Photosynthesis

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

Photosynthesis in the Archean era.

Abstract: The earliest reductant for photosynthesis may have been H2. The carbon isotope composition measured in graphite from the 3.8-Ga Isua Supercrustal Belt in Greenland is attributed to H2-driven photosynthesis, rather than to oxygenic photosynthesis as there would have been no evolutionary pressure for oxygenic photosynthesis in the presence of H2. Anoxygenic photosynthesis may also be responsible for the filamentous mats found in the 3.4-Ga Buck Reef Chert in South Africa. Another early reductant was probably H2S. Eventually the supply of H2 in the atmosphere was likely to have been attenuated by the production of CH4 by methanogens, and the supply of H2S was likely to have been restricted to special environments near volcanos. Evaporites, possible stromatolites, and possible microfossils found in the 3.5-Ga Warrawoona Megasequence in Australia are attributed to sulfur-driven photosynthesis. Proteobacteria and protocyanobacteria are assumed to have evolved to use ferrous iron as reductant sometime around 3.0 Ga or earlier. This type of photosynthesis could have produced banded iron formations similar to those produced by oxygenic photosynthesis. Microfossils, stromatolites, and chemical biomarkers in Australia and South Africa show that cyanobacteria containing chlorophyll a and carrying out oxygenic photosynthesis appeared by 2.8 Ga, but the oxygen level in the atmosphere did not begin to increase until about 2.3 Ga.

Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with ‘antisense’ rbcS

Abstract: The effect of nitrogen supply during growth on the contribution of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) to the control of photosynthesis was examined in tobacco (Nicotiana tabacum L.). Transgenic plants transformed with antisense rbcS to produce a series of plants with a progressive decrease in the amount of Rubisco were used to allow the calculation of the flux-control coefficient of Rubisco for photosynthesis (CR). Several points emerged from the data: (i) The strength of Rubisco control of photosynthesis, as measured by CR, was altered by changes in the short-term environmental conditions. Generally, CR was increased in conditions of increased irradiance or decreased CO2. (ii) The amount of Rubisco in wild-type plants was reduced as the nitrogen supply during growth was reduced and this was associated with an increase in CR. This implied that there was a specific reduction in the amount of Rubisco compared with other components of the photosynthetic machinery. (iii) Plants grown with low nitrogen and which had genetically reduced levels of Rubisco had a higher chlorophyll content and a lower chlorophyll a/b ratio than wild-type plants. This indicated that the nitrogen made available by genetically reducing the amount of Rubisco had been re-allocated to other cellular components including light-harvesting and electron-transport proteins. It is argued that there is a “luxury” additional investment of nitrogen into Rubisco in tobacco plants grown in high nitrogen, and that Rubisco can also be considered a nitrogen-store, all be it one where the opportunity cost of the nitrogen storage is higher than in a non-functional storage protein (i.e. it allows for a slightly higher water-use efficiency and for photosynthesis to respond to temporarily high irradiance).

Leaf internal diffusion conductance limits photosynthesis more strongly in older leaves of Mediterranean evergreen broad‐leaved species

Abstract: Leaf age-dependent changes in structure, nitrogen content, internal mesophyll diffusion conductance ( g m ), the capacity for photosynthetic electron transport ( J max ) and the maximum carboxylase activity of Rubisco ( V cmax ) were investigated in mature non-senescent leaves of Laurus nobilis L., Olea europea L. and Quercus ilex L. to test the hypothesis that the relative significance of biochemical and diffusion limitations of photosynthesis changes with leaf age. The leaf life-span was up to 3 years in L. nobilis and O. europea and 6 years in Q. ilex . Increases in leaf age resulted in enhanced leaf dry mass per unit area ( M A ), larger leaf dry to fresh mass ratio, and lower nitrogen contents per dry mass ( N M ) in all species, and lower nitrogen contents per area ( N A ) in L. nobilis and Q. ilex . Older leaves had lower g m , J max and V cmax . Due to the age-dependent increase in M A , mass-based g m , J max and V cmax declined more strongly (7- to 10-fold) with age than area-based (5- to 7-fold) characteristics. Diffusion conductance was positively associated with foliage photosynthetic potentials. However, this correlation was curvilinear, leading to lower ratio of chloroplastic to internal CO 2 concentration ( C c / C i ) and larger drawdown of CO 2 from leaf internal air space to chloroplasts ( D C ) in older leaves with lower g m . Overall the agedependent decreases in photosynthetic potentials were associated with decreases in N M and in the fraction of N in photosynthetic proteins, whereas decreases in g m were associated with increases in M A and the fraction of cell walls. These age-dependent modifications altered the functional scaling of foliage photosynthetic potentials with M A , N M , and N A . The species primarily differed in the rate of agedependent modifications in foliage structural and functional characteristics, but also in the degree of agedependent changes in various variables. Stomatal openness was weakly associated with leaf age, but due to species differences in stomatal openness, the distribution of total diffusion limitation between stomata and mesophyll varied among species. These data collectively demonstrate that in Mediterranean evergreens, structural limitations of photosynthesis strongly interact with biochemical limitations. Age-dependent changes in g m and photosynthetic capacities do not occur in a co-ordinated manner in these species such that mesophyll diffusion constraints curb photosynthesis more in older than in younger leaves.

Chlorophylls and Carotenoids

Abstract: The green color of leaves is a mixture of two water-insoluble pigment classes: chlorophylls and carotenoids. They cooperate in photosynthesis to safely capture sunlight. Chlorophylls collect light and transduce its energy into an electrochemical potential across the photosynthetic membrane, and further to high-energy products such as sugars. Carotenoids can also capture light, but their major and indispensable function is to protect the photosynthetic apparatus from excess light (sunburn). The combination of chlorophylls with carotenoids allows photosynthetic organisms balance between competing for light, and being killed by an overdose. The widespread occurrence of photosynthesis is paralleled by considerable variations of the pigments. This variety and also the basic similarities among the different chlorophylls and carotenoids are dealt in this article.

Allocation of nitrogen to cell walls decreases photosynthetic nitrogen‐use efficiency

Abstract: Summary 1. Nitrogen (N) is an essential limiting resource for plant growth, and its efficient use may increase fitness. We investigated photosynthetic N-use efficiency (photosynthetic capacity per unit N) in relation to N allocation to Rubisco and to cell walls in Polygonum cuspidatum Sieb. et Zucc. which germinated in May (early germinators) and August (late germinators). 2. There was a significant difference between early and late germinators in photosynthetic capacity as a function of leaf N content per unit area. Higher photosynthetic N-use efficiency in late germinators was caused primarily by a larger allocation of N to Rubisco. 3. Nitrogen allocation to cell walls was smaller in late germinators. The shorter growth period in late germinators was associated with higher photosynthetic capacity, which was achieved by allocating more N to photosynthetic proteins at the expense of cell walls. 4. The trade-off between N allocation to photosynthesis and to structural tissues suggests that plants change N allocation to increase either the rate or duration of carbon assimilation. Such plastic change would help plants maintain themselves and cope with environmental changes.