Plant physiology

About: Plant physiology is a research topic. Over the lifetime, 1537 publications have been published within this topic receiving 72038 citations.

AM1 is a potential ABA substitute for drought tolerance as revealed by physiological and ultra-structural responses of oilseed rape

Abstract: Abscisic acid (ABA) is an important signaling molecule for plants under drought tolerance. However, ABA itself has many limitations to be used in agriculture practically. Recently, AM1 (ABA-mimicking ligand) has been found to replace ABA. In this study, we have investigated AM1’s potential role for drought tolerance by growing two contrasting rapeseed (Brassica napus L.) genotypes: Qinyou 8 (drought sensitive) and Q2 (drought resistant) with exogenous ABA or AM1 application under well-watered and drought-stressed conditions. Results demonstrate that drought stress has hampered plant growth (relative height growth rate, plant biomass, leaf area), plant water status (leaf relative water content, root moisture content, leaf water potential), photosynthetic gas exchange attributes like net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), transpiration rate (E); chlorophyll fluorescence parameters like photosynthetic efficiency (Fv/Fm), effective quantum yield of PSII (Φ PSII ), photochemical quenching coefficient (qL), electron transport rate (ETR) and chlorophyll content, especially for Qinyou 8 significantly compared to well-watered plants. Whereas increased root/shoot ratio (R/S), water use efficiency (WUE) and non-photochemical quenching (NPQ) was recorded in both genotypes under drought stress. On the other hand, exogenous ABA or AM1 treatment has regulated all the above parameters in a rational way to avoid drought stress. Chloroplast transmission electron microscope images, especially for Qinyou8, have revealed that oxidative stress induced by drought has blurred the grana thylakoids, increased the size or number of plastoglobules due to lipid peroxidation, and the presence of starch granules depict weak capacity to convert them into simple sugars for osmotic adjustment. However, intact grana thylakoid, few plastoglobules with no or very few starch granules were observed in the chloroplast from ABA- or AM1-treated plants under drought. More importantly, AM1-treated plants under drought stress have responded in an extremely similar way like ABA-treated ones. Finally, it is suggested that AM1 is a potential ABA substitute for plant drought tolerance.

Differential expression of photosynthesis-related genes and quantification of gas exchange in rice plants under abiotic stress

Abstract: Abiotic stresses caused by excessive cold, iron, and salt are among the main growth and yield-limiting factors of rice. Among the metabolic processes, photosynthesis stands out for being closely related to crop yields, causing a yield decline by reduced photosynthetic capacity in plants under abiotic stresses. The purpose of this study was to evaluate the differential expression of chloroplast genes involved in photosynthesis by RNA sequencing (RNA-seq) and quantify gas exchanges in leaves of rice plants exposed to cold, iron, and salt stress for 24 h. Of all genes expressed in each stress, cold had the highest number of differentially expressed genes (DEGs) related to light and chloroplast reactions, with 535 mostly down-regulated genes. Salt and iron stress was associated with 309 and 115 genes, respectively, involved in light reactions and chloroplast. The three stresses had transcripts with GOs related to light reactions, all with more than ten different GO terms. With regard to chloroplast, cold and salt stress had 12 terms of GO, and iron stress has 9 terms of GO. For gas exchange, only the parameter net assimilation rate differed significantly between stresses, with the lowest mean under cold stress. The results showed that cold stress affects photosynthesis most drastically, both at the molecular and the physiological level, and despite decreases in the net assimilation rate, changes under iron and salt stress were minor, which may be related to the tolerance of cultivar BRS Querencia.

Excess iron alters the fatty acid composition of chloroplast membrane and decreases the photosynthesis rate: a study in hydroponic pea seedlings

Abstract: As an essential micronutrient, iron (Fe) is directly involved in several fundamental processes in the photosynthetic cells. However, it is not clear if photosynthetic traits affected by high ferrous level are associated with changes in fatty acid composition in chloroplast membranes. To accomplish this, the effects of excess Fe2+ on the fatty acid composition and the fluidity properties of the chloroplast membrane, photosynthesis rate and the chlorophyll fluorescence were investigated in pea (Pisum sativum L.) seedlings grown hydroponically in nutrient solutions with 100, 200, 400 and 600 µM Fe2+ supplied as FeSO4. Increased fluidity of the chloroplast membranes was found under higher Fe2+ treatments, and this might be attributed to the increase in relative content of unsaturated fatty acids (USFA). Excess Fe2+ decreased the chlorophyll content and the electron transport rate, deactivated reaction center of photosystem II, and declined plant net photosynthetic rate. Finally, the reduced plant dry weight was observed. The results indicate that the effects of excess Fe on photosynthesis and fluidity of chloroplast membrane depend on the stress strength and duration, and the increased fluidity of chloroplast membrane may be critical in maintenance of cellular integrity under excess but not lethiferous Fe2+ treatment.

Role of nitrogen metabolism in the development of salt tolerance in barley plants

Abstract: The 7- to 8-day-old barley (Hordeum vulgare L.) seedlings grown in KNO3 solutions (1-40 mM) were characterized by the substrate activation of nitrate reductase (NR) in the apical leaf segments (1–2 cm in length), as well as by stimulated growth, broadened leaf blades, and by vigorously developed system of shortened roots. When the seedlings were grown in the presence of 20 mM KNO3, the ability of leaf segments to generate superoxide anion radical remained at the level typical of control plants grown in water. The content of 5-aminolevulinic acid (ALA) in plants grown in the presence of 20 mM KNO3 was 2.2–2.4 times higher than in control plants. The plants grown in the presence of nitrate had an elevated content of chlorophylls a and b, heme, and protein (by 42%). At the same time, the proline content was almost twofold lower than in control plants, which was due to substantial reduction (by 40%) in activity of Δ1-pyrroline-5-carboxylate synthetase (P5CS). It is concluded that the substrate activation of NR by KNO3 under normal growth conditions results in predominant utilization of glutamic acid (the primary product of inorganic nitrogen assimilation) for biosynthesis of tetrapyrroles and protein amino acids at the expense of inhibition of proline synthesis. When barley seedlings were grown in 150 mM NaCl solution, the plant growth and the root system development were suppressed to the levels of 63 ± 6% and 61 ± 11% of the control values, respectively. In the apical leaf tissues of plants adapted to NaCl, there was a slight decrease in the total NR activity (by 10%), a significant reduction in protein content (by 32%), and a parallel increase in the content of ALA (by a factor of 4.3), chlorophylls, heme, carotenoids, proline (2.2-fold) and P5CS (1.6-fold) with respect to the control values. It is proposed that the accumulation of ALA and proline under salinity-induced suppression of nitrogen assimilation results from the predominant allocation of glutamate for biosyntheses of ALA and proline at the expense of inhibition of growth-related processes requiring intense protein synthesis. The substrate activation of NR by KNO3 under salinity conditions was associated with prevailing allocation of the assimilated nitrogen for synthesis of proline and protein amino acids, which reinforced plant cell protection against salinity and stimulated plant growth.

Physiological and molecular characterization of water-stressed Chrysanthemum under robinin and chitosan treatment

Abstract: Severe water shortage limits horticultural crop growth and development, thereby compromising plant quality. Novel tools to enhance stress tolerance in medicinal horticultural crops are crucial to cope with growing environmental challenges to world crop performance. In this study, water solutions of robinin (25, 100, and 200 ppm) and/or foliar sprays of chitosan (0, 50, and 200 ppm) were applied to Chrysanthemum morifolium Ramat subjected to a 2 (2DWI) or 6 day (6DWI) irrigation intervals for 6 weeks. Morphological, physiological, and genetic markers associated with plant-response mechanisms to water stress were explored. Robinin + chitosan-treated plants showed increased morphological performance associated with enhanced chlorophyll, carbohydrates, proline, K+, Ca+2, phenols, leaf water potential, antioxidants, and leaf water content. Superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) enzymes were more active in robinin + chitosan-treated plants, while H2O2 accumulation was diminished. Higher expression levels of the Chrysanthemum antioxidant gene of zinc-finger transcription factor gene (Cm-BBX24), Chrysanthemum roots fu (DREB1A-1), Chrysanthemum heat shock protein CgHSP70, pyrroline-5-carboxylate synthetases (P5CS), pyrroline-5-carboxylate reductase (P5CR), and proline dehydrogenase (ProDH) were found in robinin- and chitosan-treated plants. Robinin + chitosan treatment stimulated the accumulation of carbohydrates, K+, Ca+2, proline, and chlorophylls to achieve osmotic adjustment and maintain turgor pressure. Accumulation of reactive oxygen species was controlled by enzymatic and non-enzymatic means, as well as the overexpression of stress-related genes (Cm-BBX24, DREB1A-1, CgHSP70, P5CS, P5CR, and ProDH) in robinin + chitosan-treated plants. Plant-response mechanisms for enhanced drought resistance interacted under robinin + chitosan treatment to improve plant performance under stress conditions.