Developmental changes in energy dissipation in etiolated wheat seedlings during the greening process

Abstract

We studied the developmental changes in photosynthetic and respiration rates and thermal dissipation processes connected with chloroplasts and mitochondria activity in etiolated wheat (Triticum aestivum L., var. Irgina) seedlings during the greening process. Etioplasts gradually developed into mature chloroplasts under continuous light [190 µmol(photon) m -2 s -1 ] for 48 h in 5-day-dark-grown seedlings. The net photosynthetic rate of irradiated leaves became positive after 6 h of illumination and increased further. The first two hours of de-etiolation were characterized by low values of maximum (F v /F m ) and actual photochemical efficiency of photosystem II (PSII) and by a coefficient of photochemical quenching in leaves. F v /F m reached 0.8 by the end of 24 h-light period. During greening, energydependent component of nonphotochemical quenching of chlorophyll fluorescence, violaxanthin cycle (VXC) operation, and lipoperoxidation activity changed in a similar way. Values of these parameters were the highest at the later phase of de-etiolation (4-12 h of illumination). The respiration rate increased significantly after 2 h of greening and it was the highest after 4-6 h of illumination. It was caused by an increase in alternative respiration (AP) capacity. The strong, positive linear correlation was revealed between AP capacity and heat production in greening tissues. These results indicated that VXC in chloroplasts and AP in mitochondria were intensified as energy-dissipating systems at the later stage of greening (after 4 h), when most of prolamellar bodies converted into thylakoids, and they showed the greatest activity until the photosynthetic machinery was almost completely developed.

Light piping driven photosynthesis in the soil: Low-light adapted active photosynthetic apparatus in the under-soil hypocotyl segments of bean (Phaseolus vulgaris)

“…Since there was a significant enhancement in the Y(NPQ) in US-1 segments under high PFD compared to low PFD illumination, the photosynthetic apparatus present in the US-1 segment was capable for light acclimation and xanthophyll-cycle based quenching processes, typical to well-operating photosynthetic machineries. Increase in the Y(NPQ) was also found during late stages of the greening process in wheat leaves [52]. Reaction center quenching is a process of primary importance if the acceptor-side processes in the PSII are limited by different reasons [53].…”

The activity of superoxide dismutases (SODs) at the early stages of wheat deetiolation

“…It is well known that continuous illumination results in a continuous Pchlide photoreduction and Chl formation, which triggers PLB dispersion followed by formation of thylakoid membranes. The greening process is multiphasic and the individual mechanisms involved in energy trapping, protection as well as respiration are sequentially activated [ 21 , 99 , 111 – 114 ]. First, the photosystems reaction centre cores are assembled, which is followed by a progressive development of complex antenna systems.…”

“…First, the photosystems reaction centre cores are assembled, which is followed by a progressive development of complex antenna systems. It was shown that the assembly of the PSII activity started within the first 20 minutes of greening [ 83 ] and took several hours to be completed [ 83 , 111 ]. The formation of PSII reaction centers and their minor antenna components were observed within the first 3–4 hours of deetiolation, whereas LHCII polypeptides started to accumulate after that time [ 99 ].…”

Role of mitochondrial alternative oxidase in the regulation of cellular homeostasis during development of photosynthetic function in greening leaves

“…Under excess light conditions, AOX might be involved in the oxidation of excess reductants exported from the chloroplasts (Raghavendra & Padmasree, 2003; Dinakar et al, 2010). It has been reported that increases in respiratory activity, AOX capacity, heat production and AOX1a expression simultaneously occurred in wheat leaves during the first 6–12 h of de‐etiolation (Garmash et al, 2013, 2015). Furthermore, during this period, prolamellar bodies (PLBs) were already converted to thylakoids (Garmash et al, 2013), but PSI and PSII were not completely developed (Garmash et al, 2014a).…”

“…It has been reported that increases in respiratory activity, AOX capacity, heat production and AOX1a expression simultaneously occurred in wheat leaves during the first 6–12 h of de‐etiolation (Garmash et al, 2013, 2015). Furthermore, during this period, prolamellar bodies (PLBs) were already converted to thylakoids (Garmash et al, 2013), but PSI and PSII were not completely developed (Garmash et al, 2014a). Respiration and AOX capacity decreased 24 h after de‐etiolation, when clear 77‐K fluorescence emission peaks of PSI (F730) and PSII (F685 and F695) were detected (Garmash et al, 2014a).…”