Reduced abscisic acid content is responsible for enhanced sucrose accumulation by potassium nutrition in vegetable soybean seeds

Potassium fertilizer improves drought stress alleviation potential in sesame by enhancing photosynthesis and hormonal regulation

Soil-potassium (K) low availability and drought stress are limiting factors to crop productivity in arid and semiarid regions. A pot experiment with four K soil supplies (0, 60, 120 and 180 K₂O kg ha^-1) and exposed to drought stress with 50 ± 5% field capacity was performed to investigate the function of K in protecting sesame plants from the adverse effects of drought based on the related physio-biochemical traits. The water stress was applied during flowering by withholding water for 6 days, and then rewatering to a well-watered level (75 ± 5% field capacity). Results showed that drought stress substantially reduced leaf relative water content (RWC), stomatal conductance (G_s), transpiration rate (T_r), photosynthetic rate (P_n), maximum PSII yield (F_v/F_m), and actual quantum yield of PSII (Ф_PSII), leading to greater non-photochemical quenching (qN) and stomatal limitation (L_s), thereby resulting in a decreased yield in contrast with well-watered sesame plants. Incidentally, K was more effective in promoting yield production under drought stress relative to well-watered conditions, and the optimal K application was 120 kg ha^-1, which primarily attributed to the enhanced photosynthetic and plant water retaining ability. Specifically, plants receiving K supply showed greater leaf gas exchange traits, higher F_v/F_m and Ф_PSII values, and superior water use efficiency as compared to K-deficiency plants in both water regimes. Moreover, K can ameliorate the adverse effects of drought by improving salicylic acid (SA) while conversely decreasing abscisic acid (ABA) and jasmonic acid (JA) concentrations that are involved in controlling stomatal closure. It is noted that significant correlations between the seed yield, gas exchange parameters, and aforementioned endogenous hormones were observed. In conclusion, the K application can improve the sesame plant's potential to maintain functionality regarding photosynthetic response and phytohormone regulation under drought stress, and ultimately, enhancing the sesame's productivity.

Irradiation with carbon ion beams affects soybean nutritional quality in early generations

As people's demand for healthy diet increases, improving soybean seed nutritional quality is becoming as important as yield. Carbon ion beam radiation (CIBR) is an effective method to create soybean mutants, and thus breeding cultivars with better seed nutritional quality. In this study, the high-yield soybean line 'Dongsheng 28' was used, and three CIBR doses (100, 120, and 140 Gy) were used to explore the characteristics of quality separation and variation in the offspring of early mutant populations. Eleven quality traits, including protein, oil, sucrose, soluble sugar, iron (Fe), manganese (Mn), zinc (Zn), cupper (Cu), daidzin, glycitin, and genistin concentrations were analyzed in the M₂ and M₃ generations. The results revealed that the range of protein and oil concentration of all three CIBR doses changed by 38.5-42.9% and 18.8-23.8% in the M₂ and M₃ generations, respectively, while soluble sugar and sucrose concentrations changed by 48.1-123.4 and 22.7-74.7 mg/g, with significant effects by 140 Gy across the two generations. Therefore, around the optimum range, a higher CIBR dose is better for high protein, oil, and sugar varieties selection. In general, irradiation raised isoflavone concentrations, but 140 Gy had an inhibitory effect on isoflavone concentrations in the M₃ generation. Although a variety could not be released in the M₂ or M₃ generation, the results of this study have important guiding significance for the targeted cultivation of specific nutritional quality materials. For instance, a lower irradiation dose is preferable when breeding targets are higher isoflavones and Mn concentrations. It is essential to increase the irradiation dose if the breeding targets contain high levels of protein, oil, sucrose, soluble sugars, Fe, Zn, and Cu.

Genome-wide association analysis discovered new loci and candidate genes associated with low-phosphorus tolerance based on shoot mineral elements concentrations in soybean

Phosphorus (P) deficiency is one of the major limitations for soybean production. Moreover, it has been well reported P and other mineral elements function interdependently or antagonistically to control nutrients homeostasis in plants. Thus, it is urgently needed to understand the genetic mechanism of the accumulation of mineral elements in response to low-P stress. In this study, to identify single nucleotide polymorphisms (SNPs) and candidate genes controlling the accumulation of mineral elements suffering low-P stress in seedling stage of soybean plants, we measured concentrations of mineral elements, including P, Zn, Fe, Mn, Mg and Ca, in shoots of 211 soybean accessions under normal phosphorus (+P) and low phosphorus (-P) conditions in two hydroponic experiments. And genome-wide association study (GWAS) using high density NJAU 355K SoySNP array and concentrations of five of these mineral elements except P was performed. A total of 36 SNPs distributed on 13 chromosomes were identified to be significantly associated with low-P tolerance, and nine SNPs on chromosome 10 formed a SNP cluster. Meanwhile, the candidate gene GmFeB1 was found to serve as a negative regulator element involved in soybean P metabolism and the haplotype1 (Hap1) of GmFeB1 showed significantly higher shoot Fe concentration under -P condition than that of Hap2. In summary, we uncover 36 SNPs significantly associated with shoot mineral elements concentrations under different P conditions and a soybean low-P related gene GmFeB1, which will provide additional genetic information for soybean low-P tolerance and new gene resources for P-efficient soybean varieties breeding.

Potassium in plants: Growth regulation, signaling, and environmental stress tolerance

Potassium (K) is an essential element for the growth and development of plants; however, its scarcity or excessive level leads to distortion of numerous functions in plants. It takes part in the control of various significant functions in plant advancement. Because of the importance index, K is regarded second after nitrogen for whole plant growth. Approximately, higher than 60 enzymes are reliant on K for activation within the plant system, in which K plays a vital function as a regulator. Potassium provides assistance in plants against abiotic stress conditions in the environment. With this background, the present paper reviews the physiological functions of K in plants like stomatal regulation, photosynthesis and water uptake. The article also focuses upon the uptake and transport mechanisms of K along with its role in detoxification of reactive oxygen species and in conferring tolerance to plants against abiotic stresses. It also highlights the research progress made in the direction of K mediated signaling cascades.

Nutritional quality of different potassium efficiency types of vegetable soybean as affected by potassium nutrition

Pot experiments were conducted in 2017, 2019, and 2020 to examine the effects of potassium nutrition on the nutritional components of vegetable soybeans with different K efficiency at immature and mature stages. Two vegetable soybean varieties with higher K efficiency and two varieties with lower K efficiency were studied in the low available K soil under the condition of no K and normal K fertilization. The results indicated that almost all nutritional components in vegetable soybean were affected by K, genotypes, inter-annual differences, and their interactions. In general, no K fertilization increased protein and amino acid concentrations but decreased oil, soluble sugar, sucrose, K, Mg, and Fe concentrations in immature and mature vegetable soybean. The sensitivity of nutritional components to K nutrition differed among varieties. For instance, K high-efficiency varieties generally exhibited higher protein and amino acid concentrations without K application. K high-efficiency vegetable soybeans are low-K tolerance varieties to isoflavones. The results of this study provide insights for high yield and quality vegetable soybean breeding against soil K deficiency.

Potassium enhances cadmium resistance ability of Panax notoginseng by brassinolide signaling pathway-regulated cell wall pectin metabolism

The mechanism of how potassium (K) attenuates cadmium (Cd)-induced demethylation and anabolism of cell wall (CW) pectin through the brassinolide (BR) signaling pathway was verified in Panax notoginseng (Burk.). The P. notoginseng pectin methylesterase gene (PnPME1) was cloned and functionally verified in tobacco. Pectin and BR metabolism, Cd content and the pectin methylation degree (PMD) were detected in response to K, 2,4-epibrassinolide (EBL), and brassinazole treatments of P. notoginseng and tobacco under Cd stress. Activity of the main root pectin methylesterase enzyme (PME) was promoted by 22.29% under the EBL treatment, and Cd content increased by 29.03% under Cd stress. Potassium reduced PME activity and Cd content in main root pectin by 61.03% and 50.73%, respectively, under the EBL and Cd co-treatment. Potassium inhibited the promoting effects of Cd stress on the expression of PnPME1 by 57.04%. Potassium also inhibited expression of BR synthesis genes PnDET2, PnROT3, PnCYP90A1, and PnBR6OX1 by 65.61%, 52.02%, 47.36%, and 55.16%, respectively, and reduced the accumulation of Cd. The PnPME1 was located in the CW. The activity of transgenic tobacco root PME was higher than that of the wild-type, while the PMD was significantly lower. The regulatory effects of K and EBL on tobacco root pectin metabolism were consistent with those in P. notoginseng. In conclusion, K downregulated the expression of BR synthesis genes in P. notoginseng roots under Cd stress and reduced the production of BRs, which inhibited PnPME1 expression. The reduction in PME activity increased the PMD, which reduced the accumulation of Cd.

Potassium: A key modulator for cell homeostasis

Potassium (K) is the most vital and abundant macro element for the overall growth of plants and its deficiency or, excess concentration results in many diseases in plants. It is involved in regulation of many crucial roles in plant development. Depending on soil-root interactions, complex soil dynamics often results in unpredictable availability of the elements. Based on the importance index, K is considered to be the second only to nitrogen for the overall growth of plants. More than 60 enzymes within the plant system depend on K for its activation, in which K act as a key regulator. K helps plants to resist several abiotic and biotic stresses in the environment. We have reviewed the research progress about K's role in plants covering various important considerations of K highlighting the effects of microbes on soil K⁺; K and its contribution to adsorbed dose in plants; the importance of K⁺ deficiency; physiological functions of K⁺ transporters and channels; and interference of abiotic stressor in the regulatory role of K. This review further highlights the scope of future research regarding K.

Abscisic acid synergizes with sucrose to enhance grain yield and quality of rice by improving the source-sink relationship

BACKGROUND

Abscisic acid (ABA) and sucrose act as molecular signals in response to abiotic stress. However, how their synergy regulates the source-sink relationship has rarely been studied. This study aimed to reveal the mechanism underlying the synergy between ABA and sucrose on assimilates allocation to improve grain yield and quality of rice. The early indica rice cultivar Zhefu802 was selected and planted in an artificial climate chamber at 32/24 °C (day/night) under natural sunlight conditions. Sucrose and ABA were exogenously sprayed (either alone or in combination) onto rice plants at flowering and 10 days after flowering.

RESULTS

ABA plus sucrose significantly improved both the grain yield and quality of rice, which was mainly a result of the higher proportion of dry matter accumulation and non-structural carbohydrates in panicles. These results were mainly ascribed to the large improvement in sucrose transport in the sheath-stems in response to the ABA plus sucrose treatment. In this process, ABA plus sucrose significantly enhanced the contents of starch, gibberellic acids, and zeatin ribosides as well as the activities and gene expression of enzymes involved in starch synthesis in grains. Additionally, remarkable increases in trehalose content and expression levels of trehalose-6-phosphate synthase1, trehalose-6-phosphate phosphatase7, and sucrose non-fermenting related protein kinase 1A were also found in grains treated with ABA plus sucrose.

CONCLUSION

The synergy between ABA and sucrose increased grain yield and quality by improving the source-sink relationship through sucrose and trehalose metabolism in grains.

Appropriate Ammonium-Nitrate Ratio Improves Nutrient Accumulation and Fruit Quality in Pepper (Capsicum annuum L.)

Ammonium (NH4+) and nitrate (NO3−) are the two forms of inorganic nitrogen essential for physiological and biochemical processes in higher plants, but little is known about how the NH4+:NO3− ratio may affect nitrogen metabolism. This study determined the effect of NH4+:NO3− ratios on plant growth, accumulation, and distribution of nutrient elements, fruit quality, enzyme activity, and relative expression of genes involved in nitrogen (N) metabolism in pepper (Capsicum annuum L.). In a pod experiment, the NH4+:NO3− ratios of 0:100, 12.5:87.5, 25:75, 37.5:62.5, and 50:50 were arranged in a complete randomized design with three replicates. The application of NH4+:NO3− at 25:75 resulted in highest dry matter and N, phosphorus (P), and potassium (K) accumulation. Pepper treated with 25:75 ratio increased root length, surface areas, and root volume and tips. The contents of vitamin C, soluble sugar, soluble protein, total phenols, flavonoids, and capsaicinoids in the fruits were significantly higher with the NH4+:NO3− ratio of 25:75 compared with 0:100 treatment, while lowering nitrate content was found in NH4+:NO3− ratios of 25:75, 37.5:62.5, and 50:50 treatments. Activity of glutamine synthetase (GS), glutamate synthases (GOGAT) enzyme and the levels of relative expression of genes coding these enzymes were superior when the NH4+:NO3− ratio of 25:75 were applied. Therefore, an appropriate ratio of NH4+:NO3− (25:75) in nitrogen application can stimulate root development, promote enzyme activities, and enhance the productivity and fruit quality in pepper.

Potassium: A Vital Regulator of Plant Responses and Tolerance to Abiotic Stresses

Among the plant nutrients, potassium (K) is one of the vital elements required for plant growth and physiology. Potassium is not only a constituent of the plant structure but it also has a regulatory function in several biochemical processes related to protein synthesis, carbohydrate metabolism, and enzyme activation. Several physiological processes depend on K, such as stomatal regulation and photosynthesis. In recent decades, K was found to provide abiotic stress tolerance. Under salt stress, K helps to maintain ion homeostasis and to regulate the osmotic balance. Under drought stress conditions, K regulates stomatal opening and helps plants adapt to water deficits. Many reports support the notion that K enhances antioxidant defense in plants and therefore protects them from oxidative stress under various environmental adversities. In addition, this element provides some cellular signaling alone or in association with other signaling molecules and phytohormones. Although considerable progress has been made in understanding K-induced abiotic stress tolerance in plants, the exact molecular mechanisms of these protections are still under investigation. In this review, we summarized the recent literature on the biological functions of K, its uptake, its translocation, and its role in plant abiotic stress tolerance.