石 洋，萇姍姍，胡進(jìn)波，劉 元

（中南林業(yè)科技大學(xué) 材料科學(xué)與工程學(xué)院，湖南 長(zhǎng)沙 410004）

應(yīng)拉木拉伸應(yīng)力受膠質(zhì)層影響及其形成機(jī)理研究

石 洋，萇姍姍，胡進(jìn)波，劉 元

（中南林業(yè)科技大學(xué) 材料科學(xué)與工程學(xué)院，湖南 長(zhǎng)沙 410004）

應(yīng)拉木形成時(shí)往往伴隨著產(chǎn)生高拉伸應(yīng)力，以使樹(shù)木在應(yīng)對(duì)環(huán)境變化時(shí)，維持定向生長(zhǎng)。膠質(zhì)層是許多應(yīng)拉木樹(shù)種最典型的細(xì)胞結(jié)構(gòu)特征。由于具有特殊的形態(tài)構(gòu)造和化學(xué)成分，膠質(zhì)層在應(yīng)拉木拉伸應(yīng)力形成時(shí)發(fā)揮的作用不容忽視，已成為當(dāng)前的研究熱點(diǎn)。本文從應(yīng)拉木異常高的縱向干縮特性入手，分析膠質(zhì)層在應(yīng)拉木拉伸應(yīng)力產(chǎn)生中發(fā)揮的重要作用，并總結(jié)歸納應(yīng)拉木拉伸應(yīng)力形成機(jī)理的研究，在此基礎(chǔ)上提出細(xì)胞腔液體壓力假說(shuō)。針對(duì)目前拉伸應(yīng)力產(chǎn)生機(jī)理研究中諸多亟待解決的問(wèn)題，提出今后研究應(yīng)結(jié)合多學(xué)科的研究方法和手段，以深入探究膠質(zhì)層在應(yīng)拉木高拉伸應(yīng)力產(chǎn)生中的作用和拉伸應(yīng)力產(chǎn)生的根本原因。

應(yīng)拉木；膠質(zhì)層；拉伸應(yīng)力；形成機(jī)理

樹(shù)木的形態(tài)常因環(huán)境或其他因素刺激而受到影響。為了適應(yīng)這種改變，闊葉樹(shù)材形成層分化應(yīng)拉木以維持樹(shù)木的定向生長(zhǎng)[1]。與正常材不同，應(yīng)拉木的形成往往伴隨著較大拉伸應(yīng)力的產(chǎn)生，且存在著異常高的縱向干縮[2]，使得應(yīng)拉木在加工利用過(guò)程中出現(xiàn)翹曲、起毛和開(kāi)裂等多種缺陷，阻礙其高附加值利用[3]。研究發(fā)現(xiàn)，應(yīng)拉木的微觀結(jié)構(gòu)形態(tài)與化學(xué)成分也異于正常材，如微纖絲角度較小、纖維素含量高、結(jié)晶度大、木質(zhì)素含量低、中孔孔隙豐富等[4-7]。種種應(yīng)拉木的這些異于正常材的特性是與其纖維細(xì)胞壁中的膠質(zhì)層有關(guān)[5-6,8-11]。然而，有研究發(fā)現(xiàn)，部分熱帶樹(shù)種和非熱帶原始被子植物的應(yīng)拉木中缺失膠質(zhì)層，同時(shí)也發(fā)現(xiàn)這些樹(shù)種的纖維細(xì)胞相應(yīng)壁層也呈現(xiàn)出與膠質(zhì)層相近的結(jié)構(gòu)特征，以維持樹(shù)干或樹(shù)枝的定向生長(zhǎng)[10,12-15]。因此，在應(yīng)拉木高拉伸應(yīng)力形成時(shí)，膠質(zhì)層及具膠質(zhì)層特性的細(xì)胞結(jié)構(gòu)發(fā)揮著不可忽視的作用。本文主要針對(duì)已開(kāi)展的相關(guān)研究，從應(yīng)拉木的高縱向干縮特性入手，對(duì)膠質(zhì)層在應(yīng)拉木拉伸應(yīng)力形成過(guò)程中發(fā)揮的作用進(jìn)行分析，并在膠質(zhì)層膨脹/壓力假說(shuō)、膠質(zhì)層纖維素微纖絲拉伸假說(shuō)和統(tǒng)一假說(shuō)的基礎(chǔ)上提出細(xì)胞腔液體壓力假說(shuō)，以期對(duì)應(yīng)拉木高生長(zhǎng)應(yīng)力形成機(jī)理的進(jìn)一步探究打下基礎(chǔ)。

1 膠質(zhì)層與應(yīng)拉木縱向干縮

應(yīng)拉木的顯著性質(zhì)在于它異常高的縱向干縮[16-19]。通常來(lái)講，正常木的縱向干縮非常?。?.1%），在木材加工利用中，其影響可以忽略不計(jì)。且對(duì)于正常木而言，在分析縱向干縮與微纖絲角關(guān)系時(shí)發(fā)現(xiàn)，兩者呈正相關(guān)[20-21]。但此相關(guān)性并不適用應(yīng)拉木，其微纖絲角很小，但縱向干縮卻異常大，可達(dá)1%或更高[8,12,16,19,22-23]，致使木材加工過(guò)程中多翹曲和開(kāi)裂，材質(zhì)降低并給加工帶來(lái)困難。

Norberg和Meier通過(guò)超聲波振動(dòng)處理將膠質(zhì)層分離出來(lái)后，并未測(cè)量到膠質(zhì)層具有顯著的縱向收縮[24]。由于膠質(zhì)層膨松和易于與相鄰壁層分離特點(diǎn)，一些學(xué)者認(rèn)為應(yīng)拉木的高縱向收縮應(yīng)來(lái)源于微纖絲角有所變化的S1或S2層，而不是看來(lái)容易變形的膠質(zhì)層[24-26]。Clair等證實(shí)膠質(zhì)層易于與相鄰壁層分離的特征僅是一種由邊界效應(yīng)引起的“假象”[27-28]，采用掃描電鏡觀察并測(cè)量到了山毛櫸和楊木應(yīng)拉木膠質(zhì)層的縱向收縮（4.7%，圖1），并通過(guò)原子力顯微鏡證實(shí)了此結(jié)論[29]。此研究結(jié)果同時(shí)也證實(shí)了膠質(zhì)層對(duì)應(yīng)拉木的力學(xué)特性，特別是高縱向干縮方面所起的作用。

圖1 楊木應(yīng)拉木膠質(zhì)層的高軸向干燥收縮[29]Fig.1 Extensive axial drying shrinkage of gelatinous layer in Populus cv I4551

Yamamoto等通過(guò)膠質(zhì)纖維模型也分析了膠質(zhì)層對(duì)應(yīng)拉木產(chǎn)生高縱向干縮率、拉伸強(qiáng)度和彈性模量上的影響，并通過(guò)實(shí)例驗(yàn)證了此結(jié)論，但是并沒(méi)有對(duì)其中的原因進(jìn)行解釋[8,30]。Clair等[2]依據(jù)膠質(zhì)層表現(xiàn)出的一些性質(zhì)：高縱向干縮[29,31]、干燥過(guò)程中的高硬度[32]和豐富的孔隙結(jié)構(gòu)[2]等凝膠膠體的特征，通過(guò)圖2膠質(zhì)層收縮原理圖來(lái)闡釋干燥過(guò)程中膠質(zhì)層產(chǎn)生高縱向干縮的原因。從圖中可以看出，水分蒸發(fā)前，飽水的凝膠類(lèi)物質(zhì)填充在微纖絲間，水分蒸發(fā)引起膠質(zhì)層內(nèi)凝膠類(lèi)物質(zhì)的塌陷與收縮，使纖維素微纖絲產(chǎn)生彎曲，因膠質(zhì)層的收縮，進(jìn)而引起相鄰壁層的收縮最終導(dǎo)致宏觀上應(yīng)拉木的縱向干縮。

圖2 水分蒸發(fā)過(guò)程中膠質(zhì)層收縮示意[2]Fig.2 Schematic model of the evaporative drying of G-layer constituents

Goswami等[33]采用生化酶處理方法將膠質(zhì)層從組織細(xì)胞中分離，發(fā)現(xiàn)被提取的膠質(zhì)層在縱向上有拉伸，橫向上有收縮，并提出膠質(zhì)層的橫向膨脹引起了次生壁的縱向收縮，然而這種觀點(diǎn)仍有待進(jìn)一步驗(yàn)證。

2 膠質(zhì)層與應(yīng)拉木拉伸應(yīng)力形成

樹(shù)木在正常生長(zhǎng)時(shí)若受到外界環(huán)境刺激會(huì)產(chǎn)生生長(zhǎng)應(yīng)力，以保持樹(shù)干筆直、或使彎曲樹(shù)干、樹(shù)枝恢復(fù)到適應(yīng)的位置。在許多具應(yīng)拉木的溫帶樹(shù)種中，生長(zhǎng)應(yīng)力的產(chǎn)生往往伴隨著膠質(zhì)纖維的形成[34]，且膠質(zhì)纖維的含量與縱向拉伸應(yīng)力間存在一定的相關(guān)性[35]。而對(duì)不具膠質(zhì)層的應(yīng)拉木樹(shù)種，也能產(chǎn)生很高的生長(zhǎng)應(yīng)力[12,36]。研究發(fā)現(xiàn)，在不具膠質(zhì)層的應(yīng)拉木中，次生壁S2層相比于對(duì)應(yīng)木次生壁S2層微纖絲角較低，纖維素含量高，纖維素微纖絲結(jié)晶度較大，木質(zhì)素含量低，特性近似于膠質(zhì)層[4,35]。膠質(zhì)層凝膠狀的外形特征以及看起來(lái)與相鄰壁層易分離的形態(tài)，曾一度使人們對(duì)膠質(zhì)層在應(yīng)拉木高生長(zhǎng)應(yīng)力產(chǎn)生的作用上產(chǎn)生懷疑[24,37]。Clair等許多研究學(xué)者[8,10,27-29,33,38-39]通過(guò)一系列的研究表明，膠質(zhì)層作為支撐應(yīng)力的“載體”在應(yīng)拉木高拉伸應(yīng)力的產(chǎn)生中發(fā)揮著重要作用，這些研究為近一步探究應(yīng)拉木高拉伸應(yīng)力的來(lái)源提供了重要依據(jù)。

膠質(zhì)層是應(yīng)拉木纖維細(xì)胞特有的壁層結(jié)構(gòu)，其獨(dú)特的結(jié)構(gòu)特征與化學(xué)成分或影響應(yīng)拉木高拉伸應(yīng)力的產(chǎn)生。膠質(zhì)層主要成分為纖維素，含量高達(dá)78%[6]，存在較高的結(jié)晶度[18]，微纖絲角小于5o，接近平行排列[4]，有豐富的納米孔隙結(jié)構(gòu)[11]。Okuyama等通過(guò)實(shí)驗(yàn)證實(shí)微纖絲角、α-纖維素含量和纖維素結(jié)晶度均會(huì)對(duì)拉伸應(yīng)力產(chǎn)生影響，微纖絲角度越小、α-纖維素含量越高、纖維素結(jié)晶度越大時(shí)，應(yīng)拉木縱向拉伸應(yīng)力呈增大趨勢(shì)[35]。在應(yīng)拉木細(xì)胞生長(zhǎng)過(guò)程中，Chang等[7]發(fā)現(xiàn)應(yīng)拉木孔隙結(jié)構(gòu)與對(duì)應(yīng)木存在不同的變化規(guī)律。在膠質(zhì)層形成之前的階段，隨著細(xì)胞壁的成熟，應(yīng)拉木和對(duì)應(yīng)的正常復(fù)合胞間層中的孔隙結(jié)構(gòu)類(lèi)似，且均逐漸木質(zhì)化。應(yīng)拉木膠質(zhì)層沉積階段，應(yīng)拉木中孔形狀發(fā)生變化，孔徑逐漸增大，這與Goswami等[33]認(rèn)為的膠質(zhì)層膨脹行為相符合。研究者認(rèn)為膠質(zhì)層孔隙結(jié)構(gòu)的變化可能使得纖維素微纖絲處于拉伸/收縮狀態(tài)，并與應(yīng)拉木拉伸應(yīng)力的產(chǎn)生直接有關(guān)。此外，有研究者認(rèn)為填充在膠質(zhì)層纖維素骨架中的某些多糖成分也可對(duì)拉伸應(yīng)力的形成產(chǎn)生影響，如木葡聚糖、XET酶、AGPs和RGⅠ-型果膠分子等[5,40-42]。

3 應(yīng)拉木拉伸應(yīng)力形成機(jī)理

膠質(zhì)層與應(yīng)拉木高拉伸應(yīng)力的形成關(guān)系密切，但究竟是什么使膠質(zhì)層微纖絲處于拉伸狀態(tài)，至今仍無(wú)定論。不同學(xué)者對(duì)此持有不同的觀點(diǎn)，主要包括膠質(zhì)層膨脹/壓力假說(shuō)[33]，膠質(zhì)層纖維素微纖絲拉伸假說(shuō)[5,35,40-43]和統(tǒng)一假說(shuō)[43]。在眾多學(xué)者論述的基礎(chǔ)上，筆者也對(duì)應(yīng)拉木拉伸應(yīng)力的形成機(jī)理闡述了自己的觀點(diǎn)。

3.1 膠質(zhì)層膨脹/壓力假說(shuō)

膠質(zhì)層膨脹/壓力假說(shuō)基于對(duì)分離膠質(zhì)層的觀察，Goswami等[33]采用纖維素酶從楊木應(yīng)拉木中分離出膠質(zhì)層，移除膠質(zhì)層后的纖維細(xì)胞在軸向上產(chǎn)生拉伸，在橫向上產(chǎn)生收縮。因此，Goswami等認(rèn)為在應(yīng)拉木細(xì)胞成熟過(guò)程中，膠質(zhì)層產(chǎn)生橫向膨脹，并對(duì)相鄰次生壁層產(chǎn)生沿圓周方向向外的壓力。因次生壁層微纖絲角度較大，使得纖維細(xì)胞整體在縱向上產(chǎn)生較大收縮。而與之相鄰的成熟纖維細(xì)胞會(huì)產(chǎn)生拉伸應(yīng)力以牽制這種縱向收縮，最終引起應(yīng)拉木宏觀上產(chǎn)生拉伸應(yīng)力，即膠質(zhì)層的橫向膨脹可能是應(yīng)拉木中拉伸應(yīng)力產(chǎn)生的主要原因，但具體作用機(jī)理尚不明確。然而此假說(shuō)中膠質(zhì)層產(chǎn)生橫向膨脹/壓力的假設(shè)與膠質(zhì)層在實(shí)際干燥過(guò)程中的行為相矛盾。Fang等[31]的研究表明，因缺少次生壁S3層的束縛，應(yīng)拉木膠質(zhì)層在干燥時(shí)會(huì)產(chǎn)生向外（遠(yuǎn)離胞腔）的橫向收縮。由此推斷，膠質(zhì)層在缺失次生壁S3層時(shí)應(yīng)產(chǎn)生向內(nèi)（靠近胞腔）的橫向膨脹，這與假說(shuō)中膠質(zhì)層對(duì)相鄰壁層產(chǎn)生膨脹壓力的假設(shè)相違背，此假說(shuō)仍有待進(jìn)一步驗(yàn)證。

3.2 膠質(zhì)層纖維素微纖絲拉伸假說(shuō)

膠質(zhì)層纖維素微纖絲拉伸假說(shuō)于1978年由Bamber[44]最早提出，其后許多學(xué)者的觀察研究結(jié)果[30,35,38]均與此假說(shuō)一致。該假說(shuō)認(rèn)為，在膠質(zhì)纖維細(xì)胞壁成熟期間，新細(xì)胞在縱向上傾向于收縮，與之相連的內(nèi)側(cè)成熟細(xì)胞就會(huì)對(duì)它進(jìn)行限制，即對(duì)它形成了拉伸作用，再向外推，形成層在它的外側(cè)又產(chǎn)生新的細(xì)胞，新細(xì)胞同樣會(huì)受到來(lái)自緊鄰相連的內(nèi)側(cè)成熟細(xì)胞的拉伸作用，而后一個(gè)拉伸是在前一作用疊加下形成，因而這種在長(zhǎng)度上的拉伸作用向外遞增, 在樹(shù)干外圍產(chǎn)生最大的拉伸應(yīng)力[35]。但在微觀層面上，這種“自發(fā)收縮的傾向”是如何及怎樣發(fā)生在細(xì)胞壁中，尤其高縱向拉伸應(yīng)力是如何在應(yīng)拉木中產(chǎn)生，仍是一個(gè)待解決的問(wèn)題。

Clair等[10,38]采用同步輻射X射線衍射技術(shù)測(cè)得應(yīng)拉木膠質(zhì)纖維形成過(guò)程中，膠質(zhì)層纖維素晶格間距的變化與應(yīng)拉木立木的應(yīng)變值接近，從而表明應(yīng)拉木的拉伸應(yīng)力來(lái)自于膠質(zhì)層微纖絲。這為近一步探究應(yīng)拉木高拉伸應(yīng)力的來(lái)源提供了依據(jù)，但仍未解決其拉伸應(yīng)力產(chǎn)生的根本原因：是什么使膠質(zhì)層微纖絲處于拉伸狀態(tài)？有學(xué)者提出可能來(lái)自于日差變化對(duì)細(xì)胞腔中水張力的影響[35]，但此說(shuō)法后來(lái)被證實(shí)不包括在內(nèi)[45]。

因此，其根本原因應(yīng)來(lái)自于細(xì)胞內(nèi)部，且與細(xì)胞壁的形成直接相關(guān)。首先，其原因或直接來(lái)自于膠質(zhì)層微纖絲，如Yamamoto[30]通過(guò)膠質(zhì)纖維模型對(duì)多壁層纖維細(xì)胞進(jìn)行模擬，并認(rèn)為拉伸應(yīng)力來(lái)自于膠質(zhì)層纖維素微纖絲非結(jié)晶區(qū)的收縮[30,35]，但未解釋其中的機(jī)理；Abe[46]等對(duì)應(yīng)拉木進(jìn)行濕熱干燥處理，觀察到應(yīng)拉木異常顯著的縱向收縮，且收縮程度與膠質(zhì)纖維的含量呈現(xiàn)一定的正相關(guān)性，認(rèn)為這一現(xiàn)象與膠質(zhì)層纖維素非結(jié)晶區(qū)的收縮有關(guān)，但引起這種收縮的具體原因仍是一個(gè)待解決的問(wèn)題。

其次，其原因或間接來(lái)自于填充于膠質(zhì)層微纖絲間的基體物質(zhì)，因某些物理化學(xué)（離子濃度、含水率等）變化，基體物質(zhì)發(fā)生收縮或膨脹，然后將應(yīng)力“轉(zhuǎn)移”給微纖絲[2]。許多研究表明，膠質(zhì)層成熟過(guò)程中木葡聚糖和木葡聚糖內(nèi)轉(zhuǎn)糖苷酶（XET）活動(dòng)可能與應(yīng)拉木拉伸應(yīng)力的產(chǎn)生有關(guān)[5,41-42]。Bowling等[40]認(rèn)為 AGPs和 RG Ⅰ -型果膠分子可能與應(yīng)拉木的拉伸應(yīng)力產(chǎn)生有關(guān)，這些組成成分往往在一些具有膨脹特性的植物組織細(xì)胞中存在，如荊棘，藤蔓等。而一系列有關(guān)膠質(zhì)層納米孔隙結(jié)構(gòu)方面的研究[2,7,47-48]則表明，膠質(zhì)層成熟過(guò)程中孔隙結(jié)構(gòu)的變化對(duì)應(yīng)拉木拉伸應(yīng)力的產(chǎn)生作用更不容忽視。

3.3 統(tǒng)一假說(shuō)

Mellerowicz等[43]在膠質(zhì)層膨脹/壓力假說(shuō)和膠質(zhì)層纖維素微纖絲拉伸假說(shuō)的基礎(chǔ)上提出了統(tǒng)一假說(shuō)，該假說(shuō)認(rèn)為應(yīng)拉木拉伸應(yīng)力是纖維細(xì)胞在膨脹/壓力和膠質(zhì)層纖維素微纖絲拉力共同作用下產(chǎn)生的結(jié)果，如圖3所示。細(xì)胞成熟過(guò)程中，由于受到相鄰次生壁層的牽制作用，膠質(zhì)層靠近胞腔一側(cè)和靠近相鄰次生壁層一側(cè)的纖維素微纖絲收縮程度不均勻，對(duì)相鄰次生壁層產(chǎn)生向外的壓力，從而引起次生壁層的收縮，進(jìn)而誘發(fā)拉伸應(yīng)力的產(chǎn)生。這一假說(shuō)與Goswami等[33]觀察到的實(shí)驗(yàn)現(xiàn)象相一致，但仍需有力的證據(jù)支撐。

圖3 統(tǒng)一假說(shuō)模型[43]Fig. 3 Modelling about unifying hypothesis

3.4 細(xì)胞腔液體壓力假說(shuō)

筆者在前人研究的基礎(chǔ)上，通過(guò)總結(jié)和分析，認(rèn)為應(yīng)拉木高拉伸應(yīng)力的產(chǎn)生與細(xì)胞腔液體壓力有密切關(guān)系，提出細(xì)胞腔液體壓力假說(shuō)。

應(yīng)拉木膠質(zhì)纖維細(xì)胞壁在缺失次生壁S3層時(shí)，膠質(zhì)層因缺少束縛作用傾向于產(chǎn)生向內(nèi)（靠近胞腔）的橫向膨脹[31]，此時(shí)細(xì)胞腔容積減小，胞腔內(nèi)液體被壓縮，原本相對(duì)穩(wěn)定的細(xì)胞腔內(nèi)環(huán)境平衡被打破，受到壓迫的腔內(nèi)液體存在回復(fù)的趨勢(shì)，細(xì)胞壁則受到來(lái)自腔內(nèi)液體向外的作用力（見(jiàn)圖4）。由于膠質(zhì)層缺乏起硬固作用的木質(zhì)素（有學(xué)者提出膠質(zhì)層中存在少量木質(zhì)素[49-50]），胞腔液體對(duì)膠質(zhì)層的壓力可起到一定的支持作用，使細(xì)胞處于緊張狀態(tài)，維持一定形狀。這一原理與草本植物細(xì)胞膨壓類(lèi)似。草本植物中缺乏硬固的木質(zhì)素，細(xì)胞通過(guò)膨壓保持其緊張度，維持莖、葉挺立的姿態(tài)[51]。由于膠質(zhì)層與相鄰次生壁層的緊密結(jié)合，膠質(zhì)層受到的來(lái)自胞腔液體的壓力可沿圓周方向向外傳遞給相鄰次生壁層。又由于次生壁層具有較大的微纖絲角度，纖維細(xì)胞在縱向上產(chǎn)生收縮進(jìn)而誘使應(yīng)拉木拉伸應(yīng)力形成。

圖4 細(xì)胞腔液體壓力假說(shuō)示意圖像Fig. 4 Schematic illustration of liquid pressure of cell lumen hypothesis

4 結(jié)論與展望

高生長(zhǎng)應(yīng)力的形成是樹(shù)木適應(yīng)環(huán)境變化的體現(xiàn)，在維持樹(shù)木最佳形態(tài)的同時(shí)也為生產(chǎn)加工帶來(lái)不利影響。因此，研究應(yīng)拉木高拉伸應(yīng)力的形成機(jī)理，對(duì)高效利用木材資源具有重要意義。應(yīng)拉木膠質(zhì)纖維內(nèi)壁往往具有一種特殊的壁層結(jié)構(gòu)——膠質(zhì)層，膠質(zhì)層對(duì)于應(yīng)拉木拉伸應(yīng)力的產(chǎn)生具有不可忽視的作用。目前研究者將這種應(yīng)力的產(chǎn)生歸因于細(xì)胞成熟過(guò)程中膠質(zhì)層的變化。膠質(zhì)層橫向上的膨脹或縱向上的收縮，又或者兩者都有，均可能會(huì)引起應(yīng)拉木高拉伸應(yīng)力的產(chǎn)生。而引起膠質(zhì)層這種變化的原因，則來(lái)自于膠質(zhì)層自身獨(dú)特的結(jié)構(gòu)特征及化學(xué)成分。雖然許多學(xué)者提出了相關(guān)的假說(shuō)來(lái)解釋這種機(jī)理，也得到了一定的實(shí)驗(yàn)支持。但是，應(yīng)拉木中高拉伸應(yīng)力產(chǎn)生的根本原因，即“是什么使膠質(zhì)層微纖絲處于拉伸狀態(tài)？”仍是一個(gè)亟待解決的問(wèn)題。本文基于草本植物細(xì)胞膨壓原理提出細(xì)胞腔液體壓力的猜想，今后可嘗試應(yīng)用植物膨壓的測(cè)定方法，研究應(yīng)拉木膠質(zhì)纖維細(xì)胞成熟過(guò)程中胞腔內(nèi)液體對(duì)胞壁壓力的變化，并與對(duì)應(yīng)木進(jìn)行比較，探究應(yīng)拉木高拉伸應(yīng)力的形成機(jī)制。有關(guān)膠質(zhì)層和應(yīng)拉木拉伸應(yīng)力形成機(jī)理的研究涉及樹(shù)輪生物學(xué)[52]、植物形態(tài)學(xué)、植物解剖學(xué)、木材科學(xué)等學(xué)科的內(nèi)容，研究手段和理論分析應(yīng)注重多學(xué)科間的交叉，積極探索有效的研究方法與途徑，深入探究膠質(zhì)層在應(yīng)拉木高拉伸應(yīng)力產(chǎn)生中的作用。

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Research on tensile stress affected by gelatinous layer and its generation mechanism in tension wood

SHI Yang, CHANG Shanshan, HU Jinbo, LIU Yuan
(College of Materials Science and Engineering, Central South University of Forestry and Technology, Changsha 410004, Hunan, China)

To keep their oriented growth, trees form tension wood with the generation of high growth stresses when facing the variation of the surroundings. Gelatinous layer is the most typical cell structure characteristic in many tension wood species. Owing to the distinctive structure and chemical contents, the contribution of gelatinous layer to tensile stress formation of tension wood shouldn’t be neglected, and it has become a research hotspot to investigate the mechanism of tensile stress generation in tension wood. This paper starts with the peculiarly high longitudinal shrinkage of tension wood, analyzes the role of gelatinous layer in the generation of tensile stress, reviews research on the mechanism of tensile stress generation in tension wood and proposes a new hypothesis in terms of the liquid pressure of cell lumen. There still remain questions about the research of mechanism of tensile stress generation to be solved.Some proposals about combining with multidisciplinary research methods are also put forward to explore the role of gelatinous layer in tensile stress generation of tension wood and the basic mechanism of the tensile stress generation.

tension wood; gelatinous layer; tensile stress; generation mechanism

S781.2

A

1673-923X(2017)07-0123-07

10.14067/j.cnki.1673-923x.2017.07.019

2016-12-07

國(guó)家自然科學(xué)基金項(xiàng)目（31300481）；湖南省自然科學(xué)基金項(xiàng)目（2017JJ1038）；湖南省教育廳優(yōu)秀青年項(xiàng)目（16B281）；中南林業(yè)科技大學(xué)引進(jìn)高層次人才科研啟動(dòng)基金項(xiàng)目（2015YJ023）；湖南省科技計(jì)劃項(xiàng)目(2016NK2160）

石 洋，碩士研究生

萇姍姍，副教授，博士；E-mail：changelxy@aliyun.com

石 洋，萇姍姍，胡進(jìn)波，等.應(yīng)拉木拉伸應(yīng)力受膠質(zhì)層影響及其形成機(jī)理研究[J].中南林業(yè)科技大學(xué)學(xué)報(bào)，2017, 37(7):123-129

[本文編校：吳 毅]