δ13C Values and the Occurrence of Suberized Lamellae in Some Panicum Species.

Abstract

δ13C values and the occurrence of a suberized lamella were determined for leaves of some Panicum species. Mean δ13C values for C4 subtypes were: NADP-malic enzyme (ME) species, −11·50±0·92%(2 spp.); NAD-ME species with centrifugal chloroplasts in bundle sheath cells (NAD-ME(F) species), −11·95±0·35 (4 spp.); phosphoenolpyruvate carboxykinase (PEP-CK) species, −12·06±0·51 (6 spp. and 1 var.); NAD-ME species with centripetal chloroplasts in bundle sheath cells (NAD-ME(P) species, −1248 + 0·28 (9 spp. and 1 var.). The difference between mean for NAD-ME(F) and that for NAD-ME(P) species was significant at 5 % level. A suberized lamella was present in the bundle sheath cell (BSC) wall of NADP- ME species (1 sp.) and NAD-ME(F) species (2 spp.) and absent from that of NAD-ME(P) species (2 spp.). These results suggest that NAD-ME(F) species and NAD-ME(P) species differ in carbon dioxide leakage from the bundle sheath cells and also confirm the postulation that the occurrence of a suberized lamella may minimize the carbon dioxide leakage from the bundle sheath cells. However, NAD-ME(F) and NAD-ME(P) species have been reported to show the same sharp pattern of postillumination carbon dioxide burst (PIB) within 30 s of darkness. Therefore, the results obtained in this study also suggest that the sharp PIB may be caused not by the absence of suberized lamella but by some other leaf anatomical characteristics and/or biochemical processes.