Submitted to: Journal of Integrative Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2009
Publication Date: 9/1/2009
Citation: Rijavec, T., Kovac, M., Kladnik, A., Chourey, P.S., Dermastia, M. 2009. A comparative study of cytokinins in caryopsis development in the maize miniature 1 seed mutant and its wild type. Journal of Integrative Plant Biology. 51: 840-849. Interpretive Summary: Cytokinin (CK) is a major plant hormone that was first isolated and described in developing seeds of maize nearly half a century ago. Yet, very little is known on the biosynthesis of its multiple forms and their regulation in various genotypes during seed development in maize. Here in this report, based on a collaborative study of scientists at CMAVE, ARS, SAA, Gainesville, the University of Ljubljana and the National Institute of Biology, Ljubljana, Slovenia, we show that growth pattern of the miniature (mn1) seed mutant is greatly shortened as compared to its normal (Mn1) counterpart. Further, the shorter growth phase of the mn1 kernels which are severely impaired in sugar metabolism due to the mutation was associated with altered levels of certain specific forms of the CK hormone. These results are significant as they clearly show a certain level of inter-dependence or cross-talk between sugar and hormone metabolism in seed development in maize. Future studies, in progress, are aimed to identify and isolate genes that may control the levels of these specific CK forms with an ultimate aim to better manipulate towards altered sink strength and seed size in maize.
Technical Abstract: We report here a comparative developmental profile of cytokinins, both total quantity and diversity of various forms, in relation to cell size, cell number and endoreduplication in developing caryopses of a cell wall invertase-deficient miniature1 (mn1) seed mutant and its wild type, Mn1, genotype. Both genotypes showed extremely high levels of total cytokinins during very early stages, 6 and 8 days after pollination (DAP), followed by a marked reduction throughout caryopsis development. Cytometric analyses showed that during the exponential growth phase of endosperm between 6 DAP and 9 DAP, both the mean cell doubling time and the absolute growth rate were similar in the two genotypes, and no major changes were seen in the level of endoreduplication. However, the growth phase was markedly longer in Mn1 compared with the mutant, resulting in a significantly higher cell number in the Mn1 endosperm. These data correlate with the previously reported peak levels of the Mn1-encoded cell wall invertase-2 (INCW2) at 12 DAP in the Mn1 endosperm. A model showing possible crosstalk among cytokinins, cell cycle and cell wall invertase as causal to increased cell number and sink strength of the Mn1 developing endosperm is discussed.