Nitrogen Starvation Impacts the Photosynthetic Performance of Porphyridium cruentum as Revealed by Chlorophyll a Fluorescence

Long-Sheng Zhao,Xiu-Lan Chen,Yu-Zhong Zhang,Qian-Min Wang,Kang Li,Hai-Nan Su,Bai-Cheng Zhou,Bin-Bin Xie,Feng Huang,Xiao-Yan Song,Xi-Ying Zhang

doi:10.1038/s41598-017-08428-6

Abstract

Nitrogen is one of the most important nutrients needed for plants and algae to survive, and the photosynthetic ability of algae is related to nitrogen abundance. Red algae are unique photosynthetic eukaryotic organisms in the evolution of algae, as they contain phycobilisomes (PBSs) on their thylakoid membranes. In this report, the in vivo chlorophyll (Chl) a fluorescence kinetics of nitrogen-starved Porphyridium cruentum were analyzed to determine the effects of nitrogen deficiency on photosynthetic performance using a multi-color pulse amplitude modulation (PAM) chlorophyll fluorometer. Due to nitrogen starvation, the photochemical efficiency of PSII and the activity of PSII reaction centers (RCs) decreased, and photoinhibition of PSII occurred. The water-splitting system on the donor side of PSII was seriously impacted by nitrogen deficiency, leading to the inactivation of the oxygen-evolving complex (OEC) and decreased light energy conversion efficiency. In nitrogen-starved cells, a higher proportion of energy was used for photochemical reactions, and thermal dissipation was reduced, as shown by qP and qN. The ability of nitrogen-starved cells to tolerate and resist high photon flux densities was weakened. Our results showed that the photosynthetic performance of P. cruentum was severely impacted by nitrogen deficiency.

Highlights

Red algae are unique eukaryotic photosynthetic organisms, as they use giant protein complexes called phycobilisomes (PBSs) as their light-harvesting antennae on their thylakoid membranes, a primitive feature such as that found in cyanobacteria[4]
We focused on the photosynthetic characteristics of the red alga P. cruentum to study Chl a fluorescence kinetics under nitrogen deficiency and discussed the influences of nitrogen deficiency on the photosynthesis and adaptation of red algae
Chl a and phycobilin contents decreased after nitrogen-depleted cultivation[5, 23]

Summary

Introduction

Red algae are unique eukaryotic photosynthetic organisms, as they use giant protein complexes called phycobilisomes (PBSs) as their light-harvesting antennae on their thylakoid membranes, a primitive feature such as that found in cyanobacteria[4]. In red algae and cyanobacteria, PBSs are degraded during nitrogen starvation. In the unicellular red alga Porphyridium cruentum, both the size of the PBSs and their density on thylakoid membranes were observed to be reduced during nitrogen starvation[5]. Chlorophyll (Chl) a fluorescence kinetics is closely related to photosynthesis of oxygen-evolving organisms[8]. This technique has been widely used to study the photosynthesis of red algae. We focused on the photosynthetic characteristics of the red alga P. cruentum to study Chl a fluorescence kinetics under nitrogen deficiency and discussed the influences of nitrogen deficiency on the photosynthesis and adaptation of red algae. We aim to better understand the survival mechanism of red algae in nitrogen-deficient environments

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