Changes in germination, growth and soluble sugar contents of Sorghum bicolor (L.) Moench seeds under various abiotic stresses

The effect of various abiotic stresses on germination rate, growth and soluble sugar content in Sorghum bicolor (L.) Moench cv. CSH 6 seed embryos and endosperm during early germination was investigated. Under stress conditions germination, water potential and tissue water content decreased markedly. Subsequently, this reduction resulted in marked decreases in fresh weight both in embryos and endosperm. Conversely, a substantial increase in dry weight was observed. Furthermore, a considerable increase in the sugar contents in both embryo and endosperm was detected. The fructose level was always higher than glucose and sucrose in response to various stresses. However, as compared to the control the level of glucose and sucrose was higher in embryos and endosperm after stress treatments. Based upon these results a possible physiological role of sugars in the germination of sorghum seeds is discussed.     

Responses to Water Stress in Adapted and Unadapted Carrot Cell Suspension Cultures

The responses of suspension-cultured cells of carrot to polyethyleneglycol (PEG)-induced water stress were studied after transferto culture medium containing PEG at concentrations between 0%and 25%. Growth characteristics, cellular osmotic potentialand organic solute concentration changes were followed in unadaptedcells and in cell lines adapted to growth in various PEG concentrations.A decline in fresh and dry weight increase occurred in unadaptedcells with decreasing water potential, while dry weight gainwas unaffected in adapted lines. Substantial osmotic adjustmentwas observed in adapted lines, due mainly to increased glucose,fructose and sucrose. Proline concentration increased up to40-fold in adapted and 12-fold in unadapted cells and otheramino acids including alanine, histidine and arginine showedsimilar, though smaller, responses. Polyamines and glycinebetainedid not increase significantly in either adapted or unadaptedcells. Changes leading to long-term adaptation to water stressare discussed in relation to short-term stress—shock responses. Key words: Water stress, cell culture, Daucus carota, osmotic adaptation, solute accumulation     

The Effect of Sugars and Polyols on the Heat Resistance of Salmonellae

S ummary . The heat resistance at 65° of 3 strains of salmonellae in solutions of sugars or polyols was enhanced as the concentration of the solutes increased. There was no linear relationship between heat resistance and water activity ( a_w ), but for all solutes except glycerol there was a linear relationship between log D ₆₅ and concentration (% w/w) of solute. Comparison of D ₆₅ at a particular a_w or percentage (w/w) solute concentration showed that the value decreased in the order: sucrose > glucose > sorbitol > fructose > glycerol. In glycerol, D ₆₅ values were always very much lower than in any other solute. With sucrose–glycerol or sucrose–glucose mixtures, heat resistance depended both on the total concentration (% w/w) of solutes present and also on the a_w of the solution.     

Solute accumulation, solute potential, germinability and seedling vigour of seeds of finger millet (Eleusine coracana Gaertn.) raised under rain-fed conditions and under irrigation

Abstract The nature of the solutes accumulated in the grains of ten finger millet genotypes grown under rain-fed conditions with moisture stress during panicle and grain development were determined. Although grain yield decreased under stress, the solute potential (SP) of seeds from stressed plants was significantly lower (more negative), probably due to the increase in sucrose content. There were no significant changes in the content of total amino acids, free proline, reducing sugars or potassium. The contribution of sucrose to total solute potential was approximately 32% in seeds obtained from stressed plants as compared with only 15% in seeds from irrigated treatment. The germinability and seedling vigour of the seeds from stressed plants was significantly higher under simulated stress with polyethylene glycol (PEG), but was similar to that of seeds of non-stressed plants under normal conditions.     

Osmoregulation,solute distribution,and growth in soybean seedlings having low water potentials

Soybean (Glycine max (L.) Merr.) seedlings osmoregulate when the supply of water is limited around the roots. The osmoregulation involves solute accumulation (osmotic adjustment) by the elongating region of the hypocotyls. We investigated the relationship between growth, solute accumulation, and the partitioning of solutes during osmoregulation. Darkgrown seedlings were transplanted to vermiculite containing 1/8 (0.13 x) the water of the controls. Within 12–15 h, the osmotic potential of the elongating region had decreased to-12 bar, but it was-7 bar in the controls. This osmoregulation involved a true solute accumulation by the hypocotyls, since cell volume and turgor were virtually the same regardless of the water regime. The hypocotyls having low water potentials elongated slowly but, when deprived of their cotyledons, did not elongate or accumulate solute. This result indicated a cotyledonary origin for the solutes and a dependence of slow growth on osmotic adjustment. The translocation of nonrespired dry matter from the cotyledons to the seedling axis was unaffected by the availability of water, but partitioning was altered. In the first 12 h, dry matter accumulated in the elongating region of the 0.13 x hypocotyls, and osmotic adjustment occurred. The solutes involved were mostly free amino acids, glucose, fructose, and sucrose, and these accounted for most of the increased dry weight. After osmotic adjustment was complete, dry matter ceased to accumulate in the hypocotyls and bypassed them to accumulate in the roots, which grew faster than the control roots. The proliferation of the roots resulted in an increased root/shoot ratio, a common response of plants to dry conditions.Osmotic adjustment occurred in the elongating region of the hypocotyls because solute utilization for growth decreased while solute uptake continued. Adjustment was completed when solute uptake subsequently decreased, and uptake then balanced utilization. The control of osmotic adjustment was therefore the rate of solute utilization and, secondarily, the rate of solute uptake. Elongation was inhibited by unknown factors(s) despite the turgor and substrates associated with osmotic adjustment. The remaining slow elongation depended on osmotic adjustment and represented some optimum between the necessary inhibition for solute accumulation and the necessary growth for seedling establishment.     

Physical Responses of Yeast Cells to Osmotic Shock

Shock exposure of the osmophilic yeasts Saccharomyces rouxii, Torulopsis globosa and T. apicola to solutions of sucrose and polyethylene glycol of MW 200 (PEG 200) at water activity ( a_w ) values between 0.88 and 0.98 caused gradual changes in cell volumes in the test solutions, though cell volumes were consistently lower in PEG 200. Non-osmophilic yeasts, Sacch. cerevisiae , bakers'yeast and Schizosaccaromyces pombé showed responses similar to the osmophiles in sucrose solutions only, as cells in PEG 200 apparently equilibrated with external osmotic pressures by uptake of solute. Optical densities of cell suspensions supported the findings on cell volumes. Viability tests at the highest and lowest solute concentrations indicated that all test organisms withstood the osmotic shock over the test period. As the theoretical relationship between a_w and osmotic pressure breaks down in concentrated solutions, it is considered that the water relations of yeasts should not be considered exclusively in terms of a_w , but also in conjunction with osmotic pressure and solute uptake.     

Effects of accumulation of 3-O-methylglucose on growth and osmotic regulation in Chlorella emersonii

Abstract. The effect of accumulation of 3- O -methylglucose (MG) on growth and steady-stale concentrations of the endogenous osmotic solutes proline and sucrose was studied in Chlorella emersonii grown at external osmotic pressure (II) of 0.08-1.64 MPa. NaCL was used as osmoticum. The total solute content of the cells was manipulated by supplying 2 mol m⁻³ MG for 4 and 48 h. MG accumulated to 50–230 mol m⁻³ within 4h and was not metabolized. Uptake of MG resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high II. After 4 or 48 h growth in the presence of MG, the decreases in concentration of proline and sucrose were as predicted from the contribution of MG to the total solute content of the cell.     

Physiological response of Pseudomonas putida S12 subjected to reduced water activity

Abstract The effect of osmotic stress, given as decreased water activity (a_w), on growth and the accumulation of potassium and the compatible solute betaine by Pseudomonas putida S12 was investigated. Reduced a_w was imposed by addition of sodium chloride, sucrose, glycerol or polyethylene glycol to the growth medium. Accumulation of potassium and betaine was established when sodium chloride and sucrose were used to cause osmotic stress. No accumulation of these solutes was found in the presence of glycerol. Addition of polyethylene glycol to the medium strongly decreased the growth rate in comparison with the other osmolytes tested at the corresponding a_w. Although polyethylene glycol did decrease the a_w, neither potassium nor betaine was accumulated by the cells.     

Water relations and osmotic adjustment in Lycopersicon esculentum and L. pennellii during short-term salt exposure and recovery

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P-73 and its wild salt-tolerant relative L. pennellii (Correll) D'Arcy accession PE-47 growing on silica sand in a growth chamber were exposed to 0, 70, 140 and 210 m M NaCl nutrient solutions 35 days after sowing. The saline treatments were imposed for 4 days, after which the plants were rinsed with distilled water. Salinity in L. esculentum reduced leaf area and leaf and shoot dry weights. The reductions were more pronounced when sodium chloride was removed from the root medium. Reduction in leaf area and weight in L. pennellii was only observed after the recovery period. In both genotypes salinity induced a progressive reduction in leaf water potential and leaf conductance. During the recovery period leaf water potential (ψ₁) and leaf conductance (g₁) reached levels similar to those of control plants in wild and cultivated species, respectively. Leaf osmotic potential at full turgor (ψ_os) decreased in the salt treated plants of both genotypes, whereas the bulk modulus of elasticity was not affected by salinity. Leaf water potential at turgor loss point (ψ_tlp) and relative water content at turgor loss point (RWC_tlp) appeared to be controlled by leaf osmotic potential at full turgor (ψ_os) and by bulk modulus of elasticity, respectively. At lowest salinity, the wild species carried out the osmotic adjustment based almost exclusively on Cl⁻ and Na⁺, with a marked energy savings. Under highest salinity, this species accommodate the stress through a higher expenditure of energy due to the contribution of organic solutes to the osmotic adjustment. The domesticated species carried out the osmotic adjustment based always on an important contribution of organic solutes.     

Effect of hydropriming on Trigonella foenum callus growth,biochemical traits and phytochemical components under PEG treatment

The induction of secondary metabolites under osmotic stress is well documented. However, cell death is probably due to osmotic stress. This work tries to study the synergetic effect of hydropriming and polyethylene glycol (PEG) on enhancing the secondary metabolites production in fenugreek callus cultures without facing cell death. PEG initiates the stress and the hydropriming increase the plant cell response against the stress. Fenugreek calli were initiated from hypocotyl of two groups of seeds, the first was hydroprimed overnight before germination, the second remained dry. Three months old calli of the two groups were subcultured on media containing two different concentration of PEG (5, 10%). The calli growth, biochemical analysis, secondary metabolism keys, and secondary metabolites were determined after 4 weeks. PE induced oxidative stress, which increased the membrane lipid peroxidation and decreased cell viability and growth. Hydropriming enhanced the activity of antioxidant enzymes, regulating the reactive oxygen species level, accumulating the osmolytes and secondary products. Therefore the primed callus can tolerate the osmotic stress initiated with PEG. Consequently, cell biomass increased and not affected by PEG treatment. On the other hand, the calli from non-primed seeds have a significant decrease in fresh weight, and dry weight under the higher PEG treatment. The hydropriming protected the growth of the cells under PEG treatment with a high content of secondary metabolites and high antioxidant machinery. The synergetic effect of hydropriming and PEG can be used as a simple and low-cost way to produce valuable compounds in commercial industrial bioreactors.

     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.) : IV. Characteristics of the Perisperm during Seed Development

We previously reported that an apparent water potential disequilibrium is maintained late in muskmelon (Cucumis melo L.) seed development between the embryo and the surrounding fruit tissue (mesocarp). To further investigate the basis of this phenomenon, the permeability characteristics of the tissues surrounding muskmelon embryos (the mucilaginous endocarp, the testa, a 2- to 4-cell-layered perisperm and a single cell layer of endosperm) were examined from 20 to 65 days after anthesis (DAA). Water passes readily through the perisperm envelope (endosperm + perisperm), testa, and endocarp at all stages of development. Electrolyte leakage (conductivity of imbibition solutions) of individual intact seeds, decoated seeds (testa removed), and embryos (testa and perisperm envelope removed) was measured during imbibition of freshly harvested seeds. The testa accounted for up to 80% of the total electrolyte leakage. Leakage from decoated seeds fell by 8- to 10-fold between 25 and 45 DAA. Presence of the perisperm envelope prior to 40 DAA had little effect on leakage, while in more mature seeds, it reduced leakage by 2- to 3-fold. In mature seeds, freezing, soaking in methanol, autoclaving, accelerated aging, and other treatments which killed the embryos had little effect on leakage of intact or decoated seeds, but caused osmotic swelling of the perisperm envelope due to the leakage of solutes from the embryo into the space between the embryo and perisperm. The semipermeability of the perisperm envelope of mature seeds did not depend upon cellular viability or lipid membrane integrity. After maximum seed dry weight is attained (35-40 DAA), the perisperm envelope prevents the diffusion of solutes, but not of water, between the embryo and the surrounding testa, endocarp, and mesocarp tissue.     

Response of Split-Root Sour Orange Seedlings to NaCl and Polyethylene Glycol Stresses

Soil water cotent and salinity levels are seldom uniform inthe field, particularly with the use of micro-irrigation systemsthat may water only a portion of the root zone. For studyingnon-uniform salinity, a split-root experiment was designed toevaluate growth and water relations when half of the root systemof sour orange (Citrus aurantium) seedlings was stressed withsodium chloride (NaCl) or polyethylene glycol (PEG). This studyalso determined if non-stressed portions of the root systemcompensated for the decrease in water uptake by the stressedportions. One or both halves of the root system were treated for fourmonths with nutrient solution adjusted with NaCl or PEG to osmoticpotentials of –0.10, –0.20, or –0.35 MPa.Shoot dry weight was reduced by only 9% when half of the rootsystem was irrigated with saline solution at –0.10 MPa,but with both halves of the root system at –0.10 MPa,shoot and root dry weights were reduced as much as 45%. Similarly,leaf water and osmotic potentials were also more disturbed underuniform salinity than under non-uniform salinity conditions. Plant growth, leaf water potential, osmotic potential, stomatalconductance, and evapotranspiration decreased with increasingNaCl and PEG concentrations in the nutrient solution. Turgorpotential and leaf thickness increased in response to NaCl treatments.Microscopic examination showed that the increase in leaf thicknesswas due to the development of larger cells in the spongy mesophyll. Shoot growth did not correlate with the average osmotic potentialof the two root halves. Seedlings with one stressed half-rootsystem had shoot dry weight and leaf water potential valuescloser to those of the non-stressed control than to those withthe completely stressed root system. Key words: Non-uniform salinity, water relations, citrus     

Salinity response of a freshwater charophyte, Chara vulgaris

Abstract. Chara vulgaris L. growing in an oligohaline lake was adapted to laboratory conditions and subjected to long-term salinity treatments ranging from 0 to 350 mol m ³ NaCl added to the lake water (40–680 mosmol kg ¹). Osmotic potential and concentration of the main osmotically active solutes (K⁺, Na⁺, Mg²⁺, Cl and sucrose) in the vacuolar sap of the central internodal cells were estimated. C. vulgaris did regulate turgor but incompletely. Turgor decreased from 335 mosmol kg ¹ under control conditions to 52–111 mosmol kg ¹ at 350 mol m ³ NaCl. The enhancement of πⁱ was achieved by increase in both ions and sucrose. Sterile and fertile plants differed in their response to osmotic stress. In sterile plants, the ions accounted for about 87% of the vacuolar osmotic potential. The increase of πⁱ under osmotic stress was exclusively due to an accumulation of Na⁺ and Cl^-. In fertile plants, sucrose accounted for about 35% of πⁱ and ions for about 51% Under osmotic stress, sucrose content increased together with the ionic content of Na⁺ and Cl^-.     

Changes in the proportion of endogenous osmotic solutes accumulated by Chlorella emersonii in the light and dark

Abstract. The type of endogenous osmotic solute accumulated by Chlorella emersonii grown at high external osmotic pressure (π_ext) depended on the light/dark conditions: proline accumulated to high concentrations in cells in the light, while sucrose accumulated to high concentrations in the dark. These findings were made during the alternating light dark cycles used to obtain synchronized cultures, i.e. cultures containing cells at only one stage of development at any one time. Similar decreases in proline and increases in sucrose in the dark were found for cells previously grown in continuous light to obtain non-synchronized cultures, i.e. cultures containing cells at all stages of development.
In cultures synchronized at 200 mol m ⁻³ NaCl (π_ext= 1.01 MPa), recently divided 'daughter cells' at the beginning of the light periods contained 60 mol m⁻³ proline and 100mol m⁻³ sucrose, while mature cells towards the end of light periods contained 130 mol m proline and 20 mol m⁻³ sucrose. The changes in proline and sucrose which occurred in synchronized cultures were due mainly to light/dark conditions and to a much lesser extent to different stages of cell development. The proportion of proline to sucrose in daughter cells collected from non-synchronized cultures in continuous light was not different from the proportion in heterogeneous populations of cells.
Results are discussed in relation to the accumulations of two, rather than one, endogenous osmotic solute and to growth reductions of C. emersonii exposed to high external osmotic pressures.     

The effect soaking pea seeds with or without seedcoats has on seedling growth

Pea seeds (Pisum sativum L. `Alaska') with intact seedcoats (WC) and with seedcoats removed (WOC) were soaked in distilled water for 24 hours at 20°. The water, containing the pea diffusate, was decanted after the second, fourth, sixth, eighth, twelfth, and twenty-fourth hour and analyzed for total nitrogen, α-amino nitrogen, carbohydrate, and total solute dry weight. The seeds were germinated at 20° in a 16 hour photoperiod of 300 foot candles. Stem lengths and dry weights of roots, shoots and cotyledons were determined after 4, 11, and 18 days of growth. WOC seeds imbibed more water than WC seeds during the 24 hour imbibition period. Diffusates from WOC seeds always contained more solute than diffusates from WC seeds. Maltose, glucose, and fructose were not detected in the early diffusates from WOC seeds but were found in WC seed diffusates at all times. Seedlings from WC seeds had longer stems than those from WOC seeds. The dry weight of stems and roots of WC seedlings was greater than those from WOC seedlings. The dry weight of cotyledons from 18 day-old WC seedlings was less than from WOC seedlings. Water absorption by WC seeds was slower than by WOC seeds. Removal of the seedcoat allowed rapid imbibition resulting in seed injury presumably because of the loss of solutes which included monosaccharides, disaccharides, amino acids, and other nitrogen containing compounds. These results are consistent with the hypothesis that rapid imbibition disrupts membrane organization leading to reduction of seedling growth.     

Multiphasic osmotic adjustment in a euryhaline cyanobacterium

Abstract Transfer of Synechocystis PCC6714 from a freshwater medium to a saline medium caused the cells to shrink; rapid entry of NaCl resulted in a partial recovery of cellular volume within 2 min. Active extrusion of internal Na⁺ in exchange for extracellular K⁺ then occurred (within 20 min). Finally, the low- M _r carbohydrates sucrose and glucosylglycerol were accumulated and internal KC1 levels declined. In long-term growth experiments, the relative importance of sucrose as a component of the low- M _r organic solute fraction decreased and glucosylglycerol became the single most important intracellular solute. These observations demonstrate that several inorganic and organic solutes are involved in osmotic adjustment in this cyanobacterium, with sequential changes in the relative importance of each solute following transfer to a saline medium.     

Effects of accumulation of 3-O-methylglucose on levels of endogenous osmotic solutes in Chlorella emersonii

Abstract. Regulation of the concentration of osmotic solutes was studied in Chlorella emersonii grown at external osmotic pressures (II) ranging between 0.08 and 1.64MPa. NaCl was used as osmoticum. The total solute content of the cells was manipulated by applying 2 mol m⁻³ 3- O -methylglucose (MG), which was not metabolized, and accumulated at concentrations ranging between 60 and 230 mol m⁻³ within 4 h after its addition to the medium. Methylglucose uptake resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high external II. The responses were consistent with the hypothesis that proline and sucrose concentrations are controlled by a system of osmotic regulation, with turgor and/or volume as a primary signal. Short-term experiments showed that even very small increases in turgor and/or volume, due to accumulation of methylglucose, resulted in large decreases in proline and sucrose. Over the first 30-60 min the total solute concentration in the cells increased by at most 15 osmol m⁻³ which would represent an increase in turgor pressure of at most 0.04 M Pa. Yet, the decreases in proline and sucrose were as fast as those in cells exposed to a sudden decrease of 0.25 MPa in external II, when the turgor pressure would have increased by at least 0.15 MPa. High concentrations of methylglucose in cells grown at high II did not affect the rapid synthesis of proline and sucrose which started when the cells were transferred to yet higher II. Thus, methylglucose had no direct effects on proline and sucrose metabolism, and it has been assumed that it acted solely as an inert osmotic solute within the cell.     

Identification of organic solutes accumulated by purple and green sulphur bacteria during osmotic stress using natural abundance 13C nuclear magnetic resonance spectroscopy

Abstract Natural abundance ¹³C NMR spectroscopy has identified sucrose and trehalose as the principle compatible solutes accumulated by non-halophilic purple and green sulphur bacteria respectively, in response to osmotic stress. Synthesis of glycine betaine as a compatible solute was rare in non-halophilic phototrophic sulphur bacteria and appears to be limited almost exclusively to halotolerant isolates, although all isolates tested were able to accumulate exogenous glycine betaine from the growth medium in response to osmotic stress. These data support the hypothesis that the degree of halotolerance of a microorganism may be due, at least in part, to the metabolic effects of the compatible solute(s) accumulated.     

Endosperm protein of wheat seed as a determinant of seedling growth

Seed of a Mexican semidwarf wheat (Triticum aestivum L. cv. Inia 66), was obtained from a nitrogen fertilizer field trial grown in Mexico. A high positive correlation was obtained between seed protein content and seedling dry weight after 3 weeks growth (r = +0.92^**). The seedling dry weight was positively related to the protein content of the aleurone layer and endosperm, but not to the embryo. Small, 35 milligrams, high protein seeds (4.7 milligrams protein per seed) produced larger seedlings than large, 45 milligrams, low protein seeds (4.3 milligram protein per seed). There was no difference in the weight or protein content of embryos from low and high protein seeds and their growth was similar. Composite seeds of the two protein levels were produced by transferring embryos from one endosperm type to the other. After 4 weeks, there was no difference between the different embryo types grown on the same endosperm type. High protein endosperm produced more vigorous seedlings regardless of the embryo type grown on it, indicating that the factor(s) responsible for the greater growth of high protein seed is in the endosperm.     

盐分和水分胁迫对芦荟幼苗渗透调节和渗调物质积累的影响

用不同浓度NaCl和等渗聚乙二醇(PEG 6000)处理芦荟(Aloe vera L.)幼苗,10 d后测定叶片相对生长速率和厚度、叶片中主要有机溶质、无机离子含量及渗透调节能力.结果表明,-0.44、-0.88 MPa NaCl和PEG处理使芦荟叶片的相对生长速率和叶片厚度明显下降,且盐胁迫对幼苗生长的抑制和叶片含水量降低的效应明显高于等渗的水分胁迫,其叶片渗透调节能力随处理渗透势的降低而增加, -0.88 MPa PEG胁迫的芦荟幼苗的渗透调节能力高于等渗盐分胁迫.在主要渗透调节物质可溶性糖、有机酸、K 、Ca2 和Cl-中,-0.88 MPa PEG处理下含量比相同渗透势的NaCl处理下显著增加的是有机溶质,因此推断有机溶质含量高是PEG胁迫下渗透调节能力较强的主要因素.