Effects of Salt Stress on the Stem Length of Arabidopsis thaliana

Jacob PhillipsUndergraduate Student

Biology Health Sciences ConcentrationDepartment of Biology

Tennessee Technological UniversityCookeville, Tennessee 38501

IntroductionThe increasing occurrence of salt in soil due to by-products of human waste and contamination is a growing concern that affects the biological status, and in some cases, the growth of all organisms. The growth may be affected in a positive or negative way depending upon the reaction of the organisms to the stresses it must endure. These stresses are becoming more numerous everyday as humans increase contamination and become less aware of the trauma they inflict upon the environment around them. Many articles are now present on the topic of stress applied to many photosynthetic organisms, and Arabidopsis thaliana is among one of the organisms most discussed. Some of the stresses that are most examined are cold stress, drought stress, and salt stress placed upon this organism. Environmental stresses (cold, salt, and drought) reduce average yield for most major crops by 50% as compared to pathogens which are only 10-20% (Kreps et al. 2002). These stresses are being studied to determine the long-term effects on the proteins and overall health reduction of the organism. According to Teige (2004) and his colleagues a kinase known as “MKK2 was specifically activated by cold and salt stress and plants over expressing MKK2 showed increased salt and freezing tolerance.” The study of this kinase (MKK2) can be applied to determine how tolerant Arabidopsis can be made to withstand the increasing salinity in the soil. This would prove to be a beneficial application if the Arabidopsis were forced to be grown in high salinity soil or at extreme temperatures.

Studies focusing on the chemical priming of Arabidopsis by using Beta-aminobutyric acid (BABA) to examine how it inhibited pathogen attack on the organism, lead to even greater discoveries when the conclusion provided that “BABA-treated Arabidopsis plants exhibited enhanced drought tolerance…and the BABA-treated plants showed a 50% reduction in wilting in response to a 300 mM NaCl stress (Jakab et al 2005). Another study focusing on the engineering of Arabidopsis consisted of growing seedlings on salt agar to develop an “enhanced stress tolerance by detoxifying the active oxygen species more rapidly” therefore allowing a greater threshold for salt tolerance and prolonging the life of the organism (Tsugane et al. 1999). The scientific advances gained by these studies have led to the production of transgenic organisms, such as cotton plants. The plants have been engineered using the “Arabidopsis AtNHX1 gene for higher drought and stress tolerance”, hence increasing the yield of cotton produced within high salinity soil (He et al. 2005).These articles show that there are many other aspects of stress on organisms than one may think, and that we have only begun to scratch the surface of what can and will be discovered. The objective of this experiment is to determine whether a positive or negative correlation occurs between the growth of the Arabidopsis thaliana and the concentration of a salt stress applied to the soil in which the organism is being grown. It is expected that there will be a positive correlation between the stress and the growth of the organism, resulting in either an increase in the stem length or a decrease in the stem length. The null

Methods and MaterialsArabidopsis thaliana was grown according to a technique devised by Patananan and Phillips (2005) in which the seedlings were allowed ample time to germinate, and the appropriate materials needed were 4 flowering pots, Arabidopsis thaliana seedlings, and pure potting soil. Once the germination stage was completed the organisms were subjected to a concentration of 1mL of salt to 9mL of water. The salt stress was applied everyday using a 10cc syringe filled with the saltwater mixture. The control remained unstressed and received the same amount of water as the test group. Once the organisms reached maturity they were removed from the soil and the stem length measurements were obtained. The measurements were recorded on the data sheets and the mean value of the stressed and unstressed plant stem length was calculated.

ResultsThe stem length of the control group and test group were measured and recorded in table 1 and 2 below. The data shows that there was a positive correlation between the salt stress and the Arabidopsis. Although the correlation was positive the salt-stressed plants displayed a reduction in the stem length.

Discussion &ConclusionThe results displayed a positive correlation between the daily

salt stress that was applied to the test group and the control group. This correlation, however, had a negative effect on the length of the stem tissue of the Arabidopsis. The data obtained is in agreement with a study conducted by Azevedo Neto (2004) which also concluded that “plant growth of all genotypes studied was inhibited by salt stress”.

The calculation of 63.2% reduction in the stem length is, however, a more dramatic effect then described by the literature. Kreps and his colleagues (2002) were able to produce a 50% decrease in plant growth and crop yield when a salt stress was applied. This can also be explained by examining the difference in the soil in which the Arabidopsis plants were grown. The groups used in this experiment were grown in pure soil under set conditions, whereas the organisms examined by Kreps were grown in crops, which allowed for more diffusion of the stresses throughout the soil instead of being concentrated in a certain area.

In order to make the data obtained useful it must be applied for the benefit of biological studies. It is seen from the data that the stem length is decreased by the salt stress, but with current techniques such as “enhancing stress tolerance by detoxifying the active oxygen species more rapidly”, which was obtained by growing Arabidopsis seedlings on a salt agar, we can cause a mutation in the organism to gain valuable induced stress resistance (Tsugane et al 1999). The application of β-aminobutyric acid (BABA) to Arabidopsis has also increased the organism’s resistance to salt stress by “reducing the wilting rate by 50%” (Jakab et al. 2005). So, it is feasible that the application of BABA to the Arabidopsis seedlings used in this experiment would have allowed for an increase in the stem length of the test group by 50% which would have only produced a 13.2% reduction in the stem length.

The stress improvement allowed by these chemical and genetic mechanisms can allow the Arabidopsis mutants to be transgenically placed within another organism. This technological advancement has allowed many of today’s farmers to “engineer things, such as cotton, for higher drought and salt tolerance by causing the plants to express the AtNHX1 gene” (He et al 2005).

The overall purpose of studying the effects of stress on certain organisms is to gain factual knowledge into how the organism will respond to these stresses within our environment. The data and conclusions acquired can be used for profitable purposes, as well as, benefits to the ecological functioning of all organisms. The data calculated in this experiment allowed for the acceptance of my hypothesis and the rejection of the null hypothesis. This data can also be used for further studies into the process of phytoremediation.Conclusion

The data in this experiment provided a clear cut conclusion that proves the salt stress reduces the growth rate of the Arabidopsis thaliana, and therefore proves my hypothesis. The reduction of stem length by 63.2%, however, needs to be confirmed using more efficient methods of examination, such as growth within a crop of organisms to see if more soil area allows for a greater salt diffusion.

Arabidopsis Stress Response

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