MPa PEG Research Articles

Standardization of priming treatments for enhancement of seed germination and field emergence in carrot

Carrot (Daucus carota L.) seeds were subjected to solid matrix priming with moist vermiculite at 15°C and 20°C for 12, 24, 36 and 48 h. Seeds were also osmoprimed at −0.5, -1.0 and -1.5 MPa potential for 2, 4 and 6 days. Solid matrix priming for 24 h registered significantly higher seed germination (85%) and speed of germination (14.45), while priming duration of 48 h gave minimum value for speed of germination. However, no significant differences in speed of germination were found at different temperatures. Solid matrix priming for 24 h at 20°C was optimum for obtaining maximum speed of germination (14.67) and vigour index I (821.5). With increase in priming duration from 2 to 6 days, there was significant decrease in germination. Osmopriming at −1.0 MPa PEG potential significantly improved speed of germination (7.07) and was at par to PEG priming at −0.5 MPa. Osmopriming for 2 days at −1.0 MPa PEG potential recorded maximum speed of germination (9.24) over all other treatment combinations. Osmopriming at −1.0 MPa and solid matrix priming for 24 h at 20°C improved germination and field emergence over control in carrot. Hence, osmopriming and solid matrix priming can be effectively employed for improved field performance in carrot.

Germination and field emergence in osmotic and solid matrix priming in onion (Allium cepa)

Solid matrix priming for 24 hr significantly improved seed germination (81.6%) as compared to 12 hr, 36 hr or 48 hr duration. A priming duration of 24 hr gave maximum speed of germination (16.95) while priming duration of 48 hr gave minimum value for speed of germination. No significant differences in speed of germination were found at different temperatures. The interaction effect of priming duration and temperature revealed that solid matrix priming for 24 hr at 20°C is optimum for obtaining maximum speed of germination (17.34). Maximum vigour index I (848.1) was obtained in solid matrix primed seeds for 24 hr duration at 20°C temperature. Osmopriming using PEG 6000 (–1.5MPa) significantly improved seed germination (78%). With increase in priming duration from 2 days to 6 days, there was significant decrease in germination. Osmopriming at –1.0 MPa PEG potential significantly improved speed of germination (7.78) as compared to –0.5 and –1.5MPa potential. The interaction effect of PEG potential and priming duration revealed that osmopriming for 2 days at –1.0 MPa PEG potential gave maximum speed of germination (8.35) over all other treatment combinations. Osmopriming using PEG 6000 (–1.0MPa for 2 days) improved germination by 14.3 percent and field emergence by 13 percent over control. Solid matrix priming for 24 hr at 20oC also improved germination by 13 percent and field emergence by 11.3 percent over control. These results indicate that osmopriming and solid matrix priming can be effectively employed to prime onion seeds for improved field performance.

Interactive Effects of Salt and Drought Stresses on Seed Germination of <i>Ammopiptanthus mongolicus</i> in Northwest China

A study quantifying the role of the interactive effects of salt and drought stresses, generally co-occurred in deserts, on seed germination in Ammopiptanthus mongolicus was conducted in a constant temperature incubator. The experiment consisted of seven levels of salinity stress (0, 0.3, 0.6, 0.9, 1.2, 1.5 and 1.8% NaCl) as well as six drought stress levels (0, -0.2, -0.4, -0.8, -1.6 and-2.0 MPa PEG). Accordant to our expectations, the interactive effects of salinity and drought stresses were additive on seed germination percentages, germination rate, and germination energy; significant decreases were seen in all of them in response to increases in salt and/or drought stresses. Furthermore, regression coefficients of salinity (β1) were higher than drought (β2), indicating that salinity was the first factor, and drought was secondary for salt and drought mixed stresses.

Crescimento e conteúdo de prolina em plântulas de guandu submetidas a estresse osmótico e à putrescina exógena

O objetivo deste trabalho foi verificar o efeito da aplicação da poliamina putrescina no acúmulo de prolina e no crescimento inicial de plântulas de guandu cultivadas sob estresse hídrico ou salino, e avaliar se esta poliamina pode ser usada como atenuadora desses estresses. Sementes de duas cultivares de guandu, BRS Mandarim e Caqui, foram germinadas em caixas gerbox forradas com papel de filtro umedecido com 0,0, -0,2, -0,3, -0,4, -0,5 MPa de PEG 6000 ou 0, 20, 40, 60, 80 e 120 mmol L-1 de NaCl, na ausência (0 mmol L-1) ou na presença (0,5 mmol L-1) de putrescina. Utilizou-se o delineamento inteiramente casualizado, em arranjo fatorial 2x5x2 e 2x6x2 (duas cultivares, cinco níveis de deficiência hídrica ou seis níveis de estresse salino, e presença ou ausência de putrescina), com quatro repetições. O crescimento das plântulas é acentuadamente reduzido pelas condições de restrição hídrica e salinidade. A putrescina exógena incrementa, sob ambos os estresses, os teores de prolina nas plântulas de guandu, especialmente na cultivar BRS Mandarin, e atenua os efeitos da deficiência hídrica moderada nas cultivares estudadas. Os estresses de restrição hídrica e de salinidade causam acúmulo de prolina na parte aérea e nas raízes de ambas as cultivares. A prolina pode ser considerada um bom indicador bioquímico e fisiológico desses estresses em plântulas de guandu.

Nutritional capability of and substrate suitability for Pseudogymnoascus destructans, the causal agent of bat white-nose syndrome.

Pseudogymnoascus destructans, the causal agent of bat white-nose syndrome, has caused nearly six million deaths in North American bats since its introduction into the United States in 2006. Current research has shown that caves can harbor P. destructans even after the infected bats are removed and bats no longer visit or inhabit previously infected caves. Our research focuses on elucidating reservoir requirements by investigating the nutritional capabilities of and substrate suitability requirements for six different P. destructans isolates from various localities including Illinois, Indiana, New York (Type specimen), and Pennsylvania. Enzyme assays implicate that both urease and b-glucosidase appear to be constitutive, lipase and esterase activity were more rapid than proteinase activity on 6% gelatin, gelatin degradation was accompanied by medium alkalinization, the reduction of thiosulfate generated hydrogen sulfide gas, chitinase and manganese dependent peroxidase activity were not visually demonstrated within eight weeks, and keratinase activity was not evident at pH 8 within eight weeks. We demonstrate that all P. destructans isolates are capable of growth and sporulation on dead fish, insect, and mushroom tissues. Sole nitrogen source assays demonstrated that all P. destructans isolates exhibit Class 2 nitrogen utilization and that growth-dependent interactions occur among different pH and nitrogen sources. Substrate suitability assays demonstrated that all isolates could grow and sporulate on media ranging from pH 5–11 and tolerated media supplemented with 2000 mg/L of calcium and 700 mg/L of three separated sulfur compounds: thiosulfate L-cysteine, and sulfite. All isolates were intolerant to PEG-induced matric potential with delayed germination and growth at −2.5 MPa with no visible germination at −5 MPa. Interestingly, decreasing the surface tension with Tween 80 permitted germination and growth of P. destructans in −5 MPa PEG medium within 14 days suggesting a link between substrate suitability and aqueous surface tension altering substances.

Drought tolerance of Periploca sepium during seed germination: antioxidant defense and compatible solutes accumulation

Periploca sepium Bunge is a native and widespread shrub on the Loess Plateau, an arid and semi-arid region in China. To understand the adaptability of its seed germination to dry environments, we investigated the germination rate, water relations, lipid peroxidation, antioxidant capacity and accumulation of major organic solutes during seed germination under water deficit conditions. Results showed that seeds pre-treated by hydration–dehydration or −0.9 MPa PEG germinated faster than control seeds, indicating strong resistance of P. sepium to drought condition. The re-dried seeds showed higher proline, total free amino acids (TFAA) and soluble proteins (SP) contents than control dry seeds, indicating the maintenance of physiological advancement when dehydrated. Osmotic stress made seed germination stay on the plateau phase (phase II). However, germinating seeds moved into phase III immediately once transferred into distilled water. Large increases in SP and soluble sugars (SS) of both re-dried and osmotic stressed seeds help themselves to resist drought stress. The re-hydrated seeds showed significantly higher levels of proline, TFAA, SP and SS than control seeds. The largely accumulated SS during osmotic stress declined sharply when transferred into distilled water. Our data demonstrate that P. sepium’s tolerance to drought stresses during germination is associated with enhanced activity of antioxidant enzymes and accumulation of some compatible solutes. Seed physiological advancement progressed slowly under low water conditions and it was maintained when seeds were air dried. This strategy ensures high and more rapid seed germination of P. sepium under drying and wetting conditions in drought-prone regions.

GERMINATION OF UNTREATED AND PRIMED SEEDS IN RAPESEED (BRASSICA NAPUSVAROLEIFERADEL.) UNDER SALINITY AND LOW MATRIC POTENTIAL

SUMMARYSalt (NaCl) and matric stress (polyethylene glycol; PEG 6000) impacts on germination were analysed in two rapeseed (Brassica napusvaroleiferaDel.) cultivars (Exagone: salt and water stress tolerant; Toccata: salt and water stress sensitive), which had the same imbibition kinetics when incubated in distilled water. Final germination percentage (G) and time to reach 50% G (T50) were affected either by 325 mM NaCl or −0.9 MPa PEG in Toccata but not in Exagone. Cultivars did not differ for protein concentration and protease activity in any germination condition; thus, protein metabolism seems not to be implicated in response to stress. Hydroxurea and cytochalasine-D inhibited germination in Toccata exposed to −0.9 MPa PEG but not in Exagone, suggesting that Exagone tolerance could be due to a lower amount of damaged DNA and lower requirement for DNA replication due to cell elongation rather than cell division for radicle elongation. Soluble sugars concentration increased in salt-stressed seeds from Exagone more than in Toccata and this could have allowed osmotic adjustment and therefore cell elongation despite the presence of external NaCl. Priming treatments with gibberellic acid, kinetin, NaCl and PEG hastened seed germination under control conditions but had no effect or even negative effects on germination under both salt and matric stresses.

Effects of light, hydropriming and abiotic stress on seed germination, and shoot and root growth of pyrethrum ( Tanacetum cinerariifolium)

Poor germination and seedling establishment are major problems in arid and semi-arid environments, and these characteristics are considered to be important factors in later plant growth and yield. Laboratory experiments were conducted on freshly harvested pyrethrum ( Tanacetum cinerariifolium) seeds to investigate the effects of light (influenced by the seeding method) and seed hydropriming on germination, and shoot and root growth at 25 °C. Exposure to light could reduce germination from 52% to 22% and increase the mean germination time (MGT) from 7 to 12 days. The responses of hydroprimed and unprimed seeds to salt and drought stress were determined at osmotic potentials of 0 (distilled water), −0.3, −0.6, −0.9, −1.2 MPa in NaCl and PEG6000. Seed germination and seedling growth were inhibited by increasing salt and drought stress. The germination percentage of unprimed seeds was reduced from 52% to 16% in −1.2 MPa NaCl, and no seeds germinated at osmotic potentials ≤−0.9 MPa PEG. Both shoot and root growth were inhibited at osmotic potentials ≤−0.9 MPa NaCl and ≤−0.6 MPa PEG. Hydropriming shortened the delay of MGT at all osmotic potentials, and improved the germination percentage in distilled water (from 52% to 59%) and resistance to salt stress with nearly double germination (from 16% to 29%) at the highest salt concentration. When non-germinated seeds were transferred to distilled water after 20 days of incubation in total up to 12–15% of NaCl and 25–27% of PEG stressed seeds did not recover. These results show that the inhibition of the germination and seedling growth at the same osmotic potential of NaCl and PEG resulted from drought stress rather than salt toxicity, and that hydropriming is an effective tool to improve the quality of pyrethrum seeds.

Dynamics of the antioxidant system during seed osmopriming, post-priming germination, and seedling establishment in Spinach ( Spinacia oleracea)

Osmopriming is a pre-sowing treatment that improves seed germination performance and stress tolerance. To understand osmopriming physiology, and its association with post-priming stress tolerance, we investigated the antioxidant system dynamics during three stages: during osmopriming, post-priming germination, and seedling establishment. Spinach seeds ( Spinacia oleracea L. cv. Bloomsdale) were primed with −0.6 MPa PEG at 15 °C for 8 d, and dried at room temperature for 2 d. Unprimed and primed germinating seeds/seedlings were subjected to a chilling and desiccation stresses. Seed/seedling samples were collected for antioxidant assays and germination performance and stress tolerance were evaluated. Our data indicate that: (1) during osmopriming the transition of seeds from dry to germinating state represses the antioxidant pathways (residing in dry seeds) that involve CAT and SOD enzymes but stimulates another pathway (only detectable in imbibed seeds) involving APX; (2) a renewal of antioxidant system, possibly required by seedling establishment, occurs after roughly 5 d of germination; (3) osmopriming strengthens the antioxidant system and increases seed germination potential, resulting in an increased stress tolerance in germinating seeds. Osmopriming-mediated promotive effect on stress tolerance, however, may diminish in relatively older (e.g. ∼5-week) seedlings.

Germination, osmotic adjustment, and antioxidant enzyme activities of gibberellin-pretreated Picea asperata seeds under water stress

Germination of dragon spruce (Picea asperata Mast.) seeds pretreated with gibberellin (GA) in response to water stress and changes in the levels of osmotic adjustments as well as in activities of antioxidant enzymes were investigated. With decreasing water potential caused by increasing concentrations of PEG 6000, germination percentage and germination index decreased gradually; the decrease was especially prominent under the serious water stress from PEG −0.6 MPa. In contrast, osmotic regulation substances (free proline and soluble sugar contents), lipid peroxidation (MDA), and activities of antioxidant enzyme (ascorbate peroxidase, catalase, and peroxidase) increased markedly with decreased water potential. Similarly, the values in all parameters under −0.6 MPa PEG treatment were markedly higher than the control and −0.2 MPa PEG treatment. These results suggested that P. asperata seed germination was insensitive to water stress. In addition, seeds pretreated with GA had increased tolerance to water stress as measured by germination percentage and germination index, osmotic regulation substance, and antioxidant enzyme activities.

Primed carrot seeds performance under water and temperature stress

Uniformity and percentage of seedling emergence of direct-seeded vegetables have a major impact on their yield and quality. Depending on temperature and soil water potential, carrot seeds performance in the field is poor justifying the use of techniques to accelerate the germination and seedling emergence. The objective of this work was to evaluate the effects of priming treatments, with and without aeration, on carrot seeds performance under water and temperature stress. Two seed lots of carrots, Brasília cultivar, were primed in PEG 6000 -1.0 and -1.2 MPa solutions, for four and eight days, at 20ºC, using two imbibition methods: priming in paper towel moistened with the respective solutions and immersion into aerated osmotic solutions. Non-primed seeds were used as control. After priming, the seeds were dried at room temperature until reach initial seed moisture content. The seeds were submitted to the following tests: germination, first count, seedling emergence in the field, germination at sub-optimal (15ºC) and supra-optimal temperature (30ºC) and germination under water stress (PEG 6000 at -0.4 MPa). Priming in -1.0 and -1.2 MPa PEG 6000 during four and eight days can be useful for improving carrot seedling emergence in the field and seed performance under supra and sub-optimal temperatures. Aeration of the peg solution was beneficial when seeds were primed at -1.2 MPa for eight days.

Condicionamento fisiológico de sementes de pepino e relação com desempenho das plantas em campo

O presente trabalho teve como objetivo estudar procedimentos para o condicionamento fisiológico e verificar suas relações com o desempenho das sementes e plantas em campo. Foram utilizados lotes de sementes das cultivares Safira e Joia com diferentes potenciais fisiológicos, testando-se o osmocondicionamento (potenciais de -0,1, -0,2 e -0,5MPa), o hidrocondicionamento e o matricondicionamento para o tratamento das sementes. O osmocondicionamento em papel embebido em solução de PEG -0,2MPa, revelou-se eficiente, afetando mais claramente a velocidade do que a porcentagem de germinação dos lotes avaliados. Constatou-se, também, que o condicionamento fisiológico permite a formação de mudas vigorosas de pepino; no entanto, esses benefícios não se estendem até a produção de frutos em campo.

Condicionamento fisiológico de sementes de berinjela

A pesquisa objetivou avaliar métodos de condicionamento fisiológico de sementes de berinjela (Solanum melongena L.). Para tanto, sementes de três lotes, cultivar Napoli, foram condicionadas entre papel toalha com 30, 60 e 90 mL de água a 15, 20 e 25 ºC e com soluções a -0,5, -1,0, -1,5 e -2,5 MPa de PEG 6000 a 20 ºC e, em seguida, secadas a 30 °C até atingirem teores de água similares aos originais. Sementes sem (testemunha) e com condicionamento foram avaliadas quanto ao teor de água, à germinação e ao vigor (velocidade de germinação, envelhecimento acelerado, deterioração controlada e condutividade elétrica). Os tratamentos de maior desempenho (20 °C, 90 mL de água ou PEG -0,5 MPa) foram novamente aplicados às sementes que, juntamente com as da testemunha, foram armazenadas e avaliadas pelos mesmos testes aos 0, 60 e 120 dias. Há a possibilidade de condicionar fisiologicamente as sementes de berinjela, a 20 ºC, entre papel toalha, com água ou com solução -0,5 MPa de PEG 6000, seguido de secagem.

Hydration of carrot seeds in relation to osmotic potential of solution and conditioning method

The objective of this study was to monitor carrot seed hydration in water and osmotic solutions to define appropriate conditions for priming treatment. Two Brasília cultivar carrot seed lots were used. Seeds were imbibed in -1.0 and -1.2 MPa PEG 6000 osmotic solutions and in distilled water, in an incubator BOD at 20ºC, using two different hydration methods: imbibition in moistened paper towel sheets and in aerated solutions. The imbibition curves for each seed lot were drawn after determining seed moisture content at 2, 4, 6, 8, 10, 12, 24, 48, 72, 96 hours hydration in water and after 2, 4, 6, 8, 10, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, 264, 312 hours hydration in PEG 6000 solutions. Seed hydration in distilled water was faster than in PEG 6000 solutions; the primary root protrusion occurred at 48 hours imbibition as seeds reached 54% moisture content. Osmotic conditioning of carrot seeds should be performed by imbibition in PEG 6000 -1.0 or -1.2 MPa solutions to attain 40% and 45% moisture content (moistened paper) or 40% and 45% (aerated solutions).

Strategies for Adaptation of Suaeda physophora, Haloxylon ammodendron and Haloxylon persicum to a Saline Environment During Seed-Germination Stage

Germination is very important for plant establishment in arid regions. The strategies taken by halophytes during the seed germination stage to adapt to saline environments in an arid zone were investigated in Suaeda physophora (euhalophyte), Haloxylon ammodendron (xero-halophyte) and Haloxylon persicum (xerophyte). Seeds of S. physophora, H. ammodendron and H. persicum were exposed to a range of iso-osmotic NaCl and PEG solutions. Seed germination in, and recovery germination from, high NaCl were recorded. The effects of iso-osmotic NaCl and PEG on seed water uptake and changes in ion content were measured. In addition, the structure of seeds and Na+ distribution in the seed coat and embryos of dry seeds were investigated. The relative increase in fresh weight of germinating seeds was markedly reduced in -2.24 MPa PEG compared with that in -2.24 MPa NaCl, while the opposite trend was found in concentration of K+ during the initial 9 h for all species. Haloxylon ammodendron and S. physophora had a higher recovery germination from -3.13 MPa NaCl compared with H. persicum. Seeds of all species had no endosperm. More Na+ was compartmentalized in the seed coats of the two halophytic species compared with that in the xerophyte H. persicum. The effect of NaCl on seed germination was due to both osmotic stress and ion toxicity for the three species. High soil salinity and a high content of Na+ in seeds may induce more seeds to remain ungerminated in S. physophora and H. ammodendron. Morphological structure and adaptation to salinity during seed germination may determine the geographical distribution of H. ammodendron and S. physophora in certain saline regions.

The protective effects of cobalt on potato seedling leaves during osmotic stress

The protective effects of cobalt on potato seedling leaves during osmotic stress were reported and discussed in this paper. The results showed that the membrane damage was significantly alleviated after 24 h of osmotic stress when cobalt of appropriate concentrations was added in PEG solutions. During -1.0 MPa PEG osmotic stress cobalt of 25 μmol L^(-1) inhibited ethylene production rate significantly. Cobalt of 25 μmol L^(-1) had no significant influence on the content of thiobarbituric acid reacting substances or chlorophyll in the first 16 h. When the stress lasted 20 h and 24 h, treatment with cobalt effectively restrained the increment in the levels of reactive oxygen species, hampered the decline in the content of putrescine, spermidine and spermine. The decline in the activities of antioxidative enzymes, thus inhibited the accumulation of thiobarbituric acid reacting substances and alleviated the reduction of chlorophyll content. It can be concluded that when the potato leaves were deeply stressed and damaged, through the inhibition of ethylene production, cobalt alleviated the decline in polyamine content and the activities of anti-oxidative enzymes, and hence alleviated the increment in reactive oxygen species levels and membrane damage and showed protective effects on the leaves.

Comportamento fisiológico de sementes osmocondicionadas de Platymiscium pubescens Micheli (tamboril-da-mata)

O objetivo deste trabalho foi investigar alterações fisiológicas e bioquímicas em sementes osmocondicionadas de tamboril-da-mata (Platymiscium pubescens Micheli). Foram analisados o crescimento do eixo embrionário, a germinação, as alterações na parede celular, a mobilização de carboidratos e proteínas e a atividade de a-galactosidase. Observou-se que o teor de umidade das sementes da testemunha aumentou continuamente até 96 horas de embebição, enquanto as mantidas nas soluções de PEG estabilizaram-se a partir de 48 horas. A germinação ocorreu somente nas sementes mantidas em água, alcançando 30% em 120 horas. As sementes mantidas em solução-0,4 MPa de PEG por 120 horas tiveram 66% de germinação quando transferidas para água, sendo a maior em relação aos demais potenciais. A massa fresca e o comprimento do embrião aumentaram significativamente durante o período de 120 horas em solução de PEG (-0,4 MPa/120 horas), porém a massa seca teve incremento não-significativo. Os teores de arabinose e xilose em membranas lavadas com água decresceram significativamente durante o osmocondicionamento. A galactose não foi detectada na membrana em 120 horas. A arabinose mostrou ser a principal constituinte da membrana. A atividade de a-galactosidase mostrou diferença significativa durante o período de 120 horas. Os teores de ramnose, arabinose e xilose alteraram-se significativamente na fração péctica, enquanto a ramnose foi a única na fração hemicelulósica. A glicose foi detectada somente nessa última fração. Os teores de glicose no embrião e cotilédones alteraram-se significativamente durante o osmocondicionamento. Os teores de estaquiose e de rafinose não tiveram alterações significativas nos cotilédones, enquanto o de sacarose reduziu-se significativamente, mantendo-se mais alto do que os dos outros dois oligossacarídeos. O teor de proteína decresceu significativamente nas 120 horas de osmocondicionamento. Concluiu-se que o osmocondicionamento potencializou a germinação das sementes durante o processo de embebição, resultando em modificações da parede celular pela deposição de açúcares redutores.

Changes in Membrane Fluidity and Protein Composition during Release of Cucumber Seeds from Dormancy by a Higher Temperature Shift

Abstract Dormancy of seeds of cucumber ( Cucumis sativus L.) was induced by imbibing in −1.8 MPa polyethylene glycol 6000 (PEG) solution and pulsing with far red light for 15 min prior to washing and drying. When re-imbibed with water at 20 °C, dormancy was broken by raising the temperature to 30 °C for 6 h. This treatment was also effective when −0.9 MPa PEG was present during re-imbibition and high temperature. Seeds with broken dormancy were found to germinate in water over a smaller temperature range than seeds in which dormancy had not been induced. When the duration of the temperature shift to 30 °C was varied, germination percentage increased from 7 to 60% after 6 h, but longer exposures up to 12 h had no further promoting effect. The time course of germination after transfer to water following 6 h at 30 °C in PEG showed piercing of the perisperm-endosperm envelope after 9–12 h and radicle protusion after 12–15 h. If PEG was retained after high temperature treatment no visible germination was observed. Thus, to study membrane fluidity and the protein content associated with germination, seeds were sampled 9 h after high temperature treatment. To study the germinable but not germinating state, seed held in PEG for 9 h rather than in water was used. Dormant seed was sampled before the high temperature treatment. Membrane fluidity was assessed using fluorescence polarization of membrane fractions treated with DPH (1,6-diphenyl-1,3,5-hexatriene) or its derivatives. Membrane proteins were compared using one-dimensional SDS-PAGE electrophoresis. Intracellular membrane fluidity was not increased in the transition from the dormant to germinable state, but did increase in the transition to germination. There were no detected changes in intracellular membrane proteins during either transition. In plasma membrane fractions, fluidity increased during both transitions, while a marked increase in 21, 18 and 17 kD proteins was observed in the transition from germinable to germinating state. Thus modification of plasma membrane fluidity rather than changes in protein profile is associated with the high temperature release of cucumber seeds from dormancy.

Water potential and ionic effects on germination and seedling growth of two cold desert shrubs

We tested expectations that two desert shrubs would differ in germination and seedling relative growth rate (RGR) responses to Na and Ψ(s) stress. The study species, Chrysothamnus nauseosus ssp. consimilis and Sarcobatus vermiculatus (hereafter referred to by genus), differ in their distribution along salinity gradients, with Chrysothamnus inhabiting only less saline areas. In growth chamber studies, declining Ψ(s) (-0.82 to -2.71 MPa) inhibited germination of both species, and Chrysothamnus was less tolerant of Ψ(s) stress than Sarcobatus. Germination fell below 10% for Chrysothamnus at -1.64 MPa (NaCl and PEG), and for Sarcobatus at -2.4 MPa PEG. Neither species exhibited ion toxicity. There was substantial ion enhancement for Sarcobatus in lower Ψ(s), allowing for 40% germination in -2.71 MPa NaCl. For seedling RGR, species were not different at -0.29 or -0.82 MPa (0 and 100 mmol/L NaCl, respectively), but Chrysothamnus RGR declined substantially at -1.3 MPa (200 mmol/L NaCl). The greater stress tolerance of Sarcobatus was not associated with a lower RGR under nonsaline conditions. Species differences in seed and seedling Ψ(s) stress tolerance probably contribute to the restricted distribution of Chrysothamnus to less saline areas. The Na uptake of Sarcobatus seedlings enhances its ability to deal with declining Ψ(s) and establish in more saline areas.

Evidence for Transcriptional and Post Transcriptional Control of Protein Synthesis in Water-stressed Wheat Leaves: A Quantitative Analysis of Messenger and Ribosomal RNA

Although it has long been recognized that water deficit in plants can result in a reduction in protein synthesis, the detailed mechanisms behind this have not been thoroughly elucidated. In the present study, experiments were conducted to investigate the effects of water stress on protein synthesis at both transcrip- tional and post-transcriptional levels in spring wheat leaves ( Triticum aestivum L. cv. Longchun No. 10). The results revealed that stressing wheat seedlings in -0.5 MPa PEG solutions for 0, 24, 48 and 72 h resulted in a progressive decrease in leaf protein synthesis as reflected by the incorporation of 3 H-Leucine into chloroplast protein. Accompanying the decrease of protein synthesis, the synthetic rate of leaf RNA, the steady state levels of cellular mRNAs and rRNAs, as well as the translatability of poly(A) + -RNAs decreased significantly, indicating that water stress not only affected gene transcription and RNA accumulation in wheat leaves but impaired the messenger-like properties of mRNAs. Furthermore, as the loss of rRNA species might result in disruption of the ribosomal subunits and that of mRNAs might reduce the proportion of ribosomes organized as polyribosomes, it is conceivable that water stress also affected the translational level of leaf gene expression. Based on these results, the slowdown of protein synthesis in water-stressed wheat leaves can be attributed to both transcriptional and post-transcriptional control mechanisms.