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An analysis of dormancy, ABA responsiveness, after-ripening and pre-harvest sprouting in hexaploid wheat (Triticum aestivum L.) caryopses.

Gerjets T, Scholefield D, Foulkes MJ, Lenton JR, Holdsworth MJ - J. Exp. Bot. (2009)

Bottom Line: Isolated embryos showed relatively little dormancy during grain-filling and most varieties exhibited a window of decreased ABA-responsiveness around the period of maximum dry matter accumulation (physiological maturity).However, the velocity of AR of a variety was closely associated with the degree of susceptibility to PHS during AR suggesting that these characters are developmentally linked.Investigation of genetic components of AR may therefore aid breeding approaches to reduce susceptibility to PHS.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant and Crop Sciences, School of BioSciences, University of Nottingham, Nottingham, UK.

ABSTRACT
Embryo and caryopsis dormancy, abscisic acid (ABA) responsiveness, after-ripening (AR), and the disorder pre-harvest sprouting (PHS) were investigated in six genetically related wheat varieties previously characterized as resistant, intermediate, or susceptible to PHS. Timing of caryopsis AR differed between varieties; AR occurred before harvest ripeness in the most PHS-susceptible, whereas AR was slowest in the most PHS-resistant. Whole caryopses of all varieties showed little ABA-responsiveness during AR; PHS-susceptible varieties were responsive at the beginning of the AR period whereas PHS-resistant showed some responsiveness throughout. Isolated embryos showed relatively little dormancy during grain-filling and most varieties exhibited a window of decreased ABA-responsiveness around the period of maximum dry matter accumulation (physiological maturity). Susceptibility to PHS was assessed by overhead misting of either isolated ears or whole plants during AR; varieties were clearly distinguished using both methods. These analyses allowed an investigation of the interactions between the different components of seed development, compartments, and environment for the six varieties. There was no direct relationship between speed of caryopsis AR and embryo dormancy or ABA-responsiveness during seed maturation. However, the velocity of AR of a variety was closely associated with the degree of susceptibility to PHS during AR suggesting that these characters are developmentally linked. Investigation of genetic components of AR may therefore aid breeding approaches to reduce susceptibility to PHS.

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ABA responsiveness of wheat caryopses of six varieties during grain development and after-ripening of mature seeds. Whole caryopses were assayed for ABA sensitivity of germination as described in the Materials and methods at increasing days post-anthesis from PM to HR. Germination is reported using GI. Time of physiological maturity (PM) and harvest ripeness (HR) in relation to dpa are indicated for each variety. GI for post-harvest after-ripening is shown in Supplementary Fig. 3 at JXB online. Data represent means ±SE of the mean.
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fig2: ABA responsiveness of wheat caryopses of six varieties during grain development and after-ripening of mature seeds. Whole caryopses were assayed for ABA sensitivity of germination as described in the Materials and methods at increasing days post-anthesis from PM to HR. Germination is reported using GI. Time of physiological maturity (PM) and harvest ripeness (HR) in relation to dpa are indicated for each variety. GI for post-harvest after-ripening is shown in Supplementary Fig. 3 at JXB online. Data represent means ±SE of the mean.

Mentions: The degree of ABA responsiveness in intact seeds and isolated embryos has previously been associated with the capacity for dormancy in many species including wheat (Walker-Simmons, 1987; Finch-Savage and Leubner-Metzger, 2006; Holdsworth et al., 2008). However, it has recently been shown that in arabidopsis, processes of after-ripening (dormancy loss) and dormancy induction were not controlled by the same genetic loci, and should be considered separate developmental pathways (Carrera et al., 2008). To address this issue in wheat in the present study the relationships between changes in ABA responsiveness were investigated during maturation and post-harvest after-ripening in wheat caryopses and embryos. Initially, the responsiveness of whole caryopses were analysed for all six varieties during maturation (Fig. 2) and subsequently for up to 250 dpa (see Supplementary Fig. 3 at JXB online) using concentrations of ABA up to 50 μM, previously shown to be highly repressive to wheat embryo germination (Walker-Simmons, 1987). Developing intact caryopses of Option, Solstice, and Malacca showed very high levels of dormancy, even without the addition of ABA, whereas varieties Claire, Charger, and Haven all showed an initial high dormancy that was highly reduced by 100 dpa (Fig. 2). In these latter three varieties ABA was shown to have an inhibitory effect at high concentrations early during the time period investigated (ie. up to 80 dpa), but not at later time points. This indicated that responsiveness to ABA for these varieties changed during grain dehydration. Following HR, during subsequent after-ripening only Malacca, Solstice, and Option demonstrated ABA responsiveness, although this was not pronounced (see Supplementary Fig. 3 at JXB online). To determine the contribution of the embryo, the responsiveness of isolated embryos was investigated during grain development, from 30–60 dpa [corresponding to the late milk, Zadok stage 77, to hard dough, Zadok stage 87 (Tottman, 1987)]. Due to the structure of mature grains, it was not possible to isolate intact embryos from caryopses beyond 60 dpa (see Supplementary Fig. 2D at JXB online). Isolated embryos of all varieties showed a much higher GI over the investigated time period than intact caryopsis in the absence of applied ABA (Fig. 3). Several varieties showed a sustained high GI (Claire, Charger, Haven, and Solstice), whereas others (Option and Malacca) were initially more dormant and, subsequently, GI increased. Exogenous ABA had a striking effect on embryo behaviour of all varieties, at 50 μM severely reducing GI. In all cases a distinct change in sensitivity was observed over the time period analysed, such that, although GI of untreated embryos increased in all varieties (with the exception of Malacca) by the end of the time-course, application of ABA was more effective at reducing GI at the beginning and end, suggesting a window of reduced sensitivity during grain-filling, between 40 dpa and 60 dpa. Embryos of Malacca remained responsive to ABA throughout this time period.


An analysis of dormancy, ABA responsiveness, after-ripening and pre-harvest sprouting in hexaploid wheat (Triticum aestivum L.) caryopses.

Gerjets T, Scholefield D, Foulkes MJ, Lenton JR, Holdsworth MJ - J. Exp. Bot. (2009)

ABA responsiveness of wheat caryopses of six varieties during grain development and after-ripening of mature seeds. Whole caryopses were assayed for ABA sensitivity of germination as described in the Materials and methods at increasing days post-anthesis from PM to HR. Germination is reported using GI. Time of physiological maturity (PM) and harvest ripeness (HR) in relation to dpa are indicated for each variety. GI for post-harvest after-ripening is shown in Supplementary Fig. 3 at JXB online. Data represent means ±SE of the mean.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2803222&req=5

fig2: ABA responsiveness of wheat caryopses of six varieties during grain development and after-ripening of mature seeds. Whole caryopses were assayed for ABA sensitivity of germination as described in the Materials and methods at increasing days post-anthesis from PM to HR. Germination is reported using GI. Time of physiological maturity (PM) and harvest ripeness (HR) in relation to dpa are indicated for each variety. GI for post-harvest after-ripening is shown in Supplementary Fig. 3 at JXB online. Data represent means ±SE of the mean.
Mentions: The degree of ABA responsiveness in intact seeds and isolated embryos has previously been associated with the capacity for dormancy in many species including wheat (Walker-Simmons, 1987; Finch-Savage and Leubner-Metzger, 2006; Holdsworth et al., 2008). However, it has recently been shown that in arabidopsis, processes of after-ripening (dormancy loss) and dormancy induction were not controlled by the same genetic loci, and should be considered separate developmental pathways (Carrera et al., 2008). To address this issue in wheat in the present study the relationships between changes in ABA responsiveness were investigated during maturation and post-harvest after-ripening in wheat caryopses and embryos. Initially, the responsiveness of whole caryopses were analysed for all six varieties during maturation (Fig. 2) and subsequently for up to 250 dpa (see Supplementary Fig. 3 at JXB online) using concentrations of ABA up to 50 μM, previously shown to be highly repressive to wheat embryo germination (Walker-Simmons, 1987). Developing intact caryopses of Option, Solstice, and Malacca showed very high levels of dormancy, even without the addition of ABA, whereas varieties Claire, Charger, and Haven all showed an initial high dormancy that was highly reduced by 100 dpa (Fig. 2). In these latter three varieties ABA was shown to have an inhibitory effect at high concentrations early during the time period investigated (ie. up to 80 dpa), but not at later time points. This indicated that responsiveness to ABA for these varieties changed during grain dehydration. Following HR, during subsequent after-ripening only Malacca, Solstice, and Option demonstrated ABA responsiveness, although this was not pronounced (see Supplementary Fig. 3 at JXB online). To determine the contribution of the embryo, the responsiveness of isolated embryos was investigated during grain development, from 30–60 dpa [corresponding to the late milk, Zadok stage 77, to hard dough, Zadok stage 87 (Tottman, 1987)]. Due to the structure of mature grains, it was not possible to isolate intact embryos from caryopses beyond 60 dpa (see Supplementary Fig. 2D at JXB online). Isolated embryos of all varieties showed a much higher GI over the investigated time period than intact caryopsis in the absence of applied ABA (Fig. 3). Several varieties showed a sustained high GI (Claire, Charger, Haven, and Solstice), whereas others (Option and Malacca) were initially more dormant and, subsequently, GI increased. Exogenous ABA had a striking effect on embryo behaviour of all varieties, at 50 μM severely reducing GI. In all cases a distinct change in sensitivity was observed over the time period analysed, such that, although GI of untreated embryos increased in all varieties (with the exception of Malacca) by the end of the time-course, application of ABA was more effective at reducing GI at the beginning and end, suggesting a window of reduced sensitivity during grain-filling, between 40 dpa and 60 dpa. Embryos of Malacca remained responsive to ABA throughout this time period.

Bottom Line: Isolated embryos showed relatively little dormancy during grain-filling and most varieties exhibited a window of decreased ABA-responsiveness around the period of maximum dry matter accumulation (physiological maturity).However, the velocity of AR of a variety was closely associated with the degree of susceptibility to PHS during AR suggesting that these characters are developmentally linked.Investigation of genetic components of AR may therefore aid breeding approaches to reduce susceptibility to PHS.

View Article: PubMed Central - PubMed

Affiliation: Division of Plant and Crop Sciences, School of BioSciences, University of Nottingham, Nottingham, UK.

ABSTRACT
Embryo and caryopsis dormancy, abscisic acid (ABA) responsiveness, after-ripening (AR), and the disorder pre-harvest sprouting (PHS) were investigated in six genetically related wheat varieties previously characterized as resistant, intermediate, or susceptible to PHS. Timing of caryopsis AR differed between varieties; AR occurred before harvest ripeness in the most PHS-susceptible, whereas AR was slowest in the most PHS-resistant. Whole caryopses of all varieties showed little ABA-responsiveness during AR; PHS-susceptible varieties were responsive at the beginning of the AR period whereas PHS-resistant showed some responsiveness throughout. Isolated embryos showed relatively little dormancy during grain-filling and most varieties exhibited a window of decreased ABA-responsiveness around the period of maximum dry matter accumulation (physiological maturity). Susceptibility to PHS was assessed by overhead misting of either isolated ears or whole plants during AR; varieties were clearly distinguished using both methods. These analyses allowed an investigation of the interactions between the different components of seed development, compartments, and environment for the six varieties. There was no direct relationship between speed of caryopsis AR and embryo dormancy or ABA-responsiveness during seed maturation. However, the velocity of AR of a variety was closely associated with the degree of susceptibility to PHS during AR suggesting that these characters are developmentally linked. Investigation of genetic components of AR may therefore aid breeding approaches to reduce susceptibility to PHS.

Show MeSH