Coleorhiza‐enforced seed dormancy: a novel mechanism to control germination in grasses

Abstract

How the biophysical properties of overlaying tissues control growth, such as the embryonic root (radicle) during seed germination, is a fundamental question. In eudicot seeds the endosperm surrounding the radicle confers coat dormancy and controls germination responses through modulation of its cell wall mechanical properties. Far less is known for grass caryopses that differ in tissue morphology. Here we report that the coleorhiza, a sheath-like organ that surrounds the radicle in grass embryos, performs the same role in the grass weed Avena fatua (common wild oat). We combined innovative biomechanical techniques, tissue ablation, microscopy, tissuespecific gene and enzyme activity expression with the analysis of hormones and oligosaccharides. The combined experimental work demonstrates that in grass caryopses the coleorhiza indeed controls germination for which we provide direct biomechanical evidence. We show that the coleorhiza becomes reinforced during dormancy maintenance and weakened during germination. Xyloglucan endotransglycosylases/hydrolases may have a role in coleorhiza reinforcement through cell wall remodelling to confer coat dormancy. The control of germination by coleorhiza-enforced dormancy in grasses is an example of the convergent evolution of mechanical restraint by overlaying tissues.

Roles of Reactive Oxygen Species and Mitochondria in Seed Germination

“…During germination process, the epiblast and coleorhiza appears first and then the primary leaf appears from the coleoptile ( Betekhtin et al, 2018 ). The role of coleorhiza is known to protect the emerging roots during seed germination; however, it has been established that it plays the same role in monocots which micropylar endosperm plays in the dicots, i.e., it acts as a barrier for radicle protrusion to complete germination (sensu stricto) ( Holloway et al, 2021 ). The dissolution of coleorhiza occurs after 6h of imbibition of the water in rice and thus its degeneration is pre-requisite for the germination of the seeds ( Barrero et al, 2009 ).…”

Molecular mechanisms and hormonal regulation underpinning morphological dormancy: a case study using Apium graveolens (Apiaceae)

“…ABA is the key positive regulator for dormancy induction and maintenance, whereas GAs are involved in dormancy release and the promotion of germination. They act antagonistically in regulating the embryo's growth potential and the constraint weakening of tissues covering the radicle (micropylar endosperm, coleorhiza, micropylar seed (testa), or fruit (pericarp) coat) (Holloway et al, 2021;Steinbrecher and Leubner-Metzger, 2018;Yan et al, 2014). Recent work demonstrated that auxins, with indole-3-acetic acid (IAA) as the major bioactive molecule, are also a key regulator in PD seeds (Matilla, 2020;Pellizzaro et al, 2020;Shu et al, 2016).…”

Effect of Salinity Stress on Various Growth and Physiological Attributes of Two Contrasting Maize Genotypes

“…The priming avoids the time and costs consuming need for again sowing [15]. Seed priming induces endosperm weakness by hydrolase activities [16].…”