水稲における "うわ根" の形成過程, とくに生育段階に着目した場合の一例

抄録

As designated previously, shoots of rice plants consist of "shoot units", each with an apical leaf basal bud and upper and lower roots zones. And roots of upper shoot units concentrate near the soil surface and produce a net with many branched roots. These are usually called superficial roots. Up to the present, it has been believed that after such superficial root formation during the period from the young panicle formation stage to the heading, rice plants complete the formation of the root system. But as the result of an investigation of the superficial root formation by the authors, it is found that the superficial root formation continues until the full-ripe stage of rice plants. As it is well known, the developmental process of rice plants from the young panicle formation stage to the full-ripe stage is divided into the following stages: the differentiating stage of rachis branch, the spikelet differentiation stage, the reduction division stage, the pollen formation stage, the heading stage, the flowering stage (the fertilization stage), the milk-ripe stage, the dough-ripe stage, the yellow-ripe stage and the full-ripe stage. In the rice cultivar "Mubo-aikoku" grown in wagner pots, it has been clarified that the superficial root system according to progress of such stages is formed as follows : Elongation of primary roots initiated from the ninth shoot unit comes to a stop at the spikelet differentiation stage (Fig. 1). Thick secondary lateral roots and thick tertiary roots appear in the same shoot unit during the period from the spikelet differentiation stage to the flowering stage (Fig. 6 and 7). And fourth, fifth and sixth lateral roots emerge in the milk-ripe stage to elongate until the dough-ripe stage (Fig. 6 and 7). Primary roots initiated in the tenth shoot appear in the spikelet differentiation stage and the elongation ceases at the flowering stage (Fig. 1). Elongation of secondary lateral roots takes place in the milk-ripe stage and tertiary lateral roots begin to emerge at the pollen formation stage. Fourth lateral roots appear in the milk-ripe stage and cease to elongate in the yellow-ripe stage. fifth and Sixth lateral roots emerge in the tenth shoot unit at the yellow-ripe stage and elongate the full-ripe stage (Fig. 6 and 7). In the, eleventh shoot unit, growth of primary roots in length ceases in the dough-ripe stage (Fig. 1 and 3). And secondary lateral roots start to emerge in the reduction division stage. Tertiary lateral roots appear in the flowering stage and fourth lateral roots emerge in the dough-ripe stage. These continue to elongate until the full-ripe stage (Fig. 6 and 7). As to upper primary roots of the twelfth shoot unit, these roots become visible in the reduction division stage and elongate to the dough-ripe stage (Fig. 1). Secondary lateral roots appearing i1] the reduction division stage continue to grow until the full-ripe stage and tertiary lateral roots emerge in the full-heading stage, stopping elonga-tion in the yellow-ripe stage (Fig. 1 and 7). Fourth lateral roots come into sight in the yellow-ripe stage and continue to elongate until the full-ripe stage (Fig. 6 and 7). The superficial roots of all of upper shoot units, in general, show such features as : (1) the period of elongation of thick secondary roots are longer than that of thin secondary roots (Fig. 6), (2) tertiary lateral roots are found in lower primary roots of upper shoot units and fourth, fifth and sixth lateral roots are found in upper primary roots of upper shoot units (Fig. 5 and 6), (3) in tertiary, fourth, fifth and sixth lateral roots of upper primary roots of upper shoot units, two kinds of branched roots are respectively formed, one being thicker in diameter than the other (Fig. [the rest omitted]