Mechanisms of chloride partitioning in the leaves of salt-stressed Sorghum bicolor L.

Chloride transport in sheath and blade tissue and the cellular distribution of Cl^- were investigated in an attempt to determine the physiological basis of the preferential accumulation of Cl^- in sheaths of salt-stressed sorghum ( Sorghum bicolor L.). Import and export of ³⁶Cl^- in leaf sheaths and blades of intact sorghum were followed over a 2 week period. X-ray microanalysis of frozen-hydrated bulk tissue samples was used to determine the accumulation of Cl^- and other elements in the vacuoles of sheath and blade cells.
Sheath tissue accumulated Cl^- despite a relatively high Cl^- turnover rate. Chloride was shown to accumulate in most cell types of the sheath, particularly in adaxial epidermal cells. After an initial increase in the concentration of Cl^-, blade tissue regulated Cl^- levels within certain limits. Chloride levels in blades were greater in the abaxial and adaxial epidermal cells than in other cell types. The epidermal cells of blades accumulated Cl^- to approximately the same concentration as sheath epidermal cells. The Cl^- concentration in the photosynthetically active mesophyll and bundle sheath cells, however, remained low.
Thus, the partitioning of Cl^- previously observed in the leaves of salinized sorghum apparently results from the ability of bundle sheath and mesophyll cells to maintain concentrations of Cl^- at lower levels than do epidermal cells. In addition, the relatively large sheath parenchyma cells tend to serve as reservoirs for the storage of Cl^-.     

Transport and catabolism of proline betaine in salt-stressed Rhizobium meliloti

Exogenous proline betaine (N,N-dimethylproline or stachydrine) highly stimulated the growth rate of Rhizobium meliloti, in media of inhibitory concentration of NaCl whereas proline was ineffective. High levels of proline betaine uptake occurred in cells grown in media of elevated osmotic strength; on the contrary, only low activity was found in cells grown in minimal medium. The apparent K _m was 10 M with a maximal transport rate of 25 nmol min^-1 mg^-1 of protein in 0.3 M NaCl-grown cells. The concentrative transport was totally abolished by KCN (2 mM), 2,4-dinitrophenol (2 mM), and carbonyl cyanide-m-chlorophenyl hydrazone (CCCP 10 M) but was insensitive to arsenate (5 mM). Glycine betaine was a very potent inhibitor of proline betaine uptake while proline was not. Proline betaine transport was not reduced in osmotically shocked cells and no proline betaine binding activity was detected in the crude periplasmic shock fluid. In the absence of salt stress, Rhizobium meliloti actively catabolized proline betaine but this catabolism was blocked by increasing the osmotic strength of the medium. The osmolarity in the growth medium regulates the use of proline betaine either as a carbon and nitrogen source or as an osmoprotectant.Abbreviations LAS lactate-aspartate-salts - MSY mannitol-salts-yeast - CCCP carbonyl cyanide-m-chlorophenyl hydrazone - DCCD dicyclohexylcarbodiimide - KCN potassium cyanide - Hepes 4-(2-hydroxyethyl)-1-piperzine-ethanesulphonic acid     

Genetic transformation of Sorghum bicolor

Great millet (Sorghum bicolor (L.) Moench) is cultivated across the world for food and fodder. It is typically grown in semiarid regions that are not suitable for cultivation of other major cereals. Sexual incompatibility and shortage of available genes in germplasm to combat biotic and abiotic stresses resulted in marginalized yields of this crop. Genetic modification of sorghum with agronomically useful genes can address this problem. Here, we tried to review and summarize the key aspects of sorghum transformation work being carried out so far by various research groups across the world. The approaches used and the obstacles in generating transgenic sorghum are also pointed out and discussed.     

Betaine accumulation in salt-stressed sorghum

Two analytical methods for measuring betaine were compared in a study of betaine accumulation in salt-stressed sorghum. Spectrophotometric determination of betaine as the p -bromophenacyl ester is highly sensitive and specific. However, a periodide assay was found to be more convenient for screening numerous plant samples without undue sacrifice in accuracy.
The accumulation of betaine in grain sorghum [ Sorghum bicolor (L.) Moench] cvs NK 265 and Double TX was measured in salt-stressed plants grown hydroponically and in the field and in drought-stressed potted plants. Neither drought nor mild salinity (-0.2 MPa) stress was effective in stimulating betaine accumulation. However, when the osmotic potential of the culture solution was lowered to -0.8 MPa, betaine levels in the shoots rose rapidly for 12 days after initiation of salination, and then declined, apparently because of dilution by plant growth. In young leaf blades, betaine was strongly accumulated up to 70–75 μmol (g dry weight)⁻¹; the concentration in leaf sheaths was less than 6 μmol (g dry weight)⁻¹.
In the field, betaine levels in salt-stressed sorghum increased 6- to 7-fold over the basal level of the control plants. In a comparable study of two wheat species ( Triticum aestivum L. cv. Probred and T. durum Desf. cv. 1000-D), betaine increased only 3- to 4-fold over unstressed plants.     

Genotypic differences in potassium response and proline accumulation in maize during wilting

When leaf discs of six experimental hybrids of maize (Zea maysL.) grown with high as well as low levels of potassium weretreated with 5 mM KCl for 2 hr in light before exposure to long-term(43 hr) mild wilting conditions, a stimulating effect of potassiumtreatment ("potassium effect") on water-stress-induced prolineaccumulation was observed. This effect was greater in the discsgrown at a high level of potassium. Marked differences in prolineaccumulation due to wilting were observed in the different genotypes.Genotypic differences in the ‘potassium effect’were also evident. Use of potassium uptake as an index for screeningcultivars for drought tolerance may be possible. Present address: Department of Plant Science, School of Agriculture,University of Zambia. P.O. Box 2379, Lusaka, Zambia. (Received September 11, 1979; )     

A Developmental Window for Salt-Adaptation in Sorghum bicolor

Following exposure to specific NaCl treatments, certain Sorghumbicolor genotypes developed increased salinity tolerance, ‘adaptation’,which was accompanied by a morphological modification in thedevelopment of one or several leaves. Adaptation differed fromthe more common response of the plant to salinity, ‘pre–existingresistance’, which rested on the prevalent tolerance mechanismsexisting prior to the salinization treatment. Induction of adaptationwas possible only during a specific time period of plant development.This time-limited capacity for adjustment to a changing environmentalparameter, developmental window, resembled similar processesoccurring in animal development. Key words: Sorghum, adaptation, resistance, salinity, developmental window     

Changes in growth and water-soluble solute concentrations in Sorghum bicolor stressed with sodium and potassium salts

Sorghum bicolor L. Moench, RS 610, was grown in liquid media salinized with NaCl, KCl, Na₂SO₄, K₂SO₄ or with variable mixtures of either NaCl/KCl or Na₂SO₄/K₂SO₄ at osmotic potentials ranging from 0 to -0.8 MPa. The purpose was to study the effects of different types and degrees of salinity in growth media on growth and solute accumulation. In 14-day-old plants the severity of leaf growth inhibition at any one level of osmotic potential in the medium increased according to the following order: NaCl < Na₂SO₄ < KCl = K₂SO₄. Inhibition of growth by mixtures of Na⁺ and K⁺ salts was the same as by K⁺ salts alone. Roots responded differently. Root growth was not affected by Na⁺ salts in the range of 0 to -0.2 MPa while it was stimulated by K⁺ salts. The major cation of leaves was K⁺ because S. bicolor is a Na⁺-excluder, while Na⁺ was the major cation in roots except at low Na⁺/K⁺ ratios in media. Anions increased in tissues linearly in relation to total monovalent cation, but not with a constant anion/cation ratio. This ratio increased as the cation concentrations in tissues increased. Sucrose in leaf tissue increased 75 fold in Chloride-plants (plants growing in media in which the only anion of the salinizing salts was Cl^?) and 50 fold in Sulphate-plants (the only anion of the salinizing salts was SO₄^2-). Proline increased 60 and 18 fold in Chloride- and Sulphate-plants, respectively, as growth media potentials decreased from 0 to -0.8 MPa. The concentrations of both sucrose and proline were directly proportional to the amount of total monovalent cation in the tissue. Sucrose concentrations began increasing when total monovalent cations exceeded 100 μmol (g fresh weight)^?1 (the monovalent cation level in non-stressed plants), but proline did not start accumulating until monovalent cation concentrations exceeded 200 μmol (g fresh weight)^?1. Therefore, sucrose seemed to be the solute used for osmotic adjustment under mild conditions of saline stress while proline was involved in osmotic adjustment under more severe conditions of stress. Concentrations of inorganic phosphate, glucose, fructose, total amino acids and malic acid fluctuated in both roots and leaves in patterns that could be somewhat correlated with saline stress and, sometimes, with particular salts in growth media. However, the changes measured were too small (at most a 2–3 fold increase) to be of importance in osmotic adjustment.     

Identification and profiling of salinity stress-responsive proteins in Sorghum bicolor seedlings

Sorghum bicolor, a drought tolerant cereal crop, is not only an important food source in the semi arid/arid regions but also a potential model for studying and gaining a better understanding of the molecular mechanisms of drought and salt stress tolerance in cereals. In this study, seeds of a sweet sorghum variety, MN1618, were planted and grown on solid MS growth medium with or without 100mM NaCl. Heat shock protein expression immunoblotting assays demonstrated that this salt treatment induced stress within natural physiological parameters for our experimental material. 2D PAGE in combination with MS/MS proteomics techniques were used to separate, visualise and identify salinity stress responsive proteins in young sorghum leaves. Out of 281 Coomassie stainable spots, 118 showed statistically significant responses (p<0.05) to salt stress treatments. Of the 118 spots, 79 were selected for tandem mass spectrometric identification, owing to their good resolution and abundance levels, and of these, 55 were positively identified. Identified proteins were divided into six functional categories including both known and novel/putative stress responsive proteins. Molecular and physiological functions of some of our proteins of interest are currently under investigation via bioinformatic and molecular biology approaches.     

高粱LEA基因家族的鉴定及表达分析

有研究表明,干旱、低温和盐等环境胁迫能够诱导LEA基因的表达。为了探索LEA基因家族在高粱响应外界刺激过程中起到的作用,本研究通过生物信息学的方法对LEA基因家族在高粱全基因组水平进行鉴定和分析,于高粱全基因组中共鉴定出35个基因家族成员,不均匀地分布于高粱8条染色体上,结合系统进化树和保守结构域分析结果,将高粱LEA基因家族成员分为7组。亲水性分析和结构无序性预测表明高粱LEA蛋白绝大多数为亲水性且结构无序。基因结构分析显示了各分组基因结构上的保守性。高粱LEA基因的启动子分析发现了一些与激素和非生物胁迫响应相关的顺式作用元件。对激素和干旱胁迫下高粱LEA基因的表达分析发现外界胁迫能够诱导部分高粱LEA基因的表达。     

Glycine rich proline rich protein from Sorghum bicolor serves as an antimicrobial protein implicated in plant defense response

Plant Molecular Biology - That overexpression of GmKR3 enhances innate virus resistance by stimulating. Soybean mosaic virus (SMV) is found in many soybean production areas, and SMV infection is...     

Interactive effects of Ca2+ and NaCl salinity on the ionic relations and proline accumulation in the primary root tip of Sorghum bicolor

The effects of supplemental Ca²⁺ supply and NaCl salinity on the ionic relations and levels of proline and other amino acids in the primary root of Sorghum bicolor (cv. Hegari) seedlings were investigated. Two days of exposure to 150 m M NaCl resulted in a 50-fold increase in the proline level in the 0–10 mm root tips of seedlings supplied with 5.0 m M Ca²⁺, but only a 4-fold increase in seedlings with 0.5 m M Ca²⁺. In contrast to the high levels of proline in the root tip, proline accumulation was only modest in the expanded tissues of the root. The enhancement of proline accumulation in the root tip of salinized seedlings with the Ca²⁺ supplement may be related to their more favorable tissue K to Na ratio. Thus, elevated Ca²⁺ may mitigate the NaCl-induced inhibition of S. bicolor root growth via the maintenance of net K to Na selectivity and the enhancement of proline accumulation in the root tip.     

Characterization of leaf boron injury in salt-stressed Eucalyptus by image analysis

Symptoms of boron toxicity (i.e., necrosis of leaf tips and margins) have been observed on eucalyptus trees in the San Joaquin Valley of California where the trees are being tested for their effectiveness at reducing the volume of agricultural drainage effluents. In a controlled, outdoor sand-tank study, Eucalyptus camaldulensis Dehn., Clone 4544 trees were grown and irrigated with combinations of salinity and B to determine their influence on tree growth and water use. Irrigation water quality treatments were prepared to simulate the Na-sulfate salinity, high B nature of these drainage effluents. Electrical conductivities (EC_iw) of the waters ranged from 2 to 28 dS m-1 and B concentrations ranging from 1 to 30 mg L-1. As an integral component of this study , we developed a method to quantify and correlate foliar damage with leaf B concentrations. By scanning both injured and uninjured leaves into computer files and processing with image analysis, we were able to simultaneously correlate salinity stress with its overall effect on leaf area as well as to quantify the relative fraction of leaf area affected by specific-ion (i.e., B) injury. Leaf area was unaffected by B stress but was reduced by salinity only in the younger leaves. Boron injury was correlated with increasing irrigation water B only in older leaves. The relative injured area (RIA) of the older leaves was related to the B concentrations of leaves from trees grown at various salinities . A regression equation was developed from injury data obtained from trees grown under boron and salinity stress for 223 days (r2=0.90). From this relationship, we were able to estimate leaf boron concentrations from injury symptoms in leaves selected at random from main trunk branches of trees grown for 333 days under the same stress conditions. The results suggest that this method may have potential as an effective tool for monitoring the response to toxic levels of boron in eucalyptus, once B toxicity has been established by analytical means. The RIA appears to be mitigated by increased salinity of the irrigation water and is consistent with the general reduction in leaf B by salinity. The interactive effects of boron and salinity on foliar injury depends on the physiological age of the leaf.     

Free proline accumulation in drought-stressed plants

Summary Free-proline accumulation was measured in leaves of intact wheat (Triticum vulgare L. cv. Kalyan Sona), plantago (Plantago ovata Forsk-Isabgool), papavar (Papaver somnifera L. Opium poppy) and mustard (Brassica juncea L. var. Varuna) grown in the field with low to high field water content and thus they were subjected to water stress. Leaf water deficit in percentage was used to determine the degree of stress at the time of proline anlysis.Free proline content was higher in mustard leaves as compared to wheat, plantago and papavar leaves. Water stress enhances the proline content but at same water deficit level the content differ in the leaves of the plants studied.     

Metabolic implications of stress-induced proline accumulation in plants

In many plants, free proline accumulates in response to the imposition of a wide range of biotic and abiotic stresses. Controversy has surrounded the extent to which this shift in nitrogen metabolism benefits plants under adverse environmental conditions. Most attempts to account for the phenomenon have focused on the ability of proline to mediate osmotic adjustment, stabilise subcellular structures and scavenge free radicals. However, often the cytoplasmic pool of free proline even after the imposition of stress is insufficient size to account for pronounced biophysical effects.Alternatively, selective preservation of this stress-induced response may relate to endpoints other than simply augmenting the cellular pool of free proline. Proline accumulation may reduce stress-induced cellular acidification or prime oxidative respiration to provide energy needed for recovery. High levels of proline synthesis during stress may maintain NAD(P)+/NAD(P)H ratios at values compatible with metabolism under normal conditions. Consideration of the cofactor preference of plant 1-pyrroline-5-carboxylate (P5C) reductase as well as the in vivo concentrations of the two pyridine nucleotide cofactors and their respective redox ratios suggests that even a small increase in proline biosynthesis might have a large impact on the level of reduction of the cellular NADP pool. The increased NADP+/NADPH ratio mediated by proline biosynthesis is likely to enhance activity of the oxidative pentose phosphate pathway. This would provide precursors to support the demand for increased secondary metabolite production during stress as well as nucleotide synthesis accompanying the accelerated rate of cell division upon relief from stress, when oxidation of proline is likely to provide an important energy source for ADP phosphorylation. Thus, the extreme sensitivity of the metabolic processes of proline synthesis and degradation themselves may be of benefit by regulating metabolic processes adversely affected by stress. This viewpoint is supported by consideration of other physiological phenomena not directly related to stress responses, but in which proline metabolism may also play a regulatory role.A mechanism is proposed whereby the interconversions of proline and P5C in different cell types and the associated transfer of redox potential between tissues may constitute a form of metabolic signalling within higher plants. Stress-related alterations in proline metabolism may impinge on systems of redox control of plant gene expression.     

Relationship between salt accumulation and water content of dicotyledonous halophytes

Abstract. Growth rates and levels of minerals, Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺, and water were measured in dicotyledonous halophytes grown along a salinity gradient from fresh water to 720 mol m⁻³ NaCl in a controlled environment greenhouse. Ten test species from the families Chenopodiaceae, Aizoaceae, and Batidaceae exhibited growth stimulation by 180 mol m⁻³ NaCl and were classified as euhalophytes. Ten others from the families Chenopodiaceae, Aizoaceae, Asteraceae, Brassicaceae, Polygonaceae, Boraginaceae, Malvaceae, and Plumbaginaceae showed their best growth on fresh water and were classified miohalophytes. Salt, and particularly sodium, accumulated in all halophytes but to a significantly greater extent among euhalophytes than miohalophytes. The water content of most species increased when grown on 180 mol m⁻³ NaCl compared to fresh water; but at higher salinities some of the species underwent dehydration. Dehydration of the succulent S. europaca was not coupled to a proportional decrease in growth. Water content and cation accumulation in euhalophytes appeared to be coordinated to produce a constant osmotic potential gradient within the shoot tissues relative to the external salinity. In contrast, miohalophytes did not appear to regulate osmotic potential as closely as euhalophytes.     

Relationship between cation accumulation and water content of salt-tolerant grasses and a sedge

Abstract Salt-tolerant grasses and a sedge were grown at three salinities in a controlled-environment greenhouse. They were measured for growth rate, ash content, water content and cations. Fourteen species from the genera Sporobolus, Aeluropus, Leptochloa, Paspalum, Puccinellia, Hordeum, Elymus, Distichlis and Spartina survived up to the highest salt treatment (540 mol m^?3 NaCl). These were designated halophytes. Eleven species from the genera Triticum, Phragmites, Dactylotenium, Cynodon, Polypogon, Panicum, Jovea and Heleocharis only survived up to 180 mol m^?3 NaCl and were designated salt-tolerant glycophytes. All species except Distichlis palmeri grew fastest on the non-saline control treatment. All species tended to have higher Na⁺ contents and lower K⁺ and water contents on saline treatments compared to control plants. Halophytes differed from glycophytes in having statistically significant lower water contents on the non-saline treatment, and lower ash contents and Na:K ratios on 180 mol m^?3. However, the range of values among species was greater than the differences between halophytes and glycophytes. All species appeared to use Na⁺ accumulation and loss of water as the main means of osmotic adjustment. Three halophytic species were grown for a longer period of time to check the above results. The osmolality of the cell sap was measured directly by the vapour pressure method and compared to calculated values based on Na⁺, K⁺ and water contents (and assuming a balancing anion such as Cl^?). Na⁺ and K⁺ alone could account for greater than 75% of the osmotic potential at all salinities. Hence, the accumulation of organic solutes did not appear to be an important factor in the osmotic adjustment of these species. The results support the conclusion that grasses coordinate Na⁺ uptake and water loss to maintain a constant osmotic potential gradient between the shoot tissues and the external solution. The results were compared to a previous study with dicotyledonous halophytes at the same location.     

Phytochrome and Calcium Regulated Protein Phosphorylation in Sorghum bicolor

Irradiation with red light of Sorghum bicolor seedlings stimulated in vitro phosphorylation of 55 kD and several other soluble polypeptides in a development-dependent manner. The red light stimulated phosphorylation of 55 kD polypeptide was more in 6-day-old etiolated plants as compared to 5-day-old plants. The in vitro phosphorylation of 55 kD polypeptide was enhanced further when calcium was added to the extracts obtained from red light irradiated tissues of 6-day-old seedlings. This effect was inhibited in the presence of calmodulin inhibitors. There was no significant stimulation in the phosphorylation of this polypeptide by calcium in 5-day-old and 7-day-old etiolated plants. Besides 55 kD, the phosphorylation of several other polypeptides was either stimulated or inhibited by light, calcium and calmodulin inhibitors suggesting involvement of both kinases and phosphatases in light-mediated phosphorylation.