Zone Of Cell Division Research Articles

Phytochrome in etiolated annual rye

Phytochrome per fresh weight in the apical 0.5 cm of the 1.5-cm coleoptile was twice that in the basal 0.5 cm; phytochrome per dry weight and phytochrome per DNA did not vary significantly from the base to the apex. Ratios of phytochrome to fresh or dry weight in the 6-cm coleoptile were nearly constant in the basal 5 cm, but increased in the two apical 0.5-cm sections. Phytochrome per DNA in the 6-cm coleoptile did not vary significantly in the apical 4 cm, but decreased by one-half in the basal 2 cm.In the 5-cm first leaf, phytochrome per fresh or dry weight was greatest in the basal 0.5 cm (zone of cell division). Phytochrome per DNA in the leaf decreased from apex to base; the phytochrome per DNA in the basal 0.5 cm (zone of cell division) was one-third as high as in the apical 0.5 cm.Pytochrome per cell was greater in all parts of the 6-cm coleoptile compared to the 1.5-cm coleoptile, although no cell division had occurred during this elongation. Phytochrome per cell was higher in the sections of the first leaf wihch were growing primarily by cell expansion rather than by cell division. Phytochrome expressed per unit dry weight was more constant than any of the other parameters studied.It was concluded (1) that the phytochrome content of all coleoptile cells is the same at any given age (length); (2) that the phytochrome content of all nondividing leaf cells is equal at any given age (but lower than that of coleoptile cells); (3) that the phytochrome content of all cells increases in direct proportion to their expansion (increase in dry weight).

Studies on Morphogenesis in Rice Plants. : 4. On the formation of epidermis and cortical fiber in culm.

The process of the formation of epidermis and cortical fiber in the culm of rice plants was observed by histological methods. The eidermis has the zones of cell division, differentiation and elongation at the base of every internode, and the width of these zones alternates through the elongating period of each internode. Though the epidermal cells of lower internodes are shorter than those of higher internodes, the lower internodes have many longer and thicker cortical fiber cells than the higher internodes. It is due to the sliding growth by which the cortical fiber cells elongate vigorously in the lower internodes particularly. It was observed in general that the cortical fiber cells take about thirty days to make up the secondary cell wall after the end of each cell elongation.

THE APICAL MERISTEM OF FUCUS

SummaryStudies on young vegetative apices of Fucus show that after the large apical cell is differentiated it becomes surrounded by an extensive meristematic zone, the pro‐meristem. It is suggested that this is the main zone of cell division at the apex and that the apical cell itself rarely segments. But the apical cell is the main seat of control, for without it the apex shows no further growth. The size of the apical cell and of the pro‐meristem increases during growth of the vegetative branch. A new apical cell becomes associated with a portion of the pro‐meristem when forking of a branch occurs. Morphologically there is sudden change from vegetative to reproductive growth at an apex. Apical initials and a pro‐meristem function in a receptacle until all concept‐acles are laid down. Following conceptacle development there is a loss of meristematic activity at the apex, and after gamete discharge the tissues gradually disintegrate.

Differences in mitotic cycle in various tissues of Vicia faba roots as revealed by 5-amino uracil synchronization of cell division

Longitudinal sections of lateral roots of Vicia faba, pre-treated with 5-amino uracil, were analyzed for the appearance of areas of synchronized cell division. The first evidence of a recovery from the inhibitory effect of amino uracil is seen in the pre-cortical tissues proximal to the root initials. This zone of cell division moves distally toward the apex. Cell division begins in the central cylinder later than in the cortex and moves distally to the pole, ultimately including all the apex except for a small field of interphase cells in the quiescent center.

Effects of Ca Upon Metabolic and Nonmetabolic Uptake of Na and Rb by Root Segments of Zea mays

Ca exerts a strongly depressive upon the noi-metabolic diffusive entry of Na into the cells of the zone of cell division (0-1.8 mm from the root tip) of the primary root of Zea mays (9). Under the experimental conditions imposed in this previous work the maximum of Ca was achieved at a relatively very low concentration, about 0.10 meq per liter. It was postulated that Ca is active at the cell surface where it stabilizes and alters the permeability of a barrier to nonmetabolic ion entry, presumably the outer cell membrane. This supposition is based upon early work dealing with the penetration of dyes into animal cells (1) and recent work with plants (3, 4,10, 12). The low amounts of Ca which are effective also suggest an involveimenit of Ca with the cell sturface rather than coml)etition of Ca with Na for adsorption sites deeper in the cell. Our previous paper (9) was concerned only with the of Ca (and Sr) upon nonimetabolic Na uptake since only the zone of cell division was investigated and this tissue displays no capacity for metabolic accumulation of Na, Ca, Sr or Cl ionls (5, 6, 8). We are aware that none of the experimental criteria currently employed to distinguish between metabolic and nonmetabolic ion uptake is entirely free of objection. For instance, lowering the temperature drastically or administering metabolic poisons may well affect cell permeability as well as preventing operation of metabolic accumulation mechanisms. However, the simplest explanation of the following observations would seem to be that ion uptake by the tip section is entirely free of any direct connection with a metabolic ion pump: 1) Between 0? and 26? uptake is independent of temperature. 2) Labeled ions are eluted from the tissue into unlabeled solutions at about the same rate as that at which they were originally taken up. 3) Uptake of Cl is minute compared with uptake of cations. 4) Anerobiosis actually increases greatly the rate at which Sr (and probably other ions although we have not yet attempted to confirm this) in the medium comes to an apparent equilibrium with that in the tissue. 5) Although Ca stimulates the respiration of this tissue (7) it depresses the uptake of Rb, an ion whose uptake into mature tissue is stimulated by Ca (12). The fact that Ca decreases the permeability of cells to other solutes has beeln known for a long time. Equally well known is the seemingly incongruous fact first pointed out by in 1944 (17) that Ca (and other polyvalent cations) often stimulate the uptake of K and some other alkali metal ionls. It is clear that any reasonable hypothesis concerning the of Ca upon ion uptake must accommodate both of these facts. Our purpose here is to suggest or perhaps merely to reemphasize that Ca exerts 2 essentially distinct and antagonistic effects upon ion uptake. The first of these is a nonspecific depressant not directly linked with ion accumulation mechanisms and resulting from stabilization of the cell membrane with a consequent decline in permeability. The second we believe to be a specific one resulting from an involvement of Ca with the metabolic accumulation mechanismus of certain alkali cations and resulting in an increased rate of uptake of these ions. To this end we have investigated the of Ca upon Na and Rb uptake in both the zone of cell division investigated previously and the zone of cell elongation and vacuolation (1.8-3.8 mm from the root tip) where metabolic ion accumtilation takes place vigorously (5,6,8). Rb and Na were chosen as ions which respectively do and do not display the Viets effect at physiological pH's (10). We have coupled this with a study of the loss of endogenous K during ion uptake. Since the appearance of Viets' paper (17) the nature of the of Ca upon ion uptake has been the subject of many investigations (3, 4, 9, 10, 12, 14, 18). Like other aspects of ion uptake by plants it remains mysterious. Complete understanding must await identification of the carriers or other agencies responsible for metabolic ion uptake. A few papers which are especially pertinent should be mentioned. In 1957 Kahn and Hanson (12) reported that whereas Ca stimulated K uptake by excised maize roots it depressed K uptake by soybean roots. They analysed their data by the kinetic treatment of Epstein and Hagen (2). This analysis indicated that in both species Ca exerted a stimulatory and a depressant upon K uptake. The stimulatory predominated in maize. It was ascribed to an increased 1 Received November 2, 1964. 2 This report is based on work performed under Contract No. AT-(11-1) with the United States Atomic Energy Commission.

On the mechanism of anion uptake by plant roots

The uptake of Cl− by the non-vacuolated tissue of the zone of cell division of the root tip of maize from Cl-resin and CaCl2 and from their equilibrium filtrates has been studied. The results show a greater Cl-uptake from the resin NaCl2 system than from the NaCl filtrate and little or no difference between the resin CaCl2 system and the CaCl2 filtrate. These results are explained on the basis of an interaction between the negative root surfaces and the positively charged resin particles. This interaction causes a reduction in the negative charge of the root and thus reduces electrostatic opposition to the entry of Cl. The difference in Cl-uptake from NaCl and CaCl2 filtrates reflects the effect of the valence of the associated cation on the negative charge on root surfaces and membranes. The higher the valence of the cation, the lower the negative charge of the surface and the higher the Cl-uptake.

PROTEIN‐BOUND SULFHYDRYL GROUPS IN COLEUS WOUND MERISTEMS

Roberts, Lorin W. (U. Idaho, Moscow.) Protein‐bound sulfhydryl groups in Coleus wound meristems. Amer. Jour. Bot. 47(2): 110—114. Illus. 1960.–A hisiochemical examination was conducted of the development of the stem wound‐meristem of Coleus blumei Benth. with 2,2‘‐dihydroxy‐6,6‘‐dinaphthyl disulfide (DDD) and 1‐(4‐chloromercuriphenylazo)‐naphthol‐2 (Mercury Orange) to test for protein‐bound sulfhydryl groups. Specificity for the histochemical reactions was indicated by complete blocking of staining in sections pretreated with 0.001 M iodine in npropanol and 0.1 M aqueous solutions of iodoaceiamide. Both histochemical methods yielded comparable results in protein‐SH localization (zone of cell division and differentiating xylem elemments) and staining intensity. The zone of cell division did not exhibit staining at the time of initial cell division (3 days). However, the cytoplasm of the dividing cells of the wound‐meristem demonstrated protein‐SH 4—5 days following wounding. A high concentration of protein‐SH was observed in the cytoplasm of the dividing cells 7 days after wounding. Redifferentiating parenchyma cells, destined to become wound‐xylem elements, first exhibited wall staining at the time of protoplast contraction. The subsequent walled xylem stage exhibited strong staining in the reticulated striations of the secondary walls.

Cell division and gibberellic acid

In two rosette plants, Hyoscyamus niger and Samolus parviflorus, gibberellic acid causes a substantial increase in cell division in the tissues immediately underlying the apex. As the treatment continues an elongate stem is produced and, for at least 72 hours, the period considered in this study, the subapical zone of cell division expands commensurate with the growth in length. Since there was no cell elongation during the 72-hour interval, the entire increase in length was due to the production of new cells. Hence, it was possible to determine the number of cells produced in a certain time interval and compare this to the observed mitotic activity (number of mitotic figures counted). In the pith region of Samolus, peaks in mitotic activity at 24 and 48 hours were observed and ascribed to a partial synchronization of cell division initiated by the application of GA. The 24-hour interval between the two peaks probably reflects the average pith cell-generation time. Based on the above information additional calculations were made to determine the total number of cells dividing in the first 24 hours after application of GA and the karyokinesis time for pith cells.

Shoot Histogenesis: The Early Effects of Gibberellin Upon Stem Elongation in Two Rosette Plants

Sachs, Roy M., Charles F. Bretz, and Anton Lang. (U. California, Los Angeles.) Shoot histogenesis: The early effects of gibberellin upon stem elongation in two rosette plants. Amer. Jour. Bot. 46(5): 376–384. Illus. 1959.—Within 24 hr. after the application of gibberellic acid (GA) to vegetative plants of biennial Hyoscyamus and of the long-day plant Samolus, a considerable increase in mitotic activity was observed in the pith, cortical, and vascular tissues of the rosette axis immediately below the apical meristem. As the treatment continued, the zone of cell division increased commensurate with the increase in length of the stem; the new cell divisions formed transverse walls predominantly and thus contributed to stem elongation. The cell contribution from the apical meristem was but a small fraction of the total produced by the subapical tissues, suggesting that the induced subapical mitotic activity is the main site of tissue development in the shoot. There was no evidence for cell elongation for at least 72 hr. after application of GA, and, hence, the initial increase in stem length was due solely to an increase in cell number. With regard to the general problem of shoot histogenesis, our data for the rosette plants and those for Xanthium and Chrysanthemum showing extensive cell division far below the apical meristem, are in full agreement with the studies by Bindloss (1942) with tomato, and support her conclusion that “. . . it is no longer possible to think that the chief center of cell division is in a relatively short zone 60 to 100 microns from the stem tip . . . and that cell division activity in the promeristem is not solely responsible for stem length.” On the contrary, the mitotic activity in the subapical regions is undoubtedly responsible for the major part of the cells found in the stem.

SHOOT HISTOGENESIS: THE EARLY EFFECTS OF GIBBERELLIN UPON STEM ELONGATION IN TWO ROSETTE PLANTS

Sachs, Roy M., Charles F. Bretz, and Anton Lang. (U. California, Los Angeles.) Shoot histogenesis: The early effects of gibberellin upon stem elongation in two rosette plants. Amer. Jour. Bot. 46(5): 376–384. Illus. 1959.—Within 24 hr. after the application of gibberellic acid (GA) to vegetative plants of biennial Hyoscyamus and of the long‐day plant Samolus, a considerable increase in mitotic activity was observed in the pith, cortical, and vascular tissues of the rosette axis immediately below the apical meristem. As the treatment continued, the zone of cell division increased commensurate with the increase in length of the stem; the new cell divisions formed transverse walls predominantly and thus contributed to stem elongation. The cell contribution from the apical meristem was but a small fraction of the total produced by the subapical tissues, suggesting that the induced subapical mitotic activity is the main site of tissue development in the shoot. There was no evidence for cell elongation for at least 72 hr. after application of GA, and, hence, the initial increase in stem length was due solely to an increase in cell number. With regard to the general problem of shoot histogenesis, our data for the rosette plants and those for Xanthium and Chrysanthemum showing extensive cell division far below the apical meristem, are in full agreement with the studies by Bindloss (1942) with tomato, and support her conclusion that “. . . it is no longer possible to think that the chief center of cell division is in a relatively short zone 60 to 100 microns from the stem tip . . . and that cell division activity in the promeristem is not solely responsible for stem length.” On the contrary, the mitotic activity in the subapical regions is undoubtedly responsible for the major part of the cells found in the stem.