Seeds break dormancy naturally when they meet an appropriate environment, including moisture and temperature. Moreover, seed dormancy can be overcome artificially by employing different treatments. Quiescence is a kind of resting stage in normal or non-dormant seeds, which delays the seed germination due to the absence of suitable conditions such as adequate moisture, temperature, etc.
On the other hand, dormancy is an evolutionary adaptation that prevents seed germination under unsuitable ecological conditions. So, this is the key difference between quiescence and dormancy. Moreover, quiescence is a process that extends for a relatively short time period while dormancy can extend up to a few months to years.
Thus, this is another difference between quiescence and dormancy. Besides, seeds of fast plants undergo quiescence. They do not undergo dormant. Both quiescence and dormancy are processes that result in delayed seed germination. Quiescence can be defined as a condition of repressed cell division in which the seed germination is delayed due to the absence of suitable conditions such as adequate moisture, temperature, etc. So, this is a summary of the difference between quiescence and dormancy.
Considine, et al. Samanthi Udayangani holds a B. Degree in Plant Science, M. Your email address will not be published. Based on the phenotype of ga mutants deficient in GA, lack of GA leads to extreme dormancy that cannot be alleviated without exogenous application of this hormone. Additionally, the reduced dormancy rdo mutants of arabidopsis are not deficient, insensitive, or hypersensitive to either ABA or GA. Their testa color is normal as is testa shape, unlike the transparent testa tt and ats mutants, respectively both of which can display reduced dormancy.
Figure 1: Seed dormancy in arabidopsis is installed by seed produced ABA during seed development. Maternal ABA is not responsible for initiating dormancy in seeds produced on the plant. Metabolism of dormant seeds: There have been many different metabolic pathways hypothesized to play a role in alleviating dormancy in seeds over the years that this phenomenon has been studied.
Some of the evidence accumulated has debunked several of these metabolic changes from having any influence on dormancy alleviation. Others, such as the PPP, are still under investigation. Support for the PPP being involved in dormancy alleviation comes from observations that the dormancy of some species seeds can be alleviated by the application of inhibitors of respiration.
Substances that inhibit terminal oxidation and the tricarboxylic acid pathway are effective in alleviating dormancy in these seeds as are inhibitors of glycolysis. Additionally, electron acceptors can alleviate dormancy.
The electron acceptors replace oxygen in this capacity and again result in elevated amounts of NADP. Whatever is occurring to alleviate dormancy upon application of inhibitors of respiration or electron acceptors, it does not appear to be due to elevated NADP amounts. On the other hand, Bob Buchanan and co-workers are continuing to elucidate the role thioredoxin plays in permitting the reduction of disulfide bonds in storage proteins and inhibitors of alpha-amylase thereby permitting storage protein utilization in the first instance and inhibitor inactivation in the second.
One of the problems defining metabolic limitations that impose seed dormancy is that different species seeds behave differently and may alleviate dormancy through a different metabolic switch than others. Another is accurately determining the dormancy imposing tissue. For instance, lettuce embryos appear to be constrained by the endosperm and it is this tissue that imposes dormancy upon them in the absence of light.
Illuminate the seed and you alleviate dormancy. This could occur through either cell wall weakening of the endosperm or.
Excised embryos complete germination in darkness with no apparent dormancy. However, if they are placed under water stress, the excised embryos germinated in the dark fail to elongate at much less sever water deficits than embryos germinated in the light suggesting that light enables the lettuce embryo to generate more thrust than is possible in the dark.
So, the embryos in light have a lower water potential than embryos germinated in darkness. What is different between the two? Are the light-germinated-embryos more osmotically active or do they have more extendable cell walls resulting in lower turgor pressure?
Measurements of osmotic potential failed to reveal differences between light-germinated and dark-germinated embryos. However, a decrease in turgor pressure has been documented in response to light. This means that the cell walls of the embryo, when it is illuminated, weaken, allowing the cells to elongate more easily than if the embryo was held in darkness.
The mechanism though which light acts appears to be in a pH decrease in the apoplast. There is a vacuolar proton ATPase that is upregulated during germination in tomato, but to date, no report of any of the number of plasmamembrane proton ATPases known to exist being likewise regulated has been documented. However, isolated lettuce embryos do seem capable of decreasing the pH of the media they are in if illuminated, providing strong evidence that such a proton pump does exist.
Thioredoxin h activity permitting catabolic utilization of stored reserves depends on the recycling of thioredoxin h to the reduced form via NADPH. Phytochrome and Dormancy: One of the more spectacular discoveries in plant physiology involved the control light quality has on the ability of many species seeds to complete germination. There are no fewer than 5 phytochromes present in arabidopsis. These chromophores were first discovered and investigated due to the marked effect phytochrome B and possibly others, has on lettuce seed germination.
When imbibed seeds of lettuce were illuminated with a period of far-red light, the percentage of seeds that subsequently completed germination in the dark was very low. If however, the second, red light illumination was followed by another period of far-red illumination, seed germination was again drastically inhibited in the dark.
As mentioned previously, there are at least 5 different phytochromes present in arabidopsis. We argue that a common language, based on physiology, is central to enable further dissection of the quiescent and dormant states in plants.
We direct the topic largely to woody species showing a single cycle of growth and reproduction per year, as these bear the majority of global timber, fruit, and nut production, as well being of great ecological value.
However, for context and hypotheses, we draw on knowledge from annuals and other specialized plant conditions, from a perspective of the major physical, metabolic, and molecular cues that regulate cellular activity. Keywords: Bud; cell cycle; chromatin accessibility; dormancy; meristem; oxygen and redox signalling; plant; quiescence; seasonality; seed..
All rights reserved.
0コメント