張巧玉 王逸茹 安 靜 王保民 田曉莉

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根-冠互作對棉花葉片衰老的影響

張巧玉 王逸茹 安 靜 王保民 田曉莉*

中國農(nóng)業(yè)大學(xué)農(nóng)學(xué)院作物化控研究中心/ 植物生理學(xué)與生物化學(xué)國家重點(diǎn)實(shí)驗(yàn)室, 北京 100193

嫁接研究和實(shí)踐表明, 植物不同生理過程普遍存在根-冠互作的多樣性。作者曾以衰老較快的棉花品種中棉所41和衰老較慢的品種魯棉研22為材料進(jìn)行嫁接研究, 發(fā)現(xiàn)地上部對葉片衰老起主要作用。本文以中棉所41和另一個衰老較慢的品種中棉所49為材料進(jìn)行普通嫁接(I型, 單接穗單砧木)和Y型嫁接(雙接穗單砧木), 用低鉀脅迫(0.03 mmol L–1)誘導(dǎo)葉片衰老, 結(jié)果表明I型嫁接中以中棉所41為砧木的處理, 其倒四葉SPAD值顯著低于以中棉所49為砧木的處理, 提示根系對葉片衰老的作用較大。相應(yīng)地, 以中41為砧木的處理, 其根系和葉片中的ZR+Z和iPA+iP濃度及砧木和接穗木質(zhì)部汁液中的ZR+Z和iPA+iP流量在絕大多數(shù)情況下顯著低于以中49為砧木的處理, ABA的結(jié)果則相反。Y型嫁接的結(jié)果與I型嫁接相似, 但根系對葉片衰老的作用未表現(xiàn)出絕對優(yōu)勢。從根-冠-根通訊的角度對葉片衰老的根-冠互作類型多樣性進(jìn)行了討論。

棉花; 嫁接; 葉片; 衰老; 根-冠互作

葉片衰老是其發(fā)育的最后一個階段, 被認(rèn)為是一種程序性細(xì)胞死亡(PCD), 對植株將成熟葉片中積累的物質(zhì)分解并運(yùn)送至其他生長旺盛的部位進(jìn)行再利用非常關(guān)鍵[1-2]。棉花熟相包括正常成熟、早衰和貪青晚熟3種[3], 主要根據(jù)葉片衰老進(jìn)程和吐絮速率的關(guān)系劃分, 對棉花生產(chǎn)具有重要的指導(dǎo)意義。

葉片衰老受植物激素的調(diào)控, 細(xì)胞分裂素(CK)一般可以延緩葉片衰老[4-5], 而脫落酸(ABA)往往對葉片衰老起促進(jìn)作用[6-8]。CK在植物根尖合成是一個普遍接受的事實(shí)[9-14], 根系合成的CK可以通過木質(zhì)部運(yùn)輸至葉片, 并調(diào)節(jié)葉片衰老[15-17]。根系也是ABA的重要合成部位[18], 之后ABA在蒸騰流的驅(qū)動下通過木質(zhì)部導(dǎo)管向葉片中輸送[19]。嫁接試驗(yàn)也表明根系是棉花[20]和番茄[21-23]葉片衰老的主要決定部位。然而, 也有試驗(yàn)得到不同的結(jié)果。豌豆[24]和擬南芥[25]的地上部具有調(diào)節(jié)根系輸出CK的能力, Gan和Amasino[5]及Faiss等[26]發(fā)現(xiàn), 過量合成CK的砧木未能延緩接穗葉片的衰老。Koeslin-Findeklee等[27]的嫁接試驗(yàn)表明, 冬油菜在氮饑餓條件下的持綠表型主要受葉片控制。衰老較快的棉花品種中棉所41和衰老較慢的品種魯棉研22互相嫁接時發(fā)現(xiàn), 地上部是決定棉花葉片衰老(缺鉀誘導(dǎo))的主要部位[28-29]。引人注意的是, 中棉所41與另一個衰老較慢的棉花品種中棉所49互相嫁接時, 根系對葉片衰老的決定作用又占據(jù)了優(yōu)勢[30]?？梢? 葉片衰老的根-冠互作類型存在多樣性, 但其在根-冠-根之間的通訊機(jī)制尚不明確。

本文采用單砧木單接穗(I型)和單砧木雙接穗(Y型)嫁接方式比較系統(tǒng)地研究了中棉所41與中棉所49互相嫁接的根系、木質(zhì)部汁液和葉片中的活性CK及游離態(tài)ABA的水平, 并討論了根系為主型和地上部為主型調(diào)控葉片衰老的根-冠-根通訊機(jī)制。研究結(jié)果可為揭示葉片衰老的生理機(jī)制提供部分依據(jù), 并可為棉花生產(chǎn)中制定防早衰措施提供一定指導(dǎo)。

1 材料與方法

供試棉花品種中棉所41 (衰老較快, 以下簡稱中41或41)和中棉所49 (衰老較慢, 以下簡稱中49或49)由中國農(nóng)業(yè)科學(xué)院棉花研究所提供。

1.1 試驗(yàn)材料的培養(yǎng)

試驗(yàn)于中國農(nóng)業(yè)大學(xué)光照培養(yǎng)室中進(jìn)行, 光照強(qiáng)度為400 μmol cm–2s–1, 光照/黑暗時間為14 h/10 h, 晝/夜溫度為(28±2)℃/(22±2)℃, 相對濕度為70%~80%。種子經(jīng)10%雙氧水消毒15 min清洗數(shù)遍后, 置去離子水中浸24 h, 露白后播于沙床, 出苗2 d后轉(zhuǎn)移至K+濃度為0.1 mmol L–1的1/2改良Hoagland’s營養(yǎng)液中培養(yǎng), 營養(yǎng)液配方(mmol L–1) 為2.5 Ca(NO3)2, 1 MgSO4, 0.5 (NH4)H2PO4, 2×10–4CuSO4, 1×10–3ZnSO4, 0.1 Fe Na EDTA, 2×10–2H3BO3, 5×10–6(NH4)6Mo7O24和1×10–3MnSO4。營養(yǎng)液培養(yǎng)所用容器為16 cm×13 cm×16 cm的塑料盒, 幼苗基部用海綿包裹, 以預(yù)先打好孔的聚乙烯泡沫板固定于塑料盆上, 每盒4株。每塑料盒裝入營養(yǎng)液2.2 L, 每4 d更換營養(yǎng)液一次, 用氣泵24 h通氣。

1.2 嫁接處理

砧木移入營養(yǎng)液中培養(yǎng)時播種接穗, 當(dāng)砧木第1片真葉展開、接穗子葉完全展開時嫁接。參照李博等[31]的方法對2個品種進(jìn)行I型(單砧木單接穗, 表示為接穗/砧木)和Y型[單砧木雙接穗, 表示為(接穗+接穗)/砧木]嫁接。I型嫁接共4個處理, 分別為41/41、49/49、41/49、49/41; Y型嫁接的4個處理為(41+41)/41、(49+49)/49、(41+49)/41、(41+49)/49。隨機(jī)區(qū)組排列, 重復(fù)4次, 每重復(fù)3盒, 每盒4株。

將嫁接苗置刺有若干小孔的保鮮袋內(nèi)(注意避免葉片與保鮮袋直接接觸), 放在光強(qiáng)為80~100 μmol cm?2s?1、晝夜溫度為29℃/20℃的條件下緩苗, 5 d后揭掉保鮮袋, 7 d后移至400 μmol cm?2s?1光強(qiáng)下開始低鉀脅迫(0.03 mmol L–1)誘導(dǎo)衰老, 以充足供鉀(2.5 mmol L–1)為對照。

1.3 葉綠素含量測定

嫁接植株培養(yǎng)至七至八葉期時, 用SPAD-502葉綠素儀(浙江托普儀器有限公司, 中國杭州)測定各處理所有植株功能葉(倒四葉)葉綠素的相對含量, 每個葉片測量20點(diǎn), 取平均值。

1.4 根系和葉片取樣及木質(zhì)部汁液收集

測完葉綠素含量后, 取下倒四葉用去離子水沖洗干凈, 吸水紙吸干水分, 稱取0.2 g, 置–40℃冰箱中待測。

取完葉片后分別在嫁接位點(diǎn)上部(接穗下胚軸)和嫁接位點(diǎn)下部(砧木下胚軸)采用壓力室法[32]收集木質(zhì)部汁液, 所用壓力室為SEC 3005 plant Water Status Console (Soilmoisture Equipment Corp., CA, USA)。各處理2個部位同時收集, 每個部位收集4株, 重復(fù)3次。收集前用去離子水沖洗切面, 之后將干凈的氣門芯套緊在切斷的下胚軸上。設(shè)置壓力為3 bar, 收集時間為0.5 h。記錄每株收集到的木質(zhì)部汁液體積, 然后將同一處理的各株收集液混合。將一定體積收集液轉(zhuǎn)入離心管放置在–80℃低溫冰箱中冷凍48 h以上, 用凍干機(jī)(SIM FD5-6, LA, USA)凍干后貯存在–40℃待測。

選擇未進(jìn)行木質(zhì)部汁液收集的代表性植株, 剪取2~3 cm長的側(cè)根, 以去離子水沖洗并用吸水紙吸干水分, 剪碎混勻后稱取0.2 g, 置于–40℃冰箱中待測。

1.5 ABA和CKs的測定

取倒四葉和根系鮮重0.2 g, 冰浴下加入80% (v/v)甲醇溶液[含1 mmol L–1丁基羥基苯甲醚和1% (w/v) PVP]研磨, 4℃下提取4 h以上, 然后在4℃下離心15 min (4000轉(zhuǎn)min–1), 取上清液用氮?dú)獯蹈? 保存殘留物于–40℃冰箱待測。

用樣品稀釋液(含NaCl 137 mmol L–1, KCl 2.7 mmol L–1, Na2HPO410 mmol L–1, KH2PO42 mmol L–1)溶解上述凍干的木質(zhì)部汁液和氮?dú)獯蹈傻娜~片及根系提取物, 采用間接酶聯(lián)免疫吸附法(ELISA)測定樣品中的游離態(tài)ABA和ZR(玉米素核苷)及iPA(異戊烯基腺嘌呤核苷)等活性CK含量, 單克隆抗體由中國農(nóng)業(yè)大學(xué)作物化學(xué)控制研究中心制備[33]。由于ZR和iPA單克隆抗體分別與Z (玉米素)和iP (異戊烯基腺嘌呤)存在交叉反應(yīng), 因此實(shí)際測定結(jié)果為ZR+Z和iPA+iP的含量。

1.6 數(shù)據(jù)統(tǒng)計

I型和Y型嫁接試驗(yàn)均經(jīng)過3次以上重復(fù), 各次結(jié)果趨勢一致, 本文選用其中具有代表性的一次。利用SAS Ver.8 (SAS Institute Inc., Cary, NC, USA)進(jìn)行方差分析, 用Duncan’s法進(jìn)行多重比較。

1.7 砧木和接穗效應(yīng)計算

砧木和接穗效應(yīng)是指某一品種在互相嫁接處理中作為砧木或接穗時與另一個品種自身嫁接的對比。葉片SPAD值、植物激素水平及接穗木質(zhì)部汁液中植物激素水平與葉片衰老關(guān)系密切, 其砧木和接穗效應(yīng)計算公式如下, 其中粗體標(biāo)出的接穗為參與計算的接穗。

I型嫁接:

49砧木效應(yīng)= (41/49–41/41)/(41/41)

49接穗效應(yīng)= (49/41–41/41)/(41/41)

41砧木效應(yīng)=(49/41–49/49)/(49/49)

41接穗效應(yīng)=(41/49–49/49)/(49/49)

Y型嫁接:

49砧木效應(yīng) =[(41+49)/49–(41+41)×?/41]/[(41+41)×?/41]

49接穗效應(yīng) =[(41+49)/41–(41+41)/41]/[(41+41)/41]

41砧木效應(yīng) =[(41+49)/41–(49+49)×?/49]/[(49+49)×?/49]

41接穗效應(yīng) =[(41+49)/49–(49+49)/49]/[(49+49)/49]

2 結(jié)果與分析

2.1 葉片SPAD值

由圖1和表1可知, 充足供鉀條件下I型和Y型嫁接各處理接穗倒四葉的葉色和SPAD值無顯著差異, 說明在正常條件下中41和中49的葉片衰老程度基本一致。低鉀條件下, I型嫁接各處理倒4葉的SPAD平均值較充足供鉀條件下降低了44%, Y型嫁接降低了40% (表1), 說明低鉀脅迫下葉片出現(xiàn)衰老現(xiàn)象(圖2)。此外, 低鉀條件下以中41為砧木的嫁接處理倒四葉的SPAD值低于以中49為砧木的處理, 其中I型嫁接達(dá)到顯著水平, Y型嫁接差異不顯著, 各處理葉片衰老程度(圖2)與SPAD值結(jié)果一致。

低鉀條件下, 中41和中49在I型嫁接中對葉片SPAD值的砧木效應(yīng)和接穗效應(yīng)均達(dá)到顯著水平, 其中中41效應(yīng)為負(fù)值, 中49效應(yīng)為正值。2個品種的砧木效應(yīng)均大于接穗效應(yīng)(表2), 反映出砧木對葉片衰老的決定作用大于接穗。Y型嫁接中2個品種的砧木效應(yīng)和接穗效應(yīng)較I型嫁接中為低, 且均不顯著, 但砧木效應(yīng)仍大于接穗效應(yīng)。

表1 供鉀水平對I型和Y型嫁接各處理倒四葉SPAD值的影響

41: 中棉所41; 49: 中棉所49。每列數(shù)據(jù)為粗體接穗的結(jié)果; 各嫁接方式不同嫁接處理平均值后的不同字母表示在0.05水平差異顯著。

41: CCRI41, early senescence under K deficiency; 49: CCRI49, late senescence under K deficiency. The data within the same grafting method followed by the same letter are not significantly different at< 0.05 according to Duncan’s multiple range test.

表2 低鉀條件下(0.03 mmol L–1)不同嫁接方式倒四葉SPAD值的砧木和接穗調(diào)控效應(yīng)

2.2 I型嫁接

與充足供鉀相比, 低鉀脅迫下各嫁接處理倒4葉的平均ZR+Z和iPA+iP濃度分別降低67%和54%, 而ABA濃度增加171% (圖3~圖5), 這與葉片的衰老表型有關(guān)。

從圖3-A、圖4-A和圖5-A可知, 充足供鉀條件下各處理根系和葉片中的ZR+Z、iPA+iP和ABA濃度及砧木和接穗木質(zhì)部汁液中幾種植物激素的流量均無顯著差異。但在低鉀脅迫下, 以中41為砧木的處理, 其根系和葉片中的ZR+Z和iPA+iP濃度及砧木和接穗木質(zhì)部汁液中的ZR+Z和iPA+iP流量在絕大多數(shù)情況下顯著低于以中49為砧木的處理(圖3-B、圖4-B), ABA的結(jié)果則相反(圖5-B)。

從表3可看出, 中41砧木和接穗對ZR+Z和iPA+iP的效應(yīng)為負(fù)值、對ABA的效應(yīng)為正值, 而中49砧木和接穗對ZR+Z和iPA+iP的效應(yīng)為正值、對ABA的效應(yīng)為負(fù)值。砧木效應(yīng)均大于接穗效應(yīng), 且砧木對葉片激素濃度的效應(yīng)均達(dá)到顯著水平, 而接穗效應(yīng)均不顯著(圖3-B、圖4-B、圖5-B)。

A: 充足供鉀(2.5 mmol L–1); B: 低鉀脅迫(0.03 mmol L–1)。同一供鉀水平, 同一部位(指根系、葉片和木質(zhì)部汁液)數(shù)據(jù)后的不同小寫字母表示在0.05水平差異顯著(= 4)。

A: sufficient K (2.5 mmol L–1). B: low K (0.03 mmol L–1). The ZR+Z concentration (ng g–1FW) in roots (R) and the youngest fully expanded leaf (L), and ZR+Z delivery rates (ng plant–124 h–1) in xylem above- (A) and below graft union (B) were determined. Means of the same sampling part (i.e. roots, leaf, and xylem sap collected both below and above the graft union) within the same K level followed by the same letter are not significantly different at< 0.05 according to Duncan’s multiple range test (= 4).

A: 充足供鉀(2.5 mmol L–1); B: 低鉀脅迫(0.03 mmol L–1)。同一供鉀水平, 同一部位(指根系、葉片和木質(zhì)部汁液)數(shù)據(jù)后的不同小寫字母表示在0.05水平差異顯著(= 4)。

A: sufficient K (2.5 mmol L–1). B: low K (0.03 mmol L–1). The iPA+iP concentration (ng g–1FW) in roots (R) and the youngest fully expanded leaf (L), and iPA+iP delivery rates (ng plant–124 h–1) in xylem above- (A) and below graft union (B) were determined. Means of the same sampling part (i.e. roots, leaf, and xylem sap collected both below and above the graft union) within the same K level followed by the same letter are not significantly different at< 0.05 according to Duncan’s multiple range test (= 4).

2.3 Y型嫁接

與充足供鉀相比, 低鉀脅迫下各嫁接處理倒四葉的平均ZR+Z和iPA+iP濃度分別降低86%和51%, 而ABA濃度增加21% (圖6~圖8)。

與I型嫁接相同, 充足供鉀條件下Y型嫁接各處理根系和葉片中的ZR+Z、iPA+iP和ABA濃度及砧木和接穗木質(zhì)部汁液中幾種激素的流量均無顯著差異(圖6-A、圖7-A、圖8-A; 接穗木質(zhì)部汁液中的iPA+iP流量除外)。在低鉀脅迫下, 以中41為砧木的處理, 其根系和葉片中的ZR+Z和iPA+iP濃度及砧木和接穗木質(zhì)部汁液中的ZR+Z和iPA+iP流量低于以中49為砧木的處理(圖6-B、圖7-B), ABA的結(jié)果則相反(圖8-B), 但相當(dāng)多情況下差異未達(dá)到顯著水平。

Fig. 5 Effect of K deficiency on ABA level of cotton standard grafts (scion/rootstock)

A: 充足供鉀(2.5 mmol L–1); B: 低鉀脅迫(0.03 mmol L–1)。同一供鉀水平, 同一部位(指根系、葉片和木質(zhì)部汁液)數(shù)據(jù)后的不同小寫字母表示在0.05水平差異顯著(= 4)。

A: sufficient K (2.5 mmol L–1). B: low K (0.03 mmol L–1). The ABA concentration (ng g–1FW) in roots (R) and the youngest fully expanded leaf (L), and ABA delivery rates (ng plant–124 h–1) in xylem above- (A) and below graft union (B) were determined. Means of the same sampling part (i.e. roots, leaf, and xylem sap collected both below and above the graft union) within the same K level followed by the same letter are not significantly different at< 0.05 according to Duncan’s multiple range test (= 4).

表3 低鉀條件下(0.03 mmol L–1) I型嫁接倒四葉和接穗木質(zhì)部汁液中激素水平的砧木和接穗效應(yīng)

當(dāng)比較低鉀條件下的砧木和接穗效應(yīng)時(表4), 發(fā)現(xiàn)Y型嫁接的砧木和接穗效應(yīng)大多數(shù)情況下較I型嫁接為低, 且中49砧木對中41接穗木質(zhì)部汁液中iPA+iP流量的調(diào)控效應(yīng)不再為正值、對ABA流量的調(diào)控效應(yīng)不再為負(fù)值。此外, 僅中49砧木對中41接穗葉片ZR+Z和ABA濃度的調(diào)控效應(yīng)達(dá)到顯著水平, 其他砧木和接穗效應(yīng)均不顯著(圖6-B、圖7-B、圖8-B)。

3 討論

Li等[28]和Wang等[29]將衰老較快棉花品種中41與衰老較慢品種魯棉研22 (以下簡稱魯22或22)進(jìn)行I型、Y型和A型(單接穗雙砧木)嫁接, 發(fā)現(xiàn)地上部對葉片衰老的決定作用大于根系。而本文結(jié)果顯示, 將中41與另一個衰老較慢的棉花品種中49進(jìn)行I型嫁接, 根系對葉片衰老(以SPAD值表征)的決定作用大于地上部; Y型嫁接的結(jié)果雖然不如I型嫁接明顯, 但表現(xiàn)出相同的趨勢。

A:充足供鉀(2.5 mmol L–1); B: 低鉀脅迫(0.03 mmol L–1)。同一供鉀水平, 同一部位(指根系、葉片和木質(zhì)部汁液)數(shù)據(jù)后的不同小寫字母表示在0.05水平差異顯著(= 4)。

A: sufficient K (2.5 mmol L–1); B: low K (0.03 mmol L–1). The ZR+Z concentration (ng g–1FW) in roots (R) and the youngest fully expanded leaf (L), and ZR+Z delivery rates (ng plant–124 h–1) in xylem above- (A) and below graft union (B) were determined. Means of the same sampling part (i.e. roots, leaf, and xylem sap collected both below and above the graft union) within the same K level followed by the same letter are not significantly different at< 0.05 according to Duncan’s multiple range test (= 4).

A:充足供鉀(2.5 mmol L–1); B: 低鉀脅迫(0.03 mmol L–1)。同一供鉀水平, 同一部位(指根系、葉片和木質(zhì)部汁液)數(shù)據(jù)后的不同小寫字母表示在0.05水平差異顯著(= 4)。

A: sufficient K (2.5 mmol L–1). B: low K (0.03 mmol L–1). The iPA+iP concentration (ng g–1FW) in roots (R) and the youngest fully expanded leaf (L), and iPA+iP delivery rates (ng plant–124 h–1) in xylem above- (A) and below graft union (B) were determined. Means of the same sampling part (i.e. roots, leaf, and xylem sap collected both below and above the graft union) within the same K level followed by the same letter are not significantly different at< 0.05 according to Duncan’s multiple range test (= 4).

采用嫁接方式提高果樹和蔬菜對生物逆境和非生物逆境的抗性是一種常用措施, 其根-冠互作也表現(xiàn)出不同的類型, 如有的抗性砧木對某些基因型接穗具有改善和提高作用, 但對其他基因型接穗效果不佳[34-40]。可見, 根-冠互作類型的多樣性在植物的不同生理過程中普遍存在。

3.1 影響植物葉片中CK和ABA含量的因素

葉片中的CK和ABA分別對衰老起正調(diào)控和負(fù)調(diào)控作用[4-8]。本文所測定的ZR+Z和iPA+iP為活性形式的CK[41], 所測定的ABA為游離態(tài)ABA。從理論上講, 葉片中的活性CK和游離態(tài)ABA水平主要由三方面因素決定: 第一方面是根系的合成能力和輸出能力; 第二方面是莖組織中的合成、活化、降解、鈍化反應(yīng)及與木質(zhì)部之間的橫向轉(zhuǎn)移; 第三方面是葉片內(nèi)的合成、活化、降解和鈍化反應(yīng)。

A: 充足供鉀(2.5 mmol L–1); B: 低鉀脅迫(0.03 mmol L–1)。同一供鉀水平, 同一部位(指根系、葉片和木質(zhì)部汁液)數(shù)據(jù)后的不同小寫字母表示在0.05水平差異顯著(= 4)。

A: sufficient K (2.5 mmol L–1); B: low K (0.03 mmol L–1). The ABA concentration (ng g–1FW) in roots (R) and the youngest fully expanded leaf (L), and ABA delivery rates (ng plant–124 h–1) in xylem above- (A) and below graft union (B) were determined. Means of the same sampling part (i.e. roots, leaf, and xylem sap collected both below and above the graft union) within the same K level followed by the same letter are not significantly different at< 0.05 according to Duncan’s multiple range test (= 4).

表4 低鉀條件下(0.03 mmol L–1) Y型嫁接倒四葉和接穗木質(zhì)部汁液中激素水平的砧木和接穗效應(yīng)

根系合成的CK[9-14]和ABA[18]在蒸騰拉力的作用下向地上部移動[11, 19, 42-43], 但這并不是一個完全被動的過程。以CK為例, 由根系向地上部輸送的CK速率受到根系細(xì)胞保留CK能力的調(diào)節(jié)[44]。根系中的CK在裝載入木質(zhì)部導(dǎo)管之前, 必須進(jìn)行跨膜運(yùn)輸。研究表明嘌呤透性酶(PUP)[45]、均衡核苷轉(zhuǎn)運(yùn)蛋白(ENT)[46]、AtABCG14 (ATP-binding cassette G14)[14]可介導(dǎo)這一過程, 這些載體的數(shù)量和活性也直接調(diào)控著根系輸出CK的能力。此外, 位于根系木質(zhì)部裝載位點(diǎn)附件的CK氧化酶/脫氫酶(CKX)也會通過降解代謝[47]調(diào)節(jié)根系輸出的活性CK數(shù)量。

一些直接和間接證據(jù)顯示, CK和ABA在木質(zhì)部運(yùn)輸過程中發(fā)生著活躍的變化。作者未發(fā)表數(shù)據(jù)表明, 棉花下胚軸韌皮部中的CK合成基因(與同源性為55%)和運(yùn)輸基因(與同源性為55%)表達(dá)量較高, 木質(zhì)部中的ABA合成基因(與同源性為66%)、活化基因(與同源性為52%)和運(yùn)輸基因(與同源性為64%)表達(dá)量較高[48]。而CK[49]和ABA[50]均可在莖組織中橫向轉(zhuǎn)移, 即從莖薄壁細(xì)胞轉(zhuǎn)移到木質(zhì)部, 或從木質(zhì)部轉(zhuǎn)移到薄壁細(xì)胞。Zhang等[51]在羽扇豆上的同位素示蹤試驗(yàn)結(jié)果表明, [3H]ZR和[3H]DHZR通過蒸騰流被吸收后, 甚至可迅速(以核苷和/或相應(yīng)的核苷酸形式)從木質(zhì)部橫向移動到莖表皮組織。木質(zhì)部薄壁細(xì)胞中的ABA可能因木質(zhì)部汁液中較高的pH向其中富集[52]。切花玫瑰葉柄木質(zhì)部汁液中的ABA濃度與ABA傳遞速率之間缺乏聯(lián)系[53], 也表明木質(zhì)部汁液中的ABA濃度在運(yùn)輸途徑中受到調(diào)節(jié)。

大量研究結(jié)果已經(jīng)表明, 葉片具有合成、降解、活化和鈍化CK的能力。Miyawaki等[54]和Takei等[55]為葉片具有合成CK的能力提供了證據(jù), Nováková等[56]發(fā)現(xiàn)葉片中的CK水平受到CKX及-葡糖苷酶(參與CK-葡糖苷的水解)的精細(xì)調(diào)節(jié)。Koeslin- Findeklee等[27]的試驗(yàn)表明, 氮饑餓下早衰的冬油菜品種其葉片中以活性CK的鈍化反應(yīng)為主, 而持綠性品種的葉片中以CK的合成、活化和對活性CK的感知及響應(yīng)為主。葉片也具有合成ABA[57]和鈍化ABA (在ABA葡糖基轉(zhuǎn)移酶的作用下形成ABA葡萄糖酯[58])的能力。McAdam和Brodribb[59]最近的研究表明, 在VPD (蒸氣壓差)變化時, 4種被子植物中的3種其葉片ABA含量顯著升高, 而這種升高與葉片的合成能力有關(guān)。此外有研究表明, 切花玫瑰葉片氣孔敏感性(對高的相對濕度)的基因型差異也主要由葉片內(nèi)的ABA平衡/穩(wěn)態(tài)決定[53]。

3.2 植物器官間的長距離通訊

CK和ABA雖然可作為信息物質(zhì)調(diào)控植物諸多發(fā)育過程, 但其在根系、莖組織和葉片中的合成、代謝和運(yùn)輸可能受到其他根-冠信號和/或冠-根信號的調(diào)控。近些年關(guān)于植物的根-冠和冠-根長距離通訊及根-冠-根通訊回路研究取得了一些重要進(jìn)展。Notaguchi和Okamoto[60]在最近的綜述中提出, 當(dāng)土壤環(huán)境變化時, 信號分子首先在根系的某處或整個根系中產(chǎn)生, 然后通過木質(zhì)部向地上部每一個成熟葉片中(很可能是小葉脈中)傳播; 再次, 信號分子從木質(zhì)部運(yùn)輸?shù)巾g皮部, 被位于韌皮部細(xì)胞中的受體感知后發(fā)出二級信號; 最后, 二級信號分子在韌皮部汁液中輸送到庫器官, 包括自上而下輸送到根系。豆科植物根瘤形成[61-63]和植物對低氮(N)響應(yīng)[64]的根-冠-根通訊回路目前研究的比較清楚。

3.3 棉花葉片衰老根-冠互作類型多樣性的可能機(jī)制

就葉片衰老而言, 41/22和41/49分別代表地上部主導(dǎo)型和根系主導(dǎo)型根-冠互作類型。如圖9所示, 魯22和中49發(fā)出的根-冠信號可能不同, 因此中41葉片內(nèi)的受體感知到二者的信號后產(chǎn)生不同的響應(yīng), 如感知到魯22的信號后可能傾向于維持原有的CK和ABA合成、代謝能力; 但感知到中49的信號后可能CK合成、活化能力提高和/或降解、鈍化能力降低, ABA的合成、活化能力則降低和/或降解、鈍化能力提高, 從而使ZR+Z、iPA+iP和ABA濃度向中49的水平靠近。此外, 中41葉片感知到魯22和中49砧木的根-冠信號后可能形成不同種類或不同強(qiáng)度的冠-根信號, 從而引發(fā)不同的反應(yīng)。如在41/22嫁接體中, 冠-根信號對魯22砧木的CK和ABA輸出能力和/或莖組織中的CK和ABA合成、代謝及橫向運(yùn)輸具有較強(qiáng)的調(diào)節(jié)作用, 使之接近中41的水平; 而在41/49嫁接體中, 冠-根信號向下傳遞到中49砧木后傾向于維持砧木原有的CK和ABA輸出能力和/或木質(zhì)部運(yùn)輸過程。

3.4 中41與中49不同嫁接方式葉片衰老的根-冠互作類型不完全一致

中41與魯22無論采用I型、Y型還是A型嫁接方式, 均表現(xiàn)為地上部對葉片衰老起主要作用[29]。中41與中49的I型嫁接表現(xiàn)出根系起主要作用的方式, 但Y型嫁接中根系的作用不再具有明顯優(yōu)勢, 僅略大于地上部的作用。推測原因如下, 中41與中49的Y型互相嫁接體中[(41+49)/41、(41+49)/49], 在另一個與砧木品種相同的接穗存在的情況下, 與砧木品種不同的接穗接收到的根-冠信號可能不同于二者之間I型互相嫁接的根-冠信號, 致使該接穗葉片中發(fā)生不同于I型互相嫁接的變化, 即葉片的CK和ABA合成、代謝反應(yīng)不再發(fā)生類似于砧木品種的變化, 或變化強(qiáng)度降低。此外, 該接穗中的受體感知到砧木的根-冠信號后向下傳遞的冠-根信號可能也不同于I型嫁接, 因而對其下胚軸中的CK和ABA合成、代謝及橫向運(yùn)輸表現(xiàn)出一定程度的調(diào)節(jié)作用, 類似于中41和魯22組合[29]。

盡管我們初步描繪了棉花葉片衰老過程中根-冠-根的通訊回路, 但對其信號物質(zhì)并不清楚。已知植物韌皮部汁液成分比較復(fù)雜, 含有糖類、脂類、氨基酸、多肽、蛋白質(zhì)、編碼和非編碼RNAs、礦質(zhì)養(yǎng)分和植物激素等一系列物質(zhì)[65-67], 木質(zhì)部汁液成分比較簡單, 主要含有礦質(zhì)養(yǎng)分、多肽、蛋白質(zhì)和植物激素[67-69]。未來需要在眾多的木質(zhì)部汁液和韌皮部汁液成分中鑒定與棉花葉片衰老有關(guān)的根-冠信號和冠-根信號, 這將有助于人們采取針對性措施對棉花衰老予以調(diào)節(jié)。

41: 中棉所41; 49: 中棉所49; 22: 魯棉研22; 41/22: 地上部為主型; 41/49: 根系為主型; 綠色上行箭頭: 根-冠信號; 藍(lán)色下行箭頭: 冠-根信號; 箭頭粗細(xì)代表信號強(qiáng)弱。

41: CCRI41; 49: CCRI49; 22: SCRC22; 41/22: the role of shoot is more important; 41/49: the role of root is more important. Green up arrow: the signal of root-shoot. Blue down arrow: the signal of shoot-root. The thickness of arrow indicates signal strength.

4 結(jié)論

以中41為砧木的處理, 其葉片中ZR+Z、iPA+iP的含量低于以中49為砧木的處理, ABA含量則相反, 表明根系對葉片衰老的作用較大。據(jù)分析, 中41和中49互相嫁接體(41/49和49/41)接穗葉片中的受體感知到來自砧木的缺鉀信號后, 發(fā)出的冠-根信號對砧木輸出CK和ABA的能力和/或木質(zhì)部中CK和ABA的運(yùn)輸過程影響較小; 接穗葉片中CK和ABA的合成、代謝則可能發(fā)生類似于砧木品種的變化。

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Effect of Root-shoot Interaction on Cotton Leaf Senescence

ZHANG Qiao-Yu, WANG Yi-Ru, AN Jing, WANG Bao-Min, and TIAN Xiao-Li*

Center of Crop Chemical Regulation, College of Agricultural and Biotechnology, China Agricultural University / State Key Laboratory of Plant Physiology and Biochemistry, Beijing 100193, China

Researches and practices associated with grafting indicate that the diversity of root-shoot interaction is universal in different physiological processes of plant. Our previous grafting study with CCRI41, an early senescence cotton cultivar, and SCRC22, a late senescence cultivar as materials found that shoot played a major role in mediating leaf senescence of cotton. In the present study, CCRI41 and another late senescence cotton cultivar CCRI49 were used to do standard grafting (I-grafting, one scion grafted onto one rootstock) and Y-grafting (two scions grafted onto one rootstock). Leaf senescence of grafts was induced by low potassium (K; 0.03 mmol L–1). Contrary to the grafting combination of CCRI41 and SCRC22, the combination of CCRI41 and CCRI49 showed that the role of root was more important than that of shoot for leaf senescence, as characterized by SPAD reading. Accordingly, the concentration of ZR+Z or iPA+iP in roots and the youngest fully expanded leaf and their delivery rate in xylem sap regarding I-grafting combinations with CCRI41 as rootstock were significantly lower than those with CCRI49 as rootstock in most of situations. However, the results of free ABA level were exactly opposite. With respect to the Y-grafting of CCRI41 and CCRI49, the results were similar to those of I-grafting, whereas the role of root was not absolutely predominant any more. The mechanism for different root-shoot interactions in cotton leaf senescence was discussed from the perspective of root-shoot-root distance communication.

Cotton; Grafting; Leaf; Senescence; Interaction of root-shoot

本研究由國家自然科學(xué)基金項目(31271629)資助。

This study was supported by the National Natural Science Foundation of China (31271629).

致謝: 感謝課題組王曄博士在試驗(yàn)過程中提供的幫助。

2016-07-25; Accepted(接受日期): 2016-11-02; Published online((網(wǎng)絡(luò)出版日期)： 2016-11-25.

10.3724/SP.J.1006.2017.00226

田曉莉, E-mail: tianxl@cau.edu.cn, Tel: 010-62734550

E-mail: qiaoyu306@126.com, Tel: 010-62734550

URL:http://www.cnki.net/kcms/detail/11.1809.S.20161125.1201.004.html