Studies on the movement of substances in grafted plants : I. On the water ascent and the translocation of photo-assimilate in grafted Chamaecyparis obtusa

It has been proved by us that water ascent from stocks to scions occurs in grafts of Chamaecyparis obtusa, pine trees and Taxodiaceae, even immediately after grafting. Nonetheless, it is generally thought that water ascent does not occur until the unions may be made. For this reason, in order to clarify the mechanism about water ascent into scions and investigate the time-course translocation of photo-assimilate from scions to stocks, grafts of Chamaecyparis obtusa were used with the following new methods for tracing the movement of water and substances; use of shadowing chemical substance (Urokolin-M) applied to plants and taking photograph by radiation of super soft x-ray, and use of ^32P and ^14C. (1) On the water ascent from stocks soon after grafting: In the experiments 1-3a, it is inferred that water ascent from stocks occurs, not because each vascullar bundle of scions and stocks would be contacted closely enough to let water pass through the grafted parts, but scions, which have the strong absorbing power for water, may uptake the surplus water like bleeding fluid. Consequently, when the transpiration from stock leaves is increased and the negative pressure may become high in stems, water movement from stocks does not occur theoretically. In the experiment 3b, the experiment was made by setting two blocks; one of them, the leaves of stocks were exposed to a continuous light and, the other, each stock was covered in a black bag exposing only the scion to the light. Plants with roots removed were installed to the apparatus in order to give root pressure. The results obtained were very much in agreement with the theoretical discussion as mentioned above. That is, it was difficult for scions to absorb the water when the light was given to the leaves of stocks increasing the transpiration. But it was possible to absorb the water when the light was shut off with bags. As a result of x^2 test, this light effect was significant at 5% level. (2) On the translocation of photo-assimilate from scions: Scions of grafted plants were permitted to photo-assimilate ^14CO_2 for 14.5 hours at intervals of 2-7 days after grafting until 39 days, and the rates of the subsequent distribution of ^14C from scions to stocks were determined. Until 18 days after grafting, the rates were fairly low compared with the controls. However, it was recognized that photo-assimilate did move into stocks soon after grafting (0.10-0.17%). After 18 days, the translocation rates were increased and on the 39th day a plant translocated photo assimilate as normally as controls (26% vs. about 25%). Although the callus formation and union were observed with every individual and the final success was over 90%, some individuals remained to show low export rates. The results suggest that even after unions between parenchymatous tissue had been formed, the exchange of substances remained limited until the unions of phloem might occur.接穂への水分の上昇は接木直後から始まることが,われわれの実験で,マツ,ヒノキ,スギ等について確かめられているが,一般には,連絡組織ができるまでは,その上昇はほとんどないと考えられている.そこで,この上昇の機作を明らかにすることと,さらに,活着が進むに従つて,光合成物質がどの程度転流するかということについて,X線造影剤を植物に与えて超軟X線で物質の移動を追跡する方法,および放射性核種^32Pと^14Cをトレーサーとして移動を調べる2つの新しい方法を用いて,ヒノキの接木苗をもとに調べた. /(1) 接木直後の接穂への水分上昇について/ 実験1～3により,接穂に台木から水分が上昇するのは,接穂と台木の維管束が密に接触しているからということではなく,台木の接木部に存在する溢泌的な水分を,吸収力の増大した接穂が吸収することによつておこると推察できた.そのために,台木の葉からの蒸散が盛んで,幹中の負圧が大きくなる場合には,台木から接穂への水分の上昇は行なわれないと思われた.このことを,蒸散と関係の深い光について,台木に光を当てる場合と当てない場合の2通りで実験し(実験3b),光が当たつている場合には,接穂へ水分が上昇しにくく,光がない場合に上昇しやすいことがわかつた.この光の効果は,X^2 testの結果,5%の危険率で有意であつた.以上のことから,蒸散や根圧の異なる樹種や個体によつて,また台木の外的条件によつて接穂への水分上昇は異なると推察される. /(2)接穂から台木への同化物質の経時的転流について/ 接木直後から39日目までの各時点で接穂に^14CO_2を与えて,14.5時間光合成と転流を行なわせ,台木の各部分への^14C一同化物質の転流率の変化を追つてみた結果,18日目までは,対照(4～16%)に比べて僅少であつたが,接木直後でもO.10～0.17%と転流しており,柔細胞組織の癒合がなくとも微量は転流することが確かめられた.18日目以降,転流量は漸次増大し,39日目になると26%となつて対照の約25%と比べてもほぼ正常な転流量と考えられるほどの個体もあつた.しかしながら,18日目以降では,全個体について柔細胞組織の癒合が認められ,また,最終的な接木の活着率が90%以上であつたにもかかわらず,未だ転流が不十分な個体もみられた.このことから,師部の癒合がなければ,接穂からの同化物質の転流量は微量にとどまると推察される