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Purslane: response to saline stress

Kristina Mulry, Bryan Hanson, and Dana Dudle
Department of Chemistry and Biochemistry and Department of Biology, DePauw University

Introduction
Anthropogenic climate change may lead to increased soil salinity in the future because of a combination of increased temperature, reduced rainfall, and increased irrigation.  We investigated the effects of saline stress on purslane (Portulaca oleracea), a succulent, robust medicinal plant.  We investigated whether two varieties of purslane exhibit the same level of phenotypic plasticity in response to saline stress.  Because purslane is widespread and synthesizes a wide array of bioactive compounds that are associated with stress tolerance, it is possible that different varieties may employ alternative strategies when faced with similar stressors.

Methods
We grew two varieties of purslane (T-16, cultivated and WI-9, wild type) in two treatments, 0 and 200 mM NaCl.  Twenty plants of each variety were assigned to each treatment.  We grew the plants from seeds in a greenhouse and watered the plants three times a week with 56 mL of tap water or 200 mM NaCl solution added to tap water.  After 10 treatments over 21 days, we recorded the number of nodes on the stem, the number of axillary branches, the number of leaves on the main stem, and the number of flowers on each plant.  We weighed above-ground dry biomass of each plant.  We measured proline levels, betalain pigment levels, and total phenolic compounds of samples from each plant. 

Results
Both varieties of purslane showed significant changes in morphological and physiological traits in response to saline stress.  Both varieties produced fewer flowers, fewer nodes, and less dry biomass in the saline treatment.  The two varieties differed significantly in their specific responses to saline.  Variety T-16 invested more in production of proline and WI-9 invested more in synthesis of betacynanins in response to saline. 

Discussion
Our results indicate that saline stresses purslane without killing it.  The two varieties of purslane adopted different strategies to cope with saline stress.  Variety T-16 employed proline as a primary antioxidant to protect against stress while variety WI-9 employed betacyanins in this role.