镁胁迫对‘春见’橘橙生长和矿质元素分布及叶片超微结构的影响

Effects of Magnesium Stress on Growth,Distribution of Several Mineral Elements and Leaf Ultrastructure of‘Harumi’Tangor

采用砂培法,研究了不同浓度镁[0、2.4、12、24(对照)和240mg·L-1]对香橙砧‘春见’橘橙幼苗的生理胁迫反应。结果表明:(1)镁缺乏和镁过量胁迫均显著降低了株高、根长、根系活力、叶绿素含量及各部位干样质量,但显著提高了相对电导率与MDA含量,且均以无镁处理的对应值变幅最大,无镁处理还显著降低了SOD与CAT活性。(2)植株各器官镁含量随镁处理浓度的升高而增加,同一处理下叶片镁含量相对高于其他部位,上部叶镁含量高于下部叶(镁过量处理除外);镁胁迫处理不同程度地降低了各部位的锌含量,尤以2.4mg·L-1Mg2+处理明显;除无镁处理外,各处理(含对照)的下部叶钙、硼含量均大于上部叶,镁过量处理显著降低了上部叶和下部叶的钙和硼含量。(3)叶肉细胞超微结构变化显著,镁缺乏处理导致叶绿体内类囊体片层模糊,片层数明显减少,线粒体膜模糊且出现异常的黑色颗粒;镁过量处理导致叶绿体内片层消失,淀粉粒和质体小球异常增多增大,线粒体膜模糊。

To investigate the effects of magnesium（Mg）stress on physiological responses and anatomical characteristics of‘Harumi’tangor [Citrus reticulate ×（C. reticulata × C. sinenesis）] plants grafted on Xiangcheng（C. junos）rootstock,Mg at five levels（0,2.4,12,24 and 240 mg · L-1）in nutrient solution was exogenously supplied to the plants grown at sand medium,in which 24 and 240 mg · L-1 were considered as control and excess treatments,respectively,and the other three were treated as low Mg. Our results showed that,Mg stress（either under low or excess conditions）significantly decreased plant height,root length,root viability,leaf chlorophyll content as well as dry mass in various parts,whereas it induced leaf relative conductivity and MDA content. The effects were more pronounced in plants supplied without Mg（0 mg · L-1Mg2＋ treatment）,while the activities of antioxidant enzymes（SOD and CAT）in leaves declined synchronously. Mg concentration in all plant parts increased significantly as external Mg concentration increased,and it was found that compared to the other tissues,Mg tended to be accumulated more in leaves,where upper younger leaves had higher Mg concentrations than those in basal old leaves（except under excess Mg conditions）. Zn concentration showed various degrees of decreases in various tissues of plants under Mg stress treatments,especially under the low Mg treatment 2.4 mg · L-1. Moreover,concentrations of boron（B）and calcium（Ca）were higher in basal old leaves than those in upper young leaves with the exception of 2.4 mg · L-1Mg,and excess Mg decreased those concentrations in leaves of either upper or basal parts. According to the anatomical observation in leaf structure and chloroplast ultrastructure,Mg deficiency stress resulted not only in the disorganization of chloroplsts（in a darker appearance of chloroplast stroma and a reduced volume of thylakoid membranes）,but also of the other organelles like the mitochondria having blurred membranes with reduced volume and abnormal black spots）. Excess Mg treatment also caused the mitochondria having blurred membranes,however,it led to disappearance of chloroplast lamellar,increment of the number and enlargement of the volume of starch grains and plastoglobulus.