Meristem terminal

Results presented in Table VII show that sufficient light is needed for new shoot formation on explants and that the herbicide fluridone causes chlorosis in new growth just as in whole plants (12,13). These data also confirm that the apical explant, which contains the terminal meristem, is a poor system for assaying inhibitors of new shoot production. 

This same compound can be used to retard the development of both vegetative and reproductive axillary shoots if it is applied at a time when the axillary meristems are preferentially more susceptible than the terminal meristem. Work is currently in progress to evaluate this compound as a partial substitute for hand removal of undesired lateral flower buds from chrysanthemums. Estimates have been made that the hand-labor costs to remove floral disbuds from a 100-foot bed of standard mums is at least 24-40. It is expected that the chemical can be used in such a way that at least 50% of the disbudding operation can be accomplished chemically at a substantial savings in labor cost to the florist. 

According to the investigations of Moreland (1969) terbutol inhibits the growth of roots and rhizomes at the terminal meristems. Root growth of seedling grass is inhibited—leaves become deformed and do not grow. These symptoms indicate that terbutol, like other carbamates, is a mitosis poison. 

Most plants exhibit "apical dominance" which means that the presence of a terminal (distal) meristem tends to suppress lateral shoot initiation (11). Since lateral shoot production is an important characteristic to assess in hydrilla, the frequency of shoot production was determined in sequentially cut (distal to proximal) explants (Table VI). Even though the 4 cm apical meristem contained several nodes, almost none of these produced new shoots. However, nearly half the 2-node explants subtending the cut apical meristem produced new shoots. There was no apparent difference in percent of new shoots produced once the apical meristem was removed. 

Figure 32-8 (A) The life cycle of a flowering plant with emphasis on egg-cell formation and seed development. (B) Some further details of embryo development. T, terminal cell B, basal cell C, cotyledon A, axis SC, seed coat En, endosperm EP, embryo proper S, suspensor SM, shoot meristem Pd, protoderm RM, root meristem. From Goldberg et al.i66 with modification.

Developing trees contain two major types of meristems (1) terminal or apical meristems and (2) lateral meristems. Apical meristems are located at the tips of all stems and branches (both termed shoots) where they are contained within terminal buds they are also located within the tip regions of all roots. In the tip regions, the meristematic zone is usually protected by another zone of cells called the root cap. Root hairs, or microscopic roots, have no apical meristems, but these minute structures are lateral projections of roots that do have apical meristems. 

Fig. 2.1. Duration of phases of the cell cycle in the apical meristem of Vida fabci at 19°. Values in parentheses indicate duration of each phase in h. M mitosis Gj period between division and the onset of S S period of DNA synthesis (DNA content doubles) G2 period between termination of DNA synthesis and initiation of mitosis (organization of newly synthesized DNA into chromosomes). Total cycle time = 19.3 h. (After Evans and Scott 1964)...

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