Increase In Osmotic Potential Research Articles

Expanding the understanding of Volvariella volvacea autolysis at 4°C with transcriptomics and metabolomics

Volvariella volvacea is a type of high-temperature edible fungus that is prone to low-temperature autolysis, which makes postharvest storage and long-distance transportation difficult. In this study, transcriptomics integrated with metabolomics analysis provided the profiling of genes and metabolites in V. volvacea fruiting bodies stored at 4 °C. According to the transcriptomics and metabolomics analysis, 1613 and 1846 differentially expressed genes, 126 and 136 differential metabolites were identified at 12 h and 24 h compared to control (0 h), respectively. 6 common metabolic pathways were found by integrated analysis, of which starch and sucrose metabolism and pyruvate metabolism were further analyzed. The results exhibited that low-temperature autolysis was the consequence of the intracellular and extracellular interactions. Expression changes of genes (CEL2, CEL3, CEL6B and GH5–1) involved in cellulose metabolism led to the degradation of cellular structure. The rapid reduction of soluble sugar resulted in a decrease in the cytoplasmic concentration and an increase in osmotic potential, thereby liquefying the surface of fruiting bodies. The differential metabolites and genes of malate metabolism participated in the electron supply of the electron transport chain, but long-term low temperature made the intracellular energy supply insufficient, causing cold damage. This study provides a theoretical basis for further understanding in the mechanisms of low-temperature autolysis of V. volvacea.

Induction of compact growth in Campanula portenschlagiana plants by ethanol treatments

ABSTRACT Reducing plant height for ornamental potted plants is an important factor. Conventionally, a compact growth is obtained through the extensive use of chemical growth retardants that can be hazardous to human health or the environment. In this study, ethanol irrigation was successfully proven to produce compact growth in the economically important ornamental plant Campanula portenschlagiana. The vegetative growth decreased when ethanol concentration was increased from 0.5% to 6%. Similarly, there was also a significant reduction in root length, while higher ethanol treatments from 4% were toxic and caused injuries. Further, higher ethanol levels led to partially leave yellowing or necrosis. An increase in osmotic potential was observed, but it was not significantly different between untreated plants and those treated under moderate ethanol concentration (0.5–2%). Considering the generative parameters, ethanol from 2% delayed flower formation and the longevity of flowers treated with the higher ethanol concentration (4–6%) is also significantly reduced. Generally, ethanol at moderate concentrations of 2% has desirable effects on vegetative growth traits, while it already affects generative growth, but without other obvious damage to the plants. Thus, it has been successfully demonstrated that ethanol watering is an alternative to other growth regulating agents or applications.

Comparative morphological, physiological, biochemical and genomic studies reveal novel genes of Dunaliella bioculata and D. quartolecta in response to salt stress.

Salinity is an essential abiotic stress in plants. Dunaliella is a genus of high-salt-tolerant microalgae. The present study aimed to compare the characterizations of D. bioculata and D. quartolecta at different levels and investigate novel genes response to salt stress. High chlorophyll contents were detected in D. bioculata on the 35th d of salt stress, while high lipid and carotenoid contents were detected in D. quartolecta via morphological and biochemical analyses. Physiological analysis showed that D. quartolecta cells had a smaller increase in osmotic potential, a smaller decrease in the Na+/K+ ratio and photochemical efficiency (Fv/Fm), and a lower relative conductivity than D. bioculata cells. The genomic lengths of D. quartolecta and D. bioculata were 396,013,629bp (scaffold N50 = 1954bp) and 427,667,563bp (scaffold N50 = 3093bp) via high-throughput sequencing and de novo assembly, respectively. Altogether, 25,751 and 26,620 genes were predicted in their genomes by annotation analysis with various biodatabases. The D. bioculata genome showed more segmental duplication events via collinearity analysis. More single nucleotide polymorphisms and insertion-deletion variants were detected in the D. bioculata genome. Both algae, which showed a close phylogenetic relationship, may undergo positive selection via bioinformatics analysis. A total of 382 and 85 novel genes were screened in D. bioculata and D. quartolecta, with 138 and 51 enriched KEGG pathways, respectively. Unlike the novel genes adh1, hprA and serA, the relative expression of livF and phbB in D. bioculata was markedly downregulated as salinity increased, as determined by qPCR analysis. The relative expression of leuB, asd, pstC and proA in D. quartolecta was markedly upregulated with the same salinity increase. Dunaliella quartolecta is more halophilic than D. bioculata, with more effective responses to high salt stress based on the multiphase comparative data.

Southeastern Rear Edge Populations of Quercus suber L. Showed Two Alternative Strategies to Cope with Water Stress

Climate change models predict an increase in aridity, especially in the regions under Mediterranean-type climates such as the Mediterranean Basin. However, there is a lack of ecophysiological studies supporting the selection of the more drought-adapted ecotypes for reforestation programs. In this study, we analyzed the anatomical and functional adaptations of 18-month-old seedlings to drought on 16 Quercus suber L. populations from the southeastern rear edge of the species distribution in northern Tunisia growing in a common garden, in order to identify the most appropriate material to use in reforestations. The results evidenced that populations from more xeric habitats displayed the highest leaf dry mass per area (LMA) and lowest leaf area (LA) values, together with the largest increase in the bulk modulus of elasticity (Δε) in response to drought (i.e., elastic adjustment). On the other hand, some populations with intermediate values of aridity, LMA and LA displayed the sharpest increase in proline concentration (ΔPro), with a concomitant increase in osmotic potential at full turgor (Δπo) (i.e., osmotic adjustment). Therefore, two different strategies seem to drive the within-species variation of the studied Q. suber populations in response to water scarcity: (i) a water saver strategy for improving water stress tolerance through the maximization of the elastic adjustment; and (ii) a water spender strategy for maintaining water absorption and photosynthetic activity under moderate water stress through the maximization of the osmotic adjustment. We concluded that the higher elastic adjustment, together with reduced LA and increased LMA, implied a better performance under drought stress in the populations of Q. suber from more xeric habitats, which can be considered the most drought-adapted ecotypes and, consequently, the most appropriate for reforestation programs under an eventual increase in aridity.

The NAC Protein from Tamarix hispida, ThNAC7, Confers Salt and Osmotic Stress Tolerance by Increasing Reactive Oxygen Species Scavenging Capability.

Plant specific NAC (NAM, ATAF1/2 and CUC2) transcription factors (TFs) play important roles in response to abiotic stress. In this study, we identified and characterized a NAC protein, ThNAC7, from Tamarix hispida. ThNAC7 is a nuclear localized protein and has transcriptional activation activity. ThNAC7 expression was markedly induced by salt and osmotic stresses. Transiently transformed T. hispida seedlings overexpressing ThNAC7 (OE) or with RNA interference (RNAi) silenced ThNAC7 were generated to investigate abiotic stress tolerance via the gain- and loss- of function. Overexpressing ThNAC7 showed an increased reactive oxygen species (ROS) scavenging capabilities and proline content, which was accomplished by enhancing the activities of superoxide dismutase (SOD) and peroxidase (POD) in transiently transformed T. hispida and stably transformed Arabidopsis plants. Additionally, ThNAC7 activated these physiological changes by regulating the transcription level of P5CS, SOD and POD genes. RNA-sequencing (RNA-seq) comparison between wild-type and ThNAC7-transformed Arabidopsis showed that more than 40 known salt tolerance genes might regulated by ThNAC7, including stress tolerance-related genes and TF genes. The results indicated that ThNAC7 induces the transcription level of genes associated with stress tolerance to enhance salt and osmotic stress tolerance via an increase in osmotic potential and enhanced ROS scavenging.

Environmental factors effecting the germination and seedling emergence of two populations of an aggressive agricultural weed; Nassella trichotoma.

Nassella trichotoma (Nees) Hack. ex Arechav. (Serrated tussock) is an aggressive globally significant weed to agricultural and natural ecosystems. Herbicide resistant populations of this C3 perennial weed have emerged, increasing the need for effective wide-scale cultural control strategies. A thorough seed ecology study on two spatially distinct populations of N. trichotoma was conducted on this weed to identify differences in important environmental factors (drought, salinity, alternating temperature, photoperiod, burial depth, soil pH, artificial seed aging, and radiant heat) which influence seed dormancy. Seeds were collected from two spatially distinct populations; Gnarwarre (38 O 9' 8.892'' S, 144 O 7' 38.784'' E) and Ingliston (37O 40' 4.44'' S, 144 O 18' 39.24'' E) in December 2016 and February 2017, respectively. Twenty sterilized seeds were placed into Petri dishes lined with a single Whatman® No. 10 filter paper dampened with the relevant treatments solution and then incubated under the identified optimal alternating temperature and photoperiod regime of 25°C/15°C (light/dark, 12h/12h). For the burial depth treatment, 20 seeds were placed into plastic containers (10cm in diameter and 6cm in depth) and buried to the relevant depth in sterilized soil. All trials were monitored for 30 days and germination was indicated by 5mm exposure of the radicle and emergence was indicated by the exposure of the cotyledon. Each treatment had three replicates for each population, and each treatment was repeated to give a total of six replicates per treatment, per population. Nassella trichotoma was identified to be non-photoblastic, with germination (%) being similar under alternating light and dark and complete darkness conditions. With an increase of osmotic potential and salinity, a significant decline in germination was observed. There was no effect of pH on germination. Exposure to a radiant heat of 120°C for 9 minutes resulted in the lowest germination in the Ingliston population (33%) and the Gnarwarre population (60%). In the burial depth treatment, the Ingliston population and the Gnarwarre population had highest emergence of 75% and 80%, respectively at a depth of 1cm. Variation between the two populations was observed for the burial depth treatments; Gnarwarre had greater emergence than Ingliston from the 4cm burial depth, while Ingliston had greater emergence at the soil surface than Gnarwarre. The Gnarwarre population had greater overall germination than Ingliston, which could be attributed to the greater seed mass (0.86mg compared to 0.76mg, respectively). This study identifies that spatial variations in N. trichotoma’s seed ecology are present between spatially distinct populations.

A Short Non-Saline Sprinkling Increases the Tuber Weights of Saline Sprinkler Irrigated Potatoes

Previous work has shown that a short non-saline sprinkling, following saline sprinkling, increased crop growth. We incorporated this finding into an investigation of two approaches to the conjunctive use of saline and non-saline water sources for sprinkler irrigation of potatoes viz., (i) mixing waters prior to application, and (ii) keeping waters temporally separate, that is commencing each irrigation with saline water and finishing it with non-saline sprinkling. The latter approach delayed canopy senescence and increased tuber weight by at least 150%. Under both approaches, soil salinities and leaf and tuber concentrations of Na+ and Cl− were similar. Thus, the advantages of a non-saline sprinkling cannot be explained in terms of its effect on either soil osmotic potential or bulk tissue concentrations of putatively toxic ions Na+ and Cl−. We propose that the positive effect of finishing irrigations with a non-saline sprinkling may be attributed to either dilution, and hence increase in osmotic potential, of the water film that remains on the leaf after each irrigation or its effect on the distribution of the putatively toxic ions Na+ and Cl− within tissue.

Structural and metabolic changes in rhizophores of the Cerrado species Chrysolaena obovata (Less.) Dematt. as influenced by drought and re-watering.

The high fructan contents in underground organs of Cerrado species, high water solubility, and fast metabolism of these compounds highlight their role as carbon storage and as an adaptive feature in plants under drought. In this study, we showed that anatomical structure, in association with soluble compounds and metabolism of inulin-type fructans were modified in rhizophores of Crysolaena obovata submitted to water suppression and recovery after re-watering. Plants were subjected to daily watering (control), suppression of watering for 22 days (water suppression) and suppression of watering followed by re-watering after 10 days (re-watered). Plants were collected at time 0 and after 3, 7, 10, 12, 17, and 22 days of treatment. In addition to changes in fructan metabolism, high proline content was detected in drought stressed plants, contributing to osmoregulation and recovery after water status reestablishment. Under water suppression, total inulin was reduced from approx. 60 to 40%, mainly due to exohydrolase activity. Concurrently, the activity of fructosyltransferases promoted the production of short chain inulin, which could contribute to the increase in osmotic potential. After re-watering, most parameters analyzed were similar to those of control plants, indicating the resumption of regular metabolism, after water absorption. Inulin sphero-crystals accumulated in parenchymatic cells of the cortex, vascular tissues and pith were reduced under drought and accompanied anatomical changes, starting from day 10. At 22 days of drought, the cortical and vascular tissues were collapsed, and inulin sphero-crystals and inulin content were reduced. The localization of inulin sphero-crystals in vascular tissues of C. obovata, as well as the decrease of total inulin and the increase in oligo:polysaccharide ratio in water stressed plants is consistent with the role of fructans in protecting plants against drought.

Study of Germination and Seedling Growth of Black Cumin (Nigella Sativa L.) Treated by Hydro and Osmopriming under Salt Stress Conditions

Abstract The objective of the study was to determine the responsible factors for germination and early seedling growth due to salt toxicity or osmotic effect and to optimize the best priming treatment for these stress conditions. To study the effect of osmopriming and hydropriming on germination and seedling growth of black cumin (Nigella sativa L.) under salt stress conditions this experiment was conducted at Torbat-Heydariyeh University, Torbat, Iran. The treated seeds (control, hydropriming and ZnSO4) of black cumin were evaluated at germination and seedling growth for tolerance to salt (NaCl and Na2SO4) conditions at the same water potentials of 0.0, -0.3, -0.6, -0.9 and -1.2MPa. Electrical conductivity (EC) values of the NaCl solutions were 0.0, 6.5, 12.7, 18.4 and 23.5 dSm-1, respectively. Results showed that hydropriming increased germination and seedling growth under salt stress. Germination delayed in both solutions, having variable germination with different priming treatments. In NaCl treatment, germination percentage, root and shoot weight, shoot and root length were higher but mean germination time and abnormal germination percentage were lower than Na2SO4, at the same water potential. The root / shoot weight and R/S length enhanced with increase of osmotic potential in both NaCl and Na2SO4 solutions. NaCl had less inhibitor effect on seedling growth than the germination. It was concluded that inhibition of germination at the same water potential of NaCl and Na2SO4 resulted from salt toxicity rather than osmotic effect. The findings of this experiment can be useful and applied to achieve best germination and uniform emergence under field conditions for farmers of medicinal plants.

Semicontinuous Culture of Magnetospirillum gryphiswaldense MSR-1 Cells in an Autofermentor by Nutrient-Balanced and Isosmotic Feeding Strategies

An improved strategy was developed for the high-density culture of Magnetospirillum gryphiswaldense strain MSR-1 and large-scale magnetosome production in both 7.5- and 42-liter autofermentors. By using a nutrient-balanced feeding strategy and the replacement of carbon and nitrogen sources to reduce accumulation of Na(+) and Cl(-) ions, we reduced the factors that tend to inhibit cell growth, particularly the increase of osmotic potential. Semicontinuous culture was thereby achieved in the autofermentor for the first time. When the cells were harvested at 36 and 73 h, magnetosome yields (dry weight) as high as 168.3 and 83.5 mg/liter/day, respectively, were achieved. These values were, respectively, approximately 10 and 5 times higher than the yields achieved in previous studies and represent a significant improvement in magnetosome production efficiency.

An evaluation of safflower genotypes ( Carthamus tinctorius L.), seed germination and seedling characters in salt stress conditions

In order to study the effect of salinity stress on germination and early seedling growth of six safflower genotypes namely KM5, KM8, KM12, KM19, KM47 and Kose by using five concentrations of NaCl (0, -0.3, -0.5, -1 and -1.5 MPa) a factorial experiment was designed using Completely Randomized Design (CRD) with three replications in Biotechnology Laboratory, Islamic Azad University-Karaj Branch. Results of ANOVA showed that salt stress adversely affected the germination percentage, germination rate, shoot length, root length, seedling length, root/shoot length ratio, seed vigour, and germination index and mean germination time of all 6 genotypes of safflower, which demonstrates high diversity among genotypes that enabled us to screen salinity tolerant cultivar. At the highest salt level (-1.5 MPa), Kose produced maximum germination percentage and germination rate of all genotypes and they were considered as relatively tolerant. Best level of NaCl concentration in root length, shoot length, seedling length and seed vigour was -0.3 MPa. Seed vigour increased with increase in osmotic potential until -0.3 MPa but decreased in -0.5 MPa. Results of cluster analysis (Ward’s minimum variance method) at the highest salt level (-1.5 MPa) classified all genotypes into three group. According to the obtained results, we found that Kose is the most resistant and KM5, KM8 and KM47 are the most sensitive genotypes. Key words: Cluster analysis, germination indices, NaCl, seed vigour

ISO-OSMOTIC REGULATION OF NITRATE ACCUMULATION IN LETTUCE

Concerns about possible health hazards arising from human consumption of lettuce and other edible vegetable crops with high concentrations of nitrate have generated demands for a greater understanding of processes involved in its uptake and accumulation in order to devise more sustainable strategies for its control. This paper evaluates a proposed iso-osmotic mechanism for the regulation of nitrate accumulation in lettuce (Lactuca sativa L.) heads. This mechanism assumes that changes in the concentrations of nitrate and all other endogenous osmotica (including anions, cations and neutral solutes) are continually adjusted in tandem to minimize differences in osmotic potential of the shoot sap during growth, with these changes occurring independently of any variations in external water potential. The hypothesis was tested using data from six new experiments, each with a single unique treatment comprising a separate combination of light intensity, nitrogen (N) source (nitrate with or without ammonium) and nitrate concentration carried out hydroponically in a glasshouse using a butterhead lettuce variety. Repeat measurements of plant weights and estimates of all of the main soluble constituents (nitrate, potassium, calcium, magnesium, organic anions, chloride, phosphate, sulphate and soluble carbohydrates) in the shoot sap were made at intervals from about 2 weeks after transplanting until commercial maturity, and the data used to calculate changes in average osmotic potential in the shoot. Results showed that nitrate concentrations in the sap increased when average light levels were reduced by between 30 and 49% and (to a lesser extent) when nitrate was supplied at a supra-optimal concentration, and declined with partial replacement of nitrate by ammonium in the external nutrient supply. The associated changes in the proportions of other endogenous osmotica, in combination with the adjustment of shoot water content, maintained the total solute concentrations in shoot sap approximately constant and minimized differences in osmotic potential between treatments at each sampling date. There was, however, a gradual increase in osmotic potential (i.e., a decline in total solute concentration) over time largely caused by increases in shoot water content associated with the physiological and morphological development of the plants. Regression analysis using normalized data (to correct for these time trends) showed that the results were consistent with a 1:1 exchange between the concentrations of nitrate and the sum of all other endogenous osmotica throughout growth, providing evidence that an iso-osmotic mechanism (incorporating both concentration and volume regulation) was involved in controlling nitrate concentrations in the shoot.

Micronutrient and hydro priming of seed to overcome salt stress during germination in cumin (Cuminum cyminum L.)

In production of medicinal plants, seed germination is a very important problem. The treated seeds (control, hydropriming and Zn2SO4) of Cumin (Cuminum cyminum L.) were evaluated at germination and seedling growth for tolerance to salt (NaCl and Na2SO4) conditions at the same water potentials of 0.0, –0.3, –0.6, –0.9 and –1.2 MPa. Electrical conductivity (EC) values of the NaCl solutions were 0.0, 6.5, 12.7, 18.4 and 23.5 dS.m-1, respectively. The objective of the study was to determine factors responsible for germination and early seedling growth due to salt toxicity or osmotic effect and to optimize the best priming treatment for these stress conditions. Results revealed that germination delayed in both solutions, having variable germination with different priming treatments. Germination, shoot and weight, root and shoot length were higher but mean germination time and abnormal germination percentage were lower in NaCl than Na2SO4 at the same water potential. The root/shoot weight and R/S length increased with increase in osmotic potential in both NaCl and Na2SO4 solutions. NaCl had less inhibitor effect on seedling growth than the germination. It was concluded that inhibition of germination at the same water potential of NaCl and Na2SO4 resulted from salt toxicity rather than osmotic effect. Hydropriming increased germination and seedling growth under salt stress. This protocol has practical importance and could be recommended to farmers to achieve higher germination and uniform emergence under field conditions.

Hydropriming and Osmopriming Effects on Cumin(Cuminum Cyminum L.) Seeds Germination

In production of medicinal plants, seed germination is very important problem. The treated seeds (control, hydro priming and ZnSO4) of Cumin (Cuminum cyminum L.) were evaluated at germination and seedling growth for tolerance to salt (NaCl and Na2SO4) conditions at the same water potentials of 0.0, -0.3, -0.6, - 0.9 and -1.2MPa. Electrical conductivity (EC) values of the NaCl solutions were 0.0, 6.5, 12.7, 18.4 and 23.5 dSm -1 , respectively. The objective of the study was to determine factors responsible for germination and early seedling growth due to salt toxicity or osmotic effect and to optimize the best priming treatment for these stress conditions. Results revealed that germination delayed in both solutions, having variable germination with different priming treatments. Germination, shoot and weight, root and shoot length were higher but mean germination time and abnormal germination percentage were lower in NaCl than Na2SO4 at the same water potential. The root / shoot weight and R/S length increased with increase in osmotic potential in both NaCl and Na2SO4 solutions. NaCl had less inhibitor effect on seedling growth than the germination. It was concluded that inhibition of germination at the same water potential of NaCl and Na2SO4 resulted from salt toxicity rather than osmotic effect. Hydro priming increased germination and seedling growth under salt stress. This protocol has practical importance and could be recommended to farmers to achieve higher germination and uniform emergence under field conditions. Keywords—Priming, Germination, Nacl, ZnSo4, Na2So4.

Rapid stalk elongation in tulip (Tulipa gesneriana L. cv. Apeldoorn) and the combined action of cold-induced invertase and the water-channel protein gammaTIP.

Many bulbous plants need a low-temperature treatment for flowering. Cold, for example, affects the elongation of the stalk, thereby influencing the quality of the cut flower. How the elongation of the stalk is promoted by cold and which physiological and biochemical mechanisms are involved have remained obscure. As invertase has been shown to be involved in the cold-induced elongation of the flower stalks of tulips (Lambrechts et al., 1994, Plant Physiol 104: 515-520), we further characterized this enzyme by cloning the cDNA and analysing its expression in various tissues of the tulip (Tulipa gesneriana L. cv. Apeldoorn) stalk. In addition, the role of sucrose synthase was investigated. Since turgor pressure is an important force driving cell elongation, the role of a water-channel protein (gammaTIP) was studied in relation to these two enzymes. The mRNA level of the invertase found was substantially up-regulated as a result of cold treatment. Analysis of the amino acid sequence of this invertase revealed the presence of a vacuolar targeting signal. Two different forms of sucrose synthase were found, the expression of one of them appeared to be restricted to the vascular tissue while the other form was present in the surrounding tissue. Both sucrose synthases were present in the stalk during the entire period of bulb storage and after planting, but their activities declined during stalk elongation. The expression of the gammaTIP gene was restricted mainly to the vascular tissue and its expression profile was identical to that of invertase. Simultaneous expression of invertase and gammaTIP possibly leads to an increase in osmotic potential and vacuolar water uptake, thus providing a driving force for stretching the stalk cells.

CH4 oxidation in two temperate arable soils as affected by nitrate and ammonium application

The short-term effect of NaNO3 or (NH4)2SO4 application on CH4 oxidation was measured under laboratory conditions with sieved soils collected from the top layer (0–12 cm) of a loamy and a sandy soil. The soils were incubated in sealed flasks and the CH4 and CO2 concentrations in headspace were measured periodically. On each gas sampling date the soils were analysed for inorganic N, electro-ultrafiltration organic N, and pH. NH 4 + application to the loamy soil inhibited CH4 oxidation entirely whereas in the untreated control soils CH4 concentration decreased linearly with a rate of-41 nl CH4 l-1 h-1; NO 3 sup- application to this soil caused a small but significant reduction in CH4 uptake. The CH4-oxidizing ability of the sandy soil was low, even in the control. This was mainly a result of the disturbed soil structure after sieving. Both NH 4 + and NO 3 sup- treatments completely inhibited CH4 uptake in this ligh-textured soil. The adverse impact of NH 4 + persisted during the entire incubation, although in the loamy soil only 17% of the NH 4 + added was recovered after 168 h. The negative effect of NO 3 sup- was probably caused by an increase in osmotic potential. Immediate inhibition of CH4 oxidation after inorganic N addition was demonstrated in two arable soils, although the effect was directly related only in part to soil N transformations.

Effet de deux extraits biologiques sur l'embryogenèse somatique et sur la rétention des capacités de régénération chez les cals de blé (Triticum aestivum)

The effect of extracts of potato or immature wheat seeds, polyethylene glycol, or mannitol on the embryogenic capacity of calli derived from half or whole immature embryos of wheat (Triticum aestivum L.) has been studied. Calli initiated from embryo halves give the same yield of somatic embryos and regenerated plantlets as calli from whole embryo cultures. Compared to control cultures, calli initiated on potato extract are more embryogenic (> 70% embryogenic calli), form bigger embryos in a more reduced number, but that show a higher frequency of plant regeneration and longer retention of the regeneration capacity. The calli initiated on a wheat seed extract form less embryogenic calli and more but smaller somatic embryos; they have a shorter retention of their regeneration capacity. Increase in osmotic potential by addition of polyethylene glycol or mannitol to the culture medium did not improve somatic embryogenesis. Key words: Triticum aestivum, callus, embryogenesis, biological extracts.

Effect of calcium on callus friability and somatic embryogenesis inHevea brasiliensisMüll. Arg.: relations with callus mineral nutrition, nitrogen metabolism and water parameters

Des modifications de la teneur en calcium des milieux de culture influent sur le developpement embryonnaire et sur le status hydrique et mineral des cals chez Hevea brasiliensis. Des concentrations du milieu de culture inferieures a 9mM CaCl2 aboutissent a l'obtention de cals friables qui peuvent se developper en embryons somatiques, a condition de les transferer sur un milieu de culture a faible teneur en calcium. L'existance d'interactions entre le calcium et les facteurs de croissance est donc supposee. La modification de la texture ainsi que l'apparition d'une capacite morphogenetique s'accompagnent d'une chute du potentiel de turgescence et de la quantite d'eau disponible, malgre une augmentation de la teneur en eau. Cette modification s'accompagne egalement d'une modification des besoins nutritionnels en elements mineraux, d'une chute de l'absorption d'azote associees a une augmentation de potentiel osmotique et d'une chute de la synthese proteique

Seasonal variations in water relations of roses (Rosa hybrida cv. Sonia)

Parameters of water relations were measured throughout the season in phenologically identical leaves of rose plants grown in a heated greenhouse. The increase in osmotic potential observed from spring to early autumn seems to result from the decrease in the non-osmotic water fraction, and, conversely, its decrease from early autumn to winter seems to be due to an increase in the non-osmotic water fraction. These observations support the hypothesis that the non-osmotic water fraction may be correlated to starch concentration in rose leaves.

Amelioration of Chilling Injury in Phaseolus vulgaris L. by GLK-8903

GLK-8903, an experimental product whose main ingredient is produced by hydrogenation of a primary alcohol extracted from plants, showed significant potential in protecting bean (Phaseolus vulgaris L.) plants from chilling injury. The GLK-8903 protection mechanism was assessed by examining several physiological and biochemical responses. The decline in leaf water potential and the increase in osmotic potential caused by chilling exposure to 4C (day/night) were minimized by the application of GLK-8903. Chilling causes an increase in electrolyte leakage, an indication of chilling injury of the plasma membrane. Increased electrolyte leakage was reduced significantly in the GLK-8903-treated plants during chilling. This minimized leakage may be due to less damage of the plasma membrane. Plasmolysis and deplasmolysis studies of the epidermal cells suggest that GLK-8903 is able to reduce the plasma membrane perturbation in the chilling environment, as evident by: 1) the lower permeability coefficient to urea at 4C, and 2) the swelling of protoplasts in the cells of untreated tissues after chilling exposure with no swelling of the protoplast being observed in the GLK-8903-treated cells. Malondialdehyde (MDA), a product of lipid peroxidation, increased more in untreated controls than in treated plants exposed to 4C. Plasma membrane ATPase activity decreased less in GLK-8903-treated plants than in untreated controls after 3 days at 4C. The mechanism of GLK-8903-alleviated chilling injury is discussed.