CO_2加富对盐胁迫下黄瓜幼苗叶片光合特性及活性氧代谢的影响

Effects of CO_2 enrichment on photosynthetic characteristics and reactive oxygen species metabolism in leaves of cucumber seedlings under salt stress

以‘津优35号’黄瓜(Cucumis sativus L.)水培苗为试材,采用裂区设计,主区因素为CO_2浓度处理,设大气CO_2浓度(Symbol{B@400μmol/mol)和CO_2加富[(800±40)μmol/mol]2个CO_2浓度水平,裂区因素为盐胁迫处理,用NaCl模拟盐胁迫,设对照(0 mmol/L NaCl)、盐胁迫(80 mmol/L NaCl)2个盐分水平,研究了CO_2加富对盐胁迫下黄瓜幼苗生长、光合特性及活性氧代谢的影响。结果表明:盐胁迫显著抑制黄瓜幼苗的生长,并降低了叶绿素含量、ETR、Φ_(PSII)、核酮糖-1,5-二磷酸羧化酶(RuBPCase)活性及净光合速率;盐胁迫增加了丙二醛及活性氧的累积,与此同时也提高了脯氨酸含量及超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性,但降低了过氧化物酶(POD)活性。CO_2加富显著提高了盐胁迫下黄瓜幼苗的株高、茎粗、叶面积及地上部鲜重,降低了叶绿素a、叶绿素b、类胡萝卜素及叶绿素(a+b)含量,但显著提高了净光合速率和RuBPCase活性,同时降低了气孔导度及蒸腾速率,并且使其具有较高的表观电子传递速率及PSII实际光化学效率;CO_2加富显著提高了盐胁迫下黄瓜幼苗叶片脯氨酸含量及SOD、POD、CAT活性,丙二醛、过氧化氢含量和超氧阴离子产生速率显著降低。综上所述,CO_2加富可通过提高幼苗叶片净光合速率、脯氨酸含量及抗氧化酶活性,降低蒸腾速率、减少丙二醛含量及活性氧的积累,从而缓解盐胁迫对黄瓜植株造成的伤害。

We investigated the effects of CO2 enrichment on photosynthetic characteristics and metabolism of reactive oxygen species in the leaves of cucumber(Cucumis sativus L.‘Jinyou No.35’)seedlings under salt stress.In the split-plot design used,the main treatment consisted of two CO2 concentration levels[ambient[CO2]≈400μmol/mol and enriched[CO2]=(800±40)μmol/mol]and the subplot had two levels of salinity treatment(0 and 80 mmol/L NaCl).The results showed that after 7 days of experimental treatment,salt stress caused a significant reduction in growth rate(i.e.,increase in plant height,stem thickness,leaf area,and the growth of both shoot and root),ribulose-1,5-bisphosphate carboxylase(RuBPCase)activity,net photosynthetic rate(Pn)of the leaves,stomatal conductance(Gs),and transpiration rate(Tr)of cucumber seedlings.Salt stress decreased the chlorophyll[chlorophyll a,chlorophyll b,carotenoids,and chlorophyll(a+b)]content,electron transport rate(ETR),quantum of PSII(ΦPSII),and photochemical quenching(qP)but markedly increased non-photochemical quenching(NPQ);there were no significant differences in chlorophyll a/b and maximum quantum yield of PSII(Fv/Fm)between control and salt stress treatments.Moreover,the portion of excessive energy in the photosystem II(PSII)reaction center was enhanced by salt stress that increased the rate of production of the superoxide anion radical(O■)and hydrogen peroxide(H2O2)content in the leaves of cucumber seedlings.Subsequently,this resulted in an increase in malondialdehyde(MDA)content,permeability of cell membranes,and osmoticum(proline)content.Changes in antioxidative enzyme activities of cucumber seedling leaves differed between the salt stress and elevated[CO2]treatments.Superoxide dismutase(SOD)and catalase(CAT)activities increased while peroxidase(POD)activity decreased in cucumber seedling leaves treated with salt stress.However,the activity of antioxidative enzymes(such as SOD,POD,and CAT)and proline content were enhanced by elevated(CO2)Therefore,we can speculate that reactive oxygen species(ROS)quenching was limited under salt stress,leading to their accumulation and serious lipid peroxidation.However,elevated[CO2]reduced the content of MDA,H2O2,and the rate of O■production in cucumber seedling leaves under salt stress.ROS was eliminated by antioxidative enzymes under elevated[CO2],therefore,lipid peroxidation damage was less than that caused by salt stress.Elevated[CO2]increased the plant height,stem thickness,leaf area,and shoot fresh weight of cucumber seedlings significantly under salt stress.Additionally,elevated[CO2]decreased the content of chlorophyll[chlorophyll a,chlorophyll b,carotenoid,and chlorophyll(a+b)],stomatal conductance,and transpiration rate but markedly increased Pn,ETR,ΦPSII,and RuBPCase activity in leaves of cucumber seedlings under salt stress.In conclusion,elevated[CO2]alleviated the negative effects of salt stress and enhanced the resistance of cucumber plant growth to salt stress through enhanced Pn,cellular membrane stability,proline content,and antioxidative enzyme activities while transpiration rate,MDA content,and accumulation of ROS were reduced.