Nishikawa Kuniko, Ito Hiroaki, Awano Tatsuya, Hosokawa Munetaka, Yazawa Susumu
Vegetable and Ornamental Horticulture, Division of Agriculture, Kyoto University, Oiwake-cho, Kitashirakawa, Kyoto 606-8502, Japan.
Ann Bot. 2008 Jul;102(1):31-7. doi: 10.1093/aob/mcn058. Epub 2008 Apr 23.
Helichrysum bracteatum is called an 'eternal flower' and has large, coloured, scarious bracts. These maintain their aesthetic value without wilting or discoloration for many years. There have been no research studies of cell death or cell morphology of the scarious bract, and hence the aim of this work was to elucidate these characteristics for the bract of H. bracteatum.
DAPI (4'6-diamidino-2-phenylindol dihydrochloride) staining and fluorescence microscopy were used for observation of cell nuclei. Light microscopy (LM), transmission electron microscopy (TEM) and polarized light microscopy were used for observation of cells, including cell wall morphology.
Cell death occurred at the bract tip during the early stage of flower development. The cell wall was the most prominent characteristic of H. bracteatum bract cells. Characteristic thickened secondary cell walls on the inside of the primary cell walls were observed in both epidermal and inner cells. In addition, the walls of all cells exhibited birefringence. Characteristic thickened secondary cell walls have orientated cellulose microfibrils as well as general secondary cell walls of the tracheary elements. For comparison, these characters were not observed in the petal and bract tissues of Chrysanthemum morifolium.
Bracts at anthesis are composed of dead cells. Helichrysum bracteatum bracts have characteristic thickened secondary cell walls that have not been observed in the parenchyma of any other flowers or leaves. The cells of the H. bracteatum bract differ from other tissues with secondary cell walls, suggesting that they may be a new cell type.
蜡菊被称为“不凋花”，其苞片大，具颜色，干膜质。这些苞片多年来不会枯萎或变色，始终保持其美学价值。目前尚未有关于干膜质苞片细胞死亡或细胞形态的研究报道，因此本研究旨在阐明蜡菊苞片的这些特征。
采用4',6-二脒基-2-苯基吲哚二盐酸盐（DAPI）染色及荧光显微镜观察细胞核。利用光学显微镜（LM）、透射电子显微镜（TEM）和偏光显微镜观察细胞，包括细胞壁形态。
在花发育早期，苞片尖端出现细胞死亡现象。细胞壁是蜡菊苞片细胞最显著的特征。在表皮细胞和内部细胞中均观察到，初生细胞壁内侧有特征性加厚的次生细胞壁。此外，所有细胞的细胞壁均表现出双折射现象。特征性加厚的次生细胞壁具有定向排列的纤维素微纤丝，与管状分子的一般次生细胞壁类似。相比之下，在菊花的花瓣和苞片组织中未观察到这些特征。
花期的苞片由死细胞组成。蜡菊苞片具有特征性加厚的次生细胞壁，这在其他任何花或叶的薄壁组织中均未观察到。蜡菊苞片的细胞与其他具有次生细胞壁的组织不同，表明它们可能是一种新的细胞类型。
