Osmosensitivity of Sucrose Uptake by Immature Pea Cotyledons Disappears during Development

Sucrose uptake was studied in isolated, immature pea cotyledons (Pisum sativum L. cv Marzia) in relation to their developmental stage. During the developmental period examined the water content of the cotyledons decreased from ≈80% “stage 1” to ≈55% “stage 2”. When assayed in an isotonic medium (400 osmoles per cubic meter) the influx capacity per gram fresh weight for sucrose was almost constant during this developmental period. The influx could be analyzed into a saturable component (K_m ≈ 9 moles per cubic meter; V_max ≈ 150 nanomoles per minute per gram fresh weight) and an unsaturable component (k_i ≈ 0.5 nanomoles per minute per gram fresh weight [per mole per cubic meter]). Incubation in a hypotonic medium reduced the sucrose influx in stage 1 cotyledons, up to 80% reduction at 0 milliosmole (medium without mannitol), but had no effect on sucrose uptake by stage 2 cotyledons. Reduced uptake in a hypotonic medium (100 osmoles per cubic meter) could be attributed to a lowering of the V_max from 150 to 36 nanomoles per minute per gram fresh weight. During incubation of stage 1 cotyledons and stage 2-cotyledons in a hypotonic medium (200 osmoles per cubic meter) their volume increased by 16% and 5.6%, respectively, while the calculated turgor pressure increased from 0.2 to 0.6 megapascal for cotyledons of both developmental stages. Reduced sucrose influx in hypotonic medium, therefore, seems to be related to cell swelling (membrane stretching) rather than to increased turgor pressure.     

Tissue Distribution of beta-Cyanoalanine Synthase in Leaves

β-Cyanoalanine synthase, which catalyzes the reaction between cysteine and HCN to form β-cyanoalanine and H₂S, was assayed in leaf tissues from cyanogenic (Sorghum bicolor × Sorghum sudanense [sorghum]) and noncyanogenic (Pisum sativum [pea], Zea mays [maize], and Allium porrum [leek]) plants. The activity in whole leaf extracts ranged from 33 nanomoles per gram fresh weight per minute in leeks, to 1940 nanomoles per gram fresh weight per minute in sorghum. The specific activities of β-cyanoalanine synthase in epidermal protoplasts from maize and sorghum and in epidermal tissues from peas were in each case greater than the corresponding values for mesophyll protoplasts or tissues, or for strands of bundle sheath cells.

The tissue distributions for this enzyme were determined for pea, leek, and sorghum: the mesophyll protoplasts and tissues in these three plants contained 65% to 78% of the enzyme, while epidermal protoplasts and tissues contained 10% to 35% of the total leaf activity. In sorghum, the bundle sheath strands contained 13% of the leaf activity. The presence of β-cyanoalanine synthase in all tissues and species studied suggests a fundamental role for this enzyme in plant metabolism.

     

Stimulation of Isopentenyl Pyrophosphate Incorporation into Polyisoprene in Extracts from Guayule Plants (Parthenium argentatum Gray) by Low Temperature and 2-(3,4-Dichlorophenoxy) Triethylamine

Rubber particles isolated from guayule (Parthenium argentatum Gray) stem homogenates contain a polyprenyl transferase which catalyzes the polymerization of isopentenyl pyrophosphate into polyisoprene. The polymerization reaction is stimulated with the addition of an allylic pyrophosphate initiator and forms a polymer of polyisoprene with a molecular weight distribution from 10³ to 10⁷. The polymerization reaction in crude stem homogenates is not affected by the addition of an initiator probably due to the high activity of isopentenyl pyrophosphate isomerase furnishing saturating levels of dimethylallyl pyrophosphate. Polyisoprene formation in stems of guayule plants exposed to cold winter temperatures increased from 15.4 milligrams per gram dry weight in October to 24.5 milligrams per gram dry weight in January and increased from 16.2 to 38.1 milligrams per gram dry weight in the same period by additionally treating the plants with 5000 ppm of 2-(3,4-dichlorophenoxy)triethylamine. The rate of polymerization of isopentenyl pyrophosphate into polyisoprene in stem homogenates of the cold treated plants increased from 12.1 nanomoles per hour per gram fresh weight in October to 144.3 nanomoles per hour per gram fresh weight in January and increased from 17.7 to 446.8 nanomoles per hour per gram fresh weight in the same period by additionally treating the plants with 5000 ppm of 2-(3,4-dichlorophenoxy)triethylamine. These results show that the increase in polyprenyl transferase activity partially accounts for the increase in polyisoprene synthesis in guayule plants exposed to low temperature and treated with 2-(3,4-dichlorophenoxy)triethylamine.     

Alteration of thiol pools in roots and shoots of maize seedlings exposed to cadmium : adaptation and developmental cost

Roots of intact 5-day-old maize (Zea mays L.) seedlings were exposed to 3 micromolar Cd during a 7-day period. Cysteine, γ-glutamylcysteine, glutathione (GSH), and Cd-induced acid-soluble thiols (ASTs), including phytochelatins, were quantified in roots and shoots. Adaptation to Cd and its cost to seedling development were evaluated by measuring Cd content, tissue fresh weight, and rate of root elongation. Roots contained 60 to 67% of the Cd in the seedlings between 4 and 7 days of exposure. Exposure to Cd decreased the fresh weight gain in roots from day 4 onward without affecting the shoots. Between days 1.5 and 3.5 of Cd treatment, roots elongated more slowly than controls; however, their growth rate recovered thereafter and exceeded that of controls. Exposure to Cd did not appreciably affect the concentration of cysteine in the seedlings. However, the initial low concentration of γ-glutamylcysteine increased (after a lag of 6 hours in roots and 2 days in shoots), reaching a plateau by day 6 at 28.5 nanomoles per gram of fresh weight in roots and by day 5 at 19.1 nanomoles per gram of fresh weight in shoots. During the first 9 hours of Cd exposure, the concentration of GSH in roots decreased dramatically (at 31.6 nanomoles per gram of fresh weight per hour) and thereafter decreased more slowly than in controls. The depletion of GSH in the roots (366 nanomoles per gram of fresh weight) matched the synthesis of ASTs (349 nanomoles per gram of fresh weight) during the first 48 hours. The concentration of ASTs in roots increased steadily thereafter to reach 662.2 nanomoles per gram of fresh weight by 6 days of Cd exposure. In shoots, Cd had little influence on the concentration of GSH, but ASTs still accumulated to 173.3 nanomoles per gram fresh weight after 5 days. The molar ratio of thiols in ASTs to Cd increased to a maximum of 10.24 in roots after 4 hours and of 4.25 in shoots after 2 days of Cd exposure. After 4 days, the ratio reached a plateau of approximately 2 in roots and between 2 and 3 in shoots, as if a steady state of Cd chelation had been achieved in both organs. The plateau coincided with recovered root elongation or an adaptation to Cd. The reduced fresh weight gain of the roots during this time, however, indicated that the synthesis of Cd-induced thiols was at a cost to root development.     

Alcohol dehydrogenase and ethanol in the stems of trees : evidence for anaerobic metabolism in the vascular cambium

Anaerobic fermentation in plants is usually thought to be a transient phenomenon, brought about by environmental limitations to oxygen availability, or by structural constraints to oxygen transport. The vascular cambium of trees is separated from the air by the outer bark and secondary phloem, and we hypothesized that the cambium may experience sufficient hypoxia to induce anaerobic fermentation. We found high alcohol dehydrogenase activity in the cambium of several tree species. Mean activity of alcohol dehydrogenase in Populus deltoides was 165 micromoles NADH oxidized per minute per gram fresh weight in May. Pyruvate decarboxylase activity was also present in the cambium of P. deltoides, with mean activity of 26 micromoles NADH oxidized per minute per gram fresh weight in May. Lactate dehydrogenase activity was not present in any tree species we examined. Contrary to our expectation, alcohol dehydrogenase activity was inversely related to bark thickness in Acer saccharum and unrelated to bark thickness in two Populus species. Bark thickness may be less important in limiting oxygen availability to the cambium than is oxygen consumption by rapidly respiring phloem and cambium in actively growing trees. Ethanol was present in the vascular cambium of all species examined, with mean concentrations of 35 to 143 nanomoles per gram fresh weight, depending on species. Ethanol was also present in xylem sap and may have been released from the cambium into the transpiration stream. The presence in the cambium of the enzymes necessary for fermentation as well as the products of fermentation is evidence that respiration in the vascular cambium of trees may be oxygen-limited, but other biosynthetic origins of ethanol have not been ruled out.     

Levels of Free and Conjugated Abscisic Acid in Developing Floral Organs of the Navel Orange (Citrus sinensi [L.] Osbeck cv Washington)

The levels of abscisic acid (ABA) and alkaline-hydrolyzable ABA-conjugate (putatively identified as the glucosyl ester, abscisyl-β-d-glucopyranoside) were determined by enzyme immunoassay in the organs of developing navel orange (Citrus sinensis [L.] Osbeck cv Washington) flowers. Although both compounds were detected in every tissue, developmentally related differences between organs in the total and relative contents were observed. The highest ABA levels were observed in the stigma/style shortly after anthesis (11.5 ± 0.6 nanomoles ABA per gram fresh weight and 4.8 ± 0.6 nanomoles ABA-conjugate per gram fresh weight); whereas, the highest ABA-conjugate levels were observed at the same time in the floral disc (hypogynous disc plus calyx; 3.5 ± 0.1 nmol nanomols ABA per gram fresh weight and 11.8 ± 0.9 nanomoles ABA-conjugate per gram fresh weight). These results suggest that differences in ABA content reflect tissue-specific variation in the facility for ABA conjugation. Increased ABA levels were observed in the stigma/style near anthesis; however, a relationship with pollination is discounted, since `Washington' navel orange flowers are male sterile and devoid of pollen.     

Hydroxylation of N-(Delta-Isopentenyl)adenine to Zeatin: Relative Activities of Organ Systems from Actinidia arguta

By incubating explants from Actinidia arguta seedlings on a nutrient medium supplemented with 20 to 30 micromolar N⁶-(Δ²-isopentenyl)adenine (i⁶Ade) and then measuring zeatin (io⁶Ade) accumulation in tissues, the distribution of i⁶Ade hydroxylase activities in whole plants could be determined. Based on analyses with three entire plants, it is estimated that, as an organ system, roots contain approximately 68% of the plant's hydroxylase, while stems and leaves account for about 26% and 6%, respectively, of the total activity. Depending on the part of the root examined, hydroxylase activities ranged from 20 to 148 nanomoles io⁶Ade accumulated per gram fresh weight per 24 hours of incubation. Stem activities ranged from 17 to 165 nanomoles per gram fresh weight per 24 hours with the lowest activities being found at the tip. Leaf activities were substantially lower (1-10 nanomoles per leaf depending on position) than either root or stem.     

Free space iron pools in roots: generation and mobilization

A rapid and simple method for the determination of a ferric iron pool in the free space of roots is described. Formation of this pool depended on the source of iron in the nutrient solution. During growth in water culture at pH 5 to 6 with Fe-ethylenediaminetetraacetate, a free space pool of 500 to 1000 nanomoles Fe per gram fresh weight was formed in the roots of bean (Phaseolus vulgaris L. var. Prélude), maize (Zea mays L. var. Capella), and chlorophytum (Chlorophytum comosum [Thunb.] Jacques). No significant pool (less than 100 nanomoles per gram fresh weight) was formed with ferrioxamine. Upon impending Fe deficiency, bean and chlorophytum were able to mobilize this pool. Fe-deficient bean plants mobilized iron from the free space iron pool of another plant in the same vessel.     

A novel sucrose synthase pathway for sucrose degradation in cultured sycamore cells

Enzymes of sucrose degradation and glycolysis in cultured sycamore (Acer pseudoplatanus L.) cells were assayed and characterized in crude extracts and after partial purification, in an attempt to identify pathways for sucrose catabolism. Desalted cell extracts contained similar activities (20-40 nanomoles per milligram protein per minute) of sucrose synthase, neutral invertase, glucokinase, fructokinase, phosphofructokinase, and UDPglucose pyrophosphorylase (assayed with 2 micromolar pyrophosphate (PPi). PPi-linked phosphofructokinase activity was virtually dependent upon fructose 2,6-bisphosphate, and the maximum activity exceeded that of ATP-linked phosphofructokinase. Hexokinase activity, with glucose as substrate, was highly specific for ATP, whereas fructokinase activity was relatively nonspecific. At 1 millimolar nucleoside triphosphate, fructokinase activity decreased in the order: UTP > ATP > CTP > GTP. We propose two pathways for sucrose degradation. One involves invertase action, followed by classical glycolysis of hexose sugars, and the other is a novel pathway initiated by sucrose synthase. The K_m for sucrose of sucrose synthase was severalfold lower than that of neutral invertase (15 versus 65 millimolar), which may determine carbon partitioning between the two pathways. The sucrose synthase pathway proposed involves cycling of uridylates and PPi. UDPglucose pyrophosphorylase, which is shown to be an effective `PPi-scavenger,' would consume PPi and form UTP. The UTP could be then utilized in the UTP-linked fructokinase reaction, thereby forming UDP for sucrose synthase. The source of PPi is postulated to arise from the back reaction of PPi-linked phosphofructokinase. Sycamore cells contained a substantial endogenous pool of PPi (about 3 nanomoles per gram fresh weight, roughly 1/10 the amount of ATP in these cells), and sufficient fructose 2,6-bisphosphate (0.09 nanomole per gram fresh weight) to activate the PPi-linked phosphofructokinase. Possible regulation and energetic differences between the sucrose synthase and invertase pathways are discussed.     

Inheritance of the Reversal of O(2) Response of Photosynthesis in a Flaveria linearis Mutant

A mutant plant of Flaveria linearis Lag. expresses reversed O₂ response of photosynthesis (i.e. its apparent photosynthesis is stimulated at atmospheric O₂ levels). The objectives of this study were to determine the genetic inheritance of this trait and to investigate the biochemical mechanism for its expression. The mutant plant was crossed reciprocally with a plant of the closely related species Flaveria oppositifolia (DC.) Rydb. and also with another plant of F. linearis. Data on O₂ inhibition of apparent photosynthesis were analyzed on F₂ and F₃ progeny from these F₁ hybrids. In addition, test crosses (mutant × F₁ hybrid) and S₁ progeny from the mutant plant were also analyzed. All F₁ hybrids expressed inhibition of apparent photosynthesis and their progeny segregated in acceptable 3:1 and 13:3 (normal:reversed) ratios. There was little effect of environment on expression of the reversed O₂ response. Selected F₂ plants and the original mutant plant produced progeny in normal:reversed ratios which indicated the trait is controlled by two major genes which show dominant and recessive epistasis. Plants with greater than 20 nanomoles per gram fresh weight per minute of fructose-1, 6-bisphosphatase activity in the cytosol had normal O₂ response of photosynthesis. However, when plants had less than 20 nanomoles per gram fresh weight per minute of this enzyme activity in the cytosol, the O₂ was normal in some and reversed in others. It is proposed that low fructose bisphosphatase activity in the cytosol is controlled by a recessive gene (fbp). A second dominant gene is speculated to be hypostatic to the normal fructose bisphosphatase gene and controls the expression of an unknown factor that determines whether O₂ response of AP is reversed in the presence of fbp (i.e. when fructose bisphosphatase activity is low).     

Accumulation of Putrescine during Chilling Injury of Fruits

Putrescine (Put) increased 68% in lemon (Citrus limon (L.) Burm. f. cv Bearss) flavedo, 39% in grapefruit (C. paradisi Macf. cv Marsh) flavedo, 49% in grapefruit juice, and 149% in pepper (Capsicum annuum L. cv Early Calwonder) pericarp when fruits were stored at chilling temperatures. In lemon flavedo, the coefficient of correlation (r²) between Put concentration with severity of chilling was 0.90 and Put levels almost doubled; the injury index going from 1 to 2 units. Pepper pericarp, which was the most chilling-sensitive tissue tested (injury index going from 1 to 3.8 units), showed the greatest difference in Put accumulation (166 to 413 nanomoles per gram fresh weight) between storage temperatures of 7.2 and 1°C. The least difference (338 to 470 nanomoles per gram fresh weight) was found in grapefruit flavedo between storage temperatures of 15.5 and 4.4°C; the injury index going from 1 to 1.3 units.     

Sucrose Phosphate Synthase, Sucrose Synthase, and Invertase Activities in Developing Fruit of Lycopersicon esculentum Mill. and the Sucrose Accumulating Lycopersicon hirsutum Humb. and Bonpl

The green-fruited Lycopersicon hirsutum Humb. and Bonpl. accumulated sucrose to concentrations of about 118 micromoles per gram fresh weight during the final stages of development. In comparison, Lycopersicon esculentum Mill. cultivars contained less than 15 micromoles per gram fresh weight of sucrose at the ripe stage. Glucose and fructose levels remained relatively constant throughout development in L. hirsutum at 22 to 50 micromoles per gram fresh weight each. Starch content was low even at early stages of development, and declined further with development. Soluble acid invertase (EC 3.2. 1.26) activity declined concomitant with the rise in sucrose content. Acid invertase activity, which was solubilized in 1 molar NaCl (presumably cell-wall bound), remained constant throughout development (about 3 micromoles of reducing sugars (per gram fresh weight) per hour. Sucrose phosphate synthase (EC 2.4.1.14) activity was present at about 5 micromoles of sucrose (per gram fresh weight) per hour even at early stages of development, and increased sharply to about 40 micromoles of sucrose (per gram fresh weight) per hour at the final stages of development studied, parallel to the rise in sucrose content. In comparison, sucrose phosphate synthase activity in L. esculentum remained low throughout development. The possible roles of the sucrose metabolizing enzymes in determining sucrose accumulation are discussed.     

Stimulation of glutathione synthesis in photorespiring plants by catalase inhibitors

The effect of various herbicides on glutathione levels in barley (Hordeum vulgare L.), tobacco (Nicotiana tabacum L.), soybean (Glycine max [L.] Merr.), and corn (Zea mays L.) was examined. Illumination of excised barley, tobacco, and soybean plants for 8 hours in solution containing 2 millimolar aminotriazole (a catalase inhibitor) resulted in an increase in leaf glutathione from 250 to 400 nanomoles per gram fresh weight to 600 to 1800 nanomoles per gram fresh weight, depending on the species tested. All of this increase could be accounted for as oxidized glutathione. Between 25 and 50% of this oxidized glutathione was reduced when plants were darkened for 16 hours, but there was no significant decline in total glutathione. Another catalase inhibitor, thiosemicarbazide, was as effective as aminotriazole in elevating glutathione in soybean but was less effective in barley and tobacco. Glyphosate, an inhibitor of aromatic amino acid biosynthesis, had no significant effect on glutathione levels in any of the plants examined. Whereas methyl viologen (paraquat), which is a sink for photosystem I electrons, caused oxidation of leaf glutathione in all of the plants but did not increase the total amount of glutathione present.     

Isolation and Characterization of a Mutant of Arabidopsis thaliana Resistant to alpha-Methyltryptophan

Mutants of Arabidopsis thaliana have been selected for resistance to growth inhibition at the seedling stage by α-methyltryptophan (aMT). One mutant, amt-1 has been characterized in detail. The appearance and growth rate of the mutant in the absence of the inhibitor are similar to wild type, both as plants and callus. However, mutant plant growth is unaffected by 25 micromolar aMT and mutant callus growth by 50 micromolar aMT, concentrations that completely inhibit the growth of wild-type plants and callus, respectively. Tryptophan levels in mutant and wild-type plants are 24.3 ± 2.7 and 4.7 ± 1.2 micrograms per gram fresh weight, respectively, and in the corresponding callus 64.0 ± 2.6 and 31.8 ± 8.4 micrograms per gram fresh weight, respectively. Anthranilate synthase (AS) activity levels in crude extracts from whole plants are 3.09 ± 0.54 nanomoles per milligram protein per hour in amt-1 and 1.32 ± 0.21 nanomoles per milligram protein per hour in wild-type plants. In crude extracts from callus, anthranilate synthase levels are 11.54 ± 2.05 nanomoles per milligram protein per hour and 7.74 ± 1.58 in amt-1 and wild type, respectively. Enzyme extracts are inhibited by l-tryptophan; the concentrations required for 50% inhibition (I₅₀) are 3.9 and 1.9 micromolar for amt-1 and for wild type, respectively. The mutation segregates as a single nuclear allele and shows incomplete dominance. The concomitant increases in both AS activity and its I₅₀ for tryptophan suggest that the mutation amt-1 either resides in one of the AS structural genes or causes increased expression of an AS isoform with an I₅₀ greater than the average for the entire extract.     

The Occurrence of Abscisic Acid and Abscisyl-beta-d-Glucopyranoside in Developing and Mature Citrus Fruit as Determined by Enzyme Immunoassay

The contents of (+)-cis-abscisic acid (ABA) and alkaline-hydrolyzable ABA-conjugate(s) were analyzed by means of enzyme immunoassay in partially purified extracts of developing and mature sweet orange fruit (Citrus sinensis [L.] Osbeck cv Washington navel). A relatively small increase in ABA was observed in the fruit exocarp during the natural color transition from green to orange. At the same time, the ABA-conjugate level increased approximately 12-fold in this tissue. The contents of ABA and ABA-conjugate equaled 15.0 ± 0.7 and 107.8 ± 2.1 nanomoles per gram fresh weight, respectively, in the exocarp at harvest. Other tissues also contained considerable quantities of these compounds. Whereas the highest ABA content was observed in the exocarp, the highest ABA-conjugate content was observed in the central vascular axis of the fruit and equaled 187.0 ± 10.3 nanomoles per gram fresh weight. The only immunoreactive conjugate found in significant quantity in mature fruit was identified as abscisyl-β-d-glucopyranoside (ABA-GE) based on (a) immunological cross-reactivity, (b) thin layer chromatography co-chromatography with authentic standards in two solvent systems, (c) susceptibility to both chemical and enzymic degradation, and (d) mass spectroscopy.     

Nitrogen Starvation and the Regulation of Glutamine Synthetase in Agmenellum quadruplicatum

The level of glutamine synthetase activity in Agmenellum quadruplicatum strain PR-6 was dependent on the nitrogen source used for growth and on the nutritional status of the cells. During exponential growth, glutamine synthetase activity was low in cells grown on ammonia, urea, or nitrate. During the transition from nitrogen replete to nitrogen starved growth, glutamine synthetase activity began to rise. With ammonia as a nitrogen source, glutamine synthetase activity as determined in whole cells increased from 1 nanomole per minute per milliliter during exponential growth to 22 nanomoles per minute per milliliter during severe nitrogen starvation. In cells grown on nitrate the increase was from 5 to 39 nanomoles per minute per milliliter, and in cells grown on urea the increase was from 4 to 31 nanomoles per minute per milliliter.     

Protein Metabolism in Cultured Plant Tissues: III. Changes in the Rate of Protein Synthesis, Accumulation, and Degradation in Cultured Pith Tissue

During the transition of tobacco (Nicotiana tabacum) pith tissue to callus tissue, there were changes in the composition of the soluble amino acid pools, in the distribution of amino acids between pool and protein, and in the synthesis, accumulation, and degradation of proteins. The size of the leucine pool decreased from 90 nanomoles per gram fresh weight in fresh pith to 20 nanomoles in 24-hour cultured pith, followed by a return to 90 nmoles in pith cultured longer than 5 days. The latter value is the same as that reported for exponentially growing callus cells. Many other pool amino acids changed as dramatically. However, they always approached callus levels after 5 days of culturing. The total amino acid content of pith tissue (the sum of both pool and protein) remained unchanged during culturing. The value for total amino acid content (34 to 42 nanomoles per gram fresh weight) was also similar to that found in callus. The distribution of amino acids between pool and protein did change during culturing. The transition of pith tissue with 88% of its total amino acids free in the soluble pool to callus with 92% of its amino acids in protein was further characterized by changes in protein metabolism. Both protein synthesis and accumulation increased over the first 50 hours in culture to a maximum rate of 45 milligrams protein synthesized gram protein⁻¹ hour⁻¹. After 50 hours in culture, the rate of protein accumulation decreased to equal the rate of fresh weight accumulation (10 mg g⁻¹ hour⁻¹). However, protein synthesis continued at a high rate for several days, suggesting protein degradation was turned on by this time. By 5 days protein synthesis had decreased to a rate similar to that of callus.     

Genotypic Variation for Glycinebetaine among Public Inbreds of Maize

Screening of a range of public maize (Zea mays L.) inbred lines for glycinebetaine (betaine) content over two growing seasons (1987 and 1988), using fast atom bombardment mass spectrometry, has identified 19 public inbred lines which all exhibit low betaine levels (<100 nanomoles per gram fresh weight). These include common inbreds such as A188, A619, B37, H95, N6, and Oh43. Several inbreds exhibit high betaine levels (3000 to 10000 nanomoles per gram fresh weight); in these strongly betaine-positive inbreds, betaine levels tended to be, on average, 1.38-fold greater in the 1988 growing season presumably in part due to field water deficits experienced during the drought of 1988. Where several different sources of the same inbred line were available (including cytoplasmic male sterile and restored lines of A632, B37, B73, Oh43, and WF9), betaine levels were found to be similar when the inbreds were tested in the same environment. Because W22-R/r-X1 was found to be strongly betaine-positive, it should be possible to map the putative recessive gene(s) determining betaine deficiency to specific chromosome(s) from monosomics resulting from crosses between W22-R/r-X1 and betaine-deficient lines.     

Dopamine production by isolated glomeruli and tubules from rat kidneys

To locate the sites of dopamine (D) production in rat renal cortex, we separated glomeruli and proximal tubules by sieving or centrifugation in Percoll after collagenase digestion. After centrifugation layer I contained 60-80% glomeruli and 20-40% tubule fragments, half of which did not stain with alkaline phosphatase, layer II contained 0-5% glomeruli, 10-25% tubule fragments other than proximal tubules, and 70-85% proximal tubule fragments. Layer IV contained 85-95% proximal tubules. Gluconeogenic rates were (micromoles per hour per gram wet weight) as follows: I, 4 +/- 1; II, 7 +/- 2; and IV, 16 +/- 1. Norepinephrine (NE) content was (picomoles per gram wet weight) I, 310 +/- 30; II, 540 +/- 40; IV, 195 +/- 60. D content was (picomoles per gram wet weight) I, 26 +/- 6; II, 46 +/- 13; IV, 33 +/- 7. Surgical denervation 4-6 days previously reduced the norepinephrine content of layers I and II to 35 +/- 10 (p less than 0.001) and of IV to 60 +/- 20 (p less than 0.05) and the D content of layers I and II to 13 +/- 6 and 6 +/- 6 pmol/g, respectively (p less than 0.01); D content of layer IV was unchanged. D production from 10(-7) M 3,4-dihydroxyphenylalanine (DOPA) was (nanomoles per gram per minute) I, 0.2 +/- 0.03; II, 0.7 +/- 0.1; IV, 1.0 +/- 0.04. DOPA consumption was (nanomoles per gram per minute) I, 0.6 +/- 0.1; II, 1.4 +/- 0.3; and IV, 1.8 +/- 0.2. Denervation did not change D production or DOPA consumption.(ABSTRACT TRUNCATED AT 250 WORDS)     

Canopy and Seasonal Profiles of Nitrate Reductase in Soybeans (Glycine max L. Merr.)

Nitrate reductase activity of soybeans (Glycine max L. Merr.) was evaluated in soil plots and outdoor hydroponic gravel culture systems throughout the growing season. Nitrate reductase profiles within the plant canopy were also established. Mean activity per gram fresh weight per hour of the entire plant canopy was highest in the seedling stage while total activity (activity per gram fresh weight per hour times the total leaf weight) reached a maximum when plants were in the full bloom to midpod fill stage. Nitrate reductase activity per gram fresh weight per hour was highest in the uppermost leaf just prior to full expansion and declined with leaf position lower in the canopy. Total nitrate reductase activity per leaf was also highest in the upper-most fully expanded leaf during early growth stages. Maximum total activity shifted to leaf positions lower in the plant canopy with later growth stages.