Tuesday, August 21, 2012

Mistletoes and mutant albino shoots as nutrient traps

Potassium, sulphur and zinc contents of mistletoe leaves are generally higher than in their hosts because elements that are cycled between xylem and phloem in the process of phloem loading of sugars are trapped in the mistletoe. Lo Gullo et al. hypothesize that mutant albino shoots should behave similarly because they lack photosynthesis and thus cannot recycle elements involved in sugar loading. They find that comparison of the mineral nutrition of the mistletoe Scurrula elata with that of albino shoots on Citrus sinensis and Nerium oleander supports this view. The absence of phloem loading is reflected in the phloem anatomy of the abnormal shoots, whilst in mistletoes the evolution of a parasitic lifestyle has clearly eliminated substantial feeding of the host with photosynthates produced by the mistletoe.


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