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樟树Cinnamomum camphora为高大常绿乔木,是优良的绿化树、行道树及庭荫树,其材质上乘,是制造家具的好材料,可提制樟脑和提取樟油,是南方珍贵用材和特用经济树种。樟树喜光,喜温暖湿润气候,对土壤要求不严,较耐水湿,存活期长,抗海潮风,在南方沿海地区极具应用价值,但它不耐干旱、瘠薄和盐碱土,土壤含盐量要求在2‰以内,这制约着它在南方沿海地区的引种栽培。国内外关于樟树的耐盐性研究较少,且主要集中在樟树对盐胁迫的生理响应上[1-3],而对于如何提高樟树耐盐性方面,仅有研究表明施氮能缓解樟树盐胁迫带来的毒害[4]。光合作用是植物生长发育的基础,决定着植物的生产力,且对环境的变化较敏感。叶绿素荧光技术是近年来探测和分析植物光合功能的有效手段,光合色素和叶绿素荧光参数可以反映逆境对植物光合功能的影响,进而反映植物的耐受性。油菜素内酯(brassinosteroids,BRs)是一种广泛存在于植物中的甾醇类新型植物生长调节物质,在植物体内含量极低,但生理活性极高,植物经其低浓度处理便能表现出明显的生理效应[5]。它广泛参与植物各种生理过程,尤其在植物生长发育及其对逆境的响应等方面具有重要的调节作用[6]。关于外源BRs对植物抗盐性影响方面的研究已有一些报道:外源BRs可有效促进盐胁迫下植物种子萌发、幼苗生长[7-8],提高叶片光合色素含量和光合能力[9],增强抗氧化酶活性,降低膜脂过氧化产物丙二醛质量分数和质膜透性[10-11],显著改善离子稳态和渗透调节能力[12],且不同的BRs处理方式和浓度对盐胁迫下植物的调控效果存在差异[13-14]。这些研究都表明:BRs能不同程度地提高植物的耐盐性,但是BRs对盐胁迫下木本植物的研究却鲜有报道,BRs对盐胁迫下樟树幼苗的影响方面的研究更是未见报道。本实验主要研究BRs浸根处理对盐胁迫下樟树幼苗盐害指数、盐害率、相对含水率、光合色素和荧光参数的影响,揭示BRs对樟树幼苗光合功能的调节作用,为樟树耐盐能力的提高提供依据。
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盐害指数和盐害率可以直观表现出樟树盐害状况。由表 1可以看出:随着氯化钠浓度的增加,樟树的盐害指数变大,经过BRs处理后,各氯化钠浓度下的盐害指数均显著减少,其中0.3 mg·L-1的BRs减少最显著,在50,10,150 mmol·L-1的氯化钠浓度下分别减少52.9%,45.3%,53.1%,而BRs对樟树的盐害率影响不大。
表 1 BRs对氯化钠胁迫下樟树盐害指数和盐害率的影响
Table 1. Effects cf BRs cn the salt injury index and rate cf salt injury cf Cinnamomum camphora under NaCl stress
c氯化钠/
(mmcl • L-1)盐害指数/% 盐害率/% 对照 0.1 0.2 0.3 mg·L-1 对照 0.1 0.2 0.3 mg·L-1 0 0 0 0 0 0 0 0 0 50 57.5 35.4 42.1 27.1 70 83.3 75.0 50.0 100 87.5 50.0 56.7 47.9 100 100.0 100.0 100.0 150 97.5 58.3 54.2 45.8 100 90.0 100.0 91.7 -
相对含水率是反映植物体内水分状况的重要生理指标,也是反映植物抗逆性的可靠指标[19]。由图 1可以看出:50 mmol·L-1的盐胁迫对樟树的相对含水率影响不大,当氯化钠浓度达到100和150 mmol·L-1时,相对含水率显著降低。与对照相比,BRs处理过的樟树叶片,相对含水率在低氯化钠浓度下几乎不变,在高氯化钠浓度下,当BRs质量浓度为0.2和0.3 mg·L-1时显著升高。
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由图 2可以看出:50 mmol·L-1氯化钠处理对樟树的光合色素几乎没有影响,此后随着氯化钠浓度的增加,Chla,Chlb,Chl,Car质量分数和chla/b均明显降低,而Car/Chl明显上升。BRs明显影响樟树盐胁迫下光合色素的质量分数;与对照相比,50 mmol·L-1氯化钠浓度下BRs明显降低了Chla/b,Chla,Chlb,Car和Chl质量分数;当氯化钠浓度继续加大到100 mmol·L-1时,与50 mmol·L-1盐胁迫相比,对照Chla/b,Chla,Chlb,Car和Chl质量分数降幅较大,Car/Chl升幅较大,而经过BRs处理过的樟树仅Chla/b下降显著,0.3 mg·L-1的BRs更促使樟树Chla,Chlb,Car和Chl质量分数不降反升,Chla/b也有小幅度上升,Car/Chl下降较大;当氯化钠浓度达到150 mmol·L-1时,与100 mmol·L-1的盐胁迫相比,经过BRs处理过的樟树Chla,Chlb,Car和Chl质量分数降幅比对照小很多,Chla/b反而上升,Car/Chl增幅小很多,Chla,Chlb,Chl质量分数和Chla/b超过对照,Car接近对照,Car/Chl远远低于对照。
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由图 3可以看出:樟树叶片的PSⅡ最大光化学效率Fv/Fm和潜在光化学效率Fv/Fo随着氯化钠浓度的增加逐渐降低,与对照相比,100和150 mmol·L-1氯化钠浓度下,Fv/Fm和Fv/Fo有显著降低。当用BRs浸根处理后,不同BRs质量浓度对同一氯化钠浓度胁迫下的Fv/Fm和Fv/Fo影响不一样;樟树没受到胁迫时,BRs质量浓度越大,Fv/Fm和Fv/Fo越低;受到低盐胁迫时,BRs质量浓度对Fv/Fm和Fv/Fo影响不大;受到高盐胁迫时,BRs对Fv/Fm影响显著,100 mmol·L-1氯化钠浓度下,0.3 mg·L-1的BRs对应的Fv/Fm和Fv/Fo最高,150 mmol·L-1的盐浓度下,0.2 mg·L-1的BRs对应的Fv/Fm和Fv/Fo最高,0.2和0.3 mg·L-1 BRs处理的樟树叶片Fv/Fm和Fv/Fo随着氯化钠浓度的变化不显著。
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图 3表明:有效光化学量子产量Fv'/Fm'和实际光化学量子产量ФPSⅡ有相似的变化趋势,当樟树没受到盐胁迫时,BRs降低了Fv'/Fm'和ФPSⅡ值,随着氯化钠浓度的增加对照的Fv'/Fm'和ФPSⅡ有明显的下降趋势,BRs减缓了这种下降趋势,且以质量浓度为0.2,0.3 mg·L-1的BRs减缓效果最好。当氯化钠浓度达到100 mmol·L-1以后,经过BRs处理过的樟树叶片Fv'/Fm'和ФPSⅡ值比对照高,氯化钠浓度为150 mmol·L-1时,经过0.2 mg·L-1的BRs处理的樟树Fv'/Fm'和ФPSⅡ值比对照分别高15.4%,4.9%。
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当樟树没受到盐胁迫时,BRs增加了光化学猝灭系数qP和非光化学猝灭系数qN的值,随着氯化钠浓度的增加,对照的qP逐渐加大,qN先增大后减少,当氯化钠浓度达150 mmol·L-1时,显著低于对照。经过0.3 mg·L-1的BRs处理过的樟树在氯化钠浓度为50 mmol·L-1时,qP和qN的值显著低于对照,当氯化钠浓度为100和150 mmol·L-1时,qP略高于对照,qN显著高于对照,0.2 mg·L-1的BRs对这2个氯化钠浓度处理下的qN也有显著增高作用。
BRs, photosynthetic pigments, and chlorophyll fluorescence parameters in Cinnamomum camphora seedlings with NaCl stress
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摘要: 为了研究油菜素内酯(BRs)浸根处理对盐胁迫下樟树Cinnamomum camphora光合功能的调节作用,为樟树耐盐性的提高提供理论依据,采用盆栽法,以不同质量浓度(0.1,0.2,0.3 mg·L-1)的BRs对樟树幼苗浸根48 h,蒸馏水浸根为对照,然后用0,50,100,150 mmol·L-1的氯化钠溶液进行处理。结果表明:BRs浸根处理能降低盐害指数,减小随着氯化钠浓度的增加叶绿素a、叶绿素b、叶绿素总量、类胡萝卜素和叶绿素a/b的下降幅度以及胡萝卜素/叶绿素总量的上升幅度,提高高盐胁迫下叶片的相对含水量,Fv/Fm,Fv/Fo,Fv'/Fm'和ФPSⅡ,提高非光化学能量的耗散。以上说明BRs有利于樟树在盐胁迫下对光能的捕获、吸收、传递和转换,提高叶片的光合活性,缓解高盐溶液对其光合系统的胁迫影响,降低高盐对樟树的抑制作用。Abstract: To provide a theoretical basis for improvement of Cinnamomum camphora (camphor) salt resistance, a photosynthetic adjustment function of the brassinosteroids (BRs) root treatment to camphor with NaCl stress was studied. Potted plants having different concentrations (0.1, 0.2 and 0.3 mg·L-1) of BR root treatments were added to camphor seedlings with distilled water as a control. Salt stress was applied with NaCl concentrations of 0, 50, 100, and 150 mmol·L-1, 3 replications was designed. Results showed that BRs reduced the salt injury index. With an increase in salt concentration, BRs also lessened the decrease in Chla, Chlb, Chl, Car, and Chla/b; improved the increase in range of Car/Chl. When the salt concentrations from 100 mmol·L-1 to 150 mmol·L-1, BRs can inhibit the decrease in Chla/b and the increase in range of Car/Chl signifigantly (P < 0.05). BRs can also improved the relative water content of leaves, Fv/Fm, Fv/Fo, Fv'/Fm', and ФPSⅡ for salt stress with higher values; improved the photochemical energy dissipation, and when the concentrations of BRs is 0.2 and 0.3 mg·L-1, it can improved the relative water, Fv/Fm, Fv/Fo and the photochemical energy dissipation signifigantly (P < 0.05). Thus, with camphor, BRs were beneficial for capturing, absorbing, transferring, and converting light energy, for improving leaf photosynthetic activity, for alleviating the impact of high salt stress on the photosynthetic system, and for reducing the inhibitive effect of high salt on camphor.
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表 1 BRs对氯化钠胁迫下樟树盐害指数和盐害率的影响
Table 1. Effects cf BRs cn the salt injury index and rate cf salt injury cf Cinnamomum camphora under NaCl stress
c氯化钠/
(mmcl • L-1)盐害指数/% 盐害率/% 对照 0.1 0.2 0.3 mg·L-1 对照 0.1 0.2 0.3 mg·L-1 0 0 0 0 0 0 0 0 0 50 57.5 35.4 42.1 27.1 70 83.3 75.0 50.0 100 87.5 50.0 56.7 47.9 100 100.0 100.0 100.0 150 97.5 58.3 54.2 45.8 100 90.0 100.0 91.7 -
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