Photosynthetic model for citrus cultivar Huangguogan

Grafting is an effective measure to improve the photosynthetic rate of citrus. The light responses of photosynthesis in leaves of two-year old grafted Huangguogan (citrus cultivar Huangguogan), Huanggougan / Trifoliate (HG/PT), Huanggougan / Tangerine (HG/CR), and Huanggougan / Ziyang Xiangcheng (HG/CJ) were studied using the LI-COR 6400 portable photosynthesis system. Light-response curves and photosynthetic parameters were analyzed and fitted using the rectangular hyperbola model (RHM), the exponential model (EM), the non rectangular hyperbola model (NRHM), and the modified rectangular hyperbola model (MRHM). The results showed that: (1) Grafting can change the photosynthetic characteristics of Huangguogan, and the value of photosynthesis rate of HG/CJ is the greatest; (2) The light-response curves of net photosynthetic rate (PN), the light compensation point (LCP), and the dark respiration rate (RD) were well fitted using the above four models. The modified rectangular hyperbola was the best model in fitting the data; the nonrectangular hyperbola model was the second, and the rectangular hyperbola model was the poorest one.

Influence of abiotic factors on CO2-gas exchange of Pinus pallasiana, Juniperus excelsa and Arbutus andrachne

The complex interactions among environmental factors as incident light, temperature and soil water content create the need for used physiology-based models which describe plants performance under current and changing climatic conditions. In the present work the net photosynthetic rate of Pinus pallasiana D. Don, Juniperus excelsa M.Bieb. and Arbutus andrachne L. was modeled as a function of light irradiance using the modified rectangular hyperbola model, which is capable of describing the photoinhibition by the non-rectangular hyperbola function. A comparative assessment of the adaptive response of the photosynthetic apparatus plants on the effect of abiotic factors and their strategies in maintaining an optimal water balance in accordance with environmental conditions has been performed. The parameters of light curves of photosynthesis under conditions of full sunlight, moderate shading and drought are determined. In relation to light, Pinus pallasiana is characterized by wider ecological amplitude compared to Juniperus excelsa and Arbutus andrachne. Inefficient use of low-intensity of photosynthetically active radiation by immature plants Pinus pallasiana and Juniperus excelsa indicates poor shade tolerance and inability to resume in shade-type forests. Due to the low plasticity to changes in the light regime, Arbutus andrachne L. may experience a significant lack of light in strong shading. Arbutus andrachne has the highest ability to actively rearrange water regime in accordance with its external moisture supply, which causes the highest drought resistance, and Juniperus excelsa has a slightly lower capacity. Tolerance to hydrothermal stress in Pinus pallasiana is significantly lower than in Arbutus andrachne and Juniperus excelsa.

Surfing the Hyperbola Equations of the Steady-State Farquhar–von Caemmerer–Berry C3 Leaf Photosynthesis Model: What Can a Theoretical Analysis of Their Oblique Asymptotes and Transition Points Tell Us?

The asymptotes and transition points of the net CO2 assimilation (A/Ci) rate curves of the steady-state Farquhar–von Caemmerer–Berry (FvCB) model for leaf photosynthesis of C3 plants are examined in a theoretical study, which begins from the exploration of the standard equations of hyperbolae after rotating the coordinate system. The analysis of the A/Ci quadratic equations of the three limitation states of the FvCB model—abbreviated as Ac, Aj and Ap—allows us to conclude that their oblique asymptotes have a common slope that depends only on the mesophyll conductance to CO2 diffusion (gm). The limiting values for the transition points between any two states of the three limitation states c, j and p do not depend on gm, and the results are therefore valid for rectangular and non-rectangular hyperbola equations of the FvCB model. The analysis of the variation of the slopes of the asymptotes with gm casts doubts about the fulfilment of the steady-state conditions, particularly, when the net CO2 assimilation rate is inhibited at high CO2 concentrations. The application of the theoretical analysis to extended steady-state FvCB models, where the hyperbola equations of Ac, Aj and Ap are modified to accommodate nitrogen assimilation and amino acids export via the photorespiratory pathway, is also discussed.

A Robust Method for Assaying the Immunoreactive Fraction in Nonequilibrium Systems

The immunoreactive fraction r provides important information on the functional purity of radiolabeled proteins. It is traditionally determined by saturating the radioimmunoconjugate with an increasing excess of antigen, followed by linear extrapolation to infinite antigen excess in a double inverse “Lindmo plot”. Although several reports have described shortcomings in the Lindmo plot, a systematic examination is lacking. Using an experimental and simulation-based approach, we compared—for accuracy, precision and robustness—the Lindmo plot with the “rectangular hyperbola” extrapolation method based on the Langmuir model. The differences between the theoretical and extrapolated r values demonstrate that nonequilibrium and antigen depletion are important sources of error. The mathematical distortions resulting from the linearization of the data in the Lindmo plot induce fragility towards stochastic errors and make it necessary to exclude low bound fractions. The rectangular hyperbola provides robust and precise r estimates from raw binding data, even for slow kinetics.

Experimental and simulated CO2 responses of photosynthesis in leaves of Hippophae rhamnoides L. under different soil water conditions

CO2 concentrations and soil moisture conditions seriously affect tree growth and physiological mechanisms. CO2 responses of photosynthesis are an important part of plant physiology and ecology research. This study investigated the photosynthetic CO2 responses in the leaves of two-year-old Hippophae rhamnoides L. under eight soil water conditions in a semi-arid loess hilly region, and discussed the quantitative relationship between CO2 responses and soil moisture. CO2 response curves and parameters were fitted using a rectangular hyperbola model, non-rectangular hyperbola model, exponential equation, and modified rectangular hyperbola model. Results revealed that the relative soil water content (RWC) required to maintain a high photosynthetic rate (Pn) and carboxylation efficiency (CE) ranged from 42.8% to 83.2%. When RWC fell outside these ranges, the photosynthetic capacity (Pnmax), CE, and CO2 saturation point (CSP) decreased. CO2 response curves and three parameters, CE, CO2 compensation point (Γ), and photorespiration rate (Rp), were well fitted by the four models when RWC was appropriate. When RWC exceeded the optimal range, only the modified rectangular hyperbola model fitted the CO2 response curves and photosynthetic parameters better.