Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

David J. Longstreth

Abstract

This study examined the importance of the leaf aerenchyma gas space as a CO$\sb2$ source for photosynthesis in Typha latifolia L. (broadleaf cattail). In the field there was a distinct diurnal pattern of CO$\sb2$ concentration ( (CO$\sb2$)) in the aerenchyma gas space. At dawn the aerenchyma (CO$\sb2$) was 4 to 18 times above atmospheric levels. By midday the aerenchyma (CO$\sb2$) declined to near atmospheric levels and increased again in the late afternoon. It is hypothesized that this diurnal pattern may be controlled by photosynthetic demand for CO$\sb2$. Aerenchyma gas space was estimated as $>$50% of leaf volume, and the continuity of the aerenchyma gas space through the rhizome-shoot transition was confirmed using tracer dyes. Anatomical examination revealed that the aerenchyma gas space separates the anatomically similar adaxial and abaxial palisades. Each palisade was exposed to two CO$\sb2$ sources: (1) atmospheric CO$\sb2$ diffusing through the epidermal stomata along a gaseous pathway; and (2) aerenchyma gas space CO$\sb2$ diffusing through the cells of the internal surface along an aqueous pathway. Using gas exchange measurements, net photosynthetic CO$\sb2$ uptake rate (P$\sb{\rm N}$) of isolated adaxial and abaxial palisades of intact leaves was 6.0 and 4.0 $\mu$mol$\cdot$m$\sp{-2}{\cdot}$s$\sp{-1}$, and saturated at a photosynthetic photon flux density of 900 and 700 $\mu$mol$\cdot$m$\sp{-2}{\cdot}$s$\sp{-1}$, respectively. P$\sb{\rm N}$ response to (CO$\sb2$) was similar for intact leaves and dissected leaves when (CO$\sb2$) in aerenchyma gas space was held constant. At a constant epidermal (CO$\sb2$) of about 350 $\mu$L$\cdot$L$\sp{-1}$, internal P$\sb{\rm N}$ from the aerenchyma gas space increased linearly with (CO$\sb2$) to 1.92 $\mu$mol$\cdot$m$\sp{-2}{\cdot}$s$\sp{-1}$, at about 900 $\mu$L$\cdot$L$\sp{-1}$, the highest (CO$\sb2$) used. Over the same range of aerenchyma gas space (CO$\sb2$) epidermal P$\sb{\rm N}$ declined 69%. These results indicate that CO$\sb2$ can be assimilated from both the atmospheric and aerenchyma gas space CO$\sb2$ sources and that these sources of CO$\sb2$ could be "competitive." Although internal P$\sb{\rm N}$ measured in the laboratory is low, at aerenchyma gas space (CO$\sb2$) s found in the field, internal P$\sb{\rm N}$ could represent a significant carbon source for cattail.

Pages

127

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