Evidence that C 4 species in genus Stipagrostis, family Poaceae, are NADP-malic enzyme subtype with nonclassical type of Kranz anatomy (Stipagrostoid)

Abstract

The genus Stipagrostis in family Poaceae is composed of species, which have Kranz anatomy and C 4 photosynthesis. There are three classical biochemical subtypes of C 4 plants in the family based on the type of C 4 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 C 4 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.