Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2006
Publication Date: 4/9/2007
Citation: Grennan, A.K., Ort, D.R. 2007. Cool temperatures interfere with D1 synthesis in tomato by causing ribosomal pausing. Photosynthesis Research. Available at http://www.springerlink.com/content/100325/?Content+Status=Accepted&sort=p_OnlineDate&sortorder=desc&v=expanded&o=30. Interpretive Summary: Many of the commercially most significant crops in temperature North America (e.g., corn, soybean, tomato and others) are referred to as chilling sensitive. Plants that fall into this category are botanical immigrants from tropical and subtropical origins where selection pressures to deal with low temperature did not exist. Photosynthetic metabolism is among the most chill sensitive process in these plants and the chilling sensitivity of photosynthesis plays a critical role both in limiting the geographical range where these crops are grown as well as accounting for the annual variation in the economic success of these crops grown at the northern border of their cultivation. An improvement of even one degree in the low temperature tolerance would have a far-reaching beneficial impact on the agronomy of these important crop species. Cool temperatures and high light are particularly stressful for chilling sensitive crops and leads to photodamage that does not occur in temperate crops. This study identifies interference with specific steps in a chloroplast repair process as the basis for this photodamage and the subsequent inhibition of photosynthesis. By defining the mechanism of this chilling-induced interference, the work narrows the focus of future work toward solving the problem of chilling sensitivity in crops.
Technical Abstract: Photodamage occurs when leaves are exposed to light in excess of what can be used for photosynthesis and in excess of the capacity of ancillary photoprotective mechanisms. A primary site of the photodamage is the chloroplast encoded D1 protein, a component of the photosystem II (PSII) reaction-center. Even under optimal growth irradiance, D1 is photodamaged necessitating rapid turnover to prevent the accumulation of photodamaged PSII reaction centers and consequent inhibition of photosynthesis. However, this on-going process of D1 turnover and replacement was impeded in the chilling-sensitive tomato (Solanum lycopersicum) plants when exposed to high growth light at cool temperature. The decrease in D1 turnover and replacement was found not to be due to changes in the steady-state level of the psbA message. While the recruitment of ribosomes to psbA transcript, initiation of D1 translation, and the association of polysomes with the thylakoid membrane occurred normally, chilling temperatures caused ribosomal pausing during D1 peptide elongation in tomato. The pause locations were non-randomly located on the D1 transcript and caused the accumulation of photodamaged PSII centers and the consequent inhibition of photosynthesis.