Drought-Induced Changes in the Redox State of α-Tocopherol, Ascorbate, and the Diterpene Carnosic Acid in Chloroplasts of Labiatae Species Differing in Carnosic Acid Contents

Abstract

To assess antioxidative protection by carnosic acid (CA) in combination with that of other low-molecular weight (M r ) antioxidants (␣-tocopherol [␣-T] and ascorbate [Asc]) in chloroplasts, we measured endogenous concentrations of these antioxidants, their redox states, and other indicators of oxidative stress in chloroplasts of three Labiatae species, differing in their CA contents, exposed to drought stress in the field. Damage to the photosynthetic apparatus was observed neither in CA-containing species (rosemary [Rosmarinus officinalis]) and sage [Salvia officinalis]) nor in CA-free species (lemon balm [Melissa officinalis]) at relative leaf water contents between 86% and 58%, as indicated by constant maximum efficiency of photosystem II photochemistry ratios and malondialdehyde levels in chloroplasts. The three species showed significant increases in ␣-T, a shift of the redox state of ␣-T toward its reduced state, and increased Asc levels in chloroplasts under stress. Lemon balm showed the highest increases in ␣-T and Asc in chloroplasts under stress, which might compensate for the lack of CA. Besides, whereas in rosemary and sage, the redox state of CA was shifted toward its oxidized state and the redox state of Asc was kept constant, lemon balm displayed a shift of the redox state of Asc toward its oxidized state under stress. In vitro experiments showed that both CA and Asc protect ␣-T and photosynthetic membranes against oxidative damage. These results are consistent with the contention that CA, in combination with other low-M r antioxidants, helps to prevent oxidative damage in chloroplasts of water-stressed plants, and they show functional interdependence among different low-M r antioxidants in chloroplasts.Mediterranean plants are exposed to a combination of environmental stress conditions, including low water availability, high irradiance, temperature fluctuations, and nutrient deprivation. Such stresses may lead to an imbalance between antioxidant defenses and the amount of activated oxygen species (AOS), resulting in oxidative stress (Smirnoff, 1993;Pastori and Foyer, 2002;Xiong et al., 2002). AOS are necessary for inter-and intracellular signaling (Doke, 1997;Foyer and Noctor, 1999), but at high concentrations they can cause damage at various levels of organization, including chloroplasts (Halliwell and Gutteridge, 1989;Asada, 1999). Apart from the xanthophyll cycle, photorespiration and other changes in metabolic activity, which may protect the chloroplasts from oxidative damage (Demmig-Adams and Adams, 1996;Kozaki and Takeba, 1996;Eskling et al., 1997;Osmond et al., 1997), a number of enzymatic and nonenzymatic antioxidants are present in chloroplasts that control oxygen toxicity (Smirnoff, 1993;Foyer et al., 1994;Asada, 1999). Carotenoids, ␣-tocopherol (␣-T, vitamin E), ascorbate (Asc, vitamin C), and glutathione help to maintain the integrity of the photosynthetic membranes under oxidative stress (Havaux, 1998; Noctor and Foyer, 1998;Asada, 1999;Smirnoff and Wheeler, 2000;Munné-Bosch and Ale...

Carnosic Acid and Carnosol, Two Major Antioxidants of Rosemary, Act through Different Mechanisms

“…A strong accumulation of tocopherols and plastochromanol also was observed after exposure of rosemary plants to high light and heat, thus exhibiting a behavior that contrasts with that of carnosic acid. This contrasting response was observed previously for carnosic acid and a-tocopherol in sage (Salvia officinalis) and rosemary exposed to natural drought conditions (Munné-Bosch and Alegre, 2003).…”

“…Diterpene levels in field-grown rosemary plants displayed seasonal changes, with a tendency for carnosic acid losses in response to environmental stress conditions (Luis and Johnson, 2005). In particular, carnosic acid concentrations in rosemary leaves under natural conditions were found to decrease at high temperatures and low precipitation rates in summer with concomitant increases in oxidized derivatives, suggesting that cellular oxidative stress is accompanied by the consumption of carnosic acid (Munné-Bosch et al, 1999;Munné-Bosch and Alegre, 2003). Both carnosic acid and carnosol accumulate in photosynthetic green tissues only (leaves, sepals, and petals) and have be localized in the chloroplasts (Munné-Bosch and Alegre, 2001), although the synthesis of carnosic acid also has been reported in glandular trichomes (Brückner et al, 2014).…”

Cross-talk between calcium-calmodulin and nitric oxide in abscisic acid signaling in leaves of maize plants

“…Chloroplasts were isolated from leaves using the method as described by Munné-Bosch and Alegre [33]. Briefly, after grinding 5 g leaves in isolation buffer [0.33 M sorbitol, 2 mM EDTA, 50 mM Hepes-KOH (pH 7.5), 0.1% (w/v) BSA, 1 mM MgCl 2 , 1 mM MnCl 2 , 1 mM DTT], the homogenate was filtered through four layers of cheesecloth and centrifuged at 2 °C and 200 × g for 1 min.…”

Photosynthetic Potential and its Association with Lipid Peroxidation in Response to High Temperature at Different Leaf Ages in Maize

“…Malondialdehyde (MDA) is a major product of lipid peroxidation induced mainly by AOS (Pryor and Stanley 1975) and therefore is useful as a marker for oxidative stress (Cakmak and Horst 1991;Munné-Bosch and Alegre 2003). An increase in AOS such as singlet oxygen ( 1 O 2 ) can lead to a decrease in the photochemical quenching coefficient (q P ), a photoinhibition index (Foyer and others 1994), indicating that AOS accumulation may be closely associated with photosynthesis.…”