Manipulation of in Vivo Sorbitol Production Alters Boron Uptake and Transport in Tobacco

Recent evidence that some species can retranslocate boron as complexes with sugar alcohols in the phloem suggests a possible mechanism for enhancing boron efficiency. We investigated the relationship between sugar alcohol (sorbitol) content, boron uptake and distribution, and translocation of foliar-applied, isotopically enriched ¹⁰B in three lines of tobacco (Nicotiana tabacum) plants differing in sorbitol production. In tobacco line S11, transformed with sorbitol-6-phosphate dehydrogenase, the production of sorbitol was accompanied by an increase in the concentration of boron in plant tissues and an increased uptake of boron compared with either tobacco line A4, transformed with antisense orientation of sorbitol-6-phosphate dehydrogenase, or wild-type tobacco (line SR1, zero-sorbitol producer). Foliar application of ¹⁰B to mature leaves was translocated to the meristematic tissues only in line S11. These results demonstrate that the concentration of the boron-complexing sugar alcohol in the plant tissue has a significant effect on boron uptake and distribution in plants, whereas the translocation of the foliar-applied ¹⁰B from the mature leaves to the meristematic tissues verifies that boron is mobile in sorbitol-producing plants (S11) as we reported previously. This suggests that selection or transgenic generation of cultivars with an increased sugar alcohol content can result in increased boron uptake, with no apparent negative effects on short-term growth.     

Transgenically enhanced sorbitol synthesis facilitates phloem-boron mobility in rice

The tolerance of crops to a shortage of boron (B) in the soil varies markedly among species. This variation in tolerance is due, in part, to a species ability to form phloem mobile B-sugar-alcohol complexes (such as B-mannitol or B-sorbitol) which enhance the remobilization of B within the plant. Species lacking the capacity to form B-sugar alcohol complexes are intolerant of even short-term deficits in soil B supply. Here we have genetically engineered rice ( Oryza sativa L.) cultivar Taipei 309 (TP309) with the sorbitol-6-phosphate dehydrogenase (S6PDH) gene, a key enzyme for sorbitol production, and determined the effect of this transformation on the physiology of B remobilization. Sorbitol was detected in the S6PDH transgenic plants as well as in vector-transformed plants and wild-type (TP 309) plants, although the concentration of sorbitol in the S6PDH transgenic plants was significantly enhanced. Remobilization of B from mature leaves to flag leaves correlated with increased levels of sorbitol. The presence of sorbitol and detection of B remobilization in the wild-type and vector-transformed plants suggests that rice utilizes an unknown pathway for sorbitol synthesis and may partly explain the relative insensitivity of rice to B deficits when compared to other graminaceous crops.     

Sorbitol-6-Phosphate Dehydrogenase Expression in Transgenic Tobacco : High Amounts of Sorbitol Lead to Necrotic Lesions

We analyzed transgenic tobacco (Nicotiana tabacum L.) expressing Stpd1, a cDNA encoding sorbitol-6-phosphate dehydrogenase from apple, under the control of a cauliflower mosaic virus 35S promoter. In 125 independent transformants variable amounts of sorbitol ranging from 0.2 to 130 μmol g⁻¹ fresh weight were found. Plants that accumulated up to 2 to 3 μmol g⁻¹ fresh weight sorbitol were phenotypically normal, with successively slower growth as sorbitol amounts increased. Plants accumulating sorbitol at 3 to 5 μmol g⁻¹ fresh weight occasionally showed regions in which chlorophyll was partially lost, but at higher sorbitol amounts young leaves of all plants lost chlorophyll in irregular spots that developed into necrotic lesions. When sorbitol exceeded 15 to 20 μmol g⁻¹ fresh weight, plants were infertile, and at even higher sorbitol concentrations the primary regenerants were incapable of forming roots in culture or soil. In mature plants sorbitol amounts varied with age, leaf position, and growth conditions. The appearance of lesions was correlated with high sorbitol, glucose, fructose, and starch, and low myo-inositol. Supplementing myo-inositol in seedlings and young plants prevented lesion formation. Hyperaccumulation of sorbitol, which interferes with inositol biosynthesis, seems to lead to osmotic imbalance, possibly acting as a signal affecting carbohydrate allocation and transport.     

Growth promoting effect of a transgenic <Emphasis Type="Italic">Bacillus mucilaginosus</Emphasis> on tobacco planting

In this study, we have investigated the plant growth promoting effect of Bacillus mucilaginosus strain D₄B₁, a rhizosphere soil organism, and its transgenic strain NKTS-3 on tobacco planting. The transgenic strain contains a phytase expression cassette that can express high active phytase extracellularly and hydrolyze phytate in the soil to liberate inorganic phosphorus for the growth of tobacco plants. Greenhouse study and field experiments showed that both wild-type B. mucilaginosus and the transgenic strain could promote tobacco plant growth. Moreover, the transgenic strain promoted tobacco plant growth (235% more than control in pot experiments and 125% more than control in field experiments) was higher than the wild-type B. mucilaginosus (183% more than control in pot experiments and 108% more than control in field experiments). In addition, the inoculation with transgenic rhizobacteria could significantly improve root acquisition of phosphorus and increase the phosphorus content of the plant.     

Phloem Mobility of Boron is Species Dependent: Evidence for Phloem Mobility in Sorbitol-rich Species

Boron is generally considered to be phloem immobile or to haveonly limited phloem mobility in higher plants. Evidence suggests,however, that B may be mobile in some species within thePyrus,Malus andPrunusgenera. These genera utilize sorbitol as a primarytranslocated photosynthate and it has been clearly demonstratedthat B forms stable complexes with sorbitolin vitro.In the researchpresented here we demonstrate, further, that B is freely phloemmobile inPyrus, MalusandPrunusspecies and suggest that thisis mediated by the formation and transport of B-sorbitol complexes. The pattern of B distribution within shoot organs and the translocationof foliar-applied, isotopically-enriched¹⁰B was studied in sixtree species. Results demonstrate that in species in which sorbitolis a major sugar (sorbitol-rich), B is freely mobile while inspecies that produce little or no sorbitol (sorbitol-poor) Bis largely immobile. The sorbitol-rich species used here werealmond [Prunus amygdalusB. syn.P. dulcis(Mill.)], apple (MalusdomesticaB.) and nectarine (Prunus persicaL. B. var.nectarinaM.),sorbitol-poor species included fig (Ficus caricaL.), pistachio(Pistacia veraL.) and walnut (Juglans regiaL.). In sorbitol-richspecies foliar applied¹⁰B was transported from the treated leavesto adjacent fruit and specifically to the fruit tissues (hull,shell or kernel) that developed during the experimental period.Whereas, foliar-applied¹⁰B was rapidly translocated out of leaves,only a small percentage of the¹¹B present in the leaf at thetime of foliar application was retranslocated. In sorbitol-richspecies, B concentrations differed only slightly between oldand young leaves while fruit tissue had significantly greaterB concentrations than leaves. In contrast, sorbitol-poor specieshad significantly higher B concentrations in older leaves thanyoung leaves while fruit tissue had the lowest B concentration.This occurred irrespective the source of plant B (soil, solutionor foliar-applied). In a subsequent experiment the growth ofapple trees in solutions free of applied B was maintained solelyby foliar applications of B to mature leaves. These resultsindicate that B is mobile in species that produce significantamounts of sorbitol. We propose that the mobility of B in thesespecies is mediated by the formation of B-sorbitol complexes. Almond; Prunus amygdalus ; apple; Malus domestica; nectarine; Prunus persica; fig; Ficus carica; pistachio; Pistacia vera; walnut; Juglans regia; boron; phloem mobility; deficiency; toxicity; inductively coupled plasma-mass; spectrometer     

Does boron play only a structural role in the growing tissues of higher plants?

In species in which boron (B) mobility is limited, B deficiency only occurs in growing plant organs. As a consequence of the highly localized patterns of plant growth and the general immobility of B it has been extremely difficult to determine the primary function of B in plants. In species in which B is phloem mobile, the removal of B from the growth medium results in the depletion of B present in mature leaves. Thus, it is possible to develop mature leaves with increasingly severe levels of B depletion, thereby overcoming the complications of experiments based on growing tissues. Utilizing this approach we demonstrate here that B depletion of mature plum (Prunus salicina) leaves did not result in any discernible change in leaf appearance, membrane integrity or photosynthetic capacity even though B concentrations were reduced to 6-8 µg/g dwt, which is less than 30% of the reported tissue B requirement. Boron depletion, however, results in a severe disruption of plant growth and metabolism in young growing tissues. This experimental evidence and theoretical considerations suggest that the primary and possibly sole function of B, is as a structural component of growing tissues.     

Overexpression of Loquat Dehydrin Gene <Emphasis Type="Italic">EjDHN1</Emphasis> Promotes Cold Tolerance in Transgenic Tobacco

Dehydrins (DHNs) play vital roles in response to dehydration stress in plants. To examine the contribution of EjDHN to low-temperature stress in loquat (Eriobotrya japonica Lindl.), EjDHN1 was overexpressed in tobacco (Nicotiana tabacum L.). The plant growth of transgenic lines was significantly better than wild type (WT) after 4 d of recovery from cold stress. Cold stress led to membrane lipid peroxidation and reduced photosystem II (PSII) activity in leaves, and these were less severe in transgenic lines. To examine oxidative stress tolerance, the plants were treated with different concentrations of methyl viologen (MV), which inhibited plant growth both in WT and transgenic lines. After exposure to 2.0 μM MV for 10 d, the WT plants had a dramatically lower survival rate. MV treatment in leaf disks confirmed that transgenic lines accumulated less reactive oxygen species (ROS) and suffered less lipid peroxidation. The results suggested that the tolerance of the transgenic plants to cold was increased, and EjDHN1 could protect cells against oxidative damage caused by ROS production under cold stress. It also provided evidences that the enhanced cold tolerance resulted from EjDHN1 overexpression could be partly due to their protective effect on membranes by alleviating oxidative stresses.     

Glutamine synthetase in the phloem plays a major role in controlling proline production

To inhibit expression specifically in the phloem, a 274-bp fragment of a cDNA (Gln1-5) encoding cytosolic glutamine synthetase (GS1) from tobacco was placed in the antisense orientation downstream of the cytosolic Cu/Zn superoxide dismutase promoter of Nicotiana plumbaginifolia. After Agrobacterium-mediated transformation, two transgenic N. tabacum lines exhibiting reduced levels of GS1 mRNA and GS activity in midribs, stems, and roots were obtained. Immunogold labeling experiments allowed us to verify that the GS protein content was markedly decreased in the phloem companion cells of transformed plants. Moreover, a general decrease in proline content in the transgenic plants in comparison with wild-type tobacco was observed when plants were forced to assimilate large amounts of ammonium. In contrast, no major changes in the concentration of amino acids used for nitrogen transport were apparent. A (15)NH(4)(+)-labeling kinetic over a 48-hr period confirmed that in leaves of transgenic plants, the decrease in proline production was directly related to glutamine availability. After 2 weeks of salt treatment, the transgenic plants had a pronounced stress phenotype, consisting of wilting and bleaching in the older leaves. We conclude that GS in the phloem plays a major role in regulating proline production consistent with the function of proline as a nitrogen source and as a key metabolite synthesized in response to water stress.     

杨树HDA902基因在低温胁迫应答反应中的功能

组蛋白去乙酰化酶在植物非生物胁迫应答反应中具有重要的调控作用。利用RT-PCR的方法从毛果杨中克隆了组蛋白去乙酰化酶基因HDA902。利用农杆菌介导法将其遗传转化到烟草中,并对转基因植株进行低温耐受性分析。研究结果表明,HDA902在烟草中的表达显著提高了转基因株系对低温的耐受性。叶片NBT和DAB染色结果表明,在低温处理后转基因烟草比野生型烟草产生较少的活性氧。丙二醛和脯氨酸含量测定结果表明,在低温条件下,转基因烟草叶片的脯氨酸含量显著高于野生型烟草,而丙二醛含量显著低于野生型烟草。这些研究结果表明,HDA902参与低温胁迫应答反应,其过量表达提高了植株耐低温的能力。     

Over-expression of a vacuolar Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> antiporter gene improves salt tolerance in an upland rice

To develop a salt-tolerant upland rice cultivar (Oryza sativa L.), OsNHX1, a vacuolar-type Na⁺/H⁺ antiporter gene from rice was transferred into the genome of an upland rice cultivar (IRAT109), using an Agrobacterium-mediated method. Seven independent transgenic calli lines were identified by polymerase chain reaction (PCR) analysis. These 35S::OsNHX1 transgenic plants displayed a little accelerated growth during seedling stage but showed delayed flowering time and a slight growth retardation phenotype during late vegetative stage, suggesting that the OsNHX1 has a novel function in plant development. Northern and western blot analyses showed that the expression levels of OsNHX1 mRNA and protein in the leaves of three independent transgenic plant lines were significantly higher than in the leaves of wild type (WT) plants. T₂ generation plants exhibited increased salt tolerance, showing delayed appearance and development of damage or death caused by salt stress, as well as improved recovery upon removal from this condition. Several physiological traits, such as increased Na⁺ content, and decreased osmotic potential in transgenic plants grown in high saline concentrations, further indicated that the transgenic plants had enhanced salt tolerance. Our results suggest the potential use of these transgenic plants for further agricultural applications in saline soil.     

Simultaneous Overexpression of Citrate Synthase and Phosphoenolpyruvate Carboxylase in Leaves Augments Citrate Exclusion and Al Resistance in Transgenic Tobacco

Phosphoenolpyruvate carboxylase (PEPC) and citrate synthase (CS) are two key enzymes in organic acid synthesis metabolism. In the present study, a cytoplasmic form of CS from tobacco and a mutant (with reduced sensitivity to organic acid inhibition) PEPC from Synechococcus vulcanus were overexpressed simultaneously using a light-inducible promoter in tobacco leaves. The analysis for enzyme activity showed that CS and PEPC enzyme activities were increased by 235% to 257% and 218% to 236% in the selected cs and pepc (double-gene) overexpression lines, respectively, compared with those in the wild-type plants (WT). The measurement for the relative root elongation rate of the tobacco plants exposed to 30???M aluminum (Al) indicated that Al tolerance in the double-gene overexpression lines was stronger than that of the transgenic cs or pepc lines and WT plants. The ¹³C-NMR analysis with NaH¹³CO₃ showed that overexpression of CS and PEPC in the transgenic tobacco successfully constructed a new citrate synthesis pathway. Under the conditions with Al stress, the amount of citrate secreted from the double-transgenic tobacco roots was the largest among the tested plants. When grown on sandy soil supplied with a nutritional solution containing 500???M Al, the growth of the double-transgenic tobacco was better than that of the transgenic cs or pepc tobacco and WT, and their root biomass was the highest among the tested plants. These results demonstrated that construction of a new citrate synthesis pathway by simultaneous overexpression of CS and PEPC in the cytoplasm of transgenic plant leaves could enhance Al resistance in plants.     

The H+-Sucrose Cotransporter NtSUT1 Is Essential for Sugar Export from Tobacco Leaves

In many species translocation of sucrose from the mesophyll to the phloem is carrier mediated. A sucrose/H⁺-symporter cDNA, NtSUT1, was isolated from tobacco (Nicotiana tabacum) and shown to be highly expressed in mature leaves and at low levels in other tissues, including floral organs. To study the in vivo function of NtSUT1, tobacco plants were transformed with a SUT1 antisense construct under control of the cauliflower mosaic virus 35S promoter. Upon maturation, leaves of transformants expressing reduced amounts of SUT1 mRNA curled downward, and strongly affected plants developed chloroses and necroses that led to death. The leaves exhibited impaired ability to export recently fixed ¹⁴CO₂ and were unable to export transient starch during extended periods of darkness. As a consequence, soluble carbohydrates accumulated and photosynthesis was reduced. Autoradiographs of leaves show a heterogenous pattern of CO₂ fixation even after a 24-h chase. The ¹⁴C pattern does not change with time, suggesting that movement of photosynthate between mesophyll cells may also be impaired. The affected lines show a reduction in the development of the root system and delayed or impaired flowering. Taken together, the effects observed in a seed plant (tobacco) demonstrate the importance of SUT1 for sucrose loading into the phloem via an apoplastic route and possibly for intermesophyll transport as well.     

Impaired photoassimilate partitioning caused by phloem-specific removal of pyrophosphate can be complemented by a phloem-specific cytosolic yeast-derived invertase in transgenic plants.

Constitutive expression of the Escherichia coli ppa gene encoding inorganic pyrophosphatase resulted in sugar accumulation in source leaves and stunted growth of transgenic tobacco plants. The reason for this phenotype was hypothesized to be reduced sucrose utilization and loading into the phloem. To study the role of PPi in phloem cells, a chimeric gene was constructed using the phloem-specific rolC promoter of Agrobacterium rhizogenes to drive the expression of the ppa gene. Removal of cytosolic PPi in those cells resulted in photoassimilate accumulation in source leaves, chlorophyll loss, and reduced plant growth. From these data, it was postulated that sucrose hydrolysis via sucrose synthase is essential for assimilate partitioning. To bypass the PPi-dependent sucrose synthase step, transgenic plants were produced that express various levels of the yeast suc2 gene, which encodes cytosolic invertase, in their phloem cells. To combine the phloem-specific expression of the ppa gene and the suc2 gene, crosses between invertase- and pyrophosphatase-containing transgenic plants were performed. Analysis of their offspring revealed that invertase can complement the phenotypic effects caused by the removal of PPi in phloem cells.     

<Emphasis Type="Italic">SlHDA5</Emphasis>, a Tomato Histone Deacetylase Gene,Is Involved in Responding to Salt,Drought, and ABA

Histone deacetylation catalyzed by histone deacetylases is an important type of histone modification. Histone deacetylases affect various processes of plant development and involve in responding to hormones and biotic and abiotic stresses. Here, we report a tomato PRD3/HDA1 histone deacetylase gene, SlHDA5, which is expressed ubiquitously in different tissues and development stages. Expression profiles in hormone treatments showed that SlHDA5 was induced by abscisic acid (ABA) and methyl jasmonate (MeJA). Seedlings growth of SlHDA5-RNAi lines were more inhibited on the medium containing salt compared with wild type (WT). Under salt stress, chlorophyll in mature leaves degraded earlier in transgenic leaves than that in WT, and transgenic plants displayed wilting earlier and more severe than WT. After drought treatment, transgenic plants wilted and dehydrated earlier than WT, which was confirmed by lower water and chlorophyll content, and higher malondialdehyde (MDA) content in transgenic plants manifesting that the tolerance of transgenic plants to drought receded. Under the treatment of ABA, root length of transgenic seedlings was more strongly repressed by contrast with WT, suggesting repression of SlHDA5 increased seedling sensibility to ABA. Our study indicated that silencing of SlHDA5 resulted in decreasing tolerance to salt, drought, and ABA.     

An Isopentyl Transferase Gene Driven by the Stress-Inducible rd29A Promoter Improves Salinity Stress Tolerance in Transgenic Tobacco

Soil salinity is a serious worldwide problem. To improve the salt tolerance of plants, an increasing number of genes related to abiotic stress have been recently expressed by genetic engineers. In the present study, the successful introduction into tobacco of isopentenyl transferase (IPT) from Agrobacterium tumefaciens via Agrobacterium-mediated transformation is reported. A stress-inducible genetic construct was cloned using IPT under the control of the stress-inducible promoter rd29A from Arabidopsis thaliana. A total of 40 putative transgenic plant lines were obtained from independent Kan-resistant shoots. IPT integration into the tobacco genome was confirmed by polymerase chain reaction (PCR) and Southern blot analyses. Four positive transgenic lines each with a single T-DNA insertion were obtained. Real-time PCR confirmed a marked increase in IPT expression in young tobacco plants harboring rd29A-IPT after short-term exposure to salt. Ectopic IPT overexpression IPT under the control of the stress-inducible rd29A promoter resulted in significantly enhanced tolerance to salt stress. No obvious adverse effect on growth and development was observed in transgenic plants. Two IPT transgenic lines, T10 and T25, were chosen for further physiological analyses. The leaves of transgenic tobacco plants showed significantly prolonged chlorophyll retention times under a 2-week salt-stress treatment (150?mmol?L^?1). In contrast, the leaves of the non-transformed plants (wild type) gradually senesced under the same condition. After re-watering for 2?weeks, chlorophyll in transgenic plants increased to a level comparable with that in the unstressed plants. On the other hand, the level in the non-transgenic control still remained low. Malondialdehyde (MDA) levels increased in both transgenic plants and the control after salt stress. However, the MDA levels only mildly increased in transgenic plants, and dramatically increased in the control. After re-watering for 7?days, MDA in transgenic plants returned to normal, whereas the level in the control remained high. Superoxide dismutase activity also similarly increased in transgenic plants during salt stress, and returned to normal after re-watering. These results indicate that enhanced reactive oxygen species scavenging capability may play a significant role in acquiring tolerance to abiotic stress.     

Resource availability and the trichome defenses of tomato plants

We conducted two experiments to determine how resource availability influenced allocation by tomato (Lycopersicon esculentum) to trichomes, and how different patterns of trichome allocation by plants grown in different resource environments might then influence the behavior of tobacco hornworm (Manduca sexta) caterpillars. In the first experiment we used high and low levels of light and water, and then, using scanning electron microscopy, determined trichome densities on the leaves and stems. We sampled leaves and stems at several places throughout the plant to determine whether there were within-plant differences in allocation to trichomes. The results of the first experiment showed that resource availability influenced allocation to trichome growth. Patterns in high and low-light supported both the growth-differentiation balance hypothesis (GDBH) and the carbon-nutrient balance hypothesis (CNBH). However, the GDBH was not supported by differences among water treatments. Contrary, to predictions of the GDBH, plants with intermediate growth did not have the highest trichome densities, and plants with similar growth differed in trichome density. Possible biological and artifactual explanations are discussed. The first experiment also showed that there was within-plant variation in allocation to trichomes, and that plant resource availability may influence within-plant variation in allocation to trichomes. In the second experiment, we grew plants in high and low-light, and then monitored the behavior of tobacco hornworms on the stems of these plants in the laboratory. This experiment demonstrated that the light environment that tomato plants were grown in influenced the resting behavior of caterpillars. Furthermore, it demonstrated that both glandular and non-glandular trichomes impeded caterpillars from searching for food. Overall, this study indicated that plant resource availability can influence allocation to trichome defenses, and that these differences may affect insect herbivores.     

Cadmium loading into potato tubers: the roles of the periderm, xylem and phloem

The mobility of Cd in potato plants (Solanum tuberosum) was examined using both short‐term radioisotopic labelling with ¹⁰⁹Cd and long‐term growth experiments in soil supplemented with Cd, with an emphasis on the pathways through which Cd is taken up by tubers. Split‐pot experiments showed that tubers and their associated stolons and stolon roots contribute only a minor fraction to the overall Cd absorption by the plant. Most of the Cd was absorbed by the basal roots. ¹⁰⁹Cd absorbed from the soil was rapidly exported to other parts of the plant, especially the stem, with significant amounts appearing in the tubers within 30 h. Application of ¹⁰⁹Cd to leaves showed that Cd can be rapidly distributed via the phloem to all tissues. The results suggest that unlike Ca, Cd has high mobility in plants in both xylem and phloem, and that stems may have an important role in transfer between these two pathways.     

Overexpression of <Emphasis Type="Italic">CsNMAPK</Emphasis> in tobacco enhanced seed germination under salt and osmotic stresses

In this research, biological function of CsNMAPK, encoding a mitogen-activated protein kinase of cucumber, was investigated under salt and osmotic stresses. Northern blot analysis showed that the expression of CsNMAPK was induced by salt and osmotic stresses in the cucumber root. In order to determine whether CsNMAPK was involved in plant tolerance to salt and osmotic stresses, transgenic tobacco plants constitutively overexpressing CsNMAPK were generated. Northern and Western blot analysis showed that strong signals were detected in the RNA and protein samples extracted from transgenic lines, whereas no signal was detected in the wild type tobacco, indicating that CsNMAPK was successfully transferred into tobacco genome and overexpressed. The results of seed germination showed that germination rates of transgenic lines were significantly higher than wild type under high salt and osmotic stresses. In addition, seed growth of transgenic lines was much better than wild type under salt and osmotic stresses. These results indicated that overexpression of CsNMAPK positively regulated plant tolerance to salt and osmotic stresses.     

Boron re-translocation in tea (Camellia sinensis (L.) O. Kuntze) plants

Boron (B) re-translocation is an important factor determining tolerance to B deficiency in plants. In this work growth, B content of leaves with different ages, B partitioning between soluble and cell wall (CW) fractions, and B re-translocation were investigated in tea (Camellia sinensis (L.) O. Kuntze) plants grown hydroponically without (<2.5 μM) and with adequate (46 μM) B supply. Under B deficiency, the proportion of CW bound B increased in the old leaves but decreased in roots. Contrastingly, the proportion of CW bound B was not influenced by B supply in the young leaves. A continuous reduction of B content was observed in all fully expanded leaves as well as in roots of low B plants. Taken together, these results revealed considerable re-translocation of B from mature to growing leaves. Leaf extract and phloem exudate samples were analyzed and sucrose, glucose, and fructose were detected while xylitol, sorbitol, mannitol, maltose, galactose, cellobiose or rafinose were not found in these samples. In the leaf extracts, concentration of sucrose increased under B deficiency conditions, concentration of glucose decreased, while that of fructose remained unchanged. Our results provide circumstantial evidence for a considerable re-translocation of B in tea plants despite lacking polyol compounds.     

Genetic engineering of drought-resistant tobacco plants by introducing the trehalose phosphorylase (TP) gene from <Emphasis Type="Italic">Pleurotus sajor-caju</Emphasis>

This study generated transgenic tobacco plants expressing trehalose phosphorylase of Pleurotus sajor-caju (PsTP) constitutively under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Sixteen transgenic lines were selected by genomic Southern blot analysis for further study. Unlike yeast TPS1-transformed or Escherichia coli TPS1-transformed tobacco or potato, all of the PsTP transgenic tobacco lines showed normal growth phenotypes both in the culture tubes and soil mixture. The study measured the trehalose contents of PsTP-transformed tobacco plants as well as the wild type and empty vector-transformed control plants. Results showed that the PsTP transformant contained 6.3molg^–1 of plant tissues, while the wild type and the control plants had only minimal levels of trehalose. Because this study detected a significant amount of trehalose in PsTP transgenic tobacco plants, it decided to carry out a bioanalysis of the PsTP transgenic tobacco plants by drought treatment by not watering the plants for over 10days. A significant difference in drought resistance was observed from the second nonwatering day between the transgenic and the control tobacco plants. The transgenic tobacco plants had normal growth and did not wither, while the wild type and the only empty vector-transformed control plants withered severely. Among all the transgenic lines, line 10-4 showed the strongest resistance to drought stress. It did not wither even after 10days without watering. In addition, when the drought resistance of PsTP transgenic tobacco plants was tested using detached leaves, most transgenic plants, except one line, showed better capacity to retain water than the empty vector-transformed transgenic plant.