The biomechanics of seed germination

Abstract

From a biomechanical perspective, the completion of seed (and fruit) germination depends on the balance of two opposing forces: the growth potential of the embryonic axis (radicle-hypocotyl growth zone) and the restraint of the seed-covering layers (endosperm, testa, and pericarp). The diverse seed tissues are composite materials which differ in their dynamic properties based on their distinct cell wall composition and water uptake capacities. The biomechanics of embryo cell growth during seed germination depend on irreversible cell wall loosening followed by water uptake due to the decreasing turgor, and this leads to embryo elongation and eventually radicle emergence. Endosperm weakening as a prerequisite for radicle emergence is a widespread phenomenon among angiosperms. Research into the biochemistry and biomechanics of endosperm weakening has demonstrated that the reduction in puncture force of a seed's micropylar endosperm is environmentally and hormonally regulated and involves tissue-specific expression of cell wall remodelling proteins such as expansins, diverse hydrolases, and the production of directly acting apoplastic reactive oxygen. The endosperm-weakening biomechanics and its underlying cell wall biochemistry differ between the micropylar (ME) and chalazal (CE) endosperm domains. In the ME, they involve cell wall loosening, cell separation, and programmed cell death to provide decreased and localized ME tissue resistance, autolysis, and finally the formation of an ME hole required for radicle emergence. Future work will further unravel the molecular mechanisms, environmental regulation, and evolution of the diverse biomechanical cell wall changes underpinning the control of germination by endosperm weakening.

Potential Effects of Awn Length Variation on Seed Yield and Components, Seed Dispersal and Germination Performance in Siberian Wildrye (Elymus sibiricus L.)

“…It was shown that changes in latitude, longitude and altitude may result in variation in temperature, radiation, moisture and soil fertility, which influence seed yield and components [31,35]. Previous data indicate latitude exhibited a positive correlation with seed traits, whereas longitude and altitude showed a negative correlation with seed yield-related traits in several species [37,38]. The results of the current study differ with this observation, although some seed traits showed a positive correlation with latitude and a negative correlation with longitude and altitude (Table 4).…”

Seed biology – from lab to field

“…This is likely to be important in dormancy regulation because the biomechanical constraints described during germination (Steinbrecher and Leubner-Metzger, 2017) are probably established by this competitive process during seed maturation. Much variation in seed morphology in angiosperms is determined by the ratio of embryo and endosperm in the mature seed.…”

Seed dormancy and control of germination in Sisymbrella dentata (L.) O.E. Schulz (Brassicaceae)

“…Rupture of the testa, or other outer covering structures, has been described to precede rupture of the endosperm in several species and is a crucial step in germination regulation (Puglia et al . ; Steinbrecher & Leubner‐Metzger ). In S. officinale nitrate was shown to stimulate the expression of genes involved in the regulation and sensitivity to germination hormones (Iglesias‐Fernández & Matilla ; Carrillo‐Barral et al .…”

“…Unlike S. officinale, where testa rupture occurs below the micropylar region and proceeds transversally, in S. dentata it started within the micropylar region and expanded longitudinally (Carrillo-Barral et al 2013;Toorop 2015), similar to Arabidopsis thaliana (Liu et al 2005). Rupture of the testa, or other outer covering structures, has been described to precede rupture of the endosperm in several species and is a crucial step in germination regulation (Puglia et al 2015;Steinbrecher & Leubner-Metzger 2017). In S. officinale nitrate was shown to stimulate the expression of genes involved in the regulation and sensitivity to germination hormones (Iglesias-Fern andez & Matilla 2010;Carrillo-Barral et al 2014;Matilla et al 2015).…”