Light is the driving force for photosynthesis. Two techniques are commonly employed to help characterize the relationship between the light environment and photosynthesis in plants.Chlorophyll a fluorescence analysis is used to examine both the capacity for and the efficiency of the conversion of absorbed light into energy for photosynthesis. Additionally, gas exchange analysis is used to assess the utilization of that energy for carbon fixation. These techniques are used either in isolation or in combination to acquire light response curves that measure the response of the plant to sequential changes in irradiance. Light response curves can help users understand photosynthetic mechanisms, evaluate how plants respond to light conditions, or assess the extent of physiological plasticity within plants. In this chapter, we provide a generalized method for acquiring light response curves suitable for both chlorophyll a fluorescence and gas exchange techniques using commercially available apparatus. Depending on the equipment available, these methods can be applied individually or combined to acquire data simultaneously. The methods are broadly applicable to most land plants but are ideally suited to help those that are unfamiliar with these techniques.

This experimental study investigates the influence of indoor plants on three aspects of air quality in office spaces: relative humidity, indoor air temperature, and carbon dioxide concentration. Employing a Latin square design, we rotated three different treatments across three offices over six time periods. These treatments included a control (no plants), a low-volume treatment (five plants), and a high-volume treatment (eighteen plants) of Nephrolepis exaltata (Boston fern). Air quality parameters were continuously monitored at five-minute intervals using Trace Gas Analyzers. Generalised linear mixed modelling (GLMM) was employed to examine the effect of each treatment on relative humidity, indoor air temperature and CO2 concentration. We observed a significant positive correlation between the number of indoor plants and relative humidity levels. In offices without any plants, the median relative humidity was 29.1%. This increased to 38.9% in offices with 5 plants and further to 49.2% in offices with 18 plants. However, we did not find significant associations between the number of indoor plants and indoor air temperature or corrected CO2 concentration. Our research provides support for the use of indoor plants to increase relative humidity, which can have health benefits in dry climates, but does not provide support for using indoor plants to regulate indoor air temperatures or CO2 concentration in office environments.

Pendimethalin herbicide toxicity to rice plants and barnyard grass invasion have increasingly affected the productivity of direct-seeded rice (DSR) in the fields. Whether and how to promote DSR productivity and sustain weed management depend on the appropriate pre-emergence herbicide application rate to minimise its toxicity in the rice ecosystem. Pot experiments were conducted to determine the effects of pendimethalin rates (1.5, 1.75, 2.0 kg a.i. ha−1, two control treatments include the untreated control and the treated control with 1.5 kg a.i. ha−1 S-metolachlor) on barnyard grass (Echinochloa crus-galli (L.) Beaux) and their potential toxicity risk to photosynthetic performances of rice (Topaz and Sen pidao). All the pendimethalin treatments provided excellent control of barnyard grass. Among the treatments, 1.5, 1.75, 2.0 kg a.i. ha−1 pendimethalin and 1.5 kg a.i. ha−1 S-metolachlor (treated control) decreased leaf area of barnyard grass significantly by 38.9, 49.6, 49.6 and 46.2%, respectively, compared with the untreated control at 40 days after sowing (DAS). The above-ground biomass of barnyard grass significantly decreased by 40% (1.48 g plant−1) with 2.0 kg a.i. ha−1 pendimethalin and by 46.2% (1.33 g plant−1) when 1.5 kg a.i. ha−1S-metolachlor was applied at 40 DAS compared with the untreated pots. Higher pendimethalin rates increased toxicity in Topaz and Sen pidao varieties, and 2.0 kg a.i. ha−1 pendimethalin significantly reduced effective quantum yield (light-adapted) of photosystem (PS) II by 18% (0.58) and 19% (0.52), respectively, compared with the untreated control. Application of 2.0 kg a.i. ha−1 pendimethalin rate significantly decreased the maximum quantum yield (dark-adapted) of Sen pidao (0.66) compared with 1.5 kg a.i. ha−1 pendimethalin (0.68) including the untreated control. All pendimethalin treatments suppressed above-ground biomass at 55 DAS, but above-ground biomass of barnyard grass significantly decreased by 59.9% when 2.0 kg a.i. ha−1 pendimethalin was applied compared with the untreated control. Although application of 1.5 kg a.i. ha−1 pendimethalin rates reduced the effective quantum yield (light-adapted) of photosystem II of Sen pidao (0.55) by a small percentage (8%) than Topaz (0.65), it was non-toxic for both varieties compared with 2.0 kg a.i. ha−1 pendimethalin. Therefore, the use of 1.5 kg a.i. ha−1 pendimethalin can be used for effective weed management in the direct seeding of rice at an early growth stage.

Many people spend the majority of their time indoors and there is emerging evidence that interior greenery contributes to human wellbeing. Accurately capturing the amount of interior greenery is an important first step in studying its contribution to human well-being. In this study, we evaluated the accuracy of interior greenery captured using 360° panoramic images taken within a range of different interior spaces. We developed an Interior Green View Index (iGVI) based on a K-means clustering algorithm to estimate interior greenery from 360° panoramic images taken within 66 interior spaces and compared these estimates with interior greenery measured manually from the same panoramic images. Interior greenery estimated using the automated method ranged from 0% to 34.19% of image pixels within the sampled interior spaces. Interior greenery estimated using the automated method was highly correlated (r = 0.99) with interior greenery measured manually, although we found the accuracy of the automated method compared with the manual method declined with the volume and illuminance of interior spaces. The results suggested that our automated method for extracting interior greenery from 360° panoramic images is a useful tool for rapidly estimating interior greenery in all but very large and highly illuminated interior spaces.

With population growth and a shrinking rural workforce, agricultural technologies have become increasingly important. Above-ground biomass (AGB) is a key trait relevant to breeding, agronomy and crop physiology field experiments. However, measuring the biomass of a cereal plot requires cutting, drying and weighing processes, which are laborious, expensive and destructive tasks. This paper proposes a non-destructive and high-throughput method to predict biomass from field samples based on Light Detection and Ranging (LiDAR). Unlike previous methods that are based on the density of a point cloud or plant height, our biomass prediction network (BioNet) additionally considers plant structure. Our BioNet contains three modules: 1) a completion module to predict missing points due to canopy occlusion; 2) a regularization module to regularize the neural representation of the whole plot; and 3) a projection module to learn the salient structures from a bird’s eye view of the point cloud. An attention-based fusion block is used to achieve final biomass predictions. In addition, the complete dataset, including hand-measured biomass and LiDAR data, is made available to the community. Experiments show that our BioNet achieves ≈ 33% improvement over current state-of-the-art methods.

C 4 photosynthesis provides an effective solution for overcoming the catalytic inefficiency of Rubisco. The pathway is characterised by a biochemical CO 2 concentrating mechanism that operates across mesophyll and bundle sheath (BS) cells and relies on a gas tight BS compartment. A screen of a mutant population of Setaria viridis , an NADP-malic enzyme type C 4 monocot, generated using N-nitroso-N-methylurea identified a mutant with an amino acid change in the gene coding region of the ABCG transporter, a step in the suberin synthesis pathway. Here, Nile red staining, TEM, and GC/MS confirmed the alteration in suberin deposition in the BS cell wall of the mutant. We show that this has disrupted the suberin lamellae of BS cell wall and increased BS conductance to CO 2 diffusion more than two-fold in the mutant. Consequently, BS CO 2 partial pressure is reduced and CO 2 assimilation was impaired in the mutant. Our findings provide experimental evidence that a functional suberin lamellae is an essential anatomical feature for efficient C 4 photosynthesis in NADP-ME plants like S. viridis and have implications for engineering strategies to ensure future food security.

We generated antisense constructs targeting two of the five Rubisco small subunit genes (OsRBCS2 and 4) which account for between 30-40 % of the RBCS transcript abundance in leaf blades. The constructs were driven by a maize phosphoenolpyruvate carboxylase (PEPC) promoter known to have enriched expression in mesophyll cells (MCs). In the resulting lines leaf, Rubisco protein content was reduced by between 30-50 % and CO2 assimilation rate was limited under photorespiratory and non-photorespiratory conditions. A relationship between Rubisco protein content and CO2 assimilation rate was found. This was associated with a significant reduction in dry biomass accumulation and grain yield of between 37-70%. In addition to serving as a resource for reducing Rubisco accumulation in a cell-preferential manner, these lines allow us to characterize gene function and isoform specific suppression on photosynthesis and growth. Our results suggest that the knockdown of multiple genes is required to completely reduce Rubisco accumulation in MCs.

Despite significant advances to harvest index and interception efficiency, photosynthesis has remained largely unimproved through conventional breeding approaches. However, increasing photosynthetic efficiency is a key method for enhancing crop productivity, yield, and sustainability. In this study, photosynthetic and morphological traits were characterized in indica rice to examine natural variation and the potential for hybridization in the future. Additionally, broad-sense heritability (H-2) was calculated for photosynthetic traits, including, for the first time, biochemical limitations to photosynthesis. Heritability was high for CO2 assimilation in saturating light and [CO2] (A(max); H-2 = .65), the maximum rate of carboxylation (V-c,V-max; H-2 = .63), the maximum rate of electron transport (J(max); H-2 = .68), and triosephosphate utilization (TPU; H-2 = .73). Genetic advances of up to 17.7% were estimated, suggesting that it would be possible to not only select for the improvement of biochemical components of photosynthesis but also achieve significant gains in one generation. Heritability was low for CO2 assimilation at ambient [CO2] in saturating light (A(sat); H-2 = .22), suggesting that rising [CO2] may increase heritability for photosynthesis in rice.

In C4 species, β-carbonic anhydrase (CA), localized to the cytosol of the mesophyll cells, accelerates the interconversion of CO2 to HCO3-, the substrate used by phosphoenolpyruvate carboxylase (PEPC) in the first step of C4 photosynthesis. Here we describe the identification and characterization of low CO2-responsive mutant 1 (lcr1) isolated from an N-nitroso-N-methylurea- (NMU) treated Setaria viridis mutant population. Forward genetic investigation revealed that the mutated gene Sevir.5G247800 of lcr1 possessed a single nucleotide transition from cytosine to thymine in a β-CA gene causing an amino acid change from leucine to phenylalanine. This resulted in severe reduction in growth and photosynthesis in the mutant. Both the CO2 compensation point and carbon isotope discrimination values of the mutant were significantly increased. Growth of the mutants was stunted when grown under ambient pCO2 but recovered at elevated pCO2. Further bioinformatics analyses revealed that the mutation has led to functional changes in one of the conserved residues of the protein, situated near the catalytic site. CA transcript accumulation in the mutant was 80% lower, CA protein accumulation 30% lower, and CA activity ~98% lower compared with the wild type. Changes in the abundance of other primary C4 pathway enzymes were observed; accumulation of PEPC protein was significantly increased and accumulation of malate dehydrogenase and malic enzyme decreased. The reduction of CA protein activity and abundance in lcr1 restricts the supply of bicarbonate to PEPC, limiting C4 photosynthesis and growth. This study establishes Sevir.5G247800 as the major CA allele in Setaria for C4 photosynthesis and provides important insights into the function of CA in C4 photosynthesis that would be required to generate a rice plant with a functional C4 biochemical pathway.

Introduction of a C4 photosynthetic pathway into C3 rice (Oryza sativa) requires installation of a biochemical pump that concentrates CO2 at the site of carboxylation in modified bundle sheath cells. To investigate the feasibility of this, we generated a quadruple line that simultaneously accumulates four of the core C4 photosynthetic enzymes from the NADP-malic enzyme subtype, phosphoenolpyruvate carboxylase (ZmPEPC), NADP-malate dehydrogenase (ZmNADP-MDH), NADP-malic enzyme (ZmNADP-ME), and pyruvate phosphate dikinase (ZmPPDK). This led to enhanced enzyme activity and mild phenotypic perturbations but was largely neutral in its effects on photosynthetic rate. Measurements of the flux of 13CO2 through photosynthetic metabolism revealed a significant increase in the incorporation of 13C into malate, consistent with increased fixation of 13CO2 via PEP carboxylase in lines expressing the maize PEPC enzyme. However, there was no significant differences in labeling of 3-phosphoglycerate (3PGA) indicating that there was no carbon flux through NADP-ME into the Calvin-Benson cycle. There was also no significant difference in labeling of phosphoenolpyruvate (PEP) indicating that there was no carbon flux through PPDK. Crossing the quadruple line with a line with reduced glycine decarboxylase H-protein (OsGDCH) abundance led to a photosynthetic phenotype characteristic of the reduced OsGDCH line and higher labeling of malate, aspartate and citrate than in the quintuple line. There was evidence of 13C labeling of aspartate indicating 13CO2 fixation into oxaloacetate by PEPC and conversion to aspartate by the endogenous aspartate aminotransferase activity. While Kranz anatomy or other anatomical modifications have not yet been installed in these plants to enable a fully functional C4 cycle, these results demonstrate for the first-time a partial flux through the carboxylation phase of NADP-ME C4 metabolism in transgenic rice containing two of the key metabolic steps in the C4 pathway.

Convergent trait evolution is a recurrent phenomenon in all domains of the tree of life. While some convergent traits are caused by simple sequence changes, many are associated with extensive changes to the sequence and regulation of large cohorts of genes. It is unknown how organisms traverse this expansive genotype space to assemble such complex convergent phenotypes. C 4 photosynthesis is a paradigm of large-scale phenotypic convergence. Conceptual and mathematical models propose that C 4 photosynthesis evolved from ancestral C 3 photosynthesis through sequential adaptive changes. These adaptive changes could have been rapidly assembled if modifications to the activity and abundance of enzymes of the C 4 cycle was neutral in C 3 plants. This neutrality would enable populations of C 3 plants to maintain genotypes with expression levels of C 4 enzymes analogous to those in C 4 species and thus enable rapid assembly of a functional C 4 cycle from naturally occurring genotypes given shared environmental selection. Here we show that there is substantial natural variation in expression of genes encoding C 4 cycle enzymes between natural accessions of the C 3 plant Arabidopsis thaliana . We further show through targeted transgenic experiments in the C 3 crop Oryza sativa , that high expression of the majority of C 4 cycle enzymes in rice is neutral with respect to growth, development, biomass and photosynthesis. Thus, substantial variation in the abundance and activity of C 4 cycle enzymes is permissible within the limits of operation of C 3 photosynthesis and the emergence of component parts of this complex convergent trait can be facilitated by neutral variation.

Several breeding initiatives have sought to improve flag leaf performance as its health and physiology are closely correlated to rice yield. Previous studies have described natural variation of photosynthesis for flag leaves; however, none has examined their performance under the non-steady-state conditions that prevail in crop fields. Photosynthetic induction is the transient response of photosynthesis to a change from low to high light. Rice flag leaf photosynthesis was measured in both steady- and non-steady-state conditions to characterize natural variation. Between the lowest and highest performing accession, there was a 152% difference for average CO2 assimilation during induction (Ā300), a 77% difference for average intrinsic water use efficiency during induction (iWUEavg), and a 185% difference for the speed of induction (IT50), indicating plentiful variation. No significant correlation was found between steady- and non-steady-state photosynthetic traits. Additionally, measures of neither steady-state nor non-steady-state photosynthesis of flag leaves correlated with the same measures of leaves in the vegetative growth stage, with the exception of iWUEavg. Photosynthetic induction was measured at six [CO2], to determine biochemical and diffusive limitations to photosynthesis in vivo. Photosynthetic induction in rice flag leaves was limited primarily by biochemistry.

Summary Photosynthetic induction describes the transient increase in leaf CO2 uptake with an increase in light. During induction, efficiency is lower than at steady state. Under field conditions of fluctuating light, this lower efficiency during induction may cost > 20% of potential crop assimilation. Accelerating induction would boost photosynthetic and resource‐use efficiencies. Variation between rice accessions and potential for accelerating induction was analysed by gas exchange. Induction during shade to sun transitions of 14 accessions representing five subpopulations from the 3000 Rice Genome Project Panel (3K RGP) was analysed. Differences of 109% occurred in the CO2 fixed during the first 300 s of induction, 117% in the half‐time to completion of induction, and 65% in intrinsic water‐use efficiency during induction, between the highest and lowest performing accessions. Induction in three accessions with contrasting responses (AUS 278, NCS 771 A and IR64‐21) was compared for a range of [CO2] to analyse limitations. This showed in vivo capacity for carboxylation at Rubisco (Vc,max), and not stomata, as the primary limitation to induction, with significant differences between accessions. Variation in nonsteady‐state efficiency greatly exceeded that at steady state, suggesting a new and more promising opportunity for selection of greater crop photosynthetic efficiency in this key food crop.

The engineering process of C4 photosynthesis into C3 plants requires an increased activity of phosphoenolpyruvate carboxylase (PEPC) in the cytosol of leaf mesophyll cells. The literature varies on the physiological effect of transgenic maize (Zea mays) PEPC (ZmPEPC) leaf expression in Oryza sativa (rice). Therefore, to address this issue, leaf–atmosphere CO2 and 13CO2 exchanges were measured, both in the light (at atmospheric O2 partial pressure of 1.84 kPa and at different CO2 levels) and in the dark, in transgenic rice expressing ZmPEPC and wild-type (WT) plants. The in vitro PEPC activity was 25 times higher in the PEPC overexpressing (PEPC-OE) plants (~20% of maize) compared to the negligible activity in WT. In the PEPC-OE plants, the estimated fraction of carboxylation by PEPC (β) was ~6% and leaf net biochemical discrimination against 13CO2$$\left( {\Delta_{\text{bio}} } \right)$$ was ~ 2‰ lower than in WT. However, there were no differences in leaf net CO2 assimilation rates (A) between genotypes, while the leaf dark respiration rates (Rd) over three hours after light–dark transition were enhanced (~ 30%) and with a higher 13C composition $$\left( {\delta^{ 1 3} {\text{C}}_{\text{Rd}} } \right)$$ in the PEPC-OE plants compared to WT. These data indicate that ZmPEPC in the PEPC-OE rice plants contributes to leaf carbon metabolism in both the light and in the dark. However, there are some factors, potentially posttranslational regulation and PEP availability, which reduce ZmPEPC activity in vivo.

The influence of reduced glycine decarboxylase complex (GDC) activity on leaf atmosphere CO2 and 13CO2 exchange was tested in transgenic Oryza sativa with the GDC H-subunit knocked down in leaf mesophyll cells. Leaf measurements on transgenic gdch knockdown and wild-type plants were carried out in the light under photorespiratory and low photorespiratory conditions (i.e. 18.4 kPa and 1.84 kPa atmospheric O2 partial pressure, respectively), and in the dark. Under approximately current ambient O2 partial pressure (18.4 kPa pO2), the gdch knockdown plants showed an expected photorespiratory-deficient phenotype, with lower leaf net CO2 assimilation rates (A) than the wild-type. Additionally, under these conditions, the gdch knockdown plants had greater leaf net discrimination against 13CO2 (Δo) than the wild-type. This difference in Δo was in part due to lower 13C photorespiratory fractionation (f) ascribed to alternative decarboxylation of photorespiratory intermediates. Furthermore, the leaf dark respiration rate (Rd) was enhanced and the 13CO2 composition of respired CO2 (δ13CRd) showed a tendency to be more depleted in the gdch knockdown plants. These changes in Rd and δ13CRd were due to the amount and carbon isotopic composition of substrates available for dark respiration. These results demonstrate that impairment of the photorespiratory pathway affects leaf 13CO2 exchange, particularly the 13C decarboxylation fractionation associated with photorespiration.

With the development of computer vision technologies, using images acquired by aerial platforms to measure large scale agricultural fields has been increasingly studied. In order to provide a more time efficient, light weight and low cost solution, in this paper we present a highly automated processing pipeline that performs plant height estimation based on a dense point cloud generated from aerial RGB images, requiring only a single flight. A previously acquired terrain model is not required as input. The process extracts a segmented plant layer and bare ground layer. Ground height estimation achieves sub 10cm accuracy. High throughput plant height estimation has been performed and results are compared with LiDAR based measurements.

An experiment was conducted in controlled conditions in three varieties of wheat under water stress, heat and heat +water stress treatments with the objective of studying Chlorophyll a fluorescence, chlorophyll fluorescence induction kinetics and the function of Photosystem II by plant phenotyping as affected by stress. We hypothesised that during stress, specific adaptive strategies are employed by plants, such as structural and functional changes in PS II by which they acquire new homeostasis which may be protective adaptations. Water stress stress treatment was imposed on Water stress and Heat +Water stress treatments at 43 DAS. Heat treatment was imposed on 48 DAS. Maximum quantum yield of primary photochemistry was measured with PAM 2500 and OJIP was measured with FluorPen FP 100 after the onset of stress at four observation times on two days viz., pre-dawn and afternoon during stress. In addition continuous monitoring of photosynthetic efficiency was done with Monitoring PAM. Heat +Water stress stress was more detrimental as compared to Heat or Water stress alone in terms of maximum quantum yield of photochemistry. This could have been due to higher decrease in connectivity between PSII and its antennae resulting in lower photosynthetic efficiency resulting in the impairment and disruption of the electron transport. K step was observed in heat stress and heat +Water stress stress which may be because of damage to Oxygen Evolving Complex indicating that low thermostability of the complex. The stress treatments had a reduction in the plastoquinone pool size as indicated by the reduced area above the OJIP curve. Our study indicated that the instrument PAM 2500 sensed both stresses separately and combined earlier than the other instruments, so in terms of sensitivity PAM 2500 was more effective than FluorPen FP 100 and MultispeQ. Rapid screening of stress was more effectively with FluorPen FP 100 and MultispeQ than by PAM 2500.

The engineering process of C 4 photosynthesis into C 3 plants requires an increased activity of phospho enol pyruvate carboxylase (PEPC) in the cytosol of leaf mesophyll cells. The literature varies on the physiological effect of transgenic maize ( Zea mays ) PEPC ( Zm PEPC) leaf expression in Oryza sativa (rice). Therefore, to address this issue, leaf–atmosphere CO 2 and 13 CO 2 exchanges were measured, both in the light (at atmospheric O 2 partial pressure of 1.84 kPa and at different CO 2 levels) and in the dark, in transgenic rice expressing ZmPEPC and wild-type (WT) plants. The in vitro PEPC activity was 25 times higher in the PEPC overexpressing ( PEPC -OE) plants ( 20

With continued economic development in Asia the demand for high yielding varieties with premium grain quality traits is set to increase. This presents a significant challenge to plant breeders because varieties must be tailored to meet regional preferences. It is already apparent that traditional breeding techniques cannot meet this challenge and so emerging genomics technologies will have to be utilized. Genome editing tools afford the ability to efficiently and precisely manipulate the genome. Among these, the bacterial clustered, regularly interspaced, short palindromic repeat (CRISPR) associated protein 9 (Cas9) or CRISPR-Cas9 has emerged as the easiest, most economic, and efficient technology to undertake genome editing in rice. This technique allows precise site-specific gene modification or integration. In this chapter we present a method for utilizing CRISPR-Cas9 for improving grain quality traits in rice; this should enable molecular breeders to quickly and efficiently produce high yielding rice varieties tailored to meet specific cultural and regional requirements for grain quality.