J Integr Plant Biol. ›› 1964, Vol. 12 ›› Issue (2): -.

• Research Articles •    

The Uptake of p32 by Different Regions of Wheat Roots

T. H. Tsao, H. T. Liu and C. H. Yang   

Abstract: Although much has been done concerning the absorbing zone of the root, there is an obvious diversity of opinions among different workers. The present work is undertaken to obtain more critical data on this problem. The unbranched portions of the primary roots of 5–7 day old wheat seedlings cultured in tap water were used as experimental material. Radioactive phosphorus was used as tracer. Besides the usual radioactivity counting technique, the roots were marked with Indian ink at 1 mm intervals to ascertain the growing zone. Paraffin sections were made to observe the anatomical structures. It was hoped that by correlating physiological functions of different segments with its morphological structures, some insight may be obtained on the mode of ion absorption. The following results were obtained: 1. In nearly all experiments, the radioactivity distribution curve showed two distinct maxima. The first accumulation maximum occurred at 0–3 mm from the tip, corresponding morphologically to the growing region of the root in which the embryonic cells of the root tip were elongating. The second accumulation maximum was located at nearly 10 mm from the tip, corresponding to the region where root hairs originated. 2. The location of the first maximum showed some variation, appearing at 0–1 mm or 2–3 mm from the apex (Fig. 1 A & B). Similar phenomenon had been reported by Steward with Narcissus roots. The explanation for this variation remains to be sought. 3. The two maxima differed physiologically in the following way: 1) The first maximum appeared 2 minutes after the roots had been exposed to the solution, the second one appeared later and became more pronounced as time went on (Fig. 2). 2) 2,4-dinitrophenol inhibited the first maximum to a greater extent than it did the second one (Fig. 4). 3) After the roots were removed from the p32 solution to distilled water, the pre- accumulated p32 underwent redistribution within different sections of the root. The first maximum rose higher with time, while the second maximum lost radioactivity markedly (Fig. 3). 4) When p32 was supplied locally at the 0–3 mm, 0–10 mm or 0-30 mm sections of the root, the radioactivity counts at the first maximum of the three different treatments were very close together, while the counts at the second maximum deviated considerably. It was considered that the second maximum was of double origin, i.e., partly from the migration of p32 from the first maximum (Fig. 5) and partly from the direct absorption by that zone. The results lead to the belief that the growing region of the root (the region just behind the meristematic region) is most concerned with the initial absorption of p32.

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