Comparison of thermostability of PSII between the chromatic and green leaf cultivars of Amaranthus tricolor L.

Abstract

In the present study, we investigated the antioxidative potential in leaves of the chromatic (CC) versus green (GC) Amaranthus tricolor L. under moderate high-temperature stress at 45°C. Before heat stress, CC had significantly higher levels of betacyanins [about 3.2 mg g -1 (FM)] than the green [1.8 mg g -1 (FM) (p<0.01), while similar chlorophyll (Chl) content [about 2 mg g -1 (FM)] was observed between both cultivars. After exposure to high temperature (45°C) for 6 days, betacyanins in leaves of CC were remarkably increased (about 2 times of that in control samples grown at 30°C). In contrast, betacyanins in GC significantly decreased by 56% in comparison with that of the control. Chl level in CC was higher than that in GC after heat stress for 6 days. Flavonoids and total phenolics in both cultivars were increased, but much more in CC. Significantly less H 2 O 2 accumulation was observed in the leaves and stems of CC than in those of GC under heat stress. Interestingly, much stronger circadian oscillation in fluorescence was observed in both cultivars after treatment at 45°C, which suggested that heat stress stimulates endogenous rhythms of photosystem II (PSII). Under moderate high-temperature stress, Chl fluorescence parameters F v /F m (maximum quantum yield of PSII), q P (coefficient of photochemical quenching), Φ PSII (effective PSII quantum yield), and ETR (electron transport rate) exhibited a gradual decrease, NPQ (nonphotochemical quenching) showed a slight increase followed by a gradual decline, whereas F o (minimum fluorescence of a dark-adapted leaf) increased continuously. In contrast to GC, after 120 h of high-temperature treatment, CC exhibited significantly lower F o level, and higher levels of F v /F m and NPQ. It is clear that PSII in CC was more stable than that in GC. The results indicate that betacyanins are an effective antioxidant, and probably contribute greatly to the higher thermal stability of PSII and higher tolerance to heat stress.Additional key words: Amaranthus tricolor L.; betacyanins accumulation; circadian oscillation; high temperature; thermal stability of PSII.

Plant betalains: Chemistry and biochemistry

“…Among other physical stress, low temperature treatment reduced pigment degradation, thereby maintaining decent level of betalains . Interestingly, exposure to high temperature enhanced betalain biosynthesis, perhaps, to quench oxidants like H 2 O 2 and stabilise PSII (Shu et al, 2009). While data on stabilisation of PSII concomitant with increase in betalain level were convincing, the mechanism involved for the increased accumulation of the pigments was not explained.…”

“…Bladder cells of epidermal layer in leaves of Mesembryantheum chrystalinum have been shown to accumulate betalains (Ibdah, 2002). In cactus stem, betacyanins accumulate in hypodermis and outer layers of chlorenchyma (Mosco, 2012), may be, to protect the underlying photosystems through their antioxidant activity (Shu et al, 2009). Betacyanins were observed to express in long, multiple-papillate epidermal petal cells in flower of Australian native plant, Calandrinia sp.…”

Are betalain pigments the functional homologues of anthocyanins in plants?

“…Thylakoids isolated from green leaves of these plants generated less H 2 O 2 if betacyanin were added to the suspension (Wang and Liu, 2007). Similarly, H 2 O 2 production was lower in betacyanic than in acyanic leaves of Amaranthus tricolor following a heat stress (Shu et al, 2010). H 2 O 2 -induced protein oxidation in leaf extracts of Suaeda japonica was abolished when betacyanin solution was added to the mixture (Hayakawa and Agarie, 2010).…”

Betalains in Some Species of the Amaranthaceae Family: A Review

“…The function of betalains in plants is diverse: for plant propagation through pollen transfer or the dispersion of indigestible seeds by animals that are attracted by the colour of flowers and fruits; as a repelling signal to deter herbivores; to screen tissue against damaging ultraviolet (UV) radiation; for increasing pathogen resistance and improving viral defence; for providing higher tolerance to heat stress; as osmoregulators by modelling the amino acid pool from betaxanthins, among other functions [ 2 , 23 , 24 , 25 ].…”