Transformation of Thylakoid Membranes during Differentiation from Vegetative Cell into Heterocyst Visualized by Microscopic Spectral Imaging  

Abstract

Some filamentous cyanobacteria carry out oxygenic photosynthesis in vegetative cells and nitrogen fixation in specialized cells known as heterocysts. Thylakoid membranes in vegetative cells contain photosystem I (PSI) and PSII, while those in heterocysts contain predominantly PSI. Therefore, the thylakoid membranes change drastically when differentiating from a vegetative cell into a heterocyst. The dynamics of these changes have not been sufficiently characterized in situ. Here, we used time-lapse fluorescence microspectroscopy to analyze cells of Anabaena variabilis under nitrogen deprivation at approximately 295 K. PSII degraded simultaneously with allophycocyanin, which forms the core of the light-harvesting phycobilisome. The other phycobilisome subunits that absorbed shorter wavelengths persisted for a few tens of hours in the heterocysts. The wholethylakoid average concentration of PSI was similar in heterocysts and nearby vegetative cells. PSI was best quantified by selective excitation at a physiological temperature (approximately 295 K) under 785-nm continuous-wave laser irradiation, and detection of higher energy shifted fluorescence around 730 nm. Polar distribution of thylakoid membranes in the heterocyst was confirmed by PSI-rich fluorescence imaging. The findings and methodology used in this work increased our understanding of how photosynthetic molecular machinery is transformed to adapt to different nutrient environments and provided details of the energetic requirements for diazotrophic growth.

Analysis of the early heterocyst Cys-proteome in the multicellular cyanobacterium Nostoc punctiforme reveals novel insights into the division of labor within diazotrophic filaments

“…Both porphyrin and phycobilisome biosynthesis have previously been shown to be down-regulated at the transcript level in N 2 -fixing filaments [ 12 ]. In addition, our results positively correlate with the well-documented decrease in pigment and phycobiliprotein content, which take place during heterocyst differentiation [ 49 , 50 ].…”

Stress effects of cyanotoxin β‐methylamino‐L‐alanine (BMAA) on cyanobacterial heterocyst formation and functionality

“…S3). These heterocysts do not exhibit autofluorescence due to reduced photosystem II (PS II)associated antenna pigments and PS II activity (Thomas, 1970;Donze et al, 1972, Kumazaki et al, 2013Ferimazova et al, 2013;Nozue et al, 2016). We determined that the addition of BMAA to Anabaena 7120 cultures had a small effect on heterocyst frequency (Supporting Information Table S1).…”

Subcellular Localization and Clues for the Function of the HetN Factor Influencing Heterocyst Distribution in Anabaena sp. Strain PCC 7120

“…3B and 4A), but the arrangement resembles dispositions of internal membranes such as the "honeycomb" membrane system that exhibits oxidase activity (31), and HetN-GFP may coincide with the thylakoid membranes that are concentrated at the poles in these cells (32). Indeed, the coincidence of HetN-GFP fluorescence with chlorophyll fluorescence (Fig.…”