Quantum Efficiency Of Photosynthesis Research Articles

Sun and shade ecotypes of Solanum dulcamara L.: Photosynthetic light dependence characteristics in relation to mild water stress.

This work extends previous studies on ecotypic differentiation in Solanum dulcamara to include interactions between irradiance and plant water status, in particular the effect of mild water stress on the responses of the photosynthetic apparatus of sun and shade ecotypes to high irradiance levels. The tolerance of shade ecotypes to high irradiance was markedly decreased by even a mild water stress, as evidenced by an aggravation of the degree of inhibition of the quantum efficiency of photosynthesis, and of other symptoms of photoinhibition that are commonly seen when shade plants are grown at high irradiances. In contrast, the photosynthetic apparatuses of ecotypes native to dry, sunny habitats were completely stable at the same water stress and irradiance levels that caused severe inhibitory effects in shade ecotypes. Growing the sun ecotypes under high irradiances resulted in a markedly higher photosynthetic capacity than when they were grown under a low irradiance level, irrespective of the water potential of the root medium.Surprisingly, stomatal factors are not responsible for the increase in sensitivity to photoinhibition that takes place when shade ecotypes are subjected to water stress, nor can they account for the differences between sun and shade ecotypes in their photosynthetic responses to high irradiance and water stress. Possible underlying causes for the observed effects of water stress and ecotypic differences in sensitivity to high light damage of the photosynthetic apparatus are discussed.

The Quantum Efficiency of Photosynthesis in Ultraviolet Light

The Quantum Efficiency of Photosynthesis in Ultraviolet Light

Energy efficiency of photosynthesis by Chlorella

The quantum efficiency of photosynthesis by Chlorella pyrenoidosa was determined by following the gas exchanges between oxygen and carbon dioxide, using a magnetic oxygen meter and an infrared carbon dioxide gas analyzer. It was found that on the average, 8.9 ± 1.0 photons are required to fix one molecule of oxygen or carbon dioxide. Cultures from different laboratories showed no appreciable difference in yields.

On the energetics of the photosyntheses in green sulfur bacteria.

The quantum efficiency of photosynthesis by the green sulfur bacterium, Chlorobium thiosulfatophilum, has been determined in systems in which thiosulfate, tetrathionate, and molecular hydrogen served as electron donors. It was found that about 10 +/- 1 quanta are used for the assimilation of 1 molecule of CO(2), and that the quantum number is independent of the nature of the electron donor. These results are considered as support for the view that also in the bacterial photosyntheses the primary photochemical reaction consists in the photolysis of H(2)O, and that the chemical energy released during the oxidation of the electron donor is not utilized for CO(2) assimilation. Hence the photosynthetic processes of the green sulfur bacteria are thermodynamically less efficient than is green plant photosynthesis.

The quantum efficiency of photosynthesis

Photosynthesis is a unique endothermic photochemical reaction in which chemical energy is gained from visible light energy by the combined action of several quanta. Nothing similar is known in the nonliving world. It was first reported a quarter of a century ago 1 that in photosynthesis the greater part of the absorbed visible light energy could be converted into chemical energy under optimum conditions. Indeed, no more than four quanta of red light seemed to be necessary to produce one molecule of oxygen gas, which is close to the thermodynamic requirement of three quanta. It is easy to understand that this result, lacking any analogy, has sometimes been doubted by theoreticians, and it is a fact that certain investigators have raised methodological objections 2. For this reason we have reinvestigated the question of the minimum quantum requirement of photosynthesis as measured by oxygen and carbon dioxide gas exchange. The present paper is a short summary of our findings by new and simplified methods.

Quantum Efficiency of Photosynthesis

IT is generally accepted that about four energy quanta of red light (I» = 660 µµ) are needed to promote the assimilation of one molecule of carbon dioxide. This conclusion is based in the main on the measurements of Warburg and Negelein1, who determined the ratio W/E, that is, the volume of carbon dioxide assimilated by Chlorella during the absorption of one calorie of light energy. They designated this ratio by I¦ and, since it is well known that I¦ increases with decrease in light intensity, the value I¦0 found with the minimum intensity was adopted.

A Photocalorimeter. The Quantum Efficiency of Photosynthesis in Algae

A Photocalorimeter. The Quantum Efficiency of Photosynthesis in Algae

Quantum Efficiency of Photosynthesis in Chlorella1

Quantum Efficiency of Photosynthesis in Chlorella¹