Proteolysis is considered as a crucial factor determining the proper development of the plant and its efficient functioning in variable environmental conditions. The role of proteases in protein quality control and protein turnover processes is well documented. The results of studies performed in recent years reveal; however, that proteolytic enzymes also participate in signal transduction pathways by releasing membrane-anchored transcription factors in the process known as regulated intramembrane proteolysis (RIP). The first described intramembrane protease was identified in human cells in 1997. In turn, the first plant intramembrane protease was identified in 2005, in Arabidopsis thaliana. To date, most studies concerning the RIP process in plants have been performed on this model plant. The knowledge concerning the potential physiological role of RIP is very limited. However, continuously accumulating information concerning this issue indicates that RIP, like the other proteolytic mechanisms, has a significant effect on plant ontogenesis, acclimatization and fertility. The aim of this article is to gather and systemize the present knowledge concerning the intramembrane proteases in A. thaliana.

The EGY3 is a pseudoprotease, located in the thylakoid membrane, that shares homology with the family of site-2-proteases (S2P). Although S2P proteases are present in the cells of all living organisms, the EGY3 was found only in plant cells. The sequence of the pseudoprotease is highly conserved in the plant kingdom; however, little is known about its physiological importance. Results obtained with real-time PCR indicated that the expression of the EGY3 gene is dramatically induced during the first few hours of exposure to high light and high-temperature stress. The observed increase in transcript abundance correlates with protein accumulation level, which indicates that EGY3 participates in response to both high-temperature and high light stresses. The lack of the pseudoprotease leads, in both stresses, to lower concentrations of hydrogen peroxide. However, the decrease of chloroplast copper/zinc superoxide dismutase 2 level was observed only during the high light stress. In both analyzed stressful conditions, proteins related to RubisCO folding, glycine metabolism, and photosystem I were identified as differently accumulating in egy3 mutant lines and WT plants; however, the functional status of PSII during analyzed stressful conditions remains very similar. Our results lead to a conclusion that EGY3 pseudoprotease participates in response to high light and high-temperature stress; however, its role is associated rather with photosystem I and light-independent reactions of photosynthesis.

University students often struggle to understand the role of water in plant cells. In particular, osmosis and plasmolysis appear to be challenging topics. This study attempted to identify student difficulties (including misconceptions) concerning osmosis and plasmolysis and examined to what extent the difficulties could be revised during a plant physiology course. A questionnaire was developed to monitor university students’ conceptual knowledge before and after a course, and both qualitative and quantitative data were obtained. The data were analyzed using the constant comparison technique and descriptive statistics. Students were found to come to university with many misconceptions that had accumulated during their education. These misconceptions are extremely difficult to change during the traditional course, which comprises lectures and practical exercises. Students’ misconceptions originate from commonly used sources such as textbooks, which are perceived as being reliable. Effective teaching of water relations in plant cells could include such didactic methods as “questioning the author,” which allow teachers to monitor students’ knowledge and help students acquire a more scientific understanding of key concepts.