Abstract:

【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.

Key words: Bambusa rutila, anther, ovary, abortion, anatomy