Exogenous Salicylic Acid Alleviates Water Deficit Stress by Protecting Photosynthetic System in Maize Seedlings

Water deficit is a significant abiotic stress affecting crop growth and production. While many studies have indicated that salicylic acid (SA) plays a crucial role in mitigating the detrimental effects of environmental stress on plants, its mechanism regulating the photosynthetic adaptability of maize seedlings under water deficit is still unclear. This study aimed to investigate the impact of exogenous SA on maize seedling performance under polyethylene glycol (PEG)-induced water deficit. The results showed that PEG treatment destroyed the integrity of chloroplast and reduced chlorophyll content and photosynthesis rate (Pn), leading to growth retardation of maize seedlings with lower biomass accumulation and leaf relative water content (RWC). Moreover, chlorophyll fluorescence index, including potential photochemical activity (Fv/Fo), maximum Photosystem II (PSII) quantum yield (Fv/Fm), and energy captured by PSII reaction center for electron transfer (Eto/RC), were decreased, but energy dissipated by unit reaction center (DIo/RC) was enhanced in maize seedlings under water deficit. In addition, PEG treatment also significantly declined the activity of Rubisco and Rubisco activase (RCA) in maize seedlings. In contrast, SA treatment enhanced the content of chlorophyll, as well as the transcription level of psbA, and RCA and Rubisco small subunit (rbcS) reduced the damaging effects of PEG treatment by protecting the integrity of chloroplast and repairing the damaged PSII reaction center, thus positively regulating photosynthetic reaction and water-deficit tolerance in maize seedlings. Our data implied that SA played an important regulatory role in plant resistance to water-deficit stress, and the result will further supply the regulatory network of SA-mediated photosynthetic adaptability.

Automated summary

Water deficit is a significant stress that affects crop growth and production. This study found that salicylic acid (SA) plays a crucial role in regulating the photosynthetic adaptability of maize seedlings under water deficit by protecting the chloroplast integrity and repairing the damaged photosystem II reaction center. SA treatment enhanced chlorophyll content and activity of key enzymes related to photosynthesis, thereby improving the water-deficit tolerance in maize seedlings.