Arginine Increases Tolerance to Nitrogen Deficiency in Malus hupehensis via Alterations in Photosynthetic Capacity and Amino Acids Metabolism

Arginine plays an important role in the nitrogen (N) cycle because it has the highest ratio of N to carbon among amino acids. In recent years, there has been increased research interest in improving the N use of plants, reducing the use of N fertilizer, and enhancing the tolerance of plants to N deficiency. Here, the function of arginine in the growth of apple (Malus hupehensis) under N deficiency was explored. The application of 100 μmol L–1 arginine was effective for alleviating N-deficiency stress. Exogenous arginine promoted the absorption and use of N, phosphorus (P), and potassium (K) under low N stress. The net photosynthetic rate, maximal photochemical efficiency of photosystem II, and chlorophyll content were higher in treated plants than in control plants. Exogenous arginine affected the content of many metabolites, and the content of many amino acids with important functions was significantly increased, such as glutamate and ornithine, which play an important role in the urea cycle. Half of the metabolites were annotated to specialized metabolic pathways, including the synthesis of phenolic substances, flavonoids, and other substances with antioxidant activity. Our results indicate that arginine promotes the plant photosynthetic capacity and alters amino acid metabolism and some antioxidants including phenolic substances and flavonoids to improve the tolerance of apple to N deficiency, possibly through the improvement of arginine content, and the absorption of mineral.

Regulation Mechanism of Exogenous Brassinolide on Bulbil Formation and Development in Pinellia ternata

The bulbil is the propagative organ of the P. ternata, which has a great effect on the yield of P. ternata. It is well known that plant hormones play important roles in bulbil formation and development. However, there is not clear about brassinolide (BR) regulation on bulbil formation and development. In this study, we revealed the effects of BR and BR biosynthesis inhibitors (propiconazole, Pcz) application on the histological observation, starch and sucrose metabolism, photosynthesis pathway, and hormone signaling pathway of P. ternata. The results showed that BR treatment reduced starch catabolism to maltodextrin and maltose in bulbil by decreasing BAM and ISA genes expression and increased cellulose catabolism to D-glucose in bulbil by enhancing edg and BGL genes expression. BR treatment enhanced the photosynthetic pigment content and potential maximum photosynthetic capacity and improved the photoprotection ability of P. ternata by increasing the dissipation of excess light energy to heat, thus reduced the photodamage in the PSII center. BR treatment increased the GA and BR content in bulbil of P. ternata, and decreased the ABA content in bulbil of P. ternata. Pcz treatment increased the level of GA, SL, ABA, and IAA in bulbil of P. ternata. BR regulated the signal transduction of BR, IAA, and ABA to regulate the formation and development of bulbil in P. ternata. These results provide molecular insight into BR regulation on bulbil formation and development.

Vertical profiles of leaf photosynthesis and leaf traits and soil nutrients in two tropical rainforests in French Guiana before and after a 3-year nitrogen and phosphorus addition experiment

Terrestrial biosphere models typically use the biochemical model of Farquhar, von Caemmerer, and Berry (1980) to simulate photosynthesis, which requires accurate values of photosynthetic capacity of different biomes. However, data on tropical forests are sparse and highly variable due to the high species diversity, and it is still highly uncertain how these tropical forests respond to nutrient limitation in terms of C uptake. Tropical forests often grow on soils low in phosphorus (P) and are, in general, assumed to be P rather than nitrogen (N) limited. However, the relevance of P as a control of photosynthetic capacity is still debated. Here, we provide a comprehensive dataset of vertical profiles of photosynthetic capacity and important leaf traits, including leaf N and P concentrations, from two 3-year, large-scale nutrient addition experiments conducted in two tropical rainforests in French Guiana. These data present a unique source of information to further improve model representations of the roles of N, P, and other leaf nutrients in photosynthesis in tropical forests. To further facilitate the use of our data in syntheses and model studies, we provide an elaborate list of ancillary data, including important soil properties and nutrients, along with the leaf data. As environmental drivers are key to improve our understanding of carbon (C) and nutrient cycle interactions, this comprehensive dataset will aid to further enhance our understanding of how nutrient availability interacts with C uptake in tropical forests. The data are available at https://doi.org/10.5281/zenodo.5638236 (Verryckt, 2021).

Estimating photosynthetic capacity from optimized Rubisco–chlorophyll relationships among vegetation types and under global change

The maximum rate of carboxylation (Vcmax), a key parameter indicating photosynthetic capacity, is commonly fixed as a constant by vegetation types and/or varies according to empirical scaling functions in earth system models (ESMs). As such, the setting of Vcmax results in uncertainties of estimated carbon assimilation. It is known that the coupling between leaf chlorophyll and Rubisco (ribulose-1,5-biphosphate carboxylase-oxygenase) contents can be applied to estimate Vcmax. However, how this coupling is affected by environmental changes and varies among plant functional types (PFTs) has not been well investigated yet. The effect of varying coupling between chlorophyll and Rubisco contents on the estimation of Vcmax is still not clear. In this study, we compiled data from 76 previous studies to investigate the coupling between Chlorophyll (Chl) and Rubisco (Rub), in different PFTs and under different environmental conditions. We also assessed the ability of a Rub-based semi-mechanistic model to estimate Vcmax normalized to 25 °C (Vcmax25) based on the Rub–Chl relationship. Our results revealed strong, linear Rub-Chl relationships for different PFTs (R2 = 0.73, 0.67, 0.54, and 0.72 for forest, crop, grass and shrub, and C4 plants, respectively). The Rub–Chl slope of natural C3 PFTs was consistent and significantly different from those of crops and C4 plants. A meta-analysis indicated that reduced light intensity, elevated CO2, and nitrogen addition strongly altered Rub/Chl. A semi-mechanistic model based on PFT-specific Rub–Chl relationships was able to estimate Vcmax25 with high confidence. Our findings have important implications for improving global carbon cycle modeling by ESMs through the improved parameterization of Vcmax25 using remotely sensed Chl content.

Ploidy level enhances the photosynthetic capacity of a tetraploid variety of Acer buergerianum Miq.

Background Polyploidy plays an important role in plant breeding and has widespread effects on photosynthetic capacity. To determine the photosynthetic capacity of the tetraploid variety Acer buergerianum Miq. ‘Xingwang’, we compared the gas exchange parameters, chloroplast structure, chlorophyll contents, and chlorophyll fluorescence parameters between the tetraploid Acer buergerianum ‘Xingwang’ and the diploid ‘S4’. To evaluate the effects of genome duplication on the photosynthetic capacity of Acer buergerianum ‘Xingwang’, the transcriptomes of the autotetraploid ‘Xingwang’ and the diploid ‘S4’ of A. buergerianum were compared. Methods The ploidy of Acer buergerianum ‘Xingwang’ was identified by flow cytometry and the chromosome counting method. An LI-6800 portable photosynthesis system analyzer was used to assess the gas exchange parameters of the tetraploid variety ‘Xingwang’ and diploid variety ‘S4’ of A. buergerianum. We used a BioMate 3S ultraviolet-visible spectrophotometer and portable modulated fluorometer to measure the chlorophyll contents and chlorophyll fluorescence parameters, respectively, of ‘Xingwang’ and ‘S4’. Illumina high-throughput sequencing technology was used to identify the differences in the genes involved in the photosynthetic differences and determine their expression characteristics. Results The single-cell DNA content and chromosome number of the tetraploid ‘Xingwang’ were twice those found in the normal diploid ‘S4’. In terms of gas exchange parameters, the change in stomatal conductance, change in intercellular CO2 concentration, transpiration rate and net photosynthetic rate of ‘Xingwang’ were higher than those of the diploid ‘S4’. The chlorophyll contents, the maximal photochemical efficiency of PSII and the potential photochemical efficiency of PSII in ‘Xingwang’ were higher than those of ‘S4’. The chloroplasts of ‘Xingwang’ contained thicker thylakoid lamellae. By the use of Illumina sequencing technology, a total of 51,807 unigenes were obtained; they had an average length of 1,487 nt, and the average N50 was 2,034 nt. The lengths of most of the unigenes obtained ranged from 200–300 bp, with an average value of 5,262, followed by those longer than 3,000 bp, with an average value of 4,791. The data revealed numerous differences in gene expression between the two transcriptomes. In total, 24,221 differentially expressed genes were screened, and the percentage of differentially expressed genes was as high as 46.75% (24,224/51,807), of which 10,474 genes were upregulated and 13,747 genes were downregulated. We analyzed the key genes in the photosynthesis pathway and the porphyrin and chlorophyll metabolism pathway; the upregulation of HemB may promote an increase in the chlorophyll contents of ‘Xingwang’, and the upregulation of related genes in PSII and PSI may enhance the light harvesting of ‘Xingwang’, increasing its light energy conversion efficiency.

Photosynthetic enhancement, lifespan extension, and leaf area enlargement in flag leaves increased the yield of transgenic rice plants overproducing Rubisco under sufficient N fertilization

Background: Improvement in photosynthesis is one of the most promising approaches to increase grain yields in crop plants. In our previous research using an isolated experimental paddy field, transgenic rice plants overproducing Rubisco by 30% (RBCS-sense rice plants) showed up to 28% increase in grain yields under sufficient nitrogen (N) fertilization. Furthermore, the plant N contents above-ground sections and Rubisco contents of the flag leaves were higher in the RBCS-sense rice plants than the wild-type rice plants during the ripening period, which may be reasons for the increased yields.Result: In this research, the photosynthetic capacity and canopy architecture were analyzed to explore factors for the increased yields of RBCS-sense rice plants. It was found that N had already been preferentially distributed into the flag leaves at the early ripening stage, contributing to maintaining higher Rubisco content levels in the enlarged flag leaves and extending the lifespan of the flag leaves of RBCS-sense rice plants throughout ripening periods under sufficient N fertilization. The higher amounts of Rubisco also improved the photosynthetic activity in the flag leaves throughout the ripening period. Although the enlarged flag leaves of the RBCS-sense rice plants occupied large spatial areas of the uppermost layer in the canopy, no significant prevention of light penetration to leaves below the flag leaves was observed. Additionally, since the CO2 assimilation rates of lower leaves between wild-type and RBCS-sense rice plants were the same at the early ripening stage, the lower leaves did not contribute to an increase in yields between the two genotypes.Conclusion: It was concluded that improvements in the photosynthetic capacity by higher leaf N and Rubisco contents, enlarged the leaf area, and extended the lifespan of flag leaves, causing an increase in grain yields of RBCS-sense rice plants grown under sufficient N fertilization.

Could black anti-hail net have an extra role as an amelioration agent against heat stress in kiwifruit?

BACKGROUND: Kiwifruit plants are extremely sensitive to hail storms. Black anti-hail nets are the most frequently used in kiwifruit culture, to protect both the plant and current as well as future production. OBJECTIVE: The present trial aimed to assess if the black hail net could also serve as an amelioration agent against high temperature and irradiance during the summer months. METHODS: The photosynthetic capacity, the yield, and fruit quality (carbohydrates, organic acids, phenolic compounds, and antioxidant capacity) of “Hayward” kiwifruit cultivar, both at harvest and after three months of storage were evaluated. RESULTS: Photosynthetic capacity under the net was slightly higher compared to control, while leaf temperature was always lower during the summer and autumn. The yield was significantly enhanced under the net, while the fruits exhibited higher titratable acidity, organic acids, and ascorbic acid concentration. After the storage, fruits produced from vines grown under net still had higher organic acid content, as well as total soluble solids but lower antioxidant capacity compared to control. CONCLUSIONS: Net installation above kiwifruit canopy seems to alleviate the effects of high temperature and heat load on kiwifruit vines, under saturating light intensity, inducing higher yields with good fruit quality.

IMPACT OF THE INVASIVE CUSCUTA CAMPESTRIS ON VEGETATIVE COVER AND PLANT BIODIVERSITY IN HOMA- BAY COUNTY

Purpose: This research paper focused on the impact of Cuscuta campestris on vegetative cover and plant biodiversity in Homa-Bay County. The specific objective was to investigate the impact on plant growth and development with indicator as photosynthetic capacity of preferred host plants and chlorophyll content and leaf weight as the parameters. Methodology: The study was conducted in hot-spot areas of invasion, Rachuonyo North, Homa Bay town and Suba North using Completely Randomized Experimental Block Design. The data was collected through field observation and laboratory analysis. The study used descriptive and correlation data analysis procedures to show the impact on photosynthetic capacity, ANOVA to determine statistical significant difference among the obtained results for each parameter of the infected and uninfected samples. Variance analysis were conducted using SPSS 20 (IBM Corp. Armonk, NY, USA) and differences between means tested by ANOVA. Values of P ≤ 0.05 were considered significantly different. Findings: The results showed that the invasion was more intense in Theveta peruvinia and Euphorbia tirucalli species. Mean leaf amounts of chlorophyll were observed to decline with chlorophyll a from 3.97 to 1.59 mg/g and chlorophyll b from 2.65 to 1.18 mg/g and total chlorophyll value from 6.62 to 2.76 mg/g on infection resulting to reduced photosynthetic efficiency and low organic material formation. Leaf wet and dry weight significantly decreased in both infected varieties. The mean wet weight of 17.61g in infected was significantly different, F (1, 4) = 235.74, p< .05, from the mean wet weight of 24.23g in the uninfected Yellow Oleander while the mean dry weight of 5.55g in infected was significantly different, F (1, 4) = 159.72, p< .05, from mean dry weight of 7.87g in uninfected Yellow Oleander. Similarly, significant difference, F (1, 4) = 714.64, p< .05, was observed in Calliandra calothyrsus variety. These demonstrated how C. campestris is detrimental causing ecological impacts with direct effects on plant biodiversity by reducing growth and development of infected host plant and even leading to death. Unique Contributions to Theory, Practice and Policy: The paper recommends intense sensitization of the community on the impacts of dodder from the findings for an enhanced understanding and need for management and control. The findings to be disseminated through workshops involving farmers, NGOs and community based organisations, academic conferences and publications to help create awareness on the impacts and mobilize the entire public on management and possible total eradication. Further research to investigate on nutrients of attraction in the preferred host plants with an aim of permanent solution for total eradication in order to restore the vegetative cover and plant biodiversity.

Brassinosteroids in Plants: Crosstalk with Small-Molecule Compounds

Brassinosteroids (BRs) are known as the sixth type of plant hormone participating in various physiological and biochemical activities and play an irreplaceable role in plants. Small-molecule compounds (SMCs) such as nitric oxide (NO), ethylene, hydrogen peroxide (H2O2), and hydrogen sulfide (H2S) are involved in plant growth and development as signaling messengers. Recently, the involvement of SMCs in BR-mediated growth and stress responses is gradually being discovered in plants, including seed germination, adventitious rooting, stem elongation, fruit ripening, and stress responses. The crosstalk between BRs and SMCs promotes plant development and alleviates stress damage by modulating the antioxidant system, photosynthetic capacity, and carbohydrate metabolism, as well as osmotic adjustment. In the present review, we try to explain the function of BRs and SMCs and their crosstalk in the growth, development, and stress resistance of plants.