Abstract
While the photosynthetic function of enzymes forming the Hatch-Slack cycle (phosphoenolpyruvate carboxylase PEPC, NADP-malic enzyme NADP-ME, and pyruvate phosphate dikinase PPDK) in some C4 and CAM plants is well known, the possible roles of their non-photosynthetic counterparts, present in all plants, are still studied. Various functions were suggested for non-photosynthetic isoforms of these enzymes: anaplerotic function, the role in nitrogen assimilation and mobilization, participation in pH regulation, fruit ripening, production of reducing equivalent NADPH, the role in additional bypassed reactions, in antioxidant system etc.
Moreover, non-photosynthetic PEPC, NADP-ME, and PPDK are together involved in stress. The activities of the Hatch-Slack non-photosynthetic enzymes from tobacco (Nicotiana tabacum L., cv.
Petit Havana SR1), as a model of C3 plants, were increased in the response to both biotic stress caused by Potato virus A and Potato virus Y (strain NTN and O) and abiotic stress caused by drought. The regulation of above mentioned enzymes and the possibility that these enzymes cooperate during stress response together is further discussed with regard to the fact that individual non-photosynthetic Hatch-Slack enzymes were found to be involved in other stressor-plant interactions, too.