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1.  Hydrogen peroxide functions as a secondary messenger for brassinosteroids-induced CO2 assimilation and carbohydrate metabolism in Cucumis sativus *  
Brassinosteroids (BRs) are potent regulators of photosynthesis and crop yield in agricultural crops; however, the mechanism by which BRs increase photosynthesis is not fully understood. Here, we show that foliar application of 24-epibrassinolide (EBR) resulted in increases in CO2 assimilation, hydrogen peroxide (H2O2) accumulation, and leaf area in cucumber. H2O2 treatment induced increases in CO2 assimilation whilst inhibition of the H2O2 accumulation by its generation inhibitor or scavenger completely abolished EBR-induced CO2 assimilation. Increases of light harvesting due to larger leaf areas in EBR- and H2O2-treated plants were accompanied by increases in the photochemical efficiency of photosystem II (ΦPSII) and photochemical quenching coefficient (q P). EBR and H2O2 both activated carboxylation efficiency of ribulose-1,5-bisphosphate oxygenase/carboxylase (Rubisco) from analysis of CO2 response curve and in vitro measurement of Rubisco activities. Moreover, EBR and H2O2 increased contents of total soluble sugar, sucrose, hexose, and starch, followed by enhanced activities of sugar metabolism such as sucrose phosphate synthase, sucrose synthase, and invertase. Interestingly, expression of transcripts of enzymes involved in starch and sugar utilization were inhibited by EBR and H2O2. However, the effects of EBR on carbohydrate metabolisms were reversed by the H2O2 generation inhibitor diphenyleneodonium (DPI) or scavenger dimethylthiourea (DMTU) pretreatment. All of these results indicate that H2O2 functions as a secondary messenger for EBR-induced CO2 assimilation and carbohydrate metabolism in cucumber plants. Our study confirms that H2O2 mediates the regulation of photosynthesis by BRs and suggests that EBR and H2O2 regulate Calvin cycle and sugar metabolism via redox signaling and thus increase the photosynthetic potential and yield of crops.
doi:10.1631/jzus.B1200130
PMCID: PMC3468824  PMID: 23024048
Metabolism; Photosynthesis; Reactive oxygen species; Rubisco; Sucrose
2.  Effects of nitrogen form on growth, CO2 assimilation, chlorophyll fluorescence, and photosynthetic electron allocation in cucumber and rice plants*  
Cucumber and rice plants with varying ammonium (NH4 +) sensitivities were used to examine the effects of different nitrogen (N) sources on gas exchange, chlorophyll (Chl) fluorescence quenching, and photosynthetic electron allocation. Compared to nitrate (NO3 −)-grown plants, cucumber plants grown under NH4 +-nutrition showed decreased plant growth, net photosynthetic rate, stomatal conductance, intercellular carbon dioxide (CO2) level, transpiration rate, maximum photochemical efficiency of photosystem II, and O2-independent alternative electron flux, and increased O2-dependent alternative electron flux. However, the N source had little effect on gas exchange, Chl a fluorescence parameters, and photosynthetic electron allocation in rice plants, except that NH4 +-grown plants had a higher O2-independent alternative electron flux than NO3 −-grown plants. NO3 − reduction activity was rarely detected in leaves of NH4 +-grown cucumber plants, but was high in NH4 +-grown rice plants. These results demonstrate that significant amounts of photosynthetic electron transport were coupled to NO3 − assimilation, an effect more significant in NO3 −-grown plants than in NH4 +-grown plants. Meanwhile, NH4 +-tolerant plants exhibited a higher demand for the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) for NO3 − reduction, regardless of the N form supplied, while NH4 +-sensitive plants had a high water-water cycle activity when NH4 + was supplied as the sole N source.
doi:10.1631/jzus.B1000059
PMCID: PMC3030957  PMID: 21265044
Nitrogen form; Photosynthetic electron allocation; Alternative electron flux; Nitrate reductase
3.  Survival of the biocontrol agents Brevibacillus brevis ZJY-1 and Bacillus subtilis ZJY-116 on the spikes of barley in the field*  
Fusarium head blight (FHB) caused by Fusarium graminearum is a devastating disease that results in extensive yield losses to wheat and barley. A green fluorescent protein (GFP) expressing plasmid pRP22-GFP was constructed for monitoring the colonization of two biocontrol agents, Brevibacillus brevis ZJY-1 and Bacillus subtilis ZJY-116, on the spikes of barley and their effect on suppression of FHB. Survival and colonization of the Brevibacillus brevis ZJY-1 and Bacillus subtilis ZJY-116 strains on spikes of barley were observed by tracking the bacterial transformants with GFP expression. Our field study revealed that plasmid pRP22-GFP was stably maintained in the bacterial strains without selective pressure. The retrieved GFP-tagged strains showed that the bacterial population fluctuation accorded with that of the rain events. Furthermore, both biocontrol strains gave significant protection against FHB on spikes of barley in fields. The greater suppression of barley FHB disease was resulted from the treatment of barley spikes with biocontrol agents before inoculation with F. graminearum.
doi:10.1631/jzus.2005.B0770
PMCID: PMC1389858  PMID: 16052710
GFP; Survival; Brevibacillus brevis and Bacillus subtilis; Spikes; Barley; Biocontrol

Results 1-3 (3)