Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/7/2002
Publication Date: 5/1/2002
Citation: Vilhar, B., Kladnik, A., Blejec, A., Chourey, P.S., Dermastia, M. 2002. Cytometrical evidence that the lossof seed weight in the minature 1 seed mutant of maize associated with reduced mitotic activity in the developing endosperm. Plant Physiology. 129:23-30. Interpretive Summary: Seed size, an ultimate unit of crop yields, is determined by two critical parameters: the number of cells and cell sizes in developing seeds. However, there are no reliable or suitable tools thus far to measure these traits. Here in this report a team of international scientists from the Crop Genetics & Environmental Research Unit, in Gainesville, FL and the University of Ljubljana, Ljubljana, Slovenia, describe for the first time results from digital image analysis of tissue sections of developing seeds. These two-dimensional data are then converted into 3-D images that allow a computer to estimate the total number of cells and DNA content per cell in developing seeds. Using this approach, it was shown that the miniature seed mutant produces small seeds because there were reductions in both cell number and cell size in developing seeds of the mutant. This approach is readily applicable to any system to measure both the number of cells and their respective sizes in a tissue. This tool will be particularly suitable to determine the impact of environmental stress that often leads to greatly reduced seed size.
Technical Abstract: The miniature1 (mn1) seed mutant is the most drastic nonlethal single gene mutation wherein the mutants loose >70% of the seed weight relative to the wild type. The causal basis of it is the loss of the Mn1-encoded cell wall invertase in developing endosperm (Plant Cell 4:297-305 and 8:971-83). We report here our newly developed three- dimensional model of endosperm, constructed from the longitudinal sections of normal (Mn1) and mutant (mn1) 16 DAP kernels. We used quantitative image analysis to determine spatial distribution of cells in relation to their size, nuclear DNA content (C-values) and the total number of cells in each endosperm. Several observations are noteworthy: (1) The total endosperm volume, was 31 mm3 with 740K cells in the wild type, and 8 mm3 (25%) with 410K cells (55%) in the mutant. (2) There was no detectable change in the level of endoreduplication in the two genotypes. (3) A positive correlation between cell volume and C-values in both genotypes suggested that cell volume and endoreduplication were interdependent processes. Collectively, these data suggest that invertase-deficiency leads to, among other developmental and metabolic effects, reduced mitotic activity presumably due to the impaired in vivo release of hexose sugars, an essential signal for cell division in developing seeds.