Poplar hybrid 741 [Populus alba × (P. davidiana + P. simonii) × P. tomentosa] leaves were rooted within 8 d when cultured in vitro on 1/2 Murashige and Skoog (MS) medium. The spatial distribution of endogenous indole-3-acetic acid (IAA) in the rhizogenesis was investigated, using an immunohistochemical approach. In addition, the effect of 2,3,5-triiodobenzoic acid (TIBA) on IAA distribution was also analyzed. The results showed that a strong IAA signal was detected in the vascular bundles of the basal regions of the petioles 3 d after root induction. Furthermore, the signal in vascular bundles of the basal regions of the petioles was stronger than that of the middle regions of the petioles. Application of TIBA on lamina delayed both the accumulation of IAA in the vascular bundles and rhizogenesis. These data indicate that an endogenous IAA rise in vascular bundles is among the first signals leading to the rhizogenesis, and that it results from transportation of the hormone from the lamina of the leaf to the base of the petiole, rather than by in situ IAA generation.

Changes in ultrastructure of meristematic cells as well as growth and lipid peroxidation in roots of 3-d-old seedlings obtained from control (C), hydroprimed (H) and hydroprimed with melatonin (H-MEL) seeds after 2 d of incubation at 25 or 5 °C and 2 d of re-warming after chilling were investigated. Under 25 °C hydropriming (H and H-MEL) inhibited root growth, but after chilling and re-warming a positive MEL effect on root elongation was observed. The results show decreased lipid peroxidation in H-MEL roots already after chilling, but the significant extent of MEL impact was seen after re-warming. Similarly at the ultrastructural level, the protective effect of MEL at chilling was also visible, especially in plastids, and this effect maintained also after re-warming.

Frost tolerance of ten Bulgarian winter wheat (Triticum aestivum L.) cultivars (Milena, Pobeda, Sadovo-1, Enola, Kristal, Laska, Svilena, Russalka, No301 and Lozen) and five foreign cultivars (Mironovskaya 808, Bezostaya-1, Rannaya-12, Skorospelka-35 and Chinese Spring) was studied in two experimental seasons following natural cold acclimation and in one experiment carried out in controlled acclimation conditions. Considerable intercultivar variability in plant survival was observed after freezing at -21 °C following sufficient cold acclimation, or at -18 °C following insufficient or controlled acclimation. In seven cultivars, the effects of chromosome 5A on frost tolerance were investigated in their F₂ hybrids with chromosome 5A monosomic lines of cultivars with high, intermediate and low frost tolerance. The effects of chromosome 5A depended on the stress severity and the genetic background of the hybrids and varied even in cultivars of similar frost tolerance and vernalization requirements. Effects of other chromosomes besides 5A on frost tolerance were assumed. The analysis of six microsatellite loci located in the interval from centromere to Vrn-1 on of chromosomes 5AL, 5BL and 5DL showed that the major loci determining frost tolerance in Bulgarian winter wheats were Fr-A2 on chromosome 5AL, and, to a lesser extent, Fr-B1 on chromosome 5BL. A strong association of the 176 bp allele at locus wmc327 tightly linked to Fr-A2 with the elevated frost tolerance of cvs. Milena, Pobeda, Sadovo-1, Mironovskaya-808 and Bezostaya-1 was revealed. Relatively weaker association between frost tolerance and the presence of the 172 bp allele at locus Xgwm639 tightly linked to Fr-B1 was also observed.

Apocynin was used as an inducer of nitric oxide (NO) synthesis in leaves of two maize (Zea mays L.) cultivars (SHS 3031 and DKB 240). The transcription of γ-glutamylcysteine synthetase (γ-ecs), glutathione synthetase (gshs), chalcone synthase (chs), flavanone 3-β-hydroxylase (fht1), glutathione S-transferase (gst23), ascorbate peroxidase (apx1, apx2), catalase (cat1, cat3), and superoxide dismutase (sod2) genes were quantified in leaves of maize and NO presence was detected by fluorescence microscopy. An increase in the fluorescence after apocynin treatment was not observed in leaves of DKB 240 but leaves of SHS 3031 showed higher fluorescence after 6 and 12 h of apocynin treatment. We observed that γ-ecs, apx1, cat1, and sod2 transcription increased after 24 h of apocynin treatment in SHS 3031.

The effect of nitrogen forms on photosynthesis and anti-oxidative systems of barley plants under chromium stress was studied in a hydroponic experiment. The treatments comprised three chromium concentrations (0, 75, and 100 μM) and three N forms (NH₄)₂SO₄, urea, and Ca(NO₃)₂. In comparison with the urea or (NH₄)₂SO₄ fed plants, the Ca(NO₃)₂ fed plants had higher net photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, transpiration rate, photosynthetically active radiation utilization efficiency, variable to maximum chlorophyll fluorescence ratio, and the content of chlorophylls and carotenoids. Cr toxicity caused oxidative stress in all plants but the Ca(NO₃)₂ fed plants had the least oxidative stress. Moreover, the Ca(NO₃)₂ fed plants had higher activities of anti-oxidative enzymes and content of non-enzymatic antioxidants than the urea or (NH₄)₂SO₄ fed plants. In addition, the Ca(NO₃)₂ fed plants had higher N and lower Cr content in all plant tissues than the urea or (NH₄)₂SO₄ fed plants. The current results indicate that the reasonable choice of N fertilizer is important for barley production on the Cr-contaminated soils.

A cDNA encoding γ-tocopherol methyltransferase from Brassica napus (BnTMT) was overexpressed in soybean [Glycine max (L.) Merr.] under the control of seed-specific promoter of Arabidopsis fatty acid elongase 1 (FAE1) or soybean glycinin G1. Two and three transgenic plants were selected, respectively, after Agrobacterium-mediated transformation. Polymerase chain reaction (PCR) and Southern blots confirmed that BnTMT was single-copy integrated into the genome of transgenic plants. RT-PCR analysis showed that the expression of BnTMT was higher in the immature cotyledons than in the mature cotyledons, while no expression was detected in the leaves. Moreover, the expression level under the control of FAE1 was higher than that of G1. HPLC analysis indicated that the seed-specific expression of BnTMT resulted in 11.1-fold and 18.9-fold increase in α- and β-tocopherol content, respectively, in T₂ seed. These results suggested that introducing BnTMT into soybean can be used to increase the vitamin E composition in seeds.

Small heat shock proteins (sHSPs) are crucial components of the plant response to heat shock. We identified and analyzed eight sHSP genes of Capsella bursa-pastoris to better understand the ability of this species to adapt. Eight genes were initially cloned and sequenced from the mature embryo cDNA pool. They belong to the cytosolic I (CI), cytosolic II (CII), and cytosolic III (CIII) subfamilies. One CI sHSP gene was homologous to that of C. rubella. Sequence analysis using 3' RACE revealed that there are two or more variable 3'-untranslated regions (UTRs) in these sHSP transcripts. The transcriptional levels of the eight sHSP genes were analyzed in different organs and developmental stages via qRT-PCR. Eight genes were significantly up-regulated in young leaves exposed to heat stress at 42 °C, and also showed differential responses to ABA treatment. We also compared expression of these genes with corresponding Arabidopsis sHSP genes and found some differences between the two species.

In this article, we present the response of Medicago truncatula Gaert. cv. Jemalong plants expressing constitutively the Dsp22 gene from Craterostigma plantagineum to water stress and rehydration. The Dsp22 gene encodes an ELIP-like protein thought to protect the chloroplast against photooxidative damage during the dehydration and rehydration. The Dsp22 transgenic homozygous M. truncatula plants showed higher amount of chlorophyll (Chl), lower Chl a/Chl b ratio and higher actual efficiency of energy conversion in photosystem 2 (Φ_PSII) after rehydration, when compared to the wild type. The combined data from the Chl a fluorescence analysis, pigment quantification and biomass accumulation showed that transgenic M. truncatula plants are able to recover from water deprivation better than wild type plants.

Most perennial and winter annual temperate grasses have a vernalization requirement (VR) for flowering, that is, they require a cold period before they can flower in response to long days. From a F1 mapping population of the outbreeding perennial forage grass Festuca pratensis Huds. (meadow fescue) previously used to map several quantitative trait loci (QTLs) for VR, we produced two F2 populations divergently selected for high or low VR. The two populations were characterised for flowering behaviour and gene expression of VRN1 as well as other MADS-box genes with a putative function in the induction of flowering. Expression of FpVRN1 and the VRN1-like genes FpMADS2 and FpMADS3 was associated with flowering but the response of gene expression to vernalization differed between genes and populations. The expression of the SVP-like genes FpMADS10 and FpMADS16 was not affected by vernalization and did not differ between the two F2 populations.

Date palm (Phoenix dactylifera L.) cv. Khenizi caulogenic meristems were initiated from achlorophyllous leaves excised from in vitro shoot cultures and then proliferated on a specific culture medium supplemented with 70 g dm^-3 sucrose. Regeneration rates obtained when using standard vitrification, droplet-vitrification, and encapsulation-vitrification protocols reached 26.7, 60.0, and 40.0 %, respectively. Only explants smaller than 3 mm in diameter were found to survive cryogenic treatments. Sucrose preculture, cold hardening and loading solution pretreatments showed significant effects on regeneration rates. Moreover, our results indicate that both sucrose preculture and cold acclimation of explants increased proline content. Cryopreservation of date palm tissue with high proliferation capacity can directly benefit large scale micropropagation projects.

This study aimed to investigate seed germination, seedling growth, and antioxidative responses in two wheat cultivars, Ningchun and Xihan, exposed to different H₂O₂ concentrations. Ningchun exhibited higher germination rate but lower root and shoot growth than Xihan when exposed to H₂O₂ treatment. Assays using fluorescent dye H₂DCFDA and propidium iodide showed a significantly enhanced H₂O₂ content and a cell elongation inhibition in H₂O₂-treated roots. The malondialdehyde content was elevated with increasing exogenous H₂O₂ concentration. Moreover, treatments of seedlings with H₂O₂ scavenger, catalase (CAT), and antioxidant, butylated hydroxytoluene, partly abolished H₂O₂-induced negative effect on root growth. In both untreated and H₂O₂-treated leaves, SOD activity in Ningchun was higher than that in Xihan, but POD and APX activities in Ningchun were lower than those in Xihan, leading to elevated H₂O₂ level in Ningchun leaves but decreased H₂O₂ content in Xihan ones under H₂O₂ treatment.

During the first year of hybrid poplar development, we assessed radial growth dynamics quantified by the proportion of secondary xylem tissue within the stem area, the vessel area percentage, the content of both lignin and cellulose, the lignin monomeric composition, and the macromolecular properties of cellulose. The intraannual radial growth dynamics in the proportion of secondary xylem tissue was fitted by the Gompertz regression line whereas changes in the vessel area percentage were fitted maximally by a cubic regression line. Under constant temperature and photoperiod, this study revealed that nonlinear patterns of radial growth dynamics are the result of a developmental programme which drives cambial activity and ageing. The increased proportion of guaiacyl units found may be important for the greater stability of the lignin structure in the first year of hybrid poplar development. The tensile strength of juvenile wood was ensured by the trade-off between a slight increase in the degree of polymerization of cellulose and a slight decrease in the content of cellulose during ageing.

Treatment with 0.5 mM salicylic acid (SA) significantly alleviated growth inhibition induced by drought in wheat seedlings, manifested by less decreassed fresh mass, dry mass, plant height, root length, and less increased lipid peroxidation. Under drought stress, SA significantly increased the content of ascorbate (ASA) and glutathione (GSH). We determined the full-length cDNA sequences of genes encoding the glutathione-S-transferase 1 (GST1) and 2 (GST2) and we also measured the transcription of eight genes related to ASA-GSH cycle. The results indicated that exogenous SA significantly enhanced the transcription of GST1, GST2, glutathione reductase (GR), and monodehydroascorbate reductase (MDHAR) genes during almost the entire drought period, but only increased those of dehydroascorbate reductase (DHAR) at 12 h, glutathione peroxidase (GPX1) at 48 h, phospholipid hydroperoxide glutathione peroxidase (GPX2) at 12 and 24 h, and glutathione synthetase (GSHS) at 12, 24, and 48 h. This implies that SA alleviates the detrimental effects of drought stress on wheat seedling growth by influencing the ASA-GSH cycle.

Glutathione-S-transferases (GSTs) are ubiquitous enzymes that play a key role in stress tolerance and cellular detoxification. The GST gene GsGST14 selected from the gene expression profiles of Glycine soja under alkaline stress was transformed into alfalfa (Medicago sativa L.). Transgenic alfalfa plants showed 1.73-1.99 times higher GST activity than wild-type plants. Transgenic alfalfa grew well in the presence of 100 mM NaHCO₃, while wild-type plants exhibited chlorosis and stunted growth, even death. There were marked changes in malondialdehyde content and relative membrane permeability caused by alkaline stress in non-transgenic lines compared to transgenic lines. The results indicate that the gene GsGST14 could enhance alkaline resistance in transgenic alfalfa.

There is evidence that the plasma membrane (PM) permeability alterations might be involved in plant salt tolerance. This review presents several lines of evidence demonstrating that PM permeability is correlated with salt tolerance in plants. PM injury and hence changes in permeability in salt sensitive plants is brought about by ionic effects as well as oxidative stress induced by salt imposition. It is documented that salinity enhances lipid peroxidation as well as protein oxidative damage, which in turn induces permeability impairment. PM protection, and thus retained permeability, in tolerant plants under salt imposition could be achieved through increasing antioxidative systems and thereby reducing lipid peroxidation and protein oxidative damage of PM. It appears that specific membrane proteins and/or lipids are constitutive or induced under salinity, which may contribute to maintenance of membrane structure and function in salt tolerant plant species. Furthermore, protecting agents (e.g., glycinebetaine, proline, polyamines, trehalose, sorbitol, mannitol) accumulated in salt tolerant species/cultivars may also contribute to PM stabilization and protection under salinity. Based on the presented evidence that PM permeability correlates with plant salt tolerance, we suggest that PM permeability is an easy and useful parameter for selection of genotypes of agriculture crops adapted to salt stress.

Pea (Pisum sativum L.) somaclones of cultivars Adept, Komet and Bohatýr were obtained after selection in vitro with Fusarium solani filtrate and fusaric acid (FA). R2 regenerants were analysed by random amplification of polymorphic DNA (RAPD; OPAB4, P-14, UBC-556) and inter-retrotransposon amplification polymorphism (IRAP; Ogre) markers. Marker UBC-556 showed different banding patterns for each cultivar, but without specific bands for selected and control plants. Markers OPAB4, P14 and Ogre were useful for clear discrimination between selected and non-selected variants of all three cultivars. Flow cytometry analysis proved the same genome size of selected and non-selected pea lines. Therefore in vitro selection by pathogen derived agents could be the efficient method for obtaining of pea somaclones with increased resistance to F. solani.

Protocols for in vitro plant multiplication from somatic tissues and production of artificial seeds through encapsulation of nodes were developed for Aristolochia tagala Cham., a rare and valuable medicinal plant, as a measure of conservation and as a prerequisite for genetic transformation procedure. A maximum number of adventitious shoots were regenerated from leaf-derived callus on Murashige and Skoog (MS) medium containing 6-benzylaminopurine (BAP; 2 μM), α-naphthaleneacetic acid (NAA; 0.5 μM), and phloroglucinol (PG; 10μM). Nodes collected from in vitro established shoot cultures were encapsulated in 3 % (m/v) sodium alginate and 1 % (m/v) calcium chloride. Multiple shoots were successfully regenerated from the encapsulated nodes cultured on MS medium supplemented with 3 μM BAP and 0.5 μM kinetin (KIN). Regenerated shoots from callus and artificial seeds were successfully rooted and acclimated to greenhouse conditions. Since roots of A. tagala are primarily used in traditional medicine, a protocol for regenerating roots directly from the leaf derived callus was also developed. Maximum root length was obtained when the callus was cultured in MS medium supplemented with KIN (1 μM), indole acetic acid (IAA; 0.5 μM), NAA (0.1 μM), and PG (10 μM). Biochemical parameters were studied in calli grown with and without PG in the medium to establish a correlation between these parameters and shoot morphogenesis. An increment of antioxidant enzymes (peroxidase and catalase) and metabolites (sugars and proteins), and a decrease in the amount of polyphenol oxidase was observed in the calli which were grown in the presence of PG.

Rice (Oryza sativa L.) seedlings were grown hydroponically in Hoagland's nutrient solution under controlled conditions to investigate the effects of NaCl pretreatment on their response to subsequent application of cadmium (Cd) alone and Cd + NaCl combination. The Cd stress caused growth retardation in all plants, significantly reduced pigment content, stomatal conductance (g_s), and net photosynthetic rate (P_N). Cd stress significantly increased malondialdehyde and proline content. Compared to Cd treatment alone, combination stress had more detrimental effects on the above parameters. However, the NaCl pretreatment was beneficial in improving the plant growth and plant tolerance to Cd alone or combination stress.

This study investigated the effects of pH and nitrogen form and concentration on cadmium (Cd) uptake by potato (Solanum tuberosum L.) grown in hydroponic culture. Potato plants grown in a pH-buffered nutrient solution for 10 d were exposed for 24 h to 25 nM CdCl₂ labelled with ¹⁰⁹Cd. Plants showed a significantly higher Cd uptake and accumulation at pH 6.5 than at pH 4.5 and 5.5. Nitrogen supplied as nitrate (NO₃ ^-) generally resulted in a higher Cd uptake and accumulation than N supplied as ammonium (NH₄ ⁺). This effect was most pronounced at pH 6.5. The N concentration increasing from 6.5 to 26 mM resulted in a decreased Cd influx when either NO₃ ^- or NH₄ ⁺ was used. Cd translocation to the shoot was increased when NO₃ ^- was used as the sole N source. In conclusion, pH had a strong influence on Cd uptake by roots and N form is especially important for Cd translocation within the potato plant.

Germination of Lepidium apetalum Wild. seeds is invariably arrested by cold stress. cDNA-amplified fragment length polymorphism (AFLP) technique was used to isolate genes relevant to chilling stress (4 °C) during seedling emergence. 43 transcript-derived fragments (TDFs) were found to be up-regulated and 17 down-regulated during chilling stress. Eighteen TDF of up-regulated genes were cloned and sequenced. Some of these genes are involved in the stress response, some play important roles in energy and substrate metabolism, and some encode unknown proteins such as TDF119. Two sequences, designated TDF217 and TDF223, may correspond to novel genes. The expression profiles of 6 from 18 TDFs were analyzed by quantitative real-time PCR under chilling and abscisic acid (ABA) stress. It was demonstrated that all 6 genes were significantly induced by chilling and their expression was decreased when the temperature was shifted from 4 to 25 °C. The transcriptional levels of 5 TDFs were strongly enhanced also in response to exogenous ABA. Based on the characteristics of genes isolated from seedlings exposed to cold stress, we conclude that Lepidium adapts to cold stress by regulating many signal transduction pathways, including both ABA-dependent and ABA-independent signaling pathways.

We isolated PaAP3, a homolog of the class B MADS-box transcription factor gene APETALA3 (AP3), from the monoecious plant London plane tree (Platanus acerifolia Willd.). PaAP3 encodes a protein that shares good levels of identity with class B genes from Arabidopsis thaliana (35 and 51 % identity with PISTILLATA (PI) and AP3, respectively), and also with class B genes of other woody species (59 % identity with PTD from Populus trichocarpa and 66 % with TraAP3 from Trochodendron aralioides). Reverse transcription polymerase chain reaction showed that PaAP3 was expressed in both the female and male flowers of P. acerifolia, but almost no signal was detected in the vegetative tissues or mature embryos. The PaAP3 expression in male flowers showed a relationship with developmental stage. There was a small transient increase during differentiation of the flower primordia in June, but maximal levels occurred during December when flower development appeared arrested. Increased PaAP3 expression was also detected in March of the following year, corresponding to meiotic divisions of the microspore mother cells, but this was lost by April when the pollen was mature.

Choline monooxygenase (CMO) is the first regulatory enzyme in the biosynthetic pathway for glycine betaine, an effective osmoprotectant in Kochia scoparia, a highly drought- and salt-tolerant species. In seedlings, CMO transcript levels are rapidly increased in response to both NaCl and osmotic stress treatments. The mRNA level in shoots was substantially higher than in roots. The rapid induction seen in whole plants was in contrast to the apparent down-regulation observed in suspension-cultured K. scoparia cells in response to the same salt stress. Treatment with exogenous abscisic acid (ABA) or fluridone shows that CMO induction proceeds via an ABA-independent signal transduction pathway. Examination of the CMO upstream regulatory region reveals a number of stress response-related elements, some of which may be involved in the stress tolerance shown by this species.

Daucus carota is cultivated widely but grows best in cool climates. Suppression subtractive hybridization (SSH) is a PCR based method used to selectively amplify differentially expressed cDNAs and simultaneously suppress non-target cDNA. A subtraction forward library was constructed using RNA isolated from the leaves of unstressed and cold stressed carrot plants to determine the genes upregulated during cold stress. Out of the hundreds of clones obtained, sequences of 41 promising clones were submitted to the NCBI EST database. Sequence analyses revealed that these genes have significant roles in signal transduction, osmolyte synthesis and transport, regulation of transcription, translation and protein folding. Semiquantitative real-time polymerase chain reaction analysis (sqRT-PCR) of Dc cyclin, Dc WD and Dc profilin shows that the first two genes were upregulated while Dc profilin was constitutively expressed, but the analyses of the same with SSH, a much more sensitive technique showed an upregulation of all three genes.

An efficient in vitro plant regeneration system has been developed using dark preincubated leaf explants of Rhodiola crenulata, a traditional Tibetan medicinal plant. The leaf explants, preincubated in the dark for 5 d, developed an average of 9.1 shoots per explant on a medium containing 15 μM N ⁶-benzyladenine (BA) and 2.5 μM gibberellic acid (GA₃). The biochemical mechanism underlying dark-induced shoot organogenesis was investigated by measuring polyphenol oxidase (PPO) activity. Dark preincubation significantly reduced PPO activity in leaf explants during the initial period of shoot organogenesis and reduced browning compared to explants cultured in the light. Up to 88.4 % of the regenerated shoots formed roots and developed into complete plantlets on a medium containing 5 μM indoleacetic acid (IAA) within 25 d. Approximately 82 % of the regenerated plantlets survived transplantation and grew vigorously in the greenhouse.

The aim of the present study was to describe the occurrence of three pectic epitopes, recognized by JIM7, LM19, and LM5 antibodies, during somatic (SE) and zygotic (ZE) embryogenesis in Arabidopsis thaliana. The epitopes recognized by JIM7 and LM19 antibodies showed different distributions during SE stages. Moreover, in the early stages of somatic embryo development, a cytoplasmic occurrence of LM19 epitope was detected. Distribution of a pectic epitope recognized by LM5 antibody corresponded to a vascular system differentiation pattern. Occurrence of LM5 epitope was the same in both zygotic and somatic embryos and often restricted to newly synthesized walls of two adjacent cells. These data suggest that both low and high methyl-esterified pectins (recognized by LM19 and JIM7 antibodies, respectively) are developmentally regulated during SE stages and (1→4)-β-D-galactan epitope (recognized by LM5 antibody) may play a role in cell cytokinesis.

The gene, designated TaMADS2, was obtained from wheat leaves infected with the wheat stripe rust fungus by in silico cloning and RT-PCR. TaMADS2 encodes a predicted 159-amino-acid polypeptide that contains a highly conserved MADS domain. Phylogenetic analysis revealed that TaMADS2 is a type I MADS-box gene. The TaMADS2 transcript was detected in wheat leaves, stems, and roots. The expression of TaMADS2 was substantially down-regulated in the compatible interaction between wheat and Puccinia striiformis f. sp. tritici (Pst) at 36 and 48 h post-inoculation (hpi), whereas in the incompatible interaction the down-regulation was only observed at 48 hpi. Exogenous salicylic acid (SA) and abscisic acid (ABA) greatly induced the expression of TaMADS2 at 12 h post treatment (hpt), whereas methyl jasmonate (MeJA) down-regulated TaMADS2 at 6 hpt by approximately two-fold.

Gibberellic acid (GA) promotes cotton fiber cell elongation under in vitro culture conditions and GA signal transduction is mediated by DELLA proteins. Our laboratory has cloned several DELLA genes from cotton and generated transgenic lines in Arabidopsis over-expressing the DELLA gene (GhRGL) and the DELLA-domain deletion mutant gene (Ghrgl). Comparative transcriptome profiling was performed on Arabidopsis transgenic lines over-expressing both GhRGL and Ghrgl. KEGG pathway analysis indicated that the differential genes participated in many important pathways, such as response to gibberellic acid, fatty acid metabolism, etc., and the expression patterns of 93 genes were validated by RT PCR in all transgenic lines and the wild-type plants. Gene ontology annotation identified that these genes were involved in sucrose synthesis, actin nucleation, root hair development, and various hormone signal responses.

In Phalaenopsis, lowering irradiance has been used to delay flower stalk development but the accompanying biochemical changes remain poorly understood. We cultured two commercial Phalaenopsis-type orchids, Phalaenopsis cv. Sogo Yukidian V3, and Doritaneopsis cv. Walnut Valley Halo ES09 under reduced irradiance by under-bench shading (approximately 15 % of mean control irradiance) for 15 weeks in a greenhouse under the natural photoperiod. Besides delaying flower stalk development as expected, the treatment greatly decreased the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase, phosphoenolpyruvate carboxylase, and NAD⁺-malic enzyme, and reduced the nocturnal malate accumulation and daytime starch deposition, the typical diurnal metabolite fluctuations of crassulacean acid metabolism (CAM) plants. As well, the content of sucrose and starch was reduced at dawn and dusk whereas the content of glucose and fructose only at dawn. The persistent decrease in the sucrose content under shading may be an inhibitory signal of flower stalk induction.

In this study, we report a function of myo-inositol-O-methyltransferase (Imt1) in response to low temperature stress using transgenic Arabidopsis thaliana. Imt1 gene was constructed identical to the Imt1 gene from a halophyte Mesembryanthemum crystallinum. After cold stress, the Imt1 transgenic plants exhibited stronger growth than the wild type plants. The elevated cold tolerance of the Imt1 over-expressing plants was confirmed by the lower electrolyte leakage and accumulation of malondialdehyde, but higher proline and soluble sugar contents in transgenic than wild type plants.

Fluctuation in proline content is a widespread phenomenon among plants in response to heavy metal stress. To distinguish between the participation of water deficit and copper on changes in proline metabolism, potted plants and floating leaf discs of tobacco were subjected to CuSO₄ treatments. The application of copper increased the proline content in the leaves concomitantly with decreased leaf relative water content and increased abscisic acid (ABA) content in the potted plant. Excess copper increased the expression of two proline synthesis genes, pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT) and suppressed proline catabolism gene, proline dehydrogenase (PDH). However, in the experiment with tobacco leaf discs floating on CuSO₄ solutions, the excess copper decreased proline content and suppressed the expression of the P5CS, OAT and PDH genes. Therefore, proline accumulation in the potted tobacco plants treated with excess Cu treatment might not be the consequence of the increased copper content in tobacco leaves but rather by the accompanied decrease in water content and/or increased ABA content.