木竹的花器官形态与解剖结构研究

【目的】竹类植物极少开花。以箣竹属竹种木竹(Bambusa rutila)的花器官为研究对象,对木竹的花器官形态以及解剖结构特征进行系统的观察与描述,为竹类植物的分类学及生殖生物学研究提供新的理论信息。【方法】选择木竹不同发育阶段的小穗和小花为实验材料,采用外观形态观察结合石蜡制片的方法,对小穗与小花进行解剖结构观察,研究木竹花器官各部分的形态与解剖发育过程。【结果】木竹结实率极低。成熟小穗均长4.756 cm,宽4.0~5.0 mm。小穗顶生或腋生,每个小穗约含5~12朵小花,基部小花先开放,开花顺序由形态学的下端向上端依次开花,顶端的小花通常败育,小穗基部具潜伏芽。完整小花包括外稃1枚、内稃1枚、浆片3枚,雄蕊6枚和雌蕊1枚构成,成熟的小穗苞片与外稃尖端呈紫红色。木竹的小花为开放型小花,属于雌雄异位、雌雄同熟型。开放时花丝伸长,花药悬垂于小穗外,成熟的花药长6.0~6.5 mm,异花授粉。浆片呈卵圆形,半透明状上部具流苏状纤毛,偏紫红色,大小接近。雌蕊子房具棱,长2.5~3.0 mm,上部具绒毛,花柱短,柱头长,羽毛状3分枝柱头,呈紫红色。花药在进入减数分裂前的阶段发育同步,但减数分裂并不同步,出现二分体和四分体共存于同一花药室的情况。木竹的小孢子母细胞减数分裂过程中,四分体的排列方式为左右对称型,分裂方式为连续型。次生造孢细胞阶段,花药壁由外到内依次为表皮、药室内壁、中层和绒毡层,各由1层细胞组成,细胞质浓厚,细胞核显著,部分绒毡层细胞具有双核现象。次生造孢细胞时期,细胞排列紧密,细胞质浓厚,细胞核较大,核仁显著。造孢组织细胞发生游离,进入小孢子母细胞时期,花药壁中层细胞消失,药室空间增大。花药成熟后,花药壁仅有表皮和纤维层,绒毡层退化。成熟花粉粒为2细胞型。雄蕊的败育包括两种类型,第1种类型花药壁发育异常,第2种类型花粉粒发育异常。子房1室,双珠被,倒生胚珠,侧膜胎座,胚囊发育正常。【结论】木竹小穗属于混合花序,木竹花药很容易见到花粉粒败育,子房虽然发育正常,但多数都未受精,这可能是导致木竹结实率低的主要原因。

A study on the morphology and anatomical structure of Bambusa rutila spiklets

【Objective】Bamboo plants seldom bloom. The floral organs of Bambusa rutila were used as samples to observe and describe their morphology and anatomical characteristics, and to further supply the study of bamboo plant taxonomy and reproductive biology with new theoretical information.【Method】Spikelets and florets of Bambusa rutila at different developmental stages were chosen as samples, and the methods of morphological observation combined with paraffin sectioning were employed. This was done to observe the anatomical structure of the spikelets and to study the dynamic changes in the morphological characteristics of the floral organs at different developmental stages.【Result】The seed setting percentage of the spikelets of B. rutila was extremely low. The mean length of mature spikelets was approximately 4.756 cm, with a width of 4.0-5.0 mm. The spikelets were usually produced on the top or lateral nodes of the floral branches and each spikelet contained approximately 5-12 florets. The florets at the base of the spikelets flowered first and then they continually bloomed from the bottom to the top. The florets at the top were usually abortive and there was a latent bud at the base of the spikelets that was covered by bracts. Based on the anatomical observations, an intact floret of B. rutila usually contained one lemma, one palea, six stamens, three ciliate lodicules, and one pistil. The bracts and lemma tips of mature spikelets were usually a purplish-red hue. The florets of B. rutila were of the opening type and belonged to a combination of dichogamy and herkogamy types. The anthers would hang out of the spikelets because of the filament elongation when florets were in bloom. The length of mature anthers was approximately 6.0-6.5 mm and they underwent cross-pollination. The lodicules were generally oval in shape and semitransparent with a hairy margin and a purplish red color, all of which were similar in size. The ovaries had ridges on their surface, with a length of 2.5-3.0 mm and villi on the top. The pistils had a short stylus but a long feathery stigma with three branches, which were also purplish red in color. The sporogenous cells in anthers developed synchronously, but meiosis with both dyad and tetrad spores in an anther chamber did not occur consistently. During meiosis, the cell arrangement of the tetrad was symmetrical and the cell division was continuous. The anther walls consisted of the epidermis, endothecium, middle layer, and tapetum at the secondary stage of sporogenous cells, all of which were composed of only one layer of cells with dense cytoplasm and apparent nuclei. Notably, some tapetum cells contained two nuclei. All sporogenous cells were arranged closely with dense cytoplasm, large nuclei, and prominent nucleoli. As they entered into the microsporocyte stage, the middle layer of the anther walls disappeared and the anther chamber space expanded. After the maturation of the anthers, only the epidermis and fiber layer were left in the anther walls. The tapetum and middle layer cells degraded completely, and significant fibrosis occurred in the endothecium cells that formed the fibrous layer. The mature pollen cells were 2-celled. There were two types of abortions in stamens, viz., one occurring after the anther walls developed abnormally and the other after pollen grains developed abnormally. The ovary of B. rutila developed normally with one locule, a double perianth, an inverted ovule, and a lateral membrane placenta. The embryo sac also developed normally.【Conclusion】The spikelets of B. rutila are a type of mixed inflorescence. Abortive pollens were easily observed in mature anthers of B. rutila and most ovaries were unfertilized even though they developed normally. This might be the main reason for the low seed setting percentage of B. rutila.