In previous work irrigation effect on grapevine leaf conductance and photosynthetic rate was assayed in two contrasting cultivars: Tempranillo, a common spanish cultivar, and Manto Negro, a majorcan cultivar with enhanced drought resistance. The objective of the present study was to compare irrigation effect on leaf photosynthesis capacity estimated by light and CO2 response curves in both cultivars. Differences between treatments and cultivars in A (photosynthetic rate) vs PPFD (photosynthetic photon flux density) response curves were achieved during the ripening measurements in which midday leaf Psi of -1,6 and -1,2 MPa for Manto Negro and Tempranillo respectively were recorded in unirrigated plants. For this treatment, at ambient CO2 and saturating light A was similar for both cutivars (6 and 5 mu mol CO2 m(-2)s(-1)) but apparent quantum yield was more reduced in Manto Negro.At saturating light, A. (photosynthetic rate) vs Ci (internal CO2 concetration) curves showed similar values for irrigation and drought until ripening. In that sampling time, Tempranillo showed a coincident reduction in Amax, at saturating Ci in irrigated and water stressed plants. In Manto Negro, irrigation enables to maintain these parameters unchanged but, under drought, was a clear reduction in Amax at saturating Ci and initial slope were found. Photosynthetic capacity was independent of moderate irrigation during berry growth and veraison for both cultivars. During the ripening period, moderate irrigation enables to maintain photosynthetic capacity in Manto Negro but not in Tempranillo, however for some parameters such as quantum yield and initial slope of A vs. Ci curve, the higher drought effects were recorded for Manto Negro.

Attempts to select C-3 plants with slow rates of photorespiration and increased rates of net photosynthesis have met with little success. This review analyses the properties of mutant genotypes of tobacco (Nicotiana tabacum L. cv. Wisconsin), derived from selection of haploid plants (produced by in vitro mutagenesis of anthers) which survived in CO2 concentrations close to the compensation point, Survivors were diploidized and doubled-haploid plants were self-pollinated to obtain seeds (the selected genotypes). Several glasshouse and field experiments showed that the method of selection at low CO2 concentrations gave genotypes with increased capacity for total dry matter accumulation; increases were similar (mean 24%; range 14-36%) in different conditions for two selected genotypes (SP422 and SP451) when compared to the parental genotype Wisconsin-38. This increase was related to a greater leaf area per plant (mean increase 19%; range 9-43%), to faster photosynthetic rates in mature and old leaves and to similar rates of dark respiration per unit leaf area, but smaller rates per unit dry matter. These changes were related to a greater number of mesophyll cells of smaller size in the selected genotypes. However, the increased productivity could not be related to reduced photorespiration rate or CO2 compensation point nor to improved Rubisco properties (e.g. increased specificity factor) which the selection method was designed to achieve. Selection by survival at low CO2 produced genotypes able to invest more assimilate in growing larger leaves and to maintain a better leaf carbon balance than the parent genotype. These features improved light capture and carbon accumulation and thus increased dry matter production.

Winter wheat (Triticum aestivum L., cv. Mercia) was grown at two different atmospheric CO, concentrations (350 and 700 mu mol mol(-1)) two temperatures [ambient temperature (i.e. tracking the open air) and ambient +4 degrees C] and two rates of nitrogen supply (equivalent to 489 kg ha(-1) and 87 kg ha(-1)). Leaves grown at 700 mu mol mol(-1) CO2 had slightly greater photosynthetic capacity (10% mean increase over the experiment) than those grown at ambient CO2 concentration, but there were no differences in carboxylation efficiency or apparent quantum yield. The amounts of chlorophyll, soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area did not change with long-term exposure to elevated CO2 concentration. Thus winter wheat, grown under simulated field conditions, for which total biomass was large compared to normal field production, did not experience loss of components of the photosynthetic system or loss of photosynthetic competence with elevated CO2 concentration. However, nitrogen supply and temperature had large effects on photosynthetic characteristics but did not interact with elevated CO2 concentration. Nitrogen deficiency resulted in decreases in the contents of protein, including Rubisco, and chlorophyll, and decreased photosynthetic capacity and carboxylation efficiency. An increase in temperature also reduced these components and shortened the effective life of the leaves, reducing the duration of high photosynthetic capacity.

Leaf photosynthesis, stomatal conductance, internal CO2 concentration and leaf composition (photosynthetic pigments, total soluble protein and Rubisco content) during leaf ontogeny of field grown Nicotiana tabacum L. lines selected for survival at low atmospheric CO2 concentrations are described.Selection at low CO2 concentrations resulted in lines with higher total dry matter production than their parent cultivar, but this could not be related to improved photosynthesis which the selection method was designed to achieve (shown in previous work).In the present work we report higher rates of photosynthesis in the selected lines in mature and old leaves, not found in young leaves when the capacity for photosynthesis was maximum. Differences in the regulation of the photosynthetic carbon reduction cycle as well as differences in the diffusive characteristics of the mesophyll, due to changes in the size of the cells, may be the cause for the higher rates of photosynthesis during leaf senescence in the selected lines.

Despite large differences in total dry matter at final harvest, no significant differences (p less-than-or-equal-to 0.05) were detected in the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) or in its regulation by carbamylation between tobacco genotypes selected for survival at low CO2 and their source cultivar. Irrigated and water stressed plants of these genotypes differed in the diurnal pattern of Rubisco activity in their leaves. In irrigated plants Rubisco was not fully active even in the presence of saturating irradiance in the middle of the day. The maximum total activity reached during the day was higher in water stressed plants than in irrigated ones. Through the day decarbamylation of lysine 201 increased progressively in water stressed plants but remained less significant in the regulation of Rubisco activity than tight binding inhibitors.

ABSTRACTThe requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi‐controlled plant growth facility is described which allows the study of elevated CO2 and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO2 concentrations of 363 and 692 cm3 m−3 for targets of 350 and 700 cm3 m−3 respectively. Temperatures were set to follow outside ambient or outside ambient +4°C, and hourly means were within 0.5°C of the target for 92% of the time for target temperatures greater than 6°C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifieal light with natural photoperiod) was 2% greater than the total measured outside over the same period.

The photosynthetic characteristics (responses to CO2 and light), ribulose-1,5-bisphosphate carboxylase (Rubisco) properties, and the size and number of cells of the mesophyll of Nicotiana tabacum L. leaves of genotypes selected for survival at low atmospheric CO2 concentrations are described. When grown in the greenhouse with nutrient solutions, the total dry matter production of the selected genotypes was 23% greater than that of the parent genotype; this increase was related to a greater number of mesophyll cells of smaller size in the selected plants compared to the parent. However, it was not related to changes in the photosynthetic characteristics nor to Rubisco properties. These results suggest that the increased dry matter accumulation of the selected genotypes is not due to a reduction in photorespiration nor an increase in the CO2 assimilation rates. Rather, the selection of haploid tobacco plantlets in low CO2 has resulted in plants with greater leaf area (shown in previous work), due to the production of more cells of smaller size and to lower respiration rates per unit of leaf dry mass (previous work), thus increasing light capture, reducing the loss of assimilates and increasing total plant dry matter production.

Dry mass production, leaf characteristics and diurnal photosynthesis of two N. tabacum L. genotypes selected for survival at low CO2 and the parent Wisconsin-38 (control plants) were measured on water-stressed and well-watered plants in the field. Differences in photosynthesis per unit leaf area were small and not significant between genotypes, but different patterns of photosynthesis were observed in stressed and non-stressed plants, with water stress reducing total net carbon fixation by 45% in all genotypes. More dry mass was produced by the selected genotypes than by Wisconsin-38 under irrigation. Production was smaller and the same for all three genotypes when stressed. The increased dry mass of the selected genotypes was related to greater total leaf area per plant which was accompanied by more cells per unit leaf area but smaller cell volume than in the control plants. The decrease in dry mass production under water stress was related to a decrease in total leaf area per plant and a decrease in cell number per unit leaf area; however, cell volume increased.

Four self-pollinated, doubled-haploid tobacco, (Nicotiana tabacum L.) lines (SP422, SP432, SP435, and SP451), selected as haploids by survival in a low CO2 atmosphere, and the parental cv Wisconsin-38 were grown from seed in a growth room kept at high CO2 levels (600-700 parts per million). The selected plants were much larger (especially SP422, SP432, and SP451) than Wisconsin-38 nine weeks after planting. The specific leaf dry weight and the carbon (but not nitrogen and sulfur) content per unit area were also higher in the selected plants. However, the chlorophyll, carotenoid, and alkaloid contents and the chlorophyll a/b ratio varied little. The net CO2 assimilation rate per unit area measured in the growth room at high CO2 was not higher in the selected plants. The CO2 assimilation rate versus intercellular CO2 curve and the CO2 compensation point showed no substantial differences among the different lines, even though these plants were selected for survival under CO2 compensation point conditions. Adult leaf respiration rates were similar when expressed per unit area but were lower in the selected lines when expressed per unit dry weight. Leaf respiration rates were negatively correlated with specific leaf dry weight and with the carbon content per unit area and were positively correlated with nitrogen and sulfur content of the dry matter. The alternative pathway was not involved in respiration in the dark in these leaves. The better carbon economy of tobacco lines selected for low CO2 survival was not apparently related to an improvement of photosynthesis rate but could be related, at least partially, to a significantly reduced respiration (mainly cytochrome pathway) rate per unit carbon.

Growth parameters, leaf characteristics and plant productivity under field conditions were determined in three Nicotiana tabacum L. genotypes. Two of these genotypes, SP422 and SP451 were derived by self-pollination from double-haploid ones that had been selected as haploids by survival in a low CO2 atmosphere chamber, and subsequently diploidized. The third genotype, cultivar Wisconsin-38 (W-38), which had been used as haploid source cultivar, served as a control in this experiment. Mean Crop Growth Rate (CGR) and Net Assimilation Rate (NAR) were higher in SP451 than in the control during the growth period previous to flowering. For SP422 such differences occurred during the last growth period. Leaf chlorophyll and nitrogen concentrations, as well as leaf area per plant, were significantly higher in selected genotypes. Specific leaf matter in selected genotypes was slightly lower for SP422 and higher for SP451. CO2 exchange rate of excised leaves did not show significant differences among genotypes. Plant production was clearly higher in both selected genotypes, with mean values by 12% (SP422) and 36% (SP451) higher than the control genotype. The differences found between the two selected genotypes may be understood as two different ways to survive under low CO2 atmosphere.

Leaf photosynthesis and dark respiration largely determine biomass accumulation by plants, so that both parameters has been used as a selection criteria to improve crop’s yield (1, 2).