Rice Seminal Root Research Articles

Effect of herbicides and safeners on the elongation of rice seminal root.

Effect of herbicides and safeners on the elongation of rice seminal root.

Comparison of the growth of rice seminal roots between Japonica and Japonica-Indica hybrids by the use of root-tip culture method.

Using a culture method of excised root tip reported by KAWATA et al., the growth of seminal root tips of Japonica and Japonica-Indica hybrids were compared. Plant materials used were 20 cvs. of Japonica-Indica hybrids bred in Korea, 10 cvs. of Korean paddy rice and 10 cvs. of Japanese paddy rice. The 1 cm long root tips were excised from seminal roots and two root tips were grown in each flask containing 15 ml of the culture solution. They were grown at 27° or 3O°C in the dark for three weeks. The results obtained were as follows ; 1. Root length at 27°C varied from 10.9 to 18.0 cm in the Japonica and from 13.2 to 19.7 cm in the Japonica-Indica hybrids. At 30°C, it was from 9.1 to 19.0 cm in the former and from 16.7 to 27.3 cm in the latter (Table 1). 2. At 27° and 30°C, Japonica-Indica hybrids had more number of the primary branched roots than the Japonica (Table 2). Root dry weight was from 0.9 to 2.0 mg in the Japonica and from 3.2 to 5.7 mg in the Japonica-Indica hybrids at 27°C (Fig. 4), while it was from O.9 to 2.3 mg in the former and from 4.2 to 10.1 mg in the latter at 30°C (Fig. 5-b). 3. Excised root growth of the Japonica were better at 27°C than 30°C, while in the case of the Japonica-Indica hybrids this was reverse (Fig. 5-a, 5-b).

Formation of Root Hair in Crown Roots of Rice Plants and Carbohydrates

The effects of defoliation, shading, and foliar application of sugar on root hair formation and growth in crown roots has not yet been determined. The present investigation was carried out to study the morphogenetical effects of carbohydrates on the development of root hairs in crown roots. The following results were obtained. Roots of plants cultured in the control plot bore root hairs longer and more dense than those in the defoliated and shaded plots (Table 3 and 4). The foliar application of sugar accelerated the formation and growth of root hairs (Table 5). It was also found that glucose (10%) is somewhat superior to, or as effective as, sucrose and fructose in aiding root hair formation and growth in rice seminal roots cultured by "bi-media culture". It is evident that a prima facie connection exists between root hair formation and carbohydrates supplied from the top.

The Effects of Sugar Supply on the Growth and Development of Rice Seminal Root in Sterile Culture

The effects of sugar supply on the growth and development of rice root were studied by means of the following two methods for the culture of isolated seminal root provided with scutellum: one was the ordinary "floating culture" in which the whole explant was bathed in the culture solution containing sugar and the inorganic salts of White modified, another was Raggio-Raggio's "bi-media culture" in which the scutellum end of the explant was placed into sugar-containing agar medium and the root portion was bathed in the inorganic salts solution (fig.1). Sugars used were sucrose, D-glucose and D-fructose. Comparing two methods of culture in the growth responses of cultured root to different sugars at various concentrations in medium, the following points were noted. At the first, glucose was the best sugar source for the growth of root in both the culture. Secondly, the optimum concentration of glucose for root growth was distinctly lower in "floating culture" (4 percent) than in "bi-media culture" (7 percent), and the highest concentration of glucose permitting root to grow without any noticeable growth injuries was also lower in the former (4 percent) than in the latter (11 percent). Thirdly, fructose was injurious for root growth even at thc low concentration of 1 percent in "floating culture", while, in "bi-media culture" it supported root growth as well as glucose and sucrose. At the last, the morphological differences were reveald between the root of "floating culture" and that of "bi-media culture" maintaining each on the optimum concentration of glucose. The former, compared with the latter, had dense and developed branching secondary-root as well as thick seminal root, but had sporadic and restrained root hair on root axis. Since these characteristics of the root of "floating culture" in growth responses to sugar and in morphology were considered to be the effects of unnatural manner of sugar feeding, then it might be suggested that "floating culture" was less suitable method of culture for the study of root morphogenesis than "bi-media culture". On the growth responses of cultured root to the concentration of glucose or sucrose in medium, the data obtained in this study led to the conclusion that the higher the sugar concentration, the greater the length and the diameter of the seminal root as well as the density and the total length of the branching secondary-root, if the sugar concentration in medium was below the optimum, irrespective of the method of culture

The Morphogenetic Responses of Excised Seminal Roots of Rice Plants to the Changing Conditions of Sugar Supply

Excised rice seminal roots with scutella were cultured aseptically in vitro by means of "bi-media culture" method. The morphogenetic responses of roots to the changes of the concentration of sugar supplied as glucose solution through the basal parts of the roots were studied. The sugar concentration of the media was changed after the roots were pre-cultured for 7 days and then cultured for succeeding 7 days. When the concentration of glucose was changed from 0.5% to 7%, the elongation rate of primary roots and lateral roots increased immediately after the treatment. The increase in diameter of primary roots which owed to the expansion of individual cortical cells was also observed. On the other hand, when the concentration of glucose was changed from 7% to 0.5%, the elongation rate of primary roots and the thicker laterals did not decrease, but the elongation of the thinner laterals was restricted. The addition of 0.5% of mannose to 6.5% of glucose following the pre-culture with 7% of glucose strictly restricted the elongation of pimary roots and laterals. The results indicate the important role of sugar provision from shoot to root in determining the length, diameter and branching patterns of crown roots of rice plants.

Studies on the Developmental Physiology of the Relationship between the Cortical Disintegration and Lateral Root Growth in Rice Seminal Roots

It became clear that the successive elongation in seminal root and the development of laterals depended upon the nitrogen and phosphorous derived from the cortical disintegration in aged root parts, after supply of the same from endosperm to seminal root had ceased. This result indicates that the seminal root axis on and after 4th day was composed of two parts, the one formed by utilization of nitrogen and phosphorous from endosperm and the other from aged root regions. Two types of lateral roots in growth pattern emerged from these parts respectively. The first type emerging from the former regions had an increasing protein synthetic pattern during the growth. On the other hand, the second type gave a pattern increasing cell wall substance synthesis during the growth. While the synthetic character in nitrogen and phosphorous metabolism was converted into catabolic one on each parts in root axis, begining with the rooting of laterals, the increase of lacunae formation synchronized with them. In these parts about 50 to 60 % of the nitrogen and phosphorous contained in root cylinder was translocated to younger root parts during cortical disintegration. For this reason, the cortex of rice root seems to be regarded as the reserve tissue of nitrogen and phosphorous compounds.

Studies on the Developmental Physiology of the Lateral Roots in Rice Seminal Roots

During the growth of seminal root, the dividing character of root apex is converted into the elongating one and the protein synthetic character into the cell wall synthetic one, when supply of nitrogen and phosphorous from endosperm to seminal root ceases. The changes in the characters of root apex effected the morphogenetic processes of the root, that is, the decrease in number of cortical layers in main root axis due to the fall of the dividing activity in epidermis-cortex initial cells, and the decrease in cell number of central cylinder, especially of phloem elements in the lateral root axis. The lateral roots are divided into the following three types according to size of root diameter and presence of an inner-cortical sclerenchymatous tissue as well as of a central metaxylem vessel. S type (Photo. 3) : Lack of an inner-cortical sclerenchymatous tissue and of a central meta-xylem vessel, degenerative tendency of phloem elements, 50∼60μ in root diameter. L type (Photo. 1) : The same structure and tissue orientation as seminal root fundamentally, 120∼140μ in root diameter. T type (Photo. 2) : The same structure and tissue orientation as L type except lack of an inner cortical sclerenchymatous tissue, 80∼110μ in root diameter. It was observed that laterals of S type were dominantly distribute dover all parts, especially over the parts formed by utilizing nitrogen and phosphorous derived from the cortical disintegration of aged root region, but laterals of L and T type were detectable only in the parts formed by utilization of the same from endosperm. All these laterals were active in the absorption of NH4-nitrogen and phosphorous.

Histogenetical Studies on Cortical Disintegration in Rice Roots

Several lines of investigation have been carried on the formation of lysigenous lacunae of rice plant roots. The results obtained so far, however, do not agree with each other on the mechanism of formatlon and physiological significance of the lacunae. It was reported by many investigators that the development of the lacunae of rice plant roots growing under anaerobic soil conditions was remarkable as compared with that of aerobic soil conditions. It was assumed that oxygen needed for root respiration would be supplied mainly by leaves via stems and lysigenous lacunae when the rice plant was kept in anaerobic soil. On the other hand, an investigator asserted that the physiological role of lysigenous lacunae of rice plant roots should be reexamined from that the formation of lysigenous lacunae had relations with the development of lateral roots, that the fomation of lateral roots in the soil of paddy field was generally accelerated when it was in oxidative state and that the development of lacunae, on the contrary, was slowed down when the soil was reductive. In an attempt to throw the light on the differences observed in these works, the histogenesis and the changes in the volume of lacunae and lateral roots were studied in rice seminal roots growing under two kinds of soil conditions in oxidation-reduction potentials. The phenomenon of cortical disintegration may be consisted of two phases, emergence and enlargement. With the exception of roots, 2 days old growing under reductive soil conditions, the emergence of cortical disintegration was always observed with the primordia of lateral roots. In two days roots growing under reductive soil conditions, the emergence of cortical disintegration was found, but the initiation of lateral root primordia was observed nowhere. While the enlargement of cortical disintegration was noticeable more distinctively in the roots growing under oxidative soil conditions (hereinafter referred to as O) than in the roots growing under reductive soil conditions (hereinafter referred to as R) for 4 days after seeding. Though there were little differences in the density of lateral roots and the primordia on the same aged parts (e. c. was 0.9 cm length from root base in O and 0.6 cm in R), for 4 days after seeding O exceeded distinctly R in the volume of lateral roots per centimeter and the growth of lateral roots in length of which the longest lateral roots represented of each region abovementioned. On and after the 4th, R was superior to O in the percentages of lacunae, the volume of lateral roots and the growth of lateral root in length. On the basis of such results, it was assumed that the emergence of cortical disintegration and the initiation of lateral roots have a close relationship with each other in time and position, and the enlargement of cortical disintegration was restricted by the velocity and the volume of the growth of lateral roots. Anyhow, the results of this experiment seem to indicate that whether the development of cortical disintegration will become well in R or O, depends mainly on the growth of lateral root in volume or velocity. A difference, as previously stated, in observations among investigators with refference to the extent of the development of cortical disintegration in R and O may be consolidated by these results.

On the Culture of the Rice Seminal Roots with Scutella in vitro.

The seminal roots with various tissues of the caryopsis, whole seminal roots and 1cm long seminal root tips of rice, variety Noorin No. 29, were cultured with several kinds of media. On the medium containing only White's inorganic salts plus 6.0 percent sucrose, the seminal roots with scutella (Fig. 1, ii) showed very good growth (about 50-60 cm in root length). On the other hand, the seminal roots with scutella were cultured by adopting the manner of feeding sucrose from the side of scutellum in small vial and inorganic salts through the root in flask (Fig. 2). In these cultures especially in the case of A type culture, it was found that the seminal roots grew more than 100 cm (with the maximum of 152 cm in the case of A type culture), when the concentration of sucrose was raised to 12.0 percent. These results suggest that culture of the seminal root with scutellum by using A type culture is a useful method for studies on the physiology and morphogenesis of rice roots.