Trehalase in plants In plant kingdom, though trehalose has been reported from several pteridophytes including Selaginella lepidophylla and Botrychium lunaria; the sugar is rare in vascular plants and reported only in ripening fruits of several members of Apiaceae and in the leaves of the desiccation-tolerant angiosperm Myrothamnus flabellifolius. But, the enzyme trehalase is ubiquitous in plants. This is puzzling that trehalase is present in higher plants, though its substrate is absent. No clear role has been demonstrated for trehalase activity in plants. However, trehalose inhibits the synthesis of its precursor, trehalose 6-phosphate, a plant metabolism regulator; hence, its removal may be required. It has been suggested that trehalases could play a role in defense mechanisms or the enzyme could play a role in the degradation of trehalose derived from plant-associated microorganisms. Fungal trehalase Two distinct trehalases have been reported from S. cerevisiae. One is regulated by cAMP-dependent phosphorylation and localized to the cytosol. The second trehalase activity is found in the vacuoles. The pH optimum of cytosolic trehalse was determined to be approximately 7.0 and is thus referred to as 'neutral trehalase' (NT); whereas the vacuolar trehalase is most active at pH 4.5 and consequently termed 'acid trehalase' (AT). These enzymes are encoded by two different genes – NTH1 and ATH1 respectively. Neutral trehalase The cytosolic trehalase enzyme, NT, has been purified and characterized extensively from S. cerevisiae. In non-denaturing gels this enzyme protein exhibited a molecular mass of 160 kDa, while in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) it showed a mass of 80 kDa. This hydrolase enzyme is specific for trehalose. The Km of NT has been reported to be 5.7mM. The gene responsible for trehalase activity in S. cerevisiae is NTH1. This gene is with an open reading frame of 2079 base pairs (bp), encoding a protein of 693 amino acids, corresponding to a molecular mass of 79569 Da. NT activity is regulated by protein phosphorylation-dephosphorylation. Phosphorylation with cAMP-dependent protein kinase activates NT. Dephosphorylation of the purified phosphorylated enzyme by alkaline phosphatase caused an almost complete inactivation of the enzyme activity; but a recovery of the enzyme activity could be observed by rephosphorylation while incubating with ATP and protein kinase. The activity of NT in crude extracts is enhanced by polycations, while the activity of purified phosphorylated NT is inhibited by them. The activation of crude extracts was found to be due to the removal of polyphosphates,