High Energy Charge as a Requirement for Axis Elongation in Response to Gibberellic Acid and Kinetin during Stratification of Acer saccharum Seeds

Abstract

The growth potential of embryonic axes of Acer saccharum Marsh. increased during moist storage at 5 C but not at 20 C. During the period of increasing growth potential, the oxygen consumption of the axes remained constant. It was possible to distinguish three phases of the stratification-germination process at 5 C with respect to response of the axis to gibberellic acid and kinetin. From 0 to 10 days the growth regulators had no effect on elongation; from 10 to 60 days axis elongation was stimulated; and between day 60 and day 75, when germination had begun, the growth substances were inhibitory. The adenylate energy charge remained low (0.15) in axes of dry dormant seeds but increased to 0.78 following imbibition of water and 10 days of moist storage at 5 C. This phenomenon was not specifically related to low temperature stratification, since a rapid increase in the energy charge of the axes also occurred following imbibition and moist storage at 20 C. The excised axes would elongate in response to the growth substances only when a high energy charge (approximately 0.8) was maintained.as half the average number of anhydride-bound phosphate groups per adenosine moiety) for the termination of dormancy is provided from several sources. Olney and Pollock (10) reported that during stratification of cherry seeds an increased rate of respiration occurred in the embryonic leaf primordia, and this was accompanied by the accumulation of phosphate within the axis in the form of sugar phosphates, high energy nucleotides, and nucleic acids. They concluded that a block in phosphate metabolism appeared to be associated with the dormant state. Pradet et al. (13) noted that the energy charge of germinating lettuce seeds was reduced under anaerobic conditions, and Simmonds and Simpson (17) found that dry storage of wild oat caryopses in an atmosphere of nitrogen resulted in a decreased rate of germination of the excised embryos in response to gibberellic acid while storage in oxygen resulted in an increased response of the embryos to gibberellic acid. Although Ching and Ching (6) recently observed a steep rise in the energy charge of embryos during stratification of ponderosa pine seeds, a causal relationship between the low temperature treatment and a high energy charge has not been established.The objectives of the present work were to observe the response of the embryonic axis of A. saccharum to applied hormones during the various stages of stratification and to determine the effect of both low and high temperature stratification on the amounts of available energy in the adenylate system of the axis during these phases.Seeds of Acer saccharum Marsh. have morphologically mature but dormant embryos which require a period of stratification under cold, moist conditions before germination will occur (20). Previous work with this genus (7,21) has shown that the stratification-germination period of intact seeds may be divided into three phases: (a) the initial phase, evidenced by a rapid rise in respiratory activity and at l...

Temperature Effects on Oxidative Metabolism of Dormant Sugar Pine Seeds

“…Dormant sugar maple seeds imbibed at 20°C showed a decline in respiration and ATP levels, but only after a prolonged period of 10 to 22 d (20). While our results do not explain what processes occur during stratification which allow sugar pine seeds to move out of a dormant condition into a growing one, they provide a possible explanation as to why dormant sugar pine seeds are unable to germinate at warmer temperatures.…”

Assessing tree germination resilience to global warming: a manipulative experiment using sugar maple (Acer saccharum)

“…These findings coincide with those of other previous studies McCarragher et al, 2011), who found little (<3%) or no seeds germinating beyond this temperature. At these warmer temperatures, the level of inhibitors remains high and restricts the Sugar maple germination and climate warming 159 morphological and anatomical changes required for embryonic axis growth, thus reducing the likelihood of germination (Simmonds and Dumbroff, 1974). Increased seed respiration rates also occur, which have been shown to be responsible for loss of seed viability at higher temperatures (Simmonds and Dumbroff, 1974).…”

“…While in this study we did perform pre-incubation treatments as a means of getting seeds to germinate uniformly (at least in terms of a starting point) (Janerette, 1978a), our study reinforces the fact that slight variations/abnormalities within the seed and seed structures of the same species may exist. As pointed out by Simmonds and Dumbroff (1974), lower incubation temperatures help facilitate the production of gibberellins, cytokinins and the removal of inhibitors (abscisic and phenolic acids) in sugar maple seeds (Enu-Kwesi and Dumbroff, 1980). Attaining a full energy charge necessary for normal cellular function also occurs at lower temperatures, and could become limited if temperatures are too high.…”

“…At these warmer temperatures, the level of inhibitors remains high and restricts the Sugar maple germination and climate warming 159 morphological and anatomical changes required for embryonic axis growth, thus reducing the likelihood of germination (Simmonds and Dumbroff, 1974). Increased seed respiration rates also occur, which have been shown to be responsible for loss of seed viability at higher temperatures (Simmonds and Dumbroff, 1974). We also found a much higher frequency of the presence and development of fungal communities, which were not present at cooler temperatures (<9°C).…”

“…Sugar maple provides an ideal candidate to investigate these concerns, as it maintains a large range and is sensitive to climate (Goldblum et al, 2010). While some studies have assessed germination percentage (directly or indirectly) within the sugar maple range, most have been limited to either a single seed origin or have only provided minimal insight into the influence of temperature on germination (Webb and Dumbroff, 1969;Simmonds and Dumbroff, 1974;McCarragher et al, 2011). To our knowledge, only limited research in Acer has been conducted at the northern range margin (Tremblay et al, 1996;Graignic et al, 2014), while largely ignoring the mid-and southern species range.…”