イネの畸形小穂の発生機構 : 第1報 ジベレリンで誘発した畸形小穂の形態分析

抄録

On the way to comparative studies of the deformities caused by gibbefellin treatment in the spikelets of 17 rice varieties, the writer take the methodological position that the developmental studies of deformed spikelets are basically important in order to interpret scientiftcally the morphological nature of such spikelets, classify them systematically and to understand their developmental physiology experimentally. Since we have only fragmental knowledge on the development of deformed spikelets the constitution of them was analyzed theoretically and some hypotheses were drawn as follows. 1) The hypothesis on the development of normal spikelet : The apical meristem of spikelet primordium normally degrades right after the differentiation of a lemma primordium on it and then the other floral organs, these are, a palea, two lodicules, six stamens and a pistil, differentiate successively on the floral primordium initiated from the axil of the lemma primordium. This spikelet primordium generally develops in the normal spikelet that has the constitution as shown in model N (fig. 3-5.) The axis of the spikelet is not single but consists of two axes namely a spikelet axis and a floret one. The floret axis is a branch initiated from the axil of lemma on the spikelet axis. The palea corresponds to a prophyll on the floret axis in it's morphological nature and the two empty glumes do "sterile Iemma" on spikelet axis, two rudimentary glumes do the so-called "glume" on spikelet axis. Since the apical meristem degrades soon after the differentiation of a lemma primordium it is expected that the tip of main vascular bundle in spikelet axis exists in the region of the axis between the upper empty glume and the palea. 2) The hypothesis on the development of deformed spikelets : So far as the writer's observations in this study, the deformed spikelets are of two kinds. The spikelets of first group (Group I of the deformed spikelets) have the constitution (of a floret and those of second group (Group II of the deformed spikelets) have the constitution of bi-florets. a) On the development of the spikelets in group I. When the floral organs differentiate irregularly on the floret primordium under so me abnomal conditions, the spikelet primordium develops in a spikelet having variform floret. The typical variations observed in these spikelets are as follows. (i) The variations in the nerve number are from 1 to 6 in lemma, from 2 to 5 in palea (figs. 2-10, 14). (ii) The variations in the number of stamens are from to 0 and l0 (fig. 2-13). (iii) The variations in the number of pistil are from 0 to 3. There are various mediate types of multi-pistils. b) On the development of the spikelets in group II. When the apical meristem degrades after successive differentiation of two lemma primordiaon it, the spikelet primordium develops in a spikelet having bi-florets constiution because two floret primordia can be born on each axil of two lemma primordia. Though the spikelet primordium has a potentiality to develop two perfect florets in it (model II fig. 3-2), as differentiation of floral organs on each floret primordium takes place under various abnormal conditions in actual state, generally it can not have two perfect florets. Usually the lower florets are almost imperfect (figs. 2-6, 3, 4, 2, 7, 8) and the upper florets are perfect (fig. 2-4) or more (dominant than the lower ones (figs. 2-9, 12). Thus all of these spikelets are explained as modified types of the model II shown in fig.3-2 consistently.