Breakage of Pseudotsuga menziesii seed dormancy by cold treatment as related to changes in seed ABA sensitivity and ABA levels

Abstract

The main aims of the present work were to investigate whether a chilling treatment which breaks dormancy of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) seeds induces changes in the sensitivity of seeds to exogenous ABA or in ABA levels in the embryo and the megagametophyte, and whether these changes are related to the breaking of dormancy. Dormant seeds germinated very slowly within a narrow range of temperatures (20-30 degrees C), the thermal optimum being approximately 25 degrees C. The seeds were also very sensitive to oxygen deprivation. Treatment of dormant seeds at 5 degrees C improved further germination, and resulted in a widening of the temperature range within which germination occurred and in better germination in low oxygen concentrations. In dry dormant seeds the embryo contained about one-third of the ABA in the megagametophyte. ABA content of both organs increased during the first 4 weeks of chilling. It then decreased sharply in the megagametophyte to the level in the embryo after 7-15 weeks of chilling. At 15 degrees C, a temperature at which dormancy was expressed, the ABA level increased in the embryo and the megagametophyte of dormant unchilled seeds whereas it decreased in the organs of chilled seeds. The longer the chilling treatment, the faster the decrease in ABA after the transfer of seeds from 5 degrees C to higher temperatures, and the decrease was faster at 25 than at 15 degrees C. These results suggest that the breaking of dormancy by cold was associated with a lower capacity of ABA biosynthesis and/or a higher ABA catabolism in the seeds subsequently placed at 15 or 25 degrees C. Moreover, the chilling treatment resulted in a progressive decrease in the sensitivity of seeds to exogenous ABA. However, seeds remained more sensitive to ABA at 15 than at 25 degrees C. The possible involvement of ABA synthesis and of responsiveness of seeds to ABA in the breaking of dormancy by cold treatment is discussed.

Dormancy termination of western white pine ( Pinus monticola Dougl. Ex D. Don) seeds is associated with changes in abscisic acid metabolism

“…After an initial increase in ABA level during moist chilling, ABA decreased in both the megagametophyte and embryo; in the former, ABA declined 4-fold during 7 weeks of moist chilling. The longer the duration of moist chilling, the faster the rate of ABA decline during subsequent germination (Corbineau et al 2002).…”

“…the seed coat and megagametophyte) may maintain the seed in a dormant state by limiting ABA metabolism and preventing the leaching out of ABA, and, in Douglas fir seeds, they may facilitate accumulation of de novosynthesized ABA. Corbineau et al (2002) quantified ABA during moist chilling of Douglas fir seeds. After an initial increase in ABA level during moist chilling, ABA decreased in both the megagametophyte and embryo; in the former, ABA declined 4-fold during 7 weeks of moist chilling.…”

“…For example, endogenous ABA levels decline in beechnut (Fagus sylvatica) embryos to the same extent regardless of dormancy status, yet [ 3 H]ABA turnover is greater in embryos subjected to a dormancy-breaking cold pretreatment than in embryos that remain dormant because of their maintenance at 23°C (Le Page-Degivry et al 1997). Increased ABA catabolism is associated with dormancy termination of seeds of yellow-cedar (Chamaecyparis nootkatensis), beechnut, Douglas fir (Pseudotsuga menziesii), and barley (Hordeum vulgare) (Le Page-Degivry et al 1997;Schmitz et al 2000Schmitz et al , 2002Corbineau et al 2002;Jacobsen et al 2002).…”

CYP707A1 and CYP707A2, Which Encode Abscisic Acid 8′-Hydroxylases, Are Indispensable for Proper Control of Seed Dormancy and Germination in Arabidopsis

“…As an effect of after ripening, the deterioration of ABA biosynthetic capacity or increase of GA sensitivity has been reported in Arabidopsis (Ali-Rachedi et al, 2004), barley (Jacobsen et al, 2002), sunflower (Helianthus annuus; Bianco et al, 1994), and tobacco (Grappin et al, 2000). Moreover, the increase of GA sensitivity and biosynthetic ability or decrease of ABA sensitivity is reported as an effect of stratification (Groot and Karssen, 1992;Corbineau et al, 2002;Yamauchi et al, 2004).…”

Effects of Fluridone Treatment on Seed Germination and Dormancy-associated Gene Expression in an Ornamental Peach (<i>Prunus persica</i> (L.) Batsch)

“…ABA catabolic genes are induced during seed development to inactivate ABA, and are associated with dormancy release in some higher plants (Corbineau et al, 2002;Feurtado et al, 2004;Jacobsen et al, 2002). In Arabidopsis, AtCYP707A2 was associated with the rapid decline of ABA in germinating seeds (Kushiro et al, 2004) and CYP707A3 plays an important role in degrading endogenous ABA during dehydration (Umezawa et al, 2006).…”