Heat induced impairments and recovery of photosynthetic machinery

Photosynthesis is one of the most heat sensitive cellular processes. Oxygen evolvingcomplex together with the associated cofactors in photosystem II (PSII), the ATPgenerating system and carbon fixation by Rubisco are the main targets of elevatedtemperatures. The impairments of photosynthetic machinery (PM) lead to the oxidativeburst and to generation of excess of ¹O₂ in PSII, O₂.- and H₂O₂, mainly in PSI. One of themain targets of generated reactive oxygen species is the system of protein synthesis,which plays the important role in the repair of PM after damage. It is suggested that thecrucial factors for the recovery of PM from heat-induced damage are the balance between(pro)oxidant and antioxidant levels, rate of photosynthetic protein synthesis, especiallyD1 and D2 proteins, as well as accumulation of antioxidants and other protectivecompounds. Thermostability of thylakoid membranes as well as extrinsic proteins andRubisco play a key role in the heat resistance of PM. Recent results on photosyntheticresponse under heat stress evidence for the key role of protein kinases, particular thehistidine kinase Hik34, transcription factors and several low-molecular compounds, suchas glycinebetaine and proline, in a response of the PM to heat stress. However, littleinformation is available about the components, which are involved in heat stresssignaling (perception and transduction), involving chloroplast heat sensors and signalingproteins, second messengers and gene signaling networks. In this chapter, we summarizerecent results in the study of the molecular mechanisms of impairments, heat signalingand acclimation of PM under heat stress.