Abstract
Several studies have assessed the function and significance of the presence of dead, hardened husks on germination and seedling growth in several grass species and reached to inconsistent results. Here, we assess the roles of husks (dead lemma and palea) and an inner membrane surrounding the grains on germination behaviour and seedling growth of Brachypodium hybridum, one of three species of the genetic model B. distachyon complex, in an arid mountain of Arabia. The interactive effects between temperature and the incubation light were assessed on germination of husked and dehusked-demembraned grains. Germination and seedling growth were assessed for different combinations of grain treatments (soaked and non-soaked husked, dehusked-membraned and dehusked-demembraned). Dehusked-demembraned grains were also germinated in different dormancy regulating compounds (DRCs) and light qualities (light, dark and different red: far red [R: FR] ratios). The results indicated an insignificant difference between husked and dehusked-membraned grains on final germination and the germination rate index (GRI), with the former producing significantly bigger seedlings. Removal of the inner-membrane resulted in a significant reduction in all traits. Soaking grains in water resulted in significant enhancements in germination and seedling growth of only husked grains. Husked-membraned and demembraned grains germinated more significantly and faster at lower rather than higher temperatures. None of different concentrations of several DRCs succeeded in enhancing final germination of dehusked-demembraned grains. Red-rich light significantly enhanced germination of dehusked-membraned grains in comparison to other light qualities. It could be concluded that the role of husks is to mainly enhance seedling growth, while the major role of the membrane is to increase final germination. The ability of red-rich light in enhancing the germination of dehusked-membraned but not dehusked-demembraned grains suggest a role for the inner membrane in regulating dormancy through differential filtering of light properties.
Highlights
Grasses have evolved modified inflorescence structures around flowers comprised of lemma and palea [1]
Dead structures around fruits of Arabidopsis thaliana and Sinapis alba had active hydrolytic enzymes that can be released upon hydrolyses to increase the survival rate of emerged seedlings [5]
There was no significant difference in final germination the inner membrane on grain germination and seedling growth of
Summary
Grasses have evolved modified inflorescence structures around flowers comprised of lemma (external structures) and palea (internal structures) [1]. Raviv et al reviewed the biochemical activities of dead structures enclosing the fruits of several plant species belonging to different families, including Poaceae, and concluded that these structures contain various active enzymes involved in the hydrolysis process (e.g., nucleases, proteases, and chitinases) and detoxification of reactive oxygen species [3]. Such enzymes can control seed germination and enhance growth of germinated seedlings [3,4]. The same authors indicated that the dead structures enclosing fruits could provide the embryo with a nutritional element, such as nitrate, potassium, phosphorus and sulfur
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