Short-term elevated temperature and CO2 promote photosynthetic induction in the C3 plant Glycine max, but not in the C4 plant Amaranthus tricolor.

The continuous increases of atmospheric temperature and CO2 concentration will impact global photosynthesis. However, there are few studies considering the interaction of elevated temperature (eT) and elevated CO2 (eCO2 ) on dynamic photosynthesis, particularly for C4 species. We examine dynamic photosynthesis under four different temperature and [CO2 ] treatments: (1) 400ppm×28°C (CT); (2) 400ppm×33°C (CT+); (3) 800ppm×28°C (C+T); and (4) 800ppm×33°C (C+T+). In Glycine max L., the time required to reach 50% (T 50%A ) and 90% (T 90%A ) of full photosynthetic induction was smaller under the CT+, C+T, and C+T+ treatments than those under the CT treatment. In Amaranthus tricolor L., however, neither T 50%A nor T 90%A was not significantly affected by eT or eCO2 . In comparison with the CT treatment, the achieved carbon gain was increased by 58.3% (CT+), 112% (C+T), and 136.6% (C+T+) in G. max and was increased by 17.1% (CT+), 2.6% (C+T) and 56.9% (C+T+) in A. tricolor . The increases of achieved carbon gain in G. max were attributable to both improved photosynthetic induction efficiency (IE) and enhanced steady-state photosynthesis, whereas those in A. tricolor were attributable to enhanced steady-state photosynthesis.

Contributions of species shade tolerance and individual light environment to photosynthetic induction in tropical tree seedlings.

It has long been debated whether tree leaves from shady environments exhibit higher photosynthetic induction efficiency (IE) than those from sunny environments and how the shade tolerance of tree species and the light environment of leaves contribute to the dynamics of photosynthesis. To address these questions, we investigated leaf photosynthetic responses to simulated changes of light intensity in seedlings of six tree species with differential shade tolerance. The seedlings were growing under different light environments in a lowland tropical forest. We proposed an index of relative shade tolerance (RST) to assess species-specific capacity to tolerate shade, and we quantified the light environment of individual leaves by the index of daily light integral (DLI), the averaged daily total light intensity. We obtained the following results. Photosynthetic IE, which is the ratio of the achieved carbon gain to the expected carbon gain, was significantly higher for species with a higher RST than for that with a lower RST. The impacts of light environment on the IE of individual leaves within the same species varied largely among different species. In the three species with relatively low RST, the IE of individual leaves decreased at higher DLIs when DLI < 10 mol m-2 d-1. Seedlings with high initial stomatal conductance before induction (gs50) possessed a higher IE than those with low gs50 from the same species. A trade-off existed between IE and steady-state photosynthetic rates. These results suggest a complex interaction between the shade tolerance of species and the light environments of individual leaves for photosynthetic induction and provide new insights into the adaptation strategy for understory seedlings under sunfleck environments.

Elevated CO2 Enhances Dynamic Photosynthesis in Rice and Wheat.

Crops developed under elevated carbon dioxide (eCO2) exhibit enhanced leaf photosynthesis under steady states. However, little is known about the effect of eCO2 on dynamic photosynthesis and the relative contribution of the short-term (substrate) and long-term (acclimation) effects of eCO2. We grew an Oryza sativa japonica cultivar and a Triticum aestivum cultivar under 400 µmol CO2 mol-1 air (ambient, A) and 600 µmol CO2 mol-1 air (elevated, E). Regardless of growth [CO2], the photosynthetic responses to the sudden increase and decrease in light intensity were characterized under 400 (a) or 600 µmol CO2 mol-1 air (e). The Aa, Ae, Ea, and Ee treatments were employed to quantify the acclimation effect (Ae vs. Ee and Aa vs. Ea) and substrate effect (Aa vs. Ae and Ea vs. Ee). In comparison with the Aa treatment, both the steady-state photosynthetic rate (P N) and induction state (IS) were higher under the Ae and Ee treatments but lower under the Ea treatment in both species. However, IS reached at the 60 sec after the increase in light intensity, the time required for photosynthetic induction, and induction efficiency under Ae and Ee treatment did not differ significantly from those under Aa treatment. The substrate effect increased the accumulative carbon gain (ACG) during photosynthetic induction by 45.5% in rice and by 39.3% in wheat, whereas the acclimation effect decreased the ACG by 18.3% in rice but increased it by 7.5% in wheat. Thus, eCO2, either during growth or at measurement, enhances the dynamic photosynthetic carbon gain in both crop species. This indicates that photosynthetic carbon loss due to an induction limitation may be reduced in the future, under a high-CO2 world.

Concurrent Increases in Leaf Temperature With Light Accelerate Photosynthetic Induction in Tropical Tree Seedlings.

Leaf temperature changes with incident light intensity, but it is unclear how the concurrent changes influence leaf photosynthesis. We examined the time courses of CO2 gas exchanges and chlorophyll fluorescence of seedling leaves in four tropical tree species in response to lightflecks under three different temperature conditions. The three conditions were two constant temperatures at 30°C (T 30) and 40°C (T 40), and a simulated gradually changing temperature from 30 to 40°C (T dyn). The time required to reach 50% of the full photosynthetic induction under T 40 was similar to, or even larger than, that under T 30. However, the induction of assimilation rate (A) and electron transport rate of photosystem II (ETR II) and Rubisco activation process were generally accelerated under T dyn compared to those at either T 30 or T 40. The acceleration in photosynthetic induction under T dyn was significantly greater in the shade-tolerant species than in the shade-intolerant species. A modified photosynthetic limitation analysis indicated that the acceleration was likely to be mainly due to ETR II at the early stage of photosynthetic induction. The study suggests that concurrent increases in leaf temperature with light may increase leaf carbon gain under highly fluctuating light in tropical tree seedlings, particularly in shade-tolerant species.

Paired design study by real-time PCR: miR-378* and miR-145 are potent early diagnostic biomarkers of human colorectal cancer.

BACKGROUND: Although microRNAs offer great potential as cancer biomarkers, effective clinical dignostics and tumor maker have not been verified to diagnose with colorectal cancer (CRC). The purpose of our study is to systematically assess the expression of miRNAs in matched cancer and normal tissue samples to identify promising diagnostic microRNA (miRNA) biomarkers for CRC. METHODS: In our study, we examined by Real-Time PCR the expression levels of 96 mature miRNA in 32 CRC patients with differently expressed tumors versus normal colon tissues. Using enter and stepwise variable selection methods separately, conditional logistic regression was conducted to identify miRNAs associated with CRC. The classification performance of these indicators was assessed under the Fisher discriminant analysis. Receiver operating characteristic curve analyses were applied to obtain diagnostic utility of the differentially expressed miRNAs. RESULTS: In this study, we confirmed 11 overexpressed miRNAs with no less than twofold difference, and 85 downexpressed miRNAs with up to 0.5-fold difference in CRC from 96 aberrantly expressed miRNAs being identified by real-time PCR. Conditional logistic regression results confirmed that miRNA-378 and miRNA-145 expression profile was statistically significant. The error diagnosis rate of these two miRNAs are 0.194 and 0.113, separeately, showing by discriminant analysis. CONCLUSIONS: MiRNA-145 and miRNA-378* are potential biomarkers for early detection of CRC, which may help in diagnosing CRC in early period.