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

doi:10.11686/cyxb2018314

Abstract

Abstract: 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.

Key words: alfalfa, morphological characteristics, anatomic structure, root, drought stress

ZHANG Cui-mei, SHI Shang-li, LIU Zhen, YANG Fan, ZHANG Zhen-ke. Effects of drought stress on the root morphology and anatomical structure of alfalfa (Medicago sativa) varieties with differing drought-tolerance[J]. Acta Prataculturae Sinica, 2019, 28(5): 79-89.

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