尖叶拟船叶藓光系统Ⅱ光合荧光特性、活性氧代谢与耐脱水生理生态适应的关系

Influence of dehydration and rehydration on photosynthetic chlorophyll characteristics and reactive oxygen species metabolism in Dolichomitriopsis diversiformis

以广布湿生藓类——湿地匐灯藓(Plagiomnium acutum)为比较材料,研究东亚特有濒危植物尖叶拟船叶藓(Dolichomitriopsis diversiformis)在不同快速脱水和复水胁迫下PSⅡ的叶绿素光合荧光变化和活性氧代谢及抗氧化系统变化,探讨两种藓类生理生态适应性差异的成因,以初步确定尖叶拟船叶藓受水分条件限制分布狭窄趋于濒危的原因。结果显示:(1)尖叶拟船叶藓的光合电子传递在脱水后可被极微弱光完全抑制,其抑制光强的恢复明显慢于湿地匐灯藓;其PSⅡ最大光化学效率(Fv/Fm)和实际光化学量子效率(YⅡ)先降而后升,恢复较慢;光化学淬灭(q P)复水后恢复较快,非光化学淬灭(NPQ)的绝对值和变化速率则始终低于湿地匐灯藓。(2)尖叶拟船叶藓活性氧水平明显高于湿地匐灯藓;其SOD、CAT、APX等抗氧化系统酶活性整体变化幅度较大,抗氧化保护物质(As A)含量则明显低于湿地匐灯藓。以上结果表明尖叶拟船叶藓受到环境水分因子限制的原因主要有:(1)PSⅡ的反应中心色素(P680)对脱水伤害较为敏感;(2)复水修复过程中抗氧化保护系统的保护能力偏低。

Dolichomitriopsis diversiformis,an endangered moss species which is unique to East Asia,is now distributed in a very narrow area. From our early field investigation of its habitat,we found that the species is restricted by moisture content of atmosphere and growth matrix. In order to disclose the endangered mechanism of D. diversiformis under water stress,and to elucidate eco-physiological differences of bryophytes in similar humidity habitat,Plagiomnium acutum,a widespread species was selected to compare with D. diversiformis. Therefore, their photosynthetic chlorophyll characteristics of phtosystem Ⅱ( PSⅡ),such as electron transport rate( ETR)- photosynthetic available radiation( PAR) curves,maximal photochemical efficiency( Fv / Fm),photosystem quantum yielding( Y( Ⅱ)),photochemical qunching( q P) and nonphotochemical qunching( NPQ) were detected by PAM 2500 and IMAGING PAM. Furthermore,metabolism of reactiveoxygen species( superoxide anion and hydrogen peroxide),activities of antioxidative enzymes( superoxide dismutase( SOD),catalase( CAT) and ascorbate peroxidase( APX)) and content of ascorbic acid( ASA) in the two moss species during desiccation and rehydration were determined in our studies. Results of ETR-PAR curve indicated that desiccation reduced the inhibitory light density of both species; but when water content recovered,the inhibitory light density restored to normal status. Compared with P. acutum,ETR of D. diversiformis was blocked completely by very weak light density after60 min dehydration and recovered much more slowly in rehydration. And the results of other PSⅡ chlorophyll fluorescence characters also gave similar evidences. Fv / Fm and Y Ⅱ of both bryophytes were decreased under desiccation and then increased in rehydraion,but the value of D. diversiformis declined more quickly during desiccation and recovered more slowly in rehydration. That is to say,photosynthetic electron transport of PSⅡ in D. diversiformis can be not only reduced by water loss but also destroyed completely by deep desiccation. Meanwhile,variation of q P and NPQ of both species manifested an interesting occurance. q P of D. diversiformis declined more quickly than P. acutum in desiccation and returned to normal condition much more quickly than that of P. acutum. In other words,photosynthetic reaction which is represented by photochemical qunching is protected primarily in D. diversiformis. But photochemical quenching restoration would bring out more production of reactive oxygen species. Otherwise,though NPQ of both species increased in desiccation and decrease in rehydration,yet the absolute value of D. diversiformis maintained a relative low level. These results suggested that the photo-protective mechanism supported by xanthophyll cycle in D. diversiformis should be weaker than in P. acutum.All these results indicate that PS Ⅱ of D. diversiformis,especially reaction central pigment( P680) is more sensitive to dehydration than P. acutum. Results of reactive oxygen species metabolism showed that absolute value of superoxide anion production and hydrogen peroxide content in D. diversiformis were significantly higher than in P. acutum. Furthermore,though anti-oxidative enzymes, such as SOD, CAT, APX also increased similar of reactive oxygen species under desiccation,yet their activities in D. diversiformis decreased more quickly in rehydration. In conclusion,the sensitivity of photosystem Ⅱ and the low efficiency of antioxidative system in rehydration are probably two major eco-physiological restricting factors of D. diversiformis narrow distribution.