Food availability and sunlight are factors which can affect a persons genotype

15.3 Interactions of Ozone with CO2 and/or Elevated Temperature

Two genotypes of young silver birch trees were exposed to 2 × ambient ozone and CO2 in open-top chambers over 2 years in Finland (Kontunen-Soppela et al., 2010b; Table 15.1; see also Ernst, 2013, this volume) and studied for transcriptional profiles and key physiological characteristics during leaf senescence. Ozone-tolerant clone showed greater responses in the gene expression profile as compared to sensitive clone. Ozone stress downregulated many genes related to photosynthesis and glycolysis, while the expression of genes related to leaf ageing increased in a clone-dependent manner. The changes in gene expression were associated with decline in the photosynthetic light reactions, decreased concentration of Rubisco, chlorophyll and soluble sugars, but not to net photosynthesis rates or growth parameters, indicating complex relationship between gene regulation and physiological response. In the late season, ozone also increased the expression of genes related to oxidative stress (e.g. NADH plastoquinone oxidoreductase) and genes encoding enzymes of secondary metabolism, concomitant with the increased concentration of phenolic acids but decreased concentration of flavonone aglycones and DHPPG (Kontunen-Soppela et al., 2010b; Oksanen et al., 2005; Peltonen et al., 2005; Table 15.3). Elevated CO2 downregulated the expression of genes related to carbohydrate metabolism and senescence, concomitant with the delayed leaf abscission and accumulation of secondary metabolites, indicating a possible trade-off in carbon allocation (Kontunen-Soppela et al., 2010b; Peltonen et al., 2005). Combined exposure to both stress factors indicated that CO2 counteracted ozone responses, alleviating several negative effects of ozone at least temporarily (Kontunen-Soppela et al., 2010b; Peltonen et al., 2005).

Changes in gene expression of paper birch (Betula papyrifera Marsh.) leaves collected from the long-term ozone and CO2 experiment Aspen FACE (USA) (Figure 15.1; Pregitzer and Talhelm, 2013, this volume) were studied using novel multivariate and clustering methods (Kontunen-Soppela et al., 2010a; Table 15.1; see also Ernst, 2013). Ozone-exposed trees showed downregulation of light harvesting- and carbon fixation-related genes (encoding Rubisco, Rubisco activase, glyseraldehyde-3-P-dehydrogenase), accompanied by lower net photosynthesis (Riikonen et al., 2008; Table 15.3). Increased expression of genes related to ROS formation (encoding, e.g., ascorbate oxidase, arginine decarboxylase, metallothioneins, ACC synthase), photorespiration (encoding e.g. catalase, aminotransferase, glycolate oxidase), electron transport (encoding alternative oxidase, AOX, proton gradient regulation), lignin biosynthesis (encoding e.g. cinnamoyl-reductase, peroxidases) and repair (6-4 photolyase, DeGP2) were related to active defence against oxidative stress and protection/repair of the photosynthesis apparatus (Kontunen-Soppela et al., 2010a). Increase in the expression of genes related to proteolysis (encoding e.g. Cys and Asp proteases, ubiquitin), glycolysis and TCA cycle in the late season was associated with enhanced senescence of ozone-exposed leaves, and related energy demands for degradation and transport. Trees under elevated CO2 showed increased gene expression related to nitrogen metabolism, reflecting increased N assimilation and uptake from soil as reported by Zak et al. (2007). In addition, an increase in expression of TCA cycle and glycolysis genes and concomitant decrease in genes encoding oxidative phosphorylation indicated increased carbon supply and allocation for amino acid, fatty acid and polyphenol synthesis under elevated CO2 (Kontunen-Soppela et al., 2010a). Changes in gene expression under combined exposure to elevated ozone and CO2 were similar but smaller compared to ozone alone, indicating again the counteractive action of ozone and CO2 also at molecular level.

Taken together, our studies indicate the targets of ozone and CO2 action in several genes related mainly to photosynthesis, defence against oxidative stress, repair and senescence, serving as valuable and realistic basis for more detailed mechanistic studies. Consistently with our results, laboratory experiments by Bohler et al. (2007, 2011) indicated downregulation of proteins relating to light reactions and Calvin cycle in ozone-exposed poplars, accompanied by enhanced catabolism (reflecting the increased need for energy and reducing power for detoxification and repair). Although ozone caused changes in transcription levels of genes of mature beech (Fagus sylvatica) trees, growing under elevated ozone in field conditions, were inconsistent between sun and shade leaves and limited to few processes, some upregulation of secondary metabolism, signal transduction, ethylene biosynthesis and amino acid transporters, playing a role in stress response were also observed (Olbrich et al., 2010). Opposite impacts of ozone and CO2 on poplar growth and wood formation were also found by Richet et al. (2012), except that lignin content was increased by both factors as a result of different action mechanisms.

Saplings of silver birch and European aspen were also exposed to combined action of elevated ozone and temperature (T) in field conditions (Figure 15.2) over 1–2 growing seasons and measured for growth, gas exchange and antioxidant capacity, emissions of VOCs and changes in key gene expressions (DXS, DXR, IPP isomerase) regulating the formation of terpenoids (Hartikainen et al., 2009, 2012; Loreto and Fares, 2013; Mäenpää et al., 2011; Riikonen et al., 2009; Table 15.1). In aspen, elevated T induced large increases in emissions of monoterpenes and green leaf volatiles (GLVs), while impacts of ozone were minor (Hartikainen et al., 2009). Tolerance of certain genotypes to high temperature stress, indicated by increased leaf growth, was linked to increased emissions of isoprene and α-pinene together with thick palisade layer of leaf mesophyll, facilitating efficient photosynthesis per leaf area. In birch, elevated T increased growth, delayed leaf senescence and increased total emissions of mono-, homo- and sesquiterpenes, co-occurring with reduced transcription of genes encoding DXS, DXR and IPP isomerase, operating in chloroplastic MEP (methylerythritol 4-phosphate) pathway indicating negative regulation (Hartikainen et al., 2012; Kasurinen et al., 2012). Elevated ozone led to increases in the expressions of these three genes despite the unaffected emissions of mono-, homo- and sesquiterpenes, but the emissions of GLVs and MeSA (methyl salicylate) reduced together with the decline in photosynthesis and growth (Hartikainen et al., 2012; Kasurinen et al., 2012).

In addition to VOCs, also low-molecular-weight metabolites of birch were affected by increasing night-time temperature (from 6 to 22 °C) (Mäenpää et al., 2012; Table 15.1). High temperature induced specifically the biosynthesis of triterpenoids, hydrolysable tannins, fructose, DHPPG, myricetin 3-glucuronide and quinic acid along with the increased stem and leaf area growth and dark respiration rate, while proanthocyanidins tended to decrease (Mäenpää et al., 2012). In addition to temperature acclimation, these metabolic alterations indicated shifts in developmental stage of leaves. As a conclusion, our studies with birch and aspen have demonstrated the impacts of increasing daytime and night-time temperatures both on low-molecular-weight and volatile compounds, and related gene expression.

Social Change and the Nutrition Transition

Although genotype may influence individual susceptibility to weight gain and difficulty achieving weight loss, the etiology of the obesity epidemic lies primarily in the macrosocial changes that began slowly 250 years ago in Western Europe and North America, diffused, and accelerated rapidly throughout the world in the last half of the twentieth century. The mechanization of agriculture and innovations such as the Green Revolution in the 1960s exponentially increased worldwide food production. At the same time, the industrial and digital revolutions fueled economic growth, urbanization, trade, and increased household buying power in societies where market economies provide a reasonably universal, meritocratic access to education and employment. Recent transportation and communication technologies facilitated a dramatic increase in trade and intensified global supply chains that move services and goods, including meat, fish, vegetables, fruits, grains, and dairy products, from one end of the earth to the other with a minimal amount of human labor. In the process, food has been transformed into a commercial commodity. These macrosocietal changes not only have eroded environment quality but also have promoted a nutrition transition to a less healthy diet. This transition has been exacerbated by other social changes in affluent societies such as the United States.

Many changes in American household structure, including delayed marriage, increased divorce, and women's movement into paid labor force have increased demand for relatively inexpensive restaurant meals, including fast food and take out. Health, United States 2007 notes that spending on food away from home now accounts for 42% of the average annual food bill compared to 26% in 1970. Restaurant meals have always been larger and contain higher fat and sugar than home-cooked meals. Over the past three decades, however, they have been supersized in response to decreasing food costs and increasing competition for customers. Schools have contributed to the nutrition transition to improve their budgets. Many allow fast food outlets and soda and snack machines on their campuses for a share of the profits. At the same time, they have reduced physical education and time for recess.

Department of Agriculture data illustrate the transition in the American diet since 1950. Average annual consumption of red meat, poultry, and fish reached a combined 195 pounds per person in 2000, 57 pounds more than the average annual consumption in the 1950s. Annual per capita consumption of flour and cereals, including baked goods, snacks, fast food buns, and tortillas, increased from 155 to 200 pounds during the same period and annual per capita consumption of sugar and other sweeteners increased from 109 to 152 pounds. Although milk consumption declined by 38%, cheese consumption increased by startling 287%. More than half this cheese is consumed in prepared foods such as pizza, fast-food sandwiches, and tacos. Overall, the average daily calorie intake increased by 800 calories between 1957 (the low point for the century) and 2000. It increased 500 calories between 1970, generally considered the tipping point of the obesity epidemic, and 2000. Given that one pound of body weight is approximately equivalent to 3500 calories, a person already eating enough calories to sustain body weight would gain a pound a week from an additional daily intake of 500, unless their physical activity increased by a corresponding amount. This has not been the case for most Americans.

Increased food consumption in the United States has coincided with the transition from a mid-twentieth century economy based on agriculture and industry to a postindustrial, information economy where few jobs involve more than minimal physical labor, housework has been increasingly mechanized, the typical suburban household has two to three vehicles in the garage, and sedentary leisure activities such as watching television or movies, gaming, and surfing the net have multiplied. Children now average approximately 4 h day−1 in such passive activities, which does not bode well for obesity levels over the next 20 years. In a report on the built environment, the Institute of Medicine (IOM) notes that nearly one-third of adolescents and 55% of the adults do not meet the minimum recommended 30 min of moderately intense activity at least 5 days a week.

Conclusion

HNR and LNR genotypes did not differ much in their N utilization efficiency under field conditions because of the decline in nitrate assimilation due to the sharp decrease in soil nitrate levels at that stage when N fertilizers were applied as basal dose or in two splits (Abrol, 1990). The plants therefore could express their full genetic potential. Application of N in four splits maintained the nitrate levels in the soil during reproductive stage of plant growth. Application of N fertilizers enhanced NR activity at later stages of growth with yield improvement. Enhancement was more in HNR genotypes (Abrol et al., 1999).

Many studies have suggested that the NR activity alone could be considered as an index of reduced N availability in the plant and plants with high NR activity possess greater potential for accumulation of reduced N if soil nitrate is available throughout the growing period. However, studies in contrasting wheat genotypes with large variation in NR activity showed that there is a difference in amount of N assimilated, and HNR genotypes had much higher potential of harvesting N and mobilize the same to grains due to well-coordinated system of N uptake and utilization.

5.5.5 High throughput phenotyping

Connecting a genotype to phenotype is the most important criterion to understand the potential of a given genotype for particular environments. Traditional phenotyping methods deal with only a few specific plant traits limiting the in-depth analysis of constituent traits that link genotype to phenotype. Besides, they are labor and time-intensive, delaying the measurement of traits in large segregating populations, making the breeding process sluggish (Pratap et al., 2019). In recent years, next-generation high-throughput phenotyping platforms (HTPP) allowed the rapid phenotyping of multiple traits within no time. Understanding the relationships between different plant developmental stages became easier with HTPPs. Sorghum is currently being studied under field as well as controlled conditions by using this high throughput phenotyping technology. Many above- and below-ground biomass traits were successfully studied using this technology. Latest technologies like remote sensing (Shafian et al., 2018), autonomous ground robots (Fernandez, Bao, Tang, & Schnable, 2017), advanced imaging (Potgieter et al., 2017), and machine learning (Vijayarangan et al., 2018) have been successfully deployed in sorghum in field phenotyping. Recently, leasyScan, a sensor to plant concept where 3D imaging of leaf area in association with gravimetric measurement of plant water use, was developed and being used at ICRISAT. It allowed screening of large segregating populations in different species, enabling molecular breeding process more vigorous. Different physiological and phenological traits like plant height, leaf area, canopy temperature and conductance, stomatal conductance, seedling vigor, and normalized difference vegetation index can be measured successfully using high throughput phenotyping technology. In addition to plant-related traits, grain physical and chemical characteristics can be studied using a single near-infrared spectrum using near-infrared reflectance spectroscopy (NIRS). The generation of calibration models for each grain constituent allowed vigorous use of NIRS technology on agricultural harvesters. Indexing of grain characteristics on substantially large field plots became possible using NIRS with minimum handling and sampling errors.

Publisher Summary

The relationship between genotype and phenotype is complex whether one focuses on the mechanisms that relate gene structure to protein function or on variation. Mechanisms such as gene regulation, alternative splicing, ADAR (adenosine deaminase acting on RNA), somatic recombination, and the formation of protein multimers lead to a many-to-many relationship between genes and proteins. Alternative splicing, the formation of protein multimers, epigenetics, epistasis, and a host of other complicating factors, including the environment, all act to complicate this relationship. The environment can alter phenotype without changing genotype. Genetic mechanisms can lead to stabile phenotypes despite changing genes or environment. Developmental processes often produce patterns rather than traits. In addition, chance further complicates the situation. Much of modern biology is predicated on the assumption that by knowing the genotype of an individual one can predict the phenotype, or even vice versa, but in many situations this may not be possible.

2 Radiation interception and radiation use efficiency

Breeding creates genotypes with the highest economic yield, with a specific quality for a specific environment. The specific environment is mainly determined by temperature. In environments with mean monthly temperatures below 5 °C or above 25 °C, for instance, potato normally is not grown commercially. In subtropical regions rice is often grown during the warmest part of the year and potato (or wheat) during the cooler part of the year. This is illustrated in Fig. 1.

In the Mediterranean area the growing season is limited in spring by low temperatures at planting and by high temperatures and drought towards harvest. In northern Europe low temperatures limit the length of the growing season in spring (late frosts in March, April and May but also at the end of the season temperatures are low again (early frosts in September and October).

Beside temperature, other factors may determine the available length of the growing season. In tropical highlands, for instance, temperatures are suited for potato production throughout the year. Rainfall at the equator, however, is in two main rainy seasons six months apart, necessitating two crops per year. Theoretically this would restrict the length of the growing season to 6 months for ware potato crops as part of this crop is used as seed for the next crop because no separate seed potato production system exists at the farmers’ level. But practically this period has to be reduced by 2 to 3 months because the tubers that are harvested, start to sprout again after two to three months only. Ideal genotype (ideotypes) should then have a length of the growing cycle of 100 days. Longer cycles would lead to an imbalance of the growing and seed rest periods. In temperate climates rainfall often determines the workability of the soil and hence planting or sowing and the harvest period. Another important factor that may limit the length of the growing season and consequently the length of the growth cycle is related to market prices. Prices are often higher at the beginning of the harvest period of crops that are harvested fresh, necessitating a reduction of the length of the season.

Ideotypes have a length of the growth cycle characterized by a green leaf area that maximizes interception of solar radiation during the available growing season to accumulate as much dry matter as possible. Earlier genotypes, too early divert dry matter to the harvestable parts (grains or tubers) so that not sufficient assimilates are available for the foliage that then senesces and dies. Genotypes that are too late still have full ground cover with green leaves at the end of the available growing season which is indicative of an unfavourable distribution of dry matter to the foliage and to the harvestable parts of the crop. To identify ideotypes with the desired length of the growth cycle first the length of the available growing season is determined as it is restricted by adverse growing conditions or market demands. Secondly, an assesment is made of the yield determining factors (temperature, radiation, daylength and cultivar) that cannot be changed nor influenced by the farmer once the crop is planted, with emphasis on the influence of such factors on the length of the growth cycle. A simple model describing growth and development of crops is based on light interception, utilization of light to produce dry matter, allocation of dry matter to the harvestable parts and of the percentage of water in the harvestable parts. Haverkort and Kooman (1997) descibed the use of crop growth modeling in breeding for genotypes with the aid of such a LINTUL model: Light Interception and Utilization of Light, based on the principle that the amount of light that is intercepted by the crop is converted into crop dry matter through a conservative light use efficiency (Equation 1). This principle is illustrated in Fig. 2 for the potato crop.

The dry matter distribution pattern as influenced by temperature and photoperiod between foliage and harvestable produce determines the length of the growing season and is used to genetically match the length of the growth cycle with that of the growing season.

B. Genotypic Responses

Significant differences among genotypes in a given environment or in response to environmental changes indicate the existence of genetic variation (broad-sense heritability). The amount of this genetic variation is the most important characteristic of a species in predicting its evolutionary potential for adaptation to environmental change because the expected shift in the mean of a character is directly proportional to its heritability (Bradshaw, 1984).

We estimated the broad-sense heritabilities (H2) of the investigated quantitative characters under ambient CO2, under elevated CO2, and over both levels pooled for plants growing both in the competition-free tubes (Table IIIA) and in the diversity treatments (Table IIIB). The estimates for ambient and elevated CO2 were calculated from mixed-model analyses of variance as the quotient of the variance component due to differences among genotypes (SG2) and the sum of this component and the residual variance (SRes2) within plots (Falconer, 1989):

Table III. Heritabilities of the Measured Quantitative Characters in Ambient CO2 (H2(1)), Elevated CO2 (H2(2)), over the Two CO2-Levels Pooled (H2(3)), and of the Responses of These Characters to CO2 (Response–Heritability (H2(4)))

(H2(1))(H2(2))(H2(3))(H2(4))(A)

Without competition

With competition

aThe response–heritability was calculated using the mean square of the CO2-by-genotype interaction from an analysis of variance.

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