镁对槟榔幼苗光合特性和叶绿体超微结构的影响

【目的】研究不同供镁水平对槟榔幼苗叶片叶绿体超微结构及光合特性的影响，为槟榔的平衡施肥矫治技术和高产优质栽培提供理论依据。【方法】以三叶龄‘热研1号’槟榔幼苗为试材进行了沙培试验。采用1/2 MS完全营养液，即对照处理Mg浓度为0.75 mmol/L，缺Mg (–Mg) 和高Mg (+Mg) 处理分别为不添加Mg和添加Mg 2.25 mmol/L。幼苗生长5个月后，取样测定槟榔幼苗非结构性碳水化合物含量、蔗糖合成酶 (SS) 和蔗糖磷酸合成酶 (SPS) 活性、叶绿素荧光动力学参数，观测叶绿体超微结构。【结果】1) 缺镁处理导致槟榔叶绿素相对含量 (SPAD)、光系统Ⅱ (PSⅡ) 的最大光化学效率F_v/F_m、实际光化学效率Y(Ⅱ)和光化学淬灭系数qP显著降低，而高镁处理组与对照差异不显著；2) 缺镁处理槟榔叶片的可溶性糖、蔗糖含量较对照均显著升高，而淀粉含量显著降低；高镁处理组淀粉含量显著高于对照组，但可溶性糖和蔗糖含量差异不显著；3) 缺镁胁迫致使叶绿体膜解体，基粒片层大部分消失，类囊体片层结构断裂，噬锇颗粒数目增多；高镁处理时叶绿体发生变形，叶绿体膜模糊，基粒片层部分消失，噬锇颗粒和淀粉粒增多。【结论】缺镁胁迫下，槟榔幼苗叶绿体超微结构发生变异，叶绿素合成及碳代谢受阻，光合效率降低，而高镁处理对槟榔叶片的影响显著小于缺镁处理。

Effects of different magnesium nutrition levels on photosynthetic characteristics and chloroplast ultrastructure of areca palm seedlings

【Objectives】In this paper we investigated the effects of different magnesium nutrition levels on the chloroplast ultrastructure and photosynthetic characteristics of areca palm seedling leaves, which provided a theoretical basis for the balanced fertilization treatment and high yield and high quality cultivation of areca palm.【Methods】The three-leaf age of ‘Reyan No.1’ areca palm seedlings were used in a sand culture experiment. The 1/2 MS nutrient solution was used as control, in which the Mg concentration was 0.75 mmol/L(CK); and the Mg deficient and sufficient treatments were prepared by adding Mg 0 mmol/L (–Mg) and Mg 2.25 mmol/L(＋Mg). After the seedlings grew for 50 days in the treated solution, plant samples were taken. The non-structural carbohydrate contents, the activitiesof sucrose synthase enzymes (SS) and sucrose phosphate synthaseenzymes (SPS), chlorophyll fluorescence kinetic parameters and the chloroplast ultrastructure in the leaves of areca palm seedlings were observed.【Results】1) –Mg treatment resulted in a significant decrease in the relative chlorophyll content (SPAD) of betel nut, the maximum photochemical efficiency F_v/F_m of photosystem Ⅱ (PSⅡ), the actual photochemical efficiency Y(Ⅱ) and the photochemical quenching coefficient qP; but all the above parameters were not significantly different between +Mg treatment and CK. 2) The contents of soluble sugar and sucrose in the leaves under –Mg treatment were significantly higher than those in CK, while the starch content was significantly lower. The starch content in +Mg treatment was significantly higher than in CK, but the soluble sugar and sucrose contents were not significant. 3) Under –Mg treatment, the chloroplast membrane became disintegrated, most of the grana lamellae disappeared, the thylakoid structure was broken, and the number of osmiophilic granule increased. Under +Mg treatment, the chloroplast shape was deformed, the chloroplast membrane was blurred, and the grana lamellae partially disappeared. The osmiophilic granules and starch granules increased.【Conclusions】Magnesium deficiency could damage the chloroplast ultrastructure of areca palm seedlings, inhibit the metabolism of chlorophyll and carbon and in turn reduce the photosynthetic efficiency. High level of magnesium supplying is less possible to cause unfavorable effect on areca palm leaves.