Ecophysiological analysis of woody species in contrasting temperate communities during wet and dry years

This study employed an intensive sampling regime in which leaf gas exchange and tissue-water relations were measured simultaneously on the same leaf at midday on 19 tree species from three distinct forest communities during wet (1990) and dry (1991) growing seasons. The study sites were located on a xeric barrens, a misic valley floor, and a wet-mesic floodplain in central Pennsylvania, United States. The xeric, mesic, and wetmesic sties had drought-related decreases in gravimetric soil moisture of 53, 34 and 27%, respectively. During the wet year, xeric and mesic communities had high seasonal mean photosynthetic rates (A) and stomatal conductance of water vapor (g _wv) and low midday leaf water potential (), whereas the wet-mesic community had low A and g _wv and high midday . The mesic and wet-mesic communities had dry year decreases in predawn , g _wv and A with the greatest drought effect occurring in the mesic community. Regression analysis indicated that species from each site that exhibited high wet-year A and g _wv tended to have low midday . This trend was reversed only in the mesic community in the drought year. Despite differences in midday , all three communities had similar midday leaf turgor pressure (_p) in the wet year attributable to lower osmotic potential at zero turgor ( ⁰ ) with increasing site droughtiness. Lower wet year ⁰ in the xeric community was due to low symplast volume rather than high solute content. Species with the lowest ⁰ in the wet year often did not have the lowest ¹⁰⁰ possibly related to differences in tissue elasticity. Moreover, increased elasticity during drought may have masked osmotic adjustment in ¹⁰⁰ but not in ⁰ , via dilution of solutes at full hydration in some species. Despite the sampling regime used, there were no relationships between gas exchange and osmotic and elastic parameters that were consistently significant among communities or years. This result questions the universal, direct effect of osmotic and elastic adjustments in the maintenance of photosynthesis during drought. By including a large number of species, this study provided new insight to the ecophysiology of contrasting forest communities, and the community-wide impact of drought on contrasting sites.     

Chloroplast volume: cell water potential relationships and acclimation of photosynthesis to leaf water deficits

Studies were undertaken to determine if there is an association between nonstomatally-mediated acclimation of photosynthesis to low water potential (w) and the maintenance of chloroplast volume during water stress. Spinach plants either kept well watered throughout their growth (non-acclimated), or subjected to water stress such that leaf w dropped to -1.5 megapascals (MPa) and then were rewatered (acclimated) were subjected to drought episodes. During these stress periods, photosynthesis was maintained to a greater extent in acclimated plants as compared to non-acclimated plants at w below -1 MPa.Estimates of internal leaf [CO₂] suggested that photosynthetic acclimation to low w was not primarily due to altered stomatal response. As w dropped from initial values, a decline in steady state levels of ribulose 1,5-bisphosphate (RuBP) occurred in both non-acclimated and acclimated plants. RuBP decline was less severe in acclimated plants.Low w effects on chloroplast volume in non-acclimated and acclimated plants were estimated by measuring the volume of intact chloroplasts isolated from plants in solutions which were made isotonic to declining leaf osmotic potential during the drought episodes. Chloroplast volume was maintained to a greater extent at low w in acclimated, as compared with non-acclimated plants. Although substantial osmotic adjustment occurred in both non-acclimated and acclimated plants, the extent of osmotic adjustment was the same. These data were interpreted as supporting the hypothesis that cellular-level acclimation to low w is associated with chloroplast volume maintenance, and this physiological acclimation is correlated with enhanced photosynthetic capacity of the leaf at low w.Abbreviations [CO₂]_i internal leaf CO₂ concentration - s osmotic potential - RWC relative water content - RuBP ribulose 1,5-bisphosphate - w water potential     

An elongated segment of DNA observed between two human α globin genes

Summary Detailed restriction enzyme analysis of the DNA from a Chinese female showed that one of her chromosomes had a >17.5 kb deletion of DNA, including the , 2, and 1 globin genes, which is present in many Southeast Asians with an -thalassemia-1 chromosome. Her normal chromosome had the expected cluster of -like globin genes (5----2-1-3), but the segment of DNA between the two globin genes was elongated by some 0.5–0.7 kb. Analyses of various restriction sites suggested that this normal variant of the human globin gene complex is due to a crossover between a normal chromosome with () and a chromosome with an -thalassemia-2 (–^3.7) and an -21-hybrid gene.     

Temperature and moisture effects on C and N mineralization from surface applied clover residue

A better understanding of the effect of temperature (T) and moisture on soil microbial activity should improve our ability to predict N mineralization from soil organic matter and crop residues. The objective of this study was to evaluate the effects of water potential () and T on C and N mineralization from unamended Cecil loamy sand soil (clayey, kaolinitic, thermic Typic Kanhapludult) and from crimson clover (Trifolium incarnatum L.) residues applied on the soil surface. Cecil soil was packed into acrylic plastic cylinders, adjusted to -5.0, -1.5, -0.03, or -0.003 MPa, treated with clover residues on the surface or left unamended, and incubated at 10, 20, 28, or 35°C for 21 d. Headspace gas samples for CO2 and N2O determinations were taken periodically and NH3 evolved was trapped. Inorganic N in soil and residue extracts was analyzed after 21 d. When increased from -5.0 to -0.003 MPa, total CO2 evolved from unamended soil increased linearly with ln(-), whereas total CO2 evolved from clover residue increased exponentially with . In both cases the effect of was enhanced as T increased. Two-dimensional (T, ) equations were developed to describe these effects. Apparent net mineralized N from the clover residue increased with until it reached a maximum between -0.5 and -0.03 Mpa.     

The irreversibility of inner mitochondrial membrane permeabilization by Ca2+ plus prooxidants is determined by the extent of membrane protein thiol cross-linking

We have previously shown that mitochondrial membrane potential () drop promoted by prooxidants and Ca²⁺ can be reversed but not sustained by ethylene glycol-bis(-aminoethylether)-N,N,N,N-tetraacetic acid (EGTA) unless dithiothreitol (DTT), a disulfide reductant, is also added [Valle, V. G. R., Fagian, M. M., Parentoni, L. S., Meinicke, A. R., and Vercesi, A. E. (1993).Arch. Biochem. Biophys. 307, 1–7]. In this study we show that catalase or ADP are also able to potentiate this EGTA effect. When EGTA is added long after (12 min) the completion of swelling or elimination, no membrane resealing occurs unless the EGTA addition was preceded by the inclusion of DTT, ADP, or catalase soon after was collapsed. Total recovery by EGTA is obtained only in the presence of ADP. The sensitivity of the ADP effect to carboxyatractyloside strongly supports the involvement of the ADP/ATP carrier in this mechanism. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized membrane proteins shows that protein aggregation due to thiol cross-linkage formed during drop continues even after is already eliminated. Titration with 5,5-dithio-bis(2-nitrobenzoic acid) supports the data indicating that the formation of protein aggregates is paralleled by a decrease in the content of membrane protein thiols. Since the presence of ADP and EGTA prevents the progress of protein aggregation, we conclude that this process is responsible for both increased permeability to larger molecules and the irreversibility of drop. The protective effect of catalase suggests that the continuous production of protein thiol cross-linking is mediated by mitochondrial generated reactive oxygen species.     

Measurements of electrical potential differences across yeast plasma membranes with microelectrodes are consistent with values from steady-state distribution of tetraphenylphosphonium inPichia humboldtii

Summary Electrical potential differences across the plasma membrane () of the yeastPichia humboldtii were measured with microelectrodes (filled with 0.1m KCl) inserted into cells immobilized in microfunnels. The registered signals were reproducible and stable for several minutes. On attainment of stable reading for the specific membrane resistanceR _sp was determined by applying square-current pulses to the preparation. Both andR _sp were pH dependent and displayed equal but opposite deflection, reaching its maximal value of –88±9 mV (n=13) andR _sp its minimal value of 10 k·cm² (maximal conductance) at pH 6.5. Uncouplers and the polyene antibiotic nystatin depolarized the cells, decreasing to –21±15 mV (n=10) with concomitant decrease ofR _sp. Comparison of values from microelectrode measurements with those calculated from the steady-state distribution of tetraphenylphosphonium ions agreed within 10 mV under all physiological conditions tested, except at pH values above 7.0. During microelectrode insertion transient voltage signals (a few msec long) were detected by means of an oscilloscope. These voltage signals were superimposed on the stable recordings described above. These short voltage signals disappeared in uncoupled cells. The closely related values obtained by two independent methods (direct measurements with microelectrodes and calculation from steady-state distribution of a lipophilic cation) provide evidence that these values reffect the true membrane potential of intact cells.     

Structural and Functional Rearrangements of Mesophyll as a Probable Basis for the Cytokinin-Dependent Assimilate Translocation in Detached Leaves

The effects of benzyladenine (BA) on the mesophyll functioning, such as osmotic potential (), the effect of the inhibitors of ⁺-ATPase on the influx of ¹⁴C-sucrose, the direction of carbon metabolism, and the rate of dark respiration, were followed in the detached leaves of pumpkin (Cucurbita pepo L.) and broad beans (Vicia faba L.). BA elevated and established a gradient of (_p) between the treated and untreated leaf regions. The inhibitors of H⁺-ATPase did not affect the BA-induced influx of ¹⁴C-sucrose. The changes were accompanied with the elevated synthesis of starch and other polymeric compounds and the diminished synthesis of the substances of relatively low molecular weight. The stimulation of dark respiration was short and inconsiderable. The author concludes that the BA-induced transport was a passive process related to a increase. Leaf expansion accompanied by the synthesis of high-molecular-weight substances essential for cell growth and by starch synthesis apparently increased the sink capacity of the BA-treated detached leaves. The diminished efflux from the leaf blade was probably related to a lowered level of the transportable carbon compounds restricting their entry into the phloem. The influx induction could result from the activation of growth and metabolic processes, the decline in the number of organic molecules per cell volume unit, and the development of _p between the source and sink leaf regions.     

The carotenoids of Flavobacterium strain R1560

The main carotenoid of Flavobacterium strain R1560 has been identified as (3R,3R)-zeaxanthin. Also present were small amounts of 15-cis-phytoene, phytofluene, -carotene (7,8,7,8-tetrahydro-, -carotene plus 7,8,11,12-tetrahydro-, -carotene), neurosporene, lycopene, -zeacarotene, -carotene, -carotene, -cryptoxanthin, rubixanthin, 3-hydroxy--zeacarotene and several apo-carotenals. Zeaxanthin production was inhibited by nicotine (10 mM), and lycopene and rubixanthin accumulated. The biosynthesis of zeaxanthin is discussed in terms of pathways and also of half-molecule reaction sequences. The presence of zeaxanthin may be a characteristic of a group of Flavobacterium species, and may thus be useful in the taxonomic classification of these organisms.     

Preparations of Ψ-peptide bond and peptide-aldehyde inhibitors of atrial granule serine proteinase, a candidate processing enzyme of pro-atrial natriuretic factor

Pseudo-peptide bond inhibitors (-bond inhibitors) and peptide-aldehyde inhibitors of atrial granule serine proteinase, the candidate processing enzyme of pro-atrial natrieuretic factor, are prepared in high yield and purity by novel synthetic routes. The -bond compounds retain essential residues for enzyme binding, but place the enzyme inhibition site in the midst of the peptide sequence. Thus, Bz-APR--LR and Bz-APR--SLRR can be considered readthrough inhibitors of atrial granule serine proteinase. The most potent -peptide, Bz-APR--SLRR (IC₅₀=250 M), is about fivefold less potent than the best peptide-aldehyde inhibitor (EACA-APR-CHO), and both the -bond and peptide-aldehyde compounds are competitive, reversible inhibitors of the enzyme. The -bond peptides containing two C-terminal Arg residues are three-to tenfold more potent than the analogous compounds containing only one C-terminal Arg residue, confirming the importance of both Arg residues in the enzyme processing recognition site. As expected, because of their moderate potencies, the -peptides are not useful affinity ligands for purification of atrial granule serine proteinase, but both peptide aldehydes are effective affinity ligands [Damodaran and Harris (1995),J. Protein Chem., this issue].Abbreviations AGSP atrial granule serine proteinase - ANF atrial natriuretic factor - Bz benzoyl - DIEA diisopropylethylamine - DIPCDI diisopropylcarbodiimide - DMF dimethylformamide - DMSO dimethylsulfoxide - EACA 6(e)-aminocaproic acid - EtOAc ethyl acetate - HEPES N-2-hydroxyethylpiperazine-N-propanesulfonic acid - HOBt N-hydroxybenzotriazole - HPLC high-performance liquid chrornatography - NMR nuclear magnetic resonance - PEG polyethylene glycol-3350 - PyBOP benzotriazole-1-yl-oxy-trispyrrolidino-phosphonium-hexafluorophospate - TEA triethylamine - TFA trifluoroacetic acid - THF tetrahydrofuran - TLC thin-layer chromatography - UV ultraviolet - pseudo-peptide bond -CH₂-NH-. Single-letter abbreviations are used to denote amino acids     

Refinement of the protein backbone angle ψ in NMR structure calculations

Cross-correlated relaxation rates involving the C-H dipolar interaction and the carbonyl (C) chemical shift anisotropy (CSA) have been measured using two complementary 3D experiments. We show that the protein backbone angle can be directly refined against such cross-correlated relaxation rates (^{H C,C}) and the three-bond H/D isotope effect on the C chemical shifts (³C _(ND)). By simultaneously using both experimental parameters as restraints during NMR structure calculations, a unique value for the backbone angle is defined. We have applied the new refinement method to the -Spectrin SH3 domain (a -sheet protein) and to the Sgs1p HRDC domain (an -helical protein) and show that the quality of the NMR structures is substantially improved, judging from the atomic coordinate precision and the Ramachandran map. In addition, the -refined NMR structures of the SH3 domain deviate less from the 1.8 Å crystal structure, suggesting an improved accuracy. The proposed refinement method can be used to significantly improve the quality of NMR structures and will be applicable to larger proteins.     

Water relations and growth of shrubs before and after fire in a semi-arid woodland

Summary Plant water relations and shoot growth rate of shrubs resprouting after fire or unburnt were measured in a semi-arid poplar box (Eucalyptus populnea) shrub woodland of eastern Australia. In vegetation unburnt for about 60 years, the dawn xylem water potential (_x) of the dominant shrub species was about-1.0 MPa when the soil was wet and-8.0 MPa when the soil was very dry. At any one time, the dominant shrub species,Eremophila mitchellii, E. sturtii, Geijera parviflora andCassia nemophila, were similar in _x butAcacia aneura andDodonaea viscosa were consistently higher in _x than this group when the soil was moist and lower when the soil was dry. The dominant tree species,Eucalyptus populnea andE. intertexta, appeared to have access to additional water beneath the hardpan which is located 60–80 cm below the surface. When shrubs were under extreme water stress (_x of-8 MPa), the trees had a _x of-3 to-3.6 MPa. Following a fire, both _x and leaf stomatal conductance (g _s) of resprouting shrubs were higher for about 5 years than comparable-aged unburnt vegetation, with relative differences in _x increasing with drought stress. Elongation rate of resprouts was positively linked to prefire shrub height in 3 of 4 species. However, shrubs resprouting after high intensity fires had substantially higher rates of shoot elongation than after low intensity fires which were in turn higher than for foliar expansion of unburnt shrubs. It is concluded that the growth rate of resprouting shrubs is primarily determined by physiological/ morphological factors associated with plant size but is also assisted by greater availability of water and possibly nutrients for a period after fire.     

Estimation of Membrane Potential Δψ in Reconstituted Plasma Membrane Vesicles Using a Numerical Model of Oxonol VI Distribution

A model of membrane potential-dependent distribution of oxonol VI to estimate the electrical potential difference across Schizosaccharomyces pombe plasma membrane vesicles (PMV) has been developed. was generated by the H⁺-ATPase reconstituted in the PMV. The model treatment was necessary since the usual calibration of the dye fluorescence changes by diffusion potentials (K⁺ + valinomycin) failed. The model allows for fitting of fluorescence changes at different vesicle and dye concentrations, yielding in ATP-energized PMV of 80 mV. The described model treatment to estimate may be applicable for other reconstituted membrane systems.     

Phlorizin binding to isolated enterocytes: Membrane potential and sodium dependence

Summary Phlorizin binding is studied in isolated intestinal epithelial cells of the chick. Cells are ATP depleted to allow extensive manipulation of ionic gradients and membrane potential (). Phlorizin binding is assayed at steady state. Carrier specific phlorizin binding is defined asd-glucose (90 mM) inhibitable binding. Specific binding displays simple Michaelian kinetics as a function of phlorizin. indicating the presence of a single homogeneous binding site. Sodium concentrations and modify the apparent binding affinity but not the maximum number of binding sites. In contrast, the activation curve as a function of sodium concentrations is sigmoid and the apparent maximum number of binding sites at saturating sodium is phlorizin dependent. The rate of phlorizin association is both and sodium-concentration dependent. Dissociation is sodium-concentration dependent but not dependent. Theoretical analysis indicates binding order of substrates is random. In addition, data suggests that the phlorizin/sodium stoichiometry is 2:1. The dependence can be explained by two models: either translocation is the -dependent step and the free carrier is anionic, or sodium binding is the -dependent step.     

Chloroplast acclimation to low osmotic potential

Photosynthetic potential of isolated chloroplasts was investigated during in situ water deficits. An eight day stress cycle imposed on spinach plants reduced leaf _w by 0.57MPa, and leaf by 0.50MPa, resulting in partial turgor maintenance during the stress cycle. Pressure/volume curves confirmed the occurrence of osmotic adjustment. Leaf depression was associated with an altered response of chloroplasts to low in vitro. Optimum reaction medium for photosynthesis shifted from –1.04 to –1.57MPa, and low was not as inhibitory to photosynthesis of plastids pre-exposed to stress in situ. These data indicate that chloroplasts acclimate to low external in response to leaf water deficits. This response was still evident four days after a stress cycle ended, but was nearly reversed eight days after stress. Repeated stress cycles in situ did not increase the degree of chloroplast acclimation to low in vitro. Fast dehydration of leaves did not induce this apparent chloroplast acclimation.Abbreviations osmotic potential - _w water potential - PEG polyethylene glycol 8000 - MPa megapascals     

Secondary structural effects on protein NMR chemical shifts

For an amino acid in protein, its chemical shift, (, )_s, is expressed as a function of its backbone torsion angles ( and ) and secondary state (s): (, )_{s=, )_coil+(, )_s}, where (, )_coil represents its chemical shift at coil state (s=coil); (, )_s (s=sheet or helix) is herein defined as secondary structural effect correction factor, which are quantitatively determined from Residue-specific Secondary Structure Shielding Surface (RSS) for ¹³CO, ¹³C, ¹³C,¹H, ¹⁵N, and ¹HN nuclei. The secondary structural effect correction factors defined in this study differ from those in earlier investigations by separating out the backbone conformational effects. As a consequence, their magnitudes are significantly smaller than those earlier reported. The present (, )_sheet and (, )_helix were found varying little with backbone conformation and the 20 amino acids, specifically for ¹³CO, ¹³C, and ¹H nuclei. This study also carries out some useful investigations on other chemical shift prediction approaches – the traditional shielding surfaces, SHIFTS, SHIFTX, PROSHIFT, and identifies some unexpected shortcomings with these methods. It provides some useful insights into understanding protein chemical shifts and suggests a new route to improving chemical shifts prediction. The RSS surfaces were incorporated into the program PRSI [Wang and Jardetzky, J. Biomol. NMR, 28: 327–340 (2004)], which is available for academic users at http://www.pronmr.com or by sending email to the author (yunjunwang@yahoo.com).     

Protocol-dependence of equivalent circuit parameters of toad urinary bladder

Summary Determinations of current-voltage relationships are widely employed in the characterization of epithelial sodium transport. In order to determine the protocol dependence of transport parameters in the toad urinary bladder, studies were carried out in the presence and absence of amiloride, an inhibitor of active sodium transport. With symmetric positive and negative perturbations of the transepithelial electrical potential difference (0±100 mV) for 30 sec, the amiloride-sensitive current-voltage (i ^a -) relationship was near linear over the range –75+100 mV, indicating constancy of the conductance ^a and the apparent electromotive force E _Na, lumped parameters of the standard electrical equivalent circuit model of the active transport system. With a reverse protocol (±1000 mV) or 15 min perturbations thei ^a - relationships were highly nonlinear. Nonlinearity reflected voltage dependence of parameters: perturbations that increased active transport decreased E _Na and increased ^a, as evaluated from 10 sec perturbations of ; slowing of active transport produced the converse changes. These effects are usefully analyzed in both quasi-steady states and true steady states by means of a detailed equivalent circuit incorporating the significant ionic currents across each plasma membrane. Precise understanding of the significance of ^a and E _Na will require characterization of the partial ionic conductances on perturbation of .     

The mitochondrial membrane potential (deltapsi(m)) in apoptosis; an update

Mitochondrial dysfunction has been shown to participate in the induction of apoptosis and has even been suggested to be central to the apoptotic pathway. Indeed, opening of the mitochondrial permeability transition pore has been demonstrated to induce depolarization of the transmembrane potential (_m), release of apoptogenic factors and loss of oxidative phosphorylation. In some apoptotic systems, loss of _m may be an early event in the apoptotic process. However, there are emerging data suggesting that, depending on the model of apoptosis, the loss of _m may not be an early requirement for apoptosis, but on the contrary may be a consequence of the apoptotic-signaling pathway. Furthermore, to add to these conflicting data, loss of _m has been demonstrated to not be required for cytochrome c release, whereas release of apoptosis inducing factor AIF is dependent upon disruption of _m early in the apoptotic pathway. Together, the existing literature suggests that depending on the cell system under investigation and the apoptotic stimuli used, dissipation of _m may or may not be an early event in the apoptotic pathway. Discrepancies in this area of apoptosis research may be attributed to the fluorochromes used to detect _m. Differential degrees of sensitivity of these fluorochromes exist, and there are also important factors that contribute to their ability to accurately discriminate changes in _m.     

Effects of water stress on the gas exchange,the activities of some enzymes of carbon and nitrogen metabolism,and on the pool sizes of some organic acids in maize leaves

Water-stressed maize (Zea mays L.) leaves showed a large decrease in leaf conductance during photosynthesis. Net CO₂ uptake and evaporation declined fast at mild stress (=–0.6 to –1.0 MPa) and slower at more severe stress (=–1.0 to -1.2 MPa), whereas the CO₂ concentration in the intercellular spaces (C_i) did not drop to the CO₂ compensation point. The activities of the enzymes of photosynthetic carbon metabolism tested in this study dropped by approx. 30% at =-1.2 MPa. Glutamine synthetase activity was unaffected by water stress, whereas the activity of nitrate reductase was almost completely inhibited. The decline of enzyme activities in relation to was correlated with a concomitant decrease in the content of total soluble protein of the stressed leaves. The total leaf pools of malate, pyruvate and oxaloacetate decreased almost linearly in relation to , thus obviously contradicting the almost constant C_i. In comparison to the controls (=0.6 MPa) the content of citrate and isocitrate increaed markedly at =-0.9 MPa and decreased again at =-1.2 MPa.Abbreviations PCR photosynthetic carbon reduction cycle - PCO photosynthetic carbon oxidation cycle - PEP phosphoenolypyruvate - RuBP ribulose-1,5-bisphosphate     

Correlation between 15N NMR chemical shifts in proteins and secondary structure

Summary An empirical correlation between the peptide ¹⁵N chemical shift, ¹⁵N_i, and the backbone torsion angles _i, _i–1 is reported. By using two-dimensional shielding surfaces (_i1–1), it is possible in many cases to make reasonably accurate predictions of ¹⁵N chemical shifts for a given structure. On average, the rms error between experiment and prediction is about 3.5 ppm. Results for threonine, valine and isoleucine are worse (4.8 ppm), due presumably to ₁-distribution/-gauche effects. The rms errors for the other amino acids are 3 ppm, for a typical maximal chemical shift range of 15–20 ppm. Thus, there is a significant correlation between ¹⁵N chemical shift and secondary structure.     

Effects of shoot and root application of thiamin on salt-stressed sunflower plants

Plants of sunflower (Helianthus annuus L. cv Giza2) were salt-stressed with a combination of NaCl and CaCl₂ inconcentrations having different osmotic potentials (s from 0 to –1.0MPa) and were treated with 5 and 10mg L^–1 of thiamin either sprayed on the shoot orapplied to the root. The membranes of leaf discs from salt-stressed plantsappeared to be less stable (more injured) under heat(51°C) and drought (40% polyethylene glycol6000) stresses than control plants. Salinity slowed the rate of growth (lengthand dry mass production), lowered leaf relative water content (RWC) and leafandroot water potential (w), decreased the contents of chlorophyll (Chl),soluble sugars (SS) and the K⁺/Na⁺ ratio butenhanced total free amino acids (TAA), Na⁺,Ca²⁺and Cl^– accumulation in the shoot and root system. Root orshoot application of thiamin reduced membrane injury by either heat ordehydration stress, lowered leaf w, improved uptake of K⁺,and increased leaf RWC, Chl, SS, TAA contents and dry mass production. Theeffects of salinity (s), thiamin (Thi.) and their interaction(s×Thi) on the parameters tested were significant.Salinity was dominant (as indicated by ² values) in affectingthe contents of Ca²⁺, Cl^–, TAA and membranestability to heat and leaf w. The role of thiamin was dominant forNa⁺, K⁺ and SS contents and the contribution ofinteraction was dominant for growth parameters, Chl. and root w.