J Integr Plant Biol. ›› 1973, Vol. 15 ›› Issue (2): -.

• Research Articles •    

Phenomena of Protoplasmic Withdrawal in Withering Leaves of Higher Plants and the Possible Role of Protoplasmic Movement in Translocation

Lou Chen-hou, Shao Li-mei and Duan Ching-hsia   

Abstract: Ordinarily, translocation in higher plants is mainly concerned with sugar transport in sieve tubes. As the protoplasm retains an appreciable amount of complexproteins in corporating various essential mineral elements, exhaustive evacuation ofcellular content in withering leaves is an important aspect of translocation worthy ofserious consideration. It is not only for its theoretical implications in connection withother aspects of translocation, but also for its significant role in crop productivity. Improvement in yield and quality of cereal grains at the senescence stage of the cropdepends largely upon whether the plant is killed untimely by early frost before exhaustive evacuation of cellular content from withering leaves is completed. The present investigation is a continuation of our previous works and is engaged in asystematic investigation of the sequence of events taking place in partial disintegration and exhaustive evacuation of protoplasm in withering leaf sheaths of Allium andwheat, by employing the easily stainable and recognizable chromatic substance of the nucleus as the main indicator. The. experimental results reaffirm our early proposal that exhaustive evacuation of cellular content in withering leaves is only rendered possible by intercellular movement of protoplasm itself after partial disintegration. Evacuation starts from the migration of the protoplasm into the leaf vein and continues its course in the conducting channel. Frequently, nuclear material may evenintrude into the vessel due to overcrowding. The most conspicuous indication of the partial disintegration of protoplasm is the dissolution of nucleus and the release of its constituents. The released chromatic substance gradually changes its form during it smigration toward the vascular bundle. Appreciable deposition of calcium salt crystalsin various forms which usually appears in the otherwise emptied cells of completelysenescent leaves seems to be the debris left over by decalcification during protoplasmic disintegration. Not only is the transport of cellular content in senescent tissues carried out byinter cellular movement of protoplasm, our early work has shown that such intercellular movement also occurs in the tender growing zone. Intercellular movement of protoplasm in higher plants should be considered a kind of cellular movement inmorphogenesis which is a common phenomenon in animal embryology as well as in slime molds, as the cellular morphogenetic movement in mycellium of higher fungiand in ordinary tissues of higher plants must necessarily traverse through the narrow channels connecting the rigid cellulose compartments. It seems to us the only plausible and effective way of complete withdrawal of cellular content from the deteriorating organ and its subsequent migration into the newly grown is to rely upon inter-cellular movement of protoplasm. On the other hand, storage food such as starchmust first degrade into water-soluble form so as to conform itself to the mass flow of sap. Accordingly, a dual performance of phloem transport is proposed here with: both rapid mass flow of sap and slow protoplasmic migration can be taking placesimultaneously in the phloem. According to evidences presented in recent literatureby Kamiya, Pollard, and others, the various modes of protoplasmic movement inliving cells, whether it be the movement of the whole protoplasm, or the streaming of hyaloplasm within the ectoplasm, are probably “propelled” by contractile protein fibrils possessing ATPase activity. Consequently, both types of phloem transport can bedriven by contractile protein fibrils as well if they are under proper patterns of organization in the protoplasm. As to how one mode of action, the export of photosynthates from a normal leaf, is switched over to partial disintegration and evacuation of protoplasm, the key seems to be the againg of leaves which eventually reaches an irreversible state of senescenceand is possibly associated with the appearance of nuclear dissolution.

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