Physical dormancy in Senna multijuga (Fabaceae: Caesalpinioideae) seeds: the role of seed structures in water uptake

Abstract

Structural studies in seeds with physical dormancy (PY) are important to better understand its causes and release when subjected to treatments for dormancy breaking. The aims of this study were to (1) characterize the PY break; (2) examine the role of different seed structures in water uptake; and (3) identify the water gap in Senna multijuga seeds. Imbibition patterns of dormant and non-dormant (subjected to dormancy breaking treatments) seeds and the morphological changes during dormancy breaking and germination were evaluated. To identify the water gap, the micropyle and lens were blocked separately, and the water absorption by seed parts was determined. Structural characteristics of the seed coat were also examined. Immersion in water at 80°C was efficient in breaking seed dormancy and imbibition occurred first at the hilar region, through the lens. Water was not absorbed through the micropyle or the extra-hilar region. S. multijuga seeds have a testa with a linearly aligned micropyle, hilum and lens. The seed coat consisted of a cuticle, macrosclereids, one (hilar region) or two (extra-hilar region) layer(s) of osteosclereids and parenchyma cell layers. The lens has typical parenchyma cells underneath it and two fragile regions comprised of shorter macrosclereids. Heat treatment stimulated the lens region, resulting in the opening of fragile regions at the lens, allowing water to enter the seeds. It is concluded that short-term exposure to a hot water treatment is sufficient for the formation of a water gap in S. multijuga seeds, and only the lens acts in the imbibition process.

Variability in hardseededness and seed coat thickness of three populations of Desmanthus virgatus (Fabaceae, Mimosoideae)

“…The thickness of this layer decreases considerably at the lens, as also reported for D. illinoensis (Olszewski et al, 2013) and several species of Mimosoideae and Papilionoideae (Dell, 1980;Rodrigues-Junior, Faria, Vaz, Nakamura, & José, 2014;Serrato-Valenti et al, 1995). This indicates that the lens area is physically the weakest part of the seed coat, and thus, most prone to breakage during different treatments (Baskin et al, 2000;Hu et al, 2009;Rodrigues-Junior et al, 2014;Serrato-Valenti et al, 1995;Ventura de Souza, Voltolini, Santos, & Paulilo, 2012 However, in the present work, the thickness of this layer at the lens was very variable and depended on a greater number of variables that was the case for the sector opposite to the lens. This could indicate that the thickness of this layer behind the lens is more sensitive to the maternal environment when compared to its opposite sector, indicating a greater phenotypic plasticity.…”

“…However Hopkinson and English (2004) reported that tears could occasionally occur in the testas of immature seeds due to the stresses associated with buckling of the embryo during drying, and these then could become points of first water entry. Hu et al (2009) reported that seeds may respond differently to different types of dormancy-breaking treatments, which could result in water uptake through different sites (Rodrigues-Junior et al, 2014). These possibilities should be considered in future studies.…”

“…Hu et al. () reported that seeds may respond differently to different types of dormancy‐breaking treatments, which could result in water uptake through different sites (Rodrigues‐Junior et al., ). These possibilities should be considered in future studies.…”

Classificação Fisiológica De Sementes Florestais Quanto À Tolerância À Dessecação E Ao Comportamento No Armazenamento

“…However, the low germination percentage can be attributed to a possible physical dormancy. Several papers have been reported physical dormancy in seeds of the Senna genus, for example, Senna macranthera (POZITANO e ROCHA, 2011), Senna Silvestris (MARANHO and PAIVA, 2012), Senna multijuga (RODRIGUES-JUNIOR et al, 2014), among others. Jayasuriya et al (2013) studying 100 Fabaceae species from Sri Lanka, found 94 presenting orthodox behaviour, of those 91 presented some kind of dormancy and 86 presented physical dormancy.…”

Sensitivity cycling in physically dormant seeds of the Neotropical tree Senna multijuga (Fabaceae)

“…) and physically dormant (Rodrigues‐Junior et al . ) seeds. For dormancy to be broken naturally in S. multijuga seeds, an opening needs to be formed in the lens, which acts as a water gap (Rodrigues‐Junior et al .…”