油菜素内酯对盐渍下油菜幼苗生长的调控效应及其生理机制

为了探讨油菜素内酯对植物耐盐性的调控,以甘蓝型油菜"南盐油1号"为试验材料,研究了外源24-表油菜素内酯(24-EBL)对100、200 mmol/L Na Cl胁迫下油菜幼苗干重(DW)、相对含水量(RWC)、渗透调节能力(OAA)、叶片气体交换参数、气孔限制值(Ls)等的调节效应,还测定了不同器官的Na+、K+、Cl-含量,并计算各器官的K+/Na+和SK,Na。结果表明:(1)在不同浓度的盐胁迫下,油菜幼苗DW显著下降,胁迫下外源喷施10-12、10-10、10-8、10-6mol/L 24-EBL作用下,油菜植株干重均不同程度的上升,且植株干重都在10-10mol/L 24-EBL(EBL2)处理下达到最大值,分别比100、200 mmol/L Na Cl胁迫下增加29%和20%。与对照相比,非盐胁迫下外源喷施10-12、10-10、10-8、10-6mol/L 24-EBL,油菜幼苗植株干重与对照相比均无显著变化。(2)不同Na Cl浓度胁迫下,油菜叶片的RWC显著下降,外施EBL2可显著提高油菜叶片的RWC和OAA。(3)不同浓度Na Cl胁迫下,油菜幼苗叶片净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)和蒸腾速率(Tr)均不同程度下降,而Ls显著上升,而外喷EBL2可不同程度的提高Pn、Gs、Ci、Tr,降低Ls。(4)与对照相比,Na Cl胁迫下油菜幼苗叶片、叶柄和根的Na+和Cl-含量均显著上升,Na Cl浓度愈高,Na+和Cl-含量上升愈显著。而K+含量均下降,外源EBL2可显著降低幼苗各器官的Na+和Cl-含量,对幼苗叶片K+含量没有影响,但提高了叶柄和根中的K+含量。上述表明,合适浓度的24-EBL外喷可明显提高油菜的耐盐水平,且不同浓度Na Cl胁迫下,最适24-EBL浓度均为10-10mol/L。主要是因为外源喷施24-EBL能显著改善离子稳态和渗透调节能力,从而改善盐胁迫下油菜幼苗的光合作用、水分状况,提高其耐盐性。而24-EBL对盐处理下油菜植株气孔限制的显著改善是其促进其光合、水分利用的重要原因,也是其对100 mmol/L Na Cl处理的油菜生长调控效果优于200 mmol/L Na Cl处理的重要原因之一。结果还显示,在叶片中,24-EBL外施可通过排Na+和Cl-来维持植株离子稳态,而对K+影响不大;在根、茎中可通过排Na+、排Cl-、吸K+维持稳态。

Regulation of exogenous brassinosteroid on growth of salt-stressed canola seedlings and its physiological mechanism

Brassinosteroids are a new group of steroid phytohormones that have high bioactivity and are widely spread in the plant kingdom. They are not only essential regulators of plant normal growth and development, but also can alleviate various abiotic stresses at very low concentration. This study evaluated effects of foliar spraying 24-epibrassinoide (24-EBL) on dry weight (DW), relative water content (RWC), osmotic adjustment ability (OAA), leaf gas exchange parameters, stomatal limitation values (Ls), the contents of Na⁺, K⁺, Cl^-, K⁺/Na⁺ ratio and S_K,Na in different organs of canola seedlings under 100 and 200 mmol/L NaCl. The results showed that: (1) DW of canola seedlings was decreased significantly under 100 and 200 mmol/L NaCl, however, 10^-12,10^-10, 10^-8, 10^-6 mol/L 24-EBL foliar spraying application all increased the DW of stressed plant. Also, 10^-10 mol/L 24-EBL (EBL2) treatments made the seedling DW peaked in both salt-stressed canola plants, and 29% and 20% higher than the values of only 100 or 200 mmol/L NaCl stress treatment, respectively. It was suggested that 10^-12, 10^-10, 10^-8, 10^-6 mol/L 24-EBL foliar spraying application alone made no significant difference to biomass accumulation of canola under non-salt treatment. (2) RWC of canola leaves was decreased under NaCl treatments, and EBL2 application promoted RWC and OAA of salt-stressed canola. (3) Under NaCl treatments, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO₂ concentration (Ci) and transpiration rate (Tr) of canola leaves were declined at varying degree and limitation values (Ls) was increased markedly. However, EBL2 application partly reversed all the parameters at varying degree. (4) Compared with control, the contents of Na⁺ and Cl^- in leaves, petioles and roots of canola were increased significantly, while its K⁺ was decreased significantly. EBL2 application reduced the contents of Na⁺ and Cl^- in all canola organs, did not affected K⁺ content in the leaves significantly, and increased K⁺ content in petioles and roots. In general, the appropriate range concentration of foliar spraying 24-EBL obviously promoted salt resistance of canola seedlings. however, the optimal 24-EBL concentration of canola growth promotion was 10^-10 mol/L at each NaCl treatment level. The promotion of canola salt resistance was due to 24-EBL promoting the plant ion homeostasis and osmotic adjustment, then, improved plant water status and photosynthesis. Promotions of photosynthesis and water use efficiency in salt-stressed canola were owing to significant alleviation on stomatal limitation of stressed plant leaves caused by 24-EBL. The results also suggested that improvement of ion homeostasis in leaves caused by 24-EBL was as the result of exclusion of Na⁺ and Cl^-. However, not only exclusion of Na⁺ and Cl^-, but also K⁺ uptake increase was as the result of 24-EBL application contributing to ion homeostasis improvement in roots and stems.