Evidence that C4 species in genus Stipagrostis, family Poaceae, are NADP-malic enzyme subtype with nonclassical type of Kranz anatomy (Stipagrostoid)

The genus Stipagrostis in family Poaceae is composed of species, which have Kranz anatomy and C4 photosynthesis. There are three classical biochemical subtypes of C4 plants in the family based on the type of C4 acid decarboxylase [NADP-malic enzyme (NADP-ME), NAD-malic enzyme (NAD-ME), and phosphoenolpyruvate carboxykinase (PEP-CK)], features of leaf anatomy, and of chloroplasts and mitochondria structure and/or position in the distinctive Kranz sheath cells. Initially, from some information on biochemistry and chloroplast ultrastructure, Stipagrostis species were suggested to be NADP-ME type. Yet, they have been classified as classical NAD-ME type C4 species based on the occurrence of a double parenchyma sheath around the veins with an outer Kranz sheath that has chloroplasts in a centripetal position. We show through analysis of photosynthetic enzymes and their immunolocalization, and microscopy of leaf structure in the species Stipagrostis pennata, that members of this genus are a novel “nonclassical” NADP-ME type, which we will call Stipagrostoid.