奈良教育大学学術リポジトリNEAR
Observations on Histological Changes in Xylem of Corchorus capsularis L. Induced by TIBA and NAA
著者 HIGASHIMURA Takako
journal or
publication title
奈良教育大学紀要. 自然科学
volume 21
number 2
page range 39‑47
year 1972‑11‑15
URL http://hdl.handle.net/10105/2780
Observations on Histological Changes in Xylem of Corchorus capsularis L. Induced by TIBA and NAA
{ With 4 Text-figures) Takako Higashimura
(Biological Laboratory, Nara University of Education, Nara, Japan) (Received May 30, 1972)
Summary
TIBA alone or a mixture of TIBA and NAA has been applied to growing stems of erect jute seedlings. Cambial activity was promoted in the upper half of the applied site, being gradually reduced in the lower half, and resulted in complete cessation at the basal part.
Xylem formed in the upper half after the application was characterized by inhibition of radial elongation of cell walls and by development of groups of vessel elements with a conspicuous angular appearance in transverse section, whereas that in the lower half by acceleration of elongation of cell walls and by no formation of vessel elements.
Based on these facts, it was considered that developmental changes in xylem might be induced through competition between TIBA and auxins in plants or exogeneously supplied.
Introduction
The author has attempted to elucidate the mechanism of the formation of nor- mal tension wood in stems horizontally placed according to the mutual effects of auxins and TIBA (Higashimura, 1970. 1971). The present study was undertaken to confirm the physiological relations between NAA and TIBA on the basis of histolo- gical observations on the developmental changes in xylem induced by the same treatment as before to the erect stems of jute seedlings with buds and leaves completely excised.
Materials and methods
Seedlings of jute plant just beginning to unfold the eighth leaf were transplanted eight each in single file to narrow wooden boxes, and maintained in the vertical posi- tion prior to the onset of and during the experimental treatment. The treatment was initiated with complete excision of buds as well as leaves with the intention of decreasing the effects brought about through endogeneous auxins at a time when the
39
40 Takako Higasiiimura
seedlings attained a height of 18-20 cm and secondary growth was well established in their fourth internode. Plant growth substances were used as dispersions in anhy- drous lanolin at the concentration and with the combinations indicated in Table, and lanolin paste was applied as a belt in 7mm width all around the forth internode that was actively forming secondary xylem. The plants were harvested after one week treatment. In addition to treated plants, untreated controls were also examined.
For histological observaton, sections were cut from the uppermost to the lowest through the applied site in succession and stained with a combination of haematoxylin and safranin.
Table 1. Concentrations and combinations of plant growth substances.
plant growth substances concentrations
TIBA alone
combination of TIBA and NAA
1%~2%
1% TIBA and 0.5% NAA
1% TIBA and 0.1% NAA
2% TIBA and 0.5% NAA
2% TIBA and 0.1% NAA
Experimental results Observations on the vertical controls
During the experimental period, only two layers or three of xylem cells, which are small-sized, thin-walled and unlignified (Fig. 1, X2), are differentiated from cambium.
t-
Fig. 1. Part of a transverse section cut from the erect stem non-applied showing xylem developed during the experimental period.
ca cambium, Xi cells differentiated prior to the onset of the experiment, X2 cells differentiated posterior to the onset of the experiment.
Abbreviations mentioned above are the same in the following figures.
Xca. 240
42 Takako Higasiiimura
Observations on the stems applied by 1% TIBA
Cambial activity (Fig. 2-1, ca) is actively promoted in the upper half of the applied site, following a remarkable increase of layers of xylem cells, compared with that in the controls (Fig. 1, ca). Of xylem cells differentiated after the application, those extending from four layers to seven, which were newly differentiated with little or no influence of TIBA, are inhibited from elongating in a radial direction, developing into small-sized and flattened cells with thin walls (Fig.2-1, r). On the other hand, those extending from six layers to twelve, which were subsequently formed under the effect of TIBA, are of various shapes and sizes, developing into vessel elements with thickened and heavily lignified walls, and present an irregularly angular appearance (Fig. 2-1, v). These vessel elements surround the girth of xylem in groups.
In the lower half of the applied site, cambial activity declines successively towards the basal part, where it ceases completely, after the application of TIBA. Accor- dingly, an increase in the number of layers of xylem cells newly formed is basipe- tally lessened, and not found in the basal part at all. On the other hand, xylem cells differentiated immediately before the application of TIBA, that is, those un- touched by the influence of TIBA, are markedly elongated in a radial direction with a result of thickening of the xylem, relative to an increase in the number of layers of cells. These xylem cells are entirely thin-walled and unlignified, showing no indication to develop into vessel elements (Fig. 2-3, XO, as like as those in the xylem below the applied site (Fig. 2-4, Xi).
Observations on the stems applied by 2% TIBA
Activity in cambium and anatomical features in xylem are similar in general situations to those in the stems applied by 1% TIBA. Thus, in the upper half, a great increase in the number of layers of xylem cells is brought about. These cells extending from three layers to five, which were differentiated just before the applica- tion of TIBA, and accordingly, with little or no effect of TIBA, are all thin-walled, flattened and small-sized through prevention from radially elongating (Fig. 3-1, r) but those extending from six layers to twelve, which were differentiated after the application, are irregularly angular in shape and various in size, having thickened and heavily lignified walls, and surround all around the girth of the xylem (Fig. 3- 1, v).
Cambial activity declines gradually towards the lower half, and ceases completely
at the basal part, with the result that the number of xylem cells newly formed after
the application are basipetally decreased and at the basal part an increase in xylem
cells is not occurred at all.
44 Takako Hioasiiimura
Observations on the stems applied by an equal mixture of 1% TIBA
and 0.5% NAA or 0.1%
In either case, general features in xylem are hardly different. Cambial activity becomes gradually active from the upper part of the applied site towards the middle, where it is found that the number of xylem cells increases considerably. Xylem cells differentiated after the application are nearly as large as those differentiated imme- diately before the application, and are mostly thin-walled and unlignified (Fig. 3-2, 3-3, Xi and X2).
As the cambial activity declines basipetally in the lower half, the number of layers of xylem cells newly formed after the application is also decreased gradually.
In the basal part of the applied site, several layers of xylem cells which were just differentiated immediately before the application, and cambial cells are remarkably elongated in a radial direction. The situation resembles that shown in the basal part of the site applied by 1% TIBA alone (Fig. 2-2, X! and ca).
Observations on the stems applied by an equal mixture of 2% TIBA and
0.5% NAAor 0.1%
When 0.5% NAA is used with TIBA cambial activity (Fig. 4-1, ca) is exceed- ingly promoted in the upper half, showing marked increase in the number of layers of xylem cells. Of xylem cells differentiated after the application, those extending from five layers to six, which were formed at the beginning, are all inhibited from radially elongating, and are flattened, small-sized and thin-walled (Fig. 4-1, r).
Those extending from six layers to twelve, which were successively formed, are various in size, showing, irregularly angular appearance, and develop into vessel elements with thickened and lignified walls (Fig. 4-1, v). Thus, the outer girth of xylem is surrounded entirely by these vessel elements. The situation resembles that found in the upper half of the stems applied by 1% TIBA alone (Fig. 2-1, v).
In the case in which 0.1% NAA was used in place of 0.5% NAA, cambial activity is reduced to some extent, though more remarkable than that in the controls (Fig.
1, ca). Xylem formed after the application consists for the most part of flattened, small-sized, thin-walled and unlignified cells (Fig.4-2, f), and however, cells which are about to lignify are found scattering in the xylem in a small number (Fig. 4-3, arrows).
In the lower half, cambial activity declines gradually and ceases completely in either case in which 0.5% NAA or 0.1% is used in the mixture. As a result of that, the thickness of xylem formed after the application is gradually decreased from the middle part towards the lower. In the case in which 0.5% NAA was used, however, vessel elements are basipetally reduced in number. Thus, in the vicinity of the basal
part of the applied site, xylem cells are for the most part thin-walled and no for- mation of vessel elements is occurred,
46 Takako Hioashimura
Observations on the stems applied by 1% TIBA and simultaneously placed in the inverted position
Cambial activity is remarkably accelerated throughout the applied site, and thus the number of layers of xylem cells is gradually increased. Xylem cells formed after the application are flattened and small-sized due to inhibition from elongating radi- ally, and thin-walled. Vessel elements are not formed at all throughout the applied site (Fig. 4-4, f).
Consideration
TIBA is well known to act as an auxin-antagonist either through direct compe- tition with auxin or by blocking its movement in the plant. On general survey of the present experimental results, cambial activity is gradually accelerated in the upper half of the applied site, initiating at the uppermost part and reaching the most remarkable extent at the middle, and is successively declined in the lower half, completely ceasing from cambial division at the basal part. The phenomenon may be considered to show that the changes in cambial activity are induced through com-
petition between TIBA and auxins, though Cronshow and Morey (1968) suggested that TIBA brings about reduction in the rate of cambial activity, and that simultaneous
application of auxin with TIBA stimulates the rate of cambial activity. Namely, basipetal movement of auxins remained in plants with buds and leaves entirely ex- cised or of those exogeneously supplied is partially inhibited along the site applied by TIBA alone or by TIBA and auxins simultaneously, under the effect of competi- tion between TIBA and auxins. Thus, auxin concentrations come to reach the level sufficient to promote cambial division in the vicinity of the middle of the applied site. As the result of it, in the lower half an amount of auxins basipetally trans- ported is rapidly decreased. Relative to auxins, therefore TIBA may become to have so great an influence on the cambium that it causes cambial activity to cease completely.
In addition, in the xylem extending from the uppermost towards the middle of the applied site elongation of cell walls and development of vessel elements with thickened walls are suppressed, and reversely, an acceleration of elongation of cell walls followed by thinning and a rapid decrease in the formation of vessel elements are brought about in the basal part. These vessel elements are conspicuous by their narrow and angular appearnce with markedly thickened walls in transection, although those occurred in non-applied, normal stems are relatively wide in general.
Such characteristics found in vessel elements formed in the stems applied by TIBA may be considered due to the fact that TIBA has an effect so as to suppress the elongation of cell walls when it reaches the level of relatively high concentrations as a result of competition with NAA existing at the same time. However, considered
from the fact that vessel elements with thickened walls are not formed at all in the applied site as seen in the stems applied by 1% TIBA and kept in the inverted position or the fact that abnormal deposition of a mass of cell wall materials is
induced at the the tip of root hairs of Lepidium sativum seedlings which were germinated on plates soaked with dilute solution of TIBA (1949), it may be suggested that thickening of cell walls, that is, deposit of wall materials, are brought about
through a mutual effect of TIBA and NAA, though precise mode of action of which is still unknown.
References
Cronshow, J., and P.E. Morey, 1968 : Developmental changes in the secondary xylem of Acer rubrum induced by various auxins and 2,3,5-tri-iodobenzoic acid. Protoplasma 65, 287-313
Gorter, C, J,. 1949:Action of 2,3,5-tri iodobenzoic acid on growth of root hairs. Nature 164, 800-801
Higashimura, T., 1970 : Mutual effect of auxins and 2,3,5-tri-iodobenzoic acid on the deve- lopment of tension wood in the herbaceous stems horizontally kept. Bull. Nara Univ.
Educ. 19, No.2, 83-92
1971 :Mutual effect of TIBA and NAA on the development of xylem in Ricinus communis. Bull. Nara Univ. Educ. 20, No.2, 29-44
