低硼及高硼脅迫對棉花幼苗生長與脯氨酸代謝的影響

曾紫君 曾 鈺 閆 磊 程 錦 姜存倉

研究簡報

低硼及高硼脅迫對棉花幼苗生長與脯氨酸代謝的影響

曾紫君 曾 鈺 閆 磊 程 錦 姜存倉*

華中農業大學資源與環境學院 / 微量元素研究中心, 湖北武漢 430070

以‘鄂抗10號’棉花品種為材料, 采用營養液培養, 設置不加硼(B0, 0 mg L-1)、低硼(B0.002, 0.002 mg L-1)、適硼(CK, B0.2, 0.20 mg L-1)、高硼(B50, 50 mg L-1) 4個硼(Boron, B)水平, 探究低硼和高硼脅迫處理下棉花幼苗生長及脯氨酸代謝的響應。結果表明, B0、B0.002及B50處理較CK顯著抑制植株生長, 表現出較低的植株鮮重和干重, 根系伸長受到抑制。在供硼處理下, 隨著硼濃度的升高, 棉花幼苗根、莖和葉中硼含量均呈梯度性上升, 其中, B0.2和B50處理下葉片中硼含量均高于根和莖; 而在B0和B0.002處理下, 根中的硼含量高于葉和莖。低硼和高硼處理下葉片中脯氨酸含量明顯增加, 而根中脯氨酸含量顯著減少。進一步分析葉片和根中脯氨酸合成代謝相關酶活性發現, B0.002和B50處理較CK增加棉花幼苗葉片Δ1-吡咯啉-5-羧酸合成酶(Δ1-pyrroline-5-carboxylate synthetase, P5CS)和鳥氨酸轉氨酶(Ornithine-δ-aminotransferase, OAT)活性而降低脯氨酸脫氫酶(Proline dehydrogenase, ProDH)的活性; 葉片中Δ1-吡咯啉-5-羧酸還原酶(Δ1-pyrroline-5-carboxylate reductase, P5CR)活性在B50處理下顯著高于CK, 而B0.002處理下該酶活性變化差異不顯著。另外, B50處理較CK顯著降低棉花幼苗根中OAT和P5CR酶活性, 而B0.002處理顯著增加根中P5CS和ProDH的活性。表明低硼和高硼脅迫均抑制棉花幼苗的生長。硼脅迫條件下, 脯氨酸主要積累在棉花幼苗葉片中, 根中脯氨酸含量顯著降低。缺硼和硼毒害時, 棉花幼苗葉片中脯氨酸的積累主要是通過調節脯氨酸Glu和Orn途徑中的關鍵酶(OAT、P5CS合成酶和ProDH分解酶)活性, 使得脯氨酸的合成速度高于其降解。而在根中, 缺硼脅迫下主要是促進脯氨酸的降解導致根中脯氨酸含量降低, 高硼脅迫下主要是通過降低OAT和P5CS合成酶以及ProDH分解酶活性來抑制脯氨酸的合成及其分解, 但是對脯氨酸合成的抑制作用遠大于其降解, 最終導致根系脯氨酸含量降低。

棉花; 硼; 脯氨酸; 合成和降解

硼(B)是植物必需的微量營養元素[1], 但硼從缺乏到過量的范圍過窄, 因此植物易出現缺硼和硼毒害現象[2-3]。棉花是重要的經濟作物, 我國是世界上主要產棉國之一, 種植區域主要分布在長江、黃河流域和新疆內陸[4]。受土壤類型和氣候條件等的影響, 中國棉區土壤硼含量一般由北向南、由西向東逐漸降低[5-6]。我國棉花主產區普遍處于硼缺乏范圍, 土壤有效硼含量為0.47 mg kg-1, 而長江中下游棉區土壤有效硼易流失, 僅為0.33 mg kg-1, 屬于嚴重缺硼土壤, 易導致棉花蕾而不花[6-7]。硼被認為是棉花最易缺乏的微量元素[8], 硼肥的施用可提高棉花的產量和品質, 但近年來, 由于硼肥的不當施用, 造成部分棉區還是面臨缺硼狀況, 制約棉花產量的提高[9-10]。因此, 深入研究分析棉花對硼脅迫的響應機理對提高其抗逆性、促進農業增效和農民增收具有重要的意義。

研究表明, 植物在脅迫條件下會發生復雜的生理生化反應, 而脯氨酸(proline, Pro)作為一種小分子滲透保護物質, 在植物抵御各種逆境脅迫中發揮重要的作用, 其作用表現為滲透調節劑[11]、活性氧清除劑[12]、氧化還原平衡劑[13]及蛋白質和亞細胞結構穩定劑[14-15]等。有研究發現, 植物在重金屬脅迫[16]、堿脅迫[17]、鹽脅迫[18]和高溫干旱[19]等脅迫下會積累大量脯氨酸。Delauney等[20]認為, 植物體內脯氨酸積累主要是因為脅迫刺激了其從頭合成。植物體內合成脯氨酸有2條途徑, 分別為谷氨酸途徑(glutamate pathway, Glu)和鳥氨酸(ornithine pathway, Orn)途徑。參與催化谷氨酸合成脯氨酸的酶主要有Δ1-吡咯啉-5-羧酸合成酶(Δ1-pyrroline-5-carboxylate synthetase, P5CS)和Δ1-吡咯啉-5-羧酸還原酶(Δ1-pyrroline-5- carboxylate reductase, P5CR)[21]。在鳥氨酸途徑中, 脯氨酸的合成主要是在鳥氨酸轉氨酶(ornithine-δ-aminotransferase, OAT)和Δ1-吡咯啉-5-羧酸還原酶(Δ1-pyrroline-5-carboxylate reductase, P5CR)的催化下進行的[22-23]。其中, P5CS和OAT被認為是脯氨酸合成過程中Glu和Orn途徑中的關鍵酶[24]。植物控制脯氨酸積累的第2個因素是其降解, 該過程是合成途徑的逆轉, 但涉及的酶不同。脯氨酸在脯氨酸脫氫酶(proline dehydrogenase, ProDH)和吡咯啉-5-羧酸脫氫酶(pyrroline-5-carboxylate dehydrogenase, P5CDH)催化下氧化為谷氨酸, 其中, ProDH被認為是脯氨酸降解途徑的限速酶[25-26]。

目前, 關于植物在硼脅迫下的研究較多, 而關于硼脅迫誘導的脯氨酸的合成代謝變化的研究較少。事實上, 脯氨酸的合成與代謝是一個復雜的生理生化過程, 參與脯氨酸累積過程的酶所起的作用程度是不同的。在遭受脅迫時, 植物體內會積累脯氨酸, 但脯氨酸的合成途徑究竟是哪一條居于主導地位并不清楚。本研究在前人工作的基礎上, 以‘鄂抗10號’為供試材料, 采用營養液培養, 主要研究硼脅迫下棉花幼苗生物量和脯氨酸在不同器官分配積累的不同響應機制, 力求探索其可能的適應機制, 以期進一步揭示硼脅迫如何影響植物體內脯氨酸代謝提高其抗逆性。

1 材料與方法

1.1 試驗設計

試驗于2019年8月在華中農業大學日光溫室進行, 試驗材料為‘鄂抗10號’棉花種子。試驗設置4個B濃度(B源用H3BO3), 分別為不加硼(B0, 0 mg L-1)、低硼(B0.002, 0.002 mg L-1)、適硼(CK, B0.2, 0.20 mg L-1)和高硼處理(B50, 50 mg L-1), 每個處理設置4個重復。試驗所用營養液參考Hoagland和Arnon[27]。各營養物質用量如下: 0.240 g L-1NH4NO3、0.100 g L-1Na2HPO4·12H2O、0.100 g L-1NaH2PO4·2H2O、0.360 g L-1CaCl2·2H2O、0.500 g L-1MgSO4·7H2O、1.81 mg L-1MnCl2·4H2O、0.22 mg L-1ZnSO4·7H2O、0.08 mg L-1CuSO4·5H2O、0.09 mg L-1Na2MoO4·2H2O和32.5 mg L-1Fe-EDTA, 所用試劑均為分析純。

1.2 試驗方法

挑選均勻飽滿的種子, 在36℃條件下烘箱處理48 h以破除種子休眠, 然后用60℃的溫開水浸泡6 h, 將浸泡好的種子置于濕潤的紗布上催芽, 待初生根長至1 cm左右時再將其置于塑料桶上繼續培養。子葉展開后轉移到5 L黑塑料袋避光的塑料桶中加入營養液培養, 每桶2株。先用1/4濃度營養液培養1周, 再用1/2濃度營養液培養1周, 繼而用全量濃度進行后期培養, 總共培養38 d后收獲。每4 h通氣20 min, 每周更換1次營養液。

1.3 樣品采集與測定

1.3.1 樣品采集 將采集的樣品用超純水洗凈, 分為根、莖和葉3個部位。各部位分別稱鮮重后裝入信封袋, 于105℃的烘箱中殺青30 min, 后在75℃下烘干至恒重, 稱完干物質質量后粉碎過篩用于硼含量的測定。

1.3.2 樣品測定 根系形態和生長參數的測定: 采用根系掃描儀(Epson Perfection V700)掃描根系, 并使用WinRHIZO根系分析系統測定總根長(total root length, TRL)、總表面積(total surface area, TSA)、根總體積(total root volume, TRV)、側根數、根尖數和根平均直徑(average diameter of root, RAD)等根系生長指標。硼含量測定: 稱取粉碎后的樣品在馬弗爐中500℃干灰化5 h, 用0.1 mol L-1的HCl溶液浸提, 取濾液用姜黃素比色法測定各部位硼含量[28]。脯氨酸含量的測定: 參照王學奎[29]和吳成龍等[17]的方法。稱取根和葉片干樣0.02 g, 用3%磺基水楊酸溶液5 mL進行研磨提取, 在沸水浴中提取10 min, 冷卻之后吸取2 mL濾液置于25 mL試管中, 加入冰醋酸和酸性茚三酮溶液各2 mL, 沸水浴加熱30 min后加入4 mL甲苯顯色, 在520 nm處比色。脯氨酸代謝酶的測定: 參照Shan等[30]和Rocha等[31]方法提取P5CS、ProDH、P5CR和OAT四種酶液, 略有修改, 采用Elisa試劑盒(江蘇酶標生物有限公司)測定酶活。由于不加硼(B0)處理下植株生長受到嚴重抑制, 收樣時生物量較少, 故沒有足夠的材料用于脯氨酸含量及脯氨酸代謝酶活性的測定。

1.4 數據處理

采用Microsoft Excel軟件作圖, 用統計分析軟件SPSS 21對各處理試驗數據進行統計和分析, 運用Duncan程序進行不同處理之間的差異顯著性檢驗, 顯著水平為<0.05。

2 結果與分析

2.1 不同硼濃度處理對棉花幼苗生物量的影響

由圖1可以看出, 不加硼(B0)和低硼(B0.002)處理下植株的根系生長明顯受到抑制。B0處理下植株老葉葉片變厚變脆, 頂芽受損, 腋芽大量發生而形成多頭棉; 新葉較小, 邊緣及主脈失綠, 葉片上卷呈杯狀; 根短粗, 兼有褐色。高硼(B50)處理下棉花幼苗老葉最先出現硼毒癥狀, 主要表現在老葉葉尖和葉片邊緣灼傷、失綠黃化, 出現黃褐色壞死斑點, 且下部葉的中毒癥狀和生理變化比上部葉明顯。

B0: 0mg L-1硼處理; B0.002: 0.002mg L-1硼處理; B0.2: 對照, 0.2 mg L-1硼處理; B50: 50 mg L-1硼處理。

B0: 0mg L-1of boron treatment; B0.002: 0.002mg L-1of boron treatment; B0.2: CK, 0.2 mg L-1of boron treatment; B50: 50 mg L-1of boron treatment.

與CK相比, 其他3種處理下植株的根、莖、葉以及整株植株的干鮮重明顯降低且達到顯著差異, 其中B0處理對植株干鮮重影響較大(表1)。B0條件下植株的根、莖、葉鮮重較CK分別降低78.86%、78.24%、66.16%, B0.002處理下植株的根、莖、葉鮮重較CK分別降低49.71%、46.37%、38.51%, B50處理下植株的根、莖、葉鮮重較CK分別降低47.43%、39.64%、39.52%, 表明植株受缺硼影響較其他脅迫處理大, 與其他部位相比, 植株根系對硼脅迫反應更敏感。與低硼處理相比, 高硼處理下植株的根和莖鮮重有增加的趨勢而葉片的鮮重降低, 但差異不顯著。

表1 不同硼處理對棉花幼苗生長指標的影響

表中數據代表平均值±標準誤差, 含4個獨立的重復試驗。同列數值后不同小寫字母表示處理間在0.05水平差異顯著。B0: 0 mg L-1硼處理; B0.002: 0.002 mg L-1硼處理; B0.2: 對照, 0.2 mg L-1硼處理; B50: 50 mg L-1硼處理。

The data in the table represent the mean ± standard error, including four independent repetitions. Values with a column followed by different lowercase letters represent significant differences among the treatments at the 0.05 probability level. B0: 0 mg L-1of boron treatment; B0.002: 0.002 mg L-1of boron treatment; B0.2: CK, 0.2 mg L-1of boron treatment; B50: 50 mg L-1of boron treatment.

2.2 不同硼濃度處理對棉花幼苗根系形態指標的影響

當硼濃度從低水平增加到正常水平時, 植株的總根長(TRL)、總表面積(TSA)、根總體積(TRV)、側根數、根尖數也相應增加且差異顯著(表2)。而當硼處理從正常水平進一步提高到過量水平時, 這些根系生長參數顯著降低。不加硼、低硼和高硼處理下的根長較正常硼處理分別減少88.54%、47.06%、40.47%, 側根數分別減少90.46%、52.13%、45.21%, 總表面積分別減少85.63%、48.95%、42.21%。根平均直徑(RAD)隨硼濃度的增加呈梯度性下降, 在正常硼處理時有所恢復但到高硼處理時又下降, 不加硼處理時達到了最大值, 不加硼條件下的根較CK平均直徑增加24.64%。表明缺硼及高硼處理都會影響植株根系的生長, 導致根系生長能力下降, 影響作物吸收能力。

2.3 不同硼濃度處理對棉花幼苗各部位硼含量及積累量的影響

在供硼處理下, 隨著硼濃度的升高, 根、莖和葉中的硼含量均呈上升趨勢, 其中葉片中硼含量的差異達到顯著水平(表3)。在正常硼和高硼條件下, 硼含量顯示為葉片>根>莖; 而在不加硼和低硼條件下, 硼含量顯示為根>葉片>莖。B0處理植株葉片中的硼含量較CK顯著降低73.05%。

無論何種處理, 植株葉片中的硼積累量均顯著高于莖和根中。隨著硼濃度的升高, 植株各部位硼積累量均顯著增加。葉片中各硼處理間的差異較根和莖中顯著, B0、B0.002處理下葉片中硼積累量較CK分別降低92.63%、82.74%, B50處理下升高3.5倍。

2.4 不同硼濃度處理對棉花幼苗葉片和根中脯氨酸含量的影響

由表4可知, 低硼(B0.002)和高硼(B50)處理下葉片中脯氨酸的含量較CK分別增加8.32%和26.87%; 而在根中, 脯氨酸含量分別降低26.84%和34.51%。在所有處理中, 植株不同部位的脯氨酸含量均顯示為葉片高于根。

2.5 不同硼濃度處理對棉花幼苗葉片和根中脯氨酸代謝酶活性的影響

由圖2可知, B0.002處理下葉片中OAT、P5CS酶活性較CK分別增加19.41%和17.38%; 相同的, B0.002處理下根中OAT、P5CS酶活性增加, 但OAT酶活性未達到顯著差異。與CK相比, 低硼條件下葉片和根中ProDH酶活性呈現出相反的趨勢, 即根中ProDH酶活性顯著增加29.60%, 葉片中ProDH酶活性顯著降低。高硼處理下葉片中OAT、P5CR、P5CS酶活性顯著增加, 而ProDH酶活性降低。高硼處理下根中OAT、P5CR酶活性較CK顯著降低23.40%和63.83%, 而P5CS和ProDH酶活性出現降低趨勢, 但未達到顯著差異。

表2 不同硼處理對棉花幼苗根系生長的影響

表中數據代表平均值±標準誤差, 含4個獨立的重復試驗。同列數值后不同小寫字母表示處理間在0.05水平差異顯著。處理同表1。

The data in the table represent the mean ± standard error, including four independent repetitions. Values with a column followed by different lowercase letters represent significant differences among the treatments at the 0.05 probability level. TRL: total root length; TSA: total surface area; TRV: total root volume; RAD: average diameter of root. Treatments are the same as those given in Table 1.

表3 不同硼濃度處理對棉花幼苗各部位硼含量及積累量的影響

表中數據代表平均值±標準誤差, 含4個獨立的重復試驗。同列數值后不同小寫字母表示處理間在0.05水平差異顯著。處理同表1。

The data in the table represent the mean ± standard error, including four independent repetitions. Values with a column followed by different lowercase letters represent significant differences among the treatments at the 0.05 probability level. Treatments are the same as those given in Table 1.

表4 不同硼濃度處理對棉花幼苗葉片和根中脯氨酸含量的影響

表中數據代表平均值±標準誤差, 含4個獨立的重復試驗。同列數值后不同小寫字母表示處理間在0.05水平差異顯著。處理同表1。

The data in the table represent the mean ± standard error, including four independent repetitions. Values with a column followed by different lowercase letters represent significant differences among the treatments at the 0.05 probability level. Treatments are the same as those given in Table 1.

3 討論

3.1 低硼及高硼脅迫對棉花幼苗生長的影響

眾所周知, 硼是植物必需的微量元素之一[1], 硼缺乏或過量都會對植物的生長發育造成傷害。耿明建等[32]通過對不同硼效率棉花品種根系參數差異研究發現, 缺硼顯著抑制棉花根系的伸長, 各品種根體積、根長、總吸收面積等根系生長參數均顯著降低。劉磊超等[33]研究發現, 缺硼顯著降低枳橙幼苗的干物質積累, 抑制其生長。本試驗結果也發現相似的結論, 即缺硼顯著抑制棉花幼苗生長, 降低植株的干鮮重。此外, 硼缺乏也會降低棉花幼苗的總根長、根尖數、總根體積和總根表面積, 抑制根的生長和新根的形成。高硼脅迫下, 植物的生長發育同樣受到影響。桑雯等[34]通過對硼毒下柑橘根葉蛋白質組學研究發現, 硼毒害嚴重影響柑橘根、莖、葉的生長, 老葉端和葉邊緣變黃并隨時間延長而壞死脫落。本試驗結果發現, 高硼脅迫下, 首先在葉尖觀察到葉黃化, 然后擴展到邊緣, 最后整片葉子, 與幼葉相比, 老葉更早的受到硼毒性的影響, 且硼毒癥狀并未在根系中發現, 分析原因可能是棉花屬于硼難以在韌皮部中移動的植物, 所以當硼進入根系后在植物體內主要隨著蒸騰流通過木質部向上運輸, 從而使老葉最先出現硼毒害癥狀[35-37]。與葉片相比, 即使處于高硼處理(B50)下, 棉花根系硼的積累量仍然較低, 這也解釋了硼毒癥狀未出現在根系上的原因之一。本研究中, 硼過量時, 棉花幼苗根系總長度、表面積和體積等參數明顯降低, 這表明50 mg L-1濃度硼對植株產生毒害作用, 進而抑制根系生長。Asad等[38]在柑橘研究中發現, 硼過量時抑制柑橘幼苗根系的生長、根長和直徑降低。

3.2 低硼及高硼脅迫對棉花幼苗葉片和根硼含量的影響

植物具有感知硼水平的變化并調節其在體內重新分配的能力, 這種調節作用對于硼脅迫條件下保證植物生存具有重要的意義[39]。張君等[40]研究發現, 給陸地棉葉緣施硼后, 根系中的硼含量下降。本試驗研究發現, 在正常硼和高硼條件下, 棉株葉片中的硼含量高于根和莖, 說明當葉片吸收的硼已經能夠滿足植物對硼的需求時, 那么根系對硼的吸收量就會減少。Liu等[41]研究發現, 紐荷爾臍橙在低硼脅迫下, 硼由根向地上部的運轉受到限制, 導致根中硼含量高于葉中。本試驗研究中也發現, 在不加硼和低硼條件下, 棉株根中硼含量高于葉和莖中, 其原因可能是: (1)缺硼導致棉花幼苗顯著發育不良, 葉面積小, 從而蒸騰作用大幅下降, 抑制了硼向上運輸; (2) 硼缺乏造成植物根尖疏導組織發育不良, 引起導管組織損傷[42-43], 使硼難以向地上部運輸, 造成根中硼含量明顯高于葉片和莖中。通過對棉花幼苗各部位硼積累量的測定分析發現, 無論何種處理, 植株葉片中硼積累量均顯著高于莖和根中。植株各部位硼積累量隨著硼濃度的提高均顯著增加, 葉片中各硼處理間的差異較根和莖中顯著。盧曉佩等[44]研究發現, 在不同硼處理下, 2種砧木葉片中硼積累量均顯著高于根和莖中。

柱上不同小寫字母分別表示在根、葉片中處理間在0.05水平上差異顯著。處理同表1。

Bars labeled with different lowercase letters represent significant differences among the treatments at the 0.05 probability level in roots and leaves, respectively. Treatments are the same as those given in Table 1.

3.3 低硼及高硼脅迫對棉花幼苗葉片和根脯氨酸含量的影響

脯氨酸的積累是植物受到逆境脅迫的一種信號, 大量積累的脯氨酸可調節胞內滲透勢, 減輕脅迫對植物造成的傷害。通過研究外源脯氨酸對缺硼下棉花幼苗生長和脯氨酸代謝影響中發現, 在缺硼脅迫時, 棉花幼苗葉片和根中的脯氨酸含量均顯著增加[45]。Riaz等[46]在枳殼中發現, 缺硼處理可促進枳殼幼苗葉片中脯氨酸的積累。研究表明, 植物體內游離脯氨酸的含量在不同部位表現不同, 其多集中于光合器官和生殖器官中[47]。本試驗發現, 在硼脅迫下, 棉花幼苗葉片中的脯氨酸含量顯著增加, 其脯氨酸含量是根的數倍, 說明棉花在硼脅迫下優先保護其光合器官, 以適應逆境脅迫, 提高其抗逆性。脯氨酸生物合成和降解的限速步驟分別由Δ1-吡咯啉-5-羧酸合成酶(P5CS)和脯氨酸脫氫酶(ProDH)催化[16]。本試驗結果顯示, 棉花在硼脅迫下, 其脯氨酸的積累是由Glu和Orn途徑共同起作用的, 其合成和代謝途徑見圖3。低硼脅迫顯著提高葉片和根中Orn途徑OAT合成酶和Glu途徑P5CS合成酶活性, 降低P5CR合成酶活性。但是由于P5CS合成酶是脯氨酸合成途徑中的關鍵酶, 脯氨酸的積累受P5CS合成酶的影響要高于P5CR合成酶, 且低硼脅迫降低葉片中的ProDH降解酶的活性, 提高了根中ProDH降解酶的活性, 使得葉片中脯氨酸的合成速率高于其降解, 根中脯氨酸的降解高于其合成, 最終棉花幼苗葉片中脯氨酸含量高于根中, 導致葉片中脯氨酸的積累。同樣, 在高硼脅迫下, 葉片中Orn途徑OAT合成酶和Glu途徑P5CS合成酶及P5CR合成酶活性均顯著提高, 而ProDH降解酶活性顯著降低, 使得葉片中脯氨酸的合成遠高于其降解, 最終葉片中積累了大量脯氨酸; 而在根中, 主要是通過降低OAT和P5CS合成酶以及ProDH分解酶活性來抑制脯氨酸的合成及其分解, 但是對脯氨酸合成的抑制作用遠大于其降解, 最終導致棉花幼苗在高硼脅迫下根系脯氨酸含量降低。Liu等[48]的研究結果發現, 小麥幼苗在鹽脅迫下, 當使用100 mmol L-1NaCl處理時, 小麥幼苗根部脯氨酸的積累最高, 此時P5CS合成酶活性最高, 而ProDH降解酶活性較低, 使得根中積累了大量脯氨酸來緩解鹽分脅迫帶來的傷害。

Glutamate: 谷氨酸; Ornithine: 鳥氨酸; GSA: 谷氨酰半醛; P5C: 吡咯啉-5-羧酸; Proline: 脯氨酸; P5CS: Δ1-吡咯啉-5-羧酸合成酶; P5CR: Δ1-吡咯啉-5-羧酸還原酶; OAT: 鳥氨酸轉氨酶; ProDH: 脯氨酸脫氫酶; P5CDH: 吡咯啉-5-羧酸脫氫酶。

GSA:g-glutamate-semialdehyde; P5C: pyrroline-5-carboxylate; P5CS: Δ1-pyrroline-5-carboxylate synthetase; P5CR: Δ1-pyrroline-5-carboxylate reductase; OAT: ornithine-δ-aminotransferase; ProDH: proline dehydrogenase; P5CDH: pyrroline-5-carboxylate dehydrogenase.

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Effects of boron deficiency/toxicity on the growth and proline metabolism of cotton seedlings

ZENG Zi-Jun, ZENG Yu, YAN Lei, CHENG Jin, and JIANG Cun-Cang*

College of Resources and Environment, Huazhong Agricultural University / Microelement Research Center, Wuhan 430070, Hubei, China

To investigate the response of cotton seedlings growth and proline metabolism to low- and excess-boron stress treatment conditions, the experiment was conducted using ‘E kang 10’ as experimental material using hydroponic method in a greenhouse of Huazhong Agricultural University. Boron (B) were applied at four levels at 0 mg L-1(B0, no boron), 0.002 mg L-1(B0.002, low concentration boron), 0.20 mg L-1(B0.2, CK, sufficient concentration boron), and 50 mg L-1(B50, high concentration boron). The results showed that B0, B0.002, and B50 treatments significantly decreased the fresh and dry weights of plants, and inhibited root elongation relative to sufficient boron (CK, B0.2) treatment. With the increase of B concentration, B content in roots, stems, and leaves of cotton seedlings increased gradiently. Among them, B contents in the leaves under B0.2 and B50 treatments were higher than those in roots and stems, while B content in the roots was increased in leaves and stems under B0 and B0.002 treatments. Under low- and high-boron stress treatments, the content of proline in leaves increased dramatically, while proline in roots decreased. Further analysis of related enzyme activities in proline metabolism, we found that B0.002 and B50 treatments promoted the activities of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine-δ-aminotransferase (OAT) in leaves, but decreased the activity of proline dehydrogenase (ProDH) compared to CK; and the activity of Δ1-pyrroline-5- carboxylate reductase (P5CR) in leaves under B50 treatment was obviously increased, but there was no significant difference under B0.002 treatment. In addition, compared with CK, B50 treatment reduced the enzyme activities of OAT and P5CR in roots, while B0.002 treatment prominently increased the activities of P5CS and ProDH.The results showed that both low- and excess-boron stress inhibited the growth of cotton seedlings. Under boron stress, proline mainly was accumulated in the leaves of cotton seedlings, and the content of proline in roots decreased significantly. In the case of boron deficiency and boron toxicity, the accumulation of proline in leaves was mainly through regulating the activities of key enzymes (OAT, P5CS synthetase, and ProDH degrading enzyme) in proline Glu and Orn pathways, resulting in the proline synthesis rate higher than its degradation rate. However, in roots, the proline content was decreased mainly by promoting the degradation of proline under boron deficiency stress. Under high boron stress, proline synthesis and decomposition were inhibited mainly by reducing the activities of OAT, P5CS synthetase and ProDH decomposing enzyme, but the inhibitory effect on proline synthesis was much greater than its degradation, which eventually led to the decrease of proline content in roots.

cotton; boron; proline; synthesis and degradation

本研究由國家自然科學基金項目(41271320)和中央高校基本科研業務費專項資金項目(2017PY055)資助。

This study was supported by the National Natural Science Foundation of China (41271320)and the Fundamental Research Funds for the Central Universities (2017PY055).

10.3724/SP.J.1006.2021.04206

姜存倉, E-mail: jcc2000@mail.hzau.edu.cn

E-mail: zjzeng.hzau.edu.cn@webmail.hzau.edu.cn

2020-09-08;

2021-01-13;

2021-02-18.

URL: https://kns.cnki.net/kcms/detail/11.1809.S.20210217.0858.002.html