王龍樂(lè),張 鑫,鄒定輝,3,*,陳斌斌

1 華南理工大學(xué)環(huán)境與能源學(xué)院,廣州 510006 2 華南理工大學(xué)科學(xué)技術(shù)處,廣州 510006 3 廣東省大氣環(huán)境與污染控制重點(diǎn)實(shí)驗(yàn)室,廣州 510006

干出脫水對(duì)羊棲菜葉狀體與生殖托熒光特性的影響及其在沉水狀態(tài)下的恢復(fù)

王龍樂(lè)1,張 鑫2,鄒定輝1,3,*,陳斌斌1

1 華南理工大學(xué)環(huán)境與能源學(xué)院,廣州 510006 2 華南理工大學(xué)科學(xué)技術(shù)處,廣州 510006 3 廣東省大氣環(huán)境與污染控制重點(diǎn)實(shí)驗(yàn)室,廣州 510006

在有性繁殖時(shí)期,潮間帶海藻羊棲菜(Hizikiafusiformis)的葉狀體與生殖托遭受低潮干出脫水的影響。為闡明羊棲菜在有性繁殖時(shí)期不同部位對(duì)干出脫水的耐受能力,研究了羊棲菜的葉狀體和雌、雄生殖托在干出脫水過(guò)程中以及隨后的沉水恢復(fù)狀態(tài)下葉綠素?zé)晒鈩?dòng)力學(xué)參數(shù)變化。實(shí)驗(yàn)結(jié)果表明,羊棲菜葉狀體及其生殖托的PS II有效光化學(xué)量子產(chǎn)量[Y(II)]分別在0—73%和0—60%的脫水率范圍內(nèi)未發(fā)生顯著變化,而繼續(xù)脫水則會(huì)顯著降低藻體的Y(II),表明羊棲菜葉狀體和生殖托的Y(II)下降的脫水界限值分別為73%和60%,對(duì)脫水耐受能力較強(qiáng)。在連續(xù)干出脫水過(guò)程中,葉狀體和生殖托的最大相對(duì)電子傳遞速率(rETRmax)和光強(qiáng)耐受能力(Ik)都顯著下降,且在嚴(yán)重脫水狀態(tài)(失水率為75%)下,羊棲菜葉狀體和雌、雄生殖托的Y(II)分別比干出初始時(shí)降低了12%、31%和37%,且復(fù)水后其雌、雄生殖托的Y(II)無(wú)法恢復(fù),甚至持續(xù)降低。同時(shí)葉狀體和生殖托的rETRmax、Ik和光能利用效率(α)都顯著下降,說(shuō)明嚴(yán)重脫水使藻體不同部位的PS II反應(yīng)中心受到了不可逆的損傷。在持續(xù)大幅度脫水過(guò)程(失水率高于60%)中及隨后的沉水恢復(fù)過(guò)程中,比較藻體各部位的Y(II)值發(fā)現(xiàn),葉狀體 > 雌生殖托 > 雄生殖托,表明嚴(yán)重脫水對(duì)雄生殖托的影響最大,對(duì)葉狀體的影響最小。在有性生殖階段,為了羊棲菜能有性繁殖成功,應(yīng)避免藻體,尤其是生殖托經(jīng)受到嚴(yán)重的干出脫水脅迫。

羊棲菜；干出；脫水；葉綠素?zé)晒?；葉狀體；生殖托；有性繁殖

羊棲菜(Hizikiafusiformis)是一種重要的大型經(jīng)濟(jì)褐藻,具有較高的營(yíng)養(yǎng)和藥用價(jià)值[26]。在我國(guó)浙江和福建等地已有一定規(guī)模的養(yǎng)殖生產(chǎn)。自然生長(zhǎng)的羊棲菜主要分布于低潮帶,以巖石作為固著基質(zhì)。因此,在低潮時(shí),特別是在大潮低潮時(shí),羊棲菜與其他潮間帶海藻一樣,常暴露在空氣中(即處于干出狀態(tài)),且其葉狀體和生殖托均經(jīng)歷了干出脫水和復(fù)水的過(guò)程,這兩種組織對(duì)干出脫水的響應(yīng)機(jī)制是否一致并沒(méi)有得到詳盡的研究和報(bào)道。生殖托作為有性生殖的器官,具有產(chǎn)生精子或卵子的窩空,這些較為復(fù)雜的結(jié)構(gòu)占據(jù)了生殖托一定的空間,其中,雌生殖托的生殖部分大于雄生殖托的生殖部分,因此,生殖托的含水量低于葉狀體的,且雌生殖托的含水量小于雄生殖托的[27-28]。這種生理結(jié)構(gòu)上的差異可能導(dǎo)致兩個(gè)部位對(duì)干出脫水響應(yīng)的差異。本文以羊棲菜(Hizikiafusiformis)的葉狀體和雌、雄生殖托作為實(shí)驗(yàn)材料,探討其在干出過(guò)程中和沉水狀態(tài)下的葉綠素?zé)晒鈩?dòng)力學(xué)曲線和參數(shù)變化,研究其在干出失水過(guò)程中光合作用PS II的反應(yīng),以進(jìn)一步認(rèn)識(shí)其生物學(xué)規(guī)律,闡釋影響羊棲菜有性繁殖的環(huán)境因素。

1 材料與方法

1.1 材料

從汕頭南澳島云澳灣低潮時(shí)采集處于有性繁殖時(shí)期的成體羊棲菜(Hizikiafusiformis)藻體,放入盛有少量海水塑料袋中,用保溫箱(保持溫度為4 ℃)在最短時(shí)間內(nèi)運(yùn)回實(shí)驗(yàn)室。藻體在實(shí)驗(yàn)室內(nèi)室溫(22—25 ℃)和光強(qiáng)約100 μmol m-2s-1(光周期L∶D為12 h∶12 h)的條件下用過(guò)濾的自然海水進(jìn)行暫養(yǎng),每天24 h 通空氣。以暫養(yǎng)期間的第2天至第5天內(nèi)的羊棲菜作為實(shí)驗(yàn)材料。實(shí)驗(yàn)前分別收集羊棲菜的葉狀體(羊棲菜“葉片”)、雌生殖托、雄生殖托,在海水中放置2 h(通空氣)后,進(jìn)行干出失水與恢復(fù)的實(shí)驗(yàn)研究。

1.2 藻體的干出處理與失水率的測(cè)定

實(shí)驗(yàn)時(shí)將羊棲菜各部分藻體(葉狀體、雌生殖托、雄生殖托)從海水中取出,置于實(shí)驗(yàn)臺(tái)上,藻體從而處于干出狀態(tài)下,輕輕地用吸水紙吸去藻體表面的可見(jiàn)水珠。把各部分藻體平鋪于培養(yǎng)皿中 (每 1 cm2面積放置1.0 g初始濕重的藻量),于室溫25 ℃左右、相對(duì)濕度約70%的實(shí)驗(yàn)室里自然失水,每隔1 h測(cè)定培養(yǎng)皿中藻體的重量,每個(gè)處理設(shè)置5個(gè)重復(fù)。

藻體水分損失率(Water loss,WL) 的確定,按公式WL%=(Wo-Wt)/(Wo-Wd) × 100計(jì)算。其中Wo為初始濕量(g),Wt為經(jīng)過(guò)一段時(shí)間干燥后的重量(g),Wd為干重(即在實(shí)驗(yàn)后于80 ℃烘箱中放置24 h的烘干重)。在藻體脫水過(guò)程中進(jìn)行葉綠素?zé)晒鈪?shù)的測(cè)定,每個(gè)處理設(shè)置5個(gè)重復(fù)。

1.3 藻體的恢復(fù)實(shí)驗(yàn)

當(dāng)羊棲菜各部分藻體(葉狀體、雌生殖托、雄生殖托)干出至脫水率約為50%和75%,藻體重新置于實(shí)驗(yàn)室內(nèi)海水中,進(jìn)行藻體葉綠素?zé)晒鈪?shù)的恢復(fù)實(shí)驗(yàn)?；謴?fù)條件為室溫(22—25 ℃)和光強(qiáng)約100 μmol m-2s-1,培養(yǎng)海水為過(guò)濾的自然海水(通氣)。在藻體恢復(fù)過(guò)程中定期進(jìn)行葉綠素?zé)晒鈪?shù)的測(cè)定,每個(gè)處理設(shè)置5個(gè)重復(fù)。

1.4 熒光參數(shù)的測(cè)定

羊棲菜不同組織的葉綠素?zé)晒鈪?shù)用脈沖調(diào)制熒光儀(WATER-PAM,德國(guó)產(chǎn))進(jìn)行測(cè)定。向干出狀態(tài)下不同脫水程度的葉狀體、雌生殖托和雄生殖托連續(xù)照射8個(gè)光強(qiáng)梯度的光化光(66—1000 μmol m-2s-1,光源為熒光燈),照射時(shí)間間隔為10 s,得到快速光曲線(Rapid Light Curve, RLC),通過(guò)計(jì)算可得出光系統(tǒng)II的有效光化學(xué)量子產(chǎn)量(Photosystem II effective quantum yield, Y(II))、最大相對(duì)電子傳遞速率(Maximum relative electron transport rate,rETRmax)、光能利用效率(Light use efficiencies, α)和耐受光強(qiáng)(Tolerance of high irradiance, Ik)。計(jì)算公式分別為：

rETR=I ×Y(II) × 0.84 × 0.5,其中I表示光合有效輻射,0.84表示I被光合色素吸收的比例,0.5表示分配到PS II的I比例,rETR反映了經(jīng)過(guò)PS II的相對(duì)線性電子流速率[30]。

對(duì)RLC的非線性曲線擬合公式為：rETR=rETRmax× tanh (α× I /rETRmax)[31],其中rETRmax為最大相對(duì)電子傳遞速率,被認(rèn)為是對(duì)PS II實(shí)際電子傳遞速率的實(shí)時(shí)反應(yīng)；α為RLC的初始斜率,表示藻體的光能利用效率。

耐受光強(qiáng)Ik=rETRmax/ α, Ik越高,植物對(duì)強(qiáng)光的耐受力越強(qiáng)[30]。

1.5 統(tǒng)計(jì)與分析

采用SPSS 19.0和OriginPro 8.5 (Origin Lab Crop., USA)軟件進(jìn)行數(shù)據(jù)分析,應(yīng)用One-way ANOVA分析不同試驗(yàn)處理間的差異,設(shè)置顯著水平為P<0.05。

2 結(jié)果

2.1 脫水條件

圖1 羊棲菜不同部位藻體的光系統(tǒng)Ⅱ(PS Ⅱ)有效光化學(xué)量子產(chǎn)量隨失水率的變化(n=5)Fig.1 Changes of photosystem II (PS II) effective quantum yield [Y(II)] in different tissues of Hizikia fusiformis with increased water loss during emersion (n=5)

羊棲菜不同部位藻體的PS II有效光化學(xué)量子產(chǎn)量[Y(II)]與藻體脫水率的關(guān)系如圖1所示。羊棲菜葉狀體和雌、雄生殖托的干出脫水率分別不超過(guò)73%和64%、60%時(shí),其Y(II)都沒(méi)有明顯變化(P>0.05),且不同部位的藻體Y(II)間沒(méi)有顯著差異(P>0.05)。但繼續(xù)干出脫水就導(dǎo)致藻體的Y(II)顯著降低(P<0.05),當(dāng)葉狀體和雌、雄生殖托的脫水率分別達(dá)到84%和90%、79%時(shí),其Y(II)分別為0.27±0.12和0.02±0.02、0.00±0.01,分別下降了57%和97%、99%。

由圖2可以看出,羊棲菜藻體的不同部位的相對(duì)電子傳遞速率(rETR)都先隨光強(qiáng)的升高而快速上升,當(dāng)光強(qiáng)高于600 μmol m-2s-1后基本達(dá)到平穩(wěn)狀態(tài)(圖2)。由表1可以看出,在干出初始(0)時(shí),雌、雄生殖托的rETRmax、α都略高于葉狀體的,但未達(dá)到統(tǒng)計(jì)學(xué)上的顯著水平(P>0.05),雌、雄生殖托的耐受光強(qiáng)(Ik)沒(méi)有差別(P>0.05),而都顯著低于葉狀體的Ik(P<0.05)。在藻體干出脫水率達(dá)50%時(shí),羊棲菜藻體不同部位的α保持穩(wěn)定,而rETRmax和Ik都明顯下降(P<0.05)；此時(shí)藻體不同部位間的rETRmax和α差異不顯著,雌、雄生殖托的Ik也無(wú)顯著差異,但都明顯低于葉狀體的Ik(P<0.05)。當(dāng)藻體繼續(xù)干出至嚴(yán)重脫水(75%)時(shí),與干出初始狀態(tài)相比,葉狀體和雌、雄生殖托的rETRmax分別降低了33%,67%和78%(P<0.05),α分別降低了16%、42%和59%(P<0.05),不同部位的參數(shù)間差異明顯(P<0.05),葉狀體的最高,雌生殖托次之,雄生殖托最低。

圖2 羊棲菜不同部位藻體分別在失水0(A)、50%(B)、75%(C)條件下相對(duì)電子傳遞速率的快速光響應(yīng)曲線(n=5)Fig.2 The rapid light curve of relative electron transport rate (rETR) in different tissues of emersed Hizikia fusiformis at 0 (A), 50% (B), and 75% (C) water loss (n=5)

Table1ParametersoftherapidlightcurveindifferenttissuesofemersedHizikiafusiformisat0,50%,and75%waterloss(n=5)

羊棲菜藻體TissuesofH.fusifor-mis失水率Waterloss/%最大相對(duì)電子傳遞速率Maximumrelativeelectrontransportrate/(μmolelectronsm-2s-1)光能利用效率Lightuseefficiencies耐受光強(qiáng)Toleranceofhighirradiance/(μmolm-2s-1)葉狀體Fronds0122.21±4.98a*0.19±0.02a691.25±43.35a50109.43±9.55b0.19±0.01a580.98±50.70b7581.90±7.26c0.16±0.01b514.96±45.66c雌生殖托0129.63±5.37a0.24±0.02a533.22±39.50bcFemalereceptacles50107.95±6.80b0.21±0.01a511.09±32.17c7543.13±7.30d0.14±0.01b315.04±53.33d雄生殖托0129.49±5.68a0.22±0.01a593.66±40.29bMalereceptacles5098.65±9.08b0.21±0.02a470.07±43.29c7527.85±4.30e0.09±0.01c301.35±46.53d

*顯著性水平為0.05,用不同字母表示

2.2 復(fù)水條件

圖3 羊棲菜不同部分藻體在失水50%后的沉水恢復(fù)過(guò)程中光系統(tǒng)Ⅱ(PSⅡ)有效光化學(xué)量子產(chǎn)量的變化(n=5)Fig.3 The recovery of photosystem II (PS II) effective quantum yield [Y(II)] in different tissues of Hizikia fusiformis at 50% water loss (n=5)

圖4 羊棲菜不同部位藻體在失水75%后的沉水恢復(fù)過(guò)程中光系統(tǒng)Ⅱ(PSⅡ)有效光化學(xué)量子產(chǎn)量的變化(n=5)Fig.4 The recovery of photosystem II (PS II) effective quantum yield [Y(II)] in different tissues of Hizikia fusiformis at 75% water loss (n=5)

由圖3可知,當(dāng)羊棲菜藻體失水50%時(shí),其不同部位的Y(II)都能維持較高水平,與脫水初始狀態(tài)(0)時(shí)沒(méi)有顯著差異(P>0.05),葉狀體的Y(II)略高于雌、雄生殖托的Y(II),但未達(dá)到顯著水平(P>0.05)。在沉水恢復(fù)2 h內(nèi),葉狀體的Y(II)沒(méi)有明顯變化,而雌、雄生殖托的Y(II)快速(0.5 h)升高到干出初始時(shí)的Y(II)水平。

由圖4可知,當(dāng)羊棲菜藻體失水75%時(shí),葉狀體和雌、雄生殖托的Y(II)分別降低12%、31%和37%。在沉水恢復(fù)過(guò)程中,在0.5 h時(shí)葉狀體和雌、雄生殖托的Y(II)都有所升高,在隨后的幾個(gè)小時(shí)的恢復(fù)過(guò)程中,葉狀體的Y(II)有小幅度下降而后保持穩(wěn)定,維持在0.56±0.04。雌、雄生殖托在0.5—8 h的恢復(fù)過(guò)程中表現(xiàn)出持續(xù)下降的趨勢(shì),18 h后下降到0.3；雌生殖托在沉水恢復(fù)開(kāi)始階段Y(II)已經(jīng)低于0.4,而復(fù)水18 h時(shí)降低到0.15。這表明羊棲菜葉狀體的Y(II)能恢復(fù)到初始水平,脫水耐受能力強(qiáng)；而生殖托的Y(II)無(wú)法恢復(fù)初始水平,其耐受脫水能力較差。

3 討論

在限制光合生物生長(zhǎng)的眾多因子中,水分是最重要的因子[9]。生長(zhǎng)于低潮帶的海藻羊棲菜在低潮時(shí),特別是在大潮低潮時(shí),將暴露在空氣中長(zhǎng)達(dá)4 h。由于海藻不具有陸生高等植物的氣孔或蠟質(zhì)角質(zhì)層那樣的可減小水分損失的解剖結(jié)構(gòu),因此,羊棲菜在低潮干出狀態(tài)下,將發(fā)生干燥失水作用,即水分從藻體表面水膜或細(xì)胞內(nèi)散化至大氣中[32]。本文結(jié)果表明,羊棲菜葉狀體PS II的Y(II)在干出脫水率為0—73%范圍內(nèi)沒(méi)有顯著差異,這與高潮帶海藻條斑紫菜(Porphyrayezoensis)類(lèi)似,其的Y(II)下降的脫水率的界限值達(dá)到60%[15]。而羊棲菜干出至半脫水(50%)狀態(tài)下,最大相對(duì)電子傳遞速率(rETRmax)和耐受光強(qiáng)(Ik)都顯著降低,而Y(II)和光合效率(α)與干出初始狀態(tài)沒(méi)有明顯差異,這可能是羊棲菜藻體通過(guò)增加了光能耗散和降低光合電子傳遞速率,保護(hù)PS II反應(yīng)中心[8, 33]。對(duì)羊棲菜葉狀體光合放氧對(duì)干出脫水響應(yīng)的研究結(jié)果也證實(shí)了這一點(diǎn),受現(xiàn)有大氣CO2水平的限制,葉狀體光合放氧速率隨著干出脫水率的增加而降低[23],脫水率為50%時(shí)其光飽和光合速率下降72%,光合固碳所需的同化力顯著降低,藻體通過(guò)降低色素含量和使PS II反應(yīng)中心部分可逆失活來(lái)維持光能吸收和光能利用的平衡[34- 36]。石莼對(duì)干出的響應(yīng)也類(lèi)似,干出脅迫導(dǎo)致石莼激活的PS II反應(yīng)中心的數(shù)量下降,藻體對(duì)光的利用能力下降,表現(xiàn)為耐受光強(qiáng)下降[19]。另一方面,Beer和Rahnberg發(fā)現(xiàn)適量失水能夠減小藻體表面水層厚度,降低CO2溶解阻力,從而增加海藻的光合效率[37],也有助于維持海藻的Y(II)和α的穩(wěn)定。

當(dāng)繼續(xù)脫水至失水75%時(shí),藻體Y(II)、rETRmax、α和Ik都明顯下降,表明其PSII反應(yīng)中心受到顯著脅迫作用。在隨后的復(fù)水恢復(fù)過(guò)程中,藻體的Y(II)未能升高甚至持續(xù)降低,可能是嚴(yán)重脫水致使細(xì)胞內(nèi)產(chǎn)生并累計(jì)了大量活性氧(ROS)自由基[34, 38],ROS損傷了PS II反應(yīng)中心的D1蛋白和葉綠素,致使電子傳遞受阻,而在恢復(fù)過(guò)程中需重新合成D1蛋白和色素使得Y(II)難以在短期內(nèi)恢復(fù)[39-40]。甚至,有些海藻在較強(qiáng)脅迫下光合色素分解,并可能發(fā)生質(zhì)膜融合,光合結(jié)構(gòu)被破壞[41],即使復(fù)水也無(wú)法恢復(fù)其光合能力。因此,羊棲菜葉狀體耐受脫水能力上限為73%。相關(guān)研究表明,潮間帶海藻脫水耐受能力與其垂直生態(tài)位相關(guān),潮間帶上部區(qū)域的海藻耐脫水能力更強(qiáng)[14],如潮間帶邊緣海藻Fucusserratuss耐受60%的脫水率,掌狀海帶(Laminariadigitata)可以耐受55%的脫水率[20],而潮間帶上部的海藻條斑紫菜(Porphyrayezoensis)、溝鹿角菜(Pelvetiacanaliculata)和Fucusspiralis的可耐受高達(dá)90%的脫水率[15, 42-43]。這種脫水耐受能力與光合作用相關(guān)酶周?chē)姆肿迎h(huán)境有關(guān),包括無(wú)機(jī)鹽濃度、多糖組成、CO2濃度等,該分子環(huán)境的重要性是降低質(zhì)膜破裂的風(fēng)險(xiǎn),同時(shí)促進(jìn)細(xì)胞內(nèi)必需水分的滯留,從而維持海藻一定的光合作用能力[36, 44]。而本研究結(jié)果表明羊棲菜的脫水耐受能力甚至強(qiáng)于一般潮間帶海藻,這可能是由于同種海藻在不同環(huán)境下適應(yīng)后所反映出干出脫水耐受能力也有差異[34]。

對(duì)羊棲菜雌、雄生殖托干出過(guò)程中脫水耐受性的研究表明,其葉綠素?zé)晒鈩?dòng)力學(xué)參數(shù)對(duì)脫水率增加的響應(yīng)表現(xiàn)出與葉狀體相似的變化趨勢(shì)。在生殖托干出脫水率為0—60%范圍內(nèi),其Y(II)沒(méi)有顯著變化,生殖托干出至半脫水(50%)時(shí),其而rETRmax、α以及Ik顯著降低,說(shuō)明此時(shí)羊棲菜生殖托的PS II受到干出的脅迫作用,但并未受到損傷,藻體可以通過(guò)一系列的保護(hù)機(jī)制來(lái)維持PS II反應(yīng)中心活性。這與P.yezoensis的雄性細(xì)胞對(duì)失水的耐受能力接近,脫水50%時(shí)的條斑紫菜雄性細(xì)胞光合活性不受影響[15]。也與羊棲菜葉狀體的并無(wú)顯著差異。但是脫水率繼續(xù)上升,雌、雄生殖托的Y(II)明顯降低,嚴(yán)重失水至75%時(shí),雌、雄生殖托的rETRmax、α和Ik都急劇下降,復(fù)水后Y(II)不能恢復(fù)甚至持續(xù)降低,且雄生殖托的Y(II)、rETRmax、α和Ik都顯著低于雌生殖托,表明此時(shí)雌、雄生殖托的PS II都受到了不可逆的損傷。因此,羊棲菜生殖托也具有較強(qiáng)的脫水耐受能力,其Y(II)下降的脫水率界限約為50%,顯著低于葉狀體。這可能是由生殖托和葉狀體的生理結(jié)構(gòu)的差異導(dǎo)致的,生殖托的含水量低于葉狀體的含水量,因此失去相同比例的水分對(duì)生殖托的光合活性的影響較大[27]。另一方面,雖然羊棲菜生殖托的光飽和光合速率比葉狀體高[45],但是一般大型海藻如Sargassumintegerrium[35]和Porphyrayezoensis[15]的營(yíng)養(yǎng)器官具有比生殖器官或幼孢子體更強(qiáng)的抗逆能力,也是導(dǎo)致羊棲菜生殖托比葉狀體對(duì)干旱脅迫的響應(yīng)更加敏感的原因之一。在相同干出脫水程度下,雌生殖托的Y(II)一直顯著高于雄生殖托的Y(II)。且在脫水率為50%和75%時(shí)下,雌生殖托的rETRmax,α和Ik均顯著高于雄生殖托的對(duì)應(yīng)值,隨后的沉水恢復(fù)過(guò)程中,雖然雌、雄生殖托的Y(II)都由于嚴(yán)重脫水的不可逆損傷而無(wú)法恢復(fù)到干出初始水平,但是雌生殖托的Y(II)依然高于雄生殖托的。這與Dring等[20]對(duì)褐藻的研究結(jié)果一致,干出脫水對(duì)雄生殖托的損傷較雌生殖托的大。所有這些結(jié)果表明,在干出脫水過(guò)程中,雌生殖托的光合活性高于雄生殖托,且持續(xù)大幅度脫水(WL>60%)時(shí),雌生殖托耐脫水能力強(qiáng)于雄生殖托。因此,嚴(yán)重干出脫水對(duì)雄生殖托的影響更大。

雖然在自然生境中低潮時(shí),羊棲菜在空氣中暴露1—4 h,持續(xù)飛濺的水和泡沫一定程度上會(huì)降低海藻的干出脫水程度,藻體失水率最高僅達(dá)50%[23]。羊棲菜葉狀體和生殖托的PS II反應(yīng)中心通過(guò)降低PS II電子傳遞效率、可逆失活增強(qiáng)光耗散來(lái)維持較高的Y(II),充分抵御失水的脅迫,被認(rèn)為時(shí)一種內(nèi)損耗的被動(dòng)適應(yīng)方式[33, 45]。這種應(yīng)對(duì)干出的策略無(wú)法兼顧光合速率,同時(shí)容易受到其他環(huán)境因子如光照強(qiáng)度、溫度和營(yíng)養(yǎng)鹽供應(yīng)等影響[33- 35]。從這個(gè)意義上講,盡管羊棲菜PS II反應(yīng)中心脫水耐受能力較高,但其應(yīng)對(duì)脫水脅迫的策略對(duì)光合能力和生長(zhǎng)不利,因此,羊棲菜在栽培過(guò)程中要減少干出時(shí)間,延長(zhǎng)沉水生長(zhǎng)時(shí)間,促進(jìn)其快速光合作用和生長(zhǎng)。

綜上所述,羊棲菜藻體有很高的干出脫水耐受能力,葉狀體要高于生殖托,雄生殖托要高于雌生殖托。大幅度脫水不會(huì)損傷羊棲菜葉狀體的PS II反應(yīng)中心,葉狀體PS II活性對(duì)脫水脅迫的耐受能力甚至超過(guò)一般潮間帶海藻,接近高潮位的海藻。而半脫水也不影響羊棲菜生殖托的PS II活性,大幅度脫水會(huì)嚴(yán)重降低生殖托的PS II活性,且該損傷不可逆。因此,在羊棲菜的有性生殖階段,嚴(yán)重的干出脫水是影響羊棲菜有性繁殖成功的一個(gè)重要因素。

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EffectsofdesiccationonchlorophyllfluorescencecharacteristicsinthefrondsandreceptaclesofemersedHizikiafusiformisandtheirrecoveryuponre-submersion

WANG Longle1, ZHANG Xin2, ZOU Dinghui1,3,*, CHEN Binbin1

1SchoolofEnvironmentandEnergy,SouthChinaUniversityofTechnology,Guangzhou510006,China2TheScienceandTechnologyDavision,SouthChinaUniversityofTechnology,Guangzhou510006,China3GuangdongProvincialKeyLaboratoryofAtmosphericEnvironmentandPollutionControl,Guangzhou510006,China

The fronds and reproductive tissues (female and male receptacles) of intertidal-grownHizikiafusiformisexposed to air and faced desiccation when the tide is low during sexual reproduction period. In this study, we determined photosystem II (PS II) effective quantum yield [Y(Ⅱ)] and the parameters of rapid light curves of desiccation tissues: fronds, and female and male receptacles, at different desiccated states. We also measured Y(II) of desiccation tissues upon rewetting after 50% and 75% water loss. Our objective was to reveal whether there are differences of desiccation tolerance or not among fronds and reproductive tissues ofH.fusiformiswhen exposed to air during sexual reproduction period. The results showed that Y(II) exhibited no significant changes within the range of 0—73% water loss from fronds, and within the range of 0—60% water loss from female and male receptacles. However, the values of Y(II) were sharply reduced with the water loss more than 73% in fronds, and more than 60% in receptacles. Severe dehydration of 75% water loss reduced Y(II) values by 12%, 31%, and 37% in fronds, and female and male receptacles, respectively. The values of Y(II) of submersed tissues (fronds and receptacles) followed by 50% always remained high levels. However, the values of Y(II) of both severe-desiccated female and male receptacles could not recover, and continued to decrease even after re-submersion, suggesting that the PS II reaction center in receptacles ofH.fusiformisunderwent irreversible damage when water loss reached up to 75%. Our results showed that PS II reaction center in fronds ofH.fusiformisexhibited greater desiccation tolerance of than that in receptacles. The maximum relative electron transport rates (rETRmax), light use efficiency (α), and the tolerance of high irradiance (Ik) for emersed fronds and receptacles ofH.fusiformisexhibited no significantly differences at the initial desiccation state. BothrETRmaxand Ikdecreased significantly with increased water loss. Particularly,rETRmaxwere reduced by 33%, 67%, and 78% in fronds, and female and male receptacles, respectively, after 75% of water loss. Furthermore, α were hardly affected by 50% of water loss, but it were reduced by 16%, 42%, and 59% of their initial value when fronds, and female and male receptacles lost 75% water, respectively. The values of Y(II),rETRmax, Ik, and α of the fronds were higher than those of the receptacles, and the parameters of the female receptacles were always higher than those of the male receptacles after 60% water loss of desiccation tissues under emersed state, and the results showed the same trends when followed by submersed state. Those indicated that male receptacles were the most susceptible, while the fronds were relative less susceptible by severe dehydration. It was concluded that severe desiccation is an important factor affecting the reproduction success ofH.fusiformisduring the sexual reproduction period, and the factors alleviating desiccation such as sea spray and shingle-overlapping would benefit the emersed fronds and receptacles ofH.fusiformis.

Hizikiafusiformis; emersion; desiccation; chlorophyll fluorescence; fronds; receptacles; sexual reproduction

廣東省科技計(jì)劃項(xiàng)目(2016A020222001)；中國(guó)博士后科學(xué)基金面上資助(2016M592483)

2016- 09- 22; < class="emphasis_bold">網(wǎng)絡(luò)出版日期

日期:2017- 07- 12

*通訊作者Corresponding author.E-mail: dhzou@scut.edu.cn

10.5846/stxb201609221912

王龍樂(lè),張?chǎng)?鄒定輝,陳斌斌.干出脫水對(duì)羊棲菜葉狀體與生殖托熒光特性的影響及其在沉水狀態(tài)下的恢復(fù).生態(tài)學(xué)報(bào),2017,37(22):7710- 7717.

Wang L L, Zhang X, Zou D H, Chen B B.Effects of desiccation on chlorophyll fluorescence characteristics in the fronds and receptacles of emersedHizikiafusiformisand their recovery upon re-submersion.Acta Ecologica Sinica,2017,37(22):7710- 7717.