干旱胁迫对远志种子萌发及幼苗生长和生理特性的影响

以远志(Polygala tenuifolia Willd.)为研究对象,采用不同浓度(2.5%~25%)聚乙二醇(PEG-6000)模拟不同程度的干旱胁迫,探讨干旱胁迫对远志种子萌发及幼苗生理生化特性的影响。结果表明:(1)随着干旱胁迫强度的增加,远志种子的发芽启动时间推迟,发芽率、发芽势、发芽指数和活力指数降低,但种子发芽率在2.5%~15%PEG胁迫下与对照无显著性差异,而在20%PEG胁迫下均显著低于对照,在25%PEG胁迫下种子不能萌发;在干旱胁迫条件下,远志幼苗生物量降低,胚芽生长受到显著抑制,胚根长度则先伸长后缩短。(2)远志幼苗叶绿素含量在2.5%~10%PEG范围内随胁迫强度的增加和时间的延长而持续上升,在15%和20%PEG胁迫下则表现为先上升后下降,在10%PEG胁迫处理第15天时含量最高,为对照的1.34倍。(3)幼苗叶片的游离脯氨酸、可溶性糖和可溶性蛋白含量随PEG胁迫强度的增加和时间的延长而增加,各指标均在20%PEG胁迫处理第15天时含量最高,分别为对照的1.99倍、1.53倍和1.50倍。(4)随着PEG胁迫时间的延长,远志幼苗叶片超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性先上升后下降,并在10%PEG胁迫处理第10天时活性最强;过氧化物酶(POD)活性随着胁迫时间的延长表现出先上升后下降又上升的特性,并在20%PEG胁迫处理第5天时活性最强;叶片丙二醛(MDA)含量在15%和20%PEG胁迫处理下持续上升,在2.5%~10%PEG胁迫范围内先上升后又有所下降。研究发现,远志种子在轻、中度干旱胁迫下仍可正常萌发,而且幼苗能通过调节自身生长、渗透调节物质含量和抗氧化酶活性主动适应干旱环境,对干旱环境表现出较好的适应能力。

Seed Germination and Seedling Growth Physiological Characteristics of Polygala tenuifolia Willd. under Drought Stress

The seed germination, seedling physiological and biochemical indexes of Polygala tenuifolia Willd. under drought stress were studied in this paper as the different PEG 6000 treatments (2.5%-25%) were carried out in the experiments. The results showed that: (1) the initial germination time of P. tenuifolia seeds were delayed with the increasing of drought stress degree, and the seed germination rate, germination potential, germination index and vigor index were all decreased. However, the seed germination rate do not performance significant difference in 2.5%-15% PEG range compared to control while it significantly reduced under 20% PEG treatment (P<0.05). The seeds could not germinate absolutely at severe drought stress (25% PEG). The biomass and embryonic bud of P. tenuifolia were decreased, while the radical increased firstly and then decreased with the increasing of drought stress degree. (2) The seedling chlorophyll content increased with the increasing of treatment concentration and duration in 2.5%-10% PEG range, increasing firstly and then decreased at 15% and 20% PEG treatments. The highest chlorophyll content was observed in 10% PEG treatment at 15 days of P. tenuifolia, with 1.5 fold of the control. (3) The contents of free proline, soluble sugar and soluble protein continuously ascended with the increasing of treatment concentration and duration. The highest free proline, soluble sugar and soluble protein contents were recorded in the leaf tissue of P. tenuifolia at 15 days under 20% PEG treatment, with 1.99 fold, 1.53 fold and 1.50 fold of the control, respectively. (4) The activities of superoxide dismutase (SOD) and catalase (CAT) increased firstly and then decreased with the increasing of treatment duration, and the highest values of SOD and CAT activities were recorded in 10% PEG treatment at 10 days. The activity of peroxidase (POD) increased firstly and secondly decreased and finally increased, then decreased with the increasing of treatment duration, and the higher value of POD activity was recorded in 20% PEG treatment at 5 days. Malondialdehyde (MDA) content continuously ascended at 15% and 20% PEG solution, while increased firstly and then decreased in 2.5%-10% PEG range. The results demonstrated that the P. tenuifolia showed good adaptability to drought stress cause of the seeds could keep normal germination under light and moderate drought stress, and the seedlings could active adapt to drought stress environment by changing growth, osmotic substance content and antioxidant enzyme activity.