Not all of the seeds sown under each condition germinated over the course of the experiment (there were always some seed for each pot that didn't germinate). There are a few reasons for this. One of the most usual causes of failures with seed is sowing too deeply; a seed has only enough food within itself for a limited period of growth and a tiny seed sown too deeply soon expends that energy and dies before it can reach the surface. Another common cause is watering. Seeds need a supply of moisture and air in the soil around them. Keeping the soil too wet drives out the air and the seed quickly rots, whereas insufficient water causes the tender seedling to dry out and die. However, due to the fact that hydroponics are in use in the glass house limits these effects. This is because the watering occurs in the plant from the soil upwards, allowing water to creep up until it glistens. Most seeds will of course only germinate between certain temperatures. Too low and the seed takes up water but cannot germinate and therefore rots, too high and growth within the seed is prevented. Fortunately the glass house is maintained at a steady temperature of 22ºC and as such this can be discounted as a possible source of error .
The three different ecotypes showed a variety of responses whilst under different germination conditions. The N1601 ecotype showed the greatest responsiveness to the differing conditions. Under the 2 nd condition a p value of 0.01 was obtained indicating that the overnight incubation in the walk in fridge was enough to statistically improve the rate of germination. During the 5 th condition (leave in the freezer at -20 ºC for 2 hours) the t-test returned a p value of 0.04 and again during the liquid Nitrogen experiment stratification had an effect on the N1601 strain as another p value of 0.04 was obtained. None of the other ecotypes showed a significant change in the rate of germination in response to the different temperatures. One of the reasons behind this is possibly due to the method and optimum conditions in which the seeds are stored at the Nottingham Arabidopsis Stock centre. All the seeds in the stock centre are stored under two conditions, medium term storage and long term storage. For Medium storage the seeds are left in a controlled environment maintained at 15 ºC with a relative humidity of 15%. This dries the seeds to approximately 5-6% moisture content. For long term storage the moisture content of the seeds is decreased to 5-6% again, but the seeds are then placed in a Sarstedt screw top 1ml vial and are then stored at -20 ºC . Indeed the storage method for these seeds is so efficient that they can even be kept for decades/centuries. Although the N933 ecotypes rate of germination was sometimes improved by the different conditions the overall conclusion that can be drawn from the results is that stratification had no significant effect. It was also discovered during the course of the experiment that when the pots were in either the freezer or the fridge the soil didn't reach the desired temperatures of -20 ºC (when left in the freezer) or 4 ºC when in the fridge. This is why conditions 7 and 8 were both added to the experiment half way through the practical. For example when a thermometer was left in the soil of condition 8 (-20 ºC for 8hours (overnight)) it only gave a temperature of -15 ºC . It was also found that for condition 6 the temperature that the top soil reached was only -8 ºC . However this was in fact a blessing in disguise as it was decided to redo the results again, not only for the temperatures sake but also because it was discovered that for the 1 st replicate of the N933 ecotype up to 52 seeds had germinated. This was very strange especially seeming only 20 seeds were to be sown in each pot. The reason for this can only be put down to experimental error, and as such the revelation that the temperature only reached -8 ºC gave a second reason to redo this condition. However the repeat of this condition did not yield any data of particular importance. The other two ecotypes (N20 and N1601) yielded pretty similar results in the first attempt at condition 6 and the second, with 8 seed germinating on day 3 compared to 10 on the second attempt (N20), and with 6 seeds germinating on both attempts with N1601.
There was a slight problem with the sciriad fly, as a couple of times it was noticed that there were larvae eating some the seedlings, however overall this didn't have any major/significant effect on my experiment as only a handful of sciriad fly were able to survive the intercept insecticide, and as such cause relatively little damage (at most 1-2 seedlings per pot were eaten). The rapid expansion of liquids to solids during the freezing process may have led to water inside the seed expanding and causing physiological/enzymatic damage. This may be why the 7 th condition (liquid Nitrogen) performed better than the freezer condition where the seed was left incubated at -20 ºC for 8 hours. As the liquid Nitrogen only remained for approximately 10 seconds per treatment. This can be further backed up but not proven, by the fact that the conditions that only remained in the freezer for 1+2 hours showed improved germination rate. This is possibly due to the fact the contents of the seed may not have had enough time in the freezer for the contents of the seed to freeze and therefore expand causing the damage that would otherwise hinder germination, but instead improved stratification. However due to the fact that they were in the fridge/freezer for only a few hours and the fact that their relative moisture content was 5% it is quite unlikely that this is the case. However Ooms et al in 1993 stated that Arabidopsis thaliana has a poorly developed desiccation tolerance, and this could be a possible reason why not all of the seeds germinated as successfully as the could have. Pritchard et al also carried out an experiment in 1995 titled The Effect of Moisture Content on the Low Temperature Responses of Araucaria hunsteinii Seed and Embryos.' Their main conclusion from the experiment (in relation to seed longevity) stated The results demonstrate that reducing the temperature (of storage) has opposite effects on seed germination rate from that of longetivity, decresing the former and increasing the latter.' This agrees with the assumption that I made earlier, stating that perhaps due to the optimal storage conditions at which the NASC keeps their seed negates the effects of stratification.
Abstract,Introduction,Germination,Dormancy,Temperature,Light,Ecotypes
Ecotype-Storage,Soil preperation,Seed Sowing,Germination-Conditions,Measurement of Results
Cond1,Cond1rep,Cond2,Cond3,Cond4,Cond5,Cond6,Cond6rep,Cond7,Cond8