An unexpected fact was observed during the study of pericarp and aleurone layer thickness in Z. perennis x Gaspe hybrids: F2 grains with multilayer aleurone. This result is completely unusual, mainly because none of the parents present this characteristic. In the same way, our attention was attracted to the high frequency in which multilayer aleurone kernels come out. Aleurone with a 2 to 6-cell layer appears with the same frequency in F2 kernels in both directions of crossing between Gaspe and perennial teosinte (see Fig. 1). Thirty two of 100 kernels studied presented multilayer aleurone; that is to say, a third of F2 grains have this character.
Aleurone layer thickness is not strictly associated with the number of cells in the layer, but multilayer kernels have significantly thicker aleurone (average 75.7 microns) than those with a single layer (average 42.6 microns). Aleurone layer thickness in those multilayer kernels is not uniform, since there are zones with different numbers of layers. Even within the same kernel, single-aleurone zones are adjoined to multilayer ones. Nevertheless, exceptional kernels can be observed with a homogeneously distributed multilayer in all the grain periphery. Sometimes its thickness reaches 140 microns.
At first, we thought that the multilayer aleurone character was associated with floury endosperm, as occurs in Coroico maize. However, after checking the kernels once more, we could notice that this trait appears indifferently not only in floury but in hard endosperm kernels. Up to now it could not be determined if there is any association to other kernel traits, nor the effect produced on endosperm protein quality and quantity. The reason for its spontaneous appearance is still unknown, but in view of the high frequency in which this character comes out in hybrids between perennial teosinte and Gaspe progeny, it is probable for the multilayer aleurone trait to be the consequence of a single mutation.
Figure 1: Photomicrograph of free hand section from the abgerminal side of the kernel showing multilayer aleurone. 290x. a-aleurone; e-endosperm; p-pericarp.
Luis M. Bertoia and Jorge L. Magoja
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