Physiological mechanisms of 2,4-epibrassinolide treatment in enhancing salt-alkali stress tolerance in Corylus heterophylla×C.avellana hybrid seedlings

MA Chao; CHEN Weiqing; LIU Zaiguo; HAO Jing; ZHAO Mengjiong; LU Juan

doi:10.13925/j.cnki.gsxb.20240602

Abstract：[Objective]The present study was conducted to assess the impact of exogenous 2,4-epibras-sionolide(EBR)on the growth and physiological responses of Corylus heterophylla × C.avellana hy-brid seedlings under saline-alkali stress,with the objective of enhancing their tolerance to such adverse conditions.[Methods]The experiment was initiated with two-year-old seedlings from root suckers propagated by green branch layering with the hazelnut variety Dawei,widely cultivated in Xinjiang.These seedlings were transplanted into pots containing a mixture of garden soil,perlite,and humus in a ratio of 2∶1∶1.The seedlings were subjected to four treatments:(1)the control with normal cultivation(CK),(2)saline-alkali stress with a solution of 200 mmol·L-1 NaCl∶Na2CO3 in a ratio of 1∶1(SA),(3)sa-line-alkali stress combined with 0.2 μmol·L-1 EBR(SE),and(4)saline-alkali stress combined with 0.2μmol·L-1 EBR and 24 μmol·L-1 brassinazole(BRZ)(SEB).The seedlings were irrigated with the saline-alkali solution every three days for a total of three applications,and EBR or BRZ was applied every two days for five times.After 30 days of stress imposition,phenotypic observations were recorded,and sam-ples were collected for subsequent analysis.[Results]The saline-alkali stress significantly inhibited the growth of the seedlings,but the application of 0.2 μmol·L-1 EBR notably mitigated this inhibitory ef-fect.The EBR treatment led to a significant increase in the net photosynthetic rate(Pn),stomatal conduc-tance(Gs),and transpiration rate(Tr)by 33.33％to 54.10％compared to the saline-alkali stress treat-ment alone.This enhancement in photosynthetic parameters suggested that EBR played a crucial role in maintaining the photosynthetic capacity under stress conditions,which was vital for the energy and car-bon skeletons required for plant growth and survival.Furthermore,the EBR treatment significantly en-hanced the content of chlorophyll a(Chl a),chlorophyll b(Chl b),and total chlorophyll(Chl a+b)by 37.05％to 41.38％.The increase in chlorophyll content indicated that EBR may protect the photosyn-thetic pigments from degradation,thereby preserving the light-harvesting capacity of the plant.Regard-ing physiological and biochemical indicators,the EBR treatment markedly increased the activities of su-peroxide dismutase(SOD),peroxidase(POD),and catalase(CAT),and significantly reduced the levels of hydrogen peroxide(H2O2)and superoxide anion generation rate(O2-)by 38.52％and 51.66％,respec-tively.These results indicated that EBR enhanced the plant's antioxidant defense system,which was cru-cial for scavenging reactive oxygen species(ROS)and preventing oxidative damage to cellular compo-nents.Additionally,EBR significantly promoted the accumulation of soluble sugars(SS),soluble pro-teins(SP),and proline(Pro)contents,increasing these parameters by 29.43％to 63.31％compared to the saline-alkali stress treatment.The accumulation of these osmoprotectants suggested that EBR helped the plant to maintain cellular hydration and protect against cellular dehydration under saline-al-kali stress.In terms of ion balance,EBR treatment significantly decreased the sodium ion(Na+)content and the sodium-potassium ratio(Na+/K+)by 20.80％and 56.88％,respectively,while increasing the po-tassium ion(K+)content by 45.65％.These findings indicated that EBR played a role in modulating ion homeostasis,which was essential for maintaining cellular functions and reducing the toxic effects of so-dium ions.In the context of organic acid metabolism,EBR treatment significantly increased the levels of succinic acid,citric acid,malic acid,and tartaric acid by 21.74％,76.75％,47.15％,and 63.77％,re-spectively.The increase in organic acid content suggested that EBR may enhance the plant's ability to cope with saline-alkali stress through various mechanisms,including osmotic adjustment,ion chelation,and detoxification.Regarding endogenous hormones,EBR treatment significantly reduced the abscisic acid(ABA)content by 20.58％and increased the content of indole-3-acetic acid(IAA),gibberellins(GA),and zeatin riboside(ZR)by 38.40％,21.58％,and 21.14％,respectively.The modulation of hor-mone levels by EBR indicated its role in regulating plant growth and stress responses,which was cru-cial for plant adaptation to saline-alkali conditions.[Conclusion]The exogenous application of EBR significantly enhanced the tolerance of Corylus heterophylla × C.avellana hybrid seedlings to saline-al-kali stress through multiple pathways,including the alleviation of oxidative damage,promotion of pho-tosynthesis,enhancement of osmotic adjustment,maintenance of ion balance,regulation of organic acid metabolism,and modulation of endogenous hormone balance.These findings suggested that EBR could be a promising plant growth regulator for improving the productivity of hazelnut in saline-alkali soils,offering new insights and approaches into enhancing the yield and quality of crops in such challenging environments.