The C4 biochemical pathway, and the anatomy of lemongrass (Cymbopogon citratus (DC) Stapf.) cultivated in temperate climates

Abstract

ABSTRACT Leaf anatomy (light and transmission electron microscopy, immunogold localisation of Rubisco) and physiology (C4 photosynthetic enzyme activities, CO2 assimilation and stomatal conductance) were studied in lemongrass, Cymbopogon citratus (DC) Stapf., cultivated in temperate climates (northwestern Italy). The leaf blade had an NADP-ME Kranz anatomy, with bundle sheath cells containing chloroplasts located in a centrifugal position. Dimorphic chloroplasts, agranal and starchy in the bundle sheath and granal starchless in the mesophyll cells, were also observed. Rubisco, as determined by immunolocalisation, occurred only in the bundle sheath chloroplasts. Pyruvate, orthophosphate dikinase (PPDK), NADP malic dehydrogenase (NADP-MDH), NADP malic enzyme (NADP-ME), PEP-carboxykinase (PCK), and NAD malic enzyme (NAD-ME) activities were also measured, indicating an NADP-ME C4 photosynthetic pathway. Some kinetic properties and chemicalphysical parameters of lemongrass NADP-ME and NADP-MDH as well as CO2 compensation point and stomatal conductance values confirmed these preliminary data. C. citratus appeared to be well adapted to the varying environmental conditions typical of temperate climates, by retaining high NADP-MDH and NADP-ME activities and a low CO2 compensation point.