Leaf Anatomy and Carbon Discrimination in NAD-malic EnzymePanicumSpecies and their Hybrids Differing in Bundle Sheath Cell Ultrastructure

Abstract

The relationship between leaf anatomy, ultrastructure and carbon discrimination was investigated in leaves of two F1hybrids (F1−1 and F1−2) between two different types of the grassPanicum[an NAD-malic enzyme (ME) C4species], which differ in bundle sheath ultrastructure. The female parent was Kabulabula grass, which has centrifugal chloroplasts in bundle sheath cells and is designated an NAD-ME(F) species, while the male parent was Makarikari grass, which has centripetal chloroplasts in the bundle sheath cells and is designated an NAD-ME(P) species. Suberin lamellae are present in Kabulabula grass but are lacking in Makarikari grass. Both F1hybrids had the same chromosome number (2n=36) as the parents but exhibited both univalent (about 45%) and bivalent (about 55%) chromosome pairing which was the major basis for the identification of F1hybrids. In F1−1, elongated bundle sheath cell chloroplasts are arranged mainly in a centripetal position, similar to those in the male parent, Makarikari grass. In contrast, most of the bundle sheath cells in F1−2 are packed with starch-containing chloroplasts, although in some cells chloroplasts tended to be centripetally arranged. In both F1hybrids, suberin lamellae were found in the bundle sheath cell walls, similar to the female parent, Kabulabula grass. The δ13C values of both F1hybrids were −11.4 to −11.7‰, almost the same as those of Kabulabula grass (−11.4‰), but significantly higher than those of Makarikari grass (−12.7‰). These results indicate that the chloroplast orientation in the bundle sheath cells and the presence of suberin lamellae are not obligatorily linked in their expression and suggest that suberin lamellae may play an important role in discrimination against13C.