LEAF ANATOMY AND CARBON DISCRIMINATION IN NAD-MALIC ENZYME PANICUM SPECIES AND THEIR HYBRIDS DIFFERING IN BUNDLE-SHEATH CELL ULTRASTRUCTURE

The relationship between leaf anatomy, ultrastructure and carbon discr imination was investigated in leaves of two F-1 hybrids (F-1-1 and F-1 -2) between two different types of the grass Panicum [an NAD-malic enz yme (ME) C-4 species], which differ in bundle sheath ultrastructure. T he female parent was Kabulabula grass, which has centrifugal chloropla sts in bundle sheath cells and is designated an NAD-ME(F) species, whi le the male parent was Makarikari grass, which has centripetal chlorop lasts in the bundle sheath cells and is designated an NAD-ME(P) specie s. Suberin lamellae are present in Kabulabula grass but are lacking in Makarikari grass. Both F-1 hybrids had the same chromosome number (2n =36) as the parents but exhibited both univalent (about 45%) and bival ent (about 55%) chromosome pairing which was the major basis for the i dentification of F-1 hybrids. In F-1-1, elongated bundle sheath cell c hloroplasts are arranged mainly in a centripetal position, similar to those in the male parent, Makarikari grass. In contrast, most of the b undle sheath cells in F-1-2 are packed with starch-containing chloropl asts, although in some cells chloroplasts tended to be centripetally a rranged. In both F-1 hybrids, suberin lamellae were found in the bundl e sheath cell walls, similar to the female parent, Kabulabula grass. T he delta(13)C values of both F-1 hybrids were -11.4 to -11.7 parts per thousand, almost the same as those of Kabulabula grass (-11.4 parts p er thousand,), but significantly higher than those of Makarikari grass (-12.7 parts per thousand). These results indicate that the chloropla st orientation in the bundle sheath cells and the presence of suberin lamellae are not obligatorily linked in their expression and suggest t hat suberin lamellae may play an important role in discrimination agai nst C-13. (C) 1997 Annals of Botany Company.