Accumulation Of Osmotic Solutes Research Articles

Comparative proteomic analysis of alfalfa revealed new salt and drought stress-related factors involved in seed germination.

Salinity and drought are two major environmental factors that limit the growth and yield of many forage crops in semi-arid and arid regions. Alfalfa (Medicago sativa L.) is one of the most important forage crops in many countries. We aim to investigate the molecular mechanisms of alfalfa in response to salt and drought stresses in this study. Physiological and proteomic analyses were applied to examine the Zhongmu NO.3 alfalfa seed germination stage with 200mM NaCl and 180g·L-1 polyethylene glycol (PEG) treatments. The germination ability of the seed and the accumulation of osmotic solutes were quite different between the NaCl and PEG treatments. More than 800 protein spots were detected by proteomics technology on two-dimensional electrophoresis (2-DE) gels. The abundance of twenty-eight proteins were decreased or increased after salt and drought stress. Seventeen of these proteins were identified and classified into six functional categories through mass spectrometry (MS). The six groups involved in salt- and PEG-mediated stress included defense response, energy metabolism, protein synthesis and degradation, oxidative stress, carbohydrate metabolism-associated proteins, and unknown proteins. We discovered that some proteins related to carbohydrate metabolism and energy production increased in abundance under salt- and PEG-mediated drought stress. This demonstrates a common mechanism of energy consumption during abiotic stresses. Further study of these proteins with unknown function will provide insights into the molecular mechanisms of abiotic stress and the discovery of new candidate markers.

Evaluation of salicylic acid (SA) application on growth, osmotic solutes and antioxidant enzyme activities on broad bean seedlings grown under diluted seawater

Exogenously applied salicylic acid has been shown to be an essential signal molecule involved in both local defense reactions and induction of systemic resistance response of plants after salt stress. Our study was aimed at evaluating the foliar spray with different levels (0.0, 0.5 and 1.0 mM) of salicylic acid (SA) on broad bean (Vicia faba L) seedlings grown under diluted seawater on growth and some related physiological responses. Seawater irrigation negatively affected growth parameters, free amino acids and K+, while the contents of soluble sugars and protein, proline, ClO?, Na+, ion leakage, lipid peroxidation and antioxidant enzyme activities were significantly increased. Foliar spray with SA improved all growth parameters and increases the activities of antioxidant enzymes. On the other hand, plants treated with SA had lower ClO? and Na+, while K+had a reverse pattern. Based on our findings, the effectiveness of SA in inducing seawater stress tolerance depends upon the concentration of SA applied. The inducer effect of SA was greater with 1 than 0.5 mM treatment. This effect includes the stimulation of antioxidant enzyme activities and regulation of osmotic adjustment through accumulation of osmotic solutes and regulation of absorption and distribution of inorganic ions. Key words: Antioxidant enzyme activities, inorganic ions, proline.

Effects of Osmotic Stress on the Growth of Etiolated Mung Bean Seedlings

AbstractThe alterations in growth and water status of dark‐grown mung bean tissues following sudden osmotic stress were investigated. Photographic measurements of hypocotyl elongation revealed that stress (−0.2 to −0.8 MPa) induced growth cessation within one minute, with resumption occurring at lower rates after a latent period; periods which tended to increase in accordance with whether the seedlings were 4, 5 or 6 days old. Tissue water status was related to growth as water and osmotic potentials were highest in the expanded root region and the lowest in the growing hypocotyl region. These rankings were not verified under osmotic stress, and values were reduced in the course of 24 h. Turgor levels were similar in all tissues and were not altered by stress. The responses were not caused by substantial water loss, which was detected only after 24 h of stress, and could have resulted from the accumulation of osmotic solutes. The results indicate that plants exposed to sudden osmotic stress, besides exhibiting rapid growth cessation, show growth resumption at lower rates and no subsequent short‐term changes in any water status measure of the growing region. Because growth resumes without further detectable turgor increments, water status alterations are unlikely to be the cause of the observed immediate growth stoppage.

Changes in cellular osmotic potential and mechanical properties of cell walls during light‐induced inhibition of cell elongation in maize coleoptiles

The growth rate of maize (Zea mays L. cv. Cross Bantam T51) coleoptiles in the dark was highest at the basal zone and decreased towards the tip. Growth was strongly inhibited by white fluorescent light (5 W m−2), especially in the basal zone of coleoptiles. Light irradiation caused an increase in the values of stress‐relaxation parameters, the minimum stress‐relaxation time and the relaxation rate and a decrease in the extensibility (strain/stress) of the cell walls at all zones. In addition, during growth, the accumulation of osmotic solutes was strongly inhibited by white light irradiation, resulting in an increased osmotic potential. The influences of white light on the mechanical properties of the cell wall and the osmotic potential of the tissue sap were most prominent in the basal zone. Significant correlations were observed between the increment of coleoptile length and the mechanical properties of the cell walls or the osmotic potential of the tissue sap and osmotic solutes content. Furthermore, light inhibited the outward bending of split coleoptile segments. These facts suggest that white light inhibits elongation of maize coleoptiles by modifying both the mechanical properties of the cell walls and cellular osmotic potential, which control the rate of water uptake.

Quantitative Models Characterizing Seed Germination Responses to Abscisic Acid and Osmoticum

Mathematical models were developed to characterize the physiological bases of the responses of tomato (Lycopersicon esculentum Mill. cv T5) seed germination to water potential (psi) and abscisic acid (ABA). Using probit analysis, three parameters were derived that can describe the germination time courses of a seed population at different psi or ABA levels. For the response of seed germination to reduced psi, these parameters are the mean base water potential ( psi(b), MPa), the standard deviation of the base water potential among seeds in the population (sigma(psib), MPa), and the "hydrotime constant" (theta(H), MPa.h). For the response to ABA, they are the log of the mean base ABA concentration ([unk]ABA(b), m), the standard deviation of the base ABA concentration among seeds in the population (sigma(ABA) (b), log[m]), and the "ABA-time constant" (theta(ABA), log[m].h). The values of psi(b) and [unk]ABA(b) provide quantitative estimates of the mean sensitivity of germination rate to psi or ABA, whereas sigma(psi) (b) and sigma(ABA) (b) account for the variation in sensitivity among seeds in the population. The time constants, theta(H) and theta(ABA), indicate the extent to which germination rate will be affected by a given change in psi or ABA. Using only these parameters, germination time courses can be predicted with reasonable accuracy at any medium psi according to the equation probit(g) = [psi - (theta(H)/t(g)) - psi(b)]/sigma(psib), or at any ABA concentration according to the equation probit(g) = [log[ABA] - (theta(ABA)/t(g)) - log[[unk]ABA(b)]]/sigma(ABA) (b), where t(g) is the time to radicle emergence of percentage g, and ABA is the ABA concentration (m) in the incubation solution. In the presence of both ABA and reduced psi, the same parameters can be used to predict seed germination time courses based upon strictly additive effects of psi and ABA in delaying the time of radicle emergence. Further analysis indicates that ABA and psi can act both independently and interactively to influence physiological processes preparatory for radicle growth, such as the accumulation of osmotic solutes in the embryo. The models provide quantitative values for the sensitivity of germination to ABA or psi, allow evaluation of independent and interactive effects of the two factors, and have implications for understanding how ABA and psi may regulate growth and development.

Osmotic Relations during Elongation Growth in Coleoptiles of Five Cereal Species

Summary The relationship between growth, change in cell osmotic pressure and accumulation of osmotic solutes was investigated in coleoptiles of seedlings of maize (Zea mays L.), oats (Avena sativa L.), wheat (Triticum aestivum L.), rye (Secale cereale L.) and barley (Hordeum vulgare L.). In dark-grown maize coleoptiles, cell osmotic pressure decreased by 25 % between days 3 and 8 after sowing. In etiolated seedlings of oats, wheat, rye and barley, coleoptile growth in darkness was accompanied by a 40–50% decrease in cell osmotic pressure, depending on species. One day after transfer to white light coleoptile growth ceased due to the emergence of the primary leaves. In irradiated coleoptiles of maize and oats a substantial decrease in cell osmotic pressure occurred, but in wheat, rye and barley only minor changes were detectable. In all five species investigated coleoptile growth in darkness was accompanied by a corresponding increase in the amount of osmotic solutes. After irradiation with white light a loss of osmotic solutes occurred, possibly as a consequence of an enhanced membrane permeability during coleoptile senescence.

Osmotic relations during elongation growth in hypocotyls of Helianthus annum L.

The relationship between growth, change in cell osmotic pressure and accumulation of osmotic solutes was investigated in hypocotyls of sunflower (Helianthus annum L.) seedlings. During growth in darkness the osmotic pressure decreased by 50% between days 2 and 6 after sowing. After irradiation of dark-grown seedlings with continuous white light (WL) an inhibition of hypocotyl growth was measured, but the osmotic pressure of the growing cells was not lower than in the dark-grown control. Growth in darkness and after WL irradiation was accompanied by an increase in the amount of osmotic substances (soluble sugars) which was proportional to the increase in length of the organ. During growth in continuous WL the cell osmotic pressure decreased by 45 % between days 2 and 6 after sowing. The transfer of WL-grown seedlings to darkness ("re-etiolation") resulted in a rapid acceleration of hypocotyl growth, but the cell osmotic pressure was the same as that of the WL grown control. Growth in continuous WL was accompanied by a corresponding accumulation of osmotic substances (soluble sugars). The transition from WL to darkness resulted in an enhanced accumulation of osmotica and an increase in cell-wall extensibility. The results indicate that the relative maintenance of cell osmotic pressure during rapid hypocotyl growth in darkness is caused by an enhanced accumulation of soluble sugars into the growing cells of the organ.