By inbreeding and selection of hard endosperm, we have obtained after many generations, lines which carry the floury-2 gene with a normal phenotype. Modified floury-2 lines are of the yellow flint type and possess a high proportion of hard endosperm, which makes them indistinguishable from other normal flint lines (see Figure 1). When comparing the protein quality of modified floury-2 with original floury-2 (floury endosperm), we have not found significant differences for tryptophan content (see Table 1).
This fact induced us to investigate the endosperm's sub-cell structure in order to establish if modifications had occurred. Mature kernels of a floury-2 line with floury endosperm (AD-O2 fl2) and two lines of modified floury-2 were thin-sectioned and prepared for the microscopic observation of the endosperm, in accordance with Wolf and Khoo (Stain Tech. 45:277, 1970). The prepared material was stained with Coomassie Brilliant Blue R250.
The results obtained may be seen in Figure 2. Floury-2 with floury phenotype has no visible zein bodies, as has been established by other authors. Notwithstanding, on the small layer of hard endosperm in the back part of the grain, we have observed zein bodies in line AD-O2 fl2.
In the modified versions of line AD-O2 fl2, it can be noticed that the protein matrix is densely populated with zein bodies.
The three lines studied are near isogenic and have the same protein quality, but when the endosperm hardness is modified, zein bodies are visible at optical microscope level. This has led us to deduce that the presence or absence of zein bodies bears no indication as to protein quality.
While known mutants repress zein synthesis and consequently the protein quality increases, the microscopic observations of the endosperm structure do not give in every case an idea of the quantity of zein (and consequently its quality).
The results obtained indicate a close association between hard endosperm and presence of zein bodies in this particular case. Nevertheless, the protein quality does not associate with the floury endosperm, so that the material developed may be interesting to improve the protein quality, without modifying the normal phenotype of the grain (flint).
Figure 1. Photograph of longitudinally split kernels: left--floury-2; middle--modified floury-2; right--extremely modified floury-2.
Figure 2. Destarched 3-4 um thick sections of endosperm showing protein bodies. A--floury-2; B--modified floury-2; C--extremely modified floury-2.
Jorge Luis Magoja and Luis Maximo Bertoia
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