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The effect of growth under saline condition (100 mol m-3 NaCl in the nutrient solution) on the influx and the efflux of glucose from roots of cotton plants was analysed utilising the non metabolisable glucose analogue [14C]-3-O-methylglucose ([14C]3-OMG). Apical segments (1 cm long) excised from cotton roots took up [14C]3-OMG. At each tested concentration (5–500 mmol m-3), the influx was completely inhibited by the presence of the protonophore carbonylcyanide-m-chlorophenyl hydrazone (CCCP) indicating that it is mediated by a H+-coupled co-transport mechanism. The CCCP-sensitive [14C]3-OMG influx was lower in the root segments excised from plants grown on saline solution than in the controls, and this was particularly evident at lower external concentrations. This difference was not due to a lower H+ apoplastic availability. In fact, the saline condition did not affect the pH of the rhizosphere and indeed the H+–ATPase activity, evaluated in plasma membrane vesicles purified from saline-treated plants, was higher (+23%) than in the controls. The lower uptake of [14C]3-OMG into saline treated root segments was related to an enhanced value of the apparent Km of the carrier for the glucose analogue. This effect is discussed in relation to either the more positive value of the transmembrane electric potential difference (ΔΨ) measured in these root segments, or a competitive inhibition of Na+ on the H+ binding site of the carrier. Growth in saline solution slightly affected the efflux of the [14C]3-OMG preloaded in root segments, changing the membrane permeability to the molecule. The results strongly suggest that the higher (2.5 fold) net exudation of glucose, observed in short-term (4 h) collection experiments, from roots of cotton plants grown in saline condition, is mainly due to an effect of the saline growth condition on the system involved in the reabsorption of the hexose rather than on its efflux.

The changes in polypeptide profiles (2D-PAGE) occurring in the soluble and microsomal fractions of parenchymatic tissue of potato (Solanum tuberosum L.) tubers were studied during the last 30 d of maturation and during storage at 23°C and 3°C. The major changes were observed in the last period of tuber maturation, when several polypeptides disappeared and new ones appeared. At both 23°C and 3°C specific polypeptides disappeared in dormant tubers and new polypeptides appeared during storage. At 3°C specific changes in protein composition occurred, particularly in the microsomal fraction. The changes in polypeptide profiles are discussed in relation to the transition from “sink” to “source” of the tuber, the onset of dormancy and of sprouting ability and the activation of cold acclimation responses. The results are also discussed on the basis of the physiological and biochemical changes that occur in the parenchymatic tissue.

In the last 30 d of potato (Solanum tuberosum L.) tuber growth metabolic activity decreased. Levels of glucose-6-P and sucrose in whole tuber tissues declined and in tuber slices there was a decrease in the uptake from the medium and in the incorporation into macromolecules of [U-14C]sucrose. During storage at 23°C only the uptake of [U-14C]sucrose increased concomitant with tuber sprouting, indicating a possible involvement of the transport mechanisms in dormancy breaking. At 3°C, levels of reducing sugars and sucrose increased in response to the low temperature and increased release of K+ and malondialdehyde levels indicated cell membrane damage. The cell membrane functionality was restored at sprouting. The sprouting potential of the tubers was evaluated using the sprouting ability of single-bud explants (“seedcores”) in response to water, GA3 or ABA dips. This sprouting potential of tubers changed with stage of tuber growth and storage duration and temperature, indicating that the tissue hormonal state changed strongly throughout tuber life, probably in relation with the “sink” to “source” transition.

The activities of l-[U-14C]leucine uptake and incorporation into proteins of embryos and endosperm of seeds of Phacelia tanacetifolia Benth. cv Bleu-Clair were analysed during the first 24 h of incubation under conditions optimal for germination (16°C in darkness) and in two inhibitory conditions: 16°C in the light and 30°C in darkness. Blocking germination induced by light or 30°C was accompanied by the inhibition of l-[U-14C]leucine uptake and incorporation in embryos. In the endosperm, the activation of l-[U-14C]leucine uptake was of the same magnitude for the non-inhibited and the light-inhibited seeds and much higher for the 30°C-inhibited seeds; the activation of l-[U-14C]leucine incorporation was quantitatively similar in all three conditions, with the patterns of newly synthesised proteins qualitatively different in the endosperm from light- or 30°C-inhibited seeds. The results showed that germination of P. tanacetifolia seeds is controlled by light or super-optimal temperature through the inhibition of the activation of transport and protein synthetic activities in embryo without effect on the endosperm. We suggest, on the basis of the translational activity, the possibility that in the inhibitory conditions the blockade of the embryo to operate as a sink affects the transition of the endosperm to operation as a source.

The effects of Ni 2+ on Raphanus sativus seeds during the first 48 h of germination were investigated. Increasing concentrations of Ni 2+ (0, 80, 100, 200 and 400 μM) progressively inhibited the growth of radish seedlings. In parallel, Ni 2+ affected the restoration of reabsorption of K + and Mg 2+ and the release of Ca 2+ into the incubation medium. The transport mechanisms appeared to be well operative, as indicated by the negative values of the transmembrane electrical potential. Ni 2+ strongly affected the reactivation of oxygen uptake and the increase in energy charge, the mobilisation of sugar and phospho-organic compounds and inhibited the synthesis of DNA, RNA and proteins. The presence of Ni 2+ retarded the degradative and synthetic changes of protein of the soluble and microsomal fractions, occurring in seeds during germination; moreover, in both the soluble and microsomial fractions, two polypeptides from each were not expressed.

A low-molecular-mass protein able to bind GTP in both native and SDS-denaturating conditions was detected in the cytosol of embryos from wheat (Triticum aestivum L.) seeds germinated for 40 h. The protein fulfilled most of the distinguishing criteria common to eukaryotic small GTP-binding proteins. It retained the ability to bind GTP after SDS/PAGE and nitrocellulose blotting. The protein eluted from Sephadex G-200 gel filtration with a Ve/Vo value corresponding to a molecular mass of 18 kDa, whereas on SDS/PAGE the molecular mass was 20 kDa. The native protein, which showed an intrinsic GTPase activity highly sensitive to NaF, bound the guanine nucleotide with high specificity and with a relatively high affinity (Kd approximately 85 nM). The GTP-binding protein was not detectable in other subcellular fractions; in the microsomal fraction, two other peptides of low molecular mass (23.5 and 21.5 kDa) with GTP-binding activity were detected. These results indicate that in the cytosolic fraction of germinating wheat embryos there is a 20-kDa protein which is biochemically similar to the known small GTP-binding proteins that currently have been detected almost exclusively in the membrane fraction of plant material.

To elucidate the inhibitory effect of light on the germination of the negatively photoblastic seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair), we have compared the changes that occur during the first 24 h of imbibition in the dark and in the light. Here. we give data on transcription products, translation activity, activities of some enzymes involved in the metabolic reactivation of seeds (glucose-6-phosphate dehydrogenase. pyruvate kinase, glucokinase and malate dehydrogenase), and the capability to absorb L-[U- 14 C]-leucine. During the first stages of imbibition, the changes in the protein pattern and in the mRNA populations that occurred were not related to the light/dark regimes. Differences due to the light treatment did not appear until after 24 h, when new microsomal proteins appeared in the dark and some mRNA populations encoding low molecular mass polypeptides were increased in the light. The translation activity, measured as L-[U- 14 C]-leucine incorporated into proteins and as the ratio polysomes/ monosomes, increased with time in both darkness and light, but to a much higher extent in the dark. The activities of the four enzymes tested were higher in the light than in the dark before 16 h, then decreased in the light and increased sharply in the dark. Together with the behaviour of the increase in the ratio polysomes/monosomes in the dark, this suggests an increased rate of protein degradation in the dark during the period 0-16 h. The absorption of L-[U- 14 C]-leucine was severely inhibited by light during the whole period studied, as expected since light inhibits the reactivation of the transport mechanisms at the plasma membrane. In seeds imbibed in the dark and then transferred to light, the inhibition by light of absorption and of incorporation into proteins of L-[U- 14 C]-leucine, as well as the inhibition of the increase in the ratio poly-somes/monosomes, was effective before the 22nd h; after which time the control exerted by light disappeared.

31 P nuclear magnetic resonance spectroscopy (NMR) was used to study the response of Phacelia tanacetifolia seeds to dark and light conditions during the first 72 h of incubation. Changes in the chemical shifts (δ) of the pH-dependent 31 P-NMR signals from the vacuolar and the cytoplasmic orthophosphate pools were correlated with the different incubation conditions. In the dark (favorable to germination), the cytoplasmic pH remained nearly constant over the whole period considered, while the vacuolar pH shifted to more acidic values after the 24th h of incubation. In the light (inhibiting germination), the values of cytoplasmic pH tended to become more acidic than in the dark after the 24th h of incubation, while the vacuolar pH remained practically constant. When seed germination was inhibited in the dark by butyric acid (BA), a permeant weak acid, the values of cytoplasmic and vacuolar pH were similar to those of the ungerminated seeds incubated in the light. When, vice versa, seed germination was promoted in the light by fusicoccin (FC), the values of cytoplasmic and vacuolar pH were similar to those of the dark-germinated seeds. A progressive augmentation of P i metabolism occurred both in the dark and in the light up to the 24th h of incubation,Subsequently, light blocked any further evolution of this parameter. Treatment with butyric acid in the dark again mimicked the effect of light, while FC reversed the negative effect of light. The data show that in Phacelia tanacetifolia seeds germination is linked to a more alkaline cytoplasmic pH. The finding that the light-dependent metabolic inhibition occurs after an early activation of metabolism, i.e. after the first 24 h, suggests that the effects of light on the cytoplasmic and vacuolar pH depend on the early metabolic processes involved in the control of the homeostasis of cell pH and/or on the inhibition of the reactivation of the transpose mechanisms

Kiwi ( Actinidia deliciosa ) calli were grown for two successive 45-day subcultures on agarised medium in order to evaluate the metabolic changes occurring during the growth of the callus. At different times (10, 35 and 45 days of each subculture), increase in fresh weight, oxygen uptake rate, levels of inorganic cations (K + , Ca 2+ , Mg 2+ and Na + ) and of some metabolites (sucrose, glucose-6-phosphate, malic acid, amino acids and adenosine phosphates) were measured. After an adaptive growth phase (0–6 days) and a phase of high growth (6–12 days), the callus growth rate decreased sharply and then remained essentially constant up to the 45th day. The parameter listed above changed with time following a similar pattern in the two analysed subcultures. In the first 10 days, most of them increased (in particular, oxygen uptake rate and the energetic status of the cells); the levels of Na + decreased. After the first 10 days, the levels of glucose-6-phosphate (glu-6-P) and of the adenylate pool and the availability of the high-energy phosphate bonds of ATP and ADP decreased and the Na + levels began to increase; in this period, the rate of oxygen uptake increased, but this corresponded to neither increased availability of the high-energy phosphate bonds of ATP and ADP nor increased growth rate. In the last period (35–45 days) the main metabolic parameters dropped, with a large increase in Na + levels. Transfer onto new medium restored, after the adaptive period, the maximum growth and the levels of the parameters listed above. The data show that during the subculture periods of Actinidia deliciosa calli important metabolic changes occur. They are probably linked to a different status of suffering (for reduction of nutrient availability, accumulation of catabolic products, and/or variations in oxygen and CO 2 diffusion) with the activation of metabolic mechanisms of adaptation and repair. These metabolic changes appear not severe enough to inhibit the growth of the calli. The results obtained with Actinidia deliciosa calli are discussed in relation to protocols of selection and micropropagation.

Apple (Malus domestica Borkh.) trees are often affected by a severe June fruit drop, which is often correlated with competition phenomena involving fruit nutrition. This research was initiated to determine if June drop in `Gloster'/M.9 apple could be correlated with a diminished nutrient availability in developing seeds and fruit. During the test period [30 to 62 days after full bloom (AFB)], the fruit that abscised had a diameter similar to that reached by persisting fruit 13 days earlier. Biochemical parameters related to nutritional status of fruit were measured when an abscission peak occurred 38 days AFB. Persisting fruit (control) and abscised fruit were compared along with fruit that abscise 13 days later. The cortex tissue obtained from the two kinds of abscised fruit showed a higher level of soluble reducing sugars and sucrose and a lower content of K+, acid hydrolyzable polysaccharides, and protein compared to the control. Further, the Ca2+ content was higher in abscised fruit than in controls of the same age, whereas there was no difference when fruit of the same size were compared. Total amino acid level was similar in control and abscised fruit at the same age, but there was a lower amino acid level in abscised fruit of the same size. Histological analysis of cortex tissue indicated that abscised fruit have larger cells with less evident nuclei and thinner cell walls than controls. Compared to control fruit, abscised fruit showed the same average number of seeds and a severe inhibition of seed growth; seeds from both kinds of abscised fruit had the same or higher levels of the parameters measured. No positive correlations were observed between fruit abscission and nutrient content of seeds or fruit.

We studied the recovery of ATP from soil. A soil-water suspension was prepared by two different methods (simple stirring or ballottini mill treatment) at different pH levels and in the presence of different chemicals [Na2SO4, Na3PO4, Na5P3O10, adenosine, ethylenediaminetetra-acetic acid (EDTA), TRIS]. The ATP recovery was evaluated by adding [3H]-8′ ATP to the solution and comparing the values obtained by radioactivity measurements with those obtained by an enzymatic assay. Strongly acidic (pH lower than 1.0) or alkaline (pH 10.0) extractions yielded the best ATP recoveries compared with intermediate pH values. At pH 10.0, the addition of Na3PO4 or Na5P3O10 gave a high level of ATP recovery, 68 and 96%, respectively. No ATP hydrolysis occurred under alkaline extraction conditions. Under acidic extraction conditions, the addition of adenosine, EDTA, Na2SO4, or Na5P3O10 improved ATP recovery but it was never higher than 34%. The results were discussed in terms of the effects of different physical and chemical conditions on cell disruption, ATP stability, ATP interactions with soil components, and ATP solubilization.

The effects of an osmotic shock (300 mM mannitol, –0. 67 MPa) or/and increased external hydrostatic pressure on seedlings (42-h-germinated seeds) of radish (Raphanus sativus L. cv. Tondo Rosso Quarantino) were investigated. The osmotic shock did not inhibit H+ extrusion and net K- uptake, and did not affect the levels of malic acid, reducing sugars, sucrose or amino acids or of the energy charge (i. e. the synthesis of energy-rich phosphate bonds), but inhibited the synthesis of proteins. RNA and DNA, measured as incorporation of labelled precursors. When the osmotic shock was applied together with an increased external hydrostatic pressure of the same magnitude (+0. 67 MPa), the same metabolic parameters and the inhibition of synthesis of RNA and DNA were not substantially affected, while the inhibition of protein synthesis was practically reversed and the energy charge decreased; the recovery of protein synthesis was not due to a change in labelled leucine uptake capability. Increased external hydrostatic pressure alone decreased the energy charge without affecting the other parameters considered. The possibility that protein synthesis activity is directly controlled by cell turgor pressure (internal hydrostatic pressure) is discussed.

The effect of increasing osmotic values of the medium (mannitol) on the growth and the response mechanisms of seeds of radish (Raphanus sativus L., cv. Ton do Rosso Quarantino) during the early phase of germination was investigated in the presence or absence of fusicoccin (FC). Decreasing the water potential in the medium inhibited the growth and the evolution of protein synthesis and enhanced H+ extrusion, net uptake of K+ and malic acid synthesis. FC, which stimulates these latter functions, counteracted the inhibitory effect of the decreasing water potential of the medium on growth and protein synthesis. Neither in the absence nor in the presence of FC did decreasing water potential of the medium enhance the synthesis of soluble sugars and amino acids to support the osmotic pressure of the seeds. The osmotic and water potentials of the seeds increased during germination. FC made the increase more rapid, while mannitol kept both potentials low. The pressure potentials of the seeds also decreased with time, and both FC and mannitol enhanced this change. If the seeds were without turgor, the development of protein synthesis was blocked. The seeds counteract the effect of decreasing water potentials in the medium by: a) enhancing H+ extrusion (and, as a consequence, wall loosening and transport mechanisms) and the synthesis of malic acid as apparent in the presence of FC; b) regulating the osmotic potentials of the cells (with a lower dilution of the osmotic compounds present in the seeds due to the diminished uptake of water); c) controlling the growth through the effects of a) and b) on the pressure potentials (internal hydrostatic pressure) of the seeds and on protein synthesis.

Calli of Actinidia deliciosa were cultured on medium with 30 mM sucrose and 0.2 M 3-O-methyl-D-glucose (3-OMG) and their metabolic adaptation to the hyperosmotic condition was studied. 3-OMG concentration in the tissue reached that of the medium. Experiments with labelled 3-O-methyl-D-U-14C]glucose (3-OM[U-14C]G) showed that it was partially metabolised but not oxidised to CO2. In vivo 31P-NMR showed that in 3-OMG-treated calli a phosphorylated compound, with a chemical shift similar to that of monophosphoesters, was accumulated. The 3-OMG-treated calli showed more negative water (Ψw) and osmotic (Ψπ) potentials than the controls. In the following of subcultures an increase in organic and inorganic osmolytes, together with increase in O2 uptake and decrease in ATP/ADP ratio occurred. The data show that, even if 3-OMG can not be considered a classic osmotic agent due to its permeability, it induced metabolic changes similar to those described for osmotic adaptation, suggesting that the adaptations might be due to a physical or metabolic effect of 3-OMG not linked to a difference between Ψπ and Ψw agar

Ophiobolin B (OPH B), a sesterpene metabolite of Helminthosporium oryzae, inhibits proton extrusion from maize coleoptiles. Moreover OPH B counteracts the biological activity of fusicoccin (FC), another terpenoid toxin produced by Fusicoccum amygdali having a similar basic chemical structure: OPH B inhibits FC-promoted proton extrusion, potassium uptake and cell enlargement. The findings suggest that the effect of OPH B in stimulating electrolites, glucose and aminoacid leakage, reported in a previous paper, can be explained by the capacity of the toxin to inhibit proton extrusion.

Germination of Rhaphanus sativus seeds is accompanied in its early phase by a consistent loss to the medium of the main cations. During the first ten hours there is a general efflux of K + , Na + , Mg 2+ and Ca 2+ , while in the following period K + is actively taken up so that after eighteen hours almost no K + is detected in the external medium. When seed germination is stimulated by fusicoccin (FC) the development of uptake capacity is markedly anticipated. Moreover, inhibition of seed germination by abscisic acid (ABA) inhibits the development of K + uptake. The ABA-induced inhibition is reversed by FC and also, even if to a lesser extent, by gibberellic acid (GA 3 ). Preliminary data suggest that a K + activated ATPase present in membrane preparation is involved in the mechanism of active K + uptake in the seeds.

The presence of Ni 2+ in the incubation medium of maize roots induces an early and significant enhancement of the rate of proton extrusion, an inhibition of K + and leucine uptake and a slight stimulation of 3- O -methylglucose (3- O -MG) and phosphate uptake. The uptake of Ni 2+ is accompanied by a rapid depolarization of the trans-membrane electrical potential (PD). At the 1-mM concentration, both the uptake and the depolarizing effect of Ni 2+ are quantitatively similar to those of K + . These data suggest that the primary effect of Ni 2+ is the depolarization of PD, which would activate H + extrusion; the other transport phenomena would thus be differently influenced by the changes of the electrical and H + gradients. Some probable secondary consequences of Ni 2+ accumulation in the tissue are also discussed.

‘Maygold’ apples were dipped in CaCl 2 or GA 3 as post-harvest treatments. Bitter pit was reduced by CaCl 2 and GA 3 . Pitted fruits always had low Ca 2+ levels. The cellular fractionation of the flesh tissue of untreated apples showed a negative correlation between soluble Ca 2+ , acid labile Ca 2+ and bitter pit. An increase of Ca 2+ in these fractions by means of CaCl 2 treatments did not prevent the disorder. GA 3 , at the more effective concentration for protecting fruits, increased the soluble Ca 2+ of pitted flesh tissue. The possibility that the disorder is linked to an alteration of the Ca 2+ transport mechanism at cell level is suggested as a plausible explanation.

Radioactive dihydrofusicoccin (3H-FC), known to have the same biological activity as fusicoccin on plant tissues, has a specific affinity in vitro for sites localized on subcellular, postmitochondrial particles from maize coleoptiles. The analysis of the kinetics of dihydrofusicoccin binding suggests the presence of two classes of sites, one class with a high affinity and a second class with a lower affinity. The high affinity class of sites has a dissociation constant (Kd) of 1.2 × 10−9 mol dm−3, and an apparent pH optimum at 5.5. Binding is antagonized by non-physiological pH, high temperatures and protein-reactive substances like HgCl2, p-chloromercuribenzensulphonate and glutaraldehyde. Treatment of dihydrofusicoccin-bound membrane preparations with Triton X-100 leads to the solubilization of a protein fraction associated with dihydrofusicoccin. These data suggest a protein nature for the receptor sites.

Radioactive fusicoccin ([3H]FC) associates in vitro with subcellular, post-mitochondrial particles from corn coleoptiles, as shown by the appearance of radioactivity in high speed pellets. This binding is specific, not readily chaseable, and saturable by 10−4M unlabelled FC. Auxins do not cross-compete for these sites. The binding is heat-labile at 60°C and has a pH optimum around 6. Differential centrifugation and isopycnic sucrose density gradients with parallel determination of markers indicate the localization of the FC binding sites at the plasmalemma. This is in agreement with the known in vivo effects of this fungal toxin.

A poly(U)-binding activity is present in the high-speed supernatant fraction of embryo homogenates from wheat seeds. The factor responsible for such activity was found to have a stimulatory effect on the elongation factor 1 (EF-1). It copurifies with EF-1L, the lighter form of EF-1, through Sephadex G-200, DEAE-cellulose, hydroxyapatite and poly(U)-Sepharose 4B column chromatography. The two factors could be separated only through a heating step which destroyed EF-1 activity whilst leaving most of the poly(U)-binding activity unaltered.

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.

The ATPase activity present in plasmalemma-enriched preparations from maize coleoptiles shows an optimum at pH 6, a strong dependence on Mg(2+), and is stimulated by K(+) and other monovalent cations, both organic and inorganic. The activation of ATPase by K(+) obeys Michaelis Menten kinetics, saturation being reached at 50 mM K(+) concentration. K(+), Mg(2+)-stimulated ATPase activity is strongly inhibited by N,N'-dicyclohexylcarbodiimide and by diethylstilbestrol and, to a lesser extent, by octylguanidine.

The higher susceptibility to stalk necrosis of the grape (Vitis vinifera L.) cultivar ‘Bonarda’ (clusters with few berries) than the cultivar ‘Barbera’ (clusters with many berries) was correlated to higher K + Ca 2+ ratios in the tissue and to a different functioning of the transport mechanism. At the middle of the meristematic growth phase of the berries, segments excised from grapevine clusters of the more susceptible cultivars showed lower proton extrusion activity, lower K+ and Ca2+ leakage and similar uptake capacity both for K+ and for Ca2+. These results are discussed in regard to the onset of stalk necrosis in grapevine clusters.

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+.

Nickel affects the proton extrusion capacity in segments of maize seedling roots; as in the field condition, this effect is enhanced by phosphate and counteracted by Ca++ and Mg++. The effect of nickel on the proton‐extruding activity can explain either nickel toxicity and its stimulating effect on plant growth. Such hypothesis is discussed in this paper.

The growth of squash fruit was followed in the field under normal and drought conditions. The following phenomena were observed: a) under drought conditions the fruit growth is normal in the night while it becomes more and more reduced with progress of time in the daylight period; b) the decrease of growth capacity in the daylight period does not correspond to a dehydration of the fruit tissues and it is accompanied by a conversion of polysomes to monosomes; c) the water deficit also causes a decrease of RNA and protein content in the fruit tissues, but this situation does not affect the rate of growth in the night. The data suggest that under conditions the fruit growth is controlled by water availability through protein synthesis; under ample water supply, water availability or some other factor, rather than RNA and protein level, is limiting the fruit growth.

Fusicoccin (FC), a diterpene glucoside very active in stimulating proton/K + exchange in higher plant tissues, is shown to increase in vitro the K + Mg 2+ -stimulated ATPase activity of plasmalemma-enriched membrane preparations from maize coleoptiles and from spinach leaves. The concentration/activity curve of the effect of FC on ATPase closely parallels that of the in vivo effect on K + uptake. DAK, a derivative of FC inactive in vivo on K + uptake and associated responses, is also inactive on the ATPase activity in vitro. These results are consistent with the hypothesis that the stimulating effects of FC on proton extrusion and cation uptake are due to its capacity to activate at cell membrane level a H + /K + exchange system depending on ATP as an energy source.

The presence of Ni2+ in the incubation medium of maize root segments (Zen mays L. cv. Dekalb XL 640) induces an early and significant enhancement of the rate of proton extrusion both in the absence and presence of fusicoccin; with time, an inhibition of proton extrusion and a leakage of K+ appear. The inhibition of proton extrusion is accompanied by a decrease in the dark CO2 fixation and by a decrease in the level of malate in the cells. Ni2+ inhibits in vitro phosphoenolpyruvale carboxylase activity of maize roots. The data indicate a correlation between the operativity of the proton pump and that of the malate-pH stat mechanism for the homeostasis of cytoplasmic pH.

Proton extrusion of maize root Zea mays segments, was inhibited by the presence of Cr (o.n. + 6; present in solution as CrO42-, Cr2O72-) in the incubation medium: the minimum inhibiting concentration was 2 × 10−3 mol m−3 and the inhibition progressively increased with Cr concentration. Cr inhibited proton extrusion. Also, when this activity was stimulated by the presence of K+ or fusicoccin (FC) in the incubation medium, the K+ and FC stimulating effect was still present when proton extrusion was inhibited by Cr. In addition, Cr inhibited K+ uptake. This inhibition was higher (50%) at K+ concentrations up to 1 mol m−3 lower (15%) at higher K+ concentrations. This result indicates that the system responsible for K+ uptake operating at low K+ concentrations is more sensitive to Cr inhibition. Cr had no effect on transmembrane electric potential (PD). The depolarizing and hyper-polarizing effect of K+ and FC, respectively, were not affected by Cr; but Cr enhances the depolarizing effect of the uncoupler carbonylcyanide m-chlorophenylhydrazone (CCP). These results indicate that Cr inhibited the proton translocating mechanism coupled with K+ uptake, but did not change the net transport of charges through the plasmalemma. The Cr effect is discussed, taking into account the possibility of a direct effect of Cr at the membrane level or, alternatively, of an effect on some metabolic processes controlling membrane function.

The important work of Beevers and collaborators on the metabolic evolution of the castor bean endosperm demonstrates the fitness of this material for the study of the biochemical activation during the early phase of seed germination. As shown by these authors. both respiration in vivo and the oxidative activity of mitochondrial preparations markedly increase during the first 2 to 3 days of germination (1, 4). Parallel qualitative changes of the enzymatic pattern are revealed by the appearance and the rapid rise of the activity of malate synthetase and isocitritase. 2 enzymes involved in the conversion of lipids into carbohydrates (7, 24). The finding of an increase of the protein nitrogen in the mitochondrial fraction (1) provided a first suggestion that the observed rises of enzyme activities could be related to de novo enzyme synthesis. A series of investigations in this laboratory confirmed and extended the above observations. The increase of enzvme activities in the endosperm of the germinating castor bean seed was found to be a general phenomenon, involving all of the glycolytic enzymes investigated, glucose-6-P and 6-P-gluconate dehydrogenases (11), ornithine transcarbamylase, ascorbate oxidase (Forti G. and M. Ranalletti. personal comn'unication), ribonuclease (24), and in the mitochon(dria, malate dehydrogenase, succinate-cytochrome c reductase and cytochrome oxidase (3). Studies on the development in vivo of mitochondrial enzymes, and on reactivation in vitro of some glycolytic enzymes indicated that some of the enzyme activities inicrease in the very early period of germination is due to the transition from the inactive to the

Respiratory activity, RNA contents and protein synthesis capacity of isolated ribosomes of tubers of Solanum tuberosum, cv. Tonda di Berlino, at progressive stages of development have been determined. In the immature, still growing tubers, respiration steadily decreases with the increase of fresh weight. The entering into dormancy of the tubers collected when immature corresponds to a rapid drop of respiration to the values characteristic of mature tubers. The RNA contents per tuber increase progressively during maturation. A decrease of the RNA contents per tuber (ca. 50 %) is observed in the period between the moment of harvesting and the end of dormancy. The endogenous capacity of isolated ribosomes to carry on amino acid polymerization strongly decreases during tuber development, while the activity supported by polyuridilic acid remains almost unchanged when measured at optimum Mg2+ concentrations, and becomes larger for the more mature tubers at superoptimum Mg2+ concentrations. These changes of the protein synthesis system during tuber development are compared with those occurring during seed maturation.

Changes of glycolytic substrates level during ripening of the castor bean seed. — The changes of the concentration of carbohydrates and of the main glycolytic substrates in the castor bean seed during the ripening phase were investigated. The following results were obtained: The level of unphosphorylated sugars and of acid hydrolysable polysaccharides remains almost unchanged, with a tendency to a rise during the ripening phase. The slight increase of these compounds, together with the transition of the R. Q. from high to low values, might be interpreted as an indication of a shift of the seed from the a metabolism of fat synthesis to one of conversion of lipids into sugars, such as is observed in the germinating castor bean seeds. Hexose monophosphate level sharply decreases during the last period of maturation. However, the level of these substrates does not fall so low as to suggest a severe limitation for the pentose-P pathway activity. Fructose diphosphate, DOAP, GAP, 3 PGA, 2 PGA, PEP and p...

Fusicoccin inhibits the germination of pea (Pisum sativum L. cv Progress 9) seeds by decreasing the growth of the embryonal axis and by stimulating the fresh weight increase of the cotyledons. The growth of isolated embryonal axes in the presence of sucrose and KCl is stimulated by fusicoccin. The effect of fusicoccin on the seeds is not counteracted by sucrose and KCl. Fusicoccin promotes preferentially in the cotyledons a hyperpolarization of the transmembrane electric potential and an increase in the uptake capacity, suggesting the reinforcement of the sink strength of the cotyledons in comparison with the one of the embryonal axis and therefore the inhibition of translocation from the cotyledons of some substance necessary for the growth of the embryonal axis.

Two forms of EF-1 are present in the high-speed supernatant fraction from wheat embryo homogenate. In embryos from dry seeds EF-1H, is 55% of the total amount of EF-1, while after 40 h of germination this form completely disappears. When germination and protein synthesis are accelerated by means of 6-benzyladenine, the rate of conversion of EF-1H is increased. On the other hand, the block of germination and of the evolution of protein synthesis by abscisic acid, block this conversion; the block of water uptake, that stops germination and causes a decrease in protein synthesis, reverses the conversion of EF-1H to EF-1L, increasing EF-1H from 15% to 40% of the total.

The seeds of Phacelia tanacetifolia Benth. cv Bleu Clair incubated at 30 degrees C in the dark did not germinate and did not activate K(+) uptake capacity. The administration of 1 millimolar K(+) in the early phase of incubation stimulated RNA and protein synthesis. The possible role of K(+) in promoting the marcromolecular syntheses during the early phase of germination is discussed.