Studies on the Differentiation and Growth of Vascular Bundles in Crop Plants. : III. Effects of decapitation or longitudinal incision on the root apex of Zea Mays.

[摘要] The process of regeneration was observed histologically, after the tip of seedling root, 2--3cm long, of Zea Mays had been decapitated or incided longitudinally. 1. Decapitation case --- The observation of the root tip which had been decapitated in the plane at different distances from the growing point, revealed that the tissue between the growing point and the part 400μ deep toward the base from the point regenerates a normal root apex (table 1). It was then confirmed that the decapitation brings about a callus formation and the pattern of the root apex is regenerated immediatly and centripetally (fig. 3). After the completion of a root apex, the new root tip starts elongating. 2. Incision case--With a single or a cross incision of a root apex, two or four normal roots were regenerated (fig. 1). The histological observation on incisions at different depths from the growing point, revealed that the callus formation is limmited within the wounded zone 400μ away from the growing point (table 2). The callus fomation in this case spreads basipetally from the growing point, and even late metaxylar vessels produce their derivatives. The position of a new growing point can be recognized at the very early stage of regeneration (fig. 4, 5), but the stele in the basal portion begins to be reconstructed befote the recompletion of the root apex (compare fig. 6A with fig. 4B). The observation on the transections indicated that the kind of the tissue, into which the derivatives of late metaxylar vessels mature, depends upon the position of derivatives in the horizontal plane (fig. 6). All the late metaxylar vessels differentiated soon after the apical meristem has been regenerated, are always connected with some of the old vessel elements (fig. 7). It may thus be concluded that not only basipetal but also acropetal as well as horizontal functions among cells or tissues shoud be recognized in the part of the root tip 400μ deep from the growing point toward the base, and these three functions work together to maintain the normal organization and differentiation. Fig. 1. Normal four roots regenerated after a longitudinal cross inclsion of the root apex. 7 days after the operation. - Fig. 2. External view of root tips 2 days after the incision. Incising depths from the growing point are, from the right, 50-100μ, 100-150μ, 200-250μ, 300-400μ, 400-500μ, and 600-700μ, - Fig. 3. Longitudinal sections of root tips decapitated at the plane 100-150μ away from the growing point. LX, late metaxylar vessel ; DG, dermatogen; CG, calyptrogen. A: 1 day after the operation, callus parenchymatous cells being derived all over the wounded plane. B: 2 days after the operation. C: 4 days after the operation, the pattern of root apex having been almost reformed. ×80. - Fig. 4. Longitudinal sections of the halves of root tips incised longitudinally. The wounded plane is in the right part of each photograph. A : 7 hours, B : 1 day, C : 2 days after the operation. GP, growing point. Note that wound callus formation spreads basipetally from the old growing point and the position of a new growing point has already become recognizable 1 day after the operation. Fig. 5. Transections of a root tip 1 day after incision. A : 200-250μ, B: 150-200μ, C : 100μ, each away from the growing point at the time when the root tip was operated. D: left, 90μ away from the growing point, and right, close to the growing point. Cell division can be recognized more frequently in the apical part than in the basal, and all the late metaxylar vessels have produced their derivatives. ×140. - Fig. 6. Transections of the root tips at the portion of 100-150μ away from the growing point at the time when the root tips were incised. The wounded, plane is in the lower part of each photograph. A: 2 days, B: 4 days, C: 7 days after the operation. EN, endodermis; PX, protoxylar vessel. [the rest omitted]

[学科分类] 农业科学（综合）