Photosynthesis in newly-developed leaves of heat-tolerant wheat acclimates to long-term nocturnal warming

Description

Other

MS Excel and R/R Studio.

Funding provided by: ARC Centre of Excellence in Plant Energy Biology
Crossref Funder Registry ID: https://ror.org/01a1mq059
Award Number: CE140100008

Funding provided by: Grains Research and Development Corporation
Crossref Funder Registry ID: https://ror.org/02xwr1996
Award Number: US1904-003RTX – 9177346

Funding provided by: Grains Research and Development Corporation
Crossref Funder Registry ID: https://ror.org/02xwr1996
Award Number: US00080

Funding provided by: University of Greenwich
Crossref Funder Registry ID: https://ror.org/00bmj0a71
Award Number:

Methods

T_crit: leaf discs were excised during the day from the middle section of detached dark-adapted and were exposed to a temperature ramp at a constant rate of 1°C min⁻¹ from 20 to 65 °C with simultaneous continuous measurement of F0 taken. T_crit was calculated as the intersection point of two regression lines extrapolated from the flat and steep portion of the F0–temperature response curve.

Leaf gas exchange and An-Ci curves: Five LI-COR portable photosynthesis systems (LI-6400XT, LI-COR Inc., Lincoln, NE, USA) were used for gas exchange measurements. The LI-COR units were fitted with 6 cm2 leaf chambers with red-blue light source (6400-18 RGB Light Source, LI-COR). Leaves were exposed to saturating irradiance of 1500 μmol photons m⁻² s⁻¹ within the LI-COR leaf chamber, with both the LI-COR leaf chamber/block, and the whole plants were placed within the temperature-controlled cabinet. The LI-COR leaf chamber was initially set to 20°C, reference line atmospheric [CO₂] of 400 ppm, a flow rate of 500 μmol s⁻¹, and relative humidity maintained between 40 and 75%. photosynthetic [CO₂] response curves (A:C_i curves) were generated, at constant irradiance of 1500 μmol photons m⁻² s⁻¹, by varying the [CO₂] inside the LI-COR leaf chambers as follows: 30, 50, 100, 150, 250, 400, 400, 600, 800, 1000, 1200, 1400 and 400 μmol mol⁻¹. The A:C_i curves were repeated with the leaves exposed to measurement temperatures of 25, 30, 35, 40 and 50 °C.

Modelling photosynthetic capacity: Model parameters for each growth and measurement temperature were estimated following the FvCB model and using the Plantecowrap package (Stinziano et al., 2018) in the R computing environment (R-Development-Core-Team, 2021). 

The kinetic parameters used in modelling photosynthetic capacity for wheat were: mesophyll conductance at 25°C (g_m = 5.5 mmol m⁻² s⁻¹ Pa^-1); activation energy of mesophyll conductance (E_a = 47.65 kJ mol^-1); apparent Michaelis-Menten constant for Rubisco carboxylation in 21% oxygen (K_air = 772 µmol mol^-1); activation energy of K_c (93.72 kJ mol^–1); photorespiratory CO2 compensation point or Gamma star at 25°C (Γ* = 37.74 µmol mol^–1, equivalent to µbar bar^–1); and Gamma star activation energy (24.42 kJ mol^–1). The temperature response of V_cmax, J₁₅₀₀ and TPU were modelled using non-linear least squares fit of the Arrhenius temperature response function accounting for deactivation (Medlyn et al., 2002, Kattge and Knorr, 2007). The deactivation energy (E_d) was assumed to be 200 kJ mol^–1, the activation energy (E_a) and entropy factor (DS) were estimated from iterative fits of the model.

Metabolites: Metabolite extraction was conducted using a gas chromatography coupled to mass spectrometry (GC-MS) procedure.