Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

David J. Longstreth

Abstract

Dark-grown suspension cells of alligator weed (Alternanthera philoxeroides (Mart.) Griseb) were established in Murashige and Skoog medium and used to characterize several cellular responses to an abrupt increase in salinity (0 to 200 mol m$\sp{-3}$ NaCl). The fresh weight and cell density of salt-treated cells of alligator weed more than doubled by 7 d. Cell viability declined to 77% by 1 d, but recovered to 86% by 7 d after salt treatment. These responses indicate that alligator weed cells survived and adapted to an abrupt increase in salinity. Osmotic potential ($\psi\sb\pi$) of salt-treated cells declined to the $\psi\sb\pi$ of the salt treatment medium and symplastic volume decreased by 36% at 2 h. This decrease in $\psi\sb\pi$ at 2 h was primarily due to increased (Na$\sp+$) and (Cl$\sp-$), although concentrations of K$\sp+$, reducing sugars and quaternary ammonium compounds (QAC) also increased. From 2 h to 6 h after transfer to salt treatment, there was further but slower decline in cellular $\psi\sb\pi$, an increase in symplastic volume and cellular turgor potential ($\psi\sb{\rm p}$) became positive. By 3 d, $\psi\sb{\rm p}$ was similar in control and salt-treated cells and the fresh weight of salt-treated cells was increasing. Cellular concentrations of sucrose, proline and total free amino acids also increased in salt-treated cells at 7 d. Decreases in cellular (Na$\sp+$) and (Cl$\sp-$) between 1 and 7 d indicate efficient regulation of these ions in alligator weed cells during prolonged salinity. These responses to an abrupt increase in salinity were accompanied by increased staining and incorporation of $\sp{35}$S-methionine into two soluble polypeptides and induction of two membrane polypeptides as early as 12 h after the beginning of salt treatment. The response of alligator weed cells was distinct from that of tobacco cells, which did not attain positive $\psi\sb{\rm p}$ during the first 24 h, exhibit recovery of cell viability by 7 d or show an increase in fresh weight over the 21 d period after an abrupt increase in salinity. These results characterize several facets of cellular response to salinity and demonstrate the value of the alligator weed suspension system for studies of plant response to salinity.

Pages

122

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