Why large seeds with physical dormancy become nondormant earlier than small ones

Rodrigues-Junior, Ailton G.; Mello, Ana Caroline Marques Pereira; Baskin, Carol C.; Baskin, Jerry M.; Oliveira, Denise María Trombert; Garcia, Queila Souza

doi:10.1371/journal.pone.0202038

Cited by 22 publications

(21 citation statements)

References 24 publications

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“…lens, hilum and pleurogram. Unlike breaks in the lens (Rodrigues-Junior et al, 2018), breaks in the pleurogram were not indicated by a clear decrease in palisade layer thickness. Irwin and Barneby (1982) described the morphology of seeds of 146 Senna species from the New World, 76 % of which had a pleurogram.…”

Section: Discussionmentioning

confidence: 67%

A function for the pleurogram in physically dormant seeds

et al. 2018

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• Background and Aims Different structures have been shown to act as a water gap in seeds with physical dormancy (PY), and in Fabaceae they are commonly located in the hilar region. However, the function of the pleurogram, a structure in the extra-hilar region that is common in legume seeds, remains unknown. Our aims were to review the literature for occurrence of the pleurogram in Fabaceae, determine if the pleurogram can open, and compare the functional morpho-anatomy of water gaps in seeds of 11 Senna species. • Methods Imbibition tests showed that all 11 species had PY. Structural features of the hilar and extra-hilar regions of the seeds were investigated using light and scanning electron microscopy, and dye-tracking was performed to trace the pathways of water through the seed coat. • Key Results A pleurogram has been reported for 37 legume genera. Water gaps differed among Senna species, with lens, hilum, micropyle and pleurogram taking up water after PY was broken. In Senna alata seeds, only the pleurogram acted as a water gap, whereas in S. reniformis and S. silvestris water entered the seed through both the pleurogram and the hilar region. In the pleurogram of S. alata and S. reniformis, the palisade layer moved outward, exposing the hourglass cells, whereas in S. silvestris the palisade layer was broken. • Conclusions The pleurogram acts as a water gap in some of the 11 Senna species examined, but it is non-functional in others. Opening the pleurogram occurs due to the formation of a linear slit in the palisade layer. The pleurogram is of functional significance by creating a wide opening, whereby water can reach the embryo and start germination. This is the first report of the pleurogram functioning as a water gap. Because this structure is shared by at least 37 genera, it also may be a water gap in many other legume species.

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Section: Discussionmentioning

confidence: 67%

A function for the pleurogram in physically dormant seeds

et al. 2018

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“…Taylor, 2005;Zeng Seed Science Research 279 et al, 2005). Rodrigues-Junior et al (2018b; 2) state 'it is rather difficult to detect a relationship between seed coat thickness and level of dormancy'. Some studies of Caesalpinioideae and Mimosoideae species have related palisade thickness to water impermeability (e.g.…”

Section: Palisade Thicknessmentioning

confidence: 99%

Markedly different patterns of imbibition in seeds of 48 Acacia species

2019

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The seeds of most Australian acacias have pronounced physical dormancy (PY). While fire and hot water (HW) treatments cause the lens to ‘pop’ almost instantaneously, for many Acacia species the increase in germination percentage can be gradual. If PY is broken instantly by HW treatment, why is germination often an extended process? Control and HW treatments were performed on seeds of 48 species of Acacia. Seeds were placed on a moist substrate and imbibition was assessed by frequently weighing individual seeds. In the two soft-seeded species all control seeds were fully imbibed within 6–24 h, while in hard-seeded species very few control seeds imbibed over several weeks. In 10 species over 50% of the HW-treated seeds imbibed within 30 h, but mostly the percentage of imbibed seeds gradually increased over several weeks. Some seeds in a replicate would imbibe early, while others would remain unimbibed for many days or weeks then, remarkably, become fully imbibed in less than 24 h. While HW treatment broke PY almost instantaneously, it appeared that in many Acacia species some other part of the testa slowed water from reaching the embryo. This process of having staggered imbibition may be a way of ensuring not all seeds in a population germinate after small rain events. Thus it appears the lens acts as a ‘fire gauge’ while some other part of the seed coat acts as a ‘rain gauge’.

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“…Thus, soil humidity is a key factor modulating the germination timing of some water-impermeable seeds. In this way, studies have investigated this water-dependent mechanism to break PY and related it to the increasing internal vapour pressure in the seed caused by the association between humidity and high temperatures, which dislodge the weak regions in the seed coat forming the water gap (see Rodrigues-Junior et al 25 and Jayasuriya et al 63 ).…”

Section: Resultsmentioning

confidence: 99%

“…of this kind of dormancy [21][22][23][24][25] and an investigation on water-impermeable seeds in this genus may allow new advances in the evolution of this restrict coat-imposed dormancy. Thus, we addressed the following questions: (1) What is known about seed dormancy in Cassia?…”

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What kind of seed dormancy occurs in the legume genus Cassia?

Rodrigues-Junior

Santos

Hass

et al. 2020

Sci Rep

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Cassia is a diverse legume genus widespread in the (sub-)tropical zone of the world. Several studies have been done on this genus; however, significant changes have occurred at the taxonomic level over the years. this has led to inaccurate information about seed dormancy in Cassia since many species are no longer included in the genus. thus, our work aims to investigate and update the information about the kind of dormancy that occurs in seeds of Cassia species and also look into two notorious species in this group (C. fistula and C. javanica) to compare myxospermous vs. non-myxospermous seeds regarding dormancy and germination traits. Seed dormancy reports were found for 53 Cassia species, and the only kind of seed dormancy found for these species was physical dormancy (pY). nondormancy was not found, and all seeds had a blockage to water uptake during the dormant state, that is, all have PY. Of these 53 species, only 18 are currently included in the genus Cassia. C. fistula and C. javanica have fully developed embryos, and dormancy is only conferred by the (water-impermeable) seed coat. the lens in the seed coat is the only structure that creates a water pathway to break pY in C. fistula. Myxospermous seeds came out of dormancy faster than non-myxospermous ones. PY seems to be the only kind of seed dormancy that has evolved in Cassia. The extent of this kind of dormancy in all subtribe cassiinae is also discussed. Cassia L. sensu stricto was first proposed by Irwin and Barneby 1,2 , who segregated Cassia sensu lato into three genera (Cassia L., Chamaecrista Moech. and Senna Mill.), establishing the subtribe Cassiinae (Leguminosae: Caesalpinioideae). The genus Cassia was considered as the largest genus in Caesalpinioideae 3,4 , but currently it is comprised of only about 30 species 5. Their fruits usually are indehiscent (also divided by transversal septa), unlike those of Senna, which are typically dehiscent and without septa separating the seeds 2. The woody indehiscent pods of Cassia are quite tough, as well as the seeds. Additionally, Cassia fruits are not fleshy, but with remnants of pulp. The presence of these fruit traits suggests that large mammals could disperse Cassia seeds. However, a possible absence of seed dispersers for some species leads to speculation that these indehiscent fruits were likely dispersed by megafauna that are now extinct. Janzen and Martin 6 reported that some fruit traits are better related to extinct animals (seed dispersal anachronisms), since some tough fruits may not be consumed (and seeds dispersed) by smaller extant animals. The absence of dispersers affects seed fate 6 , not only because of the lack of dispersal but also due to the ability of dispersers to break over the tough fruits and release the seeds. Concerning seed dormancy, Baskin and Baskin 7 proposed a classification system that includes five classes (see Baskin and Baskin 7), wherein dormancy is associated with the embryo or other seed components (e.g. the seed coat). Among these five classes of dormancy, physic...

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Why large seeds with physical dormancy become nondormant earlier than small ones

Cited by 22 publications

References 24 publications

A function for the pleurogram in physically dormant seeds

A function for the pleurogram in physically dormant seeds

Markedly different patterns of imbibition in seeds of 48 Acacia species

What kind of seed dormancy occurs in the legume genus Cassia?

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