Abstract
Our primary objectives in this study are to make clear the histological process of transformation of lemma and leafy-organ in proliferated spikelets to the foliage leaf in rice. For this purpose, an X-ray mutant of rice, which was selected from plants two generations after 20 kR X-ray irradiation of dry seed of Japonica cultivar, 'Reimei', was used. In this mutant spikelets are proliferative, changing from Spikelet-type (S-type) to Pistil-type (P-type) to Leafy shoot-type (L-type) as seasons change. Lemmas of S-type proliferation and P-type proliferation were the same on their shapes as normal lemma, but leaf-like organ in the leafy-shoot of L-type proliferation was almost the same as the first leaf on its shape. Leafy-organ above the fifth from the base in the leafy-shoot of L-type proliferation differentiated to blade and sheath. The number of longitudinal veins in this mutant lemmas and leafy-organ was more than that in normal lemma; the number in S-type proliferation was about seven, that in P-type proliferation was seven to nine, and that in L-type proliferation was nine to eleven. Transverse veins were frequently observed in P-type proliferation and L-type proliferation. In the outer surface of S-type lemma, tubercle formation was poorly expressed, and, wart-shaped protuberances and many papillae differentiated in place of the poorlydeveloped tubercles, and, comb-shaped undulations of tangential cell wall in the outer epidermis also was poorly expressed, changing to wave-shaped one as that of the tangential cell wall in the first foliage leaf epidermis. In P-type and L-type proliferations, rows of long-cell and short-cell system differentiated instead of tubercles in their lemma surfaces. In contrast with normal lemma, lemmas and leafy-organs in all of proliferations have cork-silica cell pairs, and those of P-type and L-type proliferations have stomata in their outer surfaces respectively. Leafy-organ of L-type proliferation has lysigenous aerenchyma in its inner tissue. Thus, lemmas of S-type and P-type proliferations, and leafy-organ of L-type one have one of the characters expressed only in foliage leaves. In this study, light microscopic observation on the surface of lemma and leafy-organ of S-type, P-type, and L-type proliferation showed that the epidermal system thereon was transformed to one closely resembling to that of rice leaf surface.
