Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

2006

Thesis Director

Janice Coons

Thesis Committee Member

Henry Owen

Thesis Committee Member

Gordon Tucker

Abstract

Stylisma pickeringii (Torr.) Gray var. pattersonii (Fern. & Schub.) Myint (Convolvulaceae) is listed as an endangered plant species in Illinois and is commonly known as Patterson bindweed or Patterson dawnflower. It is a prostrate vine that occurs in well-drained sand prairies and sandy open woods. High temperature, low moisture holding ability and blowing sand in these prairies create a harsh environment for seedling establishment.

Seedlings of Stylisma pickeringii show a unique pattern of development, which may enhance their ability to become established. Following radicle and cotyledon emergence, an enlarged ring encircling the radicle, referred to as the transition zone, develops. A shoot arises laterally from this hypocotyl region, which is situated below the soil surface. All further growth above the soil surface continues from this region. Previous studies indicated that light is involved with seedling development, but it is unclear whether photoperiod or total irradiance, or both are influencing this process.

The first objective of this study was to determine the effect of photoperiod and light intensity on seedling development of Stylisma pickeringii, especially the effect on the lateral shoot development. The second objective of this study was to document the anatomical development of S. pickeringii seedlings, as well as determine the origin of the lateral shoots.

For light studies, plants were grown from seed both in Promix:Sand (1:1) and in vitro on Murashige and Skoog medium with long days (16 hours light/ 8 hours dark) and short days (8 hours light/ 16 hours dark) at two light intensities (700 and 350 µmol s¹m²). Development of radicles, cotyledons and shoots was measured to determine the effect of light on seedling development. Radicles and cotyledons emerged sooner with higher light intensity than with lower light intensity, whereas photoperiod had no significant effect. However, shoot emergence was earlier with long days than short days. With short days, shoots developed faster at the higher light intensity than at the lower light intensity. Overall development of seedlings, including the unique shoot development, was more controlled by total irradiance than by photoperiod.

For anatomical studies, plants were grown from seed in vitro on Murashige and Skoog medium. Seedlings were removed from tubes and placed in FAA at 5 day intervals until day 35. Tissues were embedded in Paraplast and sectioned at 10 µm both longitudinally and transversely. Permanent slides were made using the Safranin O and Fast Green staining procedure. Development of the meristematic region, resembling a shoot apical meristem, occurs basally in a cavity created by the fusion of cotyledonary petioles. Once the developing shoot is too large to be contained within the cavity, it becomes outwardly visible as it tears through the fused petioles that encircle it.

This adaptation enables the young shoot to mature within the protected sheath before it emerges into the harsh sand prairie environment. While the lateral shoot is a distinctive characteristic of Stylisma pickeringii seedlings, the fused cotyledonary petioles and its sunken shoot apical meristem may be the most significant factors enhancing seedling establishment.

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