Autophagy induced accumulation of lipids in pgrl1 and pgr5 of Chlamydomonas reinhardtii under high light

Chlamydomonas (C) reinhardtii cells (wild-type CC125 and 137AH, and cyclic electron transport dependant mutants pgrl1 and pgr5) were grown in high light 500 µmol photons m−2 s−1 where the growth was significantly enhanced after three days. The starch and lipid contents were also increased; however, starch content was decreased in pgr5. Further, the Nile Red fluorescence shows that a significant amount of lipid bodies were observed in pgr5 cells under high light. Similarly, the electron micrographs show that large vacuoles were formed in high light stress despite the change in stacks of grana structure. We also observed increased production of reactive oxygen species (ROS) that could lead to autophagy. Inline, a significant increase of ATG8 protein was noticed in pgr5, which is a hallmark characteristic for autophagy formation. Consequently, the triacylglycerol (TAG) content was increased due to DGAT and PDAT enzymes’ expression, especially in pgr5. Here, the TAG synthesis would have been obtained from degraded membrane lipids in pgr5. Additionally, mono, polyunsaturated, and saturated fatty acids were identified more in the high light condition. Our study shows that the high light induces ROS, leads to autophagy and TAGs accumulation, which is stored as an energy source to acclimatize the algae.

Plastid terminal oxidases in Chlamydomonas: connections with astaxanthin and bio-hydrogen production

Background: as a plasto quinol oxidase involved in plastoquinol oxidation in higher plants and microalgae, the plastid terminal oxidase (PTOX) was first recognized in the tomato mutant GHOST (GH) and Arabidopsis mutant IMMUTANS (IM). Genome sequence analysis revealed that duplication of the PTOX gene occurs in certain eukaryotic microalgae, but not in cyanobacteria and most higher plants. PTOX may also be involved in carotenoid synthesis and play a critical protective role against stress, such as high light, heat shock and hyperosmosis. However, the connections of PTOX with astaxanthin and bio-hydrogen production and their functional relationship between two PTOX genes in the model green microalga Chlamydomonas is unknown. Results: we successfully knocked down two ptoxs through RNAi in Chlamydomonas, respectively. We demonstrated that expression levels of both PTOXs were increased under stress conditions, and interestingly when one PTOX was silenced the other’s transcriptional level was significantly raised. Conclusions: this shows a complementary relationship under high light condition. In addition, the astaxanthin accumulation level was up-regulated in silenced ptox2 strain, compared to the wide type strain. What’s more, significantly increased hydrogen production was observed in silenced ptox1 strain. In conclusion, PTOXs in Chlamydomonas are connected with not only astaxanthin accumulation but also hydrogen production, and their knock-down strains provide new insights in manipulating microalgae for high light stress tolerant strains, carotenoid production and even biofuels.

Invasive Species Removal Promotes Habitat Restoration but Does Not Immediately Improve the Condition of a Threatened Plant Subspecies

Impacts of invasive species on rare species are relevant to conservation. We studied the response of Leedy's roseroot Rhodiola integrifolia subsp. leedyi, a subspecies listed as threatened under the Endangered Species Act, to removal of the invasive species Japanese knotweed Fallopia japonica. Japanese knotweed has invaded the largest known population of Leedy's roseroot, affecting about 10% of all Leedy's roseroot in the world. Japanese knotweed shaded Leedy's roseroot, but the two did not share belowground resources because of their position on cliffs. To study this interaction and, ultimately, to restore Leedy's roseroot habitat to an open, high-light condition, we removed Japanese knotweed in a three-treatment block design. We measured Leedy's roseroot abundance, growth, and reproduction in treatment blocks and in uninvaded areas before and after treatment. Compared with uninvaded areas, Japanese knotweed invasion negatively affected Leedy's roseroot abundance, growth, and reproduction. Light interception by Japanese knotweed degraded the habitat for Leedy's roseroot. Herbicide removal of Japanese knotweed resulted in increased light and temperature compared with untreated invaded plots but did not affect Leedy's roseroot abundance, growth, or reproduction over the 2 y of our study. These results show that invasive species removal is conducive to restoring Leedy's roseroot habitat, but recovery in the subspecies may lag behind restoration of the habitat, suggesting that additional action or time may be required to restore preinvasion performance of Leedy's roseroot. Results of this study may inform restoration efforts for other systems and contribute to the literature on interspecific interactions.

A Research of an Improved Method for Lane Detection in a High Light Condition

Most of the methods, which being used to the normal light, are easy to make a mistake in the high light condition. An improved method is proposed in this paper to solve these problems. It includes a series of pretreatment for road image, like white balance, contrast enhancement, edge enhancement. Then the method makes an image segmentation to increase the efficiency of the identification. Use an improved Hough transformation to recognize the parameters of lane line. Finally, establish a trapezoidal interested region to achieve a real-time dynamic extraction of lane lines parameters from the continuous image. The results of identification show that the improved method for the high light condition makes a better work and its more accurate and efficient to acquire the parameters.

PsaK2 Subunit in Photosystem I Is Involved in State Transition under High Light Condition in the Cyanobacterium Synechocystis sp. PCC 6803

To avoid the photodamage, cyanobacteria regulate the distribution of light energy absorbed by phycobilisome antenna either to photosystem II or to photosystem I (PSI) upon high light acclimation by the process so-called state transition. We found that an alternative PSI subunit, PsaK2 (sll0629 gene product), is involved in this process in the cyanobacterium Synechocystis sp. PCC 6803. An examination of the subunit composition of the purified PSI reaction center complexes revealed that PsaK2 subunit was absent in the PSI complexes under low light condition, but was incorporated into the complexes during acclimation to high light. The growth of the psaK2 mutant on solid medium was inhibited under high light condition. We determined the photosynthetic characteristics of the wild type strain and the two mutants, the psaK1 (ssr0390) mutant and the psaK2 mutant, using pulse amplitude modulation fluorometer. Non-photochemical quenching, which reflects the energy transfer from phycobilisome to PSI in cyanobacteria, was higher in high light grown cells than in low light grown cells, both in the wild type and the psaK1 mutant. However, this change of non-photochemical quenching during acclimation to high light was not observed in the psaK2 mutant. Thus, PsaK2 subunit is involved in the energy transfer from phycobilisome to PSI under high light condition. The role of PsaK2 in state transition under high light condition was also confirmed by chlorophyll fluorescence emission spectra determined at 77 K. The results suggest that PsaK2-dependent state transition is essential for the growth of this cyanobacterium under high light condition.