增加烟草一级和二级侧根是抵御干旱的生理机制

Role of increasing first-and second-order lateral roots of tobacco for drought tolerance

【目的】挖掘植物自身的抗旱能力是提高农业水分利用效率的有效措施。本研究通过比较水分胁迫处理下5个烤烟品种苗期根系发生和伸长以及叶片光合特性的变化,探讨烤烟抗旱能力差异的生理机制,为烟草生产的可持续发展提供理论依据。【方法】采用水培试验,设置对照和水分胁迫处理(添加2.5%PEG处理来模拟中度干旱),研究5个烤烟品种苗期的地上部和根系的生物量、一级和二级侧根的发生和伸长,利用Li-Cor 6400光合测定系统测定叶片的光合速率和气孔导度等参数,利用FLIR手持式红外热成像仪测定新展开叶的叶片温度,分析烟草抗旱能力差异明显的生理机制。【结果】水分胁迫条件下5个烤烟品种的生长差异明显。与对照处理相比,水分胁迫对大平板和农大202的生长影响不明显,但柳叶尖、金星6007和中烟100的地上部和根系生物量显著被抑制,降幅范围在66%~83%,达到差异极显著水平。水分胁迫抑制5个烤烟品种一级和二级侧根的伸长,但大平板和农大202的一级侧根数目和二级侧根密度显著增加,最终导致根系生物量没有下降;另外3个烟草品种柳叶尖、金星6007和中烟100的侧根发生增加趋势不明显。水分胁迫处理下抗旱能力强的大平板和农大202地上部生物量和叶片温度变化不明显,而叶片的净光合速率显著下降,但其降幅显著低于3个抗旱能力弱的烤烟品种。与对照处理相比,抗旱能力弱的柳叶尖、金星6007和中烟100叶片的气孔导度和蒸腾速率显著下降,叶片温度上升5~7℃。进一步的研究表明,PEG处理下耐旱能力强烤烟品种侧根数目的显著增加是地上部维持较强光合能力的主要原因。【结论】抗旱能力强的烟草品种苗期受到水分胁迫时其一级和二级侧根显著增加,进而能保持较高的光合特性。

【Objectives】Drought stress is one of key environmental factors of limiting the growth and productivity of plants. However, which physiological processes to make plant more tolerant to drought stress remains unclear. The purpose of this study was to investigate the special physiological responses of droughttolerant tobacco（Nicotiana tabacum L.） adapted to drought stress.【Methods】A hydroponic culture experiment was conducted to analyze effect of drought stress（mimicking moderate drought-stress condition by application of2.5% PEG） on five tobacco cultivars with contrasting responses to drought stress in this study. We investigated plant growth, including dry weight of shoot and root, formation and elongation of lateral roots in five tobacco cultivars. Meanwhile, we analyzed net photosynthetic rate and gas exchange parameters through Li-Cor 6400 photosynthetic analysis system and leaf temperature through an infrared camera（SC 620, FLIR Systems, Inc.,USA） with a spectral sensitivity ranging from 7.5 mm to 13 mm and a spatial resolution of 0.65 mrad.【Results】Significant differences were observed in plant growth among five tobacco cultivars under drought stress compared with the control treatment. Compared with the control treatment, two tobacco cultivars（Dapingban and Nongda 202） kept the similar shoot and root dry weight as those under drought stress. However, three other tobacco cultivars showed the drought-inhibited shoot and root growth with the decrement ranging from 66% to83%. Accordingly, the two tobacco cultivars were considered as drought-tolerant tobacco cultivars and the three others as drought-susceptible cultivars. Further result showed that although drought stress decreased the elongation of first-and second-order lateral roots in five tobacco cultivars, formation of first-and second-order lateral roots was increased by drought stress only in two drought-tolerant tobacco cultivars. Interestingly,although significant decrement of shoot biomass induced by drought stress wasn＇t observed in two droughttolerant tobacco cultivars, the net photosynthetic rate was decreased by drought stress relative to control treatment. The decrement of net photosynthetic rates of two drought-tolerant tobacco cultivars was less than three drought-susceptible tobacco cultivars. Furthermore, compared with the control treatment, the stomatal conductance and transpiration rate were decreased only in three drought-susceptible cultivars. After number of first-order lateral roots under the PEG treatment was trimmed to the similar level as that under the control treatment during the experimental stage, surprisingly, the shoot dry weight, net photosynthetic rate, stomatal conductance and transpiration rate of nongda202 were decreased to comparable extents as comparison with those in three drought-susceptible tobacco cultivars under the PEG treatment. This suggested that increment of lateral root formation was the main reason for two drought-tolerant tobacco cultivars to keep plant growth under drought stress relative to the control treatment.【Conclusions】The results indicated that compared with the control treatment, the formation of first-and second-order lateral roots was induced by moderate drought stress in drought-tolerant tobacco cultivars, and it resulted in higher photosynthetic characteristics in droughttolerant than in drought-susceptible tobacco cultivars under drought stress.