Spotlight on macronutrients: Touchy-feely calcium…

Calcium (Ca) acts – amongst other things! – as a so-called ‘second messenger’, and participates in many processes of plant growth and development.
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Image: Wikimedia Commons.
Image: Wikimedia Commons.

Most essential plant nutrients exert their roles when integrated into organic compounds and macromolecular structures – e.g. nitrogen and sulphur (see previous blog items on those macronutrients). Others – such as magnesium (Mg) – may also act in their ionic form as ‘enzyme activators’. But calcium (Ca)  is almost in a class of its own as it acts – amongst other things! – as a so-called ‘second messenger’,  and participates in many processes of plant growth and development. As a second messenger, levels of Ca2+ in the cytoplasm vary dramatically in response to many environmental and developmental stimuli, which subsequently trigger different physiological responses.  Such a role for Ca is also relevant to interactions between plants and other organisms, as demonstrated by Lehcen Benikhlef et al. in the case of microbial attack.  However, their work goes even further than that because they showed that light ‘mechanical sweeping’ of leaves of arabidopsis led to development of a strong resistance to Botrytis cinerea (a necrotophic fungus that attacks plants and causes ‘grey mould’). This was preceded by a rapid change in Ca concentration and a release of ROS (reactive oxygen species),  and was accompanied by ‘changes in cuticle permeability, induction of the expression of genes typically associated with mechanical stress and release of biologically active diffusates from the surface’. OK, so, it’s a bit more than just Ca, but what a fascinating chain of events. Maybe we should all be handling our plants more often to encourage them to develop pathogen resistance. After all, they do talk of ‘healing hands’


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