Control of the appearance of ascorbate peroxidase (EC 1.11.1.11) in mustard seedling cotyledons by phytochrome and photooxidative treatments

Abstract

In photosynthetic cells the plastidic ascorbate-glutathione pathway is considered the major sequence involved in the elimination of active oxygen species. Ascorbate peroxidase (APO; EC 1.11.1.11) is an essential constituent of this pathway. In the present paper control of the appearance of APO was studied in the cotyledons of mustard (Sinapis alba L.) seedlings with the following results: (i) Two isoforms of APO (APO I, APO II) could be separated by anion-exchange chromatography; APO I is a plastidic protein, while APO II is extraplastidic, very probably cytosolic. (ii) The appearance of APO is regulated by light via phytochrome. This control is observed with both isoforms. Moreover, a strong positive control over APO II appearance (very probably over APO II synthesis) is exerted by photooxidative treatment of the plastids. (iii) Additional synthesis of extraplastidic APO II is induced by a signal created by intraplastidic pigment-photosensitized oxidative stress. The response is obligatorily oxygen-dependent and abolished by quenchers of singlet oxygen such as α-tocopherol and p-benzoquinone. (iv) A short-term (4 h) photooxidative treatment suffices to saturate the signal. Signal transduction cannot be abolished or diminished by replacing the plants in non-photooxidizing conditions. Several observations indicate that control of APO synthesis by active oxygen is not an experimental artifact but a natural phenomenon.

The Role of Phytochrome in Stress Tolerance

“…Thus, in addition to the phytochrome signaling pathway, antioxidant enzymes such as peroxidases, and non‐enzymatic antioxidants such as flavonoids (see high light stress section) and carotenoid molecules, are antioxidants that have been found to be modulated by phytochromes under stress conditions. This and other related findings have been reported for many years (Drumm and Schopfer 1974; Thomsen et al 1992; Zhong et al 1997) including now extensive recent studies on HO enzymes (Cui et al 2011; Xu et al 2011) and interaction with hormones (Monteiro et al 2011). Moreover, besides light signals perceived by phytochromes, coordinated responses to stress require a fully integrated signaling network, incorporating information from others photoreceptors and interactions with a wide range of molecules, this being an important emerging topic that must be addressed in future investigations.…”

Effects of postharvest oligochitosan treatment on anthracnose disease in citrus (Citrus sinensis L. Osbeck) fruit

“…Under physiological conditions, ROS can be scavenged off, and oxidative damage can be minimized because of the existence of antioxidant enzymes and non-enzyme antioxidants, such as SOD, CAT, POD, APX, GR, AsA, and GSH. Activities of SOD, CAT, and POD, as well as the balance of AsA-GSH cycle in cells are crucial for determining the steady-state levels of superoxide radicals and H 2 O 2 [43]. SOD catalyzes the conversion of O 2− to H 2 O 2 , which is subsequently decomposed into H 2 O and O 2 by CAT or POD [44].…”

Photosynthetic electron transport regulates the expression of cytosolic ascorbate peroxidase genes in Arabidopsis during excess light stress.

“…It has been reported that APX activity can be regulated by phytochrome (Thomsen et al, 1992), and a diurna1 rhythm of APX7 mRNA abundance has recently been shown in Arabidopsis (Kubo et al, 1995). An involvement of photoreceptors in the rapid regulation of APX7 and APX2 gene expression is less likely because the timing of the responses mediated by a photoreceptor during changes in light intensity is usually measured in hours (Millar et al, 1995).…”