Quantifying Light Response of Leaf-Scale Water-Use Efficiency and Its Interrelationships With Photosynthesis and Stomatal Conductance in C3 and C4 Species.

Light intensity (I) is the most dynamic and significant environmental variable affecting photosynthesis (A n), stomatal conductance (g s), transpiration (T r), and water-use efficiency (WUE). Currently, studies characterizing leaf-scale WUE-I responses are rare and key questions have not been answered. In particular, (1) What shape does the response function take? (2) Are there maximum intrinsic (WUEi; WUEi-max) and instantaneous WUE (WUEinst; WUEinst-max) at the corresponding saturation irradiances (I i-sat and I inst-sat)? This study developed WUEi-I and WUEinst-I models sharing the same non-asymptotic function with previously published A n-I and g s-I models. Observation-modeling intercomparison was conducted for field-grown plants of soybean (C3) and grain amaranth (C4) to assess the robustness of our models versus the non-rectangular hyperbola models (NH models). Both types of models can reproduce WUE-I curves well over light-limited range. However, at light-saturated range, NH models overestimated WUEi-max and WUEinst-max and cannot return I i-sat and I inst-sat due to its asymptotic function. Moreover, NH models cannot describe the down-regulation of WUE induced by high light, on which our models described well. The results showed that WUEi and WUEinst increased rapidly within low range of I, driven by uncoupled photosynthesis and stomatal responsiveness. Initial response rapidity of WUEi was higher than WUEinst because the greatest increase of A n and T r occurred at low g s. C4 species showed higher WUEi-max and WUEinst-max than C3 species-at similar I i-sat and I inst-sat. Our intercomparison highlighted larger discrepancy between WUEi-I and WUEinst-I responses in C3 than C4 species, quantitatively characterizing an important advantage of C4 photosynthetic pathway-higher A n gain but lower T r cost per unit of g s change. Our models can accurately return the wealth of key quantities defining species-specific WUE-I responses-besides A n-I and g s-I responses. The key advantage is its robustness in characterizing these entangled responses over a wide I range from light-limited to light-inhibitory light intensities, through adopting the same analytical framework and the explicit and consistent definitions on these responses. Our models are of significance for physiologists and modelers-and also for breeders screening for genotypes concurrently achieving maximized photosynthesis and optimized WUE.

[Photosynthetic physio-ecological characteristics in soybean leaves at different CO2 concentrations.] / 不同CO2æµ“åº¦ä¸‹å¤§è±†å¶ç‰‡çš„å ‰åˆç”Ÿç†ç”Ÿæ€ç‰¹æ€§.

The availability of CO2, a substrate for photosynthesis, affects the photosynthesis process and photosynthate production. Using the Li-6400-40B, we measured the photosynthetic electron transport rate and the photosynthetic light-response curves of soybean (Glycine max) leaves at different CO2 concentrations (300, 400, 500 and 600 µmol·mol-1). By fitting these parameters with a mechanistic model characterizing the light response of photosynthesis, we obtained aseries of photosynthetic parameters, eco-physiological parameters, as well as the physical parameters of photosynthetic pigments. The results showed that the electronic use efficiency, maximum electron transport rate, and maximum net photosynthetic rate increased with the increase of CO2 concentration. The light compensation point and dark respiration rate decreased with the increase of CO2 concentration. In addition, the light-use efficiency and intrinsic (instantaneous) water-use efficiency increased with the increase of CO2 concentration, and their values differed significantly among different CO2 concentrations. There was no significant difference on the maximum carboxylation efficiency among different CO2 concentrations. Those results suggested that CO2 concentration could affect the primary light reaction of photosynthesis in soybean leaves, and thus higher CO2 concentration could decrease the minimum average lifespan of excitons at the lowest excited state, which would enhance the velocity of light energy transport and the use efficiency of photosynthetic electron flow.

[Distribution and SNPs of the rice CMS-related gene in AA-genome of Oryza species].

The moiety of a chimeric gene in mitochondrial genome, orf79 and orfH79, probably related to BT-type and HL-type CMS of rice respectively, has 98% homology and only 4 nucleotide variation in DNA sequence. Of which, the former comes from Oryza sativa L., and the latter originates from Oryza rufipogon Griff. That means the orf79/ orfH79 may widely exist in Oryza species with AA genome. In order to investigate the distribution and difference of orf79/ orfH79 in the Oryza species, 190 cultivated rice accessions (including O. sativa and O. glaberrima) and 104 accessions of AA-genome Oryza wild species (including O. nivara, O. rufipogon, O. barthii, O. longistaminlata, O. glumaepatula, and O. meridion-alis) were detected with PCR amplification. Of which, 31 accessions mainly from AA-genome Oryza species were found to share the special amplified fragment with the control of Yuetai A and Shijin A. The special amplified fragments were all recovered and sequenced. Phylogenetic analysis based on DNA sequences showed that the 31 accessions were fallen into two groups, correspondingly representing HL-type and BT-type cytoplasm group. Further, the results revealed that the HL-type cytoplasm distributed mainly in annual O. nivara, and the BT-type cytoplasm centered in cultivated varieties or perennial O. rufipogon.

[Genetic variation of main restorer lines of hybrid rice in China was revealed by microsatellite markers].

A total of thirty-five restorer lines of hybrid rice (Oryza sativa L.) were analyzed by twenty-five SSR (simple sequence repeats) primer pairs, which disperse on 12 chromosomes in rice. Those primers detected 65 alleles among 35 restorer lines of hybrid rice. Per primer pair detected 2.6 alleles on the average. PIC (polymorphism index content) values ranged from 0.206 to 0.682. PIC value is 0.414 on the average. The result from cluster analysis shows that hybrid rice restorer lines have abundant resource in China, but the genetic diversity is small and the genetic background is vulnerable among them. The utilization of rice heterosis was limited seriously.

[Genetic analysis and identification of three groups three-line hybrid rice and their parents by RAPD markers].

A total of 248 arbitrary 10-mer oligonucleotide primers were screened using RAPD (random amplified polymorphic DNA) techniques with the genome DNA of three groups of three-line hybrid rice and their parents. Thirteen primers produced 43 polymorphism fragments. Six primers of them produced 20 obviously repeatable polymorphic markers among rice lines tested. Using this RAPD markers,the hybrid rice combinations (sterile-line, maintainer-line, restorer-line and F1) can be effectively identified, and the genetic relationship among them can be shown.