Identification of tannic cell walls at the outer surface of the endosperm upon Arabidopsis seed coat rupture

Abstract

The seed coat is specialized dead tissue protecting the plant embryo from mechanical and oxidative damage. Tannins, a type of flavonoids, are antioxidants known to accumulate in the Arabidopsis seed coat and transparent testa mutant seeds, deficient in flavonoid synthesis, exhibit low viability. However, their precise contribution to seed coat architecture and biophysics remains evasive. A seed coat cuticle, covering the endosperm outer surface and arising from the seed coat inner integument 1 cell layer was, intriguingly, previously shown to be more permeable in transparent testa mutants deficient not in cuticular component synthesis, but rather in flavonoid synthesis. Investigating the role of flavonoids in cuticle permeability led us to identify periclinal inner integument 1 tannic cell walls being attached, together with the cuticle, to the endosperm surface upon seed coat rupture. Hence, inner integument 1 tannic cell walls and the cuticle form two fused layers present at the surface of the exposed endosperm upon seed coat rupture, regulating its permeability. Their potential physiological role during seed germination is discussed.

Female gametophyte expressedArabidopsis thalianalipid transfer proteins AtLtpI.4 and AtLtpI.8 provide a link between callose homeostasis, pollen tube guidance, and fertilization success

“…We observed however, that it was engulfed by a sharp callose layer ( Figure 6E ) that interestingly tended to open towards the micropylar end. The position of this callose boundary appears reminiscent of a recently reported cutin-based apoplastic lipid barrier that is deposited by the ovule inner integument during embryo sac development (Coen et al, 2019), but different from the seed coat cuticle, covering the endosperm outer surface (Demonsais et al, 2020). Thin sections revealed that this sharp callose boundary was also present in the ltp1.4/1.8 double mutant ovules, but in contrast to wild-type, massive callose accumulation was also apparent inside the embryo sac of the ltp1.4/1.8 mutants.…”

Genetic Mapping and Identification of the Candidate Gene for White Seed Coat in Cucurbita maxima

“…DMACA (4-(Dimethylamino) cinnamaldehyde) is used as an indicator of procyanidins and flavan-3-ol [ 14 , 24 , 48 ]. To determine the composition of color pigment of seed coat qualitatively, DMACA staining was conducted in Wuminglv, Agol, Diaogua, Lizimanhui, and 76 inbred accessions including 29 white and 47 yellow seed coat accessions.…”

“…The integument layers include endothelium and two adjacent layers. The outer integument layers include subepidermal layers and epidermal cell layers [ 13 , 14 ]. A secondary thickened cell wall is formed in subepidermal cell layers and is deposited around the epidermis layers.…”

“…Proanthocyanidins are also known as concentrated tannic acid, and the seed coat is brown when the proanthocyanidins are oxidized [ 13 ]. Flavonoid metabolisms (predominantly tannins) are produced in endothelium and deposited to form brown seed coat after oxidization in mature seeds [ 12 , 14 , 18 , 19 ]. By analyzing the components of different color seed coats in Arabidopsis, Brassica rapus , and other plants, the key enzyme regulation steps from phenylpropanes to proanthocyanidins have been determined clearly [ 20 ].…”

Secrets of the seed: uncovering the real identity of the endosperm‐surrounding cuticle

“…During their discussions, it became clear that something was wrong with their previous conclusions about the cuticle. In this issue of The Plant Journal , the group unravels the real identity of what was thought to be a thick cuticle (Demonsais et al , 2020).…”