干旱胁迫对鹰嘴紫云英种子萌发及幼苗叶绿素荧光特性的影响

Effects of drought stress on seed germination and chlorophyll fluorescence characteristics of seedling of Astragalus cicer

摘要:

为探明鹰嘴紫云英(Astragalus cicer)在干旱胁迫下的种子萌发及幼苗叶绿素荧光特性，本研究采用聚乙二醇(PEG‐6000)溶液模拟干旱胁迫，在鹰嘴紫云英种子萌发期共设置 7 个浓度处理，分别为 0(对照)、5%、10%、15%、20%、25%、30%，分析种子萌发及生长特性；幼苗期共设置 4 个浓度处理， 分别为 0(对照)、10%(轻度)、20%(中度)、30%(重度)，分析不同胁迫时间(0、2、4、6、8、10 d)下的幼苗光合色素含量及荧光参数动态变化特征。结果显示：(1)在 5%~10%PEG 下，种子萌发和胚根生长得到一定程度促进，发芽势、胚根长度、干重等显著上升，而随胁迫程度加深，种子萌发及生长受到明显抑制，于 30%PEG 下，发芽率趋近于 0，相对胁迫率趋近于 100%。(2)轻度胁迫下，光合色素含量小幅度上升，非光化学淬灭系数(NPQ)显著增加，第 10 天较对照增加 110. 6%(P＜0. 05)；中度胁迫下，叶绿素 b 含量、NPQ 呈先升高后降低趋势，实际光化学量子 Yield 含量、相对光合电子传递速率(ETR)于胁迫末期显著降低，第 10 天较对照分别减少 34. 2%、50. 6%；重度胁迫下，叶绿素含量呈降低趋势，而类胡萝卜素含量于胁迫中期明显增加，第 6 天较对照增加 20. 5%，Yield、ETR 于胁迫后期明显减小，第 10 天较对照分别减少 42. 5%、61. 4%。综上所述，鹰嘴紫云英对轻度、中度干旱胁迫具有较强耐受性，能在幼苗期提升叶片内光合色素含量、加快光合电子传递速率、增加光化学电子产量、增强热耗散性能等一系列生理调节措施来适应逆境，而对重度干旱胁迫抵抗力较差，种子萌发及生长受到严重抑制，幼苗光合系统遭到严重破坏，叶绿素含量及荧光参数显著下降。

Abstract:

In order to investigate the seed germination and chlorophyll fluorescence characteristics of Astragalus cicer seedlings under drought stress，polyethylene glycol (PEG‐6000) solution was used to simulate drought stress.Seven concentration treatments were set up at the germination stage of the seeds of Astragalus cicer，which were 0 (control)，5%，10%，15%，20%，25%，30%，respectively. The characteristics of seed germination and growth were determined after treatment. The seedings were treated with drought stress induced by 0(CK)，10(mild stress)，20 (moderate stress)，30(severe stress) percent solution of PEG for 0，2，4，6，8 and 10 days respectively to determine the dynamic change of photosynthetic pigment content and chlorophyllfluorescence parameters in seedlings. The re‐ sults showed that under 5%~10% PEG treatment，seed germination and radicle growth were promoted to a certain extent，germination viability，radicle length and dry weight increased significantly. However，the germination and growth of seeds were significantly inhibited with the increasing stress degree. Under 30% PEG treatment，germina‐ tion rate was close to 0，and relative stress rate was close to 100%. Besides，under mild stress，the photosynthetic pig‐ ment content was slightly increased，and the non ‐ photochemical quenching coefficient (NPQ) was significantly in‐ creased，which was 110. 6% higher than that of the control on day 10(P＜0. 05). Under moderate stress，chlorophyll b content and NPQ increased first and then decreased. The actual photochemical quantum yield content and relative photosynthetic electron transport rate (ETR) decreased significantly at the end of stress，and decreased by 34. 2% and 50. 6% compared with the control on day 10，respectively. Under severe stress，chlorophyll content showed a de‐ creasing trend，while carotenoid content increased significantly at the middle stage of stress and increased by 20. 5% compared with the control on the 6th day. The Yield and ETR decreased significantly at the late stage of stress and decreased by 42. 5% and 61. 4% compared with the control on the 10th day，respectively. In conclusion，Astragalus cicer has strong tolerance to mild and moderate drought stress，and can adapt to the stress by a series of physiological adjustment measures，such as increasing photosynthetic pigment content in leaves，accelerating photosynthetic elec‐ tron transfer rate，increasing photochemical electron production，and enhancing heat dissipation performance at seed‐ ling stage. However，tolerance of Astragalus cicer to severe drought stress was poor，the seed germination and growth were severely inhibited，the seedling photosynthetic system was seriously damaged，and the chlorophyll content and fluorescence parameters were significantly decreased.