Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Would transformation of C3 crop plants with foreign Rubisco increase productivity? A computational analysis extrapolating from kinetic properties to canopy photosynthesis

Abstract: Genetic modification of Rubisco to increase the specificity for CO 2 relative to O 2 ( t ) would decrease photorespiration and in principle should increase crop productivity. When the kinetic properties of Rubisco from different photosynthetic organisms are compared, it appears that forms with high t t have low maximum catalytic rates of carboxylation per active site ( k c c ). If it is assumed that an inverse relationship between k c c and t exists, as implied from measurements, and that an increased concentration of Rubisco per unit leaf area is not possible, will increasing t result in increased leaf and canopy photosynthesis? A steady-state biochemical model for leaf photosynthesis was coupled to a canopy biophysical microclimate model and used to explore this question. C 3 photosynthetic CO 2 uptake rate ( A ) is either limited by the maximum rate of Rubisco activity ( V cmax ) or by the rate of regeneration of ribulose-1,5bisphosphate, in turn determined by the rate of whole chain electron transport ( J ). Thus, if J is limiting, an increase in t t t will increase net CO 2 uptake because more products of the electron transport chain will be partitioned away from photorespiration into photosynthesis. The effect of an increase in t on Rubisco-limited photosynthesis depends on both k

Plant aging increases oxidative stress in chloroplasts.

Abstract: Aging has received considerable attention in biomedicine, but little is known about the regulatory mechanisms responsible for the aging not associated with senescence in plants. This study provides new insights into the relationship between oxidative stress and plant aging, and points out chloroplasts as one of the target organelles of age-associated oxidative stress in plants. We simultaneously analyzed lipid oxidation, photosynthesis, chlorophyll content, de-epoxidation state of the xanthophyll cycle, and levels of chloroplastic antioxidant defenses such as β-carotene and α-tocopherol in leaves of the same age in 1-, 3- and 7-year-old Cistus clusii Dunal plants growing under Mediterranean field conditions. Enhanced formation of malondialdehyde in leaves (2.7-fold) and chloroplasts (2.8-fold), decreased photosynthetic activity (25%), and lower chlorophyll (ca. 20%) and chloroplastic antioxidant defense levels (ca. 25%–85%) were observed in 7-year-old plants, when compared with 1- and 3-year-old plants. The differences observed, which were associated with plant aging, were only noticeable in mature non-senescing plants (7-year-old plants). No differences were observed between pre-reproductive (1-year-old plants) and young plants (3-year-old plants). This study shows that from a certain age, oxidative stress increases progressively in chloroplasts as plants age, whereas photosynthesis is reduced. The results indicate that the oxidative stress associated with the aging in plants accumulates progressively in chloroplasts, and that the contribution of oxidative stress to aging increases as plants age.

Sink strength regulates photosynthesis in sugarcane.

Abstract: The relationship in sugarcane (Saccharum spp.) between photosynthetic source tissue and sink material was examined through manipulation of the sink:source ratio of field-grown Saccharum spp. hybrid cv. N19 (N19). To enhance sink strength, all leaves, except for the third fully expanded leaf, were enclosed in 90% shade cloth for varying periods of time. Variations in sucrose, glucose and fructose concentrations were measured and the effects of shading on the leaf gas exchange and fluorescence characteristics recorded. Changes in carbon partitioning caused by shading were examined based on the uptake and translocation of fixed 14CO2. Following a decline in sucrose concentrations in young internodal tissue and shaded leaves, significant increases in the CO2-saturated photosynthetic rate (Jmax), carboxylation efficiency (CE) and electron transport rate were observed in unshaded leaves after 8 d of shading treatment. It was concluded that up-regulation of source-leaf photosynthetic capacity is correlated with a decrease in assimilate availability to acropetal culm sink tissue. Furthermore, a significant relationship was revealed between source hexose concentration and photosynthetic activity.