Shoot Histogenesis: Subapical Meristematic Activity in a Caulescent Plant and the Action of Gibberellic Acid and Amo‐1618

Abstract

Sachs, R. M., A. Lang, C. F. Bretz and Joan Roach. (U. California, Los Angeles.) Shoot histogenesis: subapical meristematic activity in a caulescent plant and the action of gibberellic acid and Amo—1618. Amer. Jour. Bot. 47(4): 260—266. Illus. 1960.–Studies on gibbereilininduced stem formation in rosette plants (Sachs et al., 1959) have shown that a zone of intensive meristematic activity, arising below the existing apical meristem, is almost solely responsible for stem histogenesis, i.e., the formation of the cells constituting the elongate stem. An extensive subapical zone of meristematic activity is also present in caulescent plants, such as Chrysanthemum morifolium, Amo‐1618 ([4‐hydroxy‐5 isopropyl‐2 methylphenyl] trimethylammonium chloride, 1‐piperidine carboxylate) completely inhibits subapical meristematic activity in chrysanthemum, causing the plants to assume a dwarfed, rosette‐like habit of growth. Gibberellic acid, applied either simultaneously, or following the Amo—1618 treatment, completely prevents or reverses the effect of Amo—1618, making the plants retain or resume their normal growth habit. Amo—1618 and gibberellic acid have relatively little effect upon the activity of the apical meristem of Chrysanthemum. Thus, while the apical meristem proper (eu‐ or promeristem) is the site of shoot organization and the ultimate source of the cells of the entire shoot, the subapical zone of division, termed the subapical meristem, is largely responsible for stem histogenesis in caulescent as well as in rosette plants. Gibberellins, or native, gibberellin‐like substances appear to regulate the activity of the subapical meristem and thus to play an important role in shoot development. Amo—1618 and related compounds seem to exert their dwarfing effect in plants by acting as antagonists of gibberellins, at least with respect to the latters' function in regulating the subapical meristematic activity in the shoot.

CENL1Expression in the Rib Meristem Affects Stem Elongation and the Transition to Dormancy inPopulus

“…When injected into the central corpus, LYCH distributed in a rectangular area without entering the RM (data not shown). Together, these experiments provided support for the classic notion that the RM is a morphogenetic unit in its own right (Sachs et al, 1960;Esau, 1977).…”

“…Cells in the corpus of the SAM divide more or less randomly, following space-filling requirements, while those recruited by the subtending RM start to divide periclinally to produce the ribs of the RZ. Following these established criteria (Sachs et al, 1960;Esau, 1977), the poplar SAM includes a two-cell layered tunica and a corpus of five to six cell layers ( Figures 7A and 7B). Immediately adjacent to the corpus is the RM composed of about two to four cell layers ( Figure 7B).…”

Effects of Succinamic Acid 2,2-Dimethylhydrazide Treatment on Cell Size, Acid Invertase and Sucrose Phosphate Synthase Activities, and Sugar Content of Melon Fruit

“…Growth retardants often exert their effects on plants via their inhibitory effect on endogenous GA biosynthesis, which is involved in cell elongation (Cathey, 1964;Masuda et al, 1970;Yamada, 1976). For example, the retardant AMO-1618 inhibits cell elongation by disrupting GA biosynthesis in the stem of chrysanthemum (Sachs et al, 1960). As SADH also inhibits endogenous GA synthesis (Yamada, 1976), it is considered that impaired cell enlargement in fruits treated with SADH is due to the inhibition of endogenous GA biosynthesis.…”

Effects of the Growth Retardant CCC on Floral Initiation and Growth in Pharbitis nil

“…GA3 application to cotyledons also reverses inhibition of flowering, but the material is probably rapidly translocated to the apex. B) The growth retardant Amo-1618 completely inhibits subapical meristematic activity in Chrysanthemum (9). Anatomical observations in Pharbitis showed that CCC strongly reduces cell number in the first internode which is just beginning to expand at the time of induction.…”