Determinants of photochemical characteristics of the photosynthetic electron transport chain of maize

Abstract

Introduction: The photosynthetic electron transport chain (ETC) is the bridge that links energy harvesting during the photophysical reactions at one end and energy consumption during the biochemical reactions at the other. Its functioning is thus fundamental for the proper balance between energy supply and demand in photosynthesis. Currently, there is a lack of understanding regarding how the structural properties of the ETC are affected by nutrient availability and plant developmental stages, which is a major roadblock to comprehensive modeling of photosynthesis.

Methods: Redox parameters reflect the structural controls of ETC on the photochemical reactions and electron transport. We conducted joint measurements of chlorophyll fluorescence (ChlF) and gas exchange under systematically varying environmental conditions and growth stages of maize and sampled foliar nutrient contents. We utilized the recently developed steady-state photochemical model to infer redox parameters of electron transport from these measurements.

Results and discussion: We found that the inferred values of these photochemical redox parameters varied with leaf macronutrient content. These variations may be caused either directly by these nutrients being components of protein complexes on the ETC or indirectly by their impacts on the structural integrity of the thylakoid and feedback from the biochemical reactions. Also, the redox parameters varied with plant morphology and developmental stage, reflecting seasonal changes in the structural properties of the ETC. Our findings will facilitate the parameterization and simulation of complete models of photosynthesis.

Keywords: leaf characteristics; maize; photosynthesis; photosynthetic electron transport; plant growth stages; redox parameters.

Figure 1

Examples demonstrating the performance of the steady-state photochemical model for predicting the linear electron transport rate (J_PSII ) as a function of the fraction of open PSII reaction centers (q_l ) for top canopy leaves at different growth stages. Inset: Comparison of measured vs. modeled J_PSII . (A): Jointing (17 July); (B): Flowering (29 July); (C): Filling (20 August); (D): Maturity (7 September).

Figure 2

Examples demonstrating the performance of the steady-state photochemical model for predicting the linear electron transport rate (J_PSII ) as a function of the fraction of open PSII reaction centers ( $q_l$ ) at the flowering stage. Inset: Comparison of measured vs. modeled J_PSII . (A): Bottom; (B): Lower middle; (C): Upper middle; (D): Top.

Figure 3

The relationships between the redox parameter U and leaf characteristics during summer maize growth. (A): U-leaf thickness; (B): U-Ca; (C): U-N; (D): U-K.

Figure 4

Loading plot of partial least squares regression for redox parameters and leaf characteristics. (A): U; (B): R ₂; (C): c_s .

Figure 5

Histogram of regression coefficients of leaf characteristics affecting redox parameters. (A): U; (B): R ₂; (C): c_s . S: Specific leaf weight; L: Leaf thickness. ∗ Significant impact at p< 0.05.

Figure 6

The relationships between redox parameter R₁ and leaf K content during summer maize growth.

Figure 7

The relationships between redox parameter R₂ and leaf characteristics during summer maize growth. (A): R₂ -specific leaf weight; (B): R₂ -leaf thickness; (C): R₂ -N; (D): R₂ -P; (E): R₂ -Ca.

Figure 8

The relationships between redox parameter q_r and leaf characteristics during summer maize growth. (A): q_r -specific leaf weight; (B): q_r -N; (C): q_r -P.

Figure 9

The relationships between redox parameter a_q and specific leaf weight during summer maize growth.

Figure 10

The relationships between redox parameter E_T and leaf P content during summer maize growth.

Figure 11

The relationships between redox parameter b_s and leaf P content during summer maize growth.

Figure 12

The relationships between redox parameter c_s and leaf characteristics during summer maize growth. (A): c_s - leaf thickness; (B): c_s -Ca.

Figure 13

The relationships among redox parameters during summer maize growth. (A): a_q -U; (B): a_q -R ₂; (C): a_q -b_s ; (D): a_q -c_s ; (E): b_s -q_r ; (F): b_s -c_s ; (G): E_T -R₁ ; (H): U-R₂ .

Figure 14

The temporal variations of redox parameters during summer maize growth. (A): U; (B): R₁ ; (C): R₂ ; (D): q_r ; (E): E_T ; (F): a_q ; (G): b_s ; (H): c_s .

Figure 15

The temporal variations of leaf characteristics during summer maize growth. (A): specific leaf weight; (B): leaf thickness; (C): N; (D): P; (E): Ca; (F): K.