Dehydration of germinating perennial ryegrass seeds can alter rate of subsequent radicle emergence

Perennial ryegrass (Lolium perenne L.) seeds (caryopses) germinateat or near the soil surface, where water potential can fluctuatewidely. This study examined germination of ‘Del Ray’perennial ryegrass seeds when imbibition was interrupted bydehydration prior to radicle emergence. Seeds were hydratedfor 0 to 40 h (26C), dehydrated at atmospheric water potentialsof –4, –40, –100 and/or –150 MPa for4–168 h, then rehydrated. Germination (radicle elongation 1 mm), seedling growth, solute leakage, and endogenous abscisicacid (ABA) levels were measured. Treatment differences in finalgermination percentage, seedling growth, and solute leakagewere generally not significant. However, the onset of radicleemergence was delayed and the rate of germination slowed whendehydration at –150 MPa was initiated after 36 or 40 hhydration. Slowed germination rates were not observed when dehydrationwas initiated before 36 h, when dehydration occurred at –4MPa, or when dehydration at –150 MPa was preceded by dehydrationat –4 MPa for 24 h. Exogenous abscisic acid (ABA) concentrationsabove 10^–6 M inhibited germination. However, endogenouswhole seed ABA levels declined during imbibition due to leaching,and did not increase during dehydration treatments that delayedgermination. These results illustrate that rate of late-occurringdehydration treatments is critical in determining subsequentgermination response. We propose that seed response to late-occurringdehydration may be of ecological significance in timing radicleemergence to coincide with adequate soil moisture for seedlingestablishment. Key words: Abscisic acid, seed germination, timing     

Effect of hydration on plasma volume and endocrine responses to water immersion

To determine the effect of hydration on the early osmotic and intravascular volume and endocrine responses to water immersion the hematocrit, hemoglobin, plasma renin activity (PRA), and plasma electrolyte, aldosterone (PA), and vasopressin (PVP) concentrations were measured during immersion following 24-h dehydration; these were compared with corresponding values following rapid rehydration. Six men and one woman (age 23-46 yr) underwent 45 min of standing immersion to the neck preceded by 45-min standing without immersion, first dehydrated, and then 105 min later after rehydration with water. Immersion caused an isotonic expansion of the plasma volume (P less than 0.001), which occurred independently of hydration status. Suppression of PRA (P less than 0.001) and PA (P less than 0.001) during both immersions also occurred independently of hydration status. Suppression of plasma vasopressin was observed during dehydrated immersion (P less than 0.001) but not during rehydrated immersion. It is concluded that plasma tonicity is not a factor influencing PVP suppression during water immersion.     

Soil nitrification and foliar δ15N declined with stand age in trembling aspen and jack pine forests in northern Alberta,Canada

Aims

Seed germination and seedling emergence are vulnerable to water stress in arid environments. When precipitation is low and unpredictable during the early growing season, seeds near the sand surface often suffer from hydration/dehydration during germination. We investigated the responses of seedling emergence and survival of a sand dune grass with high sand stabilization value to amount and frequency of precipitation and depth of burial in sand.

Methods

Effects of amount and frequency of precipitation, burial and hydration/dehydration on seedling emergence of Leymus secalinus, were examined using standard procedures.

Results

Seedling emergence was affected by amount and frequency of monthly precipitation and depth of burial, and it decreased as precipitation frequency decreased with same amount of precipitation. Highest emergence percentage was obtained with 100 or 150 mm precipitation at 1–4 cm depth. Hydration/dehydration treatments decreased germination and increased dormancy percentage. Young seedlings with root lengths of 0–1 mm desiccated up to 30 days revived after rehydration.

Conclusions

Seedling emergence of L. secalinus is adapted to 150 mm monthly precipitation with frequency of 10–30 times per month, 1–4 cm burial depth and dehydration interval of 1–2 days. Alteration of amount and/or frequency of precipitation caused by climate change could markedly affect seedling emergence and population regeneration of this species.     

Relationship between initiation of cell elongation and cell division in radicles of germinating seeds

The initiation of axial organ growth in germinating broad bean (Vicia faba var. minor) and cotton (Gossypium hirsutum) seeds was studied in terms of cell elongation and cell division. Seed imbibition occurred in polyethylene glycol (M.W.6000) solutions at various concentrations that retarded the radicle protrusion and maintained the tissue hydration at various levels. The triggering of cell elongation in broad bean hypocotyl or cotton radicle depended on tissue hydration up to the threshold level. The initiation of cell elongation was independent of the processes preparing for the initiation of cell division in the meristems. The appearance of mitotic activity in roots was examined relative to water content in the meristem, time of radicle emergence, and root length. The initiation of cell division did not directly depend on hydration level reached and time of radicle protrusion; however, the commencement of mitoses was determined by the presence of a threshold number of elongating cells. The possibility of a mitotic factor formed by elongating cells is discussed.Abbreviations PEG polyethylene glycol     

Characterization of Solute Efflux from Dehydration Injured Soybean (Glycine max L. Merr) Seeds

Soybean (Glycine max L. Merr) seeds lose their tolerance of dehydration between 6 and 36 hours of imbibition. Soybean axes and cotyledons were excised 6 hours (tolerant of dehydration) and 36 hours (susceptible) after commencing imbibition and subsequently dehydrated to 10% moisture. Kinetics of the efflux of potassium, phosphate, amino acid, sugar, protein, and total electrolytes were compared in the four treatments during rehydration. Only slight differences were observed in the kinetics of solute efflux between the two cotyledon treatments dehydrated at 6 and 36 hours suggesting that the cotyledons may retain their tolerance of dehydration at this stage of germination. Several symptoms of injury were observed in the axes dehydrated at 36 hours. An increase in the initial leakage of solutes during rehydration, as quantified by the y-intercept of the linear regression line for solute efflux between 2 and 8 hours suggests an increased incidence of cell rupture. An increase in the rate of solute efflux (slope of regression line between 2 and 8 hours) from fully rehydrated axes was observed in comparison to axes dehydrated at 6 hours. The Arrhenius activation energy for potassium, phosphate, and amino acid efflux decreased and for protein remained unchanged. Both observations indicate an increase in membrane permeability in dehydration-injured tissue. Increasing the H⁺ concentration of the external solution increased K⁺ efflux from both control and dehydrated/rehydrated samples, increased sugar efflux from axes at 6 hours imbibition but decreased sugar efflux from axes at 36 hours imbibition, indicating changes in membrane properties during germination. The dehydration treatment did not alter the pattern of the pH response of axes dehydrated at 6 or 36 hours but did increase the quantity of potassium and sugar efflux from dehydration injured axes. These results are interpreted as indicating that dehydration of soybean axes at 36 hours of imbibition increased both the incidence of cell rupture during rehydration and altered membrane permeability of the rehydrated tissue.     

Architectural and biochemical changes in embryonic tissues of maize under cadmium toxicity

Heavy metals greatly alter plant morphology and architecture, however detailed mechanisms of such changes are not fully explored. Two experiments were conducted to investigate the influence of cadmium (CdCl₂·2.5H₂O) on some germination, morphological, biochemical and histological characteristics of developing embryonic tissue of maize. In the first experiment, maize seeds were germinated in increasing levels of CdCl₂ (200–2000 μm ) in sand and measurements were taken of changes in germination and seedling development attributes. Based on these parameters, 1000 μM CdCl₂ was chosen for detailed biochemical and histological measurements. In the second experiment, seeds were germinated in Petri dishes and supplied with 0 (control) or 1000 μM CdCl₂ (Cd‐treated). Radicle, plumule, coleoptile and coleorhiza were measured for biochemical and histological changes. The highest amount of Cd was in the coleorhiza and radicle. Free proline, soluble sugars, anthocyanin, soluble phenolics, ascorbic acid, H₂O₂ and MDA were significantly higher in coleorhizae, followed by the coleoptile, radicle and plumule. Although the radicle and coleorhiza were relatively poor targets of Cd than the other tissues, Cd stress reduced cortical cell size and vascular tissues, and deformed xylem and phloem parenchyma in all plant parts. In conclusion, the main reason for reduced germination was the influence of Cd on architecture of the coleorhiza and coleoptile, which was the result of oxidative stress and other physiological changes taking place in these tissues.     

Kinetics of recovery of leaf hydraulic conductance and vein functionality from cavitation-induced embolism in sunflower

The kinetics of leaf vein recovery from cavitation-induced embolism was studied in plants of sunflower cv. Margot, together with the impact of vein embolism on the overall leaf hydraulic conductance (Kleaf). During the air-dehydration of leaves to leaf water potentials (Psi L) of -1.25 MPa, Kleaf was found to decrease by about 46% with respect to values recorded in well-hydrated leaves. When leaves, previously dehydrated to Psi L= -1.1 MPa (corresponding to the turgor loss point), were put in contact with water, Kleaf recovered completely in 10 min and so did leaf water potential. Functional vein density was estimated in both dehydrating and rehydrating leaves in terms of total length of red-stained veins infiltrated with a Phloxine B solution per unit leaf surface area. Veins were found to embolize (unstained) with kinetics showing a linear relationship with Kleaf so that about a 70% loss of functional veins corresponded with a Kleaf loss of 46%. Cavitated veins recovered from embolism within 10 min from the beginning of leaf rehydration. These data indicate that: (a) leaves of sunflower underwent substantial vein embolism during dehydration; (b) vein embolism and leaf hydraulic efficiency apparently recovered from dehydration completely and rapidly upon rehydration; (c) vein refilling occurred while conduits were still at more negative xylem pressures than those required for spontaneous bubble dissolution on the basis of Henry's law. The possible consistent contribution of vital mechanisms for vein refilling is discussed.     

Effects of dehydration and rehydration on the intravascular space in horses

• 1.1. The resistance of sub-tropical horses, and desert-dwelling horses to 72 hr dehydration/24 hr rehydration was investigated via changes in red cell parameters and plasma protein concentration.
• 2.2. Red cell count, haemoglobin and haematocrit increased up to 48 hr dehydration. Between 48 and 72 hr dehydration these parameters decreased, implying a fluid shift onto the intravascular space from the interstitium/hindgut. Most parameters had regained baseline values by 24 hr rehydration.
• 3.3. Mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration and total plasma protein were not significantly different between breeds at, or between most stages of hydration.
• 4.4. Protection of plasma volume during dehydration/rehydration was aided by maintaining intravascular protein (especially albumin) levels. Red cells were transiently dehydrated and overhydrated but resisted osmolysis.

     

Changes in DNA and microtubules during loss and re-establishment of desiccation tolerance in germinating Medicago truncatula seeds

Desiccation tolerance (DT) in orthodox seeds is acquired during seed development and lost upon imbibition/germination, purportedly upon the resumption of DNA synthesis in the radicle cells. In the present study, flow cytometric analyses and visualization of microtubules (MTs) in radicle cells of seedlings of Medicago truncatula showed that up to a radicle length of 2 mm, there is neither DNA synthesis nor cell division, which were first detected in radicles with a length of 3 mm. However, DT started to be lost well before the resumption of DNA synthesis, when germinating seeds were dried back. By applying an osmotic treatment with polyethylene glycol (PEG) before dehydration, it was possible to re-establish DT in seedlings with a radicle up to 2 mm long. Dehydration of seedlings with a 2 mm radicle, with or without PEG treatment, caused disassembly of MTs and appearance of tubulin granules. Subsequent pre-humidification led to an almost complete disappearance of both MTs and tubulin granules. Upon rehydration, neither MTs nor tubulin granules were detected in radicle cells of untreated seedlings, while PEG-treated seedlings were able to reconstitute the microtubular cytoskeleton and continue their normal development. Dehydration of untreated seedlings also led to an apoptotic-like DNA fragmentation in radicle cells, while in PEG-treated seedlings DNA integrity was maintained. The results showed that for different cellular components, desiccation-tolerant seedlings may apply distinct strategies to survive dehydration, either by avoidance or further repair of the damages.     

The Morphology of Germination in Setaria lutescens (Gramineae): The Effects of Covering Structures and Chemical Inhibitors on Dormant and Non-dormant Florets

The sequence of organ emergence in embryos of the yellow foxtailgrass (Setaria lutescens) is similar to that reported for othergrasses: coleorhiza, radicle, coleoptile and first leaf. Thecoleorhiza emerges by forcing open a hinged flap on the lemma.Coleorhiza trichomes form soon after emergence. The radicleprotrudes through the abaxial surface of the coleorhiza. Thecoleoptile elongates in a downward direction initially as itpasses between the lemma and palea, but immediately turns upward.The first leaf emerges by protruding through a slit-like creaseon the adaxial surface of the coleoptile. Embryos excised fromdormant florets are shown to germinate as well as those fromnon-dormant florets. Experiments are described which show theinhibitory effects of the embryo covering structures; the lemma,palea and caryopsis coat. Other experiments are discussed concerningthe effects on germination of the inhibitors abscisic acid andcycloheximide. An intermediate concentration of cycloheximide(10^–4 M) does not decrease germination percentage, butrather inhibits radicle growth but no coleoptile elongation.The significance of these observations is discussed.     

The validity of multifrequency bioelectrical impedance measures to detect changes in the hydration status of wrestlers during acute dehydration and rehydration

The objective of this study was to examine the validity of multifrequency direct segmental bioelectrical impedance analysis (DSM-BIA) measures to detect changes in the hydration status of wrestlers after they underwent 3% acute dehydration and a 2-hour rehydration period. Fifty-six National Collegiate Athletic Association wrestlers: (mean ± SEM); age 19.5 ± 0.2 years, height 1.73 ± 0.01 m, and body mass (BM) 82.5 ± 2.3 kg were tested in euhydrated, dehydrated (-3.5%), and 2-hour rehydration conditions using DSM-BIA to detect the changes in hydration status. The hydration status was quantified by measuring the changes in plasma osmolality (P(osm)), urine osmolality (Uosm), urine specific gravity (U(sg)), BM, and weighted segmental impedance at frequencies of 5, 20, 50, 100, and 500 kHz. Weighted segmental impedance significantly increased after a 3.5% reduction in the body weight for all the 5 frequencies evaluated, but it did not return to baseline at 2-hour rehydration. P(osm) (303 ± 0.6 mOsm·L(-1)), Uosm (617 ± 47 mOsm·L(-1)), and U(sg) (1.017 ± 0.001) all significantly increased at postdehydration and returned to baseline at 2-hour rehydration. Estimations of extracellular water were significantly different throughout the trial, but there were no significant changes in the estimations of the total body water or intracellular water. The results of this study demonstrate the potential use of DSM-BIA as a field measure to assess the hydration status of wrestlers for the purpose of minimal weight certification before the competitive season. When employing DSM-BIA to assess the hydration status, the results indicated that the changes in weighted segmental impedance at the frequencies evaluated (5, 20, 50, 100, and 500 kHz) are sensitive to acute changes in dehydration but lag behind changes in the standard physiological (plasma and urinary) markers of hydration status after a 2-hour rehydration period.     

Determining the effect of hydration upon the properties of ligaments using pseudo Gaussian stress stimuli

The level of tissue hydration is known to effect viscoelastic material properties. However, prior studies have not fully investigated the effect of hydration on dynamic behavior nor compared the results of transient and dynamic behavior. The material properties of medial collateral rat knee ligaments were studied in relation to hydration, using (sequentially) 0.3 osmolar artificial interstitial fluid (AIF), solutions of AIF plus sucrose with osmolarity 1.05, 1.80 or 2.55, and then AIF. In each solution, the complex compliance was determined as a function of frequency, and the creep response was measured. Complex compliance was determined from a constitutive model created by applying a 0.4+/-0.2 MPa pseudo Gaussian (PGN) stress stimulus to the ligament. Dehydration caused a reduction in cross-sectional area that was linearly related to the osmolarity of the solution. Reductions of up to 52% were observed and were reversible upon rehydration. Dehydration caused a reduction in the creep rate that was not immediately recovered upon rehydration. The storage compliance was reduced by up to 50% with dehydration; these changes were reversed upon rehydration. The loss compliance and phase angle were not affected by dehydration. Transient and dynamic experiments examine different viscoelastic characteristics and both types of tests appear to be necessary to fully characterize the effects of hydration.     

Dehydration Injury in Germinating Soybean (Glycine max L. Merr.) Seeds

The sensitivity of soybean (Glycine max L. Merr. cv Maple Arrow) seeds to dehydration changed during germination. Seeds were tolerant of dehydration to 10% moisture if dried at 6 hours of imbibition, but were susceptible to dehydration injury if dried at 36 hours of imbibition. Dehydration injury appeared as loss of germination, slower growth rates of isolated axes, hypocotyl and root curling, and altered membrane permeability. Increased electrolyte leakage due to dehydration treatment was observed only from isolated axes but not from cotyledons, suggesting that cotyledons are more tolerant of dehydration. The transition from a dehydration-tolerant to a dehydration-susceptible state coincided with radicle elongation. However, the prevention of cell elongation by osmotic treatment in polyethylene glycol (−6 bars) or imbibition in 20 micrograms per milliliter cycloheximide did not prevent the loss of dehydration tolerance suggesting that neither cell elongation nor cytoplasmic protein synthesis was responsible for the change in sensitivity of soybean seeds to dehydration. Furthermore, the rate of dehydration or rate of rehydration did not alter the response to the dehydration stress.     

海洋深层矿物水可有效促进人体脱水后再水合

为了探讨摄入海洋性矿物质水对脱水后再水合作用的影响,本研究招募18名年轻男性为受试者,采双盲交叉实验设计,将所有受试者平均分成安慰剂组与海洋性矿物质组,于高温环境进行单次中强度运动至脱水体重的3%,摄入脱水量1.5倍的水份,在脱水后4 h内测量尿液量,并在脱水后24 h和48 h测量体重、尿液颜色、血红细胞与血比容。研究表明:摄入水份后24 h体重已经恢复至脱水前,但是两组无显著差异;摄入海洋性矿物质在4 h内所产生的尿液量高于安慰剂组;血红细胞数目与血比容于补水后24 h与48 h低于脱水前,但是两组无显著差异;尿液颜色在补水后24～48 h高于脱水前,但是摄入海洋性矿物质在24 h的尿液颜色低于安慰剂组。本研究初步认为,摄入海洋性矿物质可以加速身体恢复的程度,建议摄入海洋性矿物质来促进身体的再水合作用。     

Weakening of muskmelon perisperm envelope tissue 4

Muskmelon (Cucumis melo L.) embryos are enclosed in an envelopeof tissue consisting of a layer of endosperm and a multi-cell-layeredperisperm that the radicle must penetrate for germination tooccur. The force and energy required to penetrate the perispermenvelope tissue were measured using an Instron universal testingmachine at a crosshead speed of 5 mm min^–1 after 0, 10,15, 22, 23, and 25 h of imbibition at 25C. The cellular structureof perisperm envelope tissue surrounding the radicle was observedafter 10, 15, 20, 25, and 48 h of imbibition using scanningelectron microscopy. The force required to puncture 5-mm-long,micropylar seed pieces declined steadily from 1.65 N in driedseeds to 0.65 N after 21 h of imbibition. The penetration energydeclined from 3.0 N mm in dry seeds to 1.1 N mm at 21 h afterthe start of imbibition when the first seeds germinated. Theforce and energy required to penetrate germinated seed pieceswere 0.55 N and 0.9 N mm, respectively, so the net punctureforce and energy needed to rupture the micropylar region ofthe perisperm envelope was roughly 0.10 N and 0.2 N mm at radicleemergence, respectively. Instron measurements of penetrationforce and energy decreased dramatically at crosshead speedsless than the 5 mm min^–1. Crosshead speeds greater than5 mm min^–1 may overestimate the pressure needed to ruptureperisperm and endosperm tissues. Intracellular cracks were firstobserved in SEM images 15 h after the start of imbibition, andafter 20 h cracking was apparent throughout the micropylar regionof the perisperm envelope. The perisperm envelope ruptured inone of two ways, coincident with radicle emergence. In approximately85% of muskmelon seeds, a large crack formed in the perispermenvelope adjacent to the radicle, while in roughly 15 % a circulararea of the perisperm envelope detached during radicle emergence.In dead seeds, the penetration force remained constant from10–24 h after the start of imbibition, and there wereno visible signs of tissue degradation. Cellular degradationand weakening of the perisperm envelope tissue precedes radicleemergence in muskmelon seeds. Key words: Seed, Instron, turgor, cell wall, electron microscopy, Cucumis melo     

A rapid effect of kinetin on rehydration of tobacco leaf tissue

Partly dehydrated tobacco leaf tissue (Nicotiana rustica), stripped of the lower epidermis, was used to study the effect of kinetin on the rate of rehydration. Depending on the rate of rehydration in untreated tissue, kinetin either increased or decreased rehydration rates. The response to kinetin was very rapid and could be discerned in less than 2 minutes. On extensive dehydration, the tissue lost the capacity to respond to kinetin. Salinity stress, which decreases the endogenous level of cytokinins in the plant, conditions the leaf to stimulation of rehydration by kinetin.     

Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean

Controlled environment experiments were performed to determinethe effects of temperature and water potential on germination,radicle elongation and emergence of mungbean (Vigna radiata(L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (15–45°C) and water potentials (0 to –2.2 MPa) on germinationand radicle elongation rates were studied using an osmoticumtechnique, in which seeds were held against a semi-permeablemembrane sac containing a polyethylene glycol solution. Linearrelationships were established between median germination time(Gt₅₀) and water potential at different temperatures, and betweenreciprocal Gt₅₀ (germination rate) and temperature at differentwater potentials. Germination occurred at potentials as lowas –2.2 MPa at favourable temperatures (30–40 °C),but was fastest at 40 °C when water was not limiting, withan estimated base temperature (T_b) of about 10 °C. Subsequentradicle elongation, however, was restricted to a slightly narrowertemperature range and was fastest at 35 °C. The conceptof thermal time was used to develop an equation to model thecombined effects of water potential and temperature on germination.Predictions made using this model were compared with the actualgermination obtained in a related series of experiments in columnsof soil. Some differences observed suggested the additionalimportance of the seed/soil/water contact zone in influencingseed germination in soil. Seedling emergence appeared to reflectfurther the radicle elongation results by occurring within anarrower range of temperatures and water potentials than germination.Emergence had an estimated T_b of 12.6 °C and was fastestat 35 °C. A soil matric potential of not less than about–0.5 MPa at sowing was required to obtain 50% or moreseedling emergence. Key words: Germination, temperature, water potential     

Phase behavior and glass transition of 1,2-dioleoylphosphatidylethanolamine (DOPE) dehydrated in the presence of sucrose

The effect of sucrose on the phase behavior of 1,2-dioleoylphosphatidylethanolamine (DOPE) as a function of hydration was studied using differential scanning calorimetry and X-ray diffraction. DOPE/sucrose/water dispersions were dehydrated at osmotic pressures (Pi) ranging from 2 to 300 MPa at 30 degrees C and 0 degrees C. The hexagonal II-to-lamellar gel (H(II)-->L(beta)) thermotropic phase transition was observed during cooling in mixtures dehydrated at Pior=57 MPa, the H(II)-->L(beta) thermotropic phase transition was precluded when sucrose entered the rigid glassy state while the lipid was in the H(II) phase. Sucrose also hindered the H(II)-to-lamellar crystalline (L(c)), and H(II)-to-inverted ribbon (P(delta)) lyotropic phase transitions, which occurred in pure DOPE. Although the L(c) phase was observed in dehydrated 2:1 (mole ratio) DOPE/sucrose mixtures, it did not form in mixtures with higher sucrose contents (1:1 and 1:2 mixtures). The impact of sucrose on formation of the ordered phases (i.e., the L(c), L(beta), and P(delta) phases) of DOPE was explained as a trapping of DOPE in a metastable H(II) phase due to increased viscosity of the sucrose matrix. In addition, a glass transition of DOPE in the H(II) phase was observed, which we believe is the first report of a glass transition in phospholipids.     

Protection mechanisms against excess light in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa

Mechanisms of avoidance and protection against light damage were studied in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa.In C. wilmsii, a combination of both physical and chemical changes appeared to afford protection against free radical damage. During dehydration leaves curled inwards, and the abaxial surface became exposed to light. The tissue became purple/brown in colour, this coinciding with a three-fold increase in anthocyanin content and a 30% decline in chlorophyll content. Thus light-chlorophyll interactions are progressively reduced as chlorophyll became masked by anthocyanins in abaxial layers and shaded in the adaxial layers. Ascorbate peroxidase (AP) activity increased during this process but declined when the leaf was desiccated (5% RWC). During rehydration leaves uncurled and the potential for normal light-chlorophyll interaction was possible before full hydration had occurred. Superoxide dismutase (SOD) and glutathione reductase (GR) activities increased markedly during this stage, possibly affording free radical protection until full hydration and metabolic recovery had occurred.In contrast, the leaves of X. viscosa did not curl, but light-chlorophyll interactions were minimised by the loss of chlorophyll and dismantling of thylakoid membranes. During dehydration, free radical protection was afforded by a four-fold increase in anthocyanin content and increased activities of AP, GR and SOD. These declined during rehydration. It is suggested that potential free radical damage may be avoided by the persistence of anthocyanins during the period of thylakoid membrane re-assembly and full chlorophyll restitution which only occurred once the leaves were fully rehydrated.