دانلود رایگان مقاله معماری ابرمولکولی غشا فتوسنتزی در جلبک قرمز در پاسخ به گرسنگی نیتروژن

ABSTRACT

The availability of nitrogen is one of the most important determinants that can limit the growth of photosynthetic organisms including plants and algae; however, direct observations on the supramolecular architecture of photosynthetic membranes in response to nitrogen stress are still lacking. Red algae are an important evolutionary group of algae which contain phycobilisomes (PBSs) on their thylakoid membranes, as do cyanobacteria. PBSs function not only as light-harvesting antennae but also as nitrogen storage. In this report, alterations of the supramolecular architecture of thylakoid membranes from red alga Porphyridium cruentum during nitrogen starvation were characterized. The morphology of the intact thylakoid membrane was observed to be round vesicles. Thylakoid membranes were reduced in content and PBSs were degraded during nitrogen starvation. The size and density of PBSs were both found to be reduced. PBS size decreased by less than one-half after 20 days of nitrogen starvation, but their hemispherical morphology was retained. The density of PBSs on thylakoid membranes was more seriously affected as time proceeded. Upon re-addition of nitrogen led to increasing of PBSs on thylakoid membranes. This work reports the first direct observation on alterations in the supramolecular architecture of thylakoid membranes from a photosynthetic organism in response to nitrogen stress.

4. Discussion

AFM is a powerful tool for investigating supramolecular structures of membrane proteins with high resolution [19]. In recent years, AFMbased research on photosynthetic membranes from purple bacteria and higher plants has increased. However, direct observations of changes in the supramolecular architecture of photosynthetic membranes from any photosynthetic organism in response to nitrogen stress are still lacking. In our previous work, we reported on the supramolecular architecture of thylakoid membranes from red alga (P. cruentum) that was observed using AFM, and showed that AFM is useful for studying red algal thylakoid membranes [25]. Therefore, we used AFM as well as other techniques to investigate the supramolecular architectures of photosynthetic membranes from P. cruentum during nitrogen starvation.