Abstract: Apocynum pictum Schrenk, a halophyte, is commonly used as a traditional Chinese medicine, tea, and fiber crop. To improve the growth of A. pictum in saline soil, its responses to halotolerant plant growth-promoting bacteria (PGPB) were investigated at germination and during early growth stages. Inoculation with either Enterobacter sp. Av16 or Acinetobacter sp. Av23 significantly improved seed germination percentage and alleviated the adverse effects of salinity on seedling growth of A. pictum. Under salt stress, PGPB increased leaf area and improved photosynthetic pigments, including chlorophyll a+b and carotenoids, as well as intercellular carbon dioxide (C_i) and transpiration rate (T_r). More importantly, PGPB alleviated salt-induced damage to the photosynthetic apparatus by stabilizing the photosystems and optimizing electron transport processes. This was evidenced by increases in the density of reaction centers per cross-section (RC/CS_m) and the efficiencies of electron transfer to photosystem I (δR_o and ΦR_o). Consequently, PGPB improved chlorophyll fluorescence and key photosynthetic parameters, including the maximum quantum yield (ΦP_o), performance index on absorption basis (PI_abs), overall performance index (PI_total), and net photosynthetic rate (P_n). Furthermore, PGPB activated antioxidant enzymes, such as superoxide dismutase (SOD) and catalase (CAT), reducing the accumulation of reactive oxygen species (ROS) in A. pictum. In summary, PGPB enhanced A. pictum seed germination and photosynthetic capacity by stabilizing photosystems, improving stomatal gas exchange, and mitigating oxidative stress under salt stress. These findings highlight the potential of PGPB inoculation as a sustainable strategy to enhance salt resilience in A. pictum.

耐盐植物促生菌Enterobacter sp. Av16和Acinetobacter sp. Av23减轻盐胁迫对白麻（Apocynum pictum）种子萌发和幼苗光合作用的抑制

[1]AbdelkefiN, LouatiI, MechichiHZ, et al., 2024. Enhanced salt stress tolerance in tomato plants following inoculation with newly isolated plant growth-promoting rhizobacteria. Sci Hortic, 328:112921.

[2]AktarN, HossainS, AminR, et al., 2023. Endophytic bacteria improve jute growth through induction of phytohormones-related gene expression. Physiol Mol Plant Pathol, 127:102115.

[3]AzeemMA, KhanS, AliF, et al., 2025. Halotolerant Bacillus Aryabhattai strain PM34 mitigates salinity stress and enhances the physiology and growth of maize. J Plant Growth Regul, 44:7000-7018.

[4]BharathiR, VivekananthanR, HarishS, et al., 2004. Rhizobacteria-based bio-formulations for the management of fruit rot infection in chillies. Crop Prot, 23:835-843.

[5]CastilloFJ, PenelC, GreppinH, 1984. Peroxidase release induced by ozone in Sedum album leaves: involvement of Ca²⁺. Plant Physiol, 74(4):846-851.

[6]ChauhanPS, LataC, TiwariS, et al., 2019. Transcriptional alterations reveal Bacillus amyloliquefaciens-rice cooperation under salt stress. Sci Rep, 9:11912.

[7]ChenXJ, ZhouY, CongYD, et al., 2021. Ascorbic acid-induced photosynthetic adaptability of processing tomatoes to salt stress probed by fast OJIP fluorescence rise. Front Plant Sci, 12:594400.

[8]DamalasCA, KoutroubasSD, 2025. Rapeseed (Brassica napus L.) response to salinity and seed priming with NaCl. Ann Appl Biol, 187:16-23.

[9]DebezA, KoyroHW, GrignonC, et al., 2008. Relationship between the photosynthetic activity and the performance of Cakile maritima after long-term salt treatment. Physiol Plant, 133(2):373-385.

[10]DingTL, YangZ, WeiXC, et al., 2018. Evaluation of salt-tolerant germplasm and screening of the salt-tolerance traits of sweet sorghum in the germination stage. Funct Plant Biol, 45(10):1073-1081.

[11]FuD, WuWH, MustafaG, et al., 2025. Molecular mechanisms of rice seed germination. New Crops, 2:100051.

[12]GhoshT, AttaK, MondalS, et al., 2025. Hormonal signaling at seed germination and seedling stage of plants under salinity stress. Plant Growth Regul, 105:583-600.

[13]GuoHX, DongQ, LiSM, et al., 2023. Effects of exogenous calcium on growth, chlorophyll fluorescence characteristics and antioxidant system of Fraxinus malacophylla seedlings. Plant Physiol Biochem, 201:107860.

[14]GuoLF, HanC, LiuT, et al., 2024. Integrated physiological, biochemical and transcriptomic analyses reveal the mechanism of salt tolerance induced by a halotolerant Serratia sp. NTN6 in maize. Environ Exp Bot, 221:105724.

[15]HameedA, AhmedMZ, HussainT, et al., 2021. Effects of salinity stress on chloroplast structure and function. Cells, 10(8):2023.

[16]HouYL, ZengWZ, AoC, et al., 2022. Bacillus atrophaeus WZYH01 and Planococcus soli WZYH02 improve salt tolerance of maize (Zea mays L.) in saline soil. Front Plant Sci, 13:891372.

[17]JiangDX, ChuX, LiM, et al., 2020. Exogenous spermidine enhances salt-stressed rice photosynthetic performance by stabilizing structure and function of chloroplast and thylakoid membranes. Photosynthetica, 58(1):61-71.

[18]JiangHH, QiPS, WangT, et al., 2019. Role of halotolerant phosphate-solubilising bacteria on growth promotion of peanut (Arachis hypogaea) under saline soil. Ann Appl Biol, 174:20-30.

[19]JiangL, WuXJ, ZhaoZY, et al., 2021a. Luobuma (Apocynum) – cash crops for saline lands. Ind Crop Prod, 173:114146.

[20]JiangL, SheCW, TianCY, et al., 2021b. Storage period and different abiotic factors regulate seed germination of two Apocynum species — cash crops in arid saline regions in the northwestern China. Front Plant Sci, 12:671157.

[21]JuYW, KouMZ, ZhongR, et al., 2021. Alleviating salt stress on seedlings using plant growth promoting rhizobacteria isolated from the rhizosphere soil of Achnatherum inebrians infected with Epichloë gansuensis endophyte. Plant Soil, 465:349-366.

[22]KangSM, HoqueIU, WooJI, et al., 2023. Mitigation of salinity stress on soybean seedlings using indole acetic acid-producing Acinetobacter pittii YNA40. Agriculture, 13(5):1021.

[23]KouCX, SongFY, LiDD, et al., 2024. A necessary considering factor for crop resistance: precise regulation and effective utilization of beneficial microorganisms. New Crops, 1:100023.

[24]LawsonT, TerashimaI, FujitaT, et al., 2018. Coordination between photosynthesis and stomatal behavior. In: Adams WW III, Terashima I (Eds.), The Leaf: A Platform for Performing Photosynthesis. Springer, Cham, p.141-161.

[25]LeeSY, ChoK-S, 2025. Acinetobacter sp. ME1: a multifunctional bacterium for phytoremediation utilizing melanin production, heavy metal tolerance, and plant growth promotion. J Zhejiang Univ-Sci B, 26(11):1103-1120.

[26]MaY, DiasMC, FreitasH, 2020. Drought and salinity stress responses and microbe-induced tolerance in plants. Front Plant Sci, 11:591911.

[27]MahmudFMA, IslamA, RubelMH, et al., 2023. Effects of halotolerant rhizobacteria on rice seedlings under salinity stress. Sci Total Environ, 892:163774.

[28]NingZC, LinKX, GaoMY, et al., 2024. Mitigation of salt stress in rice by the halotolerant plant growth-promoting bacterium Enterobacter asburiae D2. J Xenobiot, 14:333-349.

[29]OraczK, BouteauHEM, FarrantJM, et al., 2007. ROS production and protein oxidation as a novel mechanism for seed dormancy alleviation. Plant J, 50(3):452-465.

[30]PandaA, RanganiJ, ParidaAK, 2019. Cross talk between ROS homeostasis and antioxidative machinery contributes to salt tolerance of the xero-halophyte Haloxylon salicornicum. Environ Exp Bot, 166:103799.

[31]PoliY, NallamothuV, BalakrishnanD, et al., 2018. Increased catalase activity and maintenance of photosystem II distinguishes high-yield mutants from low-yield mutants of rice var. Nagina22 under low-phosphorus stress. Front Plant Sci, 9:1543.

[32]RahmanS, RahmaniAA, Abdul AzizM, et al., 2025. The Enterobacter sp. SA187 stimulates stress-responsive genes and promotes salt and heat stress tolerance in tomato plants. Sci Hortic, 342:114038.

[33]RamelF, SulmonC, BogardM, et al., 2009. Differential patterns of reactive oxygen species and antioxidative mechanisms during atrazine injury and sucrose-induced tolerance in Arabidopsis thaliana plantlets. BMC Plant Biol, 9:28.

[34]RaoKVM, SrestyTVS, 2000. Antioxidative parameters in the seedlings of pigeonpea (Cajanus cajan (L.) Millspaugh) in response to Zn and Ni stresses. Plant Sci, 157:113-128.

[35]SergievI, AlexievaV, KaranovE, 1997. Effect of spermine, atrazine and combination between them on some endogenous protective systems and stress markers in plants. Compt Rend Acad Bulg Sci, 51:121-124.

[36]SilvaNCQ, de SouzaGA, PimentaTM, et al., 2018. Salt stress inhibits germination of Stylosanthes humilis seeds through abscisic acid accumulation and associated changes in ethylene production. Plant Physiol Biochem, 130:399-407.

[37]SinghVK, SinghAK, SinghPP, et al., 2018. Interaction of plant growth promoting bacteria with tomato under abiotic stress: a review. Agric Ecosyst Environ, 267:129-140.

[38]StefanovMA, RashkovGD, BorisovaPB, et al., 2024. Changes in photosystem II complex and physiological activities in pea and maize plants in response to salt stress. Plants, 13(7):1025.

[39]SumanJ, RakshitA, OgireddySD, et al., 2022. Microbiome as a key player in sustainable agriculture and human health. Front Soil Sci, 2:821589.

[40]TajZ, BakkaK, ChallabathulaD, 2024. Halotolerant PGPB Staphylococcus sciuri ET101 protects photosynthesis through activation of redox dissipation pathways in Lycopersicon esculentum. Plant Physiol Biochem, 208:108482.

[41]ThevsN, ZerbeS, KyosevY, et al., 2012. Apocynum venetum L. and Apocynum pictum Schrenk (Apocynaceae) as multi-functional and multi-service plant species in Central Asia: a review on biology, ecology, and utilization. J Appl Bot Food Qual, 85:159-167.

[42]TianH, DengYQ, LiaoKT, et al., 2025. Physiological, transcriptomic, and metabolomic analyses reveal the adaptation mechanism of Betaphycus gelatinus under different salinity conditions. Algal Res, 86:103894.

[43]TianW, LiL, XiaoX, et al., 2022. Identification of a plant endophytic growth-promoting bacteria capable of inhibiting cadmium uptake in rice. J Appl Microbiol, 132(1):520-531.

[44]TolbaSTM, IbrahimM, AmerEAM, et al., 2019. First insights into salt tolerance improvement of Stevia by plant growth-promoting Streptomyces species. Arch Microbiol, 201(9):1295-1306.

[45]TsaiYC, ChenKC, ChengTS, et al., 2019. Chlorophyll fluorescence analysis in diverse rice varieties reveals the positive correlation between the seedlings salt tolerance and photosynthetic efficiency. BMC Plant Biol, 19:403.

[46]Tsimilli-MichaelM, 2020. Special issue in honour of Prof. Reto J. Strasser – Revisiting JIP-test: an educative review on concepts, assumptions, approximations, definitions and terminology. Photosynthetica, 58(SI):275-292.

[47]van den BergTE, SandersRGP, KaiserE, et al., 2025. Viewing stomata in action: autonomous in planta imaging of individual stomatal movement. Plant Cell Environ, 48(6):4533-4549.

[48]van ZelmE, ZhangYX, TesterinkC, 2020. Salt tolerance mechanisms of plants. Annu Rev Plant Biol, 71:403-433.

[49]WangGJ, ZengFL, SongP, et al., 2022. Effects of reduced chlorophyll content on photosystem functions and photosynthetic electron transport rate in rice leaves. J Plant Physiol, 272:153669.

[50]XiaoB, WangYJ, 2020. Effects of salt stress on seed germination of Apocynum venetum and Poacynum hendersonii. Pratacultural Sci, 37(2):314-319 (in Chinese).

[51]XieWY, ZhangXY, WangT, et al., 2012. Botany, traditional uses, phytochemistry and pharmacology of Apocynum venetum L. (Luobuma): a review. J Ethnopharmacol, 141:1-8.

[52]XiongB, LiL, LiQ, et al., 2023. Identification of photosynthesis characteristics and chlorophyll metabolism in leaves of Citrus cultivar (Harumi) with varying degrees of chlorosis. Int J Mol Sci, 24(9):8394.

[53]ZhangHX, ZhangGM, LüXT, et al., 2015. Salt tolerance during seed germination and early seedling stages of 12 halophytes. Plant Soil, 388:229-241.

[54]ZhuYF, WuYX, HuY, et al., 2019. Tolerance of two apple rootstocks to short-term salt stress: focus on chlorophyll degradation, photosynthesis, hormone and leaf ultrastructures. Acta Physiol Plant, 41(6):87.

Similar articles