength modifies a membrane potential (inside negative) across the envelope and that pyruvate uptake responds to the magnitude and direction of that potential (−80 mV at low ionic strength).

5. Chloride and inorganic phosphate were potent inhibitors of [¹⁴C]pyruvate uptake. Of the sulfhydryl reagents tested, N-ethylmaleimide was not inhibitory while mersalyl completely blocked [¹⁴C]pyruvate uptake and swelling in potassium pyruvate plus valinomycin. Pyruvate uptake, as measured by valinomycin induced swelling in potassium pyruvate, was highly temperature sensitive, with an energy of activation of 39 kcal/mol above 9 °C.

6. Phenylpyruvate, -ketoisovalerate, -ketoisocaproate, -cyano-4-hydroxycinnamic acid and -cyanocinnamic acid inhibited [¹⁴C]pyruvate but not [¹⁴C]-acetate uptake in the dark and also reduced pyruvate metabolism by the chloroplasts in the light.     

Glutamine, Glutamate, and Other Possible Regulators of α-Ketoglutarate and Malate Uptake by Synaptic Terminals

Abstract: The uptake of a-ketoglutarate and malate by rat brain synaptosomal preparations was found to be affected by a variety of substances at physiologically relevant concentrations. Glutamine altered the uptake of γ-ketoglutarate by causing an apparent reduction in the substrate-carrier affinity and an increase in V_max. In contrast, glutamine did not appear to affect the V_max of malate uptake, but it did increase markedly the uptake velocity at low concentrations of malate. L-Glutamate and L-as-partate were comparatively strong inhibitors of γ-keto-glutarate and malate uptake. N-Acetylaspartate was a weak inhibitor of γ-ketoglutarate uptake, a finding that contrasts with our previous observation that this compound potently inhibited γ-ketoglutarate uptake by synaptosomes obtained from the cerebellum of 8- to 14-day-old mice. Ca²⁺ exhibited a variable effect but usually enhanced the uptake of γ-ketoglutarate. The addition of small amounts of postmicrosomal supernatant to the incubation medium enhanced the uptake of γ-ketoglutarate by low-density synaptosomes. By comparison, the uptake of glutamate, glutamine, γ-aminobutyric acid, and several other amino acids was not affected. The enhancement of γ-ketoglutarate uptake by the supernatant was due to a heat labile substance that was retained by dialysis tubing (MW cutoff = 8,000) and Amicon filter cones (CF 25), and was precipitated by ammonium sulfate at 60% saturation. In experiments in which the metabolic conversion of [U-^-14C] γ-ketoglutarate to glutamate, as-partate, glutamine, and aminobutyric acid was determined, the presence of glutamine and glutamate in the incubation medium did not affect the pattern of labelling appreciably.     

Abscisic acid and gibberellic acid-regulated responses of embryos and aleurone layers isolated from dormant and nondormant barley grains

Dormant and nondormant isogenic barley grains were obtained by maturing grains under short day (SD) or long day (LD) growth conditions, respectively. Hormonal responses of isolated embryos and aleurone layers from these grains were studied. Addition of abscisic acid (ABA) reduced germination rate and percentage of embryos, and induced Rab (ABA-responsive) mRNA in aleurone layers from both types of grain. Embryos and aleurone layers from dormant grains responded stronger to ABA than those from nondormant grains. Gibberellic acid (GA₃) increased the germination rate and percentage of embryos from dormant grains and counteracted the ABA-induced inhibition of embryo germination. GA₃ did not affect the amount of Rab mRNA in aleurone layers, suggesting that expression of the Rab gene has no direct correlation with germination. The stronger response of embryos and aleurone layers from dormant grains to ABA may not be explained by higher endogenous ABA levels, but might be due to differences in hormone signal transduction. Aleurone protoplasts from dormant grains had a higher cytosolic pH than those from nondormant grains. To inhibit the ABA-induced Rab mRNA, a much higher concentration of weak acid was required for aleurone layers from dormant grains than for those from nondormant grains. A possible difference in ABA signal transduction between dormant and nondormant grains is discussed.     

Hormonal regulation of barley nuclease: investigation using a monoclonal antibody

Abstract. A monoclonal antibody prepared against barley ( Hordeum vulgare L., cv. Himalaya) nuclease (EC 3.1.30.2) was characterized with solid-state enzyme-linked immunosorbent assays and immuno-blotting. The antibody was specific for intracellular and secreted nuclease. Hormonal regulation of the synthesis and secretion of nuclease in isolated aleurone layers was investigated by immunoprecipitation of biosynthetically-labelled nuclease using polyclonal antibodies and by immunoblot analyses using the monoclonal antibody, respectively. Gibberellic acid (GA₃) induced the de novo synthesis and secretion of nuclease in a time-and concentration-dependent manner. Nuclease was detected in aleurone layers incubated in 1 mmol m⁻³ GA₃, after 24 h. The maximum rates of nuclease synthesis and secretion occurred 36–48 h after hormone treatment. A minimum concentration of 10⁻⁶ mol m⁻³ GA₃ was required for nuclease synthesis and secretion, whereas the maximum rate of nuclease secretion occurred at concentrations of 10⁻⁵ mol m⁻³ and higher. In the presence of abscisic acid, the synthesis and secretion of nuclease from GA₃-treated aleurone layers was almost completely inhibited. Based on these findings, the authors conclude that all nuclease within and secreted from aleurone layers treated with GA₃ is the result of its de novo synthesis.     

Influence of pH,malic acid and glucose concentrations on malic acid consumption by Saccharomyces cerevisiae

Malic acid consumption by Saccharomyces cerevisiae was studied in a synthetic medium. The extent of malic acid degradation is affected by its initial concentration, the extent and the rate of deacidification increased with initial malate concentration up to 10 g/l. For malic acid consumption, an optimal pH range of 3–3.5 was found, confirming that non-dissociated organic acids enter S. cerevisiae cells by simple diffusion. A full factorial design has been employed to describe a statistical model of the effect of sugar and malic acid on the quantity of malate degraded (g/l) by a given amount of biomass (g/l). The results indicated that the initial malic acid concentration is very important for the ratio of malate consumption to quantity of biomass. The yeast was found to be most efficient at higher levels of malate.     

Modulation of Calmodulin mRNA and Protein Levels in Barley Aleurone

Changes in calmodulin (CaM) mRNA and protein were investigated in aleurone layers of barley (Hordeum vulgare L. cv Himalaya) incubated in the presence and absence of calcium, gibberellic acid (GA3), and abscisic acid (ABA). CaM mRNA levels increased rapidly and transiently following incubation of aleurone layers in H2O, CaCl2, or GA3. The increase in CaM mRNA was prevented by ABA. This increase in CaM mRNA was brought about by physical stimulation during removal of the starchy endosperm from the aleurone layer. CaM protein levels did not increase in response to physical stimulation. Only incubation in GA3 plus CaCl2 brought about a rapid increase in CaM protein levels in the aleurone cell. ABA reduced the level of CaM protein below that found at the beginning of the incubation period. The rise in CaM protein preceded increases in the synthesis and secretion of [alpha]-amylase. Immunocytochemistry with monoclonal antibodies to carrot and mung bean CaM was used to localize CaM in aleurone protoplasts. Monoclonal antibodies to tubulin and polyclonal antibodies to tonoplast intrinsic protein and malate synthase were used as controls. CaM was localized to the nucleus, the vacuolar membrane, and the cytosol, but was not associated with microtubules.     

Phosphate transport in rat-liver mitochondria

1. The kinetics of the efflux of P_i and malate as well as the relationship between P_i transport and intra- and extramitochondrial pH changes were studied in rat-liver mitochondria in the presence of rotenone and oligomycin at different pH's.

2. At high pH a fast efflux of P_i from the mitochondria occurs in the first few seconds, followed by a slow re-entry of P_i into the mitochondria. Under the same conditions the exit of malate shows a time lag of 2–4 sec. The exit of malate coincides with the re-entry of P_i.

3. In the presence of butylmalonate the exit of endogenous P_i is coupled with a concomitant alkalinization of the mitochondrial matrix space, as calculated from the distribution of 5,5-[¹⁴C]dimethyloxazolidine-2,4-dione.

4. The stoicheiometry of the P_i-hydroxyl exchange was found to be 1:1.

5. The kinetics of P_i transport are consistent with previous observations that there is a direct exchange between OH⁻ and P_i, but not between OH⁻ and malate. The equilibrium distribution of H₂PO₄⁻ and OH⁻ deviates from the Donnan distribution. This may be explained by assuming a pH-dependent binding of P_i in the mitochondria.     

Influence of ammonium and extracellular pH on the amino and organic acid contents of suspension culture cells of Acer pseudoplatanus

The effects of supplied ammonium and nitrate on the amino and organic acid contents and enzyme activities of cell suspension cultures of Acer pseudoplatanus L. were examined. Regardless of nitrogen source the pH of the culture medium strongly affected the malate and citrate contents of the cells; these organic acid pools declined at pH 5, but increased at pH 7 and 8. Over a period of two days, ammonium had little effect on the responses of the organic acid pool sizes to the pH of the medium. In contrast, ammonium had a strong influence on amino acid pool sizes, and this effect was dependent on the pH of the medium. At pH 5 there was no increase in cell ammonium or amino acid contents, but at higher pH values cellular ammonium content rose, accompanied by accumulation of glutamine, glutamate and asparagine. Over several days, supplied ammonium led to an increase in activity of glutamate dehydrogenase irrespective of any changes in internal ammonium and amino acid contents. If the pH of the medium was allowed to fall below pH 4 in the presence of ammonium, phosphoenolpyruvate (PEP) carboxylase activity declined to a very low value over several days; at higher pH, the activity of this enzyme, and that of NAD malic enzyme and NAD malate dehydrogenase, remained substantial irrespective of whether the nitrogen source was NH⁺₄ or NO-₃.     

Role of antioxidants in the nitric oxide-elicited inhibition of dopamine uptake in cultured mesencephalic neurons. Insights into potential mechanisms of nitric oxide-mediated neurotoxicity

Under aerobic conditions the addition of (C₂N₅)₂N(N[O]NO)⁻ · Na⁺(DEA/NO), S-nitroso-N-macetyl penicillamine and nitric oxide (NO)-saturated buffer, but not S-nitroso- -glutathione, to dopamine solutions resulted in dopamine o-semiquinone formation that was dependent on the formation of a NO/oxygen intermediate. High pressure liquid chromatography (HPLC) electrochemical analysis of dopamine demonstrated that the DEA/NO-induced oxidation of dopamine was abrogated in the presence of the antioxidants, ascorbate and glutathione. NO spontaneously released from DEA/NO decreased [³H]dopamine accumulation in primary cultures of mesencephalic neurons in a dose-dependent fashion. In contrast, [³H]γ-aminobutyric acid uptake by mesencephalic neurons tested under the same conditions was unchanged. When DEA/NO was added to incubation buffer that contained [³H]dopamine and the antioxidant, ascorbate or glutathione, [³H]dopamine uptake was also inhibited. These data excluded that oxidation of extracellular [³H]dopamine by the intermediates of the NO/O₂ reaction could have caused this decrease. Instead, NO may have acted directly on a not yet identified target operative in the regulation of dopamine storage and release. Analysis of the rate constants for the NO reaction with ascorbate, glutathione and dopamine revealed that dopamine quinone formation was delayed by the presence of antioxidants. Since the formation of NO as well as neurotransmitter release are activated during ischemia reperfusion injury, it is possible that prolonged NO exposure could deplete antioxidants and facilitate the oxidation of dopamine and thereby cause neurotoxicity.     

Stimulation of proton extrusion by K+ and divalent cations (Ni2+, Co2+ Zn2+) in maize root segments

Entry of the divalent cations Ni²⁺, Co²⁺ and Zn²⁺ into cells of maize ( Zea mays L. cv. Dekalb XL 85) root tissue is accompanied by an acidification of the incubation medium, a decrease in both the pH of the cell sap and the level of malate in the cells, and by an inhibition of dark fixation of CO₂. K⁺, on the contrary, induces only a very low acidification of the incubation medium, does not change either the pH of the cell sap or the malate level in the cells, and induces an increase in CO₂ dark fixation. Different mechanisms are postulated for the stimulation of proton extrusion by divalent cations and K⁺.     

Localization of phytase and acid phosphatase isoenzymes in aleurone layers of barley

The localization of acid phosphatase (EC 3.1.3.2) in aleurone layers of barley (Hordeum vulgare L. cv. Himalaya) grains was studied. Phosphatase (EC 3.1.3.26) activity, assayed with phytic acid as the substrate, is present in the dry grain at low leveis and increases during incubation in H₂O at 25°C for three days. When aleurone layers are isolated from imbibed grain and incubated for 18 h in buffer with or without 50 μM gibberellic acid (GA₃), the level of extractable phosphatase activity increases two- to threefold, and phosphatase is released into the medium. GA, promotes the release of phosphatase activity: aleurone layers incubated in GA, release twice as much phosphatase as layers incubated in buffer. Nine isoenzymes of phosphatase are found in aleurone layers of barley by non-denaturing polyacrvlamide gel electropho-resis. Six of these forms, isoenzymes 1,2,3,5,6 and 8, can be extracted from dry tissue, and after three days of imbibition in H₂O an additional isoenzyme, isoenzyme 9, is found in aleurone extracts. When isolated aleurone layers are incubated for a further 22 h in buffer with or without GA₃, isoenzyme 7 is found and yet another form, isoenzyme 4, is found in layers incubated in GA₃. Eight isoenzymes are released from aleurone layers into the incubation medium. Isoenzymes 5 and 6 are released in buffer both with and without GA₃, even when cycloheximide is present; cycloheximide inhibits the release of the other isoenzymes. Isoenzymes 1-4, 7 and 8, on the other hand, are secreted into the incubation medium only when GA₃, is present. Isoenzyme 9 is not released into the incubation medium. Acid phosphatase activity was localized in aleurone tissue using cytochemical, cell fractionation, and enzymatic methods. Cytochemical localization of ATPase (EC 3.6.1.8) in aleurone tissue showed the presence of enzyme activity in cell wall, protein bodies, endoplasmic reticulum, Golgi apparatus, and mitochondria. Analysis of organelle fractions isolated by density gradient centrifugation showed that the activity of acid phosphatase isoenzymes 1, 2 and 3 was prominently associated with the phytin globoid of protein bodies, and analysis of the activity released from the cell wall by enzymatic digestion showed that it was almost exclusively isoenzymes 5 and 6.     

Effect of butyric acid on the germination of the seeds of Phacelia tanacetifolia

The effect of a weak acid (butyric acid) on the germination of seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair) has been studied. Butyric acid inhibited the early phase of germination, and the inhibition was correlated to the amount of the per-meant undissociated form present in the incubation medium. The inhibition by butyric acid in the dark was also correlated to a decrease of dark fixation of CO₂ and to a more pronounced decrease in malic acid levels during the early phase of germination; suggesting that the uptake of the uncharged form of this weak acid was followed by a release of H+ into the cytoplasm, leading to a decrease in its pH. The inhibitory effect of butyric acid in the dark on many metabolic events (rise in respiratory activity, levels of reducing sugars, glucose-6–phosphate and malic acid, dark CO₂ fixation, transport activities and macromolecular synthesis) appeared similar to the one of light. Fusicoccin (FC), which directly stimulates the H⁺ pump at the plasmalemma level, ameliorated the effect of butyric acid, as well as that of light, on germination. The bulk of these data is interpreted as suggesting that the mechanism of light inhibition of germination of Phacelia tanacetifolia seeds might be the consequence of a general block of metabolic reactivation due to the presence of an unfavourable (acidic) cytoplasmic pH; which might be explained with the lack of the phytochrome-dependent activation of the H⁺ pump at the plasmalemma level.     

Effect of solid-state buffers on the catalytic activity of papain in low water media

The catalytic activity of papain in the synthesis of Z-Gly-Phe-NH₂ in tert-butanol has been studied in the presence of solid-state acid–base buffers (acids and their sodium salts). All buffer pairs tested reduced the reaction rate compared with the control, particularly the most acidic and basic (assessed by either aqueous pK_a or the response of an organic phase indicator). The highest rates, close to the control, were found with glutamic acid/glutamate-Na, PIPES/PIPES-Na and NaH₂PO₄/Na₂HPO₄. However, these pairs were unable to erase the pH memory phenomenon, or to overcome the effect of spiking with acetic acid. Hence, at least these buffers do not seem to be able to affect the protonation state and catalytic activity of papain. In the last aqueous solution before drying, the presence of activating agents (cysteine plus EDTA) was more important than buffer ions.     

Chromatography of acid phytohormones on columns of Sephadex LH-20 and insoluble poly-N-vinylpyrrolidone, and application to the analysis of conifer extracts

The chromatographic behaviour of abscisic acid (ABA), indole-3-acetic acid (IAA), phenylacetic acid (PAA), and gibberellins A₁, A₄, A₈, A₉, A₁₃ and A₂₀ on columns of Sephadex LH-20 and insoluble poly- N -vinylpyrrolidone (PVP) eluted with buffers of different pH values is described. PVP shows considerable batch differences that must be carefully checked. Chromatography of acidic ethyl acetate-soluble fractions of Scots pine ( Pinus sylvestris L.) extracts at pH 4.5 resulted in great losses of phytohormones, due to poor solubility of the extracts. If the extracts were applied to the column dissolved in buffer of pH 7.5, subsequent elution at pH 4.5 was possible with only small losses. The performance of the chromatographic column was strongly affected by the application volume. A combined PVP/Sephadex LH-20 column eluted at pH 4.5 allows remarkable purification of pine and spruce ( Picea abies (L.) Karst.) extracts, collection of IAA in a fraction that can be directly analyzed by e.g. the indolo-α-pyrone method, and collection of another fraction containing ABA, PAA and probably most of the known C₁₉-gibberellins; whereas the C₂₀-gibberellin A₁₃ is eluted later (with IAA).     

Bradykinin effects on phospholipid metabolism and its relation to arachidonic acid turnovers in neuroblastoma × glioma hybrid cells (NG 108-15)

In neuroblastoma × glioma hybrid cells (NG 108-15) labelled with [³²P]-trisodium phosphate, [³H]-inositol and [¹⁴C]-arachidonic acid, bradykinin stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP₂) while it had no effect on the release of [¹⁴C]-arachidonic acid (AA). The effect on PIP, was time- and dose-dependent with a maximal effect on [³H]-inositol- and [³²P]-labelled cells after 10–30 s of stimulation with 10⁻⁶ M bradykinin. However, the hydrolysis of [¹⁴C]-AA labelled PIP₂ was delayed compared to the effect on [³H]- and [¹⁴C]-PIP₂ and was not detectable until after 60 s of stimulation. Bradykinin stimulation resulted in an increased formation of [³H]-inositol phosphates (IP) and [³²P]- and [¹⁴P]- and [¹⁴C]-phosphatidic acid (PA) but the time course for PA formation did not allow the time-course for PIP₂ hydrolysis. A reduced labelling of [²³P]- and [¹⁴C]-phosphatidylcholine was also found in stimulated cells suggesting that PA may derive from other sources than PIP₂. In conclusion, our results indicate that bradykinin activates phospholipase C, but not phospholipase A₂, in NG 108-15 cells.     

介质pH缓冲系统选择及其对龙须菜生长的影响

该文选择红藻门大型植物龙须菜(Gracilaria lemaneiformis)作为研究对象,通过黑白瓶法筛选出有机试剂POPSO(哌嗪-N,N-双(2-羟基乙烷磺酸)),能较好地缓冲室内龙须菜培养中介质pH的波动。在此基础上,探讨了POPSO对龙须菜生长的影响,结果表明:15 mmol·L ^-1及以上浓度的POPSO能较好地稳定介质pH值,减少系统中DIC浓度的急剧变化,但POPSO对CO₂浓度波动不起作用;试验结果还表明,介质中的CO₂浓度与龙须菜的生长速率间存在着类似酶动力学方程的关系,当介质中的CO₂浓度下降到5.25 μmol·L ^-1以下时,龙须菜生长出现抑制现象。相对稳定pH的培养环境,更有利于介质DIC中的HCO^-₃、CO^2-₃向CO₂的转换,缓解龙须菜生长的C抑制。