Características anatômicas da lâmina foliar e do colmo de gramíneas forrageiras tropicais, em função do nível de inserção no perfilho, da idade e da estação de crescimento

Abstract

An experiment was carried out to evaluate the effect of leaf age and insertion level and season of growth on the tissue proportion and the cell wall thickness of leaf blade and stem segment of signalgrass (Brachiaria decumbens), molassesgrass (Melinis minutiflora) and Tifton 85 bermudagrass (Cynodon sp). Leaf blades from bottom and top layers were sampled on the day of ligule exposure and 20 days later. The relative proportion of epidermis, xylem, phloem, parenchyma bundle sheath, sclerenchyma, stem parenchyma and leaf blade mesophyll were estimated. The thickness of cell wall of metaxylem vessels and sclerenchyma were evaluated. Leaf tissue proportion changed neither with age nor season of growth; thickness of leaf sclerenchyma cell wall was the only trait to change with age. Leaf from the top layer showed higher proportion of sclerenchyma, parenchyma bundle sheath and xylem as well as thicker cell wall in sclerenchyma and metaxylem; while leaves from the bottom layer had higher proportion of mesophyll and thinner sclerenchyma and metaxylem cell walls. While the parenchyma proportion of the stem decreased, the relative area of the sclerenchyma and the cell wall thickness increased as the plant aged. These traits showed greater values in summer samples.