The auxin influx carrier, OsAUX3, regulates rice root development and responses to aluminium stress.

In rice, there are five members of the auxin carrier AUXIN1/LIKE AUX1 family; however, the biological functions of the other four members besides OsAUX1 remain unknown. Here, by using CRISPR/Cas9, we constructed two independent OsAUX3 knock-down lines, osaux3-1 and osaux3-2, in wild-type rice, Hwayoung (WT/HY) and Dongjin (WT/DJ). osaux3-1 and osaux3-2 have shorter primary roots (PRs), decreased lateral root (LR) density, and longer root hairs (RHs) compared with their WT. OsAUX3 expression in PRs, LRs, and RHs further supports that OsAUX3 plays a critical role in the regulation of root development. OsAUX3 locates at the plasma membrane and functions as an auxin influx carrier affecting acropetal auxin transport. OsAUX3 is up-regulated in the root apex under aluminium (Al) stress, and osaux3-2 is insensitive to Al treatments. Furthermore, 1-naphthylacetic acid accented the sensitivity of WT/DJ and osaux3-2 to respond to Al stress. Auxin concentrations, Al contents, and Al-induced reactive oxygen species-mediated damage in osaux3-2 under Al stress are lower than in WT, indicating that OsAUX3 is involved in Al-induced inhibition of root growth. This study uncovers a novel pathway alleviating Al-induced oxidative damage by inhibition of acropetal auxin transport and provides a new option for engineering Al-tolerant rice species.

The small auxin-up RNA OsSAUR45 affects auxin synthesis and transport in rice.

KEY MESSAGE: This research is the first to demonstrate that OsSAUR45 is involved in plant growth though affecting auxin synthesis and transport by repressing OsYUCCA and OsPIN gene expression in rice. Small auxin-up RNAs (SAURs) comprise a large multigene family and are rapidly activated as part of the primary auxin response in plants. However, little is known about the role of SAURs in plant growth and development, especially in monocots. Here, we report the biological function of OsSAUR45 in the model plant rice (Oryza sativa). OsSAUR45 is expressed in a tissue-specific pattern and is localized to the cytoplasm. Rice lines overexpressing OsSAUR45 displayed pleiotropic developmental defects including reduced plant height and primary root length, fewer adventitious roots, narrower leaves, and reduced seed setting. Auxin levels and transport were reduced in the OsSAUR45 overexpression lines, potentially because of decreased expression of Flavin-binding monooxygenase family proteins (OsYUCCAs) and PIN-FORMED family proteins (OsPINs). Exogenous auxin application rapidly induced OsSAUR45 expression and partially restored the phenotype of rice lines overexpressing OsSAUR45. These results demonstrate that OsSAUR45 is involved in plant growth by affecting auxin synthesis and transport through the repression of OsYUCCA and OsPIN gene expression in rice.

The auxin transporter, OsAUX1, is involved in primary root and root hair elongation and in Cd stress responses in rice (Oryza sativa L.).

Auxin and cadmium (Cd) stress play critical roles during root development. There are only a few reports on the mechanisms by which Cd stress influences auxin homeostasis and affects primary root (PR) and lateral root (LR) development, and almost nothing is known about how auxin and Cd interfere with root hair (RH) development. Here, we characterize rice osaux1 mutants that have a longer PR and shorter RHs in hydroponic culture, and that are more sensitive to Cd stress compared to wild-type (Dongjin). OsAUX1 expression in root hair cells is different from that of its paralogous gene, AtAUX1, which is expressed in non-hair cells. However, OsAUX1, like AtAUX1, localizes at the plasma membrane and appears to function as an auxin tranporter. Decreased auxin distribution and contents in the osaux1 mutant result in reduction of OsCyCB1;1 expression and shortened PRs, LRs and RHs under Cd stress, but may be rescued by treatment with the membrane-permeable auxin 1-naphthalene acetic acid. Treatment with the auxin transport inhibitors 1-naphthoxyacetic acid and N-1-naphthylphthalamic acid increased the Cd sensitivity of WT rice. Cd contents in the osaux1 mutant were not altered, but reactive oxygen species-mediated damage was enhanced, further increasing the sensitivity of the osaux1 mutant to Cd stress. Taken together, our results indicate that OsAUX1 plays an important role in root development and in responses to Cd stress.

Seasonal Dynamics of Metabolites in Needles of Taxus wallichiana var. mairei.

Seasonal variations of the phytochemicals contents in needles of T. wallichiana var. mairei due to the effects of growth meteorological parameters were investigated in this study. The needles of T. wallichiana var. mairei were collected from different months and the contents of taxoids (paclitaxel, 10-deacetylbaccatin III (10-DAB), baccatin III, cephalomannine, 10-deacetyltaxol (10-DAT)), flavones (ginkgetin, amentoflavone, quercetin) and polysaccharides were quantified by ultra performance liquid chromatography (UPLC) and the resonance light scattering (RIL) method. The content of taxoids gave the highest level of 1.77 ± 0.38 mg·g-1 in January, and the lowest value of 0.61 ± 0.08 mg·g-1 in September. Unlike taxoids, the content of flavonoids was the highest in August. The content of polysaccharides reached peak value of 28.52 ± 0.57 mg·g-1 in September, which was two times higher than the lowest content of 9.39 ± 0.17 mg·g-1 in January. The contents of paclitaxel, 10-DAB, 10-DAT and polysaccharides significantly depended on meteorological parameters. The mean of minimum temperature (R = -0.61) and length of daylight (R = -0.60) were significantly correlated to 10-DAB content, while 10-DAT level showed significant correlation with length of daylight (R = -0.70) and relative humidity (R = 0.70). In addition, temperature had significantly negative effect on the content of paclitaxel and a significantly positive effect on that of polysaccharides. This study enriched the knowledge on the accumulation pattern of metabolites and could help us to determine the collecting time of T. wallichiana var. mairei for medicinal use.

Enantioselective Separation of 4,8-DHT and Phytotoxicity of the Enantiomers on Various Plant Species.

As a candidate for bioherbicide, 4,8-dihydroxy-1-tetralone (4,8-DHT) was isolated from Caryospora callicarpa epicarp and its two enantiomers, S-(+)-isosclerone and R-(-)-regiolone, were separated by chiral high-performance liquid chromatography (HPLC) on a Chiralcel OD column with chiral stationary phase (CSP)-coated cellulose-tris(3,5-dimethylphenylcarbamate). Then, the phytotoxicity of 4,8-DHT and its enantiomers toward the seeds germination and seedling growth of the five tested plant species, including lettuce (Latuca sativa), radish (Raphanus sativus), cucumber (Cucumis sativus), onion (Allium cepa), and wheat (Triticum aestivum), were investigated and the results indicated a hormesis at low concentration of 4,8-DHT and its enantiomers, but a retardant effect at high concentration. Between the two enantiomers of 4,8-DHT, the S-(+)-isosclerone was more toxic to seeds germination and seedling growth of the five tested plant species than the R-(-)-regiolone, and also the phytotoxicity of S-(+)-isosclerone varied with different plants. For example, S-(+)-isosclerone was the most active to seedling growth of lettuce, indicating that S-(+)-isosclerone had specific effects on different organisms. Thus, all of the chirality and concentration of 4,8-DHT, as well as the affected plant species, need to be taken into consideration in the development and utilization of 4,8-DHT.

OsABCB14 functions in auxin transport and iron homeostasis in rice (Oryza sativa L.).

Members of the ATP Binding Cassette B/Multidrug-Resistance/P-glyco-protein (ABCB/MDR/PGP) subfamily were shown to function primarily in Oryza sativa (rice) auxin transport; however, none of the rice ABCB transporters have been functionally characterized. Here, we describe that a knock-down of OsABCB14 confers decreased auxin concentrations and polar auxin transport rates, conferring insensitivity to 2,4-dichlorophenoxyacetic acid (2,4-D) and indole-3-acetic acid (IAA). OsABCB14 displays enhanced specific auxin influx activity in yeast and protoplasts prepared from rice knock-down alleles. OsABCB14 is localized at the plasma membrane, pointing to an important directionality under physiological conditions. osabcb14 mutants were surprisingly found to be insensitive to iron deficiency treatment (-Fe). Their Fe concentration is higher and upregulation of Fe deficiency-responsive genes is lower in osabcb14 mutants than in wild-type rice (Nipponbare, NIP). Taken together, our results strongly support the role of OsABCB14 as an auxin influx transporter involved in Fe homeostasis. The functional characterization of OsABCB14 provides insights in monocot auxin transport and its relationship to Fe nutrition.

OsMOGS is required for N-glycan formation and auxin-mediated root development in rice (Oryza sativa L.).

N-glycosylation is a major modification of glycoproteins in eukaryotic cells. In Arabidopsis, great progress has been made in functional analysis of N-glycan production, however there are few studies in monocotyledons. Here, we characterized a rice (Oryza sativa L.) osmogs mutant with shortened roots and isolated a gene that coded a putative mannosyl-oligosaccharide glucosidase (OsMOGS), an ortholog of α-glucosidase I in Arabidopsis, which trims the terminal glucosyl residue of the oligosaccharide chain of nascent peptides in the endoplasmic reticulum (ER). OsMOGS is strongly expressed in rapidly cell-dividing tissues and OsMOGS protein is localized in the ER. Mutation of OsMOGS entirely blocked N-glycan maturation and inhibited high-mannose N-glycan formation. The osmogs mutant exhibited severe defects in root cell division and elongation, resulting in a short-root phenotype. In addition, osmogs plants had impaired root hair formation and elongation, and reduced root epidemic cell wall thickness due to decreased cellulose synthesis. Further analysis showed that auxin content and polar transport in osmogs roots were reduced due to incomplete N-glycosylation of the B subfamily of ATP-binding cassette transporter proteins (ABCBs). Our results demonstrate that involvement of OsMOGS in N-glycan formation is required for auxin-mediated root development in rice.

The auxin response factor, OsARF19, controls rice leaf angles through positively regulating OsGH3-5 and OsBRI1.

Auxin and brassinosteroid (BR) are important phytohormones for controlling lamina inclination implicated in plant architecture and grain yield. But the molecular mechanism of auxin and BR crosstalk for regulating lamina inclination remains unknown. Auxin response factors (ARFs) control various aspects of plant growth and development. We here report that OsARF19-overexpression rice lines show an enlarged lamina inclination due to increase of its adaxial cell division. OsARF19 is expressed in various organs including lamina joint and strongly induced by auxin and BR. Chromatin immunoprecipitation (ChIP) and yeast one-hybrid assays demonstrate that OsARF19 binds to the promoter of OsGH3-5 and brassinosteroid insensitive 1 (OsBRI1) directing their expression. OsGH3-5-overexpression lines show a similar phenotype as OsARF19-O1. Free auxin contents in the lamina joint of OsGH3-5-O1 or OsARF19-O1 are reduced. OsGH3-5 is localized at the endoplasmic retieulum (ER) matching reduction of the free auxin contents in OsGH3-5-O1. osarf19-TDNA and osgh3-5-Tos17 mutants without erected leaves show a function redundancy with other members of their gene family. OsARF19-overexpression lines are sensitive to exogenous BR treatment and alter the expressions of genes related to BR signalling. These findings provide novel insights into auxin and BR signalling, and might have significant implications for improving plant architecture of monocot crops.

Auxin response factor (OsARF12), a novel regulator for phosphate homeostasis in rice (Oryza sativa).

Phosphorus (P) is crucial nutrient element for crop growth and development. However, the network pathway regulating homeostasis of phosphate (Pi) in crops has many molecular breeding unknowns. Here, we report that an auxin response factor, OsARF12, functions in Pi homeostasis. Measurement of element content, quantitative reverse transcription polymerase chain reaction analysis and acid phosphatases (APases) activity assay showed that the osarf12 mutant and osarf12/25 double mutant with P-intoxicated phenotypes had higher P concentrations, up-regulation of the Pi transporter encoding genes and increased APase activity under Pi-sufficient/-deficient (+Pi/-Pi, 0.32/0 mM NaH2 PO4) conditions. Transcript analysis revealed that Pi-responsive genes--Phosphate starvation (OsIPS)1 and OsIPS2, SYG1/Pho81/XPR1(OsSPX1), Sulfoquinovosyldiacylglycerol 2 (OsSQD2), R2R3 MYB transcription factor (OsMYB2P-1) and Transport Inhibitor Response1 (OsTIR1)--were more abundant in the osarf12 and osarf12/25 mutants under +Pi/-Pi conditions. Knockout of OsARF12 also influenced the transcript abundances of the OsPHR2 gene and its downstream components, such as OsMiR399j, OsPHO2, OsMiR827, OsSPX-MFS1 and OsSPX-MFS2. Results from -Pi/1-naphthylphthalamic acid (NPA) treatments, and auxin reporter DR5::GUS staining suggest that root system alteration and Pi-induced auxin response were at least partially controlled by OsARF12. These findings enrich our understanding of the biological functions of OsARF12, which also acts in regulating Pi homeostasis.

OsARF16, a transcription factor, is required for auxin and phosphate starvation response in rice (Oryza sativa L.).

Plant responses to auxin and phosphate (Pi) starvation are closely linked. However, the underlying mechanisms connecting auxin to phosphate starvation (-Pi) responses are largely unclear. Here, we show that OsARF16, an auxin response factor, functions in both auxin and -Pi responses in rice (Oryza sativa L.). The knockout of OsARF16 led to primary roots (PR), lateral roots (LR) and root hair losing sensitivity to auxin and -Pi response. OsARF16 expression and OsARF16::GUS staining in PR and LR of rice Nipponbare (NIP) were induced by indole acetic acid and -Pi treatments. In -Pi conditions, the shoot biomass of osarf16 was slightly reduced, and neither root growth nor iron content was induced, indicating that the knockout of OsARF16 led to loss of response to Pi deficiency in rice. Six phosphate starvation-induced genes (PSIs) were less induced by -Pi in osarf16 and these trends were similar to a knockdown mutant of OsPHR2 or AtPHR1, which was a key regulator under -Pi. These data first reveal the biological function of OsARF16, provide novel evidence of a linkage between auxin and -Pi responses and facilitate the development of new strategies for the efficient utilization of Pi in rice.

Separation and purification of flavonoid from Taxus remainder extracts free of taxoids using polystyrene and polyamide resin.

An efficient separation process of flavonoid from Taxus wallichiana var. mairei remainder extracts free of taxoids was developed in this study. AB-8 macroporous resin and polyamide resin offered the fine adsorption capacity, and its adsorption rate at 30°C fitted well to the Langmuir and Freundich isotherms. Resin dynamic adsorption and desorption experiments were conducted to optimize the separation process of total flavonoids from T. wallichiana var. mairei remainder extracts free of taxoids. The optimum parameters for adsorption by AB-8 resin were as follows: (1) the concentration of flavonoids in a sample solution of 5.61 mg/mL with a processing volume of 2 bed volume (BV) (60 mL); (2) for desorption, ethanol-water (80:20, v/v), with 6 BV as an eluent at a flow rate of 2 BV/h. After a one-run treatment with AB-8 resin, the content of flavonoids was increased 5.10-fold from 4.05 to 20.65%. The optimum parameters for adsorption by polyamide resin were as follows: processing volume of 2 BV (30 mL); for desorption, ethanol-water (70:30, v/v), with 8 BV as an eluent at a flow rate of 2 BV/h. After one-run treatment with polyamide resin, the content of total flavonoids increased from 20.65 to 65.21%. The method will provide a potential approach for large-scale separation and purification of flavonoid for its wide pharmaceutical use.

Autotoxicity and allelopathy of 3,4-dihydroxyacetophenone isolated from Picea schrenkiana needles.

Bioassay-guided fractionation of the diethyl ether fraction of a water extract of Picea schrenkiana needles led to the isolation of the phenolic compound 3,4-dihydroxy- acetophenone (DHAP). The allelopathic effects of DHAP were evaluated under laboratory conditions on P. schrenkiana, rice (Oryza sativa L.), wheat (Triticum aestivum L.), radish (Raphanus sativus L.), lettuce (Latuca sativa L.), cucumber (Cucumis sativus L.) and mung bean (Phaseolus radiatus L.). DHAP significantly inhibited seed germination and seedling growth of P. schrenkiana at concentrations of 2.5 mM and 0.5 mM (p < 0.05). Soil analysis revealed that P. schrenkiana forest soils contained exceptionally high DHAP concentrations (mean = 0.51 ± 0.03 mg/g dry soil), sufficient to inhibit natural P. schrenkiana recruitment. DHAP also exhibited strong allelopathic potential. It significantly inhibited wheat and lettuce seed germination at concentrations of 1 mM and 0.5 mM (p < 0.05). The active compound also completely inhibited root growth of the six test species at high concentrations. Our results suggest a dual role of DHAP, both as an allelochemical and as an autotoxicant. The potential for a single plant needle-leached compound to influence both inter- and intra-specific interactions emphasized the complex effects that plant secondary metabolites might have on plant population and community structure.

Two Rubisco activase isoforms may play different roles in photosynthetic heat acclimation in the rice plant.

Studies on some plant species have shown that increasing the growth temperature gradually or pretreating with high temperature can lead to obvious photosynthetic acclimation to high temperature. To test whether this acclimation arises from heat adaptation of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activation mediated by Rubisco activase (RCA), gene expression of RCA large isoform (RCA(L)) and RCA small isoform (RCA(S)) in rice was determined using a 4-day heat stress treatment [40/30 degrees C (day/night)] followed by a 3-day recovery under control conditions [30/22 degrees C (day/night)]. The heat stress significantly induced the expression of RCA(L) as determined by both mRNA and protein levels. Correlative analysis indicated that RCA(S) protein content was extremely significantly related to Rubisco initial activity and net photosynthetic rate (Pn) under both heat stress and normal conditions. Immunoblot analysis of the Rubisco-RCA complex revealed that the ratio of RCA(L) to Rubisco increased markedly in heat-acclimated rice leaves. Furthermore, transgenic rice plants expressing enhanced amounts of RCA(L) exhibited higher thermotolerance in Pn and Rubisco initial activity and grew better at high temperature than wild-type (WT) plants and transgenic rice plants expressing enhanced amounts of RCA(S). Under normal conditions, the transgenic rice plants expressing enhanced amounts of RCA(S) showed higher Pn and produced more biomass than transgenic rice plants expressing enhanced amounts of RCA(L) and wild-type plants. Together, these suggest that the heat-induced RCA(L) may play an important role in photosynthetic acclimation to moderate heat stress in vivo, while RCA(S) plays a major role in maintaining Rubisco initial activity under normal conditions.

Phenolics and plant allelopathy.

Phenolic compounds arise from the shikimic and acetic acid (polyketide) metabolic pathways in plants. They are but one category of the many secondary metabolites implicated in plant allelopathy. Phenolic allelochemicals have been observed in both natural and managed ecosystems, where they cause a number of ecological and economic problems, such as declines in crop yield due to soil sickness, regeneration failure of natural forests, and replanting problems in orchards. Phenolic allelochemical structures and modes of action are diverse and may offer potential lead compounds for the development of future herbicides or pesticides. This article reviews allelopathic effects, analysis methods, and allelopathic mechanisms underlying the activity of plant phenolic compounds. Additionally, the currently debated topic in plant allelopathy of whether catechin and 8-hydroxyquinoline play an important role in Centaurea maculata and Centaurea diffusa invasion success is discussed. Overall, the main purpose of this review is to highlight the allelopacthic potential of phenolic compounds to provide us with methods to solve various ecology problems, especially in regard to the sustainable development of agriculture, forestry, nature resources and environment conservation.

[Effects of Broad bean wilt virus 2 isolate infection on photosynthetic activities and chloroplast ultrastructure in broad bean leaves].

The effects of Broad bean wilt virus 2 (BBWV 2) isolate B935 and PV131 infection on photosynthetic activities and chloroplast ultrastructure in broad bean (Vicia faba) were investigated. As the disease progressed, net photosynthetic rate (P(n)), stomatal conductance (G(s)) of leaves, the chlorophyll content and chlorophyll a/b ratio decreased while the intercellular CO(2) concentration (C(i)) of leaves rose in comparison with that of the healthy plants (Figs. 1, 2). After BBWV 2 infection, F(v)/F(m), F(v)'/F(m)', Phi(PSII) and q(P) values all became lower, but the NPQ values were higher, than the healthy control plants (Fig. 3). Electron microscopy showed that BBWV 2 infection disrupted the chloroplast structure. Most of the B935-infected chloroplasts showed inhibition of lamellar development or membrane vesiculation (Fig. 4B, C) and PV131-infected chloroplasts showed swollen or disintegrated membrane (Fig. 4D-F). Chloroplasts of PV131-infected leaves were different from those of normal ones to a higher degree than those of the B935-infected ones, which suggests that the disruption of chloroplast structure by virus invasion is responsible for the suppression of photosynthesis, which is more serious with PV131 than with B935.

Effects of climate warming on plant autotoxicity in forest evolution: a case simulation analysis for Picea schrenkiana regeneration.

In order to explore how plant autotoxicity changes with climate warming, the autotoxicity of P. schrenkiana needles' water extract, organic extract fractions, and key allelochemical DHAP was systemically investigated at the temperature rising 2 and 4°C based on the data-monitored soil temperature during the last decade in the stage of Schrenk spruce regeneration (seed germination and seedling growth). The results showed that the criterion day and night temperatures were 12°C and 4°C for seed germination, and 14°C and 6°C for seedling growth, respectively. In the presence of water extract, the temperature rise of 2°C significantly inhibited the germination vigor and rate of P. Schrenkiana seed, and a temperature rise of 4°C significantly increased the inhibition to the seedling growth (P < 0.05). Among the three organic fractions, the low-polar fraction showed to be more phytotoxic than the other two fractions, causing significant inhibitory effects on the seed germination and growth even at low concentration of 0.1 mg/mL, and the inhibition effect was enhanced as temperature increased. The temperature rise significantly enhanced the promotion effect of DHAP, while the inhibition effect of temperature rise became less important with increasing concentration of DHAP. This investigation revealed that autotoxicity of P. schrenkiana was affected by the climate warming. As expected, it provided an insight into the mechanism and effectiveness of allelopathy in bridging the causal relationship between forest evolution and climate warming.

Isolation and physiological characteristics of a premature senescence mutant in rice (Oryza sativa L.).

A rice pse(t) (premature senescence, tentatively) mutant line, was isolated from 4,500 independent T-DNA inserted transgenic lines. The symptoms of premature senescence appeared more severely than those of the control plants (Zhonghua 11, japonica) at the last development stage. To characterize the mutant and provide basic information on the candidate genes by mapping to a physical region of 220-kb, experiments were carried out in two phytotrons under controlled temperature of 24 degrees C and 28 degrees C, respectively. The content of chlorophyll, soluble protein and MDA (malondialdehyde), net photosynthesis, the antioxidant enzyme activities of SOD (superoxide dismuase) (EC 1.15.1.1) and POD (peroxidase) (EC 1.11.1.7) and the peptidase activities of leaves were measured from top to bottom according to the leaf positions at the flowering stage. Compared with the control plant, the mutant showed the following characteristics: (1) Higher net photosynthesis rate (P(n)) appeared in the 1st and 2nd leaves, contents of chlorophyll and soluble protein were also higher in the 1st leaf; (2) The activities of SOD, POD and peptidase were higher according to the leaf position from top to bottom; (3) The symptom of premature senescence was accelerated in the mutant at 28 degrees C treatment. The MDA content and the SOD and POD activities between the 24 degrees C and 28 degrees C treatment mutants were not significantly different. Content of chlorophyll and soluble protein of leaves mutant decreased rapidly at 28 degrees C treatment. The results show that pse(t) is sensitive to high temperature. The probable function of PSE(T) is discussed.

Rubisco Activase Is Also a Multiple Responder to Abiotic Stresses in Rice.

Ribulose-1,5-bisphosphate carboxylase/oxygenase activase (RCA) is a nuclear gene that encodes a chloroplast protein that plays an important role in photosynthesis. Some reports have indicated that it may play a role in acclimation to different abiotic stresses. In this paper, we analyzed the stress-responsive elements in the 2.0 kb 5'-upstream regions of the RCA gene promoter and the primary, secondary and tertiary structure of the protein. We identified some cis-elements of multiple stress-related components in the RCA promoter. Amino acid and evolution analyses showed that the RCA protein had conserved regions between different species; however, the size and type varied. The secondary structures, binding sites and tertiary structures of the RCA proteins were also different. This might reflect the differences in the transcription and translation levels of the two RCA isoforms during adaptation to different abiotic stresses. Although both the transcription and translation levels of RCA isoforms in the rice leaves increased under various stresses, the large isoform was increased more significantly in the chloroplast stroma and thylakoid. It can be concluded that RCA, especially RCAL, is also a multiple responder to abiotic stresses in rice, which provides new insights into RCA functions.

Characteristics of photosynthesis in rice plants transformed with an antisense Rubisco activase gene.

Transgenic rice plants with an antisense gene inserted via Agrobacterium tumefaciens were used to explore the impact of the reduction of Rubisco activase (RCA) on Rubisco and photosynthesis. In this study, transformants containing 15% to 35% wild type Rubisco activase were selected, which could survive in ambient CO2 concentration but grew slowly compared with wild type controls. Gas exchange measurements indicated that the rate of photosynthesis decreased significantly, while stomatal conductance and transpiration rate did not change; and that the intercellular CO2 concentration even increased. Rubisco determination showed that these plants had approximately twice as much Rubisco as the wild types, although they showed 70% lower rate of photosynthesis, which was likely an acclimation response to the reduction in Rubsico activase and/or the reduction in carbamylation.

[The immunogold localization of Rubisco and its activase in chloroplasts of barley and maize leaves].

Cellular localization of Rubisco and Rubisco activase (RCA) in the C(3) plant barley (Hordeum vulgare L.) and the C(4) plant maize (Zea mays L.) leaves was investigated using immunogold-labeling electron microscopy. The results showed that the leaf anatomy and the immunolocalization of the two photosynthetic enzymes were markedly different between barley and maize. In barley, the mesophyll chloroplasts had well-developed grana and their stroma was densely labeled with immunogold particles for Rubisco and for RCA. In maize, the mesophyll chloroplasts had well-developed grana but their stroma was scarcely labeled with immunogold particles, indicating a low Rubisco content. But the chloroplasts of the bundle sheath cells had only few rudimentary grana and their stroma was densely labeled with immunogold particles for Rubisco. A higher density of immunogold particles for RCA was located both in chloroplast stroma of the bundle sheath cells and the mesophyll cells. These results showed that the structure and function of chloroplasts are different between C(3) plants and C(4) plants.