A dynamic phosphoproteomic analysis provides insight into the C4 plant maize (Zea mays L.) response to natural diurnal changes.

As sessile organisms, plants need to respond to rapid changes in numerous environmental factors, mainly diurnal changes of light, temperature, and humidity. Maize is the world's most grown crop, and as a C4 plant it exhibits high photosynthesis capacity, reaching the highest rate of net photosynthesis at midday; that is, there is no "midday depression." Revealing the physiological responses to diurnal changes and underlying mechanisms will be of great significance for guiding maize improvement efforts. In this study, we collected maize leaf samples and analyzed the proteome and phosphoproteome at nine time points during a single day/night cycle, quantifying 7424 proteins and 5361 phosphosites. The new phosphosites identified in our study increased the total maize phosphoproteome coverage by 8.5%. Kinase-substrate network analysis indicated that 997 potential substrates were phosphorylated by 20 activated kinases. Through analysis of proteins with significant changes in abundance and phosphorylation, we found that the response to a heat stimulus involves a change in the abundance of numerous proteins. By contrast, the high light at noon and rapidly changing light conditions induced changes in the phosphorylation level of proteins involved in processes such as chloroplast movement, photosynthesis, and C4 pathways. Phosphorylation is involved in regulating the activity of large number of enzymes; for example, phosphorylation of S55 significantly enhanced the activity of maize phosphoenolpyruvate carboxykinase1 (ZmPEPCK1). Overall, the database of dynamic protein abundance and phosphorylation we have generated provides a resource for the improvement of C4 crop plants.

Genome-wide transcriptome and proteome profiles indicate an active role of alternative splicing during de-etiolation of maize seedlings.

MAIN CONCLUSION: AS events affect genes encoding protein domain composition and make the single gene produce more proteins with a certain number of genes to satisfy the establishment of photosynthesis during de-etiolation. The drastic switch from skotomorphogenic to photomorphogenic development is an excellent system to elucidate rapid developmental responses to environmental stimuli in plants. To decipher the effects of different light wavelengths on de-etiolation, we illuminated etiolated maize seedlings with blue, red, blue-red mixed and white light, respectively. We found that blue light alone has the strongest effect on photomorphogenesis and that this effect can be attributed to the higher number and expression levels of photosynthesis and chlorosynthesis proteins. Deep sequencing-based transcriptome analysis revealed gene expression changes under different light treatments and a genome-wide alteration in alternative splicing (AS) profiles. We discovered 41,188 novel transcript isoforms for annotated genes, which increases the percentage of multi-exon genes with AS to 63% in maize. We provide peptide support for all defined types of AS, especially retained introns. Further in silico prediction revealed that 58.2% of retained introns have changes in domains compared with their most similar annotated protein isoform. This suggests that AS acts as a protein function switch allowing rapid light response through the addition or removal of functional domains. The richness of novel transcripts and protein isoforms also demonstrates the potential and importance of integrating proteomics into genome annotation in maize.

The developmental dynamics of the Populus stem transcriptome.

The Populus shoot undergoes primary growth (longitudinal growth) followed by secondary growth (radial growth), which produces biomass that is an important source of energy worldwide. We adopted joint PacBio Iso-Seq and RNA-seq analysis to identify differentially expressed transcripts along a developmental gradient from the shoot apex to the fifth internode of Populus Nanlin895. We obtained 87 150 full-length transcripts, including 2081 new isoforms and 62 058 new alternatively spliced isoforms, most of which were produced by intron retention, that were used to update the Populus annotation. Among these novel isoforms, there are 1187 long non-coding RNAs and 356 fusion genes. Using this annotation, we found 15 838 differentially expressed transcripts along the shoot developmental gradient, of which 1216 were transcription factors (TFs). Only a few of these genes were reported previously. The differential expression of these TFs suggests that they may play important roles in primary and secondary growth. AP2, ARF, YABBY and GRF TFs are highly expressed in the apex, whereas NAC, bZIP, PLATZ and HSF TFs are likely to be important for secondary growth. Overall, our findings provide evidence that long-read sequencing can complement short-read sequencing for cataloguing and quantifying eukaryotic transcripts and increase our understanding of the vital and dynamic process of shoot development.

The proteome and phosphoproteome of maize pollen uncovers fertility candidate proteins.

Maize is unique since it is both monoecious and diclinous (separate male and female flowers on the same plant). We investigated the proteome and phosphoproteome of maize pollen containing modified proteins and here we provide a comprehensive pollen proteome and phosphoproteome which contain 100,990 peptides from 6750 proteins and 5292 phosphorylated sites corresponding to 2257 maize phosphoproteins, respectively. Interestingly, among the total 27 overrepresented phosphosite motifs we identified here, 11 were novel motifs, which suggested different modification mechanisms in plants compared to those of animals. Enrichment analysis of pollen phosphoproteins showed that pathways including DNA synthesis/chromatin structure, regulation of RNA transcription, protein modification, cell organization, signal transduction, cell cycle, vesicle transport, transport of ions and metabolisms, which were involved in pollen development, the following germination and pollen tube growth, were regulated by phosphorylation. In this study, we also found 430 kinases and 105 phosphatases in the maize pollen phosphoproteome, among which calcium dependent protein kinases (CDPKs), leucine rich repeat kinase, SNF1 related protein kinases and MAPK family proteins were heavily enriched and further analyzed. From our research, we also uncovered hundreds of male sterility-associated proteins and phosphoproteins that might influence maize productivity and serve as targets for hybrid maize seed production. At last, a putative complex signaling pathway involving CDPKs, MAPKs, ubiquitin ligases and multiple fertility proteins was constructed. Overall, our data provides new insight for further investigation of protein phosphorylation status in mature maize pollen and construction of maize male sterile mutants in the future.

Posttranslational Modification of Maize Chloroplast Pyruvate Orthophosphate Dikinase Reveals the Precise Regulatory Mechanism of Its Enzymatic Activity.

In C4 plants, pyruvate orthophosphate dikinase (PPDK) activity is tightly dark/light regulated by reversible phosphorylation of an active-site threonine (Thr) residue; this process is catalyzed by PPDK regulatory protein (PDRP). Phosphorylation and dephosphorylation of PPDK lead to its inactivation and activation, respectively. Here, we show that light intensity rather than the light/dark transition regulates PPDK activity by modulating the reversible phosphorylation at Thr-527 (previously termed Thr-456) of PPDK in maize (Zea mays). The amount of PPDK (unphosphorylated) involved in C4 photosynthesis is indeed strictly controlled by light intensity, despite the high levels of PPDK protein that accumulate in mesophyll chloroplasts. In addition, we identified a transit peptide cleavage site, uncovered partial amino-terminal acetylation, and detected phosphorylation at four serine (Ser)/Thr residues, two of which were previously unknown in maize. In vitro experiments indicated that Thr-527 and Ser-528, but not Thr-309 and Ser-506, are targets of PDRP. Modeling suggests that the two hydrogen bonds between the highly conserved residues Ser-528 and glycine-525 are required for PDRP-mediated phosphorylation of the active-site Thr-527 of PPDK. Taken together, our results suggest that the regulation of maize plastid PPDK isoform (C4PPDK) activity is much more complex than previously reported. These diverse regulatory pathways may work alone or in combination to fine-tune C4PPDK activity in response to changes in lighting.

Light-regulated phosphorylation of maize phosphoenolpyruvate carboxykinase plays a vital role in its activity.

Phosphoenolpyruvate carboxykinase (PEPCK)-the major decarboxylase in PEPCK-type C4 plants-is also present in appreciable amounts in the bundle sheath cells of NADP-malic enzyme-type C4 plants, such as maize (Zea mays), where it plays an apparent crucial role during photosynthesis (Wingler et al., in Plant Physiol 120(2):539-546, 1999; Furumoto et al., in Plant Mol Biol 41(3):301-311, 1999). Herein, we describe the use of mass spectrometry to demonstrate phosphorylation of maize PEPCK residues Ser55, Thr58, Thr59, and Thr120. Western blotting indicated that the extent of Ser55 phosphorylation dramatically increases in the leaves of maize seedlings when the seedlings are transferred from darkness to light, and decreases in the leaves of seedlings transferred from light to darkness. The effect of light on phosphorylation of this residue is opposite that of the effect of light on PEPCK activity, with the decarboxylase activity of PEPCK being less in illuminated leaves than in leaves left in the dark. This inverse relationship between PEPCK activity and the extent of phosphorylation suggests that the suppressive effect of light on PEPCK decarboxylation activity might be mediated by reversible phosphorylation of Ser55.

Extraction and spatio-temporal analysis of phenological dates of winter wheat in north Henan Province of China from 2003 to 2018 based on MODIS NDVI time series.

Monitoring of spatio-temporal changes in crop phenology is an important part of the remote sensing of agricultural ecosystems. In this study, the segment turning point method was utilised to determine several phenological dates of winter wheat in northern Henan from 2003 to 2018. The spatio-temporal variation characteristics of these main phenological dates were analyzed, and the effects of temperature and precipitation on phenological changes were investigated. The results showed that: (1) The segment turning point method had strong space-time adaptability, and the RMSE of extracted phenoloical dates of multi-stations in a single year or single station in multi-years was less than 10d. (2) Roughly bounded by 114°E, the trefoil stage, tillering stage, overwintering stage and rising stage of winter wheat in the west were earlier than those in the east of northern Henan in 2018. (3) From 2003 to 2018, the interannual change rates of the trefoil date, tillering date, overwintering date, rising date, booting date, and milky date of winter wheat were 6.92 d/10a, 4.36 d/10a, 0.74 d/10a, -0.1 d/10a, -3.97 d/10a and -2.91 d/10a, indicating the trend of delaying pre-winter phenology and advancing post-winter phenology. (4) The delay of pre-winter phenology and the advance of post-winter phenology of winter wheat were significantly related to the increase in growing season temperature. The results of the study should provide a basis for further understanding of the effects of climate change on winter wheat phenology and to provide a reference for remote sensing monitoring of winter wheat phenology.

A comprehensive analysis of the lysine acetylome reveals diverse functions of acetylated proteins during de-etiolation in Zea mays.

Lysine acetylation is one of the most important post-translational modifications and is involved in multiple cellular processes in plants. There is evidence that acetylation may play an important role in light-induced de-etiolation, a key developmental switch from skotomorphogenesis to photomorphogenesis. During this transition, establishment of photosynthesis is of great significance. However, studies on acetylome dynamics during de-etiolation are limited. Here, we performed the first global lysine acetylome analysis for Zea mays seedlings undergoing de-etiolation, using nano liquid chromatography coupled to tandem mass spectrometry, and identified 814 lysine-acetylated sites on 462 proteins. Bioinformatics analysis of this acetylome showed that most of the lysine-acetylated proteins are predicted to be located in the cytoplasm, nucleus, chloroplast, and mitochondria. In addition, we detected ten lysine acetylation motifs and found that the accumulation of 482 lysine-acetylated peptides corresponding to 289 proteins changed significantly during de-etiolation. These proteins include transcription factors, histones, and proteins involved in chlorophyll synthesis, photosynthesis light reaction, carbon assimilation, glycolysis, the TCA cycle, amino acid metabolism, lipid metabolism, and nucleotide metabolism. Our study provides an in-depth dataset that extends our knowledge of in vivo acetylome dynamics during de-etiolation in monocots. This dataset promotes our understanding of the functional consequences of lysine acetylation in diverse cellular metabolic regulatory processes, and will be a useful toolkit for further investigations of the lysine acetylome and de-etiolation in plants.

Large-scale Proteomic and Phosphoproteomic Analyses of Maize Seedling Leaves During De-etiolation.

De-etiolation consists of a series of developmental and physiological changes that a plant undergoes in response to light. During this process light, an important environmental signal, triggers the inhibition of mesocotyl elongation and the production of photosynthetically active chloroplasts, and etiolated leaves transition from the "sink" stage to the "source" stage. De-etiolation has been extensively studied in maize (Zea mays L.). However, little is known about how this transition is regulated. In this study, we described a quantitative proteomic and phosphoproteomic atlas of the de-etiolation process in maize. We identified 16,420 proteins in proteome, among which 14,168 proteins were quantified. In addition, 8746 phosphorylation sites within 3110 proteins were identified. From the combined proteomic and phosphoproteomic data, we identified a total of 17,436 proteins. Only 7.0% (998/14,168) of proteins significantly changed in abundance during de-etiolation. In contrast, 26.6% of phosphorylated proteins exhibited significant changes in phosphorylation level; these included proteins involved in gene expression and homeostatic pathways and rate-limiting enzymes involved in photosynthetic light and carbon reactions. Based on phosphoproteomic analysis, 34.0% (1057/3110) of phosphorylated proteins identified in this study contained more than 2 phosphorylation sites, and 37 proteins contained more than 16 phosphorylation sites, indicating that multi-phosphorylation is ubiquitous during the de-etiolation process. Our results suggest that plants might preferentially regulate the level of posttranslational modifications (PTMs) rather than protein abundance for adapting to changing environments. The study of PTMs could thus better reveal the regulation of de-etiolation.

Holographic Three-Dimensional Imaging of Terra-Cotta Warrior Model Using Fractional Fourier Transform.

Holographic three-dimensional (3D) imaging of Terra-Cotta Warrior model using Fractional Fourier Transform is introduced in this paper. Phase holograms of Terra-Cotta Warrior model are calculated from 60 horizontal viewing-angles by the use of fractional Fourier transform (FRT). Multiple phase holograms are calculated for each angle by adding proper pseudorandom phase to reduce the speckle noise of a reconstructed image. Experimental system based on high-resolution phase-only spatial light modulator (SLM) is built for 3D image reconstruction from the calculated phase holograms. The texture of the Terra-Cotta Warrior model is rough. The calculation of rough texture is optimized in order to show better model details. The effects of computing distance and layer thickness on imaging quality are analyzed finally.

Investigation of reducing particulate matter (PM) and heavy metals pollutions by adding a novel additive from metallurgical dust (MD) during coal combustion.

In this study, a novel additive from metallurgical dust(MD)was applied to reduce particulate matter (PM) emissions and heavy metals pollutions during coal combustion. PM samples were collected and divided into 13 stages from 0.03 µm to 10 µm. Results showed that the irregular morphology of fine particles with equal to/less than 2.5 µm (PM2.5), fine particles with equal to/less than 4 µm (PM4) and fine particles with equal to/less than10 µm (PM10) gradually became dense with increasing of MD content. The PM10 concentration with 10% MD dosage was about 3 times higher than that of raw coal. Zn, Ti, Cu and Cr were the most abundant elements in all particulate matters (PMs), meanwhile, heavy metals accumulated into large particles with increasing MD content. The mechanism of reducing PM emissions indicated that MD reacted with nucleation elements (Pb, Cd, etc.) and trapped a large amount of alkali metal (Na/K), which aggregated into large particles. The study highlights the potential of adding MD into coal to prevent the attachment of heavy metals onto ultrafine particles, thereby reducing the heavy metals emissions.

Phylogenic and phosphorylation regulation difference of phosphoenolpyruvate carboxykinase of C3 and C4 plants.

In C4 plants, phosphoenolpyruvate carboxykinase (PEPCK) plays a key role in the C4 cycle. PEPCK is also involved in gluconeogenesis and is conserved in both lower and higher organisms, including in animals and plants. A phylogenic tree constructed from PEPCK sequences from bacteria to higher plants indicates that the C4 Poaceae PEPCKs are conserved and have diverged from the PEPCKs of C3 plants. The maximum enzymatic activities of wild-type and phosphorylation mimic PEPCK proteins indicate that there is a significant difference between C3 and C4 plant PEPCKs. The conserved PEPCK phosphorylation sites are regulated differently in C3 and C4 plants. These results suggest that the functions of PEPCK have been conserved, but that sequences have diverged and regulation of PEPCK is important in C4 plants, but not in herbaceous and, in particular, woody C3 plants.

Single-Event Transgene Product Levels Predict Levels in Genetically Modified Breeding Stacks.

The concentration of transgene products (proteins and double-stranded RNA) in genetically modified (GM) crop tissues is measured to support food, feed, and environmental risk assessments. Measurement of transgene product concentrations in breeding stacks of previously assessed and approved GM events is required by many regulatory authorities to evaluate unexpected transgene interactions that might affect expression. Research was conducted to determine how well concentrations of transgene products in single GM events predict levels in breeding stacks composed of these events. The concentrations of transgene products were compared between GM maize, soybean, and cotton breeding stacks (MON-87427 × MON-89034 × DAS-Ø15Ø7-1 × MON-87411 × DAS-59122-7 × DAS-40278-9 corn, DAS-81419-2 × DAS-44406-6 soybean, and DAS-21023-5 × DAS-24236-5 × SYN-IR102-7 × MON-88913-8 × DAS-81910-7 cotton) and their component single events (MON-87427, MON-89034, DAS-Ø15Ø7-1, MON-87411, DAS-59122-7, and DAS-40278-9 corn, DAS-81419-2, and DAS-44406-6 soybean, and DAS-21023-5, DAS-24236-5, SYN-IR102-7, MON-88913-8, and DAS-81910-7 cotton). Comparisons were made within a crop and transgene product across plant tissue types and were also made across transgene products in each breeding stack for grain/seed. Scatter plots were generated comparing expression in the stacks to their component events, and the percent of variability accounted for by the line of identity (y = x) was calculated (coefficient of identity, I2). Results support transgene concentrations in single events predicting similar concentrations in breeding stacks containing the single events. Therefore, food, feed, and environmental risk assessments based on concentrations of transgene products in single GM events are generally applicable to breeding stacks composed of these events.

Facile one-pot synthesis of Fe3O4@chitosan nanospheres for MRI and fluorescence imaging guided chemo-photothermal combinational cancer therapy.

Multifunctional nanoplatforms that integrate imaging and chemo-photothermal therapy for highly efficient cancer diagnostics and therapeutics have gained great interest in recent years. Herein, we designed and synthesized biodegradable and biocompatible magnetic chitosan nanospheres (Fe3O4@CS) by a facile one-pot synthesis method. Doxorubicin (DOX, an anticancer drug) and indocyanine green (ICG) can be co-loaded into the Fe3O4@CS nanospheres (Fe3O4@CS-ICG/DOX nanocomposites) by virtue of the mesoporous structure and electrostatic interactions of CS. The fabricated nanocomposite showed excellent magnetic resonance imaging (MRI) and fluorescence imaging performances for tumors in vivo. Moreover, chemotherapy and photothermal therapy could be driven simultaneously under NIR laser irradiation. Tumor growth could be effectively inhibited by chemo-photothermal combinational therapy in vivo, achieving excellent synergistic therapeutic efficacy. That is, the proposed biocompatible Fe3O4@CS-ICG/DOX nanocomposites can be used as a kind of multifunctional nanoplatform for MRI and fluorescence imaging guided chemo-photothermal combination cancer therapy.

Fe3O4@mSiO2-FA-CuS-PEG nanocomposites for magnetic resonance imaging and targeted chemo-photothermal synergistic therapy of cancer cells.

In this work, a new multifunctional nanoplatform (Fe3O4@mSiO2-FA-CuS-PEG nanocomposite) for magnetic resonance imaging (MRI) and targeted chemo-photothermal therapy, was firstly fabricated on the basis of magnetic mesoporous silica nanoparticles (Fe3O4@mSiO2), on which folic acid (FA) was grafted as the targeting reagent, CuS nanocrystals were attached as the photothermal agent, and polyethylene glycol (PEG) was coupled to improve biocompatibility. The characterization results demonstrated that the fabricated Fe3O4@mSiO2-FA-CuS-PEG nanocomposites not only showed strong magnetism and excellent MRI performance, but also had a high doxorubicin (DOX, an anticancer drug) loading capacity (22.1%). The loaded DOX can be sustainably released, which was apt to be controlled by pH adjustment and near infrared (NIR) laser irradiation. More importantly, targeted delivery of the DOX-loaded Fe3O4@mSiO2-FA-CuS-PEG nanocomposites could be accomplished in HeLa cells via the receptor-mediated endocytosis pathway, and this exhibited synergistic effect of chemotherapy and photothermal therapy against HeLa cells under irradiation with a 915 nm laser. Therefore, the fabricated multifunctional Fe3O4@mSiO2-FA-CuS-PEG nanocomposite has a great potential in image-guided therapy of cancers.

A novel and facile synthesis of porous SiO2-coated ultrasmall Se particles as a drug delivery nanoplatform for efficient synergistic treatment of cancer cells.

A novel and facile synthetic route has been developed to fabricate porous SiO2-coated ultrasmall Se particles (Se@SiO2 nanospheres) as a drug delivery nanoplatform which combines Se quantum dots and doxorubicin (DOX) for efficient synergistic treatment of cancer cells.

Molecular Characterization of Transgenic Events Using Next Generation Sequencing Approach.

Demand for the commercial use of genetically modified (GM) crops has been increasing in light of the projected growth of world population to nine billion by 2050. A prerequisite of paramount importance for regulatory submissions is the rigorous safety assessment of GM crops. One of the components of safety assessment is molecular characterization at DNA level which helps to determine the copy number, integrity and stability of a transgene; characterize the integration site within a host genome; and confirm the absence of vector DNA. Historically, molecular characterization has been carried out using Southern blot analysis coupled with Sanger sequencing. While this is a robust approach to characterize the transgenic crops, it is both time- and resource-consuming. The emergence of next-generation sequencing (NGS) technologies has provided highly sensitive and cost- and labor-effective alternative for molecular characterization compared to traditional Southern blot analysis. Herein, we have demonstrated the successful application of both whole genome sequencing and target capture sequencing approaches for the characterization of single and stacked transgenic events and compared the results and inferences with traditional method with respect to key criteria required for regulatory submissions.

Effect of Cu substitution on structures and electrochemical properties of Li[NiCo1-xCuxMn]1/3O2 as cathode materials for lithium ion batteries.

Copper ions are one of the major associated metal ions present in the precursors of the synthesis of Li[NiCoMn]1/3O2 from the recovery of spent Li-ion batteries by wet chemical processes. To evaluate the feasibility of reusing Cu(2+) as a favourable dopant in Li[NiCoMn]1/3O2 instead of as usual removing it as an undesirable impurity, the effect of Cu-doping on the electrochemical behaviour of Li[NiCoMn]1/3O2 is investigated in this work. Li[NiCo1-xCuxMn]1/3O2 (x = 0, 0.02, 0.04, 0.06 and 0.08) is synthesized through two steps, roasting the precursors obtained from carbonate co-precipitation, and their structures and electrochemical performances are systemically investigated. The results indicate that substitution of Co with Cu was successfully achieved without any detectable second phases. The initial discharge capacity of Li[NiCo1-xCuxMn]1/3O2 gradually dropped with an increase of x but the rate property and capacity retention were remarkably enhanced. In particular, the capacity retention of the Li[NiCo0.94Cu0.06Mn]1/3O2 sample reached 95.87% within 50 cycles at a current density of 160 mA g(-1). CV and EIS revealed that such improvements are ascribed to a higher Li(+) diffusion coefficient and lower charge-transfer resistance derived from Cu(2+) doping. The results suggest that Cu can be used as a beneficial dopant to partially substitute Co in synthesizing Li[NiCoMn]1/3O2 from spent LIBs instead of having to remove it as an impurity.

Sustainable synthesis of metals-doped ZnO nanoparticles from zinc-bearing dust for photodegradation of phenol.

A novel strategy of waste-cleaning-waste is proposed in the present work. A metals-doped ZnO (M-ZnO, M = Fe, Mg, Ca and Al) nanomaterial has been prepared from a metallurgical zinc-containing solid waste "fabric filter dust" by combining sulfolysis and co-precipitation processes, and is found to be a favorable photocatalyst for photodegradation of organic substances in wastewater under visible light irradiation. All the zinc and dopants (Fe, Mg, Ca and Al) for preparing M-ZnO are recovered from the fabric filter dust, without any addition of chemical as elemental source. The dust-derived M-ZnO samples deliver single phase indexed as the hexagonal ZnO crystal, with controllable dopants species. The photocatalytic activity of the dust-derived M-ZnO samples is characterized by photodegradation of phenol aqueous solution under visible light irradiation, giving more prominent photocatalytic behaviors than undoped ZnO. Such enhancements may be attributed to incorporation of the dust-derived metal elements (Fe, Mg, Ca and Al) into ZnO structure, which lead to the modification of band gap and refinement of grain size. The results show a feasibility to utilize the industrial waste as a resource of photodegradating organic substances in wastewater treatments.

Response of mannitol-producing Arabidopsis thaliana to abiotic stress.

In celery, mannitol is a primary photosynthetic product that is associated with celery's exceptional salt tolerance. Arabidopsis plants transformed with celery's mannose-6-phosphate reductase (M6PR) gene produce mannitol and grow normally in the absence of stress. Daily analysis of the increase in growth (fresh and dry weight, leaf number, leaf area per plant and specific leaf weight) over a 12-day period showed less effect of salt (100 mm NaCl) on the M2 transformant than wild type (WT). Following a 12-day treatment of WT, M2 and M5 plants with 100 or 200 mm NaCl the total shoot fresh weight, leaf number, and leaf area were significantly greater in transformants than in WT plants. The efficiency of use of energy for photochemistry by PSII was measured daily under growth conditions. In WT plants treated with 100 mm NaCl, the PSII yield begin decreasing after 6 days with a 50% loss in yield after 12 days, indicating a severe loss in PSII efficiency; whereas, there was no effect on the transformants. Under atmospheric levels of CO2, growth with 200 mm NaCl caused an increase in the substomatal levels of CO2 in WT plants but not in transformants. It also caused a marked decrease in carboxylation efficiency under limiting levels of CO2 in WT compared with transformants. When stress was imposed and growth reduced by withholding water for 12 days, which resulted in a similar decrease in relative water content to salt-treated plants, there were no differences among the genotypes in PSII yields or growth. The results suggest mannitol, which is known to be a compatible solute and antioxidant, protects photosynthesis against salt-related damage to chloroplasts.