NaCl induced morpho-biochemical and anatomical changes in mulberry (<Emphasis Type="Italic">Morus</Emphasis> spp.)

Mulberry is an economically important tree, used for feeding the silkworm Bombyx mori L. Effect of different levels of NaCl on growth and development of mulberry has been studied using five mulberry genotypes selected on the basis of their performance under in vitro salinity. The study while endorsing the efficacy of in vitro screening of axillary buds of mulberry for salt tolerance, showed genotypic variability in its response to salinity. Salinity reduced growth and development of all genotypes. However, the putative tolerant genotypes showed better performance than the putative susceptible genotypes. Under low salinity (<0.5% NaCl) salt tolerant genotypes showed an increase in chlorophyll and protein concentrations, while in susceptible genotypes both were reduced by 3–58% at 0.5% NaCl and 50–64% at 1.00% NaCl. Leaf thickness increased by 16% at 1.00% NaCl in C776 and reduced by 1.0% in Mandalaya. The increase in chlorophyll concentration and leaf thickness under high salinity can be considered as preliminary selection parameters for salt tolerance in mulberry. The study confirmed the efficacy of in vitro method for screening of large number of genotypes for salt tolerance in mulberry.     

Transformation of potato using mannopine and cucumopine strains of Agrobacterium rhizogenes

Mannopine and cucumopine strains of Agrobacterium rhizogenes were used for genetic transformation in two cultivars of potato (Solanum tuberosum L.). An overnight pretreatment of stem fragments with NAA prior to bacterial infection was necessary to induce root formation, otherwise very few roots were produced. Whatever the potato cultivar used, rhizogenesis induced by NAA pretreament depended on the bacterial strain. In fact, when explants from both potato cultivars were pretreated with 26.5 M NAA, on average 84.4% and 71.9% produced roots after inoculation with the strains 2659 and 2659 GUS respectively. On the contrary, few rhizogenic responses (2.0–17.0%) or no response at all (0.0%) were obtained with the strains 15834 and 8196 GUS whatever NAA concentration used. Tests for confirming stable transformation of plant explants by examining both -glucuronidase activity and the presence of opines showed that 85% of the selected roots were cotransformed. Most of the transformed roots were highly branched and grew rapidly, compared to non-transformed roots with no branching and poor growth. Transgenic plants were readily regenerated with a frequency reaching 80% of total explants tested for both potato cultivars.Abbreviations BA 6-benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - df degree of freedom - F F distribution - GA₃ gibberellic acid - MS Murashige and Skoog basal medium - NAA -naphthaleneacetic acid - P probability - T-DNA transferred DNA     

In vitro response of promising mulberry (Morus sp.) genotypes for tolerance to salt and osmotic stresses

An in vitro technique for screening mulberry genotypes tolerant to salt and osmotic stress has been standardized.Five mulberry genotypes, namely G2, G3, G4 along with control varieties i.e., S34 and S13, were tested on salt and osmotic stress media. Out of 14 media combinations tested, the optimum responses were observed on Kn 1 mg/l, in the case of G3 genotype, on Kn 2 mg/l with G2 genotype, on BAP 1 mg/l with G4 genotype and on BAP 2 mg/l with S34 and S13 genotypes.With regard to their performance on salt-stress media fortified with NaCl (0.1--2.0%), Na₂CO₃ + NaHCO₃ (pH 8.5--10.0), the data revealed that the genotype G4 ranked the highest in terms of sprouting percentage and shoot length, in comparison to the control variety (S34) at each concentration of NaCl up to 1.0% and pH up to 9.5. However, in the case of osmotic stress condition (media supplemented with 1.0--10.0% PEG),the control variety i.e. S13 itself exhibited the highest sprouting percentage and shoot growth compared to the other test genotypes. The genotype G4 has been screened as a salt tolerant genotype which can be tested under respective in vivo condition.     

The effects of in vitro and ex vitro root initiation on subsequent microcutting root quality in three woody plants

In vitro- and ex vitro-rooted microcuttings of Acer rubrum L. Red Sunset, Betula nigra L., and Malux x- domestica Borkh McIntosh were distinguished by several important anatomical and morphological properties which continued to regulate both root system and whole plant quality in later stages of production. In vitro microcuttings formed adventitious roots in greater number and more quickly than ex vitro microcuttings. Roots produced in vitro were characterized by extremely enlarged cortical cells and, consequently, had a much greater diameter than ex vitro roots. However, the vascular system of in vitro roots was underdeveloped (primary vascular tissues only) as compared to ex vitro roots, which produced vascular cambium and secondary growth during the same early stage of production. At least 50% of the post-transplant in vitro adventitious roots either died immediately, or temporarily persisted during acclimatization without producing any further growth. For the surviving in vitro-produced roots, the cortex partially collapsed after transplant, and new root extensions with ex vitro-like structure were produced. Only then did the in vitro portion of the root begin to form secondary vascular tissues. Shoots from in vitro treatments continued to grow vigorously during adventitious root initiation and during acclimatization, so that the plants were significantly taller and had a greater shoot area than those receiving comparable ex vitro rooting treatment. In vitro rooting led to a horizontal root morphology which continued to distinguish these treatments from ex vitro rooted plants during later stages of production, when anatomical differences in the roots could no longer be detected.Abbreviations BA benzyladenine - IBA indole-3-butyric acid - MS Murashige and Skoog medium - NAA naphthaleneacetic acid - PPF photosynthetic photon flux - TDZ thidiazuron - WPM woody plant medium     

Hairy root culture optimization and resveratrol production from <Emphasis Type="Italic">Vitis vinifera</Emphasis> subsp. <Emphasis Type="Italic">sylvesteris</Emphasis>

Resveratrol is a polyphenolic compound produced in very low levels in grapes. To achieve high yield of resveratrol in wild grape, three Agrobacterium rhizogenes strains, Ar318, ArA4 and LBA9402, were used to induce hairy roots following infection of internodes, nodes or petioles of in vitro grown Vitis vinifera subsp. sylvesteris accessions W2 and W16, and cultivar Rasha. The effects of inoculation time, age of explants, bacterial concentration and co-cultivation times were examined on the efficiency of the production of hairy roots. Strains Ar318, ArA4 and LBA9402 all induced hairy roots in the tested genotypes, but the efficiency of ArA4 strain was higher than the other strains. The highest hairy root production was with using internodes as explants. The transformation of hairy roots lines was confirmed by PCR detection of rolB gene. Half Murashige and Skoog (MS) medium was better for biomass production compared with MS medium. HPLC analysis of resveratrol production in the hairy root cultures showed that all the genotypes produced higher amounts of resveratrol than control roots. The highest amount of resveratrol was produced from W16 internode cultures, which was 31-fold higher than that of control root. Furthermore, TLC analysis showed that treatments of hairy roots with sodium acetate and jasmonate elevated resveratrol levels both in hairy root tissue and excreted into the half MS medium. These results demonstrate that endogenous and exogenous factors can affect resveratrol production in hairy root culture of grape, and this strategy could be used to increase low resveratrol production in grapes.     

Salt oversensitivity derived from mutation breeding improves salinity tolerance in barley <Emphasis Type="Italic">via</Emphasis> ion homeostasis

Salt stress imposes a major environmental threat to agriculture, therefore, understanding the basic physiology and genetics of cell under salt stress is crucial for developing any breeding strategy. In the present study, the expression profile of genes involved in ion homeostasis including salt overly sensitive (HvSOS1, HvSOS2, HvSOS3), vacuolar Na⁺/H⁺ antiporter (HvNHX1), and H⁺-ATPase (HVA) along with ion content measurement were investigated in two genotypes of Hordeum vulgare under 300 mM NaCl. The gene expressions were measured in the roots and shoots of a salt-tolerant mutant genotype M4-73-30 and in its wild-type cv. Zarjou by real-time qPCR technique. The critical differences between the salt-tolerant mutant and its wild-type were observed in the expressions of HvSOS1 (105-fold), HvSOS2 (24-fold), HvSOS3 (31-fold), and HVA (202-fold) genes in roots after 6-h exposure to NaCl. The parallel early up-regulation of these genes in root samples of the salt-tolerant mutant genotype indicated induction of Na⁺/H⁺ antiporters activity and Na+ exclusion into apoplast and vacuole. The earlier up-regulation of HvSOS1, HVA, and HvNHX1 genes in shoot of the wild-type genotype corresponded to the relative accumulation of Na⁺ which was not observed in salt-tolerant mutant genotype because of efficient inhibitory role of the root in Na+ transport to the shoot. In conclusion, the lack of similarity in gene expression patterns between the two genotypes with similar genetic background may confirm the hypothesis that mutation breeding could change the ability of salt-tolerant mutant genotype for efficient ion homeostasis via salinity oversensitivity response.     

Responses of grass pea seedlings to salinity stress in in vitro culture conditions

Physiological and molecular mechanisms of adaptation to abiotic stresses of grass pea (Lathyrus sativus L.) are still poorly understood. Responses of four genotypes of grass pea to salinity stress in tissue culture conditions were investigated at early seedling growth stages. Salinity stress was induced in the agar media by adding 0, 50, 100 and 200 mM of NaCl. Germination and seedling emergence percentage was not significantly affected by 50 and 100 mM of NaCl. However, NaCl in 200 mM concentration lowered level of these parameters. Generally, exposure to NaCl stress significantly reduced length of grass pea seedling organs (root and shoot) but did not influence the content of dry weight in shoots and increased it in the roots in two cases. Increasing salt concentration decreased integrity of cellular membranes both in root and shoot tissues. Higher accumulation of phenolic compounds and significant changes in activity of antioxidant enzymes (peroxidase and catalase) were observed in the roots but not in the shoots. Similarly, the content of proline increased mostly in the roots from moderate (100 mM) salinity conditions. Adverse conditions did not resulted in alterations in photosynthetic pigments content of any tested genotypes. The better performance of shoots than roots may result from in vitro conditions in which experiments were conducted.

     

Tolerance of submerged germinating rice to 50–200 mM NaCl in aerated solution

This paper concerns tolerance to 50–200 mM NaCl of submerged rice (Oryza sativa cv. Amaroo) during germination and the first 138–186 h of development in aerated solution. Rice was able to germinate and the seedlings even tolerated exposure to 200 mM NaCl, albeit with severe growth restrictions. After return to 0.3 mM NaCl, growth increased, indicating that even at 200 mM NaCl there was no irreparable injury. Osmotic adjustment was achieved by using Na⁺ and Cl^– as the major osmotica. At 200 mM NaCl commenced at sowing, the shoot Na⁺ and Cl^– concentrations between 50–110 h were about 210 and 260 mM, respectively, i.e. above the external concentration. Thus, there was a high tissue tolerance to NaCl. The internal concentrations declined subsequently, concurrent with a decline in growth. At 50–200 mM NaCl, the contributions from ions to π_sap were 81–92% in roots and 62–74% in shoots. The assessed turgor pressures at 200 mM NaCl were 0.33 MPa in shoots and 0.15 MPa in roots, compared to 0.62 and 0.43 MPa at 0.3 mM NaCl. In the General Discussion section, we compare the different responses of submerged seedlings to the responses of transpiring rice plants, reported in the literature, and suggest that the submerged system is useful to evaluate effects of NaCl on turgor pressure and particularly to establish whether there are specific effects of Na⁺ and Cl^– in tissues.     

Glutathione synthesis in maize genotypes with different sensitivities to chilling

The effect of chilling on enzymes, substrates and products of sulfate reduction, gultathione synthesis and metabolism was studied in shoots and roots of maize (Zea mays L.) genotypes with different chilling sensitivity. At full expansion of the second leaf, chilling at 12 °C inhibited dry weight increase in shoots and roots compared to controls at 25 °C and induced an increase in adenosine 5-phosphosulfate sulfotransferase and -glutamylcysteine synthetase (EC 6.3.2.2) activity in the second leaf of all genotypes tested. Glutathione synthetase (EC 6.3.2.3) activity was about one order of magnitude higher than -glutamylcysteine synthetase activity, but remained unchanged during chilling except for one genotype. During chilling, cysteine and glutathione content of second leaves increased to significantly higher levels in the two most chilling-tolerant genotypes. Comparing the most tolerant and most sensitive genotype showed that chilling induced a greater incorporation of³⁵S from [³⁵S]sulfate into cysteine and glutathione in the chilling-tolerant than in the sensitive genotype. Chilling decreased the amount of³⁵S-label incorporated into proteins in shoots of both genotypes, but had no effect on this incorporation in the roots. Glutathione reductase (EC 1.6.4.2) and nitrate reductase (EC 1.6.6.1) activity were constitutively higher in the chilling-tolerant genotypes, but showed no changes in most examined genotypes during 3 d at 12 °C. Our results indicate that in maize glutathione is involved in protection against chilling damage.Abbreviations APSSTase adenosine 5-phosphosulfate sulfotransferase - EC -glutamylcysteine - GR glutathione reductase - OSH glutathione - NR nitrate reductase We thank M. Suter for preparing [³⁵S]adenosine 5-phosphosulfate, Dr. A. Fleming (both our Institute) for correcting the English and M. Soldati (Eschlikon, Switzerland) for his help with the plant material. This work was supported by COST 814 Crop development for the wet and cool regions of Europe.     

Plant regeneration from hairy-root cultures transformed by infection with<Emphasis Type="Italic"> Agrobacterium rhizogenes</Emphasis> in<Emphasis Type="Italic"> Catharanthus roseus</Emphasis>

Hypocotyl explants of Catharanthus roseus produced hairy roots when cultured on Murashige and Skoog (MS) basal medium after infection by Agrobacterium rhizogenes. Explants gave rise to adventitious shoots at a frequency of up to 80% when cultured on MS medium supplemented with 31.1 M 6-benzyladenine and 5.4 M -naphthaleneacetic acid. There was a significant difference in the frequency of adventitious shoot formation for each hairy-root line derived from a different cultivar. Plants derived from hairy roots exhibited prolific rooting and had shortened internodes. Approximately half of the plants had wrinkled leaves and an abundant root mass with extensive lateral branching, but otherwise appeared morphologically normal. Plants with hairy roots that were derived from the cultivar Cooler Apricot developed flowers with petals that were white in the proximal region, whereas the wild-type flower petals are red. PCR and Southern blot analyses revealed that plants derived from hairy roots retained the Ri TL-DNA.Abbreviations BA 6-Benzyladenine - MS Murashige and Skoog medium - NAA -Naphthaleneacetic acid - SH Schenk and Hildebrandt mediumCommunicated by I.S. Chung     

Relative importance of Na+, Cl−, and abscisic acid in NaCl induced inhibition of root growth of rice seedlings

The relative importance of endogenous abscisic acid (ABA), as well as Na⁺ and Cl^– in NaCl-induced responses related to growth in roots of rice seedlings were investigated. The increase in ammonium, proline and H₂O₂ levels, and cell wall peroxidase (POD) activity has been shown to be related to NaCl-inhibited root growth of rice seedlings. Increasing concentrations of NaCl from 50 to 150 mM progressively decreased root growth and increased both Na⁺ and Cl^–. Treatment with NaCl in the presence of 4,4-diisothiocyano-2,2-disulfonic acid (DIDS, a nonpermeating amino-reactive disulfonic acid known to inhibit the uptake of Cl^–) had less Cl^– level in roots than that in the absence of DIDS, but did not affect the levels of Na⁺, and responses related to growth in roots. Treatment with 50 mM Na-gluconate (the anion of which is not permeable to membrane) had similar Na⁺ level in roots as that with 100 mM NaCl. It was found that treatment with 50 mM Na-gluconate effected growth reduction and growth-related responses in roots in the same way as 100 mM NaCl. All these results suggest that Cl^– is not required for NaCl-induced responses in root of rice seedlings. Endogenous ABA level showed no increase in roots of rice seedlings exposed to 150 mM NaCl. It is unlikely that ABA is associated with NaCl-inhibited root growth of rice seedlings.     

The differential effect of N6-benzyl-adenine and N6-(Δ2-isopentenyl)-adenine on in vitro propagation of Paeonia suffruticosa Andr. is correlated with different hormone contents

Summary N⁶-benzyl-adenine (BA) enhanced phyllogenesis and axillary bud development of Paeonia suffruticosa during in vitro culture allowing good propagation while N⁶-(²isopentenyl)adenine (iP) did not. During the first five days of culture, the mitotic activity of BA-treated explants was higher than in the iP-treated ones. High BA levels were detected in the BA-treated explants, and this was correlated with the absence of or the low indole-3-acetic acid (IAA) content. The low iP levels measured in iP-treated explants were correlated with high endogenous IAA content; the new cytokinin / auxin ratio could explain the lack of axillary buds and the development of only one leaf. Abscisic acid (ABA) was detected neither in the controls nor in the cytokinin-treated explants during the first week. However, intensive restoration of ABA accumulation was observed in controls from the third week onwards. Both BA and iP-treated explants accumulated less ABA than the controls but this hormone appeared later in the BA-treated explants than in the iP-treated ones.Abbreviations ABA abscisic acid - BA N⁶-benzyl-adenine - BHT butyl-hydroxy-toluene - ELISA enzyme linked immunosorbent assay - FM fresh mass - HPLC high performance liquid chromatography - IAA indole-3-acetic acid - iP N⁶-(²-isopentenyl)adenine - MI mitotic index - 9RBA 9-ß-D-ribofuranosyl-BA - 9RiP 9-ß-Dribofuranosyl-iP - 9RZ 9-ß-D-ribofuranosyl-zeatin - Z zeatin     

Changes in pathogenesis-related proteins in pepper plants with regard to biological control of phytophthora blight with <Emphasis Type="Italic">Paenibacillus illinoisensis</Emphasis>

To evaluate the biocontrol effectiveness of chitinase-producing bacterium, Paenibacillus illinoisensis strain KJA-424 against pathogenic strain of Phytophthora capsici in pepper plants, growth response and kinetics of pathogen related (PR) proteins were estimated after inoculation with P. capsici (P), and with a combination of P. capsici and strain KJA-424 cell culture (P+A). Fresh weight and chlorophyll content in shoots at P+A-treated plants significantly increased by 23.4 and 34.2%, respectively after 7days of inoculation, compared to P-treated plants. Root mortality in P+A-treated plants was significantly reduced compared to P-treated plants. Seven days after inoculation, the activities of -1,3-glucanase, cellulase and chitinase in P-treated roots had decreased by 54.8, 36.5 and 52.8%, respectively, compared to P+A-treated roots, while those in P-treated leaves increased by 22.8, 36.3 and 23.8%, respectively, compared to those in P+A-treated leaves. The activities of -1,3-glucanase, cellulase and chitinase in roots are negatively correlated with root mortality. All these results suggest that the inoculation of an antagonist, P. illinoisensis alleviates root mortality, reduction of PR proteins in roots, and activates of PR proteins in leaves infected by P. capsici.     

The Effect of Salinity Pretreatment on Cd Accumulation and Cd-Induced Stress in <Emphasis Type="Italic">BADH</Emphasis><Emphasis Type="Italic">-</Emphasis>Transgenic and Nontransgenic Rice Seedlings

The influence of betaine aldehyde dehydrogenase (BADH) and salinity pretreatment on oxidative stress under cadmium (Cd) toxicity was investigated in rice cv. Xiushui 11 and its BADH-transgenic line Bxiushui 11. The results showed that plants previously treated with 4.25 and 8.5 mM NaCl, respectively, for 5 days each had higher Cd concentrations in both roots and shoots of the two rice genotypes compared with the controls. Malondialdehyde (MDA) content in both leaves and roots was increased by salinity pretreatment and was significantly lower in the salinity-pretreatment plants than in the controls when the plants were consequently exposed to Cd stress. Salinity pretreatment also increased proline content and the activities of superoxide dismutase (SOD) and peroxidase (POD) in both leaves and roots. It can be assumed that salinity pretreatment enhances the defensive ability of plants against oxidative stress through increasing activities of antioxidative enzymes. The BADH-transgenic line (Bxiushui 11) had lower Cd and MDA content, higher SOD and POD activities, and higher proline content than its wild type (Xiushui 11). The current results suggest that betaine, a product of BADH expression, improves the tolerance of rice plants to Cd stress through increasing the activities of antioxidative enzymes and osmoprotectant content.     

Salinity studies with drought-resistant species of Sporobolus

Summary Dry matter productivity under saline conditions was compared in 5 desiccation-tolerant resurrection grasses and one desiccation sensitive species, all in the genus Sporobolus. S. stapfianus was the most salt tolerant, requiring 215 mole NaCl m^-3 to reduce shoot dry matter increments to 50% of increments in plants not treated with salt. (This was comparable to published values for the salt tolerant grass Diplachne fusca.) S. lampranthus was salt sensitive, requiring 35 mol m^-3 for 50% control yields. S. festivus, S. aff. Fimbriatus, and the deisccation sensitive S.pyramidalis was moderately tolerant (150–170 mol m^-3). The moderate salt resistance of S. aff. fimbriatus was attributed mainly to exclusion of NaCl by roots. Salt export through leaf surfaces was a minor factor. Half of the leaf mesophyll cells survived 50 min immersion in 200 mol NaCl m^-3. Plants of S. aff. fimbriatus and S. pyramidalis tolerated a broad range of soil pH. Plants of 4 desiccation tolerant Sporobolus species survived air-dryness following 3 weeks pretreatment with salinities up to 200 mol m^-3     

Cloning and characterization of four <Emphasis Type="Italic">TpSnRK2s</Emphasis> from dwarf Polish wheat

Protein phosphorylation/dephosphorylation is a major signalling event induced by abiotic stresses in plants. Sucrose nonfermenting 1-related protein kinase 2 (SnRK2) plays important roles in response to osmotic stress. In the present study, four SnRK2s, TpSnRK2.1/3/7/8, were cloned and characterized from Triticum polonicum L. (dwarf Polish wheat, DPW, AABB). All of these were individually located on 2AL, 1AL, 2AL, and 5BL. Two spliced isoforms of TpSnRK2.8 (TpSnRK2.8a and TpSnRK2.8b) were observed. TpSnRK2.1 and TpSnRK2.3 were classified into the group II; TpSnRK2.7 was classified into the group I; and TpSnRK2.8a/b were classified into the group III. Expression patterns revealed that TpSnRK2.1 responded to cold, NaCl, polyethylene glycol (PEG), and abscisic acid (ABA) in both roots and leaves; TpSnRK2.3 was strongly regulated by cold, NaCl, and ABA in both roots and leaves, and by PEG in roots; TpSnRK2.7 was induced by NaCl and PEG in roots, but was not activated by ABA; and TpSnRK2.8s were significantly activated by cold, NaCl, PEG, and ABA in both roots and leaves. From the above results, we inferred that TpSnRK2.1/3/8 may participate in the responses to environmental stresses in ABA-dependent signal transduction pathway but TpSnRK2.7 is possibly involved in responses to environmental stresses in a non-ABA-dependent manner. They play important roles in specific tissues under different stresses.     

Enhanced salt stress tolerance in transgenic potato plants (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) expressing a bacterial <Emphasis Type="Italic">mtl</Emphasis>D gene

Bacterial mannitol 1-phosphate dehydrogenase (mtlD) gene was introduced into potato (Solanum tuberosum L.) by Agrobacterium tumefaciens-mediated transformation. Transgenic plants were selected on a medium containing 100 mg l⁻¹ kanamycin and confirmed by polymerase chain reaction (PCR), Southern blotting, and RT-PCR analyses. All of the selected transformants accumulated mannitol, a sugar alcohol that is not found in wildtype potato. Experiments designed for testing salt tolerance revealed that there was enhanced NaCl tolerance of the transgenic lines both in vitro and in hydroponic culture. Compared to 0 mM NaCl, the shoot fresh weight of wildtype plants was reduced by 76.5% at 100 mM NaCl under hydroponic conditions. However, under the same condition, the shoot fresh weight of transgenic plants was reduced only by 17.3%, compared to 0 mM NaCl treatment. The improved tolerance of this transgenic line may be attributed to the induction and progressive accumulation of mannitol in the roots and shoots of the plants. In contrast to in vitro experiments, the mannitol content in the transgenic roots and shoots increased at 50 mM NaCl and decreased slightly at 75 and 100 mM NaCl, respectively. Overall, the amount of accumulated mannitol in the transgenic lines was too small to act as an osmolyte; thus, it might act as an osmoprotectant. However, the results demonstrated that mannitol had more contribution to osmotic adjustment in the roots (but not in shoots). Finally, we concluded that mtlD expression in transgenic potato plants can significantly increase the mannitol accumulation that contributes to the enhanced tolerance to NaCl stress. Furthermore, although this enhanced tolerance resulted mainly from an osmoprotectant action, an osmoregulatory effect could not be ruled out.     

Effects of salt on growth,ion accumulation,photosynthesis and leaf anatomy of the mangrove,<Emphasis Type="Italic"> Bruguiera parviflora</Emphasis>

The effects of a range of salinity (0, 100, 200 and 400 mM NaCl) on growth, ion accumulation, photosynthesis and anatomical changes of leaves were studied in the mangrove, Bruguiera parviflora of the family Rhizophoraceae under hydroponically cultured conditions. The growth rates measured in terms of plant height, fresh and dry weight and leaf area were maximal in culture treated with 100 mM NaCl and decreased at higher concentrations. A significant increase of Na⁺ content of leaves from 46.01 mmol m^-2 in the absence of NaCl to 140.55 mmol m^-2 in plants treated with 400 mM NaCl was recorded. The corresponding Cl^- contents were 26.92 mmol m^-2 and 97.89 mmol m^-2. There was no significant alteration of the endogenous level of K⁺ and Fe²⁺ in leaves. A drop of Ca²⁺ and Mg²⁺ content of leaves upon salt accumulation suggests increasing membrane stability and decreased chlorophyll content respectively. Total chlorophyll content decreased from 83.44 g cm^-2 in untreated plants to 46.56 g cm^-2 in plants treated with 400 mM NaCl, suggesting that NaCl has a limiting effect on photochemistry that ultimately affects photosynthesis by inhibiting chlorophyll synthesis (ca. 50% loss in chlorophyll). Light-saturated rates of photosynthesis decreased by 22% in plants treated with 400 mM NaCl compared with untreated plants. Both mesophyll and stomatal conductance by CO₂ diffusion decreased linearly in leaves with increasing salt concentration. Stomatal and mesophyll conductance decreased by 49% and 52% respectively after 45 days in 400 mM NaCl compared with conductance in the absence of NaCl. Scanning electron microscope study revealed a decreased stomatal pore area (63%) in plants treated with 400 mM NaCl compared with untreated plants, which might be responsible for decreased stomatal conductance. Epidermal and mesophyll thickness and intercellular spaces decreased significantly in leaves after treatment with 400 mM NaCl compared with untreated leaves. These changes in mesophyll anatomy might have accounted for the decreased mesophyll conductance. We conclude that high salinity reduces photosynthesis in leaves of B. parviflora, primarily by reducing diffusion of CO₂ to the chloroplast, both by stomatal closure and by changes in mesophyll structure, which decreased the conductance to CO₂ within the leaf, as well as by affecting the photochemistry of the leaves.     

Potato plants bearing a vacuolar Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> antiporter HvNHX2 from barley are characterized by improved salt tolerance

Two cultivars of potato (Solanum tuberosum L.) were transformed with a barley antiporter gene HvNHX2 driven by the CaMV 35S promoter. The expressed transgene conferred a higher NaCl tolerance to one of the cultivars. Under salt stress, the more salt-tolerant transgenic plants had longer roots, higher dry weight, and suppressed cell expansion as compared to wild-type plants. The salt tolerance of the plants grown in vitro was not accompanied by elevated total sodium in any plant organs tested. Instead, higher potassium was found in roots of transgenic plants. Possible mechanisms of plant salt tolerance are discussed.     

Callus induction,regeneration of haploid plants and chromosome doubling in ovule cultures of pot gerbera (Gerbera jamesonii)

Gynogenetic plants of pot gerbera (Gerbera jamesonii) were successfully produced from cultures of unpollinated ovulesin vitro. Genotypic variations in the number of ovules that formed callus were found among the lines tested. One particularly responsive genotype was found among 17 genotypes tested where the frequency of callus-forming ovules was 17.5%. Four genotypes formed no callus at all. The frequency of shoot formation from the callus varied from 0–19.6% in nine genotypes. Ploidy was determined by flow cytometry, and 37 (80.4%) regenerants were haploid, seven (15.2%) were diploid, and two (4.3%) were mixoploid with both haploid and diploid cells. The doubling of chromosomes was achieved by treatment with 0.05% colchicine for 2–6 din vitro, and 24.2–34.1% of treated haploid plants were found to have been diploidized.Abbreviations BA 6-benzylaminopurine - NAA 1-naphthaleneacetic acid - IAA indole-3-acetic acid - DAPI 4 ,6-diamidino-2-phenylindole dihydrochloride - MS Murashige and Skoog (1962) basal medium