Plant physiology

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

Hormonal interplay during adventitious root formation in flooded tomato plants

Abstract: Soil flooding, which results in a decline in the availability of oxygen to submerged organs, negatively affects the growth and productivity of most crops. Although tomato (Solanum lycopersicum) is known for its sensitivity to waterlogging, its ability to produce adventitious roots (ARs) increases plant survival when the level of oxygen is decreased in the root zone. Ethylene entrapment by water may represent the first warning signal to the plant indicating waterlogging. We found that treatment with the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) and the auxin transport inhibitor 1-naphthylphthalamic acid (NPA) resulted in a reduction of AR formation in waterlogged plants. We observed that ethylene, perceived by the Never Ripe receptor, stimulated auxin transport. In a process requiring the Diageotropica gene, auxin accumulation in the stem triggered additional ethylene synthesis, which further stimulated a flux of auxin towards to the flooded parts of the plant. Auxin accumulation in the base of the plant induces growth of pre-formed root initials. This response of tomato plants results in a new root system that is capable of replacing the original one when it has been damaged by submergence.

SAUR39, a Small Auxin-Up RNA Gene, Acts as a Negative Regulator of Auxin Synthesis and Transport in Rice

Abstract: The phytohormone auxin plays a critical role for plant growth by regulating the expression of a set of genes. One large auxin-responsive gene family of this type is the small auxin-up RNA (SAUR) genes, although their function is largely unknown. The expression of the rice (Oryza sativa) SAUR39 gene showed rapid induction by transient change in different environmental factors, including auxin, nitrogen, salinity, cytokinin, and anoxia. Transgenic rice plants overexpressing the SAUR39 gene resulted in lower shoot and root growth, altered shoot morphology, smaller vascular tissue, and lower yield compared with wild-type plants. The SAUR39 gene was expressed at higher levels in older leaves, unlike auxin biosynthesis, which occurs largely in the meristematic region. The transgenic plants had a lower auxin level and a reduced polar auxin transport as well as the down-regulation of some putative auxin biosynthesis and transporter genes. Biochemical analysis also revealed that transgenic plants had lower chlorophyll content, higher levels of anthocyanin, abscisic acid, sugar, and starch, and faster leaf senescence compared with wild-type plants at the vegetative stage. Most of these phenomena have been shown to be negatively correlated with auxin level and transport. Transcript profiling revealed that metabolic perturbations in overexpresser plants were largely due to transcriptional changes of genes involved in photosynthesis, senescence, chlorophyll production, anthocyanin accumulation, sugar synthesis, and transport. The lower growth and yield of overexpresser plants was largely recovered by exogenous auxin application. Taken together, the results suggest that SAUR39 acts as a negative regulator for auxin synthesis and transport.

Effects of cobalt on plants

Abstract: Cobalt, a transition element, is an essential component of several enzymes and co-enzymes. It has been shown to affect growth and metabolism of plants, in different degrees, depending on the concentration and status of cobalt in rhizosphere and soil. Cobalt interacts with other elements to form complexes. The cytotoxic and phytotoxic activities of cobalt and its compounds depend on the physico-chemical properties of these complexes, including their electronic structure, ion parameters (charge-size relations) and coordination. Thus, the competitive absorption and mutual activation of associated metals influence the action of cobalt on various phytochemical reactions. The distribution of cobalt in plants is entirely species-dependent. The uptake is controlled by different mechanisms in different species. Biosorption involves ion-exchange mechanism in algae, but in fungi both metabolism-independent and -dependent processes are operative. Physical conditions like salinity, temperature, pH of the medium, and presence of other metals influence the process of uptake and accumulation in algae, fungi, and mosses. Toxic concentrations inhibit active ion transport. In higher plants, absorption of Co2+ by roots involves active transport. Transport through the cortical cells is operated by both passive diffusion and active process. In the xylem, the metal is mainly transported by the transpirational flow. Distribution through the sieve tubes is acropetal by complexing with organic compounds. The lower mobility of Co2+ in plants restricts its transport to leaves from stems. Cobalt is not found at the active site of any respiratory chain enzymes. Two sites of action of Co2+ are found in mitochondrial respiration since it induces different responses toward different substrates like α-keto glutarate and succinate. In lower organisms, Co2+ inhibits tetraphyrrole biosynthesis, but in higher plants it probably participates in chlorophyll b formation. Exogenously added metal causes morphological damage in plastids and changes in the chlorophyll contents. It also inhibits starch grain differentiation and alters the structure and number of chloroplasts per unit area of leaf. The role of cobalt in photosynthesis is controversial. Its toxic effect takes place by inhibition of PS2 activity and hence Hill reaction. It inhibits either the reaction centre or component of PS2 acceptor by modifying secondary quinone electron acceptor Qb site. Co2+ reduces the export of photoassimilates and dark fixation of CO2. In C4 and CAM plants, it hinders fixation of CO2 by inhibiting the activity of enzymes involved. Cobalt acts as a preprophase poison and thus retards the process of karyokinesis and cytokinesis. The action of cobalt on plant cells is mainly turbagenic. Cobalt compounds act on the mitotic spindle, leading to the formation of chromatin bridges, fragmentation, and sticky bridges at anaphase and binucleate cells. High concentrations of cobalt hamper RNA synthesis, and decrease the amounts of the DNA and RNA probably by modifying the activity of a large number of endo- and exonucleases. The mutagenic action of cobalt salts results in mitochondrial respiratory deficiency in yeasts. In cytokinesis-deficient mutant of Chlamydomonas it increases the amount of sulfhydryl compounds. Cobalt has been shown to alter the sex of plants like Cannabis sativa, Lemna acquinoclatis, and melon cultivars. It decreases the photoreversible absorbance of phytochrome in pea epicotyl and interferes with heme biosynthesis in fungi. Low concentration of Co2+ in medium stimulates growth from simple algae to complex higher plants. Relatively higher concentrations are toxic. A similar relationship is seen with crop yield when the metal is used in the form of fertilizer, pre-seeding, and pre-sowing chemicals. Toxic effect of cobalt on morphology include leaf fall, inhibition of greening, discolored veins, premature leaf closure, and reduced shoot weight. Being a component of vitamin B12 and cobamide coenzyme, Co2+ helps in the fixation of molecular nitrogen in root nodules of leguminous plants. But in cyanobacteria, CoCl2 inhibits the formation of heterocyst, ammonia uptake, and nitrate reductase activity. The interaction of cobalt with other metals mainly depends on the concentration of the metals used. For example, high levels of Co2+ induce iron deficiency in plants and suppress uptake of Cd by roots. It also interacts synergistically with Zn, Cr, and Sn. Ni overcomes the inhibitory effect of cobalt on protonemal growth of moss, thus indicating an antagonistic relationship. The beneficial effects of cobalt include retardation of senescence of leaf, increase in drought resistance in seeds, regulation of alkaloid accumulation in medicinal plants, and inhibition of ethylene biosynthesis. In lower plants, cobalt tolerance involves a cotolerance mechanism. The mechanism of resistance to toxic concentration of cobalt may be due to intracellular detoxification rather than defective transport. In higher plants, only a few advanced copper-tolerant families showed cotolerance to Co2+. Tolerance toward Co2+ may sometimes determine the taxonomic shifting of several members of Nyssaceae. Due to the high cobalt content in serpentine soil, essential element uptake by plants is reduced, a phenomenon known as “serpentine problem,” for New Caledonian families like Flacourtiaceae. Large amounts of calcium in soil may compensate for the toxic effects of heavy metals in adaptable genera grown in this type of soil. The biomagnification of potentially toxic elements, such as cobalt from coal ash or water into food webs, needs additional study for effective biological filtering.

Comparative effects of salt-stress and alkali-stress on the growth, photosynthesis, solute accumulation, and ion balance of barley plants

Abstract: We compared the effects of salt-stresses (SS, 1: 1 molar ratio of NaCl to Na2SO4) and alkali-stresses (AS, 1: 1 molar ratio of NaHCO3 to Na2CO3) on the growth, photosynthesis, solute accumulation, and ion balance of barley seedlings, to elucidate the mechanism of AS (high-pH) damage to plants and the physiological adaptive mechanism of plants to AS. The effects of SS on the water content, root system activity, membrane permeability, and the content of photosynthetic pigments were much less than those of AS. However, AS damaged root function, photosynthetic pigments, and the membrane system, led to the severe reductions in water content, root system activity, content of photosynthetic pigments, and net photosynthetic rate, and a sharp increase in electrolyte leakage rate. Moreover, with salinity higher than 60 mM, Na+ content increased slowly under SS and sharply under AS. This indicates that high-pH caused by AS might interfere with control of Na+ uptake in roots and increase intracellular Na+ to a toxic level, which may be the main cause of some damage emerging under higher AS. Under SS, barley accumulated organic acids, Cl−, SO42−, and NO3− to balance the massive influx of cations, the contribution of inorganic ions to ion balance was greater than that of organic acids. However, AS might inhibit absorptions of NO3− and Cl−, enhance organic acid synthesis, and SO42− absorption to maintain intracellular ion balance and stable pH.

Plant-Derived Sucrose Is a Key Element in the Symbiotic Association between Trichoderma virens and Maize Plants

Abstract: Fungal species belonging to the genus Trichoderma colonize the rhizosphere of many plants, resulting in beneficial effects such as increased resistance to pathogens and greater yield and productivity. However, the molecular mechanisms that govern the recognition and association between Trichoderma and their hosts are still largely unknown. In this report, we demonstrate that plant-derived sucrose (Suc) is an important resource provided to Trichoderma cells and is also associated with the control of root colonization. We describe the identification and characterization of an intracellular invertase from Trichoderma virens (TvInv) important for the mechanisms that control the symbiotic association and fungal growth in the presence of Suc. Gene expression studies revealed that the hydrolysis of plant-derived Suc in T. virens is necessary for the up-regulation of Sm1, the Trichoderma-secreted elicitor that systemically activates the defense mechanisms in leaves. We determined that as a result of colonization of maize (Zea mays) roots by T. virens, photosynthetic rate increases in leaves and the functional expression of tvinv is crucial for such effect. In agreement, the steady-state levels of mRNA for Rubisco small subunit and the oxygen-evolving enhancer 3-1 were increased in leaves of plants colonized by wild-type T. virens. We conclude that during the symbiosis, the sucrolytic activity in the fungal cells affects the sink activity of roots, directing carbon partitioning toward roots and increasing the rate of photosynthesis in leaves. A discussion of the role of Suc in controlling the fungal proliferation on roots and its pivotal role in the coordination of plant-microbe associations is provided.