Judith Croxdale

Stomatal patterning in Tradescantia: An evaluation of the cell lineage theory

The cell lineage theory, which explains stomatal patterning in monocot leaves as a consequence of orderly divisions, was studied in Tradescantia. Data were collected to test the theory at three levels of organization: the individual stoma; stomata distributed in one dimension, in linear fashion along cell files; and stomata apportioned in two dimensions, across the length and breadth of the leaf. In an attempt to watch the patterning process through regeneration, stomata in all visible stages of development were laser ablated. The results showed that the formation of stomatal initials was highly regular, and measurements of stomatal frequency and spacing showed that pattern was determined near the basal meristem when the stomatal initials arose. Following the origin of initials, the pattern was not readjusted by division of epidermal cells. Stomatal initials were not committed when first present and a small percentage of them arrested. The arrested cells, unlike stomata, were consistently positioned in cell files midway between a developed pair of stomata. At the one-dimensional level of pattern, stomata in longitudinal files were separated by a variable number of epidermal cells and the frequency of these separations was not random. The sequential spacing of stomata also was not random, and stomata separated by single epidermal cells were grouped into more short and long series than expected by chance. The stomatal pattern across the width of the leaf resulted from cell files free of stomata which alternated with cell files containing stomata, but not with a recurring periodicity. Files lacking stomata were found only over longitudinal vascular bundles. Laser ablations of developing stomata did not disrupt the pattern in nearby cells or result in stomatal regeneration. We conclude that the cell lineage theory explains pattern as an individual stomatal initial arises from its immediate precursor and satisfactorily accounts for the minimum spacing of stomata in a cell file, i.e., stoma-epidermal cell-stoma. However, the theory does not explain the collective stomatal pattern along the cell files, at the one-dimensional level of patterning. Nor does the theory account for the for the two-dimensional distribution of stomata in which regions devoid of stomata alternate with regions enriched with stomata, but not in a highly regular nor haphazard manner. We suggest that the grouping of epidermal cells and stomata separated by single epidermal cells in cell files may result from cell lineages at a specific position in the cell cycle as they traverse the zone where stomatal initials form.(ABSTRACT TRUNCATED AT 400 WORDS)

Glucose-6-phosphate-dehydrogenase activity in the shoot apical meristem, leaf primordia, and leaf tissues of Dianthus chinensis L.

The oxidation of carbohydrate by the pentose-phosphate pathway in the shoot apical meristem and developing leaf primordia of Dianthus chinensis was assessed by measuring the activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49). On a kg-1 dry weight h-1 basis, activity rose from 250 mmol in the apical meristem to 550 mmol in the first two leaf primordia and then declined to 350 mmol in the sixth pair of leaf primordia, and finally to 200 mmol in leaves just emerged from the shoot bud. Measurements of activity in the sixth leaf pair from the apex showed differential distribution in leaf tissues. Epidermal and mesophyll tissue had about the same activity as whole-leaf tissue, but vascular bundles had 70% greater activity. Within the vascular tissue, activity in the phloem was twice as high as in the xylem. When activity was expressed on a per-cell basis, there was a continuous increase from 20 fmol in the apex to 2 pmol in the sixth leaf pair. Activity on a per unit cell volume basis showed that cells of the apical meristem and the epidermis, mesophyll and xylem of the sixth leaf pair had similar values, about 30 amol; only the two youngest pairs of primordia and the phloem had values two or three times this amount.

Message from the Incoming Editor.

Professor Thomas Moore, founding editor of the Journal of Plant Growth Regulation, has stepped down. Over and above his recognition of the need for such a journal, under his steadfast leadership and the efforts of his editorial team, the journal became a respected periodical with a strong international base, specializing in publications on plant growth substances and herbicides. The plant science community is indebted to him for the strong foundation he laid for the journal and owes him a round of applause for a job well done. As the new Editor-in-Chief, it is my task to extend Prof. Moore’s vision. As you know, the study of plant growth regulation increasingly uses diverse approaches, both elaborations on traditional techniques and methods from confocal microscopy to DNA chip technology, that were but a dream when Journal of Plant Growth Regulation was established in 1982. We will keep the established strengths of JPGR as we add new features. This will be achieved in two ways. First, the journal will produce thematic issues, each containing core papers solicited by a guest editor focused on a topic related to growth regulation. The thematic papers, which may be original research articles or brief reviews, will present the state of the field and new work judged by the guest editor to be important and interesting. The guest editor will also write a short piece surveying the field, providing a rationale for the selection of papers, and indicating where the field might profitably go in the future. Each issue also will contain contributed articles. Second, the journal will accept contributed manuscripts that consider plant growth regulation from any of the many different approaches—genetics, physiology, hormones, biophysics, development, and molecular biology, for example. This expansion will provide a broader context for understanding growth and its regulation. I believe such a broadening of the journal is both necessary and desirable. Necessary, to maintain (and even strengthen) the reputation of the journal, so that the papers submitted will have the highest visibility and widest circulation. Desirable, because this holistic approach is increasingly neglected in the literature, although it is at the heart of most work in plant growth regulation—where the ties between “pure” knowledge about the chemical and other regulators of plant growth and the practical application of this knowledge for the development of commercial compounds are so clear. My desire for a holistic perspective is idealistic, and some might say harks back to the 19th century, but I believe it is essential as scientific research becomes increasingly compartmentalized with each passing year. It is important for us to surface from our microcosm of private inquiry and gaze again at the horizon to assess where we are. It is my intention that Journal of Plant Growth Regulation will become the venue for such holistic assessments, and I can think of no better timing for such a re-launch than the beginning of the new millennium. My hope is that the journal’s long-standing supporters and contributors will agree with me that these changes are improvements, and I look forward to working with you to further the journal’s commitment to the study of plant growth regulation. Along with the change in format and expansion of perspective, you undoubtedly noticed the journal has a new face. Not only has the journal logo changed, each cover will feature a color photograph or illustration from a thematic article of each issue. And, of course, color will continue to be an option for journal pages. A color budget is under editorial discretion, and authors submitting papers with color illustrations can apply for this consideration. You may also have noticed the paper stock of the journal has changed to accommodate increased numbers of article illustrations. JPGR continues to be accessible on line at http://link.springer-ny.com and at http:// link.springer.de. Readers may subscribe at no charge to LINKAlert and receive e-mail alerts with complete Tables of