Photorespiration: Studies with Whole Tissues

ABSTRACrDuring growth, Acmtab,dria mcditueraa requires the action of blue light to intainigh rates of photosynthesis. In the present study, blue light-dependent alttions of the photosynthetic apparatus, which can be detected by analysis of light-saturation curves ad by masurements of partial reactions of the photosynthetic electron transport chin, are described. Ligt-saturatio curves of photosynthesis in vivo were measured with a new closed oxygen electrode system after culture of Acetabularia in continuous red or blue Light. These curves were compared to those of 2,6-dichlorophenol-ndophenol reduction by isolated chloroplast membranes. The analysis lead to the following statements: (a) only one reaction limits electron trasport rates in vitro (dichlorophenol-indophenol redoeuio) at all Light intensiies irspective of the light quality during growth, and (b) the miting step is light driven and located in the reaction center of photosystem H. Presumbly, this same reaction determines the flow of electrons under low light intensities in vivo in cells from white, blue, and red light. In addition to photosynthesis, the rates ofdark respiration changed due to the action of blue light. Concomitantly, the light compensation point of apparent photosynthesis was shifted during monochromatic iradiations.

Section: Photosynthesis In Vivomentioning

confidence: 88%

Control of the Photosynthetic Apparatus of Acetabularia mediterranea by Blue Light

Wennicke

Schmid²

1987

“…Based on the losses caused by photorespiration, increases of CO2 exchange rate of as much as 50% may be possible (17). Identifiable sources of variation in estimating CO2 exchange in a single leaf position were (a) error inherent in the C02-depletion method of assay, (b) error associated with estimates of leaf area, and (c) variation in mg C02/dm2' h due to varying irradiance and mutual shading.…”

Section: Discussionmentioning

confidence: 99%

Relationship between Net CO₂ Assimilation and Dry Weight Accumulation in Field-Grown Tobacco

Peterson

Zelitch²

1982

To assess the variability of net photosynthetic CO2 exchange per unit leaf area and to construct budgets for stands of field-grown tobacco (Nicotiana tabacum, Connecticut Broadleaf), a number of short-time measurements were made on all available leaf positions on two varieties using a hand-held transparent chamber for conducting gas exchange measurements on leaves. Measurements of net CO2 exchange were carried out on 18 separate days during a 35-day period, beginning 22 days after the seedlings were transplanted to the field. Gas exchange assays on leaves were conducted under ambient conditions of temperature and light intensity at all times of day. Solar radiation was monitored throughout the period, and losses of respiratory CO2 from stems, roots, and leaves (in the dark) were estimated. A estimation of a carbon budget; and (c) whether one could determine from a carbon budget why one variety produced more dry weight than the other. This investigation has demonstrated the usefulness of the C02-depletion method of assaying net CO2 exchange in field studies, and clearly established the close relationship between net CO2 exchange and dry weight accumulation.We have been involved in a continuing effort to modify genetically the biochemistry of C3 plants to produce tobacco mutants with decreased photorespiration and greater than normal rates of net CO2 assimilation per unit of leaf area (1,2,10,16). To confirm that varieties with superior rates of net photosynthesis under controlled conditions of the laboratory or greenhouse perform similarly in the field, an accurate yet convenient method of measuring net CO2 uptake under field conditions was sought. Most recently, we adapted the C02-depletion system described by Clegg et al. (5,13) to tobacco leaves in the field. It is based on the short-time measurement of the decrease in CO2 concentration in a portable, hand-held transparent chamber clamped over the leaf. This method permitted the convenient assay of large numbers of samples, and the results proved to be reliable and reproducible.It became apparent from our experience and from that of others that a limited number of instantaneous measurements of rate of

“…In the past decade, the biochemistry and physiology of the photorespiratory process has received much attention (12,16 results have been less than encouraging, especially if the inhibitors are affecting reactions subsequent to the production of Pglycolate, the substrate for photorespiration (12, 16). In the long term, genetic modification to reduce photorespiration and increase photosynthetic efficiency would be most desirable; however, results to date are rather inconclusive.…”

Section: Introductionmentioning

confidence: 99%

“…In the past decade, the biochemistry and physiology of the photorespiratory process has received much attention (12,16).…”

mentioning

confidence: 99%

Photosynthetic Rate Control in Cotton

Perry

Krieg²,

Hutmacher³

1983

The purpose of this research was to determine the magnitude of photorespiration in field-grown cotton (Gossypium hirsutum L.) as a function of environmental and plant-related factors. Photorespiration rates were estimated as the difference between measured gross and net photosynthetic rates.A linear increase in photorespiration was observed as air temperature increased from 22 to 40°C at saturating photon flux density. At 22°C, photorespiration was less than 15 per cent of net photosynthesis and very comparable to the dark respiration rate. At 40°C, photorespiration represented about 50 per cent of net photosynthesis. Gross photosynthesis had a temperature optimum of 32 to 34°C. Water stress, as indicated by *L, did not alter the ratio of gross photosynthesis to net photosynthesis when the confounding effects of leaf temperature differences were accounted for in the data analyses. A reduction in both gross and net photosynthesis was apparent as 'L declined from -2.0 megapascals indicating direct effects of water stress on the photosynthetic process. Photorespiration expressed as a proportion of net photosynthesis increased as water stress intensified.Cotton cultivars possessing a fruit load had significantly higher gross and net photosynthetic rates and lower photorespiration rates than did photoperiod-sensitive cotton strains without a fruit load. Within the fruiting types, which were genetically very similar, only minor differences were observed in the photorespiration:net photosynthesis ratios. However, in the photoperiod-sensitive strains, considerable genetic variability existed when photorespiration was expressed as a proportion of net photosynthesis. These results suggest that the kinetics of ribulose-1,5-bisphosphate carboxylase:oxygenase may be different and, thus, the possibility of genetically reducing photorespiration exists.Photorespiration is an integral part of the photosynthetic process of all green plants but is especially significant in those species fixing CO2 via the C3 pathway. In the past decade, the biochemistry and physiology of the photorespiratory process has received much attention (12,16 results have been less than encouraging, especially if the inhibitors are affecting reactions subsequent to the production of Pglycolate, the substrate for photorespiration (12, 16). In the long term, genetic modification to reduce photorespiration and increase photosynthetic efficiency would be most desirable; however, results to date are rather inconclusive.The relative rates of photosynthesis and photorespiration are determined by the kinetic properties of RuBisCO2. The ratio of the velocity of each component of this dual purpose enzyme is largely determined by the relative concentration of CO2 and 02 available to the enzyme in the chloroplast stromal matrix (3, 9). Temperature has a major influence on the C02:02 ratio due to the differential solubility ofeach gas with increasing temperature.Lawlor (10) has reported that true (gross) photosynthesis, net photosynthesis, and photorespiration ...