Betalain production associated with altered sodium distribution in the New Zealand iceplant, Disphyma australe

KS Gould, G Jain and T Karl

Victoria University of Wellington

The effects of climate change and irrigation practices have increased soil salinity levels in many parts of the world, impeding growth and reducing potential yields in many crop plants. In contrast to most crops, halophytes such as Disphyma australe have adaptive mechanisms that allow them to thrive in saline soil. Previous research has shown that the presence of betacyanin, a red-pigmented alkaloid, in the leaves of D. australe seems to correlate with increased salinity tolerance. However, the mechanism by which betacyanins might mediate salinity tolerance remains unknown. We hypothesised that betacyanins might alter sodium distribution within plant tissues, thereby avoiding the cytotoxic effects of sodium on photosynthetically active tissues. We used fluorescence microscopy and cryo-SEM coupled with energy dispersive x-ray spectroscopy on betacyanic- and green-leafed D. australe to explore possible associations between sodium distribution and betacyanins. The results suggest that for red leaves, sodium concentrates largely in the betacyanin-containing epidermal cells, but for the green leaves, sodium is more generally distributed. The mechanism through which betacyanins apparently divert sodium away from photosynthetic tissues warrants further investigation.