Changes in the Strength of Lettuce Endosperm during Germination

Tao, Kar-Ling; Khan, Anwar A.

doi:10.1104/pp.63.1.126

Cited by 28 publications

(14 citation statements)

References 10 publications

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“…Puncture tests have been conducted to analyze the role of the physical barrier presented by seed coverings during germination of pepper (Capsicum annuum L.), tomato (Solanum lycopersicum L.), muskmelon (Cucumis melo L.), coffee (Coffea arabica L.), Brassicacea, and lettuce (Groot and Karssen, 1987;Mü ller et al, 2006;Silva et al, 2005;Sung et al, 1998a;Tao and Khan, 1979;Watkins and Cantliffe, 1983;Welbaum et al, 1995). These results suggested that various parts of the seed coverings played a major role in controlling germination.…”

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confidence: 99%

Structural Changes in Lettuce Seed During Germination at High Temperature Altered by Genotype, Seed Maturation Temperature, and Seed Priming

Sung¹,

Cantliffe²,

Nagata³

et al. 2008

J. Amer. Soc. Hort. Sci.

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To investigate thermotolerance in seeds of lettuce (Lactuca sativa L.), primed, nonprimed, or seeds matured at 20/10 and 30/20 °C (day/night on a 12-h photoperiod) were imbibed at 36 °C for various periods and then dissected. Structural changes in seed coverings in front of the radicle tip were observed during germination at high temperature. Thermotolerant genotypes, ‘Everglades’ and PI 251245, were compared with a thermosensitive cultivar, ‘Dark Green Boston’. In all seeds that germinated, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue (constriction of the endosperm membrane near the basal end of the seed) at the micropylar region and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition in these seeds; the protein bodies in the vacuoles enlarged and gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, and then the radicle elongated toward this ruptured area. The findings suggested that the endosperm layer presented mechanical resistance to germination in seeds that could not germinate at 36 °C. Weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of ‘Dark Green Boston’, ‘Everglades’, and PI 251245 matured at 30/20 °C had greater thermotolerance than those matured at 20/10 °C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20 °C were more readily disrupted and ruptured during imbibition than seeds matured at 20/10 °C, suggesting a reason why these seeds could germinate quickly at supraoptimal temperatures. Similar endosperm structural alterations also were observed in primed seeds. Priming led to rapid and uniform germination, circumventing the inhibitory effects of high temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, we observed that genotype, seed maturation temperature, or seed priming had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves leading to cell collapse.

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mentioning

confidence: 99%

Structural Changes in Lettuce Seed During Germination at High Temperature Altered by Genotype, Seed Maturation Temperature, and Seed Priming

Sung¹,

Cantliffe²,

Nagata³

et al. 2008

J. Amer. Soc. Hort. Sci.

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“…Tao and Khan (12) determined that endosperm strength did not appear to be directly related to radicle protrusion in lettuce seed. Halmer et al (4) reported that enzymic degradation of a mannosecontaining polysaccharide in lettuce endosperm cell walls was by red light or gibberellin.…”

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Mechanical Resistance of the Seed Coat and Endosperm during Germination of Capsicum annuum at Low Temperature

Watkins¹,

Cantliffe²

1983

Plant Physiol.

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Decoated pepper (Capsicum annuum L. cv Early Calwonder) seeds germinated earlier at 25°C, but not at 15°C, compared to coated seeds.The seed coat did not appear to impose a mechanical restriction on pepper seed germination. Scarification of the endosperm material directly in front of the radicle reduced the time to germination at both 15°C and 25°C.The amount of mechanical resistance imposed by the endosperm on radicle emergence before germination was measured using the Instron Universal Testing Machine. Endosperm strength decreased as imbibition time increased. The puncture force decreased faster when seeds were imbibed at 25°C than at 15°C. The reduction in puncture force corresponded with the ability of pepper seeds to germinate. Most radicle emergence occurred at 15°C and 25°C after the puncture force was reduced to between 0.3 and 0.4 newtons. Application of gibberellic acid4+7 (100 microliters per liter) resulted in earlier germination at 15°C and 25°C and decreased endosperm strength sooner than in untreated seeds. Similarly, high 02 concentrations had similar effects on germination earliness and endosperm strength decline as did gibberellic acid4+7, but only at 25°C. At 15°C, high 02 concentrations slowed germination and endosperm strength decline.found that, by increasing the growth rate of the embryo, this restriction could be overcome. Red light induced growth in the lettuce embryo, enabling it to grow through the endosperm. Pavlista and Haber (10) proposed that both the mechanical force of the growing embryo pushing against the endosperm, and the enzymic weakening of the endosperm were necessary for lettuce seed germination. They observed that when weakening of the endosperm was inhibited, the embryos grew and buckled in the endosperm encasing but did not germinate.Jones (6) determined that the cell walls of lettuce endosperm were increasingly degraded with longer incubation times, and following germination the walls were extensively broken down. Tao and Khan (12) determined that endosperm strength did not appear to be directly related to radicle protrusion in lettuce seed. Halmer et al. (4) reported that enzymic degradation of a mannosecontaining polysaccharide in lettuce endosperm cell walls was by red light or gibberellin. Enzymic activity increased markedly only after radicle emergence and thus did not correspond with the movement of the radicle through the endosperm.Pepper embryos are surrounded by endosperm materials which make up the bulk of food reserves for the embryo and young seedling (2). The experiments which follow test the mechanical resistance of the seed coat and endosperm during germination of Capsicum annuum at optimal and suboptimal temperatures.Seed coats and surrounding structures may influence the ability of a seed to germinate through interference with water uptake, gas exchange, diffusion of endogenous inhibitors, or by mechanical restriction of embryo growth (5, 8). In seeds that do not have hard seed coats or require scarification for water uptake, other seed parts ...

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“…In a study using the Instron Universal Testing Macnine to test puncture forces of endosperm in lettuce seed, Tao and Khan (1979) determined that endosperm strength did not appear to be directly related to radicle protrusion. Halmer et al .…”

Section: Discussionmentioning

confidence: 99%

Germination of Capsicum annuum L. at low temperature / by James Thomas Watkins.

Watkins¹

1982

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The cause of slow and nonuniform germination of pepper (Capsicum annuum L.) seeds at low temperature was investigated. There was no evidence of a Teachable or extractable germination inhibitor being activated or formed due to low temperature exposure. Auxin and kinetin applications did not effect germination rate. However, gibberellic acid (GA) treatments effectively increased germination rates at 15°a nd 25°C. Gibberellic acid 4+7 was more effective than GA 3. Gibberellic acid stimulated germination rate under osmotic stress and the presence of a GA synthesis inhibitor reduced germination rate. High oxygen (0 2) concentrations stimulated pepper seed germination rates at 25°C but inhibited germination rates at 15°. Gibberellic acid applications could not overcome the inhibitory effect of 100% 2 at 15. Seed respiratory activity was greater at 25°i n 100% 2 than in air, but the additional 2 did not alter respiratory pathways. At 15°, total respiration, respiravi loss of cellular integrity and endosperm thickness in front of the radicle. Gibberellic acid treatments stimulated endosperm breakdown. Pepper seed cell wall degrading enzyme activity increased with increased imbibition time, with temperature, and GA treatment. Pepper seed enzyme extracts preferentially degraded a galactomannan substrate but did not degrade a carboxymethylcellulose substrate indicating that manno-polysaccharides may be components of pepper seed endosperms.

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Changes in the Strength of Lettuce Endosperm during Germination

Cited by 28 publications

References 10 publications

Structural Changes in Lettuce Seed During Germination at High Temperature Altered by Genotype, Seed Maturation Temperature, and Seed Priming

Structural Changes in Lettuce Seed During Germination at High Temperature Altered by Genotype, Seed Maturation Temperature, and Seed Priming

Mechanical Resistance of the Seed Coat and Endosperm during Germination of Capsicum annuum at Low Temperature

Germination of Capsicum annuum L. at low temperature / by James Thomas Watkins.

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