Changes in surface features during desiccation of the anhydrobiotic plant parasitic nematode Ditylenchus dipsaci

The anhydrobiotic nematode Ditylenchus dipsaci is a fast-dehydration strategist, itself generating the slow rate of water loss necessary for survival. A permeability slump occurs during the initial phases of desiccation. This may be produced by changes in the nematode's cuticle. Two scanning electron microscopic techniques were used to follow changes in surface structures during desiccation. Freeze substitution and critical-point drying produced artifacts that obscured changes produced by the desiccation of the nematode. Low-temperature field emission scanning electron microscopy (FESEM) was successful in following changes that reflected those observed by light microscopy (LM). Significant changes in diameter, the lateral alae, and the cuticular annulations were demonstrated using this technique. Two types of annulations were observed: the major annulations, which extended to meet the margins of the lateral alae, and the minor annulations, which did not. With desiccation the prominence of the annulations increased, their spacing decreased, and the minor annulations extended closer to the margins of the lateral alae. These observations are consistent with the permeability slump resulting from a decrease in the width of the annulation groove and an increase in its depth. However, this requires confirmation using techniques that can follow annulation changes in individual nematodes.     

Ultrastructural changes during recovery from anabiosis in the plant parasitic nematode, Ditylenchus

Ultrastructural changes after desiccation and rehydration of the anabiotic fourth-stage juveniles of the plant parasitic nematode Ditylenchus dipsaci (Kuhn) Filipjev are described and quantified. Anabiotic juveniles retain their structural integrity, although the cuticle decreases in thickness and the muscle cell sarcoplasm condenses. In contrast the structure of the non-anabiotic nematode Panagrellus silusae is completely disorganized by desiccation. Following rehydration of D. dipsaci there is a lag phase of 2-3 hr before the nematodes become active. During this period the juveniles undergo an ordered series of morphological changes. The lipid droplets within the intestinal cells coalesce and the cuticle increases in thickness. The muscle cell sarcoplasm expands, the spacing of the thick myofilaments increases and the mitochondria swell before recovering a more normal appearance. These morphological changes, together with earlier metabolic studies, indicate that repair occurs during the lag phase prior to recovery. This may involve membrane repair and the re-establishment of the ionic gradients essential for normal muscle and nerve function.     

Water relations during desiccation of cysts of the potato-cyst nematode Globodera rostochiensis

The loss during desiccation of osmotically active water (OAW), which freezes during cooling to -45 degrees C, and osmotically inactive water (OIW), which remains unfrozen, from the cysts of the potato cyst nematode, Globodera rostochiensis, was determined using differential scanning calorimetry. Exotherms and endotherms associated with non-egg compartments were not detected after 5 min desiccation at 50% relative humidity and 20 degrees C. The pattern of water loss from the cysts indicates that water is lost from compartments outside the eggs first, that nearly all the non-egg water is OAW and that the OIW content of the cyst is contained within the eggs. Water is lost from the eggs only after the OAW content outside the eggs falls below that within the eggs. Both OAW and OIW are lost from the eggs during desiccation but the eggs retain a small amount of OIW. Other animals which survive some desiccation but which are not anhydrobiotic will tolerate the loss of OAW but not the loss of their OIW. Anhydrobiotic animals can survive the loss of both their OAW and a substantial proportion of their OIW.     

Carbohydrate metabolism and restricted oxygen supply in the eggs of the silkworm, Bombyx mori

Increased oxygen supply to diapause eggs of the silkworm (O₂-incubation) effectively prevented diapause initiation and induced the same pattern of glycogen, polyol and lactate levels as was observed in normal non-diapause eggs. Sensitivity to oxygen decreased as embryonic development proceeded. After the termination of this sensitive period, accumulation of polyols and lactate followed.Experiments were carried out to test whether changes in the oxygen permeability of the egg membranes are involved in restricting the supply of this gas to eggs at the onset of diapause. Oxygen permeability of the chorion was measured with apparatus especially designed for this purpose. Although the chorion of the diapause egg was less permeable than that of the non-diapause egg, the oxygen permeability of the chorion does not change appreciably during the early developmental stages of the diapause eggs. The changes in rate of water loss through the egg membranes were measured during the early developmental stages of the embryos. The level of water loss decreased gradually as the formation of serosal cuticle proceeded. Moreover, it was observed that the water loss up to the time of formation of serosal cuticle was closely related to the oxygen permeability of the chorion.From these results, we suggest that the formation of the serosal cuticle may be an additional cause of the restricted oxygen supply at the onset of the diapause.     

Molting-specific downregulation of C. elegans body-wall muscle attachment sites: The role of RNF-5 E3 ligase

Repeated molting of the cuticula is an integral part of arthropod and nematode development. Shedding of the old cuticle takes place on the surface of hypodermal cells, which are also responsible for secretion and synthesis of a new cuticle. Here, we use the model nematode Caenorhabditis elegans to show that muscle cells, laying beneath and mechanically linked to the hypodermis, play an important role during molting. We followed the molecular composition and distribution of integrin mediated adhesion structures called dense bodies (DB), which indirectly connect muscles to the hypodermis. We found the concentration of two DB proteins (PAT-3/β-integrin and UNC-95) to decrease during the quiescent phase of molting, concomitant with an apparent increase in lateral movement of the DB. We show that levels of the E3-ligase RNF-5 increase specifically during molting, and that RNF-5 acts to ubiquitinate the DB protein UNC-95. Persistent high levels of RNF-5 driven by a heatshock or unc-95 promoter lead to failure of ecdysis, and in non-molting worms to a progressive detachment of the cuticle from the hypodermis. These observations indicate that increased DB dynamics characterizes the lethargus phase of molting in parallel to decreased levels of DB components and that temporal expression of RNF-5 contributes to an efficient molting process.     

Rapid changes in desiccation resistance in Drosophila melanogaster are facilitated by changes in cuticular permeability

Insects can improve their desiccation resistance by one or more of (1) increasing their water content; (2) decreasing water loss rate; or (3) increasing the amount of water able to be lost before death. Female Drosophila melanogaster have previously been reported to increase their resistance to desiccation after a desiccation pre-treatment and recovery, but the mechanism of this increased desiccation resistance has not been explored. We show that female, but not male adult D. melanogaster increased their resistance to desiccation after 1 h of recovery from a 3 to 4.5 h pre-treatment that depletes them of 10% of their water content. The pre-treatment did not result in an increase in water content after recovery, and there is a slight increase in water content at death in pre-treated females (but no change in males), suggesting that the amount of water loss tolerated is not improved. Metabolic rate, measured on individual flies with flow-through respirometry, did not change with pre-treatment. However, a desiccation pre-treatment did result in a reduction in water loss rate, and further investigation indicated that a change in cuticular water loss rate accounted for this decrease. Thus, the observed increase in desiccation resistance appears to be based on a change in cuticular permeability. However, physiological changes in response to the desiccation pre-treatment were similar in male and female, which therefore does not account for the difference in rapid desiccation hardening between the sexes. We speculate that sex differences in fuel use during desiccation may account for the discrepancy.     

Water uptake and morphological changes during recovery from anabiosis in the plant-parasitic nematode, Ditylenchus dipsaci

The changes in water content and structural organization that occur during the rehydration of the anabiotic 4th-stage juveniles of the plant-parasitic nematode Ditylenchus dipsaci are described. Morphological changes include the coalescence of lipid droplets and the appearance of a hyaline layer beneath the cuticle. Changes in diameter are mainly responsible for volume changes. Changes in the appearance of the hyaline layer suggests that the muscle cells undergo some sort of repair process before activity resumes.     

Effect of osmotic desiccation on longevity and temperature tolerance of Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae)

Limited storage stability severely restricts the biological control potential of slug-parasitic nematodes. In a series of experiments, we evaluated the effects of temperature and osmotic desiccation on the short- and long-term survival of the slug-parasitic nematode Phasmarhabditis hermaphrodita. Nematode survival in petri dishes at 1,500 infective juveniles/ml did not differ significantly at 5, 10, and 15 C but declined rapidly at 25 and 30 C. At 25 C about 50% of the nematodes survived for 4 wk, but at 30 C no nematode survived past 1 day. About 50% of the nematodes survived for 32 wk at 20 C. About 35-40% of the nematodes survived up to a year at 5, 10, and 15 C. Phasmarhabditis hermaphrodita showed poor survival under osmotic desiccation in glycerol with 15 and 20% glycerol significantly reducing survival at 5 and 15 C. Although the nematodes tolerated 10% glycerol, this level of desiccation also did not enhance long-term survival at either 5 or 15 C. There was a significant decrease in nematode survival in 10% glycerol at 25 C during the first 2-3 wk, but about 16% of the nematodes survived for 6 wk in 10% glycerol as compared with only 1% survival in water. The greatest benefit of osmotic desiccation in glycerol was observed in the enhanced survival of P. hermaphrodita at temperature extremes. Over 96% of the nematodes survived a 6-hr exposure to 35 C in 10% glycerol, whereas only 9% survived in water. Similarly, over 90% of the nematodes survived an exposure to -20 C for 4 hr in 10% glycerol, but less then 2% survived in water. We conclude that 5-15 C is an optimum temperature range for the storage of P. hermaphrodita. We also conclude that osmotic desiccation in 10% glycerol can substantially increase survival of P. hermaphrodita at temperature extremes (35 and -20 C) for short periods but has no effect on nematode longevity at the optimum temperature range of 5-15 C.     

Effects of changes in temperature and saturation deficit on the survival of eggs of Trichostrongylus colubriformis (Nematoda: Trichostrongylidae)

and 1972. Effects of changes in temperature and saturation deficit on the survival of eggs of Trichostrongylus colubriformis (Nematoda: Trichostrongylidae) International Journal for Parasitology, 2: 439–447. In conformity with a hypothesis relating to survival of the developing T. colubriformis egg exposed to desiccation, samples of eggs initially at the early blastomere stage of development showed decreased mortality during development with increasing temperature of incubation up to 25°C, for approximately constant rates of evaporation. At 30°C there was a higher percentage mortality for fixed evaporation rate than at 20° or 25°C. It is suggested that at 30°C there may be an abrupt increase in the initial rate of water loss from the developing embryo resulting from a change in the permeability to water of the lipid layer of the egg envelope.

Fully embryonated T. colubriformis eggs were obtained by incubation at 20°C in the presence of a moderate saturation deficit during development. When such eggs were transferred to 30° and 40°C there was no mortality at the higher temperature, providing that the saturation deficit was substantially increased. A hypothesis proposed for survival at high temperature is based on analogy with water loss through the arthropod cuticle and is attributed to a decrease in permeability of the protein-chitin layer of the egg envelope under conditions of high evaporation rate, even though permeability of the lipid layer might be increased by high temperature.     

Role of AQP2 during apoptosis in cortical collecting duct cells

Background information. A major hallmark of apoptosis is cell shrinkage, termed apoptotic volume decrease, due to the cellular outflow of potassium and chloride ions, followed by osmotically obliged water. In many cells, the ionic pathways triggered during the apoptotic volume decrease may be similar to that observed during a regulatory volume decrease response under hypotonic conditions. However, the pathways involved in water loss during apoptosis have been largely ignored. It was recently reported that in some systems this water movement is mediated via specific water channels (aquaporins). Nevertheless, it is important to identify whether this is a ubiquitous aspect of apoptosis as well as to define the mechanisms involved. The aim of the present work was to investigate the role of aquaporin‐2 during apoptosis in renal‐collecting duct cells. We evaluated the putative relationship between aquaporin‐2 expression and the activation of the ionic pathways involved in the regulatory volume response. Results. Apoptosis was induced by incubating cells with a hypertonic solution or with cycloheximide in two cortical collecting duct cell lines: one not expressing aquaporins and the other stably transfected with aquaporin‐2. Typical features of apoptosis were evaluated with different approaches and the water permeability was measured by fluorescence videomicroscopy. Our results show that the rate of apoptosis is significantly increased in aquaporin‐2 cells and it is linked to the rapid activation of volume‐regulatory potassium and chloride channels. Furthermore, the water permeability of cells expressing aquaporin‐2 was strongly reduced during the apoptotic process and it occurs before DNA degradation. Conclusions. These results let us propose that under apoptotic stimulation aquaporin‐2 would act as a sensor leading to a co‐ordinated activation of specific ionic channels for potassium and chloride efflux, resulting in both more rapid cell shrinkage and more rapid achievement of adequate levels of ions necessary to activate the enzymatic apoptotic cascade.     

Water Stress and Protein Synthesis: V. Protein Synthesis, Protein Stability, and Membrane Permeability in a Drought-sensitive and a Drought-tolerant Moss

The effects have been studied of water stress and desiccation on protein synthesis in the drought-tolerant moss Tortula ruralis and the drought-sensitive moss Hygrohypnum luridum. At any particular level of steady state water stress, the inhibition of protein synthesis was greater in H. luridum than in T. ruralis. Water stress-induced changes in the pattern of protein synthesis, as determined by the double label ratio technique, were minor in T. ruralis, but major in H. luridum. Proteins of both mosses were found to be stable during desiccation and subsequent rehydration. Changes in membrane permeability, as indicated by the leakage of amino acid, were observed during rehydration of desiccated moss and were dependent on the rate of desiccation. The leakage was small and reversible in T. ruralis but large and irreversible in H. luridum. Although H. luridum failed to recover from complete desiccation (80% loss in fresh weight), it was able to recover fully from steady state stress under conditions where a maximum loss of 55% in fresh weight was recorded.     

Effect of PEG-treatment on the leaf growth response and auxin content in shoots of wheat seedlings

Addition of Polyethylene glycol(PEG) to the nutrient medium of wheatseedlings led to a rapid cessation of leaf growth and shrinkage, measured withahighly sensitive growth sensor, followed by a partial restoration of extensionin the subsequent 40 min. This osmotic shock resulted in IAAaccumulation in the shoots. Leaf extensibility, measured by addition of 5g as a counterweight to an extensiometer, did not change for 20min after the start of the treatment, but then increased andbecametwice as high as the initial value. Changes in leaf extensibility coincidedwitha restoration of leaf growth. Leaf shrinkage, which was observed immediatelyafter addition of the osmoticum, suggests that the initial growth response wasdue to a water deficit, which led to a decrease in cell turgor. Howeverrestoration of growth during water stress could be due to changes in cell wallrheological properties, which could be triggered by IAA accumulation.     

Impact of body melanisation on desiccation resistance in montane populations of D. melanogaster: Analysis of seasonal variation

In the montane localities of subtropical regions, winter is the dry season and ectothermic drosophilids are expected to evolve desiccation resistance to cope with drier climatic conditions. An analysis of six montane populations (600–2226 m) of D. melanogaster showed variations for body melanisation (i.e. pigmentation) and desiccation resistance across seasons as well as along altitude. During winter season, plastic changes for melanisation of three posterior abdominal segments (5th + 6th + 7th) correspond with higher desiccation resistance. Thus, we analyzed genetic and plastic effects for these ecophysiological traits by comparing wild-caught and laboratory reared individuals of D. melanogaster for autumn as well as winter season. A ratio of slope values in wild vs. laboratory populations has shown a 1.64-fold plastic effect during autumn; and a two-fold effect during winter. For body melanisation and desiccation resistance, evolutionary response to altitudinal environmental gradient is similar to the phenotypic response across seasons. Thus, our observations are in agreement with the co-gradient hypothesis. Further, we tested the hypothesis whether a thicker cuticle (either due to melanisation or cuticular lipids) leads to lesser cuticular water loss and higher desiccation resistance across seasons as well as according to altitude. Based on within and between population analyses, body melanisation was found to be positively correlated with desiccation resistance but negatively with cuticular water loss. Interestingly, there were no changes in the amount of cuticular lipids per fly across seasons as well as along altitude; and therefore cuticular lipids did not account for desiccation resistance. Cuticular water loss exhibited negative correlation with body melanisation but not with cuticular lipids as well as with changes in body size across seasons. Thus, our data suggest that seasonal changes in body melanisation confer desiccation resistance in montane populations of D. melanogaster.     

The root microtubule cytoskeleton and cell cycle analysis through desiccation of Brassica napus seedlings

Desiccation tolerance (DT) of orthodox seeds is reduced upon their germination. The main aim of this study was to estimate the range of rape seedling DT by examining the consequences of desiccation on the distribution, stability and orientation of microtubules in diverse cells. Using different parameters, such as relative water content (RWC), the tetrazolium viability test and electrolyte leakage, it has been demonstrated that a small percentage decrease in relative humidity can cause irreparable changes in membrane permeability, as well as in nuclear structure and microtubule cytoskeleton stability. Seedling root tips survived when exposed to low desiccation stress intensity, but small changes in microtubule behavior were observed. Cortical microtubules formed thick arrays, especially near the plasma membrane. Water loss also resulted in a reduction of the mitotic activity. More rapid desiccation caused microtubule depolymerization. Occasionally, abnormal tubulin aggregates were visible. Cell divisions were not detectable under these conditions. Due to the observable microtubule defects, the hypersensitivity of the microtubule cytoskeleton might be a useful and simple parameter for estimating environmental stress intensity.     

The tardigrade cuticle II. Evidence for a dehydration-dependent permeability barrier in the intracuticle

Tardigrades weighed during desiccation in high or low humidities show a short period of rapid transpiration followed by an abrupt decline in transpiration which virtually arrests water loss. The amount of water retained following this 'permeability slump' is greater at low rates of desiccation but the slump is not a metabolic phenomenon, being reproducible in dead or narcotised animals. Tardigrades rinsed in hot chloroform (62 degrees C) for 5 hr still show the characteristic permeability decline when desiccated in 80% RH. However, 25hr rinsing in hot chloroform apparently obliterates the slump. Estimates of the bound water content of tardigrades by DSC show that this can account for the dehydrated masses of these chloroform-rinsed animals and that all free water is probably transpired. Lipid analysis of the 25 hr chloroform extracts by GC-MS reveals several lipid classes, predominantly free fatty acids (C(12)-C(18)); these are not detectable in the 5 hr extracts. Control rinsing in hot water has no apparent effect on the permeability slump. TEM tracer studies with lanthanum show the lipid-rich intracuticle to serve as a transpiration barrier in dehydrated animals but not in fully hydrated specimens. There is thus strong support for the role of intracuticular lipids in effecting the permeability slump. A model to explain this phenomenon on the basis of lipid phase changes is postulated.     

Evaporative water loss, corporal temperature and the distribution of sympatric fiddler crabs (Uca) from south Texas

Desiccation and thermal stress are among the primary factors limiting terrestriality in crustaceans. Water loss was estimated as weight change in five sympatric species of Uca from south Texas for periods up to 7 hr in dry air. Simultaneously, corporal temperature was measured with a thermocouple placed under the carapace. To estimate integumental permeability to water, 115 mm2 portions of dorsal carapace were glued to U-shaped tubes containing a crab Ringer's solution. These were exposed to dry air and water permeability was estimated from weight change. In whole-animal studies, most rapid weight loss occurred in the first 5 min of exposure to dry air as the body temperature fell below ambient (25 degrees C) in all species. The three most terrestrial species exhibited significant survival over more aquatic congeners after prolonged desiccation. The greatest rate of water loss was observed in Uca subcylindrica which lost 22.9+/-3.0% body weight. Uca panacea and Uca spinicarpa lost 14.1+/-1.6% and 18.5+/-1.8%, respectively. Based on blood osmolarity changes, Uca longisignalis and Uca rapax were more resistant to water loss than Uca subcylindrica under these conditions. Water loss from sections of the dorsal carapace were highest in Uca spinicarpa (10.4 mg/hr/cm2) and Uca longisignalis (8.9 mg/ hr/cm2). Uca subcylindrica and Uca panacea were intermediate (4.5 and 4.2 mg/hr/cm2) while Uca rapax expressed the lowest value (2.9 mg/hr/cm2). These observations support the notion that water loss can effectively lower body temperature in fiddler crabs. However, an inverse relationship between terrestriality and integumental permeability was not evident in these sympatric congeners. Ultimately a balance between physiological and behavioral mechanisms must be achieved for adaptation to the semi-arid habitats in south Texas.     

Fructose and glucose ingestion and muscle glycogen use during submaximal exercise

Substrate utilization after fructose, glucose, or water ingestion was examined in four male and four female subjects during three treadmill runs at approximately 75% of maximal O2 uptake. Each test was preceded by three days of a carbohydrate-rich diet. The runs were 30 min long and were spaced at least 1 wk apart. Exercise began 45 min after ingestion of 300 ml of randomly assigned 75 g fructose (F), 75 g glucose (G), or control (C). Muscle glycogen depletion determined by pre- and postexercise biopsies (gastrocnemius muscle) was significantly (P less than 0.05) less during the F trial than during C or G. Venous blood samples revealed a significant increase in serum glucose (P less than 0.05) and insulin (P less than 0.01) within 45 min after the G drink, followed by a decrease (P less than 0.05) in serum glucose during the first 15 min of exercise, changes not observed in the C or F trials. Respiratory exchange ratio was higher (P less than 0.05) during the G than C or F trials for the first 5 min of exercise and lower (P less than 0.05) during the C trial compared with G or F for the last 15 min of exercise. These data suggest that fructose ingested before 30 min of submaximal exercise maintains stable blood glucose and insulin concentrations, which may lead to the observed sparing of muscle glycogen.     

Freezing injury in potato leaves

Time-temperature profiles of freezing leaves from frost-resistant (Solanum acaule Bitt.) and frost-susceptible (Solanum tuberosum L. subsp. tuberosum Hawkes) types of potatoes did not reveal any major differences. The pattern of change in resistance of leaves to low voltage, low frequency current during freezing was different in the frost-resistant and susceptible leaves. In tissue sections from both types of leaves, cells freeze extracellularly at cooling velocities lower than 5 C per minute. Cells from leaves of resistant plants showed a higher osmotic pressure but not a higher water permeability than those from susceptible plants. The extent of injury caused by even very slow freezing was greater than that caused by equivalent isopiestic desiccation, particularly in susceptible leaves. The higher osmotic pressure in cells of leaves from resistant plants can account for the greater desiccation resistance but not for the frost resistance observed.     

Agonist-induced cytoplasmic volume changes in cultured rabbit parietal cells

Concomitant Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange activation occurs during stimulation of acid secretion in cultured rabbit parietal cells, possibly related to a necessity for volume regulation during the secretory process. We investigated whether cytoplasmic volume changes occur during secretagogue stimulation of cultured rabbit parietal cells. Cells were loaded with the fluorescent dye calcein, and the calcein concentration within a defined cytoplasmic volume was recorded by confocal microscopy. Forskolin at 10(-5) M, carbachol at 10(-4) M, and hyperosmolarity (400 mosmol) resulted in a rapid increase in the cytoplasmic dye concentration by 21 +/- 6, 9 +/- 4, and 23 +/- 5%, respectively, indicative of cell shrinkage, followed by recovery to baseline within several minutes, indicative of regulatory volume increase (RVI). Depolarization by 5 mM barium resulted in a decrease of the cytoplasmic dye concentration by 10 +/- 2%, indicative of cell swelling, with recovery within 15 min, and completely prevented forskolin- or carbachol-induced cytoplasmic shrinkage. Na(+)/H(+) exchange inhibitors slightly reduced the initial cell shrinkage and significantly slowed the RVI, whereas 100 microM bumetanide had no significant effect on either parameter. We conclude that acid secretagoguges induce a rapid loss of parietal cell cytoplasmic volume, followed by RVI, which is predominantly mediated by Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange.     

Tolerance to oxidative stress induced by desiccation in Porphyra columbina (Bangiales, Rhodophyta)

Unravelling the mechanisms underlying desiccation tolerance is crucial in order to understand the position of algal species in the intertidal zone. The alga Porphyra columbina lives in the uppermost part of the rocky intertidal zones around the world and was selected as a model for this study. Naturally desiccated plants were collected during low tide and studied for morphological changes, oxidative burst induction, biomolecule oxidation, antioxidant responses, and photosynthetic status. Naturally hydrated plants collected during high tides were used for comparative purposes. In addition, changes induced by desiccation were assessed in vitro and the capacity to recover from desiccation was determined by rehydrating the fronds in seawater. The global results show that desiccation induces morphological and cellular alterations accompanied by a loss of ～96% of the water content. Overproduction of reactive oxygen species (ROS) was induced by desiccation and two peaks of H(2)O(2) were detected at 1 and 3 h of desiccation. However, during in vitro rehydration post-desiccation, the ROS quickly returned to the basal levels. At the biomolecular level, only a low production of oxidized proteins was recorded during desiccation, whereas the activity of diverse antioxidant enzymes increased. However, this activity diminished to near basal levels during rehydration. The photosynthetic efficiency (F(v)/F(m)) during desiccation declined by 94-96% of the values recorded in hydrated plants. This reduction was generated by the low levels of trapped energy flux per cross-section (TRo/CS), electron transport flux per CS (ETo/CS), and density of reaction centres (RC/SCo) as well as the chlorophyll content. The inverse pattern was observed for the levels of phycocyanin and phycoerythrin content. F(v)/F(m) and the photosynthetic indicators were restored to normal levels after only 5 min of rehydration. The results indicate that desiccation in P. columbina causes overproduction of ROS that is efficiently attenuated. The morphological and photosynthetic changes could be operating as tolerance mechanisms due to the fact that these responses principally prevent biomolecular alteration and cellular collapse. Thus, the activation of different physiological mechanisms helps to explain the high tolerance to desiccation of P. columbina and, at least in part, the position of this species at the highest level in the intertidal zone.