Tissue distribution of the ice-nucleating agents in larvae of the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Strong Inhibition of Ice Growth by Biomimetic Crowding Coacervates

The freezing of biological fluids is intensively studied but remains elusive as it is affected not only by the various components but also by the crowding nature of the biological fluids. Herein, we constructed spherical crowders, fibrous crowders, and coacervates by various components ranging from surfactants to polymers and proteins, to mimic three typical crowders in biological fluids, i.e., globular proteins, fibrous networks, and condensates of biomolecules. It is elucidated that the three crowders exhibit low, moderate, and strong ice growth inhibition activity, respectively, resulting from their different abilities in slowing down water dynamics. Intriguingly, the coacervate consisting of molecules without obvious ice growth inhibition activity strongly inhibits ice growth, which is firstly employed as a highly-potent cryoprotectant. This work provides new insights into the survival of freezing-tolerant organisms and opens an avenue for the design of ice-controlling materials.

Bioinspired Ice-Binding Materials for Tissue and Organ Cryopreservation

Cryopreservation of tissues and organs can bring transformative changes to medicine and medical science. In the past decades, limited progress has been achieved, although cryopreservation of tissues and organs has long been intensively pursued. One key reason is that the cryoprotective agents (CPAs) currently used for cell cryopreservation cannot effectively preserve tissues and organs because of their cytotoxicity and tissue destructive effect as well as the low efficiency in controlling ice formation. In stark contrast, nature has its unique ways of controlling ice formation, and many living organisms can effectively prevent freezing damage. Ice-binding proteins (IBPs) are regarded as the essential materials identified in these living organisms for regulating ice nucleation and growth. Note that controversial results have been reported on the utilization of IBPs and their mimics for the cryopreservation of tissues and organs, that is, some groups revealed that IBPs and mimics exhibited unique superiorities in tissues cryopreservation, while other groups showed detrimental effects. In this perspective, we analyze possible reasons for the controversy and predict future research directions in the design and construction of IBP inspired ice-binding materials to be used as new CPAs for tissue cryopreservation after briefly introducing the cryo-injuries and the challenges of conventional CPAs in the cryopreservation of tissues and organs.

Seasonal changes in supercooling points and glycerol content in overwintering larvae of the asiatic rice borer from rice and water-oat plants

The Asiatic rice borer Chilo suppressalis (Walker) occurs mainly on rice Oryza sativa L. and water-oat Zizania latifolia (Turcz). Certain ecological and physiological differentiations between rice and water-oat populations have been shown. To determine whether there is host-associated differentiation in supercooling capacity, seasonal changes in supercooling points, glycerol content, and other physiological parameters of naturally occurring C. suppressalis larvae overwintering in rice and water-oat plants were compared over the winter. Supercooling points were low in the winter (November and December), significantly higher in March, and significantly lower in the water-oat population than in the rice population in the winter. Larvae from the water-oat population experienced a significant weight loss from December to March and were heavier than those from the rice population in the winter. Body water content (percentage of fresh weight) was low in the winter and increased significantly in March; no population differences were detected. Hemolymph glycerol content was high in the winter and dropped significantly in March; interpopulation differences were significant in December. Hemolymph trehalose content increased in the winter, and no population differences were detected. Whole body glucose and lipid content varied differently between the rice and the water-oat populations over the winter. It was found that variations in hemolymph glycerol content were responsible for the host-associated seasonal changes in supercooling capacity of overwintering larvae of the Asiatic rice borer.

Changes of cold hardiness, supercooling capacity, and major cryoprotectants in overwintering larvae of Chilo suppressalis (Lepidoptera: Pyralidae)

The rice stem borer, Chilo suppressalis Walker, which is a key rice pest in northern parts of Iran, overwinters in rice stubble and weeds as mature larvae. Diapause of this pest is initiated between October to November and terminates in March. Seasonal variations in the supercooling point, survival at low temperatures, and sugar contents were studied in field-collected larvae during different phases of diapause. Ambient temperature was lowest in January and February when larvae were at the highest diapause intensity and achieved a high degree of cold hardiness at -10, -15, and -20 degrees C. Glycerol, a major cryoprotectant, reached a peak in January. It appeared that cold hardiness in the larvae is closely associated with the diapause. For the first time, this study suggests that glucose and glycogen are converted to glycerol during cold seasons, but trehalose has no definite role in the interconversion. During the coldest months, supercooling points (SCPs) increased (around -11 degrees C), and larvae could survive below their SCP values, showing that overwintering larvae of C. suppressalis are freeze tolerant in Iran. Our findings suggest that cold hardiness and diapause are essential components for this species. The overwintering larvae have high capacity of cold hardiness and can overcome severe winters. Understanding of cold hardiness and overwintering behavior of this species may help in integrated pest management of the rice stem borer in paddy fields.

Effects of diapause and cold-acclimation on the avoidance of freezing injury in fat body tissue of the rice stem borer, Chilo suppressalis Walker

Overwintering freeze-tolerant larvae of Chilo suppressalis can survive at -25 degrees C, but non-diapausing larvae cannot. We reported earlier that to prevent intracellular freezing, which causes death in overwintering larvae of the Saigoku ecotype distributed in southwestern Japan, water leaves and glycerol enters fat body cells through water channels during freezing. However, it is still unclear how diapause and low-temperature exposure are related to the acquisition of freeze tolerance. We compared the extent of tissue damage, accumulation of glycerol, and transport of glycerol and water in fat body tissues between cold-acclimated and non-acclimated non-diapausing and diapausing larvae. The tissue from cold-acclimated diapausing larvae could survive only when frozen in Grace's insect medium with 0.25 M glycerol at -20 degrees C. The protection provided by glycerol was offset by mercuric chloride, which is a water-channel inhibitor. Fat body tissue isolated from non-acclimated diapausing larvae was injured by freezing even though glycerol was added to the medium, but the level of freezing injury was significantly lower than in non-diapausing larvae. Radiotracer assays in cold-acclimated diapausing larvae showed that during freezing, water left the cells into the medium and glycerol entered the cells from the medium at the same time. Therefore, in Saigoku ecotype larvae of the rice stem borer, both diapause and cold-acclimation are essential to accumulate glycerol and activate aquaporin for the avoidance of freezing injury.

Seasonal changes in glycerol content and cold hardiness in two ecotypes of the rice stem borer, Chilo suppressalis, exposed to the environment in the Shonai district, Japan

The rice stem borer, Chilo suppressalis, is divided into at least two ecotypes in Japan, the Shonai ecotype (SN) which is distributed in the northern part of Japan, and the Saigoku ecotype (SG) which is distributed in the southwestern region. Cold hardiness is positively correlated with the level of glycerol in both ecotypes. To investigate whether ecological distribution affects glycerol accumulation and cold hardiness development in these two ecotypes, overwintering larvae of the SN and SG ecotypes were concurrently exposed to the Shonai district. Obvious differences in the progress of glycerol accumulation and cold hardiness development in SN and SG larvae were found in early winter in the Shonai district. The levels of glycerol content and cold hardiness were low in October and high in January in both ecotypes, but those levels were different within this period (November and December) between ecotypes; the levels in SN larvae quickly reached their maximum, whereas, in SG larvae levels increased slowly. Under controlled conditions, the effect of the period of acclimation at 10 degrees C and subsequent low-temperature (5 degrees C) exposure on glycerol accumulation was investigated. These results indicated that glycerol accumulation in SN was stimulated by the progression of diapause termination, whereas a higher cumulative effect on glycerol production in SG was found when diapause was in a deep state.

Methionine-rich storage protein gene in the rice stem borer, Chilo suppressalis, is expressed during diapause in response to cold acclimation

Gene expressions of acclimatized and non-acclimatized diapausing larvae were examined in Chilo suppressalis using a subtraction technique. A gene encoding a methionine-rich storage protein, CsSP1, was cloned and its complete cDNA sequence was determined. Potentially, CsSP1 encoded a 758-amino acid protein, with a calculated molecular weight of 88.8 kDa. The expression level of CsSP1 was higher in nondiapausing larvae than in diapausing ones. The CsSP1 expression was up-regulated in diapausing larvae when the temperature of cold acclimation was shifted to 5 degrees C. The up-regulated level was maintained at 40 days after incubation at 5 degrees C. In nondiapausing larvae, CsSP1 expression was down-regulated when the temperature was below developmental zero. Involvement of CsSP1 in diapause, cold tolerance acquisition and postdiapause development in C. suppressalis is discussed.

Cloning of heat shock protein genes (hsp90 and hsc70) and their expression during larval diapause and cold tolerance acquisition in the rice stem borer, Chilo suppressalis Walker

The complete cDNA sequences of heat shock protein 90 (hsp90) and of heat shock cognate protein 70 (hsc70) were cloned by reverse transcription polymerase chain reaction from the rice stem borer, Chilo suppressalis Walker. They potentially encode a 717-amino-acids (hsp90) and a 652-amino-acids (hsc70) protein, with calculated molecular weight of 82.5 and 71.3 kDa, respectively. The deduced amino acid sequence of hsp90 showed the highest homology of 97.2% to Spodoptera frugiperda hsp90. The closest match of C. suppressalis hsc70 was with Manduca sexta hsc70 at 98.0% identity. Expression of hsp90 in diapausing larvae was higher than that in non-diapausing larvae. No such up-regulation in diapausing larvae was observed for hsc70. In non-diapausing larvae, but not in diapausing ones, hsp90 expression was up-regulated by cold acclimation. Hsc70 expression slightly decreased during cold acclimation irrespective of the state of diapause. Involvement of hsp90 and hsc70 in larval diapause and cold tolerance acquisition in C. suppressalis is discussed.

Role of membrane transport of water and glycerol in the freeze tolerance of the rice stem borer, Chilo suppressalis Walker (Lepidoptera: Pyralidae)

Overwintering larvae of the rice stem borer, Chilo suppressalis accumulate glycerol and are freezing tolerant to about -25 degrees C. However, non-diapausing larvae cannot accumulate glycerol and are killed by freezing. We compared the extent of tissue damage, the effects of glycerol concentration, and the transport of glycerol and water in fat body tissues from these larvae at selected freezing temperatures. Tissues from overwintering larvae, but not non-diapausing larvae, survive when frozen at -20 degrees C with 0.25 M glycerol, but the protection afforded by glycerol is offset by the water-channel inhibitor mercuric chloride. Glycerol in higher concentration (0.75 M) affords some protection even to the fat body of non-diapausing larvae. Radiotracer assays of overwintering larvae show that water leaves the tissues during freezing while glycerol enters, and that mercuric chloride disrupts this process. Transport is also disrupted after lethal freezing at -35 degrees C. Therefore, membrane transport of water and glycerol is involved in the avoidance of freezing injury to fat body cells of the rice stem borer, apparently by mediating the replacement of water with glycerol in freezing-tolerant tissues.

Experimental studies of ice nucleation in an Antarctic springtail (Collembola, Isotomidae)

Ice nucleation was studied in field-fresh and acclimated (4 degrees C without food for 11-20 days) samples of the springtail Cryptopygus antarcticus Willem (Collembola, Isotomidae) at Rothera Research Station, Adelaide Island on the Antarctic Peninsula. Ice nucleator activity (INA) was measured by a freezing droplet technique in addition to supercooling point (SCP) profiles and polyol, sugar, and water contents. Field and acclimated samples showed bimodal SCP distributions with a distinct high group (HG; mean SCP -8 to -10 degrees C) and low group (LG: mean SCP -23 to -25 degrees C), which were significantly different. Acclimation at 4 degrees C increased the proportion of individuals in the LG relative to that in the HG without significant effects on the mean SCP of both groups. INA of the HG was significantly greater than that of the LG, and acclimation further reduced the INA of the LG. The number of active ice nucleator agents (INAs) calculated for the HG of field samples increased by 23-100 times over the temperature range -5 to -8 degrees C compared to only 7 times for the LG over the same range. These differences were accentuated in the acclimation experiments. Glucose and galactose were the main carbohydrates in both field and acclimated springtails, with the latter compound occurring in almost twice the concentration in the LG compared with that in the HG. Acclimation reduced the concentration of both compounds (glucose by 77% and galactose by 54%), whereas water content increased significantly. Digestion of food may have continued during acclimation at 4 degrees C, which could reduce the LG INA. Lowering of temperature over time is more likely to elicit a cold hardening response than constant temperature acclimation. INA numbers calculated at the nucleation temperatures for C. antarcticus samples were higher in the LG than in the HG. However, inactivation of INAs may be a key mechanism underlying cold hardening in this species, either by sequestration within the cellular matrix or by being only seasonally active.

Temperature Regulation of Supercooling and Gut Nucleation in Relation to Diapause of Pyrrhocoris apterus (L.) (Heteroptera)

The heteropteran Pyrrhocoris apterus (L.) does not survive freezing of its body fluids; there is a good correlation between values of survival at subzero temperatures and the supercooling point (SCP), i.e., the temperature at which body fluids start to freeze. The decrease of the SCP and thus the increase in cold hardiness is regulated by photoperiod and temperature. The relative importance of these factors depends on the physiological state of the insect. The SCP is about -7°C at the onset of prediapause and a decrease of about 4-5°C is associated with the development of the diapause syndrome in adults; these processes both are induced by a short-day photoperiod with temperature playing a secondary role. The induction of the diapause syndrome is a prerequisite for the subsequent decrease of the SCP by about 5-6°C during cold acclimation. An intermediate temperature of 15°C, or fluctuating outdoor temperatures and short-day photoperiods, are more suitable for the decrease of SCP than 5°C in continuous darkness. The sensitivity to photoperiod gradually disappears during the development of diapause; after the termination of diapause around the winter solstice the SCP irreversibly increases at a high temperature of 26°C even if exposed to a short-day photoperiod. The SCPs of hemolymph, gut, fat body, and gonads were compared to whole-body SCP. The gut was identified as the primary site of ice nucleation because its SCP value was very similar to the value for the whole body in both short-day and long-day insects. The SCPs of other organs, including the hemolymph, were always lower than the whole body SCP. Food was not a source of ice nucleating agents because the SCP of freshly ecdysed adults remained high after 2 weeks of starvation. In contrast, feeding was a prerequisite for the decrease of the SCP during prediapause. In postdiapause insects, the SCP increased at high temperatures in spite of the absence of food.