Expression of lauroyl-acyl carrier protein thioesterase in brassica napus seeds induces pathways for both fatty acid oxidation and biosynthesis and implies a set point for triacylglycerol accumulation

Expression of a California bay lauroyl-acyl carrier protein thioesterase (MCTE) in developing seeds of transgenic oilseed rape alters the fatty acid composition of the mature seed, resulting in up to 60 mol% of laurate in triacylglycerols. In this study, we examined the metabolism of lauric acid and 14C-acetate in developing seeds of oilseed rape that express high levels of MCTE. Lauroyl-CoA oxidase activity but not palmitoyl-CoA oxidase activity was increased several-fold in developing seeds expressing MCTE. In addition, isocitrate lyase and malate synthase activities were six- and 30-fold higher, respectively, in high-laurate developing seeds. Control seeds incorporated 14C-acetate almost entirely into fatty acids, whereas in seeds expressing MCTE, only 50% of the label was recovered in lipids and the remainder was in a range of water-soluble components, including sucrose and malate. Together, these results indicate that the pathways for beta-oxidation and the glyoxylate cycle have been induced in seeds expressing high levels of MCTE. Although a substantial portion of the fatty acid produced in these seeds is recycled to acetyl-CoA and sucrose through the beta-oxidation and glyoxylate cycle pathways, total seed oil is not reduced. How is oil content maintained if lauric acid is inefficiently converted to triacylglycerol? The levels of acyl carrier protein and several enzymes of fatty acid synthesis were increased two- to threefold at midstage development in high-laurate seeds. These results indicate that a coordinate induction of the fatty acid synthesis pathway occurs, presumably to compensate for the lauric acid lost through beta-oxidation or for a shortage of long-chain fatty acids.     

A transfer of carbon atoms from fatty acids to sugars and amino acids in yellow lupine (Lupinus luteus L.) seedlings

The metabolism of 14C-acetate was investigated during the in vitro germination of yellow lupine seeds. Carbon atoms (14C) from the C-2 position of acetate were incorporated mainly into amino acids: aspartate, glutamate, and glutamine and into sugars: glucose, sucrose, and fructose. In contrast to this, 14C from the C-1 position of acetate was released mainly as 14CO2. Incorporation of 1-14C and 2-14C from acetate into amino acids and sugars in seedling axes was more intense when sucrose was added to the medium. However, in cotyledons where lipids are converted to carbohydrates, this process was inhibited by exogenous sucrose. Since acetate is the product of fatty acid beta-oxidation, our results indicate that, at least in lupine, seed storage lipids can be converted not only to sucrose, but mainly to amino acids. Inhibitory effects of sucrose on the incorporation of 14C from acetate into amino acids and sugars in cotyledons of lupine seedlings may be explained as the effect of regulation of the glyoxylate cycle by sugars.     

Lipid peroxidation, carbohydrate hydrolysis, and Amadori-Maillard reaction at early stages of dry seed aging

Processes underlying aging of air-dry seeds were investigated. Naturally aged seeds of pea (Pisum sativum L.), cucumber (Cucumis sativus L.), and buckwheat (Fagopyrum esculentum Moench.) were separated into three fractions of different quality according to their room temperature phosphorescence (RTP): fraction I contained strong seeds; fraction II comprised weak seeds; and fraction III was composed of dead seeds. These seed fractions were used to identify the processes in air-dry seeds that account for the initial deterioration in seed quality at early stages of aging and for the possible transient improvement of seed quality at further aging. Experiments with seed powders showed that the increase in thermochemiluminescence (TCL) in the temperature range of 50?C110°C was determined by the presence of lipid peroxidation products. No difference was observed between TCL levels in fraction I and fraction II seeds; hence, lipid peroxidation is not responsible for the transition of strong seeds to the fraction of weak seeds. The TCL intensity monitored upon heating in the range of 50?C110°C increased only in the fraction of dead seeds. In fraction II seeds, a twofold increase in TCL upon heating at 150°C was observed in aged seeds; this indicates that the products of oligosaccharide hydrolysis (glucose) were more abundant in fraction II seeds than in fraction I seeds under similar conditions. This assumption was confirmed by direct determination of glucose content with a glucometer. Hence, the transition of air-dry seeds from fraction I (strong seeds) to fraction II (weak seeds) occurred due to the activation of carbohydrate hydrolysis in aging seeds. Since air-dry seeds contain no free water during aging, the seed moisture content decreases during hydrolysis, presumably, because the bound water participates in the hydrolysis reaction. The decrease in ??improved?? seeds of glucose content and the increase in moisture content suggest the activation of amino-carbonyl reaction. It is proposed that the amino-carbonyl (Amadori-Maillard) reaction is responsible for closing water channels in improved seeds, as well as for the decreased water permeability of cell membranes during seed imbibition.     

Short-term effects of thyroid hormones on lipogenic enzymes and 14C-acetate incorporation into various lipid classes: in vivo and in vitro studies

Short-term effect of 3,5,3'-triiodothyronine (T3) and 3,5-diiodothyronine (T2) on lipid metabolism in the liver of Anabas testudineus was examined. In vivo injections of both T3 and T2 at a concentration of 10 ng/g body weight increased malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) activity compared to 6-propylthiouracil (6-PTU) treated group. Treatment of 6-PTU results in the accumulation 14C-acetate into fat and thyroid hormones' treatment reduce it. In vitro experiments show that malic enzyme activity is augmented only by high concentration of T3 (10(-7) M) where as all concentrations of T2 increase its activity. In vitro studies with T3 showed a biphasic effect on cholesterol content. Conversely T2 in vitro, reduced cholesterol content with all concentrations. From these results it can be concluded that both T3 and T2 have short-term effect on lipid metabolism in Anabas.     

Mechanisms for Soil Moisture Effects on Activity of Nitrifying Bacteria

Moisture may limit microbial activity in a wide range of environments including salt water, food, wood, biofilms, and soils. Low water availability can inhibit microbial activity by lowering intracellular water potential and thus reducing hydration and activity of enzymes. In solid matrices, low water content may also reduce microbial activity by restricting substrate supply. As pores within solid matrices drain and water films coating surfaces become thinner, diffusion path lengths become more tortuous, and the rate of substrate diffusion to microbial cells declines. We used two independent techniques to evaluate the relative importance of cytoplasmic dehydration versus diffusional limitations in controlling rates of nitrification in soil. Nitrification rates in shaken soil slurries, in which NH(inf4)(sup+) was maintained at high concentrations and osmotic potential was controlled by the addition of K(inf2)SO(inf4), were compared with rates in moist soil incubations, in which substrate supply was controlled by the addition of NH(inf3) gas. Comparison of results from these techniques demonstrated that diffusional limitation of substrate supply and adverse physiologic effects associated with cell dehydration can explain all of the decline in activity of nitrifying bacteria at low soil water content. However, the relative importance of substrate limitation and dehydration changes at different water potentials. For the soil-microbial system we worked with, substrate limitation was the major inhibiting factor when soil water potentials were greater than -0.6 MPa, whereas adverse physiological effects associated with cell dehydration were more inhibiting at water potentials of less than -0.6 MPa.     

Developmental Changes in Relation to Desiccation Tolerance of Archontophoenix alexandrae (Palmae) Seeds

Germination of Archontophoenix alexandrae seeds and embryos were studied under gradient water content treatments throughout the seed development phases of maturation in 2005 to investigate seed desiccation tolerance and storage characteristics. During the maturation process, seed water content decreased gradually from55 DAF (days after flowering) to 70 DAF, and seeds reached the maximum dry-weight at 90 DAF. Seed germinability appeared after 60 DAF. Seeds germinated with a temperature range from15℃- 40℃ under alternating photoperiod (14 h light, 10 h dark, 12μmol m^{- 2}s ^{- 1} ), while the best germination percentage was obtained between 30℃- 35℃. A maximum germination capacity reached at 70 DAF. However, seed germination was greatly inhibited by light. Desiccation tolerance of seeds and embryos increasedgradually from 55 DAF to 90 DAF and reached the maximum at 90 DAF with a semilethal water content of 0.18 g/g ( seed) and 0.3 g/g ( embryo) respectively. Rapid dehydration maintained higher seed germination percentage than thatof slow dehydration when drying to the same water content. Seeds with without water content treatments failed to germinate after 1 month storage under - 18℃, whereas appropriate desiccation treatment prolonged seed longevity under 4℃, 10℃ and 15℃ storage temperatures. It revealed obviously the recalcitrant characteristics of Archontophoenix alexandrae seeds torage behaviour which are tolerant toward neither deep desiccation nor low temperatures.     

Anaerobic metabolism of immediate methane precursors in Lake Mendota.

Lake Mendota sediments and the immediate overlying water column were studied to better understand the metabolism of the methanogenic precursors H2/CO2 and acetate in nature. The pool size of acetate (3.5 microns M) was very small, and the acetate turnover time (0.22h) was very rapid. The dissolved inorganic carbon pool was shown to be large (6.4 to 8.3 mM), and the turnover time was slow (111 H.). CO2 was shown to account for 41 +/- 5.5% of the methane produced in sediment. Acetate and H2/CO2 were simultaneously converted to CH4. The addition of H2 to sediments resulted in an increase specific activity of CH4 from H(14)CO3- and a decrease in specific activity of CH4 from [2-14C]acetate. Acetate addition resulted in a decrease in specific activity of CH4 from H(14)CO3-. The metabolism of H(14)CO3- or [2-14C]acetate to 14CH4 was not inhibited by addition of acetate or H2. After greater than 99% of added [2-14C]acetate had been turned over, 42% of the label was recovered as 14CH4 20% was recovered as 14CO2 and 38% was incorporated into sediment. Inhibitor studies of [2-14C]acetate metabolism in sediments demonstrated that CHCl3 completely inhibited CH4 formation, but not CO2 production. Air and nitrate addition inhibited CH4 formation and stimulated CO2 production, whereas fluoroacetate addition totally inhibited acetate metabolism. The oxidation of [2-14C]acetate to 14CO2 was shown to decrease with time when sediment was incubated before the addition of label, suggesting depletion of low levels of an endogenous sediment electron acceptor. Acetate metabolism varied seasonally and was related to the concentration of sulfate in the lake and interstitial water. Methanogenesis occurred in the sediment and in the water immediately overlying the sediment during period of lake stratification and several centimeters below the sediment-water interface during lake turnovers. These data indicate that methanogenesis in Lake Mendota sediments was limited by "immediate" methane precursor availability (i.e., acetate and H2), by competition for these substrates by nonmethanogens, and by seasonal variations which altered sediment and water chemistry.     

Anaerobic metabolism of immediate methane precursors in Lake Mendota.

Lake Mendota sediments and the immediate overlying water column were studied to better understand the metabolism of the methanogenic precursors H2/CO2 and acetate in nature. The pool size of acetate (3.5 microns M) was very small, and the acetate turnover time (0.22h) was very rapid. The dissolved inorganic carbon pool was shown to be large (6.4 to 8.3 mM), and the turnover time was slow (111 H.). CO2 was shown to account for 41 +/- 5.5% of the methane produced in sediment. Acetate and H2/CO2 were simultaneously converted to CH4. The addition of H2 to sediments resulted in an increase specific activity of CH4 from H(14)CO3- and a decrease in specific activity of CH4 from [2-14C]acetate. Acetate addition resulted in a decrease in specific activity of CH4 from H(14)CO3-. The metabolism of H(14)CO3- or [2-14C]acetate to 14CH4 was not inhibited by addition of acetate or H2. After greater than 99% of added [2-14C]acetate had been turned over, 42% of the label was recovered as 14CH4 20% was recovered as 14CO2 and 38% was incorporated into sediment. Inhibitor studies of [2-14C]acetate metabolism in sediments demonstrated that CHCl3 completely inhibited CH4 formation, but not CO2 production. Air and nitrate addition inhibited CH4 formation and stimulated CO2 production, whereas fluoroacetate addition totally inhibited acetate metabolism. The oxidation of [2-14C]acetate to 14CO2 was shown to decrease with time when sediment was incubated before the addition of label, suggesting depletion of low levels of an endogenous sediment electron acceptor. Acetate metabolism varied seasonally and was related to the concentration of sulfate in the lake and interstitial water. Methanogenesis occurred in the sediment and in the water immediately overlying the sediment during period of lake stratification and several centimeters below the sediment-water interface during lake turnovers. These data indicate that methanogenesis in Lake Mendota sediments was limited by "immediate" methane precursor availability (i.e., acetate and H2), by competition for these substrates by nonmethanogens, and by seasonal variations which altered sediment and water chemistry.     

Pre-treatment of seeds with static magnetic field ameliorates soil water stress in seedlings of maize (Zea mays L.)

The effect of magnetic field (MF) treatments of maize (Zea mays L.) var. Ganga Safed 2 seeds on the growth, leaf water status, photosynthesis and antioxidant enzyme system under soil water stress was investigated under greenhouse conditions. The seeds were exposed to static MFs of 100 and 200 mT for 2 and 1 h, respectively. The treated seeds were sown in sand beds for seven days and transplanted in pots that were maintained at -0.03, -0.2 and -0.4 MPa soil water potentials under greenhouse conditions. MF exposure of seeds significantly enhanced all growth parameters, compared to the control seedlings. The significant increase in root parameters in seedlings from magnetically-exposed seeds resulted in maintenance of better leaf water status in terms of increase in leaf water potential, turgor potential and relative water content. Photosynthesis, stomatal conductance and chlorophyll content increased in plants from treated seeds, compared to control under irrigated and mild stress condition. Leaves from plants of magnetically-treated seeds showed decreased levels of hydrogen peroxide and antioxidant defense system enzymes (peroxidases, catalase and superoxide dismutase) under moisture stress conditions, when compared with untreated controls. Mild stress of -0.2 MPa induced a stimulating effect on functional root parameters, especially in 200 mT treated seedlings which can be exploited profitably for rain fed conditions. Our results suggested that MF treatment (100 mT for 2 h and 200 for 1 h) of maize seeds enhanced the seedling growth, leaf water status, photosynthesis rate and lowered the antioxidant defense system of seedlings under soil water stress. Thus, pre sowing static magnetic field treatment of seeds can be effectively used for improving growth under water stress.     

Hypoxia and Imbibition Injuries to Aging Seeds

The development of hypoxia and primary injuries were examined during the imbibition of aging pea seeds (Pisum sativum L., cv. Nemchinovskii). The distribution of air-dry pea seeds by their room-temperature phosphorescence revealed the presence of two fractions (I and II) in a seed lot with 72% germinability and three fractions (I, II, and III) in a seed lot with 50% germinability. The water uptake during imbibition was slower in the fraction I seeds than in the fraction-II seeds. The fraction-I seeds produced normal seedlings, whereas the fraction-II seeds either produced seedlings with morphological defects (abnormal) or did not germinate at all. The fraction-III seeds were all dead. The phosphorescence of endogenous porphyrins, emitted only at low O₂ content, was measured after 20-h seed imbibition. The fraction-I seeds emitted no discernible phosphorescence. The fraction-II comprised highly phosphorescent seeds incapable of radicle protrusion and moderately phosphorescent seeds producing abnormal seedlings. The fraction-II seeds experienced hypoxia during the imbibition because of rapid oxygen consumption by the embryo and restrictions to O₂ diffusion imposed by the seed coat. In the fraction-I seeds, the rate of oxygen consumption by the embryo was slower and the seed coat resistance to oxygen diffusion was lower than in the fraction-II seeds. Therefore, hypoxia did not arise in the fraction-I seeds. The submergence of seeds in water caused lethal injuries. The imbibition of seeds without any contact with water caused no lethal damages but did not reduce the percentage of seeds dying of hypoxia. A slow imbibition of seeds in the media containing either an osmoticum (PEG) or an inhibitor of aquaporin channels (p-chloromercuribenzoate) prevented the lethal injuries at early stages of seed hydration and retarded the appearance of oxygen deficiency in fraction-II seeds. Different rates of water uptake by fraction-I and fraction-II seeds were controlled by permeability of cell membranes rather than by permeability of seed coat. It is proposed that low permeability of plasma membranes to water in fraction-I seeds results from the predominantly closed aquaporin channels, whereas a higher permeability of weak seeds (fraction II) is due to open channels.     

Control of exercise hyperpnea during hypercapnia in humans

Previous studies have yielded conflicting results on the ventilatory response to CO2 during muscular exercise. To obviate possible experimental errors contributing to such variability, we have examined the CO2-exercise interaction in terms of the ventilatory response to exercise under conditions of controlled hypercapnia. Eight healthy male volunteers underwent a sequence of 5-min incremental treadmill exercise runs from rest up to a maximum CO2 output (VCO2) of approximately 1.5 l . min-1 in four successive steps. The arterial PCO2 (PaCO2) at rest was stabilized at the control level or up to 14 Torr above control by adding 0-6% CO2 to the inspired air. Arterial isocapnia (SD = 1.2 Torr) throughout each exercise run was maintained by continual adjustment of the inspired PCO2. At all PaCO2 levels the response in total ventilation (VE) was linearly related to exercise VCO2. Hypercapnia resulted in corresponding increases in both the slope (S) and zero intercept (V0) of the VE-VCO2 curve; these being directly proportional to the rise in PaCO2 (means +/- SE: delta S/ delta PaCO2, 2.73 +/- 0.28 Torr-1; delta V0/ delta PaCO2, 1.67 +/- 0.18 l . min-1 . Torr-1). Thus the ventilatory response to concomitant hypercapnia and exercise was characterized by a synergistic (additive plus multiplicative) effect, suggesting a positive interaction between these stimuli. The increased exercise sensitivity in hypercapnia is qualitatively consistent with the hypothesis that VE is controlled to minimize the conflicting challenges due to chemical drive and the mechanical work of breathing (Poon, C. S. In: Modelling and Control of Breathing, New York: Elsevier, 1983, p. 189-196).     

The laboratory germination of crisp lettuce seeds under moisture stress

Seeds of the crisp lettuce cultivar Pennlake were germinated using all combinations of six ‘initial’ solutions of polyethylene glycol 6000 (PEG) with osmotic potentials ranging from 0 to -8 bars and seven ‘secondary’ solutions of PEG with osmotic potentials ranging from 0 to -10 bars, to which seeds were moved after 24 or 48 h in the ‘initial’ solution. The number of seeds germinating decreased at more negative osmotic potentials of both ‘initial’ and ‘secondary’ solutions but there was an interaction between germination temperature and the osmotic potential of the ‘initial’ solution. At an ‘initial’ solution osmotic potential of 0 bars germination at 20°C exceeded that at 10°C. As the osmotic potential of the ‘initial’ solution decreased germination at 20°C decreased more than at 10°C so that at the more negative osmotic potentials germination at 10°C exceeded that at 20°C. However seeds ungerminated after 14 days germinated normally when transferred back to water, so that the average final germination was 99.5%. The results suggest that major fluctuations in soil water potential in a seedbed are unlikely to influence seed germination per se provided that a period of 24 to 48 h at 0 bars tension is available at some time. The timing of such a period relative to sowing will have a considerable effect on the time of germination and hence the time of emergence. It is concluded that factors other than the direct effect of soil moisture content on germination are involved in reducing seedling emergence under fluctuating soil moisture conditions in the field.     

Dormancy in Seeds of Charlock (Sinapis arvensis L.): Early Effects of Gibberellic Acid on the Synthesis of Amino Acids and Proteins

Charlock (Sinapis arvensis L.) seeds were imbibed with 10 mm GA(3) for 24 hours at 0 C. After equilibration at 25 C, a 5-fold increase in radioactivity in the amino acids labeled from 2-(14)C-acetate was observed within 2 hours. The total amount of amino acids was reduced to half, and the specific radioactivity increased approximately 10-fold, indicating a diversion of metabolites for amino acid and protein synthesis in GA(3)-treated seeds. The rate of incorporation of l-(14) C-leucine into protein was doubled. Autoradiographs showed that enhancement of protein synthesis was localized in the shoot and root meristems, the developing vascular tissues, and in the endosperm cells inside the testa.     

Effects of Controlled Deterioration and Osmoconditioning on Germination and Nuclear Replication in Seeds of Pepper (Capsicum annuumL.)

Unaged and controlled deteriorated (45°C for 4, 6 or 10 d) samples of a pepper seed lot were subjected to osmoconditioning in PEG at osmotic potentials of -1.1 and -1.5MPa for 6, 10 or 14d. The effect of osmoconditioning on nuclear replication activity was examined using flow cytometry.Priming of unaged seeds always induced nuclei of embryo root tips to enter the synthetic phase. In accordance with our previous findings the amount of induced nuclear replication activity was higher after priming at the lowest osmotic potential. Under the same osmotic potential the amount of priming-induced replication was correlated with the length of priming treatment and its efficiency in improving seed performance. However, the 14d treatment at -1.5MPa was as effective on seed performance as the 6d treatment at -1.1MPa, which induced higher numbers of nuclei to enter the synthetic phase.Osmoconditioning on controlled deteriorated seeds had different effects on seed germination depending on the degree of seed deterioration. Under the same osmotic treatment, the amount of priming-induced DNA synthesis was lower than in unaged seeds or was not induced at all. The activation of nuclear replication by osmoconditioning, therefore, appears influenced by the level of seed deterioration. In less deteriorated seeds (45°C for 4d), 14d priming at -1.1MPa caused shortening of mean germination time compared with unaged seeds, but was less effective in inducing nuclear replication.The effect of the length and osmotic potential of priming on nuclear replication and the role of molecular processes, other than DNA synthesis, in improving seed performance are discussed.     

Pitfalls in using sodium hypochlorite as a seed disinfectant in C incorporation studies

Seeds sterilized with sodium hypochlorite (NaOCl) retained sufficient amounts to interfere with studies of amino acid metabolism of the sterilized seeds during germination. Repeated washing in water did not remove NaOCl completely. However, soaking the seeds for 10 min in 0.01 n HCl removed NaOCl completely, without reducing germinability.Residual NaOCl reacted with the amino acids and reduced their concentrations in the incubation media. This reaction resulted in high production of CO(2) and low uptake of amino acids by the seeds. Decarboxylation of the amino acids occurred in the incubation medium outside the seed, was independent of the presence of seeds in the reaction, and therefore was not related to amino acid metabolism by the seeds. Effects of NaOCl on uptake, incorporation, and CO(2) production from indoleacetic acid were similar to those of the amino acids studied.     

Lipid participation in intracellular freezing avoidance mechanisms of lettuce seed

Freeze-fracture electron microscopy was used to study water content related freezing resistance in Grand Rapids lettuce seeds. Consistent and recognizable conformational changes occurred in lipid-water phases of lettuce seeds at different moisture contents. In air-dry lettuce seed cotyledons, the lipids lying in spherical lipid bodies near the cell wall appeared amorphous, while the structure was crystalline above 20% water content. The lipid bodies interassociated into membrane bilayers in seeds containing 20 to 25% water. Such lyotropic phase transitions in membrane lipids during lettuce seed hydration are believed to contribute to the biphasic freezing behavior observed in lettuce seeds at different moisture contents and to provide a natural freezing tolerance mechanism for highly desiccated plant tissues such as seeds.     

Canola seed germination and seedling emergence from pre-hydrated and re-dried seeds subjected to salt and water stresses at low temperatures

Low soil temperatures and low water potentials reduce and delay the seed germination of canola (Brassica rapa L., B. napus L.) in western Canada. Germination is also very sensitive to the salinity effects of nitrogen fertiliser placed with the seed, especially when the seed bed is relatively dry. The effects of pre-hydration and re-drying treatment on canola (Brassica rapa L. cv. Tobin) seed germination and seedling emergence at 10°C subjected to either a water or salt stress were determined. Low water potentials, induced by polyethylene glycol (PEG 8000), low soil moisture, or high concentrations of salts, reduced both germination and seedling emergence, and increased the time to 50% germination and emergence of seeds at 10°C. At equal osmotic potentials, Na₂SO₄ was less inhibitory on low temperature germination than either NaCl or PEG, suggesting that the sulphate ion partially alleviated the inhibitory effects of low water potential. Solutions of NaCI produced more abnormal seedlings compared to Na₂SO₄, suggesting that NaCl was more toxic than Na₂SO₄ during seedling development. Pre-hydration and re-drying partially overcame the inhibitory effects of both low water potential and salts on seed germination and seedling emergence at 10°C. The seed treatment increased the germination rate in Petri dishes and seedling emergence from a sandy loam soil. Water potentials or soil water contents required to inhibit 50% germination or emergence at 10°C were lower for treated seeds compared to control seeds. Salt concentrations inhibiting 50% emergence were higher for treated seeds than control seeds. Neither treated nor control seeds produced seedlings which emerged if the soil water content was lower than 9% or when the soil was continuously irrigated with salt solutions of 100 mmol kg^-1 of NaCl or 50 mmol kg^-1 of Na₂SO₄. These results suggest that the pre-hydration and re-drying treatment did not lower the base water potentials at which seedling emergence could occur. Abnormal seedlings were observed in both treated and control seeds, particularly if the soil was watered with NaCl solutions; however, the seed treatment reduced the number of abnormal seedlings.     

Measurement of the Water Potential of Intact Plant Tissues2PISUM SATIVUM L.)

Through the use of a microthermocouple psychrometer it has becomepossible to measure the water potential over part of the surfaceof a pea seed, starting about 19 hours after sowing in distilledwater, or later in the case of seeds germinating at lower osmoticpotentials, in both instances until well after radicles haveemerged. It has been shown that the potential of air-dry seedsis well below –6,000 joules/kg but increases rapidly duringimbibition, depending upon the water potential of the germinationmedium. Pea seeds subjected to lower external water potentialsgerminate at lower internal water potentials than they exhibitin distilled water. The water potentials of the seeds decreasejust after radicle emergence till the radicle establishes contactwith its germination medium, possibly as a result of demandfor moisture during that period due to incipient cell elongation.No detectable amounts of osmotically active substances are exudedfrom the seed during germination; the pea seed coat restrictsthe entry of polyethylene glycol molecules into the seed untilemergence of the radicle.     

Energy metabolism of sea urchin spermatozoa, with phosphatidylcholine as the preferred substrate

Phosphatidylcholine content in the spermatozoa of the sea urchin, Hemicentrotus pulcherrimus, decreased rapidly during incubation with sea water. Sea urchin sperm contained approx. 85% phospholipid in total lipid. Phosphatidylcholine (PC) was the principal lipid. Other phospholipids, however, remained at constant levels during incubation. Although the free fatty acid content gradually increased following dilution of dry sperm in sea water, the amounts of triacylglycerol and cholesterol ester were extremely low. Analysis by gas-liquid chromatography indicated most of fatty acid moieties in PC to be polyenoic. PC composed in part of unsaturated fatty acids was consumed to a greater extent during incubation than that consisting of saturated fatty acids. Furthermore, 1-palmitoyl-2-[1-14C]linoleoylphosphatidylcholine was transformed to 14C-labelled free fatty acid in a subcellular system. Thus, possibly, phospholipase A2 is present in sea urchin sperm. Also, [1-14C]oleic acid was immediately oxidized to 14CO2 by sperm. It is thus concluded that sea urchin sperm use phosphatidylcholine as a substrate for energy metabolism.     

Ample germination ability under wide‐ranging environmental conditions in a common understory tropical palm

Although palms play an important ecological role in tropical forests, characteristics related to their germinative niche remain largely unknown. We evaluated the seed germination characteristics of Geonoma schottiana, an abundant palm in the understory of different ecosystems of the Atlantic Rain Forest biome and the gallery forests of the Cerrado biome. We conducted experiments under light and dark conditions at Ψ = 0 MPa, and under two low‐water‐potential conditions and a flooded condition. Seed germination was highest at Ψ = 0 MPa under light (72%) and dark (67%) conditions. We observed moderate (51%) and low (18%) seed germination at Ψ = ?0.4 and ?0.8 MPa. About 20% of ungerminated seeds subjected to low water potentials for 300 days remained viable. No seeds germinated under flooded conditions; however, 23% of them maintained germinability. A delay in seed germination time was observed at low water potentials and an increase in synchrony occurred at Ψ = ?0.8 MPa. G. schottiana seeds did not require specific light conditions to germinate, and the species possesses germinative characteristics to cope with deficit and excess of water. Probably, this wide germination niche allows for its seeds to germinate over a wide range of habitats in different types of ecosystems.