ABSTRACT Photosynthesis is susceptible in response to nitrogen (N) deficiency. However, the acclimation of shade-tolerant and high-N sensitive species to N deficiency is unclear. Leaf morpho-physiological traits, photosynthetic performance related parameters were examined in a shade-tolerant and high-N sensitive species P. notoginseng grown under different N levels. Lower N content and Chl content were recorded in the N0-grown P. notoginseng. The maximum values of leaf morpho-physiological traits, photosynthetic rate, and photosynthetic N use efficiency (PNUE) were obtained in the N15-grown P. notoginseng. Coefficients for leaf N allocation into the carboxylation and light-harvesting system components in the N0-grown plants were significantly higher than others. N0 and N7.5 plants showed higher K phase. N addition decreased the absorption and capture of the light energy per unit area (ABS/RC and TRO/RC) and non-photochemical quenching (NPQ). Photochemical quenching (qP), electron transport rate (ETR), and effective quantum yield of photosystem II (ϕPSII) were reduced in the N0-grown plants. The reduction of light-harvesting and utilization capacity not only leads to a decrease in PNUE, but also induces the damage of PSII reaction center. Overall, the inhibition of leaf growth and photosynthetic capacity is an essential strategy for high-N sensitive and shade-tolerant plants in response to N deficiency.

https://www.tandfonline.com/doi/pdf/10.1080/17429145.2022.2141902?needAccess=true

Suppression of leaf growth and photosynthetic capacity as an acclimation strategy to nitrogen deficiency in a nitrogen-sensitive and shade-tolerant plant Panax notoginseng

Abbreviations : C c – CO 2 concentration inside the chloroplast; C i – intercellular CO 2 concentration; ETRI – electron transport rate of PSI; ETRII – electron transport rate of PSII; F 0 – minimum fluorescence; F 0 '– minimum fluorescence in the actinic light; F m – maximum fluorescence; F m ' – maximum fluorescence in the actinic light; F v /F m – maximum quantum efficiency of PSII photochemistry; g m – mesophyll conductance; g s – stomatal conductance; J a – alternative electron flux; J e(PCO) – electron flux to photorespiratory carbon oxidation; J e(PCR) – electron flux to photosynthetic carbon reduction; J max – light-saturated potential rate of electron transport; J t – electron transport rate; L b – limitation of biochemical capacity; L m – limitation of mesophyll diffusion; LMA – leaf mass per area; L s – limitation of stomatal diffusion; N area – nitrogen content per unit area; N mass – nitrogen content per unit mass; NO – nonregulated heat dissipation; NPQ – nonphotochemical quenching; P700 – primary electron donor of PSI; PIB – post-illumination burst; P m or P m ' – maximum P700 signal measured using saturation light pulse following short far-red pre-illumination in dark or light-adapted state; P N – net photosynthetic rate; PNUE – photosynthetic N-use efficiency; q P – PSII efficiency factor (the fraction of open centers); R d – mitochondrial CO 2 release in the dark; R L – light respiration rate; ROS – reactive oxygen species; V c,max – maximum carboxylation rate limited by Rubisco; Γ* – CO 2 -compensation point; Φ NA – oxidation status of PSI acceptor site; Φ ND – oxidation status of PSI donor site; Φ NO – quantum yield nonregulated heat dissipation; Φ NPQ – quantum yield of nonphotochemical quenching; Φ PSI – quantum yield of PSI photochemistry; Φ PSII – PSII operating efficiency (quantum yield of PSII photochemistry); Φ qP – quantum yield of open centers . Wheat yellow-green mutant Jimai5265yg has a more efficient photosynthetic system and higher productivity than its wild type under N-deficient conditions. To understand the relationship between photosynthetic properties and the grain yield, we conducted a field experiment under different N application levels. Compared to wild type, the Jimai5265yg flag leaves had higher mesophyll conductance, photosynthetic N-use efficiency, and photorespiration in the field without N application. Chlorophyll a fluorescence analysis showed that PSII was more sensitive to photoinhibition due to lower nonphotochemical quenching (NPQ) and higher nonregulated heat dissipation. In N-deficient condition, the PSI acceptor side of Jimai5265yg was less reduced. We proposed that the photoinhibited PSII protected PSI from over-reduction through downregulation of electron transport. PCA analysis also indicated that PSI photoprotection and electron transport regulation were closely associated with grain yield. Our results suggested that the photoprotection mechanism of PSI independent of NPQ was critical for crop productivity.

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Improvement in the photoprotective capability benefits the productivity of a yellow-green wheat mutant in N-deficient conditions

Nitrogen (N) is a primary factor limiting leaf photosynthesis. However, the mechanism of N-stress-driven photoinhibition of the photosystem I (PSI) and photosystem II (PSII) is still unclear in the N-sensitive species such as Panax notoginseng, and thus the role of electron transport in PSII and PSI photoinhibition needs to be further understood. We comparatively analyzed photosystem activity, photosynthetic rate, excitation energy distribution, electron transport, OJIP kinetic curve, P700 dark reduction, and antioxidant enzyme activities in low N (LN), moderate N (MN), and high N (HN) leaves treated with linear electron flow (LEF) inhibitor [3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU)] and cyclic electron flow (CEF) inhibitor (methyl viologen, MV). The results showed that the increased application of N fertilizer significantly enhance leaf N contents and specific leaf N (SLN). Net photosynthetic rate (Pn) was lower in HN and LN plants than in MN ones. Maximum photochemistry efficiency of PSII (Fv/Fm), maximum photo-oxidation P700+ (Pm), electron transport rate of PSI (ETRI), electron transport rate of PSII (ETRII), and plastoquinone (PQ) pool size were lower in the LN plants. More importantly, K phase and CEF were higher in the LN plants. Additionally, there was not a significant difference in the activity of antioxidant enzyme between the MV- and H2O-treated plants. The results obtained suggest that the lower LEF leads to the hindrance of the formation of ΔpH and ATP in LN plants, thereby damaging the donor side of the PSII oxygen-evolving complex (OEC). The over-reduction of PSI acceptor side is the main cause of PSI photoinhibition under LN condition. Higher CEF and antioxidant enzyme activity not only protected PSI from photodamage but also slowed down the damage rate of PSII in P. notoginseng grown under LN.

https://www.frontiersin.org/articles/10.3389/fpls.2022.796931/pdf

Responses of Linear and Cyclic Electron Flow to Nitrogen Stress in an N-Sensitive Species Panax notoginseng

In natural ecosystems, plants compete for space, nutrients and light. The optically dense canopies limit the penetration of photosynthetically active radiation and light often becomes a growth-limiting factor for the understory. The reduced availability of photons in the lower leaf layers is also a major constraint for yield potential in canopies of crop monocultures. Traditionally, crop breeding has selected traits related to plant architecture and nutrient assimilation rather than light use efficiency. Leaf optical density is primarily determined by tissue morphology and by the foliar concentration of photosynthetic pigments (chlorophylls and carotenoids). Most pigment molecules are bound to light-harvesting antenna proteins in the chloroplast thylakoid membranes, where they serve photon capture and excitation energy transfer toward reaction centers of photosystems. Engineering the abundance and composition of antenna proteins has been suggested as a strategy to improve light distribution within canopies and reduce the gap between theoretical and field productivity. Since the assembly of the photosynthetic antennas relies on several coordinated biological processes, many genetic targets are available for modulating cellular chlorophyll levels. In this review, we outline the rationale behind the advantages of developing pale green phenotypes and describe possible approaches toward engineering light-harvesting systems.

A paler shade of green: engineering cellular chlorophyll content to enhance photosynthesis in crowded environments.

Mesophyll conductance, photoprotective process and optimal N partitioning are essential to the maintenance of photosynthesis at N deficient condition in a wheat yellow-green mutant (Triticum aestivum L.)

Junjie Li

Papers

Mesophyll conductance, photoprotective process and optimal N partitioning are essential to the maintenance of photosynthesis at N deficient condition in a wheat yellow-green mutant (Triticum aestivum L.)