Fine structure of plant cells in relation to salt accumulation

Abstract

Several aspects of the process of ion uptake in plant storage tissues were studied using techniques of electron microscopy. During aging of beetroot disks in aerated solution, changes in length of endoplasmic reticulum (ER) lamellae were observed. The larnellae, which were reduced to vesicles 2 hours after cutting the tissue into disks, reappeared during the following 48 hours, and thereafter continued to increase in length for some time. This observation is discussed in relation to similar changes reported in other plant tissues, and in connection with a possible effect on ion movement, as the capacity to accumulate ions develops during the fi:r.st 12-24 hours of e:ging. After a period of 48 hours, crystalloid bodies appeared within the cisternae of the ER and the number of these bodies increased during further aging. The crystals were found to contain protein, and the possible nature of this proteL~ is discussed. The importance of calcium for membrane :integrity and its effect on the uptake of monovalent ions are well recognised phenomena. Hence, the effect of addition or withdrawal of calcium was investigated. No conclusive ultrastructural changes resulted with the exception of the apparent enlargement of ER cisternae caused by calcium removal, an observation suggesting the formation of vacuoles. Because of a possible involvement of membrane ATPases in sodium and potassium movement, as found in animal cells, the cellular localisation of ATPase was attempted using histochemical methods. This work is discussed in relation to published criticisms of the method, and also recent evidence suggesting that ATP formation may be an alternative to ion movem1:int. Studies of developmental processes following slicing of beetroot tissue by using inhibitors of RNA and protein synthesis produced interesting ultrastructural results. The re-formation of long ER lamellae durine aging was inhibited by treatment with cycloheximide, puromycin and p-fluorophenylalsnine but unaffected by actinomycin, and thus seemed dependent on protein synthesis but not on the formation of m-RNA. Actinomycin and p-fluorophenylalanine promoted the onset of crystal production indicating that the protein synthesizing system associated with the F.R is relatively stable and is concerned with the production of non-functional protein. On the other hand, aotinomycin inhibited the development of the ion accumulation mechanism, although it did not affect the developed ion uptake process. The development: is then dependent in some way on the synthesis of m-RNA after slicing. Either the required m-RNA is destroyed at the time of slicing, or a different mechanism for ion movement is operative in sliced tissue.