Ernest M. Gifford

Detection of Ribonucleic Acid with Pyronin

Pyronin, when used in the methyl green-pyronin stain, is useful in localizing ribonucleic acid (RNA). That it has rarely been used alone is perhaps a result of the observation (Kurnick 1955) that pyronin stains deoxyrobonucleic acid (DNA) of animal tissue when not competitively inhibited by methyl green. The tests described in this note indicate that pyronin alone can be used to demonstrate RNA in fixed plant tissues.

Quantitative studies of the vegetative shoot apex of Equisetum scirpoides

Equisetum scirpoides Michx., propagated from a single clone, was grown in a controlled growth chamber at 24 ± 1 C under a photoperiod of 16 hr light/8 hr darkness. The apical cell of aerial vegetative shoots gives rise to derivatives (merophytes) in a helical sequence. Each newly formed merophyte divides anticlinally to form two superposed cells that are parallel to a lateral face of the apical cell. Radial longitudinal divisions then take place in the two superposed cells. Shoot tips were fixed every 2 hr for 24 hr to determine the mitotic index of the apical cell, six subjacent cells, and the remaining cells above the level of leaf initiation. Average mitotic indices for the 24-hr period were 3.9%, 3.9%, and 7.0%, respectively. The results indicate that the apical cell is quite active mitotically; there was no clear evidence of endopolyploidy in cells of the shoot apex, young leaves or in the developing cortex, based upon cytophotometric measurements of DNA content.

Ultrastructure of Vegetative and Reproductive Apices of Chenopodium album

The apical meristem of the vegetative shoot of Chenopodium album (lambs-quarters) exhibits alterations in cytoplasmic structure as early as 3 hours after the plant has been subjected to one photoinductive cycle which promotes flowering. The endo-plasmic reticulum shows an altered distribution and there is evidence of an increase in acid phosphatase production. Dictyosomes increase in number per cell by the end of the second inductive cycle.

Comparative Development of the Spermatozoids of Cycads and Ginkgo biloba

Cycads andGinkgo biloba are the only extant seed plants that produce flagellated male gametes. Superficially, the cells of both are similar in structure and function. In both the motile organelles arise from multicentriolar bodies, the blepharoplasts, and, in both forms, these give rise to a complex fibrous band, the multilayered structure (MLS), which bears numerous flagella. Generally speaking, these structures are much alike in cycads andGinkgo. However, there are marked differences in details of their development, particularly in the presence of a “nucellar beak” inGinkgo.

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.

The apical cell of fern roots and shoots: an appraisal of its functional role in development

A brief review of the Apical Cell Theory and its relationship to apical growth in pteridophytes is presented. Currently there are two concepts regarding the importance of the apical cell during development. One group of investigators has presented evidence to demonstrate that the apical cell is mitotically active only during early initiation and organisation of apical meristems. Soon the apical cell becomes essentially inactive in cell division, and may undergo endopolyploidy. The second group has provided evidence in support of the original tenet that the apical cell plays an important and continuing role in shoot and root development and does not undergo endopolyploidy. Curiously enough, evidence for both concepts is based essentially upon the same procedures and techniques: histogenesis, determination of the mitotic index and cell-cycle durations, labelling with 3 H-thymidine, and cytophotometric measurements of DNA content of the apical cell and subjacent cells.