Persistence of red light induction in lettuce seeds of varying hydration

Incubation of lettuce seeds (Lactuca sativa L. cv. Grand Rapids) in 0.3 m mannitol allows sufficient water uptake to make seeds fully sensitive to red light. But germination is possible only after lowering the osmotic potential of the incubation medium. The red light induction of these incompletely hydrated seeds can be reversed by far red light. Their reversibility declines with time at a slower rate than seeds incubated in water. About half the seeds in 0.3 m mannitol respond to far red light when all seeds in water have escaped control by far red light. Close to 100% of the seeds remain sensitive to far red exposure if 0.6 m mannitol is used as osmoticum. The retention of the original red light stimulus is inversely related to the concentration of the incubation medium.The fresh weight of viable seeds incubated with water or with an osmoticum increases rapidly during the first 5 hours, then remains stationary for about 12 hours. After that only germinating seeds experience a second increase in fresh weight. Heat-killed seeds do not show such a discontinuity in water uptake.     

Effect on Transpiration and Water Uptake by Rapid Changes in the Osmotic Potential of the Nutrient Solution

The sudden changes in the rates of transpiration and water uptake which occurred when the osmotic potential of the nutrient solution surrounding the roots of young wheat plants was rapidly changed were studied. The transpiration was measured by the aid of the microwave hygrometer and the water uptake by a recording poto-meter specially built for this investigation. When the osmotic potential of the nutrient solution was rapidly increased by adding mannitol, there was a temporary transpiration increase. The maximum increase was greater but the total time of the temporary increase shorter when a higher mannitol concentration was used. The quantity of water transpired by the shoots due to the temporary transpiration increase seemed to be fairly constant irrespectively of the mannitol concentration. The water transport to the shoots was immediately reduced when the osmotic potential was rapidly increased. The immediate reduction was greater when a higher mannitol concentration was used. After the immediate reduction the rate of water transport increased without delay. When the osmotic potential of the nutrient solution was rapidly decreased by withdrawing mannitol there was a temporary transpiration decrease, and the water transport to the shoots was immediately increased. After this increase the rate of water transport started to decrease at once. When, however, the mannitol concentration had been 0.30 M or higher, the transpiration rate increased progressively, and the change of the rate of water transport was small. The results indicate that the primary effect of the rapidly changed osmotic potential is localized to the root surface. The rapidly reduced water transport to the shoots after adding mannitol brings about the temporary transpiration increase. The course of events after withdrawing mannitol is just the reverse to that when adding mannitol.     

用渗透胁迫鉴定小麦种子萌发期抗旱性的方法分析

本以聚乙二醇(PEG)-6000、甘露醇和蔗糖作为渗透剂模拟水分胁迫,胁迫溶液渗透势范围在-0．25MPa到-1．50MPa,分析适于进行小麦种子水分胁迫萌发试验的条件,以鉴定小麦萌发期的抗旱性。结果表明,蔗糖溶液易诱发霉茵,胚芽不能正常生长。渗透势为-0．25MPa的PEG-6000及-0．50MPa的甘露醇胁迫已经显抑制了胚芽伸长;-0．50MPa的PEG-6000及-1．00MPa的甘露醇显抑制种子萌发,随着胁迫强度增加,种子相对发芽率及胚芽长度减小,主要是因为渗透胁迫降低了种子吸水速度,胚芽的相对含水量和渗透势均低。在渗透势相同的胁迫条件下,PEG-6000对小麦种子萌发各项检测值的抑制作用均大于甘露醇。如果目的是通过鉴定小麦种子在高渗溶液中的萌发情况,评价萌发期的抗旱性。选用-0．50MPa的PEG-6000或-1．00MPa的甘露醇较为理想,若同时考虑降低试验成本,则应首选-0．50MPa的PEG-6000。     

Effects of turgor potential on 1-aminocyclopropane-1-carboxylic acid uptake into the vacuolar compartment and ethylene production in tomato pericarp slices

While solute transport and ethylene production by plant tissue are sensitive to the osmotic concentration of the solution bathing the tissue, the influence of tissue water relations and specifically tissue turgor potential on the kinetics of 1-aminocyclopropane-1-carboxylic acid (ACC) uptake into the vacuolar compartment and ethylene production have not been examined. 1-Aminocyclopropane-1-carboxylic acid transport and ethylene production were examined in tomato (Lycopersicon esculentum Mill. cv. Liberty) pericarp slices incubated in solutions having a range of mannitol, polyethylene glycol 3350 and ethylene glycol concentrations known to affect tissue water relations. Tissue osmotic and turgor potentials were derived from osmolality measurements of cell saps recovered by freeze-thawing and corrected for the contribution of the free-space solution. When relatively nonpermeable (mannitol or polyethylene glycol 3350) osmotica were used, both ACC uptake and ethylene production were greatest at a solution osmolality of 230 milliosmolal where tissue turgor potential ranged between 120 and 140 kPa. At higher and lower turgor potentials, the high-affinity saturating component of ACC uptake and ethylene production were inhibited, and ACC efflux from the vacuolar compartment was increased. The inhibition of ACC uptake was evident as a decrease in V_max with no effect on K_m. Turgor potential changes caused by adjusting solution osmolality with mannitol or polyethylene glycol 3350 were accompanied by changes in the osmotic potential and water potential of the tissue. The effects of turgor potential vs the osmotic and water potentials of tomato pericarp slices were differentiated by comparing responses to nonpermeable osmotica and mixtures of nonpermeable and permeable osmotica. Ethylene glycol-mannitol mixtures had effects on the osmotic potential and water potential of the tissue similar to those of nonpermeable osmotica but had less effect on tissue turgor, ACC transport and ethylene production. Incubating tissue in solutions without nonpermeable osmotica osmotically shocked the tissue. Increasing solution osmolality with ethylene glycol in the absence of nonpermeable osmotica increased tissue turgor and ethylene production. The present study indicates that tissue turgor is an important factor affecting the kinetics of ACC uptake into the vacuolar compartment and ethylene production in tomato pericarp slices.     

Tomato Seed Germination. Osmotic Pretreatment and Far Red Inhibition

At 25 °C germination of tomato (Lycopersicon lycopersicum)seeds is inhibited by continuous and intermittent far red illumination.It is also inhibited by a single 30 min far red irradiationgiven 8 h from the start of imbibition. The incubation of seedsin a mannitol solution inhibitory for germination has no effecton the final germination percentage after seeds are subsequentlytransferred to water. A 30 min far red irradiation at the timeof transfer results in partial inhibition of germination. Thisinhibition can be released by the continuation of osmotic incubationfor several days before the transfer to water. At the end ofa 7 d dark period of osmotic incubation, inhibition of subsequentgermination in water can be realized only by continuous farred illumination. Seeds osmotically pretreated for 7 d and afterwardsdried-back show a mean time to 50% germination significantlylower than that of untreated seeds. Moreover, besides singleand intermittent, even continuous far red light has no inhibitoryeffect on the germination of these seeds. It is concluded that,in addition to the already known germination advantages, osmoticpresowing treatment also induces the ability of seeds to germinateunder unfavourable light conditi.     

Photoinhibition of radish (Raphanus sativus L) seed germination: control of growth potential by cell-wall yielding in the embryo

The biophysical mechanism underlying photoinhibition of radish (Raphanus sativus L.) seed germination was investigated using three cultivars differing in sensitivity to continuous irradiation with far-red light (high-irradiance reaction of phytochrome). Sensitivity of germination to the inhibitory action of light was assessed by probing germination under osmotic stress (incubation in media of low water potentials adjusted with polyethylene glycol 6000) and expressed in terms of ‘germination potential’ (positive value of the water potential at which germination is inhibited by 50%). Far-red light decreases the germination potential to various degrees in the different cultivars, reflecting the light-sensitivity of germination in water. Removal of the seed coat increases the germination potential by a constant amount in darkness and light. It is concluded that germination depends on the expansive force of the embryo which can be drastically diminished by far-red light. Seed-coat constraint and expansive force of the embryo interact additively on the level of the germination potential. Photoinhibition of germination was accompanied by an inhibition of water uptake into the seed. Analysis of seed water relations showed that osmotic pressure and turgor assumed higher levels in photoinhibited seeds, compared to seeds germinating in darkness, while the water potential was close to zero under both conditions. Far-red light produced a shift (to less negative values) in the curve relating water-uptake rate to external water potential, i.e. a reduction in the driving force for water uptake. It is concluded that photoinhibition of germination results from the maintenance of a high threshold of cell-wall extensibility in the embryo.     

Turgor pressure regulation and the orientation of cortical microtubules in Spirogyra cells.

Microtubules (MTs) of cells of Spirogyra sp. were depolymerized by treatment with amiprophos-methyl (APM) for 1 h and then reorganized in 0.30 M mannitol solution. The reorganized MTs after 1.5 h incubation showed an oblique/longitudinal orientation and then became transversely oriented as the incubation was prolonged. During this incubation, the osmotic pressure of cells was measured by the plasmolysis method. The cell osmotic pressure increased with time. The calculated turgor pressure at 1.5 h was 0.11 M (mannitol equivalent) and, at 13.5 h, 0.25 M. Similar changes in MT orientation and recovery of the turgor pressure were also observed in 0.30 M sorbitol solution. These results suggest that the MT orientation may be correlated with the turgor pressure. Among fresh water algae sensitive to a saline environment, this Spirogyra was the first species shown to have a turgor regulating mechanism, although the recovery of turgor pressure was incomplete. The recovery of turgor pressure in mannitol solutions was also observed without APM treatment.     

Effect of decreased rate of water absorption on water balance of leaf tissue

The influence of decrease of water absorption rate on the transpiration rate and the development of water saturation deficit (WSD) was studied on the leaf segments of kale. Solutions of polyethyleneglycol (0-25m, 0-50m, O-75m and 1-00m) and mannitol (0-50m) were used as osmotic agents. The rate of water absorption decreased to zero when the concentration of polyethyleneglycol was 0-25m. At a concentration higher than 0-50m, water from the tissue diluted the external solution. The transpiration rate of samples affected by polyethyleneglycol or mannitol was only a little lower than that of control samples. WSD was noticeably increased only in the absorbing part of segment; in the adjoining, transporting part of segment WSD was practically the same in all variants. WSD in the transpiring part was slightly increased only in some cases. Due to decrease of osmotic potential of the external solution also the gradient of water potential changed. In the case of absorption from pure water, water potential gradually decreased from the absorbing to the transpiring part. Under the influence of polyethyleneglycol or mannitol solution the highest water potential was in the transporting part and from this point water potential decreased to both opposite sides.     

Osmotic Behavior of Oat Coleoptile Tissue in Relation to Growth

Efforts were made to estimate the water potential difference that is required, between rapidly growing oat coleoptile cylinders and dilute medium, to support the rate of water uptake involved in elongation, (a) by the traditional method of determining the concentration of mannitol in which the tissue neither gains nor loses water, and (b) by measuring the rates of osmotic exchanges induced by treating the tissue with different hypotonic mannitol concentrations. Both methods indicated large water potential differences (3 to 10 atm), in some cases approaching the osmotic pressure of the cells. However, indication was obtained that the rates of osmotic exchanges induced by mannitol solutions, and presumably also the equilibrium response sought in (a), are governed by the rate of diffusional exchange of mannitol with the free space rather than by the permeability of the tissue to water. Osmotic swelling of the tissue measured by immersing it in water after its turgor pressure had been reduced by evaporation, was at least two to four times more rapid than when mannitol was involved. The permeability to water estimated by the evaporation-immersion method indicated that rapidly elongating cylinders have water potentials between -0.8 and -2.5 atm, or between 10 and 25 per cent of their osmotic pressure.     

Maturation of black spruce somatic embryos: Sucrose hydrolysis and resulting osmotic pressure of the medium

The physiological and osmotic roles of sucrose during black spruce (Picea mariana (Mill.) B.S.P.) embryo maturation were investigated. The results showed that when both sucrose and mannitol were present in the medium, the optimum sucrose concentration varied between 4% and 6%. From these data, mannitol does not apparently replace sucrose during the maturation of somatic embryos and therefore it might not be a suitable osmoticum. For the media supplemented with 4% to 12% sucrose and various concentrations of mannitol, the osmotic pressure of the medium rose during maturation, particularly for the highest sucrose concentrations (7% to 12%). Medium containing 3% each of fructose and glucose produced fewer mature embryos compared to the medium with 6% sucrose. An increment in the osmotic potential was observed in medium with 6% sucrose in contrast to that containing 3% each of fructose and glucose. Sugar analysis revealed that the sucrose hydrolysis in the medium was detectable within 1 week of incubation and continued throughout the maturation period. Moreover, no significant uptake of the sugars was detected, since the total amount of fructose, glucose and sucrose remained constant. Our results indicate that the action of sucrose on embryo maturation is mostly achieved through an osmotic control.     

Osservazioni Sull'effetto Inibente di Elevate Pressioni Osmotiche su Diversi Tipi di Crescita

Abstract

On the inhibition of seeds germination and of growth by cell enlargement by the osmotic pressure of the medium. — The mechanism of inhibition by osmotic pressure (O.P.) of the medium on growth and respiration of germinating wheat, castor bean and lettuce sèeds and of etiolated pea internode segments was investigated.

The following results were obtained:

1 - External osmotic pressure (up to 0.3 M) of various substances such as mannitol, urea, glucose, NaCl, was shown to inhibit the germination and growth of lettuce, wheat and castor bean seeds.

2 - a) A remarkable decrease of the development of respiration during the first 48 h of germination was demonstrated in embryos of wheat seeds germinated and maintained in mannitol solutions at concentration from 0,2 to 0,3 M.

b) A slight but reproducible inhibition of óxygen uptake by O.P. was also observed in embryos isolated from wheat seeds germinated in water for 24 and 34 h and transported respectively in water or into 0,2 M mannitol solutions.

This is interpreted as indicating that high external O.P. inhibits both the respiratory metabolism and the development with time of enzyme systems supporting respiration.

3 - Mannitol solutions (0,2–0,3 M) inhibited completely growth by cell enlargement in pea internode sections, while they did not at all affect oxygen uptake and protein synthesis ( ¹⁴ C - leucine incorporation). The stimulatory effect of auxin on pea elongation was almost completely suppressed by mannitol, whereas the hormone stimulation of respiration remained unchanged.

These data are interpreted as indicating that in tissues, presenting an advanced differentiation, high external O.P. inhibits growth by a direct physico-chemical mechanism; while the inhibitory effect in embrional tissues seems to comprehend, besides this direct effect, a complicated metabolic component, apparently influencing protein synthesis.     

The Relationship between the Effects of Cytokinin on the Expension and Metabolism of Excised Cucumber Cotyledons and Water Stress

Excised cucumber (Cucumis sativus, var. Jin-ian No. 4) cotyledons were incubated with 10 ppm of BA (benzyladenine) or water for 1 h, then thouroughly rinsed with water and grown in darkness on filter paper saturated with different concentrations of mannitol solution. Up to 24 h, the fresh weight, carotenoid, RNA, DNA and lipid contents of cotyledons were determined. Although mannitol solution reduced the effectiveness of BA treatment, in the same condition of osmotic potential, the increases of fresh weight, carotenoid, RNA and DNA contents, as well as the decrease of lipid per cotyledon were always much higher in BA treated tissues. BA enhanced the rate of water uptake by the cotyledons. The fresh weight of BA and 0.2 M mannitol treated cotyledons was equal to that of water control, but the increases of carotenoid and nucleic acid contents and the decrease of lipid were much higher in tho former than the latter. 0.3 M and 0.5 M mannitol solu- tions almost interrupted the water uptake of water and BA treated cotyledons respectively. However, the increases of carotenoid and nucleic acid contents as well as decrease of lipid were still occurred in these conditions. The different osmotic potential did nearly not affect the ratio of the increases of carotenoid and nucleic acid contents between BA treatment and control. It means the effectiveness of BA was almost the same under different osmotic potential It is evident that BA stimulated simultaneously the water uptake and metabolism of the cotyledons. They are probably different processes but closely related to each other.     

The influence of the osmotic potential of the cultivation medium on the development of excised flax embryos

The development of excised flax embryos of different age was followed in nutrient media with different osmotic values. Sucrose media with the osmotic value 4.0 bar. (5%) sucrose were the most suitable for the cultivation of excised 7 and 14 days old flax embryos. Nutrient media with the osmotic potential 1·7 bar (2% sucrose) were optimal for 28 days old embryos. The most convenient osmotic potential for optimal root growth was 4.0 bar and for hypocotyls and stems 1.7 bar. High osmotic value of the cultivation media prevented the germination of the embryos and lower osmotic value promoted the germination. Mannitol, when compared with sucrose, inhibited the development and germination of the embryos. Different abnormalities often occurred on the media with mannitol. Agar media were superior to liquid media for the cultivation of explanted embryos.     

Effects of water stress on growth, osmotic potential and abscisic acid content of maize roots

Under water stress conditions, induced by mannitol solutions (0 to 0.66 M ) applied to the apical 12 mm of intact roots of Zea mays L. (cv. LG 11), a growth inhibition, a decrease in the osmotic potential of the cell sap and a significant accumulation of abscisic acid (ABA) were observed. When the roots were placed in a humid atmosphere after the stress, the growth rate increased again, even if elongation had been totally inhibited. Under a stress corresponding to an osmotic potential of -1.09 MPa in the solution, growth was totally inhibited, which means that the root cell turgor pressure was reduced to the yield threshold. These conditions led to the largest accumulation of ABA. The effect of water stress on the level of ABA was studied for three parts of the root. The greatest increase in ABA (about 10 fold) was obtained in the growth zone and this increase was apparently independent of the hydrolysis of the conjugated form. With a mannitol treatment of 1 h equivalent to a stress level of -1.39 MPa, a 4-fold increase in ABA efflux into the medium was obtained. These results suggest that there are interactions between water stress, root growth, osmotic potential and the ABA level. The growth under conditions of stress and the role of endogenous ABA in the control of plant metabolism, specially in the growth zone, are discussed.     

Rapeseed embryo development in culture on high osmoticum is similar to that in seeds

The development of Brassica napus L. cv Tower embryos of different ages cultured in vitro with and without high osmoticum (0.48 and 0.69 molar sorbitol) was compared with normal development in situ to investigate the role of a drying environment in embryo maturation. Sensitivity to osmoticum was assayed in terms of its ability to mimic normal development, i.e. to both suppress germination and maintain 12 S storage protein (cruciferin) synthesis at levels comparable to those seen in the developing seed. The osmotic conditions used block germination of predesiccation stage embryos but were not sufficient to prevent desiccation stage embryos from taking up water and germinating. At all stages tested, the osmotically treated embryos had approximately normal levels of cruciferin mRNA. Measurements of endogenous abscisic acid (ABA) levels by radioimmunoassay indicated that the osmotic effects on germination and gene expression were not mediated by elevated embryonic ABA. Comparison of the kinetics of osmotic and ABA effects on gene expression showed that the osmotic effect is more rapid. These results are consistent with the hypothesis that ABA acts by inhibiting water uptake, which mechanically prevents germination and affects gene expression in some unknown manner.     

Asymmetry of canine tracheal epithelium: osmotically induced changes

The symmetry of osmotic conductivity of the canine tracheal epithelial cells was examined in vitro. When an osmotic load of 100 mosM sucrose was added to the serosal bathing solution, no change in the transepithelial potential difference was observed in 15 tissue preparations. In contrast, when the same osmotic load was added to the mucosal bathing solution, there was a rapid decrease in the transepithelial potential difference of 3.9 +/- 0.5 mV (n = 23); ouabain (10(-4) M) eliminated this change. Tissues that had been exposed to the osmotic load added to either the mucosal or serosal side were compared with the control using light and electron microscopy. When the osmotic load was added to the mucosal fluid, there was no change in the nuclear-to-cytoplasmic area ratio of the cell types examined. However, when the same osmotic load was added to the serosal fluid, a marked increase in the nuclear-to-cytoplasmic area ratio of the ciliated cells was observed. This finding indicated cell shrinkage. Dilution potentials measured by substituting NaCl with mannitol also showed asymmetry. The morphological features are probably caused by differences in the osmotic conductivity (Lp) of the basolateral and apical cell membranes, with the Lp of the apical membrane being less than that of the basolateral membrane. The basis for osmotically induced potentials remained undetermined.     

Phytochrome-mediated germination control of maize caryopses

Maize caryopses sown in water germinate equally well either in darkness or under any light regime. However, when they are imbibed in mannitol solutions, continuous far-red light proves to be strongly inhibitory on the final germination as compared to darkness. Similar but less pronounced inhibition is also exhibited by continuous red or blue light. Intermittent far-red light can partially substitute for continuous far-red light in inhibiting maize caryopsis germination, and its effect is reversed to the intermittent red light level when red light is given immediately after each far-red illumination. These results are interpreted as a proof of existence and involvement of phytochrome in the germination control of maize caryopses, though its manifestation is realized only under osmotic stress.Abbreviations D darkness - FR far-red - R red - B blue - c-FR, c-R, c-B continuous FR, R, B, resp. - i-FR, i-R intermittent FR, R, resp.     

Theoretical and experimental studies on freezing point depression and vapor pressure deficit as methods to measure osmotic pressure of aqueous polyethylene glycol and bovine serum albumin solutions

For survival in adverse environments where there is drought, high salt concentration or low temperature, some plants seem to be able to synthesize biochemical compounds, including proteins, in response to changes in water activity or osmotic pressure. Measurement of the water activity or osmotic pressure of simple aqueous solutions has been based on freezing point depression or vapor pressure deficit. Measurement of the osmotic pressure of plants under water stress has been mainly based on vapor pressure deficit. However, differences have been noted for osmotic pressure values of aqueous polyethylene glycol (PEG) solutions measured by freezing point depression and vapor pressure deficit. For this paper, the physicochemical basis of freezing point depression and vapor pressure deficit were first examined theoretically and then, the osmotic pressure of aqueous ethylene glycol and of PEG solutions were measured by both freezing point depression and vapor pressure deficit in comparison with other aqueous solutions such as NaCl, KCl, CaCl(2), glucose, sucrose, raffinose, and bovine serum albumin (BSA) solutions. The results showed that: (1) freezing point depression and vapor pressure deficit share theoretically the same physicochemical basis; (2) theoretically, they are proportional to the molal concentration of the aqueous solutions to be measured; (3) in practice, the osmotic pressure levels of aqueous NaCl, KCl, CaCl(2), glucose, sucrose, and raffinose solutions increase in proportion to their molal concentrations and there is little inconsistency between those measured by freezing point depression and vapor pressure deficit; (4) the osmotic pressure levels of aqueous ethylene glycol and PEG solutions measured by freezing point depression differed from the values measured by vapor pressure deficit; (5) the osmotic pressure of aqueous BSA solution measured by freezing point depression differed slightly from that measured by vapor pressure deficit.     

NaCl对小麦苗叶片脯氨酸氧化酶活性和游离脯氨酸累积的影响

在含NaCl营养液中培养的小麦幼苗较之无NaCl营养液中的幼苗。其脯氨酸氧化酶活性降低,而游离脯氨酸含量则升高;培养液的渗透势越低,培养时间越长,则脯氨酸氧化酶的活性越低,且游离脯氨酸的含量越高。去除胁迫后酶活性恢复,脯氯酸含量下降。不同渗透剂对氧化酶活性抑制强弱顺序为MgCl_2>NaCl>甘露醇,引起脯氨酸累积效应的强度顺序为MgCl_2>NaCl>甘露醇。超微结构显示,高NaCl浓度下部分线粒体结构受损伤,膜和嵴部分消失。     

渗透胁迫对化感作用生物测定的影响

以加拿大蓬水提液为供体,白菜种子为受体,设计了梯度渗透、等渗溶液以及高渗透压、低化感物质浓度3组实验;通过梯度渗透试验确定受体植物可耐受的渗透势阈值,用等渗溶液排除渗透势的干扰确定植物浸提液的化感作用及其作用强度,以高渗透压、低化感物质浓度试验初步模拟自然条件下渗透势与化感物质之间的主次关系,探讨化感作用研究中培养液渗透势对试验结果的影响。结果显示,处理液渗透势在≥-0.25 MPa范围内对白菜种子萌发和幼苗生长没有显著影响;加拿大蓬水溶性物质具有化感作用,且其化感作用主要影响小白菜幼苗的生长,而对其种子萌发影响相对较小;在渗透势相同的溶液中,只要溶质中含有部分加拿大蓬水溶性物质即可对受体植物产生化感作用。研究发现,与渗透胁迫相比,化感物质是加拿大蓬水提液中影响受体植物生长发育的主要因素。