两种不同生境苦苣苔科植物的复苏特性及其对水分的光合和生理响应

Resurrection characteristics, photosynthetic and physiological response to dehydration and rehydration of two species in Gesneriaceae with different habitats

关键词:  锈色蛛毛苣苔, 心叶马铃苣苔, 脱水, 复苏植物, 叶绿素荧光, 渗透调节物质, 丙二醛(MDA), 光保护

Key words:  Paraboea rufescens, Oreocharis cordatula, dehydration, resurrection plant, chlorophyll fluorescense, osmotic adjustment substance, malonialdehyde(MDA), photoprotection

摘要:

复苏植物可以耐受极度干旱的环境,脱水至10%相对水分含量后仍然可以复苏。苦苣苔科植物包含有较多复苏植物,不同类群的复苏机理可能存在差异。该文选择分布在亚热带和温带石灰岩地区的锈色蛛毛苣苔(Paraboea rufescens)和心叶马铃苣苔(Oreocharis cordatula)两种苦苣苔科植物,并对这两个物种的叶片先分别脱水1、2、3 d,再分别复水1 d,检测不同脱水复水过程的叶片形态、相对含水量(RWC)、光合活性、膜完整性、渗透调节物质等指标的变化。结果表明:(1)锈色蛛毛苣苔的叶圆片在脱水后即发生向内折叠,脱水2 d时将叶上表面完全包裹,同时表征最大光合潜力的叶绿素荧光 F_v/F_m受到抑制; 而心叶马铃苣苔的叶片仅发生轻度皱缩,且F_v/F_m基本维持对照水平,同时具有更高的光保护能力 [Y(NPQ)]; 复水后,两个物种的叶片均展开,F_v/F_m恢复。(2)两个物种均在脱水2 d时,RWC降低至5%,相对电导率(REC)分别升高至51.8%和56.2%,渗透调节物质可溶性糖含量显著升高; 复水后,RWC、REC和可溶性糖含量均恢复到对照水平。(3)进一步脱水3 d时,锈色蛛毛苣苔和心叶马铃苣苔叶片RWC均达到1.5%,复水后的REC升高至95%,F_v/F_m消失。(4)锈色蛛毛苣苔在可复苏脱水复水过程的叶绿素a + b含量下降50%,而心叶马铃苣苔基本保持不变,说明二者均为叶绿素维持型复苏植物,可在脱水后复水时迅速恢复光合作用; 在脱水复水过程中,两个物种的丙二醛(MDA)含量均无显著变化,且保持极低水平,说明两个物种在极度干旱条件下可以维持其细胞膜脂免于被氧化。综上所述,两个物种可以耐受5% RWC脱水,均为复苏植物。剧烈脱水时,锈色蛛毛苣苔通过卷缩叶片来避免吸收过量光照对植物造成伤害; 而心叶马铃苣苔则通过光系统Ⅱ(PSⅡ)的光保护机制将吸收的过多能量通过热耗散形式散布出去,从而保护其光系统的完整性。

Abstract:

Resurrection plants usually grow in extreme habitats and have the capacity to survive from lower relative water content to 10%. There are many resurrection plants in family Gesneriaceae, and the resuscitating mechanism of different species may be different. In order to investigate whether the two species have different resurrection characteristics and physiological mechanisms in response to drought, two species of Gesneriaceae, Paraboea rufescens and Oreocharis cordatula, which are distributed in subtropical and temperate limestone areas respectively, were selected in this study. Their leaves were dehydrated for 1, 2 and 3 d respectively, and then rehydrated for 1 day. The leaf morphology, relative water content(RWC), photosynthetic activity, photosynthetic pigments, membrane integrity and osmotic adjustment substances during different dehydration and rehydration treatments were detected and analyzed. The results were as follows:(1)The leaf discs of Paraboea rufescens folded inward after dehydration, and the leaf upper epidermis was completely wrapped after dehydrated for two days, and the chlorophyll fluorescence parameter F_v/F_m, which characterized the maximum photosynthetic potential, was inhibited; Comparatively, the leaf discs of Oreocharis cordatula shrunk slightly, maintained the F_v/F_m level, and had higher photoprotection ability [Y(NPQ)]; The leaf discs of both species spread out and the F_v/F_m recovered following rewatered.(2)After two days of dehydration, the RWC of the two species decreased to about 5%, the relative electricity conductivities(REC)increased to 51.8% and 56.2% respectively, and the contents of soluble sugar increased significantly; During the following rewatered, RWC, REC and soluble sugar all recovered to the control level.(3)After further dehydration for three days, RWC of leaf discs of two species reached about 1.5%, the conductivity increased to about 95% after rehydration, and the F_v/F_m disappeared.(4)Chlorophyll a+b contents of Paraboea rufescens decreased by 50% during resuscitable dehydration and rehydration, while Oreocharis cordatula remained basically unchanged, which indicated that both of them were homoiochlorophyllous desiccation tolerance species and could quickly resume photosynthesis after rehydration following dehydration; During dehydration and rehydration, the contents of malonialdehyde(MDA)had no significant change, and remained extremely low level, which indicated two species could keep their membrane lipids from being oxidized under extreme drought conditions. To sum up, these two species can survive from dehydration to lower level of 5% RWC, therefore, they are both resurrection plants. Under severe dehydration, Paraboea rufescens can avoid the damage from excessive light absorption by curling its leaves; however, Oreocharis cordatula can spread the excessive energy by heat dissipation through photoprotection of PS Ⅱ, thus protecting its photosynthesis organs.