摘要:印度梨形孢(Serendipita indica)是一種可純培養(yǎng)的類菌根真菌,研究其與植物的共生機(jī)制及在退化土壤環(huán)境下的積極作用,對(duì)農(nóng)業(yè)土壤修復(fù)和植物抗逆栽培具有重要意義。本文深入剖析了印度梨形孢與宿主植物的共生體系,包括識(shí)別機(jī)制、植物防御反應(yīng)、真菌侵入過程及共生關(guān)系建立等環(huán)節(jié)。進(jìn)一步分析表明該真菌通過調(diào)節(jié)根系形態(tài)、調(diào)控礦質(zhì)元素轉(zhuǎn)運(yùn)蛋白表達(dá)、活化土壤養(yǎng)分及改善根系微環(huán)境等,促進(jìn)植物的土壤礦質(zhì)元素吸收,優(yōu)化了植物營(yíng)養(yǎng)狀況。這一共生關(guān)系增強(qiáng)了植物的生長(zhǎng)能力,也誘導(dǎo)了在鹽堿、重金屬和干旱的逆境環(huán)境下植物的系統(tǒng)抗性。綜合國(guó)內(nèi)外研究,本文展望了印度梨形孢在優(yōu)良品種選育及應(yīng)用前景方面的潛力。
關(guān)鍵詞:印度梨形孢;礦質(zhì)營(yíng)養(yǎng);共生機(jī)制;微生物;土壤修復(fù);抗逆性
中圖分類號(hào):S182;S184" 文獻(xiàn)標(biāo)志碼:A
文章編號(hào):1002-1302(2024)23-0015-07
馬" 俊,李" 珊,田林雙,等. 印度梨形孢與植物的共生機(jī)制及應(yīng)用研究進(jìn)展[J]. 江蘇農(nóng)業(yè)科學(xué),2024,52(23):15-22.
doi:10.15889/j.issn.1002-1302.2024.23.002
收稿日期:2023-12-15
基金項(xiàng)目:國(guó)家重點(diǎn)研發(fā)計(jì)劃(編號(hào):2022YFD1602403);國(guó)家特色蔬菜產(chǎn)業(yè)技術(shù)體系項(xiàng)目(編號(hào):CARS-24-B-04);農(nóng)業(yè)農(nóng)村部園藝作物生物學(xué)與種質(zhì)創(chuàng)制重點(diǎn)實(shí)驗(yàn)室項(xiàng)目;江蘇高?!扒嗨{(lán)工程”(編號(hào):蘇教師函[2022]29 號(hào));校級(jí)科研項(xiàng)目一般項(xiàng)目(編號(hào):2022XJY15)。
作者簡(jiǎn)介:馬" 俊(1986—),女,山東昌邑人,博士,講師,主要從事設(shè)施園藝生理生態(tài)研究。E-mail:lvlsmaggie@163.com。
通信作者:賀超興,博士,研究員,主要從事設(shè)施蔬菜根區(qū)改良。E-mail:hechaoxing@126.com。
隨著全球氣候變化和人口數(shù)量增長(zhǎng),人們面臨著糧食需求增加和食物短缺的挑戰(zhàn)。傳統(tǒng)農(nóng)業(yè)主要依靠大量施用化肥增加土壤中礦質(zhì)營(yíng)養(yǎng)含量以提高產(chǎn)量,而化肥過量使用會(huì)造成土壤質(zhì)量降低和養(yǎng)分分布不均的問題,最終導(dǎo)致農(nóng)作物產(chǎn)量降低,威脅農(nóng)業(yè)產(chǎn)出。在農(nóng)業(yè)可持續(xù)發(fā)展過程中,人們逐漸發(fā)現(xiàn)微生物在農(nóng)業(yè)生態(tài)系統(tǒng)中的重要意義,尤其是有益微生物對(duì)退化耕地土壤的修復(fù)作用,能在不影響宿主植物經(jīng)濟(jì)價(jià)值的同時(shí),兼顧環(huán)境友好作用。
印度梨形孢(Serendipita indica,曾用名Piriformospora indica)屬擔(dān)子菌門(Basidiomycota)層菌綱(Hymenomycetes)蠟殼耳目(Sebacinales)梨形孢屬(Piriformospora),具有類似梨形狀的孢子結(jié)構(gòu),主要定殖在植物根系分生區(qū)和伸長(zhǎng)區(qū)[1-2]。印度梨形孢于1998年在印度西北部的塔爾沙漠中被發(fā)現(xiàn),是一種與叢枝菌根真菌(arbuscular mycorrhiza fungi,AMF)功能類似,但又具有其獨(dú)特優(yōu)勢(shì)的植物內(nèi)生真菌[3-4]。它能夠利用厚垣孢子或菌絲在多種培養(yǎng)基上進(jìn)行離體培養(yǎng),可以在園藝作物十字花科植物,如甘藍(lán)、芥菜、菠菜、陸生蘭花等非菌根植物上定殖[5-6]。印度梨形孢在植物根系中定殖時(shí)會(huì)造成宿主細(xì)胞程序性死亡,但對(duì)根系活力或生長(zhǎng)沒有明顯副作用[2]。它能夠在大部分單子葉植物和雙子葉植物根部定殖,包含百余種重要的經(jīng)濟(jì)作物、多種藥用植物等,促進(jìn)宿主植物生長(zhǎng)、改善營(yíng)養(yǎng)、提高植株的生物和非生物脅迫耐受性[7-13]。這些特點(diǎn)使得印度梨形孢在農(nóng)業(yè)上具有更加廣泛應(yīng)用前景。
鑒于印度梨形孢作為可持續(xù)農(nóng)業(yè)的土壤修復(fù)產(chǎn)品的應(yīng)用潛力[14],本文系統(tǒng)歸納了印度梨形孢與宿主植物共生作用機(jī)制,深入分析印度梨形孢在促進(jìn)植物對(duì)土壤中礦質(zhì)元素的吸收作用機(jī)制,為進(jìn)一步研究印度梨形孢在農(nóng)業(yè)土壤修復(fù)上應(yīng)用提供參考。
1" 印度梨形孢與宿主植物共生機(jī)制
1.1" 印度梨形孢與宿主植物根系識(shí)別
印度梨形孢與植物建立共生關(guān)系首先進(jìn)行宿主識(shí)別(圖1)。該過程在叢枝菌根真菌中已被廣泛研究,并認(rèn)為獨(dú)腳金內(nèi)酯(SL)起到了重要誘導(dǎo)作用[15]。在印度梨形孢的宿主識(shí)別過程中發(fā)現(xiàn)了類黃酮物質(zhì),除此之外還在其濾液中發(fā)現(xiàn)了細(xì)胞壁降解酶、聚半乳糖苷酶和木聚糖酶的存在[16]。Nivedita等認(rèn)為水稻根部誘導(dǎo)的凝集素蛋白激酶(LecRK)可能是一種起到植物感知和識(shí)別作用的信號(hào)物質(zhì)[17]。研究還發(fā)現(xiàn)一種富含亮氨酸的植物根際信號(hào)蛋白基因(如pii-2和At1g16590)可能促進(jìn)了印度梨形孢和植物相互識(shí)別,但還需要進(jìn)一步驗(yàn)證[16]。
1.2" 印度梨形孢與植物防御反應(yīng)
真菌在進(jìn)入宿主植物后需要突破宿主細(xì)胞的先天防御系統(tǒng)。宿主植物為了抵御微生物入侵,會(huì)啟動(dòng)位于細(xì)胞表面的微生物或病原體相關(guān)分子模式(MAMP或PAMP)產(chǎn)生效應(yīng)物,該過程中受到模式識(shí)別受體(PRR)的調(diào)節(jié)[18-19]。當(dāng)印度梨形孢入侵植物細(xì)胞時(shí),有研究認(rèn)為真菌幾丁質(zhì)作為植物免疫反應(yīng)的激發(fā)劑,受到PRR和幾丁質(zhì)受體CERK調(diào)節(jié),產(chǎn)生幾丁質(zhì)脫乙?;?,將幾丁質(zhì)低聚物轉(zhuǎn)化為脫乙酰化的殼聚糖低聚物,這些低聚物無法被宿主植物的受體識(shí)別,從而避免觸發(fā)植物防御系統(tǒng)[20]。也有研究認(rèn)為印度梨形孢的定殖介導(dǎo)PRR的信號(hào)轉(zhuǎn)導(dǎo)過程失活,是因?yàn)椴荒軌蛴|發(fā)Ca2+依賴型蛋白激酶(CDPK)級(jí)聯(lián)反應(yīng)以及活性氧(ROS)免疫應(yīng)答[21]。通過對(duì)轉(zhuǎn)錄組分析印度梨形孢與宿主植物相互作用時(shí)會(huì)表達(dá)大量效應(yīng)小分泌蛋白(SSP)和細(xì)胞壁降解酶(CWDE),對(duì)印度梨形孢分泌蛋白質(zhì)組學(xué)進(jìn)行分析發(fā)現(xiàn),976個(gè)信號(hào)肽中有23個(gè)攜帶碳水化合物結(jié)合蛋白結(jié)構(gòu)域LysM,這些物質(zhì)均有可能參與幾丁質(zhì)代謝,作為效應(yīng)物干擾免疫反應(yīng)[22-24]。除了幾丁質(zhì),也有研究認(rèn)為印度梨形孢通過調(diào)節(jié)真菌葡聚糖結(jié)合蛋白基因(FGB1),分泌具有雙重功能的真菌特異性效應(yīng)物β-葡聚糖,從而抑制觸發(fā)的植物免疫反應(yīng)[25]。印度梨形孢通過避免植物應(yīng)答真菌免疫反應(yīng)的機(jī)制仍需進(jìn)一步深入研究。
有研究認(rèn)為激素在印度梨形孢定殖過程中起到重要作用。調(diào)控效應(yīng)因子PIIN_08944能夠干擾植物水楊酸介導(dǎo)的植物抗性反應(yīng)[26]。游離生長(zhǎng)素可能干擾MAMP觸發(fā)的免疫反應(yīng)[27]。赤霉素作為基礎(chǔ)防御調(diào)節(jié)物質(zhì)也參與了印度梨形孢在植物根系中的定殖過程[28]。印度梨形孢還通過介導(dǎo)植物脂氧合酶(AcLOX)和幾丁質(zhì)酶(AcCHI)參與到水楊酸和茉莉酸/乙烯信號(hào)通路中[29]。除此之外,有研究認(rèn)為印度梨形孢與茉莉酸一同招募乙烯抵抗水楊酸引起的免疫,避免定殖過程產(chǎn)生系統(tǒng)抗性[30-31]。印度梨形孢在不同物種的植物激素參與免疫應(yīng)答信號(hào)途徑中所起到的作用可能不同,并且根與葉片具有類似的感知系統(tǒng)和免疫系統(tǒng)[32-33]。
1.3" 印度梨形孢侵入過程
在擬南芥的研究中發(fā)現(xiàn),油菜素類固醇不敏感型受體激酶(BAK1)/體細(xì)胞胚胎發(fā)生受體激酶(SERK4)介導(dǎo)的磷酸化調(diào)節(jié)Ca2+通道環(huán)核苷酸門控離子通道蛋白基因CNGC20/CNGC19穩(wěn)態(tài)可以精確控制植物細(xì)胞死亡[34-35]。印度梨形孢侵入植物根系的活細(xì)胞3 d后,被定殖侵染的細(xì)胞進(jìn)入到細(xì)胞程序死亡階段[33]。之后,植物細(xì)胞質(zhì)膜內(nèi)陷,細(xì)胞器被破壞。有研究發(fā)現(xiàn)在印度梨形孢侵染7 d后,大麥細(xì)胞死亡調(diào)節(jié)因子BAX抑制劑(HvBI-1)的表達(dá)減弱,因此該內(nèi)生真菌干擾了宿主細(xì)胞的死亡程序,加速了細(xì)胞程序性死亡,從而有利于與植物形成互惠的相互作用[2]。約14 d后,表皮和皮質(zhì)細(xì)胞中形成細(xì)胞內(nèi)孢子[33]。印度梨形孢可能誘導(dǎo)赤霉素信號(hào)途徑并導(dǎo)致DELLA蛋白降解,提高促凋亡閾值并啟動(dòng)細(xì)胞死亡相關(guān)的定殖步驟,如ROS。但與病原微生物不同,宿主植物程序性死亡不會(huì)一直持續(xù)。在侵入早期和后期,MAMP觸發(fā)的免疫限制了印度梨形孢的定殖過程。同時(shí)茉莉酸/乙烯(JA/ET)和乙烯可以保護(hù)植物免受依賴細(xì)胞死亡的壞死性病原體的侵害[30]。水楊酸(SA)和吲哚硫代葡萄糖苷(IGS)也在定殖后期發(fā)揮重要作用[36]。真菌是主動(dòng)殺死宿主植物細(xì)胞還是植物感覺細(xì)胞發(fā)生內(nèi)源性變化而自主選擇程序性死亡還需要進(jìn)一步研究。
1.4" 印度梨形孢共生建立過程
印度梨形孢主要在延伸區(qū)細(xì)胞間定殖[2],而在根尖分生組織無定殖,這與叢枝菌根真菌有所不同。大部分菌絲存在于死根真皮和皮質(zhì)細(xì)胞中,通過菌絲穿透細(xì)胞,并在胞漿中原生質(zhì)體周圍構(gòu)建網(wǎng)狀結(jié)構(gòu)。也有研究認(rèn)為環(huán)核苷酸門控離子通道蛋白基因CNGC19可以為印度梨形孢在宿主植物根系中形成穩(wěn)固的共生關(guān)系提供重要保證[34-35];在穩(wěn)固的合作或競(jìng)爭(zhēng)關(guān)系中,糖代謝也起到重要的作用[37]。在玉米中研究發(fā)現(xiàn),己糖轉(zhuǎn)運(yùn)蛋白PiHXT5在共生過程中起到重要調(diào)控作用[38]。盡管有研究認(rèn)為印度梨形孢的定殖沒有對(duì)地上部糖庫產(chǎn)生影響,但研究認(rèn)為其定殖可能會(huì)增加蔗糖向根的流入量[39]。
2" 活化土壤礦質(zhì)元素促進(jìn)植物礦質(zhì)元素吸收作用機(jī)制
形成共生關(guān)系后,印度梨形孢可以引起宿主植物的土壤礦質(zhì)養(yǎng)分吸收過程發(fā)生系統(tǒng)性變化,土壤中含有大量營(yíng)養(yǎng)元素處于固定態(tài),需要經(jīng)歷溶解、吸收和運(yùn)輸?shù)冗^程才能被植物利用,制約了植物的生長(zhǎng)。此過程受到根際微環(huán)境影響[40]。
2.1" 調(diào)控根系形態(tài)及礦質(zhì)元素轉(zhuǎn)運(yùn)蛋白
根系形態(tài)對(duì)宿主植物養(yǎng)分吸收和水分平衡有重要作用。印度梨形孢能增加植物根系長(zhǎng)度、改變根系性狀、擴(kuò)大根體積和表面積、增加側(cè)根數(shù)量和分叉、促進(jìn)根毛生長(zhǎng),使植物能夠從土壤中獲得更多磷元素[41]。研究認(rèn)為印度梨形孢侵染植物細(xì)胞后,通過調(diào)控離子轉(zhuǎn)運(yùn)通道促進(jìn)礦質(zhì)養(yǎng)分活化及轉(zhuǎn)運(yùn),提高養(yǎng)分轉(zhuǎn)運(yùn)體(Mg2+、PO3-4和SO2-4轉(zhuǎn)運(yùn)蛋白)表達(dá)促進(jìn)植物對(duì)養(yǎng)分吸收。
在擬南芥的研究中發(fā)現(xiàn)印度梨形孢可以刺激硝酸鹽還原酶基因表達(dá)來促進(jìn)擬南芥的生長(zhǎng)[42]。在水稻接種印度梨形孢發(fā)現(xiàn)根系磷轉(zhuǎn)運(yùn)蛋白基因PtPT3、PtPT5、PtPT6表達(dá)上調(diào)[43-44],也有研究發(fā)現(xiàn)印度梨形孢雖然會(huì)促進(jìn)植物磷的吸收,但并不影響宿主植株的磷轉(zhuǎn)運(yùn)蛋白表達(dá)[45]。在低鉀條件下,印度梨形孢能夠幫助宿主植株提高鉀元素的轉(zhuǎn)運(yùn)和積累[38]。印度梨形孢通過調(diào)控鎂轉(zhuǎn)運(yùn)蛋白PiMgT1、高親和的硫轉(zhuǎn)運(yùn)蛋白SiSulT促進(jìn)對(duì)大量元素鎂和硫的吸收,但作用機(jī)制仍不清楚[46-47]。印度梨形孢調(diào)控植物氮、磷、鉀元素等其他礦質(zhì)元素的運(yùn)輸及轉(zhuǎn)運(yùn)機(jī)制還需要進(jìn)一步研究[48]。
2.2" 菌絲網(wǎng)絡(luò)促進(jìn)養(yǎng)分活化運(yùn)移
印度梨形孢通過外部菌絲網(wǎng)絡(luò)將植物根系與根際土壤以外的區(qū)域聯(lián)系在一起,這是因?yàn)橄噍^于較粗的根系根毛,菌絲更容易滲透到土壤團(tuán)粒間隙,通過根外菌絲間接擴(kuò)大了植物對(duì)土壤礦質(zhì)元素的吸收范圍。附著在根系表面松散的菌絲網(wǎng)絡(luò)和侵入到宿主根部細(xì)胞間生長(zhǎng)的菌絲成為宿主和菌根營(yíng)養(yǎng)交換的重要場(chǎng)所[49]。與其他真菌類似,印度梨形孢在土壤中的菌絲具有比根系更大的表面積,擴(kuò)大了礦物質(zhì)吸收面積。同時(shí)菌絲通過改善土壤結(jié)構(gòu),使更多養(yǎng)分溶解到水分中。共生體通過菌絲將土壤中磷、氮、硫、鐵等礦質(zhì)元素運(yùn)輸?shù)街仓?,增加植物?duì)礦質(zhì)元素的吸收速度,提高根系對(duì)養(yǎng)分的吸收,促進(jìn)植物生長(zhǎng)發(fā)育[48]。宿主反向提供真菌碳水化合物等營(yíng)養(yǎng)物質(zhì),促進(jìn)其菌絲和孢子生長(zhǎng)發(fā)育,提高根系侵染。
2.3" 分泌物改善根際微環(huán)境促進(jìn)養(yǎng)分增溶
菌根真菌可采用多種策略改變土壤環(huán)境中礦物組成以便吸收利用,其中重要的途徑包括改變土壤pH值、分泌多種化學(xué)物質(zhì)、增加有機(jī)酸或分泌低分子螯合劑等活化土壤中難溶養(yǎng)分。
有研究認(rèn)為印度梨形孢產(chǎn)生磷酸酶溶解土壤中不溶性多磷酸鹽和有機(jī)磷酸鹽;還有研究認(rèn)為這一過程的完成離不開酸性磷酸酶和堿性磷酸酶。研究認(rèn)為前者是共生體共有,參與磷的吸收,而后者主要由真菌產(chǎn)生,參與磷的同化[50]。目前針對(duì)磷酸酶的研究并不是很多。另外,通過對(duì)培養(yǎng)濾液分析發(fā)現(xiàn),印度梨形孢可以分泌細(xì)胞壁降解酶、幾丁質(zhì)物質(zhì)[51-52]。Badged等向土壤中加入印度梨形孢培養(yǎng)濾液發(fā)現(xiàn)次生代謝物能夠影響植株發(fā)育[53]。早期研究中發(fā)現(xiàn)印度梨形孢培養(yǎng)物濾液和宿主植物根系侵染后會(huì)分泌碳水化合物、皂苷、黃酮類、幾丁質(zhì)以及纖維素酶、聚半乳糖苷酶和木聚糖酶等細(xì)胞壁降解酶等物質(zhì),并且土壤中添加印度梨形孢可能影響宿主植物根系分泌物組成和數(shù)量,對(duì)土壤微生物群落也會(huì)造成影響[51-55]。這些物質(zhì)與土壤中礦質(zhì)營(yíng)養(yǎng)活化有關(guān),并有可能進(jìn)一步影響土壤組成和功能。
2.4" 影響根際微生物環(huán)境
土壤、根際微生物與植物根系統(tǒng)一構(gòu)成地下部分的有機(jī)整體,共同參與有機(jī)質(zhì)分解、養(yǎng)分轉(zhuǎn)換和運(yùn)輸,進(jìn)而影響植株地上部分生長(zhǎng)。印度梨形孢與宿主植物共生同時(shí)也影響宿主植物根際微生物組成和功能,對(duì)土壤微生物群落造成影響[55]。有研究表明,印度梨形孢濾液處理的根系土壤含有大量細(xì)菌、真菌和放線菌。Varma等認(rèn)為印度梨形孢及其濾液可以作為潛在的根病生物防治劑抑制小麥全蝕病病原菌(Gaeumannomyces graminis)和聚多曲霉(Aspergillus sydowii)[51]。盡管有研究認(rèn)為真菌侵染宿主植物后,根系分泌物中黃酮類化合物可能起到植物-微生物相互作用中作為信號(hào)分子的作用[54],但作用因子的化學(xué)性質(zhì)仍未知。這一點(diǎn)在叢枝菌根真菌的研究中也有報(bào)道[56]。
3" 印度梨形孢在退化土壤環(huán)境中的應(yīng)用
土壤鹽堿化使得植物根部過多積累鈉離子,直接影響植物新陳代謝,最終導(dǎo)致植物損傷、生物量下降[20]。研究中發(fā)現(xiàn)印度梨形孢可以提高鹽脅迫下宿主植物抗壞血酸還原酶的抗氧化能力[9],增加有機(jī)溶質(zhì)含量,改變Na+/K+穩(wěn)態(tài)并調(diào)節(jié)水孔蛋白的表達(dá)以維持水分狀態(tài),進(jìn)而提高植物耐鹽性,但是對(duì)于脯氨酸含量的影響存在差異[57-59]。李亮等對(duì)豆科植物進(jìn)行接菌,發(fā)現(xiàn)在鹽脅迫條件下,印度梨形孢可以作為生長(zhǎng)促進(jìn)因子提高植物耐鹽性[60]。在核桃幼苗中也發(fā)現(xiàn)了相同的作用[61]。印度梨形孢還可以調(diào)控棗椰樹等植物耐鹽基因鉀離子轉(zhuǎn)運(yùn)蛋白HKT1;5、鹽敏感蛋白SOS1基因、病程相關(guān)蛋白基因(PR-1a,PR2,PR2,PR5)和鹽脅迫相關(guān)基因OPBP1,以提高鹽脅迫耐受性[59,62]。
重金屬(鎳、銅、鎘、汞和鉛等)污染會(huì)對(duì)土壤肥力造成直接影響,達(dá)到一定濃度后會(huì)對(duì)植物生理生化造成影響[63]。研究發(fā)現(xiàn)印度梨形孢與宿主植物共生激發(fā)了重金屬解毒系統(tǒng),通過增加幼苗根冠比、提高抗氧化性、減少ROS和丙二酸(MDA)含量、降低地上部分重金屬積累、減弱重金屬毒性(脂質(zhì)過氧化物和過氧化氫酶活性)[64-67],增強(qiáng)植物螯合素基因和應(yīng)激反應(yīng)基因表達(dá),最終減輕毒害[66-68]。以重金屬鎘為例,研究發(fā)現(xiàn)印度梨形孢可以提高水稻在鎘脅迫下對(duì)礦物質(zhì)的吸收,下調(diào)糖酵解循環(huán)酶[66];Lu等研究認(rèn)為負(fù)責(zé)將鎘封存在液泡中鎘轉(zhuǎn)運(yùn)體基因OsHMA3可能對(duì)減少水稻中鎘積累起到重要作用,但是印度梨形孢對(duì)此基因是否有調(diào)節(jié)作用還需要進(jìn)一步研究[69]。主朋月等對(duì)紫花苜蓿接菌后發(fā)現(xiàn)印度梨形孢分泌生長(zhǎng)素,提高土壤脲酶和蔗糖酶的還原性,降低了地上部分鎘的含量[70]。先露露等在高丹草中也發(fā)現(xiàn)相同結(jié)果[71]。此外,印度梨形孢對(duì)植物應(yīng)對(duì)銅、汞和砷等其他重金屬脅迫的積極作用研究目前還不是很多,有待于進(jìn)一步深入研究。
干旱脅迫直接影響植物對(duì)水分和礦質(zhì)營(yíng)養(yǎng)元素的吸收,使植株生理生化受到影響。印度梨形孢定殖宿主植物后,會(huì)通過多種途徑降低植物受到的干旱傷害:(1)積極調(diào)整葉片形態(tài)、降低氣孔導(dǎo)度、改良根系構(gòu)型、改善水分狀態(tài)和增加礦質(zhì)元素吸收來緩解脅迫植物[72-75]。(2)增加葉綠素合成、調(diào)節(jié)光合相關(guān)蛋白[75-76]。(3)積累脯氨酸和滲透調(diào)節(jié)物質(zhì)含量[77]、維持植物基礎(chǔ)穩(wěn)態(tài)和細(xì)胞壁彈性。(4)增加抗氧化酶(SOD、CAT、APX)活性,激活抗氧化防御系統(tǒng)。(5)平衡植物激素(生長(zhǎng)素、水楊酸、細(xì)胞分裂素和脫落酸)[78-80]。干旱脅迫下對(duì)棉花幼苗和非洲菊幼苗接種印度梨形孢,可以保護(hù)其光系統(tǒng),提高葉片保水能力,促進(jìn)植物正常生長(zhǎng),誘導(dǎo)植株提高其抗旱性[75,81]。印度梨形孢可以上調(diào)水稻脯氨酸合成相關(guān)基因P5CS的表達(dá)[82]。接種印度梨形孢的柑橘幼苗在干旱脅迫下,通過提高根系中CAT的含量,積累MDA,降低植株滲透勢(shì),保持柑橘幼苗體內(nèi)水分[83]。這與油菜作物的研究結(jié)果[84]一致。印度梨形孢還參與水稻miRNA調(diào)節(jié),顯著上調(diào)miR396和miR159表達(dá),分別通過MYB和GRF的精細(xì)調(diào)控使植物耐受干旱脅迫[79,82]。
4" 展望
國(guó)內(nèi)外研究表明印度梨形孢具有解決土壤退化問題的能力。作為一項(xiàng)生物菌肥技術(shù),利用微生物促進(jìn)植物吸收礦質(zhì)元素,將多余重金屬固定在菌絲,將有利于減少化肥和農(nóng)藥的使用,減弱農(nóng)業(yè)系統(tǒng)對(duì)化學(xué)制劑的依賴。在有益微生物的應(yīng)用中,考慮到環(huán)保和應(yīng)用經(jīng)濟(jì)性,印度梨形孢可以離體培養(yǎng)使其更具有可商業(yè)化生產(chǎn)的優(yōu)勢(shì),但要實(shí)現(xiàn)在農(nóng)業(yè)生產(chǎn)的普遍應(yīng)用,還應(yīng)考慮以下問題。
(1)加強(qiáng)與宿主植物根系識(shí)別機(jī)制的研究。印度梨形孢可以與大多數(shù)植物共生,使其成為研究的熱點(diǎn)。但如何相互識(shí)別并形成互惠共生關(guān)系的作用機(jī)制仍需進(jìn)一步研究,尤其對(duì)印度梨形孢分泌效應(yīng)蛋白的研究將有助于了解內(nèi)生真菌與植物的互作機(jī)制,不僅可以提高生物菌肥技術(shù)的利用效率,而且能夠?yàn)閮?yōu)良品種選育提供方向。
(2)加強(qiáng)對(duì)促進(jìn)宿主礦質(zhì)元素吸收過程的研究。印度梨形孢不僅可以促進(jìn)植物的礦質(zhì)養(yǎng)分吸收,還可以緩解非生物和生物脅迫。印度梨形孢對(duì)礦質(zhì)養(yǎng)分的吸收作用與改善退化土壤質(zhì)量的作用還需要進(jìn)一步研究。盡管已有許多研究證實(shí)印度梨形孢在鹽堿土壤、重金屬土壤以及干旱土壤中對(duì)植物具有有利作用,但是其作用機(jī)制尚不明晰。
(3)對(duì)印度梨形孢的純培養(yǎng)和田間應(yīng)用需要進(jìn)一步研究。對(duì)生物菌劑效果的驗(yàn)證,還需考慮在農(nóng)業(yè)生產(chǎn)條件下的影響,如土著微生物、傳統(tǒng)農(nóng)藝措施(土壤灌溉、施肥、殺菌劑等)等對(duì)印度梨形孢的長(zhǎng)效作用,這些是進(jìn)一步大規(guī)模田間施用的重要依據(jù)。除此之外,聯(lián)合應(yīng)用納米顆粒與其他土壤有益微生物對(duì)作物生長(zhǎng)具有協(xié)同促進(jìn)作用,但最終效果還需要進(jìn)一步研究。
對(duì)印度梨形孢的研究越來越受到國(guó)內(nèi)外科研工作者重視。統(tǒng)計(jì)Web of Science數(shù)據(jù)庫中關(guān)于印度梨形孢的文獻(xiàn),發(fā)現(xiàn)其年發(fā)文量在2022年得到快速增長(zhǎng)(109篇),比2021年增加了15.89%,表明印度梨形孢具有作為植物生長(zhǎng)促進(jìn)劑或生物肥料的巨大潛力。因此,加強(qiáng)以印度梨形孢的高效應(yīng)用、培養(yǎng)物及其次生代謝產(chǎn)物為基礎(chǔ)的理論及應(yīng)用研究,積極開發(fā)菌種培養(yǎng)技術(shù)和多種微生物共生生物肥料,以使宿主植物更好地利用土壤養(yǎng)分,修復(fù)退化(或污染)的土壤和促進(jìn)植物生長(zhǎng),最終達(dá)到提高耕地利用效率,改善農(nóng)產(chǎn)品產(chǎn)量和質(zhì)量的目標(biāo),對(duì)農(nóng)業(yè)可持續(xù)發(fā)展具有積極意義。
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