Calcium is a critical component in a number of plant signal transduction pathways and the calcineurin B-like protein (CBL) family is a unique group of calcium sensors regulating a family of CBL-interacting protein kinases (CIPKs). In this study, two poplar CBL genes, PeCBL6 (GenBank acc. No. DQ907710) and PeCBL10 (GenBank acc. No. DQ899956), were characterized in transgenic Arabidopsis thaliana, particularly with regard to its role in abiotic stress resistance. Expression of the two CBL genes in poplar was induced by cold, drought, or high salinity, but not by abscisic acid (ABA) treatment. In Arabidopsis thaliana, PeCBL6 was found in the nucleus and PeCBL10 in the tonoplast. Transgenic Arabidopsis plants overexpressing PeCBL6 or PeCBL10 showed enhanced tolerance to high salinity, drought and low temperature. These results suggested that PeCBL6 and PeCBL10 may function as positive regulators of salt, drought and temperature responses.

Brassinosteroids are known to protect plants against various abiotic and biotic stresses, however, very limited information is available about the role of progesterone. Therefore the effects of Pseudomonas syringae pv. syringae (P.s.) wild type strain 61, its hrcC mutant, and the saprophytic P. fluorescens (P.f.) strain 55 were investigated in wild type Arabidopsis thaliana cv. Columbia and its rbohF knock-out mutant, with and without progesterone pre-treatment. The reactions of wild type and rbohF mutant Arabidopsis to bacterial inoculations were similar, although 2 h after injection of P.s. a larger increase of electrolyte leakage was measured in wild type than in rbohF knockout mutant leaves. The hrcC mutant caused weak necrotic symptoms and increased leakage in both types of Arabidopsis, although to a much lesser extent than P.s. The P.f. did not induce any visible symptom, but slightly increased the electrolyte leakage in both types of Arabidopsis. Inoculation by all Pseudomonas bacteria led to significant alterations in photosystem 2 efficiency as compared to control plants. Pre-treatment of leaves with progesterone diminished the necrotic symptoms, the electrolyte leakage and improve the efficiency of photosystem 2 caused by Pseudomonas bacteria.

The present study evaluated the effects of 100 and 500 μM arsenate (Na₂HAsO₄) on pigment composition and photosynthesis in Hydrilla verticillata (L.f.) Royle. Arsenic accumulation increased in concentration and duration dependent manner. The maximum accumulation [568 μg(As) g^-1(d.m.)] was observed at 500 μM concentration and 96-h exposure. This concentration led to a significant decline in chlorophyll a content and PS II efficiency during the whole experiment, and in chlorophyll b and carotenoids after 96 h, but no significant changes in photosynthetic pigments were noticed at 100 μM arsenate. Net photosynthetic rate, electron transport rate, and water use efficiency declined whereas transpiration rate increased, and stomatal conductance and photochemical quenching did not show any effect or increased. The content of reactive oxygen species increased and content of reduced ascorbate declined at 500 μM arsenate in comparison to the control.

This study was carried out to better understand the role of salicylic acid (SA) applied before cold stress in the cold tolerance mechanism. Two barley (Hordeum vulgare) cultivars, cold-sensitive (Akhisar) and cold-tolerant (Tokak), were used and 0.1 mM SA was applied to 7-d-old barley seedlings growing under control conditions (20/18 °C). The seedlings were transferred to cold chamber (7/5 °C) at the age 14, 21, and 28 d. After three days, the leaves were harvested to determine the activities of apoplastic antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) and ice nucleation activity and electrophoretic patterns of apoplastic proteins. Cold treatment decreased the activities of all enzymes in cold-sensitive cultivar, however, it increased CAT and POX activities in cold-tolerant cultivar. Exogenous SA increased enzyme activities in both cultivars. Ice nucleation activity increased by cold treatment, especially in 17-d-old seedlings in both cultivars. In addition, SA treatment increased ice nucleation activity in all examined samplings in both cultivars. SA treatment caused accumulation or de novo synthesis of some apoplastic proteins. The results of the present study show that exogenous SA can improve cold tolerance by regulating the activities of apoplastic antioxidative enzymes, ice nucleation activity, and the patterns of apoplastic proteins.

Sex-related differences in the responses of plants to CO₂ enrichment are still rarely studied. In this study, we examined the effects of elevated atmospheric CO₂ (720 μmol mol^-1) on the activities of polyphenoloxidases (PPOs) and guaiacol peroxidases (PODs) in male and female plants of two ecologically divergent willow species Salix repens and S. phylicifolia. We detected that females invested more in PPO-based defence than did males, whose PPO activity decreased as a result of CO₂ enrichment. Moreover, we found that the inherently slow-growing S. repens had markedly higher POD activity than did the more rapid-growing S. phylicifolia. The PODs of these two species also differed in their biochemical properties.

A new ethylene response factor (ERF), GmERF6, was isolated from soybean. Protein sequence alignment of GmERF6 revealed an AP2/ERF domain, two putative nuclear localization signals (NLSs) and an ERF-associated amphiphilic repression (EAR) motif. Real-time quantitative PCR analysis revealed that the expression of GmERF6 was differentially induced in soybean seedlings by drought, salt, cold, salicylic acid, ethylene, abscisic acid and methyl jasmonate. Transient expression experiments demonstrated that GmERF6 functions as a transcriptional repressor to downregulate the transcriptional levels of the reporter gene and repress the activated ability of other transcriptional activator. Transgenic Arabidopsis lines constitutively expressing GmERF6 showed an increased tolerance to drought compared to wild-type plants.

Wood ontogeny patterns were determined during the ex vitro acclimatization period in micropropagated plantlets of hybrid poplar clones T-14 [Populus tremula × (Populus × canescens)] and T-50 [(Populus × canescens) × Populus tremula]. The temporal course of developmental changes in the woody tissue was characterized on a weekly basis starting from the day of transfer to the ex vitro environment until full acclimatization was achieved on day 28. In vitro rooted plantlets had already initiated lignification of secondary xylem cells. The greatest increase in the amount of woody tissue was observed on days 21 and 28. At the end of the acclimatization period, T-14 plantlets contained on average 41.4 % of secondary xylem tissue compared to 30.3 % found in T-50 plantlets. During the course of acclimatization, both clones displayed identical patterns of vessel lumen size distribution from small vessel lumen area to large vessel lumen area. This pattern differs from the characteristic diffuse-porous pattern of approximately evensized vessel lumen area distribution typical of mature wood. At the end of acclimatization, the differences in vessel lumen area and relative conductivity between the clones were negligible. Development of secondary xylem tissue during ex vitro acclimatization promotes the establishment of vigorous regenerants with stems that show increased bending strength and stiffness.

Grafting is an important cultivation method and recent research on the mechanism of interactions between rootstock nad scion is focused on the long-distance transport of mRNA and small RNAs in the phloem. Among these transportable molecules, NACP gene coding NAM, ATAF1/2, CUC2 (NAC) domain protein might be involved in apical meristem development. Here, we report the transport of NACP mRNA between Chinese pear (Pyrus bretschneideri) cv. Yali (scion) and the wild Pyrus betulaefolia Bunge (rootstock). Our results indicated that NACP mRNA can be transported in both directions from the 3^rd to 10^th day after micro-grafting. It can also be transported to the shoot apex 30 to 70 cm away from graft-union in 2-year-old grafted trees. For further investigation, transgenic tobaccos with 35S: P. betulaefolia-NACP construct were grafted on wild-type tobaccos (Nicotiana tabacum L. cv. Samsun). The sustainable transport of Pyrus-NACP mRNA through the graft-union occurred from the 15^th day after grafting.

Drought stress enhances the production of superoxide radical (O₂ ^._) and superoxide dismutase catalyses dismutation of it to H₂O₂ and O₂, and hence provides a first line of defense against oxidative stress. Over-expression of a cytosolic copper-zinc superoxide dismutase, cloned from Potentilla atrosanguinea (PaSOD), in potato (Solanum tuberosum ssp. tuberosum L. cv. Kufri Sutlej) resulted in enhanced net photosynthetic rates (P_N) and stomatal conductance (g_s) compared to that in the wild type (WT) plants under control (irrigated) as well as drought stress conditions. Drought stress declined leaf water potential, P_N, g_s, photosystem II activity, and chlorophyll content, but increased proline and O₂ ^._ content more in WT than transgenic potato plants (SS5). The significantly higher SOD activity in SS5 coincided well with lower O₂ ^._ content suggesting its role in maintaining higher g_s and P_N in transgenic potato plants.

Soil salinity is a major abiotic stress and salt overly sensitive (SOS) pathway plays an important role in imparting tolerance to salinity by reinstating cellular ionic equilibrium. Salt overly sensitive 1 (SOS1) gene of SOS pathway has been implicated in increasing salt tolerance in plants. In this study, a 734 bp fragment of SOS1 promoter (SbUSOS1) was isolated from a halophyte Salicornia brachiata Roxb. In silico analysis of SbUSOS1 predicted several cis-acting regulatory elements such as DOF motif, GT elements, ABRE-like sequence, and root specific motifs. Functional validation of SbUSOS1 into tobacco stems and leaves using the GUS reporter gene showed that this promoter is induced by salt stress (250 mM NaCl) but not by ABA (500 μM) and cold (4 °C) stresses. This study indicated that SbUSOS1 was functional with predicted cis-acting elements that could be responsible for its salt-inducible nature. It can be used for the development of salt stress tolerant transgenic plants.

The effects of paclobutrazol (PBZ) on the ex vitro transfer efficiency of in vitro grown Dendrobium nobile seedlings were investigated. The survival percentage was increased by 41.6 % with 0.8 mg dm^-3 PBZ treatment compared to controls. The PBZ-treated D. nobile plants were shorter than control plants. Morphological and anatomical analyses showed that root diameter, especially at the root apex, became larger after treatment with PBZ which is consistent with the increases in cortical cell sizes and row numbers. In addition, the first observations of thickened velamen of the PBZ-treated seedling were made in the present study. The activities of cellulase and indole acetic acid oxidase increased in PBZ-treated plantlets, whereas that of cell wall-associated peroxidase declined compared to controls. The content of endogenous gibberellic acid and iso-pentenyladenosine of root tips changed little by PBZ but that of indole-3-acetic acid decreased by 53 %. These results indicated that PBZ could improve the transfer efficiency of D. nobile from in vitro culture to pots due to its effects on root development.

The rice OsMyb4 gene, which encodes a Myb transcription factor (TF), improves the stress tolerance/resistance when expressed in both monocotyledonous and dicotyledonous transgenic plants. In this study, a phylogenetic analysis showed the existence of putative OsMyb4 homologues in monocot and dicot species. In particular, the analysis revealed that OsMyb4 belongs to a small rice gene subfamily conserved among monocots. The expression analyses of the OsMyb4-like genes in rice, wheat, and Arabidopsis indicated that these genes are involved in the response to dehydration, cold, and wounding. Moreover, the in silico analysis of the 5' upstream regions of the Osmyb4-like genes highlighted that the positions of some cis-elements involved in the stress response were conserved among the putative promoters, especially between OsMyb4 and its putative paralog Os02g41510. Finally, our transient expression assays in tobacco protoplasts demonstrated that OsMyb4 is able to repress the activity of both its own promoter and the Os02g41510 promoter by acting on the same binding site. A compensatory mechanism of auto-regulation is consistent with the well-known complexity of the OsMyb4-activated pathway, and this mechanism could regulate the transcription of other genes belonging to the family.

Two cultivars of winter wheat (Triticum aestivum L.) differing in their drought tolerance (KTC86211 and ND7532) were subjected to a progressive soil water stress and recovery at four developmental stages. Dehydrins with molecular masses of 45 and 37 kDa were constitutively accumulated during all stages in both genotypes. The 28 kDa dehydrin accumulated exclusively at seedling stage in both genotypes. The 49 and 40 kDa dehydrins accumulated at both tillering and jointing stages but showed a genotype-specific pattern. The content of most dehydrins increased with decreased soil moisture and then decreased during recovery. These results suggest that accumulation pattern of dehydrins during water stress was related to the genotype and developmental stage.

Randomly amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) markers were applied to assess the genetic stability of micropropagated olive (Olea europaea L. cv. Maurino) plants regenerated by axillary buds. Initial olive explants, isolated from one donor tree, were multiplied on Murashige and Skoog medium for 12 repeated subcultures. A total of 40 RAPD and 10 ISSR markers resulted in 301 distinct and reproducible band classes showing homogeneous RAPD and ISSR patterns. The amplification products revealed genetic stability among the micropropagated plants and between them and the donor plant. The results demonstrate the genetic stability of nine year old mature micropropagated olive plants cultured in field, and corroborated the fact that axillary multiplication is the safest mode for multiplication of true to type plants.

The influence of freezing on phospholipase D (PLD) was studied in Chorispora bungeana Fisch. & C.A. Mey., which is a naturally cold-tolerant species. During the freezing treatment (-4 °C), PLD activities in both microsomal and mitochondrial membranes increased at day 3, remained at a high level at day 6 and then declined to a moderate level. The RT-PCR analyses showed that PLD activity partially corresponded to the CbPLD gene transcript level. The freezing treatment resulted in increases in the K _m and V _max for microsomal and mitochondrial PLD, respectively. Freezing injury, as measured by electrolyte leakage and malondialdehyde content, peaked at day 6 and then gradually decreased. Alleviation of freezing injury was related to a decreased content of membrane-associated Ca²⁺. We suggest that the specific mechanism of cold resistance of C. bungeana is linked with PLD.

Cytokinins have been implicated in delaying leaf senescence. We previously generated transgenic cotton (Gossypium hirsutum L.) plants that harbor the Agrobacterium isopentenyl transferase gene (ipt) directed by a proteinase gene promoter. Here, we report that mRNAs were isolated from ipt cotton leaves and azygous leaves and were subsequently sequenced using Illumina Solexa technology. The sequence tags were searched against the TIGR database and the related gene expression profiles were compared resulting in the identification of 1 218 differentially expressed genes (DEGs): 719 up-regulated and 499 down-regulated. Analyzing the DEGs in the ipt cotton leaves showed that these genes belonged to four pathways: flavone biosynthesis, arginine and proline metabolism, glyoxylate and dicarboxylate metabolism, and RNA degradation. These pathways increased the activities of antioxidants, inhibited the effect of ethylene, and prevented degradation of macromolecules during senescence. The expression patterns of 17 genes were evaluated by real-time PCR and results were in agreement with the patterns of sequencing analysis. The identification of the DEGs may help us to understand a role of cytokinins in leaf senescence.

Peanut plants exposed to water stress induced by polyethylene glycol (PEG) accumulated abscisic acid (ABA) and hydrogen peroxide (H₂O₂), the increase being significant at 12 and 24 h after addition, respectively. To address the question whether the increase in H₂O₂ production was related to ABA accumulation, the peanut leaves were pretreated with ABA biosynthesis inhibitor (sodium tungstate) and then exposed to water stress. Under these conditions, a decrease of ABA and H₂O₂ content were found after 12 h. The addition of 100 μM ABA restored H₂O₂ content reaching values similar to those under water stress at 12 h. We concluded that ABA accumulation is the first signal that triggers the H₂O₂ generation in peanut during first 12 h but its subsequent production is partially ABA-independent.

A cDNA encoding an ERE-binding protein (EgAP2-1) was isolated from the oil palm fruit mesocarp treated with ethylene using yeast one-hybrid assay. EgAP2-1 belongs to the AP2 subfamily of the APETALA2/ethylene-responsive factor (AP2/ERF) proteins and contains two highly conserved AP2/EREBP DNA-binding domains (DNA-BD). Sequence comparison of EgAP2-1 with other AP2 proteins revealed high conservation of the two AP2/EREBP domains and linker region among these proteins. Its protein was localized to the nucleus of onion epidermis cells and showed ERE-specific binding, transcriptional activation, and transactivation properties in yeast and in vitro. Its mRNA was highly expressed in oil palm mesocarp with elevated levels in ripening fruits but not in leaves and roots. EgAP2-1 was induced in mesocarp in response to ethylene and abscisic acid but not other hormonal stimuli, including methyl jasmonate and salicylic acid, and abiotic stresses including drought, cold, and high-salinity. Our results demonstrate a link between the regulation of EgAP2-1 expression and ethylene- and/or ABA-coordinated control of the fruit ripening and suggest a regulatory role for EgAP2-1 during fruit ripening and development in oil palm.

The gas exchange of the upper fully expanded leaf of the root parasite Striga hermonthica and of its host Sorghum bicolor was measured under wet and dry conditions to identify the mechanisms of the devastating effects of the parasite on its hosts under drought. The short-term water stress severely reduced photosynthetic rate in infected sorghum, but less in S. hermonthica. Soil water stress did not affect leaf respiration rate in either S. hermonthica or infected sorghum. This suggests that under dry conditions both infected sorghum and S. hermonthica decreased autotrophic carbon gain. The transpiration rate of S. hermonthica, a major driving force for assimilate uptake from the host, was higher and less affected by water stress than that of infected sorghum. Stomatal density on the abaxial surfaces of the leaves was higher in S. hermonthica than in sorghum. Both S. hermonthica infection and water stress decreased stomatal conductance of the sorghum leaves. S. hermonthica, irrespective of soil water status, had greater stomatal aperture on the adaxial and abaxial surfaces of its leaves than infected sorghum. These results indicate that the higher transpiration rate of S. hermonthica even under water stress, achieved through higher stomatal density on the abaxial surfaces of the leaves and greater stomatal aperture on both surfaces of the leaves, may induce the maintenance of water and solute transfers from the host to the parasite leading to severe damage to the host under drought.

A segregating population from the cross between drought sensitive (Variant-2) and drought tolerant (Cham-6) genotypes was made to identify molecular markers linked to wheat (Triticum aestivum L.) flag leaf senescence under water-stress. From 38 random amplified polymorphic DNA (RAPD) primers, 25 inter-simple sequence repeat (ISSR) primers and 46 simple sequence repeat (SRR) primers, tested for polymorphism among parental genotypes and F2 population. Quantitative trait locus (QTL) for flag leaf senescence was associated with 1 RAPD marker (Pr9), 4 ISSR markers (Pr8, AD5, AD2 and AD3), and 1 SSR marker (Xgwm382) and explained 44, 50, 35, 31, 22 and 73 % phenotypic variation, respectively. The genetic distance between flag leaf senescence gene and Pr9 was 10.0 cM (LOD score 22.9). The markers Pr8, AD5, AD2 and AD3 had genetic distances of 10.5, 14.6, 15.6 and 18.1 cM, respectively (LOD scores 22.6, 17.8, 17.5 and 14.6). The genetic distance between Xgwm382 was 3.9 cM (LOD score 33.8). Therefore, the RAPD, ISSR and SSR markers linked to the QTL for the drought-induced flag leaf senescence can be further used in breeding for drought tolerance in wheat.

We have compared the influence of two aromatic cytokinin derivatives, N ⁶-benzyladenine (BA) and meta-topolin (mT), on the in vitro multiplication and senescence of wych elm (Ulmus glabra Huds.). After 3 months of cultivation, the micropropagation rate was higher (approx. six times more shoots developed) on Murashige and Skoog (MS) medium supplemented with mT than on MS supplemented with BA. Quantification of 50 endogenous cytokinins, using a recently developed UPLC-ESI(+)-MS/MS method, showed significant differences in the cytokinin metabolites (especially different glucosides) in explants cultivated on media supplemented with BA or mT. Differences in efficiency of photosystem II was also detected.

Purple acid phosphatases (PAPs), which are normally found in plant tissues, can hydrolyze a broad spectrum of phosphate esters. In this study, a mungbean [Vigna radiata (L.) Wilczek cv. KPS1] acid phosphatase gene (VrPAP1) was isolated from seedling cotyledons. The full-length of VrPAP1 cDNA contained an open reading frame of 1 644 bp encoding 547 amino acid residues with a predicted molecular mass of 62.07 kDa. Sequence analysis showed that VrPAP1 is purple acid phosphatase. RNA blot analyses indicated that the VrPAP1 accumulated during the first hour in cotyledons of germinating seeds and reached a maximum expression after 24 h and then decreased. The VrPAP1 mRNA was observed in cotyledons, hypocotyls and leaves but not in radicles or dry seeds. DNA blot analysis indicated that VrPAP1 is a single copy gene in the mungbean genome.

The amount of free glucose and sucrose within the leaves of Stevia rebaudiana has been evaluated under different photoperiods and related to steviol glycoside (SVgly) accumulation. The diurnal dynamics of glucose and sucrose in leaves, internodes, apices, and roots revealed considerable fluctuations. Within leaves, glucose and sucrose content decreased up to three-fold during the night whereas SVgly amounts did not show any significant diurnal fluctuations. Ontogenetic variations in glucose content was markedly different under long-day (LD) and short-day (SD) regimes. Under LD, glucose content increased two-fold after the onset of flower bud formation, whereas under SD, a stagnation or small decrease was observed. This increase under LD was already noticed in the upper sink leaves at the end of the vegetative stage, possibly acting as a metabolic trigger for the phase transition to reproductive development. Under SD, glucose content appeared more controlled resulting in a better linear relationship with dry matter and SVgly content. The increased sink demands of the transitional apex led to a rapid decline in leaf sucrose which showed little or no correlation with SVgly amounts. From our results, it becomes clear that the correlation between glucose or sucrose as substrates and SVglys as products is very dynamic and is significantly influenced by day-length and ontogeny.

When exposed to an acute ozone stress, cell death occurred in leaves of the O₃ sensitive Populus deltoides × maximowiczii clone Eridano. After treatment (5 h fumigation and 24 h recovery), the damaged areas covered more than 50 % of the leaf surface. At cellular level, these lesions were preceded by some apoptotic hallmarks and by biochemical and physiological alterations evoked by the apoplastic O₃ dissociation. The cell death pattern was highly localized and involved an increase of membrane permeability, externalization of phosphatidylserine, DNA fragmentation, callose accumulation, polyphenol production, and a biphasic oxidative burst accompanied by NO overproduction. These results indicate a process of programmed cell death that could have the biological significance of limiting the spreading the oxidative burst triggered by ozone dissociation in apoplastic environment. Moreover, materials derived from cell dismantling could be remobilized toward developing structures which can conclude their ontogenetic program after the stress.

Lingonberry (Vaccinium vitis-idaea L. ssp. vitis-idaea Britton) cultivars Regal, Splendor, and Erntedank were obtained by conventional softwood cuttings (taken as a control), by in vitro shoot proliferation of node explants, and by adventitious shoot regeneration from excised leaves of micropropagated shoots. In the plants propagated in vitro, the total ascorbate content increased and its pool was more oxidized, the total glutathione content also increased but its pool became more reduced. The leaves of plants obtained from the in vitro culture showed significantly higher antioxidant enzyme activities except for dehydroascorbate reductase which was at a similar level in all plants. Total soluble phenolics, tannins, and flavonoids were enhanced in fruits of in vitro-propagated plants whereas in leaves, the levels of these metabolites (except flavonoids) were higher in ex vitro derived plants. The total radical scavenging capacity was enhanced in berries of the in vitro propagated plants. It is suggested that the active morphogenetic process, characterized by intensive formation and scavenging reactive oxygen species is reflected in the activities of antioxidant enzymes and metabolites. The reduction potential of glutathione is the most important parameter which determines patterns of growth and differentiation in the investigated plants.

Homogeneous low phosphorus availability was reported to regulate root architecture in Arabidopsis via auxin, but the roles of auxin in root architecture plasticity to heterogeneous P availability remain unclear. In this study, we employed auxin biosynthesis-, transport- and signalling-related mutants. Firstly, we found that in contrast to low P (LP) content in the whole medium, primary root (PR) growth of Arabidopsis was partially rescued in the medium divided into two parts: upper with LP and lower with high P (HP) content or in the reverse arrangement. The down part LP was more effective to arrest PR growth as well as to decrease density of lateral roots (DLR) than the upper LP, and effects were dependent on polar auxin transport. Secondly, we verified that auxin receptor TIR1 was involved in the responses of PR growth and lateral root (LR) development to P supply and loss of function of TIR1 inhibited LR development. Thirdly, effects of heterogeneous P on LRD in the upper part of PR was dependent on PIN2 and PIN4, and in the down part on PIN3 and PIN4, whereas density of total LRs was dependent on auxin transporters PIN2 and PIN7. Finally, heterogeneous P availability altered the accumulation of auxin in PR tip and the expression of auxin biosynthesisrelated genes TAA1, YUC1, YUC2, and YUC4. Taken together, we provided evidences for the involvement of auxin in root architecture plasticity in response to heterogeneous phosphorus availability in Arabidopsis.

In order to set up large-scale acclimatization protocols of micropropagated plants, an in-depth knowledge of their physiological responses during in vitro to ex vitro transfer is required. This work describes the photosynthetic performance of Ulmus minor micropropagated plants during acclimatization at high irradiance (HI; 200 ± 20 μmol m^-2 s^-1 or low irradiance (LI; 100 ± 20 μmol m^-2 s^-1). During this experiment, leaf pigment content, chlorophyll a fluorescence, gas exchange, stomata morphology, the activity of the Calvin cycle enzymes and saccharides were measured in persistent and new leaves. The results indicated that HI induces a higher photosynthetic performance compared to LI. Therefore, plants acclimatized under HI are likely to survive better after field transfer.

Changes in membrane lipid composition is a fundamental strategy for plants to resist low-temperature stress. We compared members of 11 membrane glycerolipid classes in Thellungiella salsuginea and its close relative Arabidopsis thaliana at normal growth temperature, and during cold acclimation (CA), freezing (FR), and post-freezing recovery (PFR). The results showed several properties of T. salsuginea distinct from that in A. thaliana, which included: 1) low relative content of phosphatidic acid (PA) and a rapid increase and decrease of PA during FR and PFR respectively; 2) insensitivity of lyso-phospholipids to freezing; and 3) high ratio of phosphatidylcholine to phosphatidylethanolamine. All these properties were in favour of maintaining membrane integrity and stability and therefore enable T. salsuginea to be more tolerant to freezing than A. thaliana.