A Morphological Basis for Higher Niacin in Sugary Maize

Abstract

Two ears of maize having purple aleurone and segregating for starchy and sugary kernels were taken when almost mature, so that the pericarp layer could be peeled off and the embryos removed without soaking the seed. Niacin assays were run on 10-kernel samples for the pericarp, aleurone, inner endosperm and embryo by using Lactobacillus arabinosus according to the method of the Association of Vitamin Chemists. Assay figures were given on the basis of samples dried at 50[degree]. Carbohydrate was detd. as glucose following acid hydrolysis of samples and protein by multiplying per cent nitrogen by 6.25. Pericarps from starchy and sugary kernels were identical in niacin concn. and almost identical in amt. of niacin contributed per kernel. Embryos of sugary kernels from both ears had somewhat higher niacin concn. and content. Sugary inner endosperm from both ears showed almost twice the niacin concn. of starchy, but the niacin contribution of the inner endosperm to the content of the whole kernel was 20% or less. 60 to 70% of the niacin content of both starchy and sugary kernels was found in the aleurone layer. Most of the increased niacin content in sugary endosperm was localized in the aleurone layer,and was due to the fact that there was about twice as much aleurone in sugary kernels as in starchy kernels. The purple aleurone color was used as a marker in separating the single layer of aleurone cells, but, in order to test for possible contamination of aleurone with inner endosperm tissue in the sugary kernels, the aleurone and inner endosperm layers of both starchy and sugary kernels were tested for carbohydrates and proteins, which were known to differ quantitatively in the two layers. The tests showed that the greater amt. of aleurone in sugary kernels could not be explained by differential contamination. The thickness of aleurone cells in starchy and sugary kernels was measured by embedding and sectioning pieces of the kernels in the crown region. The thickness of 10 consecutive aleurone cells at the top (center of crown), middle, and side (toward the embryo) portions of each section was measured with an ocular micrometer. In all cases the sugary aleurone cells averaged thicker than the starchy cells, the ratio of the mean thickness of the sugary cells to that of the starchy cells being 1.31 for the crown region, L.45 for the middle and 1.47 for the side.