Variation of leaf characteristics with level of insertion on a grass tiller. II.* Anatomy

Abstract

The influence of leaf insertion level on anatomical characteristics in transverse sections of blades and sheaths on primary tillers of a grass, Panicum maximum var. trichoglume, was examined in plants growing under controlled light, temperature and nutritional conditions. Leaves from insertion levels 3, 5, 7, 10 and 13 from the base of the tiller were harvested when fully expanded and 5, 10 and 20 days thereafter. The flag leaf (leaf 16) was harvested at full expansion only. Gradients in anatomical characteristics with insertion level were clearly evident in leaves compared at a similar stage of development. Leaf blades and sheaths of higher insertion level had a greater proportion of sclerenchyma and vascular tissue, thicker lignified cell walls and cuticle, and a smaller average size of mesophyll, bundle sheath and epidermal cells. Lignification and cuticle development was greater in sheaths than in blades. These anatomical changes would explain the previously reported increase in cell wall content, and decrease in digestibility, of leaves at increasing insertion level. The anatomy of the leaf blades from all insertion levels did not change as leaves aged. However, sheaths in general, and those from higher insertion levels in particular, exhibited a marked increase in lignification of sclerenchyma and thickening of cuticle in the 5 days following the emergence of the ligule. These changes in the leaf sheaths appeared to be closely associated with the large decrease in digestibility over the same period. ___________________ *Part I, Aust. J. Agric. Res., 27: 343 (1976).