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First published online October 22, 2004; 10.1104/pp.104.045195 Plant Physiology 136:3572-3581 (2004) © 2004 American Society of Plant Biologists Evidence of Programmed Cell Death in Post-Phloem Transport Cells of the Maternal Pedicel Tissue in Developing Caryopsis of Maize1Department of Biology, Biotechnical Faculty, University of Ljubljana, SI–1001, Ljubljana, Slovenia (A.K., M.D.); Program in Plant Molecular and Cellular Biology (K.C., P.C.), and Department of Plant Pathology and Agronomy (P.C.), University of Florida, United States Department of Agriculture, Agricultural Research Service, Gainesville, Florida 32611–0680
We present cellular- and ultracellular-level studies here to show developmental programmed cell death (PCD) of placento-chalazal (P-C) cell layers in maternal pedicel tissue in developing caryopses of normal seed (Mn1) and in the invertase-deficient miniature (mn1) seed mutant in maize (Zea mays). PCD was evidenced by loss of nuclei and all subcellular membranous organizations in many P-C layers. The terminal deoxynucleotidyl transferase-mediated X-dUTP nick-end labeling (TUNEL) stain that is diagnostic of apoptotic-like PCD identified spatially and temporally two distinctive subdomains, which coincided with nucellar and integumental P-C layers based on their developmental origins. The early phase of PCD in the nucellar P-C was TUNEL negative and was specific to only the fertilized caryopses, indicating that the signaling for PCD in these maternal cells originated in the zygotic tissues. In fact, the initiation of PCD coincided with endosperm cellularization and was rapidly and coordinately completed prior to the beginning of the major storage phase in endosperm. Cell shape in these cell layers was also influenced by the genotype of filial endosperm. The later phase of PCD was restricted to the integumental P-C layers underneath the nucellar cells and was TUNEL positive in both genotypes. The two subdomains of the P-C layers were also distinguishable by unique cell wall-associated phenolic compounds. Based on collective evidence, we infer that the nucellar PCD may have osmolytic etiology and may lead to activation of the post-phloem transport function of the P-C layer, whereas the integumental PCD was senescent related, in particular, protecting the maturing seed against microbes that may be transported from the maternal tissue.
1 This work was supported by the Ministry of Education, Science and Sport, Republic of Slovenia (grant no. S1–487–001/20070/99) and by the USA-Slovenia Cooperation in Science and Technology (grant no. 3311–01–838050). This was a cooperative investigation of the U.S. Department of Agriculture, Agricultural Research Service, and the Institute of Food and Agricultural Science, University of Florida. This paper is Florida Agricultural Experiment Station Journal Series Number R–10415. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.045195. * Corresponding author; e-mail pschourey{at}ifas.ufl.edu; fax 352–392–6532. Received April 25, 2004; returned for revision August 22, 2004; accepted August 23, 2004. This article has been cited by other articles:
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