Title Cytological study of pathological changes in Japanese black pine (Pinus thunbergii) seedlings after inoculation with pine- wood nematode (Bursaphelenchus xylophilus) Author(s) Nobuchi, Tadashi; Tominaga, Teruyuki; Futai, Kazuyoshi; Harada, Hiroshi Citation 京都大学農学部演習林報告 = BULLETIN OF THE KYOTO UNIVERSITY FORESTS (1984), 56: 224-233 Issue Date 1984-11-30 URL http://hdl.handle.net/2433/191793 Right Type Departmental Bulletin Paper Textversion publisher Kyoto University
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TitleCytological study of pathological changes in Japanese blackpine (Pinus thunbergii) seedlings after inoculation with pine-wood nematode (Bursaphelenchus xylophilus)
In addition to the unidentified substances, change詰 inbo1'dered pit str・ucturewere al80
obs母rvedin t1'acheids. Under a phase con-
t1'ast microscope, the ma1'go of pit memb1'ane
appeared homogeneous in healthy trees
(Photo. 6a), bl1t the radial lines were ob-
serv巴din the affected xylem (Photo. 6b).
To stl1dy pit st1'ucture at the ultrastructural
level, pits were observed under electr・on
microscopes. Under a scanning electron
microscope, microfibrils of margo showed
fine structure in healthy trees (Photo. 7a).
In the affect巴dtrees, microfibrils changed
to thickened structure and the sl1rface of
torus was also covered with 80me materials
(Photo. 7b). The observation of 111t1'athin
sections revealed that some bo1'de1'ed pit-
pai1's we1'e aspira
229
s. xyZophUua
B. mucponatu8
Con trol
惨冊唱語
。幽。ゐ岨込
20
10
{5}判ぷO且
gZ3305ω云きと
32なお
O 30
Days after in口culation
The area of the changes in bord己redpit structure.
20 10
Fig. 2
230
radial Iines in pit membrane observed under a phase contrast micr・oscopew合間 considered
to be caused by the thickening of microfibrils in appearance. The area of the pits haゎ
ing above features was measured under a phase contrast microscope (Fig. 2). 1n A group,
the changes in pit structure developed in a wide area with lapse of time after inoculation.
1n B or C g1'oups, on the other hand, pit structure changed only in a limited a1'ea near
the inoculation points.
The results shown in Fig. 2 were discussed in comparison with the data of Fig. 1. It
was revealed that the a1'邑aof changes in pit structllre coincided with that of dead ray
pa1'enchyma cells. This coincidence show告dthat the changes in pit structllre were oc-
clln・edat the time of br・eakdownof vaclloles and the following coloration of ray parenchyma
cells. Bordered pits with altered structur・ewere homogeneously distributed in xylem differ-
ing f1'om distribution patterns of unidentified sllbstances which distributed llnevenly. The
substances deposited onto pit membrane were considered to be transported from ray
parenchyma cells, because they were distributed homogeneously in xylem. That is, ray
parenchyma cells transported some substances to tracheids in the necrotic process after the
breakdown of vacuoles. As one of the reasons of pine wilt disease, water stress hypothesis
was put forward by Suzuki.!7) 1n this study the measurements of moisture contents or
transpiration stream were not performed. From the observation of pit-pairs, howeve乙 it
was revealed that many pit-pairs were not aspirated after inoculation of nematodes, and
this means that the transportation of materials from ray parenchyma cells to t1'acheids
occurred in the stage of rather heigh moisture content of xylem. After these mate1'ials
were deposited onto inner surface of tracheids, especially to pit membranes, it is considered
that the activity of water condllcting function decreased and final1y seedlings died.
From the results mentioned above the cytological changes after inoculation with nemト
todes were as follows. Parenhcyma cells showed conspicuous vacuolization in early stage
after inoculation with pine叩 woodnematodes. In this stage the population growth of nema-
todes was not observed. Vacuoles developed more conspicuously and finally burst. These
changes were considered to be res
References
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231
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232
Photo. 1 Nuc1ei of ray parenchyma cells. l{adial s日clionsstainec1 wilh safranin and ligh! green. 日) Heallhy seec11ing, (b) S日記cllinginoclllated with pine引-wood nema-todes.災:nucl臼llS.
PhoLO. 2 Vacuoles in 1・ay parenchyma cel1s in thc 日日記【Jlin耳 inoculatecl lVith pine-wood nerηatocles. (a) Vacllolcs of ray parenchyma cel1s, (b) Breakdown of vacuoles ancl 1'esulling color日tionin ray parenchyma cells. V: vacllole.
l斗10tO.3 A nematocle in the raclial resin canal (日J'l'Ow).Hadial section stained ¥Vilh Nile bluc. Photo. 4 Vaclloles in cpithelial and accompaning cclls sur1'ounding the axial re日incana¥.
Unstained radial seclion. Pholo. 5 Unidenlified sllbstances in lr・ach日id(日1ゅrows). I{adial seclion stainecl with N i1e blue. I'hoto. 6 Pits o[ tracheids observec1 llnc1e1' a phas巴 cont1'asl micJ'oscope. (a) Beallhy
PholQ. 8 A l1'an日missioneleclron microg1'aph of a bo1'derec1 piL .pair of lhe t1'acheic1s 01 lhe seeclling inoculalecl wilh pine-wuoc1 11巴ma!ocle日. OsmioplIilic ma!erial日日t!ach!o lhe pi! memb!'ane.