小麦颖果发育中筛分子和导管结构变化及酸性磷酸酶作用

Ultra-structural changes of sieve elements and tracheary elements and the roles of acid phosphatase in wheat caryopsis development

导管经历了完整的细胞程序性死亡过程(programmed cell death,PCD),形成运送水分的管状通道;而筛分子分化则经历了细胞程序性半死亡过程,形成运输有机养分的通道。为了进一步弄清二者在小麦(Triticumaestivum L.)颖果发育过程中超微结构上的变化,本研究利用生物电镜和酶的超微细胞化学定位技术比较了筛分子和导管分化过程中超微结构的变化,以及酸性磷酸酶(ACPase,acid phosphatase)活性的分布动态。结果表明:筛分子呈对称性半圆形分布于导管的两侧,且筛分子内细胞核的降解晚于导管,筛分子细胞质主要通过液泡膜内陷包裹细胞器,形成自噬体进行降解,最终仍保留了部分细胞器碎片,筛分子仍然存活;而在导管分化中,主要是液泡破裂后,胞内细胞质被完全降解,导管最终死亡,形成管状分子。ACPase作为液泡的标志性酶,在导管液泡膜破裂后,多定位于线粒体等发生降解的细胞器上。而在筛分子中,不仅在发生降解的线粒体等细胞器上检测到了ACPase活性,在成熟筛分子胞间连丝上也检测到了ACPase活性,表明ACPase不仅参与了小麦颖果筛分子和导管发育中PCD进程,可能还与细胞间物质运输有关。

Programmed cell death is known to be an essential process for tracheary elements and sieve elements. Tracheary elements undergo PCD, which forms a tubular channel for transporting wa- ter, while sieve elements go through programmed cell semi-death process to transport organic nutrients. Biological electron microscopy and ultracytoehemical technology was used to further clarify the ultra- structural changes and ACPase dynamic distribution of sieve elements and traeheary elements in wheat （Triticumaestivum L.） caryopsis development. The dynamic changes and the distribution of active prod- ucts of ACPase were studied. Results showed that the sieve elements were distributed as semi-circular at the outside of tracheary elements.The degradation of the nucleus in sieve element was later than that in tracheary elements. The organelles were wrapped by the autophagosome for degradation in the process of developing sieve elements. The mature sieve element retains some organdie fragment and is alive. When the tonoplast in traeheary elements was ruptured, the cytoplasm were degraded by the vesicles in the cell and the cytoplasm was completely degraded. Fully degraded tracheary elements were obviously dead.After the tonoplast was ruptured, ACPase as a key enzyme of vacuole in organelles including mito- chondria of tracheary elements was most notable. In the development of sieve element, ACPase activity was detected in the mitochondria and the plasmodesmata of the mature sieve cells. It is indicated that ACPase may be involved in the trans~）ortion of materials between cells.