Effects of elevated temperature on photosynthesis in desert plant Alhagi sparsifolia S

Abstract

Most plants growing in temperate desert zone exhibit brief temperature-induced inhibition of photosynthesis at midday in the summer. Heat stress has been suggested to restrain the photosynthesis of desert plants like Alhagi sparsifolia S. It is therefore possible that high midday temperatures damage photosynthetic tissues, leading to the observed inhibition of photosynthesis. In this study, we investigated the mechanisms underlying heat-induced inhibition of photosynthesis in A. sparsifolia, a dominant species found at the transition zone between oasis and sandy desert on the southern fringe of the Taklamakan desert. The chlorophyll (Chl) a fluorescence induction kinetics and CO 2 response curves were used to analyze the thermodynamic characters of both photosystem II (PSII) and Rubisco after leaves were exposed to heat stress. When the leaves were heated to temperatures below 43ºC, the initial fluorescence of the dark-adapted state (F o ), and the maximum photochemical efficiency of PSII (F v /F m ), the number of active reaction centers per cross section (RCs) and the leaf vitality index (PI) increased or declined moderately. These responses were reversed, however, upon cooling. Moreover, the energy allocation in PSII remained stable. The gradual appearance of a K point in the fluorescence curve at 48ºC indicated that higher temperatures strongly impaired PSII and caused irreversible damage. As the leaf temperature increased, the activity of Rubisco first increased to a maximum at 34ºC and then decreased as the temperature rose higher. Under high-temperature stress, cell began to accumulate oxidative species, including ammoniacal nitrogen, hydrogen peroxide (H 2 O 2 ), and superoxide (O 2˙¯) , suggesting that disruption of photosynthesis may result from oxidative damage to photosynthetic proteins and thylakoid membranes. Under heat stress, the biosynthesis of nonenzyme radical scavenging carotenoids (Cars) increased. We suggest that although elevated temperature affects the heat-sensitive components comprising of PSII and Rubisco, under moderately high temperature the decrease in photosynthesis is mostly due to inactivation of dark reactions.

Features of chlorophyll fluorescence transients can be used to investigate low temperature induced effects on photosystem II of algal lichens from polar regions ( Short Communication )

“…It is accepted that O-J is due to reduction of electron Q A to Q A -1 ; while J-I and I-P are due to reduction of PQ pool. For thermally -affected samples, another point K was reported by e. g. Xue et al (2011). The shape of the OJIP phase can be affected by several factors e.g., efficiency of excitation energy transfer among PS II units (connectivity), the state of the oxygen evolving complex, and various processes involved in transformation of absorbed light energy in photosynthetic apparatus (see e.g.…”

Short-term responses of primary processes in PS II to low temperature are sensitively indicated by fast chlorophyll fluorescence kinetics in Antarctic lichen Dermatocarpon polyphyllizum

“…Majority of them relate to the efficiency of excitation energy transport in PS II, the state of oxygen evolving complex and other processes envolved in photosynthetic apparatus. In highly stressed samples, another inflextion point K was reported between steps O and J (0.2 -0.3 ms of chlorophyll fluorescence induction), indicating a disruption of oxygen-evolving complexes (Oukarroum et al 2007, Xue et al 2011.…”

Growing Different Lactuca Genotypes Aeroponically within a Tropical Greenhouse—Cool Rootzone Temperatures Decreased Rootzone Ethylene Concentrations and Increased Shoot Growth

“…Such mortality has been rather consistently observed across many batches of experiments (results not shown). As L. serriola is a wild type that is well-adapted to desert conditions of hot-day-cool-nights, its relatively higher mortality could have been due to the lack of cooler “night” temperatures that aided recovery from heat stress (Xue et al, 2011 ), evident from the highest accumulated RZ ethylene concentrations at A10-RZ treatment (Figure 5 ).…”