海滨沙滩单叶蔓荆对沙埋的生理响应特征

海滨沙滩单叶蔓荆(Vitex trifolia L.var.simplicifolia)是优良的抗沙埋地被植物.以烟台海岸沙地单叶蔓荆为材料,通过不同厚度沙埋过程中沙上和沙下叶片抗逆生理指标的测定以揭示其抗沙埋生理调控机制.结果表明,轻度和中度沙埋5d,成株和幼株整株叶片细胞膜透性增大、POD和SOD活力增高、MDA和脯氨酸含量和叶片相对含水量(RWC)增加、可溶性糖含量下降.但同株沙上叶片细胞膜透性、MDA含量、SOD和POD活力和可溶性糖含量均高于沙下,而沙上叶片脯氨酸含量低于沙下叶片.在轻度和中度沙埋lOd,沙上叶片细胞膜透性、MDA和可溶性糖含量、叶片POD活力降低,叶片SOD活力仍有小幅度增高,但脯氨酸含量增加,沙上叶片生长旺盛.研究表明,沙埋下叶片抗氧化酶活力和脯氨酸含量与细胞膜透性和膜脂过氧化成正相关.沙埋使植株上部叶片接近沙表面而经受干旱和地面热辐射胁迫引起细胞膜脂过氧化加剧和细胞膜透性加大.同时沙埋也使沙下叶片遭遇黑暗和缺氧胁迫诱导细胞内膜脂过氧化,但也激活了叶片抗氧化酶保护系统和叶片脯氨酸的积累抑制细胞膜脂过氧化维护细胞膜的稳定.因此在沙埋过程中,叶片快速响应沙埋胁迫激活叶片抗氧化酶系统抑制膜脂过氧化作用维持氧自由基和抗氧化酶系统的动态平衡在单叶蔓荆适应轻度和中度沙埋,维护沙上叶片旺盛生长中起重要作用,也是重度全埋下沙下植株茎顶端能快速延伸弯曲生长最后顶出沙面再生的主要生理保护原因.

Physiological response of Vitex trifolia to sand burial in the sand coast

Vitex trifolia which grows in the sandy coast of Yantai, China is a plant with high resistance to sand burial and a good ground cover. It was chosen as the plant material to study how a plant adapts physiologically to sand burial. Four levels of sand burial treatment were set up: no sand burial, light (1/3 plant height), moderate (2/3 plant height) and severe sand burial (3/3 plant height). Changes in plasma membrane permeability, MDA content, osmotic regulation (proline and soluble sugar contents), and activities of antioxidant enzymes (SOD, POD, CAT) in the leaves from different levels of sand burials were monitored. On the 5th day under light and moderate levels of sand burial, leaves of both young and mature plants of V. trifolia showed increased membrane permeability, MDA content, activities of POD and SOD, proline content, and RWC while soluble sugar content as compared to controls. We also compared leaves of the same plant above and below sand burial: leaves above sand had higher membrane permeability, MDA content, activities of SOD and POD, and soluble sugar than those below sand burial. In contrast, proline content of leaves below sand was higher than the content of those above sand. With prolonged time of sand burial (10 days), membrane permeability, MDA, soluble sugar content and activity of POD decreased in buried leaves and SOD activity and proline content increased in leaves above sand. After 10 days of light and modest sand burial, leaves above sand also grew well and were stronger than those of control plants. These results indicate that antioxidant enzymes and osmotic matter are involved in adaptation of V. trifolia to sand burial through physiological regulation. The sand burial not only intensified drought and ground thermal radiation stress to leaves above sand, but also made the leaves below sand encounter stress due to deficiency of light, O2 and CO2, all of which interrupted normal metabolism and induced the production of active oxygen free radicals resulting in membrane lipid peroxidation. At the same time, sand burial stress activated antioxidant enzymes and promoted the accumulation of proline, eliminating the accumulation of free oxygen radicals and lipid peroxidation, thus maintaining the integrity of the membranes. Therefore, under sand burial, rapidly activated antioxidant enzymes (SOD and POD) hindered membrane lipid peroxidation and kept a dynamic balance between oxygen free radical production and antioxidant enzyme scavenging. This played a very important role in the rapid response of V. trifolia to sand burial stress, keeping plants growing well under light and modest sand burials. This may be the main mechanism of protection during sand burial of the whole plant, allowing the shoot apex to grow fast and emerge from the sand.