Nitric Oxide Induced by Ammonium/Nitrate Ratio Ameliorates Low-Light Stress in Brassica pekinesis: Regulation of Photosynthesis and Root Architecture

Abstract

Low-light intensity affects plant growth and development and, finally, causes a decrease in yield and quality. There is a need for improved cropping strategies to solve the problem. We previously demonstrated that moderate ammonium:nitrate ratio (NH4+:NO3−) mitigated the adverse effect caused by low-light stress, although the mechanism behind this alleviation is unclear. The hypothesis that the synthesis of nitric oxide (NO) induced by moderate NH4+:NO3− (10:90) involved in regulating photosynthesis and root architecture of Brassica pekinesis subjected to low-light intensity was proposed. To prove the hypothesis, a number of hydroponic experiments were conducted. The results showed that in plants exposed to low-light intensity, the exogenous donors NO (SNP) and NH4+:NO3− (N, 10:90) treatments significantly increased leaf area, growth range, and root fresh weight compared with nitrate treatment. However, the application of hemoglobin (Hb, NO scavenger), N-nitro-l-arginine methyl ester (L-NAME, NOS inhibitor), and sodium azide (NaN3, NR inhibitor) in N solution remarkably decreased the leaf area, canopy spread, the biomass of shoot and root, the surface area, and volume and tips of the root. The application of N solution and exogenous SNP significantly enhanced Pn (Net photosynthetic rate) and rETR (relative electron transport rates) compared with solo nitrate. While all these effects of N and SNP on photosynthesis, such as Pn, Fv/Fm (maximum quantum yield of PSII), Y(II) (actual photosynthetic efficiency), qP (photochemical quenching), and rETR were reversed when the application of Hb, L-NAME, and NaN3 in N solution. The results also showed that the N and SNP treatments were more conducive to maintaining cell morphology, chloroplast structure, and a higher degree of grana stacking of low-light treated plants. Moreover, the application of N significantly increased the NOS and NR activities, and the NO levels in the leaves and roots of mini Chinese cabbage seedlings treated with N were significantly higher than those in nitrate-treated plants. In conclusion, the results of this study showed that NO synthesis induced by the appropriate ammonia–nitrate ratio (NH4+: NO3− = 10:90) was involved in the regulation of photosynthesis and root structure of Brassica pekinesis under low-light stress, effectively alleviating low-light stress and contributing to the growth of mini Chinese cabbage under low-light stress.

Nitric oxide signal is required for glutathione-induced enhancement of photosynthesis in salt-stressed Solanum lycopersicum L

“…To explore if external GSH influenced the photosynthetic capacity of tomato seedlings under salt stress through modulating endogenous NO levels, we treated tomato seedlings under salt stress with exogenous Hb, a NO scavenger. Numerous studies have previously demonstrated the ability of external Hb to efficiently decrease endogenous NO levels in plants ( Shao et al., 2010 ; Lee and Hwang, 2015 ; Bahmani et al., 2019 ; Hu et al., 2023 ). In this investigation, the application of Hb not only resulted in a further reduction in P n and endogenous NO levels under salt stress but also attenuated the beneficial impacts of GSH treatment, including the rise in P n and endogenous NO levels.…”

Effects of Different Forms and Proportions of Nitrogen on the Growth, Photosynthetic Characteristics, and Carbon and Nitrogen Metabolism in Tomato

“…Plant roots possess a multitude of basic self-adaptive capabilities, encompassing water and nutrient absorption, soil anchorage, and the establishment of symbiotic relationships with root-associated biological communities. Consequently, the diverse forms of nitrogen can exert significant impacts on plant root structures [ 29 , 30 ]. In this study, we observed that in comparison to the sole application of a single nitrogen source, utilizing a blend of 25%NN:75%UN (T12) or 75%NN:25%AN (T4) significantly enhanced the primary root length, root surface area, root volume, and the number of root tips in tomato plants, thereby promoting the development of an extensive root system.…”