Pressure Induced Reorientation of Cortical Microtubules in Epidermal Cells of Lolium rigidum Leaves

In order to assess the effect on microtubule arrays of slowlypressurising cells over 50 s from 0.1 MPa (atmospheric pressure)to 55 MPa, microtubules in epidermal cells of Lolium rigidumleaves were visualised by immunofluorescent staining and fluorescencemicroscopy. In both control and pressure-treated leaves cellshape, measured as the ratio of cell length and width, can becorrelated to the arrangement of cortical microtubules. Microtubulearrays change from random to organised in cells whose lengthis greater than their width. In untreated leaves, elongatedcells have microtubules aligned predominantly transversely.In pressure-treated leaves, elongated cells have microtubulesaligned predominantly longitudinally. Thus, pressure treatmentresults in the rapid reorientation of organised cortical microtubulesfrom a transverse to a longitudinal orientation. (Received June 21, 1993; Accepted July 15, 1993)     

Germination and inactivation of Bacillus subtilis spores induced by moderate hydrostatic pressure

In this study, we investigated the mechanisms of spore inactivation by high pressure at moderate temperatures to optimize the sterilization efficiency of high‐pressure treatments. Bacillus subtilis spores were first subjected to different pressure treatments ranging from 90 to 550 MPa at 40°C, with holding times from 10 min to 4 h. These treatments alone caused slight inactivation, which was related to the pressure‐induced germination of the spores. After these pressures treatments, the sensitivity of these processed spores to heat (80°C/10 min) or to high pressure (350 MPa/40°C/10 min) was tested to determine the pressure‐induced germination rate and the advancement of the spores in the germination process. The subsequent heat or pressure treatments were applied immediately after decompression from the first pressure treatment or after a holding time at atmospheric pressure. As already known, the spore germination is more efficient at low pressure level than at high pressure level. Our results show that this low germination efficiency at high pressure seemed not to be related either to a lower induction or a difference in the induction mechanisms but rather to an inhibition of enzyme activities which are involved in germination process. In fact, high pressure was necessary and very efficient in inducing spore germination. However, it seemed to slow the enzymatic digestion of the cortex, which is required for germinated spores to be inactivated by pressure. Although these results indicate that high‐pressure treatments are more efficient when the two treatments are combined, a small spore population still remained dormant and was not inactivated with any holding time or pressure level. Biotechnol. Bioeng. 2010;107: 876–883. © 2010 Wiley Periodicals, Inc.     

Phospholipase Dδ negatively regulates plant thermotolerance by destabilizing cortical microtubules in Arabidopsis

The pattern of cortical microtubule arrays plays an important role in plant growth and adaptation in response to hormonal and environmental changes. Cortical microtubules are connected with the plasma membrane (PM); however, how the membrane affects cortical microtubule organization is not well understood. Here, we showed that phospholipase Dδ (PLDδ) was associated with the PM and co‐localized with microtubules in cells. In vitro analysis revealed that PLDδ bound to microtubules, resulting in microtubule disorganization. Site‐specific mutations that decreased PLDδ enzymatic activity impaired its effects on destabilizing microtubule organization. Heat shock transiently activated PLDδ, without any change of its PM localization, triggering microtubule dissociation from PM and depolymerization and seedling death in Arabidopsis, but these effects were alleviated in pldδ knockout mutants. Complementation of pldδ with wild‐type PLDδ, but not mutated PLDδ, restored the phenotypes of microtubules and seedling survival to those of wild‐type Arabidopsis. Thus, we conclude that the PM‐associated PLDδ negatively regulates plant thermotolerance via destabilizing cortical microtubules, in an activity‐dependent manner, rather than its subcellular translocation.     

MORPHOLOGY AND MOLECULAR PHYLOGENY OF A NEW MARINE SAND‐DWELLING PROROCENTRUM SPECIES,P. TSAWWASSENENSE (DINOPHYCEAE,PROROCENTRALES), FROM BRITISH COLUMBIA,CANADA1

A new marine benthic, sand‐dwelling Prorocentrum species from the temperate region of the Pacific coast of British Columbia, Canada, is described using LM and EM and molecular phylogenetic analyses. The cells have a broad oval shape, 40.0–55.0 μm long and 30.0–47.5 μm wide, and a wide U‐shaped periflagellar area on the right thecal plate. The left thecal plate consists of a straighter apical outline in the form of a raised ridge. Five to six delicate apical spines in the center of the periflagellar area are present. The nucleus is located in the posterior region of the cell, and a conspicuous pusule is located in the anterior region of the cell. The cells have golden‐brown chloroplasts with a compound, intrachloroplast pyrenoid that lacks a starch sheath. The thecal plates are smooth with round pores of two different sizes. The larger pores are arranged in a specific pattern of radial rows that are evenly spaced around the plate periphery and of irregular rows (or double rows) that form an incomplete “V” at the apical end of the plates. Large pores are absent in the center of the left and right thecal plates. The intercalary band is striated transversely and also has faint horizontal striations. Trichocysts and two types of mucocysts are present. The molecular phylogenetic position of Prorocentrum tsawwassenense sp. nov. was inferred using SSU rDNA sequences. This new species branched with high support in a Prorocentrum clade containing both benthic and planktonic species.     

Effects of the piezo-tolerance of cultured deep-sea eel cells on survival rates, cell proliferation, and cytoskeletal structures

We investigated the pressure tolerance of deep-sea eel (Simenchelys parasiticus; habitat depth, 366–2,630 m) cells, conger eel (Conger myriaster) cells, and mouse 3T3-L1 cells. Although there were no living mouse 3T3-L1 and conger eel cells after 130 MPa (0.1 MPa = 1 bar) hydrostatic pressurization for 20 min, all deep-sea eel cells remained alive after being subjected to pressures up to 150 MPa for 20 min. Pressurization at 40 MPa for 20 min induced disruption of actin and tubulin filaments with profound cell-shape changes in the mouse and conger eel cells. In the deep-sea eel cells, microtubules and some actin filaments were disrupted after being subjected to hydrostatic pressure of 100 MPa and greater for 20 min. Conger eel cells were sensitive to pressure and did not grow at 10 MPa. Mouse 3T3-L1 cells grew faster under pressure of 5 MPa than at atmospheric pressure and stopped growing at 18 MPa. Deep-sea eel cells were capable of growth in pressures up to 25 MPa and stopped growing at 30 MPa. Deep-sea eel cells required 4 h at 20 MPa to finish the M phase, which was approximately fourfold the time required under atmospheric conditions.     

Development of the cell covering in the dinoflagellate Scrippsiella hexapraecingula (Peridiniales, Dinophyceae)

The organization and development of cell coverings in two alternate phases of the life cycle in a marine dinoflagellate, Scrippsiella hexapraecingula Horiguchi et Chihara, were investigated by thin sectioning and freeze‐fracture electron microscopy. In one of these phases, the motile phase, cells have an outermost plasma membrane that is lined with flattened amphiesmal vesicles. Groups of microtubules lie beneath these vesicles. In mature motile cells, thecal plates are completely enclosed in individual amphiesmal vesicles. After settling, the cells enter the second, non‐motile phase. Here, ecdysis occurs, resulting in several steps including formation of the first pellicle layer (PI), fusion of the inner amphiesmal vesicle membranes to form the new plasma membrane, deposition of the second pellicle layer (PM) under PI, and the appearance and fusion of juvenile amphiesmal vesicles to form new territories, which eventually give rise to new thecal plates in the next motile phase. Thus, the pattern in which thecal plates are arranged in motile cells is determined at the time when the amphiesmal vesicles develop into non‐motile cells.     

Ultrastructure of cell division in the fusiform cells of the vascular cambium of Robinia pseudoacacia

 The ultrastructure of periclinally dividing fusiform cells was studied in the vascular cambium of Robinia pseudoacacia. Fusiform cell division begins in April at Madison, Wisconsin, when the cambial cells still have many characteristics of a dormant cambium. Soon afterward, the cambial cells acquire the appearance typical of an active cambium. Sequential phases of the microtubule cycle were documented: cortical microtubules bordering the cell wall during interphase, perinuclear microtubules preceding formation of the mitotic spindle, spindle microtubules, and phragmoplast microtubules. A preprophase band of microtubules was not encountered. An extended phragmosome was not encountered in periclinally dividing fusiform cells. During cytokinesis, the phragmosome is represented by a broad cytoplasmic plate which precedes the developing phragmoplast and cell plate as they migrate toward the ends of the cell.     

Temperature-assisted high hydrostatic pressure inactivation of Staphylococcus aureus in a ham model system: evaluation in selective and nonselective medium

Aims: The purpose of this study was to investigate the inactivation kinetics of Staphylococcus aureus in a ham model system by high hydrostatic pressure at ambient (25°C) and selected temperatures (45, 55°C). Selective [Baird Parker (BP) agar] and nonselective [brain heart infusion (BHI) agar] growth media were used for enumeration in order to count viable and sublethally injured cells. Methods and Results: The micro‐organism was exposed to a range of pressures (450, 500, 550, 600 MPa) at ambient temperature (25°C) for up to 45 min. Additionally, the behaviour of the micro‐organism was evaluated at mild temperatures in combination with high pressure treatment, namely: (i) 350, 400 and 450 MPa at 45°C; and (ii) 350 and 400 MPa at 55°C, for up to 12 min. Inactivation kinetics were calculated in terms of D_p and z_p values. Survival curves of S. aureus at ambient temperature were mostly linear, whereas when temperature was applied, tailing was observed in most survival curves. The estimated D_p values and therefore the number of surviving cells, were substantially higher on the selective BP agar in the whole range of pressures applied, indicating that S. aureus showed greater recovery in the selective BP agar than the nonselective BHI agar. Samples pressurized at ambient temperature needed higher pressures (over 500 MPa) to achieve a reduction of the population of the pathogen more than 5 log CFU ml^?1. The same level of inactivation was achieved at lower pressure levels when mild heating was simultaneously applied. Indeed, more than 6 log CFU ml^?1 reductions were obtained at 400 MPa and 55°C within the first 7 min of the process in BHI medium. Conclusion: Elevated temperatures allowed lower pressure levels and shorter processing times of pathogen inactivation than at room temperature. Greater recovery of the pathogen was observed in the selective (BP agar) medium, regardless of pressure and temperature applied. Significance and Impact of the Study: The obtained kinetics could be employed by the industry in selecting optimum pressure/temperature processing conditions. Attention must be given to the selection of the enumeration medium, as the use of an inappropriate medium would lead to underestimation of the surviving cells, thus imposing a risk in the microbiological safety of the product.     

Effects of high hydrostatic pressure on Clostridium sporogenes spores

Spores of Clostridium sporogenes were found to be resistant to ultra high pressure, with treatments of 600 MPa for 30 min at 20 °C causing no significant inactivation. Combination treatments including heat and pressure applied simultaneously (e.g. 400 MPa at 60 °C for 30 min) or sequentially (e.g. 80 °C for 10 min followed by 400 MPa for 30 min) proved more effective at inactivating spores. Pressure cycling (e.g. 60 MPa followed by 400 MPa at 60 °C) also reduced spore numbers. Overall, these pressure treatments resulted in less than a 3 log reduction, and it was concluded that the spores could not be inactivated by pressure alone. This could indicate that for the effective inactivation of bacterial spores, high pressure technology may have to be used in combination with other preservation methods.     

IMMUNOFLUORESCENT LOCALIZATION OF MICROTUBULES THROUGHOUT THE CELL CYCLE IN THE GREEN ALGA MOUGEOTIA (ZYGNEMATACEAE)

Indirect immunofluorescence microscopy was used to survey the three-dimensional distribution of microtubules throughout the cell cycle in the green alga Mougeotia. The network of microtubules present in the cortex of the cells at interphase gradually disappeared before mitosis. A band of cortical microtubules reminiscent of the preprophase band of higher plants surrounded the nuclei of some preprophase cells undergoing cortical microtubule disassembly. Longitudinally oriented bundles of microtubules appeared at the future spindle poles on either side of the nuclei in prophase. These bundles disappeared gradually as the spindle microtubule arrays formed. New spindles had broad poles but these became quite pointed before anaphase. Interzonal microtubules appearing at anaphase persisted until the end of nuclear migration, by which time they were concentrated into narrow bundles on either side of the centripetally forming crosswalls. During decondensation of the chromosomes and early nuclear migration, the spindle poles persisted as sites of microtubule concentration. New arrays of microtubules radiated from these microtubule centers into the cytoplasm ahead of the migrating nuclei. After cytokinesis, reinstatement of cortical microtubules was best observed in regions of the cells remote from the nuclei and associated microtubules. In contrast to higher plants, the first detectable cortical microtubules were short and already oriented transverse to the long axes of the cells.     

Laciniporus arabicus gen. et sp. nov. (Dinophyceae,Peridiniales), a new thecate,marine, sand‐dwelling dinoflagellate from the northern Indian Ocean (Arabian Sea)1

A new thecate, photosynthetic, sand‐dwelling marine dinoflagellate, Laciniporus arabicus gen. et sp. nov., is described from the subtidal sediments of the Omani coast in the Arabian Sea, northern Indian Ocean, based on detailed morphological and molecular data. Cells of L. arabicus are small (16.2–30.1 μm long and 13.1–23.2 μm wide), dorsoventrally compressed, with a small apical flap‐shaped projection pointing to the left. The thecal plate pattern is distinguished by minute first precingular plate and sulcus, which extends into the epitheca, with large anterior and right sulcal plates. The Kofoidian thecal tabulation is Po, X, 4′, 2a, 7′′, 6c, 6s, 5′′′, 2′′′′. Morphologically, the revealed plate pattern has an affinity to the Peridiniales, and LSU rDNA based phylogenetic analyses placed L. arabicus within the Thoracosphaeraceae, close to calcareous‐cyst producing scrippsielloids, predatory pfiesteriaceans, and photosynthetic freshwater peridinioids Chimonodinium lomnickii and Apocalathium spp. However, the thecal plate arrangement of L. arabicus differs noticeably from any currently described dinoflagellates, and the species stands out from closely related taxa by extensive differences in physiology and ecology.     

The Homology of Cortical Microtubules in Platyhelminth Spermatozoa: a Comparative Immunocytochemical Study of Acetylated Tubulin

Spermatozoa of certain acoels, a group of primitive Platyhelminthes, and spermatozoa of the most derived Platyhelminthes, the Cercomeridea (parasitic Platyhelminthes), show a general morphological resemblance in that they are long filiform cells with two incorporated axonemes and longitudinal cortical microtubules. A possible way to test the homology of these cortical microtubules in the different groups is to analyze the presence/absence of post-translational modifications of tubulin. An indirect immunofluorescence study showed that the doublet microtubules of the sperm axonemes are labelled by an anti acetylated-alpha-tubulin antibody in all groups, irrespective of the axoneme pattern (9 + 0, 9 + 2 and non-trepaxonematan 9 + “1” in various acoels, and trepaxonematan 9 + “1” of the temnocephalid Troglocaridicola sp., the digenean Echinostoma caproni and the monopisthocotylean monogenean Pseudodactylogyrus sp.). Significant differences are found in the sperm cortical microtubules: they are acetylated in the acoel Actinoposthia beklemischevi, but not in the digenean E. caproni and the temnocephalid Troglocaridicola sp. These results suggest that the sperm cortical microtubules of the acoels are not homologous with the morphologically similar elements found in the higher Platyhelminthes.     

The distributional changes and role of microtubules in Nod factor-challenged<Emphasis Type="Italic"> Medicago sativa</Emphasis> root hairs

The normal tip-growing pattern exhibited by root hairs of legumes is disrupted when the hair is exposed to Nod factors generated by compatible bacteria capable of inducing nodule formation. Since microtubules (MTs) play an important role in regulating directionality and stability of apical growth in root hairs [T.N. Bibikova et al. (1999) Plant J 17:657–665], we examined the possibility that Nod factors might affect the MT distribution patterns in root hairs of Medicago sativa L. We observed that Nod factor application caused rapid changes in the pattern of MTs starting as early as 3 min after perfusion. Within 3 to 10 min after Nod factor application, first endoplasmic and then cortical MTs depolymerised, initially at the proximal ends of cells. Twenty minutes after exposure to Nod factors, a transverse band of microtubules was seen behind the tip, while almost all other MTs had depolymerised. By 30 min, very few MTs remained in the root hair and yet by 1 h the MT cytoskeleton re-formed. When Nod factors were applied in the presence of 10 M oryzalin or 5 M taxol, the MTs appeared disintegrated while the morphological effects, such as bulging and branching, became enhanced. Compared to the treatments with oryzalin or taxol alone, the combinatory treatments exhibited higher growth rates. Since microtubule reorganization is one of the earliest measurable events following Nod factor application we conclude that microtubules have an important role in the early phases of the signalling cascade. Microtubule involvement could be direct or a consequence of Nod factor-induced changes in ion levels.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s00425-003-1097-1Abbreviations BNM buffered nodulation medium - CLSM confocal laser scanning microscopy - MT microtubule     

Effects of ethylene on the orientation of microtubules and cellulose microfibrils of pea epicotyl cells with polylamellate cell walls

Summary Following a 5 hours ethylene treatment, cortical cells of Pea (Pisum sativum L. var Alaska) epicotyl third internode showed a change in the orientation of both microtubules near the plasma membrane and recently deposited cellulose microfibrils. Control cortical cells had mostly transverse microtubules. The ratio of the average frequency of transverse to longitudinal microtubules was 6.0. After 5 hours of ethylene treatment, cortical cells had mostly longitudinal microtubules, with the ratio of transverse to longitudinal microtubules equal to 0.1. Epidermal cells were more variable than cortical cells with regard to the frequency of longitudinal and transverse microtubules. Observation of cortical cell walls in conventionally stained thin sections revealed that recent deposition of microfibrils had been primarily transverse in almost all of the control cortical cells sampled. In contrast, more than half of the ethylene-treated cortical cells had recent deposition oriented primarily longitudinally. This change in microtubule and microfibril orientation may be early enough to constitute the primary effect of ethylene leading to radial cell expansion.Research supported by NSF grant PCM 78-03244, A1, 2 to PBG and by a Research Corporation grant to WRE.     

Ultrastructural effects of pressure stress to the nucleus in Saccharomyces cerevisiae: a study by immunoelectron microscopy using frozen thin sections

Abstract The effects of hydrostatic pressure on subcellular structures, particularly the nucleus, of Saccharomyces cerevisiae were investigated by immunoelectron microscopy. Cells were treated with hydrostatic pressure from 0.1 to 400 MPa for 10 min at room temperature. Frozen thin sections of the cells revealed that spindle pole bodies disappeared at 100 MPa. At 150 MPa, the deposition of gold panicles for anti α-tubulin was noticed in the nucleus, although the filamentous structure of microtubules was lost. At 200 MPa, fewer gold particles were scattered in the nucleus and the nuclear membrane in several portions was also observed to be open at 300 MPa. These results show that elements of the nuclear division apparatus were susceptible to pressure stress, particularly spindle pole bodies and microtubules. The damage to spindle pole bodies, microtubules, and nuclear membrane caused by pressure stress was followed by the inhibition of nuclear division. After the release of pressure, the spindle pole bodies and microtubules of pressurized cells at below 200 MPa regained their normal appearance at 24 h.     

Pressure treatment of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> in low-moisture environments

We investigated the influence of cell hydration on the ability of Saccharomyces cerevisiae CBS 1171 to withstand extreme hydrostatic pressure in order to determine the mechanisms involved in cell resistance. Hydration conditions were modified in two different ways. We first modulated the chemical potential of water by adding glycerol in cell suspensions. Another procedure consisted in dehydrating cells aerobically and immersing them in perfluorooctane, an innocuous hydrophobic liquid used as a pressure-transmitting medium, prior to pressure treatments. This original method made it possible to transmit isostatic pressure to yeast powders without changing the initial water activity (a _w) level at which cells had been equilibrated. The a _w ranged between 0.11 and 0.99. Pressure treatments were applied at levels of up to 600 MPa for 10 min, 24 h, and 6 days. The dehydration of cells was found to strongly limit, or even prevent, cell inactivation under pressure. Notably, cells suspended in a water–glycerol mixture with a _w levels of 0.71 or below were completely protected against all pressure treatments. Moreover, cells dehydrated aerobically survived for 6 days at 600 MPa even when a _w levels were relatively high (up to 0.94). We highlighted the crucial role of water content in determining cellular damage under pressure. When water is available in a sufficient amount, high pressure induces membrane permeabilization, causing uncontrolled mass transfers that could lead to death during a prolonged holding under pressure. Possible mechanisms of membrane permeabilization are discussed.     

Cortical microtubules and cortical microfilaments in the green alga,Micrasterias pinnatifida

Summary Cortical microtubules and cortical microfilaments were visualized in cells ofMicrasterias pinnatifida treated by freeze-substitution, and the pattern of their distribution was reconstructed from serial sections. Most cortical microtubules accompanied the long microfilaments that ran parallel to the microtubules. Cortical microfilaments not accompanied by the microtubules were also found. They were short and slightly curved. Both types of cortical microfilament were not grouped into bundles, and were 6–7 nm in diameter, a value that corresponds to the diameter of filaments of F-actin.     

SYMBIODINIUM NATANS SP. NOV.: A “FREE‐LIVING” DINOFLAGELLATE FROM TENERIFE (NORTHEAST‐ATLANTIC OCEAN)1

We examined a free‐living Symbiodinium species by light and electron microscopy and nuclear‐encoded partial LSU rDNA sequence data. The strain was isolated from a net plankton sample collected in near‐shore waters at Tenerife, the Canary Islands. Comparing the thecal plate tabulation of the free‐living Symbiodinium to that of S. microadriaticum Freud., it became clear that a few but significant differences could be noted. The isolate possessed two rather than three antapical plates, six rather than seven to eight postcingular plates, and finally four rather than five apical plates. The electron microscopic study also revealed the presence of an eyespot with brick‐shaped contents in the sulcal region and a narrow anterior plate with small knob‐like structures. Bayesian analysis revealed the free‐living Symbiodinium to be a member of the earliest diverging clade A. However, it did not group within subclade A_I (=temperate A) or any other subclades within clade A. Rather, it occupied an isolated position, and this was also supported by sequence divergence estimates. On the basis of comparative analysis of the thecal plate tabulation and the inferred phylogeny, we propose that the Symbiodinium isolate from Tenerife is a new species (viz. S. natans). To elucidate further the species diversity of Symbiodinium, particularly those inhabiting coral reefs, we suggest combining morphological features of the thecal plate pattern with gene sequence data. Indeed, future examination of motile stages originating from symbiont isolates will demonstrate if this proves a feasible way to identify and characterize additional species of Symbiodinium and thus match ribotypes or clusters of ribotypes to species.     

THE ROLE OF MICROTUBULES IN THE MOVEMENT OF PIGMENT GRANULES IN TELEOST MELANOPHORES

When microtubules in teleost melanophores are disrupted with antimitotic agents, colchicine, high hydrostatic pressure, low temperature, and vinblastine, the alignment and movement of the pigment granules in these cells disappear; during recovery, the return of alignment and movement corresponds in both time and space with the repolymerization of microtubules. Furthermore, analysis of nearest neighbor distances in untreated melanophores reveals that pigment granules are closely associated with microtubules. Other structures such as microfilaments, the endoplasmic reticulum, and the cytoplasmic matrix do not appear to be involved. Thus we conclude that microtubules determine the alignment and are essential for the selective movements of the pigment granules in these cells. Investigations of the mechanism of movement show that microtubules are required for both centrifugal and centripetal migrations and that they do not change in number or location during redistribution of pigment. Our results further indicate that microtubules in melanophores behave as semistable organelles as determined by investigation with colchicine and hydrostatic pressure. These observations and others rule out a push-pull mechanism based on the polymerization and depolymerization of microtubules or one which distinguishes two operationally different sets of microtubules. We propose instead that particles move by sliding along a fixed array of microtubules.     

SUSCEPTIBILITY AND PROTECTIVE MECHANISMS OF MOTILE AND NON MOTILE CELLS OF HAEMATOCOCCUS PLUVIALIS (CHLOROPHYCEAE) TO PHOTOOXIDATIVE STRESS1

The life cycle of the unicellular green alga Haematococcus pluvialis consists of motile and nonmotile stages under typical growing conditions. In this study, we observed that motile cells were more susceptible than nonmotile cells to high light, resulting in a decrease in population density and photo‐bleaching. Using two Haematococcus strains, CCAP 34/12 (a motile cell dominated strain) and SAG 34/1b (a nonmotile cell dominated strain), as model systems we investigated the cause of cell death and the protective mechanisms of the cells that survived high light. The death of motile cells under high light was attributed to the generation of excess reactive oxygen species (ROS), which caused severe damage to the photosynthetic components and the membrane system. Motile cells were able to dissipate excess light energy by nonphotochemical quenching and to relax ROS production by a partially up‐regulated scavenging enzyme system. However, these strategies were not sufficient to protect the motile cells from high light stress. In contrast, nonmotile cells were able to cope with and survive under high light by (i) relaxing the over‐reduced photosynthetic electron transport chain (PETC), thereby effectively utilizing PETC‐generated NADPH to produce storage starch, neutral lipid, and astaxanthin, and thus preventing formation of excess ROS; (ii) down‐regulating the linear electron transport by decreasing the level of cytochrome f; and (iii) consuming excess electrons produced by PSII via a significantly enhanced plastid terminal oxidase pathway.