ULTRASTRUCTURAL CYTOLOGY OF CALLUS CULTURES OF STREPTANTHUS TORTUOSUS AS AFFECTED BY TEMPERATURE

Tissue culture cells of Stveptanthus tovtuosus var. ovbiculatus (Cruciferae) which have acquired a spherical viruslike particle located in their nucleoli, designated cell line STV, developed supergranal chloroplasts and lost the ability to differentiate vascular tissues. The effect of temperature on the ultrastructural cytology of one line of the STV tissue, STV-I, was compared with the effect of temperature on the ultrastructural cytology of tissue culture cells lacking the viruslike particles (control cell lines). At 4 C, the cellular and ultrastructural appearance of control tissue culture cells differed from that of tissue grown at 22 C by producing increased amounts of endoplasmic reticulum and dictyosomes and by reduction of chloroplast thylakoids. STV-I cells were generally moribund as a result of 4 C treatment. Chloroplast thylakoids were also reduced in control tissue following growth a t 10 C and the apparent quantities of endoplasmic reticulum and dictyosomes were similar to those observed in control cells grown at the control temperature (22 C ) , but less than those observed in tissue subjected to 4 C. STV-I tissue grown at 10 C demonstrated increased endoplasmic reticulum and dictyosomes and reduction of polysomal configurations. The mitochondria1 morphology was variable and the cells contained supergranal chloroplasts and proplastids. At the control temperature (22 C ) , the fine structural appearance of control tissue culture cells was typical of parenchyma cells, but STV-I cells contained mitochondria of variable morphology and two types of chloroplastsnormal and supergranal. Control tissue grown at 30 C also contained proplastids, but these proplastids contained starch in contrast to the proplastids in control tissue grown at low temperatures. The ultrastructural cytology of STV-I cells grown at elevated temperature (30 C ) was characterized by enlarged mitochondria containing massive lipid bodies and the presence of protoplastids with starch and supergranal chloroplasts. CELLLINE STV-1 callus cultures of Streptanthus structural basis for the reduced growth of the STV tortuosus (Kell.) var. orbiculatus (Greene) Hall cultures as well as provide an opportunity to excontains 600 A spherical particles which are amine possible alterations in the interaction beusually restricted to the nucleus and closely retween the presumptive virus and callus cells. This semble viral particles (Sjolund and Shih, 1970). study has special significance because virus inTheir appearance was first noticed five years after fected plants have been cured with temperatures in the establishment of the original callus cultures. excess of 25 C or less than 15 C (Baker, 1962; During this lengthy period in which the presumpSelsky and Black, 1962; Hollings, 1965). This tive virus was absent, callus cultures of S. torreport considers the effects of temperature on the tousus were used for the examination of chloroultrastructural cytology of S. tortuosus STV and plast differentiation and dedifferentiation (Sjolund control callus cultures. and Weier, 1971 ). The appearance of these viruslike particles was sudden and coincided wth loss MATERIALS cell lines of AND M E T H O D S ~ ~ V ~ ~ ~ ~ of the abilty to differentiate roots and vascular S. tortuosus have been established and utilized in tissues. Further examination of cell line STV previous investigations (Sjolund and Smith, 1974; callus cultures has shown that the chloroplast Endress and Sjolund, unpublished). This report, morphology became altered and that photosynhowever, compares only control cell line 872 with thetic ability was greatly impaired (Sjolund and cell line STV-I. Explants of control and STV-I Smi'th, 1974; Smith and Sjolund, 1975). In addicallus tissue were grown at 4, 10, 22 or 30 C tion, STV-I cultures are thermolabile as they are under 200 ft-c of continuous illumination and unable to grow at 30 C where control tissue grows sampled for electron microscopy at weekly interfairly well (Endress and Sjolund, unpublished). vals. The results reported here were obtained An ultrastructural examination of these cultures from tissues grown at the experimental temperagrown at different temperatures could suggest a ture for three weeks or longer. Segments of callus were fixed on ice in full strenith Karnovsky's fixative (Karnovsky, 1965) Received for publication 24 July 1975. This work represents part of a doctoral dissertation for a hr, rinsed 3-5 times with submitted by the senior author to the Department of ice cold 0.067 M phosphate buffer (pH 7.2) for Botany, University of Iowa and was supported in Part 15-30 lnin and then postfixed on ice in buffered by N.S. F. grant GU2591. present address: Statewide Air Pollution Research tetroxide for hr. Center, University of California, Riverside 92502. distilled water rinses over 15-30 min, the tissue