Kranz distinctive cells in the culm of ArundineUa (Arundinelleae; Panicoideae; Poaceae)

Abstract

The transectional anatomy of photosynthetic flowering culms of Arundinella berteroniana (Schult.) Hitchc. Chase and A. hispida (Willd.) Kuntze from South America and A. nepalensis Trin. from Africa is described and illustrated. The vascular bundles are arranged in three distinct rings, the outermost being external to a continuous sclerenchymatous band. Each of these peripheral bundles is surrounded by two bundle sheaths, a complete mestome sheath and an incomplete, outer, parenchymatous Kranz sheath, the cells of which contain large, specialized chloroplasts. Kranz bundle sheath extensions are also present. The chlorenchyma tissue is also located in this narrow peripheral zone and is interrupted by the vascular bundles and their associated sclerenchyma. Dispersed throughout the chlorenchyma are small groups of Kranz distinctive cells, identical in structure to the outer bundle sheath cells. No chlorenchyma cell is. therefore, more than two cells distant from a Kranz cell. The structure of the chlorenchyma and bundle sheaths indicates that the C4 photosynthetic pathway is operative in these culms. This study clearly demonstrates the presence of the peculiar distinctive cells in the culms as well as in the leaves of Arundinella. Also of interest is the presence of an inner bundle sheath in the vascular bundles of the culm whereas the bundles of the leaves possess only a single sheath. It has already been shown that Arundinella is a NADP-me C4 type and the anatomical predictor of a single Kranz sheath for NADP-me species, therefore, either does not hold in the culms of this genus or the culms are not NADP-me. This is only the second reported breakdown of this association between MS anatomy and the NADP-me biochemical C4 type.