干旱胁迫对不同抗旱性苜蓿品种根系形态及解剖结构的影响

以强抗旱陇中苜蓿、中抗旱陇东苜蓿和弱抗旱甘农3号紫花苜蓿为试验材料,采用营养液沙培法,以-1.2 MPa PEG-6000模拟干旱胁迫,比较不同胁迫时间(0、3、6、9、12和15 d)对不同抗旱性苜蓿品种幼苗根系形态及解剖结构的影响。结果表明:随胁迫时间的延长,陇中苜蓿的根尖数、根系干重、根系总长度、根系总表面积和木质部面积不断增大;陇中苜蓿和陇东苜蓿的维管束直径、维管束面积和韧皮部面积均不断增大;甘农3号的根系总长度、根系总表面积及皮层占根系直径比例不断增大,而其根系干重、原生和次生木质部导管直径、维管束直径及维管束面积不断减小。胁迫6 d后,陇中苜蓿和陇东苜蓿的根系总长度、根系总表面积和根体积均显著高于甘农3号;胁迫9 d后,陇中苜蓿根系平均直径、根体积、根系干重、维管束面积、木质部面积和次生木质部导管数目均显著高于陇东苜蓿和甘农3号。供试苜蓿均可通过增加根系总长度及次生木质部导管数目响应干旱胁迫。此外,陇中苜蓿可通过增加根体积、根尖数和改善根系解剖结构来适应干旱;陇东苜蓿通过增加维管束直径、维管束面积和韧皮部面积来适应干旱。相比之下,胁迫时间超过9 d时,甘农3号内部输导组织结构的变化削弱了其输导水分的能力。

Effects of drought stress on the root morphology and anatomical structure of alfalfa (Medicago sativa) varieties with differing drought-tolerance

This research studied the effects of drought stress on root morphology and anatomical structure of alfalfa (Medicago sativa) varieties with differing drought tolerance. At the seedling stage, M. sativa cv. Longzhong (strongly drought-tolerant), Longdong (moderately drought-tolerant) and Gannong No.3 (drought-sensitive) were exposed to 15 days of drought stress simulated by PEG-6000 with a water potential of -1.2 MPa. Root samples of each variety were collected every 3 days. With increasing stress exposure time, root tip number, root dry weight, total root length, total root surface area and xylem area of Longzhong as well as vascular bundle diameter and the areas of vascular bundle and phloem in roots rose continuously, as expected in growing seedlings. Meanwhile, for Longdong only the latter three measures rose continuously. For Gannong No. 3, total root length, total root surface area, and the proportion of cortex thickness to root diameter increased continuously while the root dry weight, primary and secondary xylem vessel diameters, vascular bundle diameter and vascular bundle area continuously decreased. After 6 days stress, total root length, total root surface area and root volume in Gannong No.3 were significantly lower than those in Longzhong and Longdong. After 9 days stress, the average root diameter, root volume and root dry weight, vascular bundle area, xylem area and the number of secondary xylem vessels were all significantly higher in Longzhong than in Longdong and Gannong No.3. The common responses of the tested alfalfa varieties to drought were an increased total root length and number of secondary xylem vessels. Moreover, Longzhong showed significant advantages of increased root volume and root tip number and improved root anatomical structure; Longdong was able to enhance vascular bundle diameter and the areas of vascular bundle and phloem to adapt to drought stress. In contrast, when the stress exposure time exceeded 9 days, the ability of Gannong No.3 plants to transport water was curtailed because of alterations in its internal conducting tissue.