Showing papers in "Plant Physiology in 1979"
TL;DR: The data support the hypothesis that the central vacuole of higher plant cells has an enzyme composition analogous to that of the animal lysosome.
Abstract: The hydrolase content of vacuoles isolated from protoplasts of suspension-cultured tobacco cells, of tulip petals, and of pineapple leaves, and the sedimentation behavior of tobacco tonoplasts were studied. Three precautions were found to be important for the analysis of vacuolar hydrolases and of the tonoplast. ( a ) Purification of protoplasts in a Ficoll gradient was necessary to remove cell debris which contained contaminating hydrolases adsorbed from the fungal cell-wall-degrading enzyme preparation. ( b ) Hydrolase activities in the homogenates of the intact cells or the tissue used and of the purified protoplasts had to be compared to verify the absence of contaminating hydrolases in the protoplast preparation. ( c ) Vacuoles obtained from the protoplasts by an osmotic shock had to be purified from the lysate in a Ficoll gradient. Since the density of the central vacuole approximates that of the protoplasts, about a 10% contamination of the vacuolar preparation by surviving protoplasts could not be eliminated and had to be taken into account when the distribution of enzymes and of radioactivity was calculated. The intracellular activities of the following acid hydrolases were primarily localized in the vacuole of tobacco cells: α-mannosidase, β- N -acetylglucosaminidase, β-fructosidase, nuclease, phosphatase, phosphodiesterase. A similar composition of acid hydrolases was found in vacuoles obtained from protoplasts of tulip petals. Proteinase, a hydrolase with low activity in tobacco cells and tulip petals and therefore difficult to localize unequivocally, was found to be vacuolar in pineapple leaves, a tissue containing high levels of this enzyme. Our data support the hypothesis that the central vacuole of higher plant cells has an enzyme composition analogous to that of the animal lysosome. None of the vacuolar enzymes investigated was found to be bound to the tonoplast. When vacuoles were isolated from cells labeled with radioactive choline, the vacuolar membrane was found to contain radioactivity. On sucrose gradients, the label incorporated into tonoplasts banded around a density of 1.10 grams per cubic centimeter (24% sucrose, w/w).
508 citations
TL;DR: It is suggested that in the ethylene biosynthetic pathway, IAA stimulates C(2)H(4) production by inducing the synthesis or activation of ACC synthase, which catalyzes the conversion of SAM to ACC, and Co(2+) exerts its effect by inhibiting the Conversion of ACC to ethylene.
Abstract: Auxin is known to stimulate greatly both C2H4 production and the conversion of methionine to ethylene in vegetative tissues, while amino-ethoxyvinylglycine (AVG) or Co2+ ion effectively block these processes. To identify the step in the ethylene biosynthetic pathway at which indoleacetic acid (IAA) and AVG exert their effects, [3-14C]methionine was administered to IAA or IAA-plus-AVG-treated mung bean hypocotyls, and the conversion of methionine to S-adenosylmethionine (SAM), 1-amino-cyclopropane-1-carboxylic acid (ACC), and C2H4 was studied. The conversion of methionine to SAM was unaffected by treatment with IAA or IAA plus AVG, but active conversion of methionine to ACC was found only in tissues which were treated with IAA and which were actively producing ethylene. AVG treatment abolished both the conversion of methionine to ACC and ethylene production. These results suggest that in the ethylene biosynthetic pathway (methionine → SAM → ACC → C2H4) IAA stimulates C2H4 production by inducing the synthesis or activation of ACC synthase, which catalyzes the conversion of SAM to ACC. Indeed, ACC synthase activity was detected only in IAA-treated tissues and its activity was completely inhibited by AVG. This conclusion was supported by the observation that endogenous ACC accumulated after IAA treatment, and that this accumulation was completely eliminated by AVG treatment. The characteristics of Co2+ inhibition of IAA-dependent and ACC-dependent ethylene production were similar. The data indicate that Co2+ exerts its effect by inhibiting the conversion of ACC to ethylene. This conclusion was further supported by the observation that when Co2+ was administered to IAA-treated tissues, endogenous ACC accumulated while ethylene production declined.
411 citations
TL;DR: Data are presented which indicate that vacuoles obtained by gentle osmotic shock of protoplasts in dibasic phosphate have good purity and retain their contents.
Abstract: Neutral sugar, free amino acid, and anthocyanin levels and vacuole/extravacuole distribution were determined for Hippeastrum and Tulipa petal and Tulipa leaf protoplasts Glucose and fructose, the predominant neutral monosaccharides observed, were primarily vacuolar in location Glutamine, the predominant free amino acid found, was primarily extravacuolar γ-Methyleneglutamate was identified as a major constituent of Tulipa protoplasts Qualitative characterization of Hippeastrum petal and vacuole organic acids indicated the presence of oxalic, malic, citric, and isocitric acids Data are presented which indicate that vacuoles obtained by gentle osmotic shock of protoplasts in dibasic phosphate have good purity and retain their contents
399 citations
TL;DR: It is demonstrated that ureides play a dominant role in N transport in nodulated soybeans and that the synthesis of ureide is largely dependent upon nodulation and N(2) fixation.
Abstract: Experiments were conducted to characterize the distribution of N compounds in the xylem sap of nodulated and nonnodulated soybean plants through development and to determine the effects of exogenous N on the distribution of N compounds in the xylem. Xylem sap was collected from nodulated and nonnodulated greenhouse-grown soybean plants (Glycine max [L.] Merr. “Ransom”) from the vegetative phase to the pod-filling phase. The sum of the nitrogen in the amino acid, nitrate, ureide (allantoic acid and allantoin), and ammonium fractions of the sap from both types of plants agreed closely with total N as assayed by a Kjeldahl technique. Sap from nodulated plants supplied with N-free nutrient solution contained seasonal averages of 78 and 20% of the total N as ureide-N and amino acid-N, respectively. Sap from nonnodulated plants supplied with a 20 millimolar KNO3 nutrient solution contained seasonal averages of 6, 36, and 58% of total N as ureide-N, amino acid-N, and nitrate-N, respectively. Allantoic acid was the predominant ureide in the xylem sap and asparagine was the predominant amino acid. When well nodulated plants were supplied with 20 millimolar KNO3, beginning at 65 days, C2H2 reduction (N2 fixation) decreased relative to nontreated plants and there was a concomitant decrease in the ureide content of the sap. A positive correlation (r = 0.89) was found between the ureide levels in xylem sap and nodule dry weights when either exogenous nitrate-N or urea-N was supplied at 10 and 20 millimolar concentrations to inoculated plants. The results demonstrate that ureides play a dominant role in N transport in nodulated soybeans and that the synthesis of ureides is largely dependent upon nodulation and N2 fixation.
314 citations
TL;DR: It is suggested that the mechanism of action of proline may be similar to that in its putative role of conferring protection against natural stresses when protecting the cell against solution effects caused by dehydration during freezing.
Abstract: Proline is an effective cryoprotectant for the storage of cultured cells of Zea mays L. in liquid N2. Increased freeze tolerance can be achieved by pregrowth for 3 to 4 days in medium containing proline. Cells cryoprotected with proline have an increased recovery potential when compared with cells cryoprotected with dimethylsulfoxide and glycerol. They also show a reduced postthaw viability loss and greater tolerance of a range of postthaw culture conditions. It is suggested that the mechanism of action of proline may be similar to that in its putative role of conferring protection against natural stresses. It may be protecting the cell against solution effects caused by dehydration during freezing. These findings are discussed in relation to other freeze tolerance enhancing treatments.
273 citations
TL;DR: Differences among species in the sensitivity of photosynthesis to salinity in part reflect the different A(mes)/A and r(cell) responses.
Abstract: Increasing salinity led to substantially higher ratios of mesophyll surface area to leaf area (Ames/A) for Phaseolus vulgaris and Gossypium hirsutum and a smaller increase for Atriplex patula, a salt-tolerant species. The increase in internal surface for CO2 absorption did not lead to higher CO2 uptake rates, since the CO2 resistance expressed on the basis of mesophyll cell wall area (rcell) increased even more with salinity. The differences among species in the sensitivity of photosynthesis to salinity in part reflect the different Ames/A and rcell responses.
248 citations
TL;DR: Nitrogenase-dependent acetylene reduction, nodule function, and nodule regrowth were studied during vegetative regrowth of harvested (detopped) alfalfa (Medicago sativa L.) seedlings grown in the glasshouse to study the effects of harvesting and senescence on nodules.
Abstract: Nitrogenase-dependent acetylene reduction, nodule function, and nodule regrowth were studied during vegetative regrowth of harvested (detopped) alfalfa (Medicago sativa L) seedlings grown in the glasshouse Compared with controls, harvesting caused an 88% decline in acetylene reduction capacity of detached root systems within 24 hours Acetylene reduction in harvested plants remained low for 13 days, then increased to a level comparable to the controls by day 18Protease activity increased in nodules from harvested plants, reached a maximum at day 7 after harvest, and then declined to a level almost equal to the control by day 22 after harvest Soluble protein and leghemoglobin decreased in nodules from harvested plants in an inverse relationship to protease activityNitrate reductase activity of nodules from harvested plants increased significantly within 24 hours and was inversely associated with acetylene reduction The difference in nitrate reductase between nodules from harvested plants and control plants became less evident as shoot regrowth occurred and as acetylene reduction increased in the harvested plantsNo massive loss of nodules occurred after harvest as evidenced by little net change in nodule fresh weight There was, however, a rapid localized senescence which occurred in nodules of harvested plants Histology of nodules from harvested plants showed that they degenerated at the proximal end after harvest Starch in the nodule was depleted by 10 days after harvest The meristem and vascular bundles of nodules from harvested plants remained intact The senescent nodules began to regrow and fix nitrogen after shoot growth resumed
229 citations
TL;DR: Protoplasts obtained from expanded leaves of Pisum sativum have been used for the isolation of cell organelles and the subsequent study of the intracellular distribution of the enzymes of nitrate assimilation, finding nitrite reductase and glutamate synthase located wholly in the chloroplast.
Abstract: Protoplasts obtained from expanded leaves of Pisum sativum have been used for the isolation of cell organelles and the subsequent study of the intracellular distribution of the enzymes of nitrate assimilation. The protoplasts were ruptured in a suitable medium and the total lysate subjected to sucrose density gradient centrifugation. Of the total chlorophyll more than 80% was recovered in intact chloroplasts. Nitrite reductase and glutamate synthase were found to be located wholly in the chloroplast. Glutamine synthetase was distributed between the chloroplast and the cytoplasm, with a maximum of 60% of the former. A possible role of the cytoplasmic enzyme is discussed in relation to photorespiration. There was no evidence for the association of nitrate reductase with any cell organelle or membrane fraction.
229 citations
TL;DR: Responses of the natural fields to changes in the ionic composition of the medium as well as observations of the pH pattern in the medium near the roots indicate that much of the current consists of hydrogen ions.
Abstract: With the aid of an extracellular vibrating electrode, natural electric fields were detected and measured in the medium near growing roots and root hairs of barley seedlings. An exploration of these fields indicates that both the root as a whole, as well as individual root hairs, drive large steady currents through themselves. Current consistently enters both the main elongation zone of the root as well as the growing tips of elongating root hairs; it leaves the surface of the root beneath the root hairs. These currents enter with a density of about 2 microamperes per square centimeter, leave with a density of about 0.5 to 1 microampere per square centimeter, and total about 30 nanoamperes. Responses of the natural fields to changes in the ionic composition of the medium as well as observations of the pH pattern in the medium near the roots (made with bromocresol purple) together indicate that much of the current consists of hydrogen ions. Altogether, H + ions seem to leak into growing cells or cell parts and to be pumped out of nongrowing ones.
220 citations
TL;DR: Changes in neutral sugar, uronic acid, and protein content of tomato cell walls during ripening were characterized and the ripening-related decline in galactose and arabinose content appeared to be separate from polyuronide solubilization.
Abstract: Changes in neutral sugar, uronic acid, and protein content of tomato (Lycopersicon esculentum Mill) cell walls during ripening were characterized. The only components to decline in amount were galactose, arabinose, and galacturonic acid. Isolated cell walls of ripening fruit contained a water-soluble polyuronide, possibly a product of in vivo polygalacturonase action. This polyuronide and the one obtained by incubating walls from mature green fruit with tomato polygalacturonase contained relatively much less neutral sugar than did intact cell walls. The ripening-related decline in galactose and arabinose content appeared to be separate from polyuronide solubilization. In the rin mutant, the postharvest loss of these neutral sugars occurred in the absence of polygalacturonase and polyuronide solubilization. The enzyme(s) responsible for the removal of galactose and arabinose was not identified; a tomato cell wall polysaccharide containing galactose and arabinose (6:1) was not hydrolyzed by tomato β-galactosidase.
209 citations
TL;DR: In apple polygalacturonase alone was sufficient to dissolve the middle lamella region of the cell walls, as was also found to occur in naturally ripening fruit, and in pear the cell wall areas containing plasmodesmata maintained their structural integrity throughout the ripening process.
Abstract: Ultrastructural changes in the cell walls of “Calville de San Sauveur” apples (Malus sylvestris Mill) and “Spadona” pear (Pyrus communis L.) fruit were followed during ripening. In apple, structural alterations in cell walls became apparent at advanced stages of softening and showed predominantly dissolution of the middle lamella. In pears softening was also associated with the dissolution of the middle lamella, and in addition a gradual disintegration of fibrillar material throughout the cell wall. In fully ripe fruit almost all of the fibrillar arrangement in the cell wall was lost. Application of enzyme solutions containing polygalacturonase and cellulase to tissue discs from firm pear fruit led to ultrastructural changes observed in naturally ripening pears. In apple polygalacturonase alone was sufficient to dissolve the middle lamella region of the cell walls, as was also found to occur in naturally ripening fruit. In both apple and pear the cell wall areas containing plasmodesmata maintained their structural integrity throughout the ripening process. At advanced stages of ripening vesicles appeared in the vicinity of plasmodesmata.
TL;DR: The inverse relationship between the accumulation of hydroxyproline-rich glycoproteins and the ability of the pathogen to develop in the host has been checked by the quantification, in infected tissues, of glucosamine, a characteristic component of chitin-containing fungi.
Abstract: Enrichment of the cell wall in hydroxyproline-rich glycoprotein is involved in the defense of muskmelon ( Cucumis melo ) seedlings to Colletotrichum lagenarium , the causative agent of anthracnose. The extent to which this accumulation proceeds may be experimentally modified by treating plants with ethylene or growing them in the presence of free l- trans -hydroxyproline. It appears that the increase in the wall hydroxyproline-rich glycoprotein mediated through ethylene is paralleled by an increasing resistance of the host to the pathogen. Inversely, inhibiting the synthesis of this glycoprotein in diseased plants is strictly correlated to an accelerated and more intense colonization of the host by the pathogen. In both cases, the inverse relationship between the accumulation of hydroxyproline-rich glycoproteins and the ability of the pathogen to develop in the host has been checked by the quantification, in infected tissues, of glucosamine, a characteristic component of chitin-containing fungi.
TL;DR: Intact phycobilisomes were characterized by fluorescence emission peaks of 670 to 675 nanometer at room temperature, and 678 to 685 nanometers at liquid nitrogen temperature, which varied with the species and the degree of dissociation.
Abstract: A general procedure for the isolation of functionally intact phycobilisomes was devised, based on modifications of previously used procedures. It has been successful with numerous species of red and blue-green algae (Anabaena variabilis, Anacystis nidulans, Agmenellum quadruplicatum, Fremyella diplosiphon, Glaucosphaera vacuolata, Griffithsia pacifica, Nemalion multifidum, Nostoc sp., Phormidium persicinum, Porphyridium cruentum, P. sordidum, P. aerugineum, Rhodosorus marinus). Isolation was carried out in 0.75 molar K-phosphate (pH 6.8 to 7.0) at 20 to 23 C on sucrose step gradients. Lower temperature (4 to 10 C) was usually unfavorable resulting in uncoupling of energy transfer and partial dissociation of the phycobilisomes, sometimes with complete loss of allophycocyanin. Intact phycobilisomes were characterized by fluorescence emission peaks of 670 to 675 nanometers at room temperature, and 678 to 685 nanometers at liquid nitrogen temperature. Uncoupling and subsequent dissociation of phycobilisomes, in lowered ionic conditions, varied with the species and the degree of dissociation but occurred preferentially between phycocyanin and allophycocyanin, or between phycocyanin and phycoerythrin.
TL;DR: The results indicated that the compound identified as traumatic acid is formed by autooxidation of trans- 10-ODA and that trans-10- ODA is a natural compound with growth-regulating properties.
Abstract: 12-Oxo- trans -10-dodecenoic acid ( trans -10-ODA) is an oxidation product of polyunsaturated fatty acids in plant tissues. The structural similarity of trans -10-ODA and traumatic acid, a compound considered to be a wound hormone, suggested that trans -10-ODA might be a precursor of traumatic acid. Both trans -10-ODA and traumatic acid were active in the Wehnelt bean assay. The results were more consistent with trans -10-ODA than with traumatic acid. Cucumber ( Cucumis sativus L. var. National Pickling) hypocotyls also showed a growth increase following treatment with trans -10-ODA, which suggested that trans -10-ODA has a more general influence on plant development than previously ascribed to traumatic acid. Runner beans ( Phaseolus vulgaris L. var. Kentucky Wonder) were analyzed for the presence of endogenous trans -10-ODA and traumatic acid. These are the beans from which traumatic acid was originally isolated in 1939. They contained trans -10-ODA but no traumatic acid. Young beans were a better source of trans -10-ODA than older beans and an increase in the esterified form of trans -10-ODA with age may have been due to a conversion of the free acid to the esterified form. The amount of endogenous trans -10-ODA increased when bean pod tissue was sliced and wounded. Rapid stirring and the presence of oxygen increased autooxidation of trans -10-ODA to traumatic acid in runner beans, which indicated that the compound identified as traumatic acid is formed by autooxidation of trans -10-ODA and that trans -10-ODA is a natural compound with growth-regulating properties. Enzyme extracts of runner beans synthesized trans -10-ODA from linoleic acid. No enzymic synthesis of traumatic acid was observed even when cofactors were added to the reaction mixture. This confirmed the conclusion that traumatic acid is formed by autooxidation of trans -10-ODA.
TL;DR: Results indicate that a close relation exists between the rapid increase in the cell wall-depolymerizing enzymes and the rise in respiration and ethylene production and refocused attention on the role of thecell wall and the associated plasma membrane in the early events of fruit ripening.
Abstract: Cellulase, polygalacturonase (PG), pectinmethylesterase (PME), respiration, and ethylene production were determined in single “Fuerte” avocado fruits from the day of harvest through the start of fruit breakdown. PME declined from its maximum value at the time of picking to a low level early in the climacteric. PG activity was not detectable in the preclimacteric stage, increased during the climacteric, and continued to increase during the postclimacteric phase to a level three times greater than when the fruit reached the edible soft stage. Cellulase activity was low in the preclimacteric fruit, started to increase just as respiration increased, and reached a level two times greater than at the edible soft stage. Cellulase activity started to increase 3 days before PG activity could be detected. Increased production of ethylene followed the increase in respiration and cellulase activity by about 1.5 days. These results indicate that a close relation exists between the rapid increase in the cell wall-depolymerizing enzymes and the rise in respiration and ethylene production and refocused attention on the role of the cell wall and the associated plasma membrane in the early events of fruit ripening.
TL;DR: Data suggest that the metabolism of ethylene may be related to its action, and low O(2) reduced pea seedling growth under these conditions thereby severely limiting its usefulness as a specific antiethylene treatment.
Abstract: The relationship between ethylene action and metabolism was investigated in the etiolated pea seedling ( Pisum sativum L. cv. Alaska) by inhibiting ethylene action with Ag + , high CO 2 , and low O 2 and then determining if ethylene metabolism was inhibited in a similar manner. Ag + (100 milligrams per liter) was clearly the most potent antiethylene treatment. Ag + pretreatment inhibited the growth retarding action of 0.2 microliters per liter ethylene by 48% and it also inhibited the incorporation of 0.2 microliters per liter 14 C 2 H 4 into pea tips by the same amount. As the ethylene concentration was increased from 0.2 to 30 microliters per liter, the effectiveness of Ag + in reducing ethylene action and metabolism declined in a similar fashion. Although Ag + significantly inhibited the incorporation of 14 C 2 H 4 into tissue metabolites, the oxidation of 14 C 2 H 4 to 14 CO 2 was unaffected in the same tissue. CO 2 (7%) inhibited ethylene-induced growth retardation but its effectiveness diminished at a greater rate than that of Ag + with increasing ethylene concentration. High CO 2 had just the opposite effect of Ag + since it inhibited 14 C 2 H 4 oxidation to 14 CO 2 without affecting tissue incorporation. In contrast to Ag + , CO 2 did not inhibit ethylene action and metabolism to exactly the same extent, and the inhibition of metabolism did not rapidly decline with increasing 14 C 2 H 4 concentration. However, high CO 2 did alter the ratio of 14 C 2 H 4 tissue incorporation to 14 CO 2 production in a manner consistent with changes in ethylene effectiveness. Lowering the O 2 concentration to 5% reduced ethylene-induced growth retardation from 70 to 58% at 0.22 microliters per liter and inhibited 14 C 2 H 4 (0.25 microliters per liter) tissue incorporation and oxidation to 14 CO 2 by 26 and 45%, respectively. However, in contrast to Ag + and high CO 2 which slightly promoted growth in ethylene-free air, low O 2 reduced pea seedling growth under these conditions thereby severely limiting its usefulness as a specific antiethylene treatment. Collectively these data suggest that the metabolism of ethylene may be related to its action.
TL;DR: The daily cycle of leaf elongation rate, water potential, and solute potential of maize and sorghum, as well as temperature, were monitored in the field, showing evidence that the decrease in psi.
Abstract: The daily cycle of leaf elongation rate, water potential, and solute potential of maize and sorghum, as well as temperature, were monitored in the field. Major climatic features were high radiation and a minimum air temperature of about 12 C. Leaf elongation of both crops was slowest at night, presumably because of low temperature. Peak elongation rates were in daytime when leaf water potential (Psi) was low. Solute potential also decreased during daylight, thus permitting the maintenance of appreciable turgor pressure, a critical parameter for cell expansion.Leaf Psi versus relative water content (RWC) curves were developed by sampling detached leaves at intervals as they dried quickly in the laboratory. At a given RWC, Psi was lower in leaves at midday than early in the morning, which is evidence that the decrease in psi. at midday was caused by an increase in the amount of solute in the tissue. Estimates of psi. at 100% RWC were 4 bars lower at midday than early in the morning in both crops. Soluble sugars, mainly nonreducing, accounted for most of the observed psi. decrease in sorghum leaves. Shading the leaves from light eliminated most of the solute buildup.
TL;DR: The time sequence analysis of the starch digestion pattern of the thin sectioned germinating rice (Oryza sativa L.) seed specimens using the starch film method showed that at the initial stage amylase activity was almost exclusively localized in the epithelium septum between the scutellum and endosperm.
Abstract: The time sequence analysis of the starch digestion pattern of the thin sectioned germinating rice (Oryza sativa L) seed specimens using the starch film method showed that at the initial stage amylase activity was almost exclusively localized in the epithelium septum between the scutellum and endosperm Starch breakdown in the endosperm tissues began afterward; amylase activity in the aleurone layers was detectable only after 2 days Polyacrylamide gel electrofocusing (pH 4 to 6) revealed nearly the same zymogram patterns between endosperm and scutellum extracts, although additional amylase bands appeared in the endosperm extracts at later germination stages (4 to 6 days) These are presumably attributable to the newly synthesized enzyme molecules in the aleurone cells
TL;DR: The separation of dhurrin and its catabolic enzymes in different tissues prevents its large scale hydrolysis under normal physiological conditions, which would be expected to proceed when the contents of the ruptured epidermal and mesophyll cells are allowed to mix.
Abstract: The tissue distributions of dhurrin [p-hydroxy-(S)-mandelonitrile-β-d-glucoside] and of enzymes involved in its metabolism have been investigated in leaf blades of light-grown Sorghum bicolor seedlings. Enzymic digestion of these leaves using cellulase has enabled preparations of epidermal and mesophyll protoplasts and bundle sheath strands to be isolated with only minor cross-contamination. Dhurrin was located entirely in the epidermal layers of the leaf blade, whereas the two enzymes responsible for its catabolism, namely dhurrin β-glucosidase and hydroxynitrile lyase, resided almost exclusively in the mesophyll tissue. The final enzyme of dhurrin biosynthesis, uridine diphosphate glucose:p-hydroxymandelonitrile glucosyltransferase, was found in both mesophyll (32% of the total activity of the leaf blade) and epidermal (68%) tissues. The bundle sheath strands did not contain significant amounts of dhurrin or of these enzymes. It was concluded that the separation of dhurrin and its catabolic enzymes in different tissues prevents its large scale hydrolysis under normal physiological conditions. The well documented production of HCN (cyanogenesis), which occurs rapidly on crushing Sorghum leaves, would be expected to proceed when the contents of the ruptured epidermal and mesophyll cells are allowed to mix.
TL;DR: The data are consistent with the hypothesis that starch degradation provides the carbon skeletons for anion synthesis in guard cells during stomatal opening and it appears that soluble sugars increase inGuard cells when stomata of Vicia faba open.
Abstract: Using quantitative histochemical techniques, the carbohydrate levels of guard cells from open and closed stomatal apparatus of Vicia faba L. were compared. To minimize experimental error, all comparisons were between leaflets of the same pair. Stomata on one leaflet were caused to open by light and reduced CO(2). The other leaflet, which was in darkness, had closed stomata. In one experiment, data were also collected on palisade parenchyma, spongy parenchyma, and epidermal cells.Guard cell starch concentration was higher in the leaflets with closed stomata than in open stomata by 72 +/- 16 millimoles per kilogram dry weight (anhydroglucosyl equivalents) (N = 117, P < 0.02). Variation in guard cell starch concentration from one part of a leaflet to another was small. The data are consistent with the hypothesis that starch degradation provides the carbon skeletons for anion synthesis in guard cells during stomatal opening.Sucrose concentration was higher in guard cells when stomata were open than when they were closed in all three experiments (average difference = 45 +/- 7 millimoles per kilogram dry weight [N = 59, P < 0.01]). The variability of sucrose concentration within test leaflets prevented an unequivocal interpretation of these results. When all data are considered, it appears that soluble sugars increase in guard cells when stomata of Vicia faba open.
TL;DR: It is suggested that glycinebetaine is the major cytoplasmic osmoticum (with K(+) salts) in these species at high salinities, which may be preferentially utilized as vacuolar osmotica.
Abstract: The growth and tissue water, K(+), Na(+), Cl(-), proline and glycinebetaine contents of the shoots and roots of two Chenopodiaceae, Atriplex spongiosa and Suaeda monoica have been measured over a range of external NaCl salinities. Both species showed some fresh weight response to low salinity mainly due to increased succulence. S. monoica showed both a greater increase in succulence (at low salinities) and tolerance of high salinities than A. spongiosa. Both species had high affinities for Na(+) and maintained constant but low shoot K(+) contents with increasing salinity. These trends were more marked with S. monoica in which Na(+) stimulated the accumulation of K(+) in roots. An association between high leaf Na(+) accumulation, high osmotic pressure, succulence, and a positive growth response at low salinities was noted. Proline accumulation was observed in shoot tissues with suboptimal water contents. High glycinebetaine contents were found in the shoots of both species. These correlated closely with the sap osmotic pressure and it is suggested that glycinebetaine is the major cytoplasmic osmoticum (with K(+) salts) in these species at high salinities. Na(+) salts may be preferentially utilized as vacuolar osmotica.
TL;DR: The specific activity of RuBPc isolated from severely K-deficient and K-sufficient leaflets was not significantly different, suggesting that K does not function inRuBPc activity, and the K-stimulated synthesis of Ru BPc most likely represents de novo synthesis.
Abstract: Alfalfa was grown hydroponically in 0, 0.6, and 4.8 millimolar K in order to determine the influence of tissue level of K on photosynthesis, dark respiration, photorespiration, stomatal and mesophyll resistance to CO(2), photosystem I and II activity, and synthesis and activity of ribulose 1,5-bisphosphate carboxylase (RuBPc).A severe (0.0 millimolar) and mild (0.6 millimolar) K deficiency, compared to plants grown at 4.8 millimolar K, produced a significant decrease in photosynthesis and photorespiration, but an increase in dark respiration. Both deficient K levels increased hydrophyllic resistance to CO(2), but only the severe deficiency increased stomatal resistance.Photosystem I and II activity of isolated chloroplasts was not affected by K deficiency. The apparent activity of a crude RuBPc preparation was significantly reduced in severely deficient plants. Activity of the enzyme could not be restored to normal rates by the addition of K to the reaction medium.The specific activity of RuBPc isolated from severely K-deficient and K-sufficient leaflets was not significantly different, suggesting that K does not function in RuBPc activity. Incorporation of [(14)C]leucine into RuBPc, as a measure of synthesis, by K-deficient leaflets was reduced to 15% of K-sufficient leaflets. The addition of K to the reaction medium stimulated [(14)C]leucine incorporation into RuBPc and 10 millimolar KNO(3) increased incorporation to 80% of K-sufficient leaflets. Actinomycin D and cycloheximide suppressed the K-stimulated incorporation of [(14)C]leucine into RuBPc, suggesting that the K-stimulated synthesis of RuBPc most likely represents de novo synthesis.
TL;DR: Comparisons of partitioning and utilization of assimilated C and N were compared in nonnodulated, NO(3)-fed and nodulated, N(2)-fed plants of white lupin to demonstrate that patterns of incorporation of C or net photosynthate to dry matter and exchange ofC and N among plant parts were essentially similar in the two forms of nutrition.
Abstract: Partitioning and utilization of assimilated C and N were compared in nonnodulated, NO 3 -fed and nodulated, N 2 -fed plants of white lupin ( Lupinus albus L.). The NO 3 regime used (5 millimolar NO 3 ) promoted closely similar rates of growth and N assimilation as in the symbiotic plants. Over 90% of the N absorbed by the NO 3 -fed plants was judged to be reduced in roots. Empirically based models of C and N flow demonstrated that patterns of incorporation of C and N into dry matter and exchange of C and N among plant parts were essentially similar in the two forms of nutrition. NO 3 -fed and N 2 -fed plants transported similar types and proportions of organic solutes in xylem and phloem. Withdrawal of NO 3 supply from NO 3 -fed plants led to substantial changes in assimilate partitioning, particularly in increased translocation of N from shoot to root. Nodulated plants showed a lower (57%) conversion of C or net photosynthate to dry matter than did NO 3 -fed plants (69%), and their stems were only half as effective as those of NO 3 -fed plants in xylem to phloem transfer of N supplied from the root. Below-ground parts of symbiotic plants consumed a larger share (58%) of the plants9 net photosynthate than did NO 3 -fed roots (50%), thus reflecting a higher CO 2 loss per unit of N assimilated (10.2 milligrams C/milligram N) by the nodulated root than by the root of the NO 3 -fed plant (8.1 milligrams C/milligram N). Theoretical considerations indicated that the greater CO 2 output of the nodulated root involved a slightly greater expenditure for N 2 than for NO 3 assimilation, a small extra cost due to growth and maintenance of nodule tissue, and a considerably greater nonassimilatory component of respiration in root tissue of the symbiotic plant than in the root of the NO 3 -fed plant.
TL;DR: Stomatal resistance was always high when CO( 2) concentration was high and experiments in which attempts were made to manipulate internal CO(2) concentrations gave data consistent with stomatal behavior in Crassulacean acid metabolism being controlled by internal CO (2) concentration.
Abstract: Measurements of internal gas phase CO(2) concentration, stomatal resistance, and acid content were made in Crassulacean acid metabolism plants growing under natural conditions. High CO(2) concentrations, sometimes in excess of 2%, were observed during the day in a range of taxonomically widely separated plants (Opuntia ficus-indica L., Opuntia basilaris Engelm. and Bigel., Agave desertii Engelm., Yucca schidigera Roezl. ex Ortiges, Ananas comosus [L.] Merr., Aloe vera L., Cattleya sp. and Phalanopsis sp.) and below ambient air concentrations were observed at night.Stomatal resistance was always high when CO(2) concentration was high and experiments in which attempts were made to manipulate internal CO(2) concentrations gave data consistent with stomatal behavior in Crassulacean acid metabolism being controlled by internal CO(2) concentration. Exogenous CO(2) applied in darkness at a concentration similar to those observed in the light caused stomatal resistance to increase.In pads of Opuntia basilaris Engelm. and Bigel. subjected to severe water stress internal gas phase CO(2) concentrations exhibited fluctuations opposite in phase to fluctuations in acid content. Stomatal resistance remained high and the opening response to low CO(2) concentration was almost entirely eliminated.
TL;DR: It seems possible that NO(3) (-) and NH(4) (+) are absorbed through separate regions of the cell membrane differing in lipid composition and phase transition temperatures.
Abstract: At root temperature below 14 C the absorption of 15 N from NH 4 + greatly exceeded that from NO 2 − by tillers of Lolium multiflorum and Lolium perenne under conditions where pH, external concentration, plant N status, and pretreatment temperature were varied. There was a marked increase in the temperature sensitivity of NO 3 − transport below 14 C, irrespective of the temperature at which plants were grown previously. A marked increase in the temperature sensitivity was also seen for NH 4 + transport, but this occurred at the lower temperature of 10 C. Pretreatment of roots at 8 C lowered this still further to 5 C. Above and below these transition temperatures the Q 10 values for NO 3 − and NH 4 + transport were similar. Thus, the increased absorption of NH 4 + relative to NO 3 − at low temperatures seems to be related primarily to the difference in transition temperatures. It seems possible that NO 3 − and NH 4 + are absorbed through separate regions of the cell membrane differing in lipid composition and phase transition temperatures.
TL;DR: It appeared that recently fixed photosynthate could supply all of the energy required for nitrate reduction in carbohydrate-deficient tissue, and when sufficient metabolites were present in the green tissue, light was not obligatory for the reduction of nitrate and nitrite.
Abstract: The influence of light, dark, and ambient CO 2 on nitrate assimilation in 8- to 9-day-old barley seedlings was studied. To develop the photosynthetic apparatus fully, the seedlings were grown in nitrogen-free Hoagland solution for 5 days in darkness followed by 3 days in continuous light. The seedlings reduced nitrate and nitrite in both light and dark, although more slowly in darkness. The slower nitrate reduction in darkness was not due to decreased uptake, since the steady-state internal concentration of nitrate was doubled. The faster nitrate reduction in light was attributed to recent products of photosynthetic CO 2 fixation supplying reducing energy, possibly by shuttle reactions between chloroplasts and cytoplasm. In carbohydrate-deficient tissue, it appeared that recently fixed photosynthate could supply all of the energy required for nitrate reduction. When sufficient metabolites were present in the green tissue, light was not obligatory for the reduction of nitrate and nitrite.
TL;DR: An empirical modeling technique was developed for depicting quantitatively the transport and partitioning of photosynthetically fixed C and symbiotically fixed N during 10-day intervals of a 40-day period in the growth of nodulated plants of white lupin.
Abstract: An empirical modeling technique was developed for depicting quantitatively the transport and partitioning of photosynthetically fixed C and symbiotically fixed N during 10-day intervals of a 40-day period in the growth of nodulated plants of white lupin (Lupinus albus L. cv. Ultra). Model construction utilized data for C and N consumption of plant parts and C:N weight ratios of the xylem and phloem fluids serving specific plant organs. Formulas were derived from calculating the net transport of C and N between plant parts in xylem and phloem. The models provided quantitative information on the dependence of growing organs on xylem and phloem for their supply of C and N, the cycling of N through leaflets and of C through nodules, the extent of direct incorporation of fixed N into growing nodules, and the involvement of N from shoot translocate in the nutrition of the nodulated root. Stem plus petioles abstracted considerably more N from xylem than expected from their transpirational activity. Xylem to phloem transfer of recently fixed N in mature stem and petioles was substantiated by the models, being depicted as a device for dispensing N to growing parts of the shoot extra to that attracted transpirationally in xylem or received as translocate from leaflets.
TL;DR: The system established in the present work provides a useful system for biochemical research into the mechanisms of somatic embryogenesis, and synchrony of the embryogenetic process was observed at least in the early stages of the process.
Abstract: Synchronization of somatic embryogenesis was achieved in a carrot (Daucus carota L. cv. “Kurodagosun”) suspension culture by sieving the initial heterogeneous cell population, by density gradient centrifugation in Ficoll solutions, and by subsequent repeated centrifugations at a low speed (50g) for a short time (5 seconds), followed by transferring the cell clusters obtained, which were composed of 3 to 10 cells, to a medium containing zeatin (0.1 micromolar) but no auxin. The frequency of embryo formation reached more than 90%, and synchrony of the embryogenetic process was observed at least in the early stages of the process. The system established in the present work provides a useful system for biochemical research into the mechanisms of somatic embryogenesis.
TL;DR: It is concluded that a primary action of ABA in inhibiting seed germination is the control of water uptake of the embryo tissues rather than the controlof DNA, RNA, or protein syntheses.
Abstract: The germination process of mustard seeds (Sinapis alba L.) has been characterized by the time courses of water uptake, rupturing of the seed coat (12 hours after sowing), onset of axis growth (18 hours after sowing), and the point of no return, where the seeds lose the ability to survive redesiccation (12 to 24 hours after sowing, depending on embryo part). Abscisic acid (ABA) reversibly arrests embryo development at the brink of radicle growth initiation, inhibiting the water uptake which accompanies embryo growth. Seeds which have been kept dormant by ABA for several days will, after removal of the hormone, rapidly take up water and continue the germination process. Seeds which have been preincubated in water lose the sensitivity to be arrested by ABA after about 12 hours after sowing. This escape from ABA-mediated dormancy is not due to an inactivation of the hormone but to a loss of competence to respond to ABA during the course of germination. The sensitivity to ABA can be restored in these seeds by redrying. It is concluded that a primary action of ABA in inhibiting seed germination is the control of water uptake of the embryo tissues rather than the control of DNA, RNA, or protein syntheses.
TL;DR: Leaf expansion was completed more rapidly the higher the growth photon flux density and leaves senesced more quickly in high light and Adaptive potential is greatest early in blade expansion and decreases as expansion is completed.
Abstract: Apparent photosynthesis and dark respiration were followed during development in four light environments of leaves of Fragaria virginiana Duchesne. Leaf expansion was completed more rapidly the higher the growth photon flux density and leaves senesced more quickly in high light. Maximum photosynthetic capacity coincided with the completion of blade expansion and declined quickly thereafter. Leaves were transferred from high to low and low to high photon flux densities at several stages during expansion. Leaf photosynthetic performance and anatomy were subsequently analyzed. Leaf anatomy and apparent photosynthesis per unit dry weight can be modified during expansion to reflect the predominant light conditions. Adaptive potential is greatest early in blade expansion and decreases as expansion is completed.