Photosynthesis, light energy partitioning, and photoprotection in the shade-demanding species Panax notoginseng under high and low level of growth irradiance

Abstract

Partitioning of light energy into several pathways and its relation to photosynthesis were examined in a shade-demanding species Panax notoginseng (Burkill) F.H.Chen ex C.Y.Wu & K.M.Feng grown along a light gradient. In fully light-induced leaves, the actual efficiency of PSII photochemistry (ΔF/Fmʹ), electron transport rate (ETR), non-photochemical quenching (NPQ) and photochemical quenching (qP) were lower in low-light-grown plants; this was also the case in fully dark-adapted leaves under a simulated sunfleck. In response to varied light intensity, high-light-grown plants showed greater quantum yields of light-dependent non-photochemical quenching (ΦNPQ) and PSII photochemistry (ΦPSII) and smaller quantum yields of fluorescence and constitutive thermal dissipation (Φf,d). Under the simulated sunfleck, high-light-grown plants showed greater ΦPSII and smaller Φf,d. There were positive relationships between net photosynthesis (Anet) and ΦNPQ+f,d and negative relationships between Anet and ΦPSII in fully light-induced leaves; negative correlations of Anet with ΦNPQ+f,d and positive correlations of Anet with ΦPSII were observed in fully dark-adapted leaves. In addition, more nitrogen was partitioned to light-harvesting components in low-light-grown plants, whereas leaf morphology and anatomy facilitate reducing light capture in high-light-grown plants. The pool of xanthophyll pigments and the de-epoxidation state was greater in high-light-grown plants. Antioxidant defence was elevated by increased growth irradiance. Overall, the evidences from P. notoginseng suggest that in high-light-grown shade-demanding plants irradiated by high light more electrons were consumed by non-net carboxylative processes that activate the component of NPQ, that low-light-grown plants correspondingly protect the photosynthetic apparatus against photodamage by reducing the efficiency of PSII photochemistry under high light illumination, and that during the photosynthetic induction, the ΔpH-dependent (qE) component of NPQ might dominate photoprotection, but the NPQ also depresses the enhancement of photosynthesis via competition for light energy.

Hydrogen sulfide regulates photosynthesis of tall fescue under low-light stress

“…Previous studies have reported morphological changes of plants in response to LL stress, such as thinner leaves (Fu et al 2014) and lower biomass (Gustafsson and Boström 2013). Another study reported that LL could decrease the biosynthesis of photosynthetic pigments (Zhang et al 2018) and reduce the chlorophyll (Chl) fluorescence parameters (Chen et al 2016). Under LL stress conditions, enzymes components of Calvin-Benson cycle, particularly Rubisco, exhibited an apparent tendency of diminishing activities leading to lower CO2 assimilation rate, eventually resulting in prominent depression of plant growth (Yang et al 2018).…”

Positive Selection Driving Cytoplasmic Genome Evolution of the Medicinally Important Ginseng Plant Genus Panax

“…In this study, we sequenced the chloroplast and mitochondrial genomes of three diploid and three tetraploid Panax species along with five varieties of the P. bipinnatifidus species complex. All these Panax species are shade-demanding perennial herbs and inhabit the cool shaded habitats (Liu and Xiao, 1992 ; Chen et al, 2014 , 2016 ). In the case of the agro-economically important species P. ginseng , while cultivated ginseng harbored similar level of nucleotide diversity compared to the wild ginseng in the nuclear genome, obviously lower sequence polymorphisms were found in the chloroplast genome of cultivated ginseng (Li et al, 2015 , 2017 ).…”

Photosynthetic induction is slower in young leaves than in mature leaves in a tropical invader, Chromolaena odorata

“…Previous studies have shown that there is a time lag between onset of a sunfleck to achievement of PNmax (Allen and Pearcy 2000, Bai et al 2008, Martins et al 2013, Chen et al 2016. This time lag may lead to excess excited electrons, at least temporarily, during photosynthetic induction (Watling et al 1997, Tausz et al 2005.…”

“…Plant leaves have various photoprotective mechanisms to cope with excess light energy from strong sunflecks, such as avoiding exposure to light, nonphotochemical quenching (NPQ), and photorespiratory pathways (Watling et al 1997, Tausz et al 2005, Huang et al 2015, Chen et al 2016, Yamori 2016. The rapid activation of NPQ largely dissipates the excess light energy absorbed during sunflecks (Tausz et al 2005, Watling et al 1997.…”