Leaf anatomy, chloroplast ultrastructure, and cellular localisation of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and RuBPCO activase in Amaranthus tricolor L.

Abstract

In Amaranthus tricolor the leaf structure included three layers of chlorenchyma on the vascular bundle periphery, namely, mesophyll cells (MSCs) with few chloroplasts, outer larger round bundle sheath cells (BSCs) with many chloroplasts in a centripetal position, and inner smaller BSCs with few chloroplasts around the vascular bundle cells. The ultra-thin sections showed that BSCs had abundant organelles, namely many large and round mitochondria with well-developed cristae in the cytoplasm. The chloroplasts in the BSCs were lens-like bodies, which seemed to be oval on cross sections. Granal and intergranal thylakoids were usually distinguished. Grana were stacked in parallel with prevailing plane of thylakoid lamellae. The chloroplasts in the MSCs appeared smaller than those in the BSCs and contained less stacked thylakoids but abundant peripheral reticulum. The ultra-thin sections of immunogold-labelled anti-ribulose-1,5-bisphosphate carboxylase/oxygenase (anti-RuBPCO) exhibited high density of RuBPCO labelling in the stroma region of chloroplasts of the BSCs. Some anti-RuBPCO immunogold particles were observed in the stromal region of MSCs chloroplasts. The anti-activase (A) immunogold-labelling indicated that RuBPCOA was mainly distributed in the stroma region of both BSCs and MSCs chloroplasts. From the chloroplast ultrastructure and localisation of RuBPCO and RuBPCOA we deduced that the photosynthetic carbon reduction cycle and the formation of assimilatory power function in both MSC and BSC chloroplasts of A. tricolor.