Apyrases are enzymes that transform NTP (nucleoside triphosphates)
via NDP to NMP without triggering an endergonic reaction in the
process. These enzymes have been identified in the tissues of
animals, plants (among others in Arabidopsis thaliana, legumes and
potatoes) and fungi and apparently have predominantly regulatory
functions.
Double knockout mutations of both apyrase genes from A. thaliana
inhibit pollen germination and give rise to male sterile plants.
Apyrases play a role in the formation of nodules in leguminous
plants, and are also thought to be involved in phosphate
uptake.
Regulation of transporters that, amongst other things, facilitate
the transport of xenobiotics out of the plant cell has been
demonstrated for plant apyrases. The blocking of apyrase by
specific inhibitors increases the sensitivity of the plants to
different herbicides, as well as the concentration of the applied
herbicides in the plants. Over-expression of the apyrase
psNTP9 from Pisum sativum in A. thaliana increases the resistance
of the plants to herbicides and phytohormones.
Apyrase activity in the potato tubers is very high and is probably
localised in the area of the cell wall. Together with other enzymes
that influence the ATP/ADP/AMP ratio, apyrase activity is suspected
to have a regulatory effect on starch biosynthesis in the potato
tubers.
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