We investigated the light reactions, CO 2 assimilation, but also the chloroplast ultrastructure in the upper three functional leaves (flag, 2 nd , and 3 rd leaves) of the Chinese super-high-yield hybrid rice (Oryza sativa L.) Liangyoupeijiu (LYPJ) with ultraviolet-B (UV-B) treatment during reproductive development. Photosynthetic parameters showed that the upper 3 functional leaves of LYPJ entered into senescence approximately 15 days after flag leaf emergence (DAE). Leaves in UV-B treatment exhibited greater efficiency in absorbing and utilizing light energy of photosystem II (PSII), characterized by higher chlorophyll (Chl) content and the whole chain electron transport rate (ETR). However, UV-B radiation reduced activities of Ca 2+ -ATPase and photophosphorylation. The significantly decreased activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was greatly associated with the decline in photosynthetic efficiency. The net photosynthetic rate (P N ) and stomatal conductance (g s ) suffered strong reductions before 25 DAE, and afterwards showed no significant difference between control and treatment. UV-B treatment delayed chloroplasts development of flag leaves. Chloroplast membranes later swelled and disintegrated, and more stromal thylakoids were parallel to each other and were arranged in neat rows, which might be responsible for better performance of the primary light reaction. It is likely that accumulation of starch and an increase in the number of lipid droplet and translucent plastoglobuli were results of an inhibition of carbohydrate transport. Our results suggest that long-term exposure to enhanced UV-B radiation was unlikely to have detrimental effects on the absorption flux of photons and the transport of electrons, but it resulted in the decrease of photophosphorylation and Rubisco activation of LYPJ. The extent of the damage to the chloroplast ultrastructure was consistent with the degree of the inhibition of photosynthesis.

Biomanufacturing of ethylene is particularly important for modern society. Cyanobacterial cells are able to photosynthesize various valuable chemicals. A promising platform for next‐generation biomanufacturing, the semiconductor‐cyanobacterial hybrid systems are capable of enhancing the solar‐to‐chemical conversion efficiency. Herein, the native ethylene‐producing capability of a filamentous cyanobacterium Nostoc sphaeroides is confirmed experimentally. The self‐assembly characteristic of N. sphaeroides is exploited to facilitate its interaction with InP nanomaterial, and the resulting biohybrid system gave rise to further elevated photosynthetic ethylene production. Based on chlorophyll fluorescence measurement and metabolic analysis, the InP nanomaterial‐augmented photosystem I activity and enhanced ethylene production metabolism of biohybrid cells are confirmed, the mechanism underlying the material‐cell energy transduction as well as nanomaterial‐modulated photosynthetic light and dark reactions are established. This work not only demonstrates the potential application of semiconductor‐N. sphaeroides biohybrid system as a good platform for sustainable ethylene production but also provides an important reference for future studies to construct and optimize nano‐cell biohybrid systems for efficient solar‐driven valuable chemical production.

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Nostoc commune (N. commune) is a widespread chilling-tolerant cyanobacterium, whereas its photosynthetic acclimation to chilling remains largely unknown. Here, its photosynthetic responses to chilling were investigated. During 24 h exposure to chilling temperature (4 ºC), this cyanobacterium exhibited photosystem II (PSII) photoinhibition, as evident by the significant decrease in both the PSII maximum quantum yield Fv/Fm and the PSII core protein D1 abundance. However its photosystem I (PSI) maintained stable, both the maximum photo-oxidizable P700 and the PSI core protein PsaA/B abundance remained largely unchanged after chilling. Chilling activated the non-photochemical quenching to maintain energy balance of intersystem electron transport in N. commune, its quantum yield of regulated energy dissipation in PSII (Y(NPQ)) significantly rose by 41%, so that its PSII excitation pressure (1-qP) remained stable. Furthermore, the significant stimulation of cyclic electron flow (CEF) was observed upon the transfer to chilling and subsequent recovery in N. commune, and its photodamage in the presence of chloramphenicol was similar to that in the presence of methyl viologen, suggesting that CEF contributed to the PSII repair under chilling stress. The present data provide novel insight into photosynthetic acclimation to chilling, which benefit the survival of N. commune in cold habitats or during over-wintering periods and could be used as a reference for the design of robust photosynthetic cell factory.