Abstract Detail



Anatomy and Morphology

Horner, Harry (Jack) [1].

The ‘origin enigma’ of leaf calcium oxalate druses and crystal sand crystals in environmentally-separated taxa of Peperomia (Piperales; Piperaceae).

Several recent studies that have identified druses (D) in low-land, mostly-shaded species and crystal sand (CS) in high-altitude, sun-exposed species of the genus Peperomia, provide a conundrum of sorts.  The former species all contain only D in their palisade parenchyma (PP) photosynthetic tissue and infrequently either raphides or prisms in their spongy parenchyma (SP); whereas the latter high-altitude so-called ‘Window Peperomia’ (WPs) species contain mostly D and some CS in their PP, and almost exclusively and consistently CS in their SP.  Both types of crystals have been suggested to serve as light gathering/reflecting units for either enhancing light gathering and concentration under low-light intensities for photosynthesis or dispersing visible and infrared light under high-light intensities to reduce photoinhibition and heat buildup.  Initially, only D were described in Peperomia species (before studying the WPs) but CS is very common among species in the sister genus Piper, as well as other members of the Piperales (both Peperomia and Piper represent the majority of the family).  The phylogenetic question for the entire Order Piperales (Piperaceae) with regard to crystal type is which type arose first, D or CS?  Unfortunately, no molecular marker(s) have been identified to answer this question. However, some members of an unrelated group, the Naucleeae (Rubiaceae), may shed light on this question.  Several genera of this group have species whose leaves contain crystal idioblasts in which both D and CS exist together.  This condition of two types of crystals in one cell, only found so far in these few taxa, and in a handful of other taxa, suggests it is possible both types could have formed simultaneously early in the evolution of the Piperales, and developmentally and environmentally separated once new species evolved.  In addition, ultrastructural data from other unrelated taxa (Capsicum annuum; Solanaceae) show that each D consists of a central para-crystalline nucleation site binding together the membrane-bounded individual crystal chambers into a spherical crystal aggregate; whereas individual CS crystals (Beta vulgaris; Amaranthaceae) have individual nucleation sites associated with each separate crystal.  These data indicate unidentified control(s) orchestrating a ‘nucleation site’ may occur allowing for either D or CS, or both, to form in one cell, and may, in some way, be altered by a photosynthetic or some other signal. These diverse results address a complex scenario for a specific crystal type and its function within the tissue in which it occurs.


1 - Iowa State Universsity, Genetics, Development and Cell Biology, 0106 Molecular Biology Building, 2437 Pammel Drive, Ames, IA, 50011-1079, USA

Keywords:
Peperomia
Crystal forms
Druses
Crystal sand
Phylogenetic origin.

Presentation Type: Oral Paper
Number:
Abstract ID:71
Candidate for Awards:None


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