The Dead Can Nurture: Novel Insights into the Function of Dead Organs Enclosing Embryos

Abstract

Plants have evolved a variety of dispersal units whereby the embryo is enclosed by various dead protective layers derived from maternal organs of the reproductive system including seed coats (integuments), pericarps (ovary wall, e.g., indehiscent dry fruits) as well as floral bracts (e.g. glumes) in grasses. Commonly, dead organs enclosing embryos (DOEEs) are assumed to provide a physical shield for embryo protection and means for dispersal in the ecosystem. In this review article, we will highlight recent studies showing that DOEEs of various species across families also have the capability for long-term storage of various substances including active proteins (hydrolases, ROS detoxifying enzymes), nutrients and metabolites that have the potential to support the embryo during storage in the soil and assist in germination and seedling establishment. We discuss a possible role for DOEEs as natural coatings capable of ‘engineering’ the seed microenvironment for the benefit of the embryo, the seedling and the growing plant.

Dead but Not Dead End: Multifunctional Role of Dead Organs Enclosing Embryos in Seed Biology

“…Other proteins implicated in conferring resistance to pathogenic fungi include chitinases and gluconases [33][34][35]. The proteomic data also listed S1 type endonucleases in seed coats and pericarps of A. hierochuntica [1,19,30] whose activity was reduced following exposure to salt or to a combination of salt and heat [30]. On the other hand, proteases commonly accumulated in DOEEs showed a significant increase in activity in pericarps derived from Anastatica plants treated with salt and heat [30].…”

“…Proteome analysis performed on proteins extracted from DOEEs of various plant species revealed hundreds of proteins, which were categorized into multiple molecular function groups including catalytic activity, binding activity, hydrolase, pectinesterase, and oxireductase activities. Classification for biological processes showed that many of the released proteins are involved in metabolic processes and oxidation-reduction processes as well as in response to stimulus [1,19,30]. Within the group of proteins responsive to biotic and abiotic stimulus are several defensin-like (DEFL) proteins involved in response to pathogenic fungi [32].…”

“…Multiple proteins involved in reactive oxygen species (ROS) detoxification are accumulated in DOEEs [1,19,30]. These include superoxide dismutases (SODs) that catalyze the conversion of oxygen radicals such as superoxide into hydrogen peroxide (H 2 O 2 ).…”

“…Dry fruits consist of two major groups, dehiscent, in which the fruit is splitting open at maturity to allow for seed dispersal, and indehiscent, whereby the fruit is not open at maturity and constitutes the DU (Figure 1). Thus, the DU may be categorized based on the number of dead organs enclosing the embryo (DOEEs) [1]. Accordingly, the seed is the DU of dry dehiscent fruits (e.g., Arabidopsis thaliana), whereby the embryo is covered by a single layer, the seed coat ( Figure 1A).…”

Dissection of flag leaf metabolic shifts and their relationship with those occurring simultaneously in developing seed by application of non-targeted metabolomics

“…We postulate two possible explanations for this. First, rice seed is covered with a hard hull that provides a relative stable microenvironment for the growth and development of seed, perhaps rendering its metabolome less affected by the external environment [38]. While the flag leaf, being directly exposed to the changing natural environment, is more greatly influenced by environmental changes.…”