Haustorium-endosperm relationships and the integration between developmental pathways during reserve mobilization in Butia capitata (Arecaceae) seeds

Abstract

Background and Aims Palm seeds are interesting models for studying seed reserve mobilization at the tissue level due to the abundance and complexity of reserves stored in their living endosperm cells and the development of a highly specialized haustorium. We studied structural and physiological aspects of the initial phases of reserve mobilization in seeds of a neotropical palm, Butia capitata, and sought to characterize the interactions between the different developmental pathways of the haustorium and endosperm. Methods Morphological and histochemical evaluations of the haustorium, the endosperm adjacent to the embryo, and the peripheral endosperm of dry, imbibed, dormant seeds and seeds geminating for 2, 5 and 10 d were performed. Biochemical analyses included determinations of endo-β-mannanase activity, hormonal profiling (20 hormones belonging to eight classes) and H2O2quantification in various tissues. Key Results The mobilization of haustorium reserves was associated with germination and involved distinct hormonal alterations in the endosperm related to H2O2production. The mobilization of endosperm reserves occurred as a post-germination event controlled by the seedling and involved major structural changes in the haustorium, including growth (which increased contact with, and pressure on, the endosperm) and the formation of an aerenchyma (thus facilitating O 2 diffusion). The flow of O 2 to the endosperm and changes in endogenous contents of H2O2and hormones (cytokinins, auxins, brassinosteroids and ethylene) induced the establishment of an endosperm digestion zone and the translocation of reserves to the haustorium. Conclusions The haustorium-endosperm relationship during reserve mobilization plays a pivotal role in signal integration between growth and degradation pathways in germinating seeds of Butia capitata.