The Photosynthetic Recovery And The Expression Of Photosynthesis-related Genes In Nostoc Flagelliforme During Rehydration

Nostoc flagelliforme Bornet & Flah. is a terrestrial and highly desiccation-tolerant blue-green alga, being distributed in the arid or semiarid areas of dry desert and grassland. It has great economic value and is very significant for the ecology of the dry desert and grassland. Unfortunately its resources have been over-exploited due to the increasing market demands. As a result, the ecological balance of its habitats has been damaged. As a consequence, many scientists have paid great attention to its protection and a number of studies have been carried out since 1998. In this paper, we reviewed the studies of N. flagelliforme in recent years, and then investigated the physiological changes of N. flagelliforme having been driedly stored for different periods and the expression of its photosynthetic genes during rehydration.During rehydration, the weight of N. flagelliforme increased in three phases with the times of 2 min, 0.5 h and 24 h. Owing to the physiological activities of living cells, the difference was observed in the third phase for N. flagelliforme dried for 2 or 8 years.The photosynthetic activity was fully recovered within 24 h rehydration in N. flagelliforme after 2 years of drying storage, but that of samples dried for 8 years was only 33.4% of the former samples after 24 h rehydration. This indicated that longer storage in dryness required more time for the photosynthetic recovery. The PSI activity was rocovered almost within 15 min, suggesting that their function was restored very quickly. However, the PSII activity was recovered mainly in the third phase. After 24 h rehydration, the chlorophyll fluorescence or PSII photosynthetic electron transport activity could not be detected in samples dried for 8 years.During the process of rehydration, the rapid light curve of N. flagelliforme dried for 2 years was assayed with WATER-PAM. The E_k values increased during rehydration, indicating that N. flagelliforme could utilize high light more efficiently. The ETR_max and a also increased in this process, indicating the recovery of its electron transport activity during rehydration.Then, the expression of possible photosynthetic genes (rbcL, rbcX, psbA1 and psbA2) in N. flagelliforme was investigated during rehydration. The rbcL, rbcX, psbA1 and psbA2 transcripts of N. flagelliforme dried for 2 years were up-regulated during the rewetting process, but their levels were less in samples dried for 8 years. Within 15 minutes rehydration, the abundance of psbA1 gene reached 36% of fully recovered samples, but the abundance of psbA2 gene was very low in the second phase of rehydration. This indicated that Rubisco and D1 protein in PSII reaction center were damaged during water loss or dry storage, and they should be repaired during rehydration. The difference in the expression of psbA1 and psbA2 suggested that the revovery of photosynthetic machine may be a complex process during rehydration although it is not clearly known now. The longer storage in dryness the recovery of photosynthetic genes expression needed more time, indicating that long-time storage might cause seriously damage on DNA or transcription-related proteins and this may be related with ROS production.