Elizabeth G. Cutter

Regulation of Leaf Form in Centaurea solstitialis L. I. Leaf Development on Whole Plants in Sterile Culture

Some factors controlling heteroblastic development in Centaurea solstitialis L. are reported and discussed. Whole plants were grown in sterile culture, and it was demonstrated that the level of available carbohydrates partly accounts for the heteroblastic series. Growing plants in sterile culture supplemented with gibberellic acid prevented the development of the adult leaf form, whereas Centaurea plants grown in media supplemented with Cycocel (CCC) formed adult leaves earlier than plants growing in media lacking CCC. When transferred to a GA-supplemented medium, plants already producing the adult leaf undergo transition to flowering, and all new leaves develop as the juvenile form. It is proposed that the heteroblastic series is in part regulated by the endogenous levels of gibberellins.

A Morphogeneticist’s View of Correlative Inhibition in the Shoot

The complexity of shoot form depends, in part, on a number of correlative effects between various organs. The best known of these is apical dominance, the effect of the terminal apex on the lateral buds, but there are also correlative effects between the lateral buds themselves, and growing leaves or leaf primordia may affect other leaves or the axillary buds which they subtend. Correlative inhibition between buds has been recognized most frequently in the case of cotyledonary buds (Snow44; Sachs36; McIntyre24), but exists also between two buds at higher nodes in decussate or bijugate species, at least if the buds are of unequal size. In most species with paired leaves the buds may possess different developmental potentialities, one of each pair developing as a vegetative shoot and the other as a flower, inflorescence or thorn; in others they merely develop as shoots of unequal size (Champagnat5; Goebel13; Loiseau21; Raciborski35). Such species provide good material for the study of the less common correlative effects in the shoot. Various experiments have been or will be reported in more detail elsewhere (Cutter8; Cutter and Chiu9), but are discussed briefly now along with a more general consideration of the morphogenetic aspects of the phenomenon of apical dominance.

MODIFICATION OF PEA LEAF MORPHOLOGY BY 2,3,5-TRIIODOBENZOIC ACID

Single node explants of conventional, afila, and tendril-less peas (Pisum sativum L.) were cultured on a nutrient medium containing 2-200 μM TIBA. In conventional and tendril-less shoots, TIBA caused the development of: (i) a simple leaf rather than a compound leaf; (ii) a terminal leaflet in place of a normal tendril; (iii) a paripinnate leaf instead of the normal imparipinnate leaf; (iv) a ring fasciation; and (v) congenital fusion of two lateral leaflets. Tendrils borne on afila leaves were swollen radially and deeply cloven in the presence of TIBA. Pea leaf determination is a gradual process. Conventional pea tendrils are competent to form leaflet laminae, but they do not normally receive optimum levels of the appropriate signal at an early, critical stage. Afila tendril primordia are not competent to develop into leaflets. Tendrilless leaf primordia receive and can respond to signals for leaflet development. They are determined earlier than conventional leaves.

Scanning electron microscopy of developing plant organs.

Shoot apices and young meristematic leaves can be examined directly with the scanning electron microscope without prior fixation or metal coating. The form of the shoot apex, cellular organization, andleaf arrangement (phyllotaxis) can be observed, perphaps as they have never been visualized before.

Gametophyte Plasticity and Its Bearing on Sex Expression in Todea barbara (L.) Moore

Gametophytes of Todea barbara (L.) Moore were raised in axenic culture at various plant densities, pHs, and light irradiance levels. The effect of density was most evident in the stunting of growth and the failure to elaborate sex organs at high density, as well as irregular development at low density. Optimum density was from 5 to 30 plants/mm2 Extremes of pH inhibited female sex organ formation and promoted gametophyte regeneration. Slightly acidic pHs of 6.0 and 6.5 were optimum for overall growth and organogenesis. The effect of light of different spectral compositions was very marked: plants raised in tungsten light failed to develop as cordate gametophytes but were exclusively elongate, strap-shaped male plants possessing numerous antheridia; those raised in fluorescent light were cordate shaped and female or hermaphrodite. Unusual types of growth were found, such as prothalli possessing either one wing, a tetrahedral apical cell, or a cylindrical process. The types of meristematic growth were characterized into five categories. The role of the meristem in sex expression of individual plants is considered. The diversity of types of growth, some of which may be protracted, is discussed in the terms of the possible reproductive strategy of the fern in the wild, where factors additional to light, pH, and density may be expected to vary.

Proliferation of cells in the central cylinder of the reduced mutant in lanceolate tomato.

When the reduced phenotype in homozygous lanceolate tomato is cultured on a sterile nutrient medium, there is a considerable amount of cell division within the central cylinder. Such proliferation may occur in response to a stimulus furnished to the shoot by the root.