Abstract Detail

Anatomy and Morphology

HORNER, HARRY T [1], YOON, HANA [2], MEKALA, DIVYA [3].

Crystal density and size variations in leaves of two variegated and one pseudo-variegated species of Peperomia (Piperaceae).

A number of low-land, partially-shaded species of Peperomia display variegated and differentially-thickened leaves that have variable regions being green and the remaining regions being yellow or white. Several older and more recent studies suggest leaf crystals may be light gathering or reflecting units, among other possibilities, to either enhance or deflect light to protect the leaf photosynthetic organelles. To anatomically test this idea, a hypothesis was developed that leaf tissues and cells containing crystals with chloroplasts (green regions) should display larger and more abundant crystals per unit area than leaf tissues containing crystals without chloroplasts (yellow regions). Two available variegated species (P. obtusifolia variegata [Pov] and P. scandens variegata [Psv]), and one ‘pseudo-variegated’ species (Peperomia prostrata [Pp]) from two ISU greenhouses were chosen for this study. Whole leaves or punches from both green and yellow/white leaf regions were either cleared or vibratome sectioned to identify the types of crystals present with bright-field and polarizing light optics, and scanning electron microscopy, and to statistically measure crystal sizes and their densities per selected leaf region. Both Pp and Pov have only druses in their palisade parenchyma (PP), whereas Psv contains druses in its PP and raphide bundles in its spongy parenchyma (SP). Of the three species, pseudo-variegated Pp has dimorphic leaves with one leaf type being lens shaped and the other leaf type being flat (similar to the other two species). In the flat-shaped leaves the concentration of druses in the PP associated with the main and lateral veins (white) is more pronounced giving the pseudo-variegated appearance, compared to the inter-veinal regions (areoles), and overall more pronounced than in the lens-shaped leaves. The results of the study of the two true variegated species indicate the number of crystals, druse diameters and densities of both types of crystals vary between the green and yellow leaf regions, and between the PP and SP layers of Psv. The trend for the variegated Pov and Psv species is for more druses covering a larger percentage of the green regions (with the exception of a higher number of raphide bundles occurring in PsvYellow regions). These results suggest that higher druse density favor green photosynthetic regions, not yellow regions, and supports our hypothesis of the `potential involvement in enhanced photosynthesis in these species, due to higher light gathering and reflection, and possibly in leaves of other unrelated taxa. The results for Pp are under further study.

1 - Iowa State University, Genetics, Development and Cell Biology, 2200 Osborn Drive, 3A Bessey Hall, Ames, IA, 50011-4009, USA
2 - Iowa State University, Freshmen Honors Program, Ames, IA, USA
3 - Iowa State University, Freshmen Honors Program, Ames, IA, 50011, USA

Keywords:
crystals
leaves
Peperomia
variegation.

Presentation Type: Oral Paper
Session: 20, Anatomy and Morphology
Location: Fort Worth Ballroom 7/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 10:15 AM
Number: 20009
Abstract ID:64
Candidate for Awards:None