Carotenoid composition and photochemical activity of four sandy grassland species

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.

Section: Effects Of Elevated Temperature On Psiisupporting

confidence: 89%

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

Wang¹,

Li²,

Lin

et al. 2011

“…A high q P was beneficial to increase electron transport and quantum yield, which was confirmed by the higher F v '/F m ' and ETR of F. delavayi relative to F. cirrhosa. NPQ represented the energy dissipated as heat (Veres et al 2006), and redundant energy becomes a potential source of damage to the photosynthetic apparatus (Melis 1999). F. delavayi had a high NPQ, which could protect photosynthetic reaction centres from damage induced by irradiation.…”

Section: Correlations Between P N and Environmental Factorsmentioning

confidence: 99%

Diurnal changes in gas exchange and chlorophyll fluorescence parameters of Fritillaria cirrhosa and F. delavayi under field conditions

Chen

2009

To determine what factors limit the growth of wild Fritillaria cirrhosa and Fritillaria delavayi in field conditions, we investigated diurnal changes of the net photosynthetic rate (P N ) and the correlation between P N and various environmental factors. Parameters of chlorophyll (Chl) fluorescence were evaluated to test whether ecological fragility caused the extinction of wild F. cirrhosa and F. delavayi. Our study reveals for the first time that F. cirrhosa and F. delavayi did not encounter significant stress under field conditions. A small reduction in maximum photochemical efficiency was observed under high irradiance. The maximum P N of F. cirrhosa was 30 % higher than F. delavayi (p<0.05), and a similar difference was observed for apparent quantum yield (27.3 %, p<0.01). F. delavayi was better adapted to a wide range of irradiances and high environmental temperature. Correlation between P N and environmental factors (without considering the effects of interactions among environmental factors on P N ) using leaves of F. cirrhosa revealed that the three primary influencing factors were air pressure (p<0.01), relative humidity (p<0.01), and soil temperature (p<0.05). In F. delavayi, the influencing factors were relative humidity (p<0.01), soil temperature (p<0.05), CO 2 concentration (p<0.05), and air pressure (p<0.05). Path analysis (considering effects among environmental factors on P N ) showed that air temperature (negative correlation), photosynthetic photon flux density (PPFD) and relative humidity were the three primary limiting factors influencing the growth of F. cirrhosa. For this species, relative humidity reacted indirectly with air pressure, which was reported singularly in other species. Limiting growth factors for F. delavayi were PPFD, air pressure (negative correlation), soil temperature (negative correlation) and air temperature (negative correlation).

“…The resulting surplus of energy becomes a potential source of damage to the plant (Melis 1999), as it can lead to formation of destructive oxidative molecules, which can damage the photosynthetic apparatus in photoinhibition (Aro et al 1993), and the q NP can represent the energy dissipated as heat energy (Vasil'ev et al 1998, Veres et al 2006, which can not be utilized to transport photosynthetic electrons. The higher q NP in C. praecox showed that the energy absorbed in the physiological range of irradiances might be much higher than photochemical utilization.…”

Section: Chl Fluorescencementioning

confidence: 99%

Comparative photosynthesis characteristics of Calycanthus chinensis and Chimonanthus praecox

LingZhi¹,

Lü²,

Wang³

et al. 2007

Calycanthus chinensis is an endangered plant of the national second-grade protection of China restricted in a small area in Zhejiang Province. We studied parameters of photosynthesis, chlorophyll (Chl) contents, and Chl fluorescence (minimum fluorescence, F 0 , maximum fluorescence, F m , variable fluorescence, F v , and F v /F m ) of C. chinensis and Chimonanthus praecox. C. chinensis had lower compensation irradiance but higher saturation irradiance than C. praecox. Hence C. chinensis has more advantage in obtaining and utilizing photon energy and higher Chl content, and is more adaptive to higher temperature and propitious to thermal dissipation than C. praecox. In addition, C. chinensis produces abundant, well-preserved seed with a higher germination rate and a wider adaptability to temperature than C. praecox. Thus C. chinensis is prone to survival and viability, and gets rid of the endangered plant species of the national secondgrade protection of China.