Light stress effects and antioxidative protection in two desert plants

Abstract

1. The enzyme catalase was investigated as a sensitive marker of light stress in Retama raetam stems and Atriplex halimus leaves. While the activity of catalase was readily photoinactivated in vitro when crude extracts from these tissues were exposed to a photon flux of 500μmolm–2s–1 photosynthetic active radiation (PAR), no apparent losses of the extractable catalase activities were observed when tissues were harvested from desert plants at noon when light levels were as high as 2200μmolm–2s–1 PAR. 2. When stems of R. raetam or leaves of A. halimus were exposed to natural daylight of 1000μmolm–2s–1 PAR in the presence of cycloheximide (CHI), in order to prevent the new synthesis of catalase, or at a temperature of 42–44°C, only minor losses of catalase activity occurred in stems of R. raetam, but a marked apparent photoinactivation of catalase was observed in leaves of A. halimus. 3. Similarly, stronger declines of the ratio Fv/Fm, indicating more severe photoinhibition of photosystem II (PSII), were observed in A. halimus, compared with R. raetam. 4. For R. raetam, activities of some antioxidative enzymes and the carotenoid contents were higher in plants growing in the desert than in plants collected from non‐desert locations. 5. During the daily increase of light and temperature the antioxidants ascorbate and glutathione became more oxidized and violaxanthin was converted to zeaxanthin in R. raetam stems, while these antioxidants became more reduced and zeaxanthin was not notably accumulated in A. halimus leaves. 6. The results suggest that the desert plants R. raetam and A. halimus apply different strategies of protection against light‐stress damage. In the stems of R. raetam antioxidative protection appears to play the major role, while A. halimus appears to avoid light damage in the field by the mutual shading of leaves and reflection of light at the leaf surface.

The tolerance of Atriplex halimus L. to environmental stresses

“…Since it possesses the C 4 carboxylation pathway, the optimum temperature for photosynthesis is relatively high, around 35ºC (Shomer-Ilan et al, 1981;Le Houérou, 1992;Zervoudakis et al, 1998). Streb et al (1997), studying leaves of A. halimus plants exposed to photosynthetically active radiation in the field as high as 2200 µmol m -2 s -1 , found a limited capacity for the dissipation of light energy and for scavenging of ROS. They concluded that A. halimus is able to withstand high light intensity due to mutual shading of leaves and reflection of light from the leaf surface by a layer of salt crystals formed after the collapse of vesiculated hairs (Mozafar and Goodin, 1970), which gives the leaves a greenish-grey colour (Figure 1).…”

Dissecting the roles of osmolyte accumulation during stress

“…During stress, increased H 2 O 2 production by elevated glycolate oxidase activity may further upset the balance between the production of reactive oxygen intermediates and the quenching activity of antioxidants if lipid peroxidation disrupts peroxisomal membrane integrity, causing leakage of H 2 O 2 into other compartments (Willekens et al 1997). In C 3 plants subjected to stress, endogenous catalase activity in the light may be inadequate for destruction of H 2 O 2 generated during photorespiration (Foyer, Lelandais & Kunert 1994;Streb, Tel-Or & Feierabend 1997). Examination of transgenic tobacco plants with ≈ 10% of wild-type catalase activity has indicated the importance of catalase in maintaining redox balance during salt stress, even under lowintensity light (Willekens et al 1997).…”

Effect of Decreasing Oxygen Concentration on Plant Metabolism in Response to Different Environmental Stresses.

“…The steppe regions have very poor vegetation and a very short vegetative period since these conditions limit plant growth (68,138). The high light intensity, high temperature and the temperature difference between night and day increases the generation of reactive oxygen species and thus the risk of oxidative damage.…”

“…The high light intensity, high temperature and the temperature difference between night and day increases the generation of reactive oxygen species and thus the risk of oxidative damage. The plants may have developed two strategies to adapt to these severe conditions: antioxidant protection and avoidance from oxidative stress (68). The damage from the electron transfer system results in the formation of free radicals (singlet oxygen, superoxide radical and hydroxyl radicals).…”

“…Ranunculus glacialis growing at the same altitude has a weak antioxidant system (69,137). The activity of antioxidant enzymes and amount of carotenoids in Retama raetam, a desert plant, has been found to be higher than in non-desert plants (68).…”