Freezing tolerance, cold acclimation and oxidative stress in potato. Paraquat tolerance is related to acclimation but is a poor indicator of freezing tolerance

Potato is a species commonly cultivated in temperate areas where the growing season may be interrupted by frosts, resulting in loss of yield. Cultivated potato, Solanum tuberosum, is freezing sensitive, but it has several freezing-tolerant wild potato relatives, one of which is S. commersonii. Our study was aimed to resolve the relationship between enhanced freezing tolerance, acclimation capacity and capacity to tolerate active oxygen species. To be able to characterize freezing tolerant ideotypes, a potato population (S1), which segregates in freezing tolerance, acclimation capacity and capacity to tolerate superoxide radicals, was produced by selfing a somatic hybrid between a freezing-tolerant Solanum commersonii (LT₅₀=-4.6°C) and -sensitive S. tuberosum (LT₅₀=-3.0°C). The distribution of non-acclimated freezing tolerance (NA-freezing tolerance) of the S1 population varied between the parental lines and we were able to identify genotypes, having significantly high or low NA-freezing tolerance. When a population of 25 genotypes was tested both for NA-freezing and paraquat (PQ) tolerance, no correlation was found between these two traits (R = 0.02). However, the most NA-freezing tolerant genotypes were also among the most PQ tolerant plants. Simultaneously, one of the NA-freezing sensitive genotypes (2022) (LT₅₀=-3.0°C) was observed to be PQ tolerant. These conflicting results may reflect a significant, but not obligatory, role of superoxide scavenging mechanisms in the NA-freezing tolerance of S. commersonii. The freezing tolerance after cold acclimation (CA-freezing tolerance) and the acclimation capacity (AC) was measured after acclimation for 7 days at 4/2°C. Lack of correlation between NA-freezing tolerance and AC (R =-0.05) in the S1 population points to independent genetic control of NA-freezing tolerance and AC in Solanum sp. Increased freezing tolerance after cold acclimation was clearly related to PQ tolerance of all S1 genotypes, especially those having good acclimation capacity. The rapid loss of improved PQ tolerance under deacclimation conditions confirmed the close relationship between the process of cold acclimation and enhanced PQ tolerance. Here, we report an increased PQ tolerance in cold-acclimated plants compared to non-acclimated controls. However, we concluded that high PQ tolerance is not a good indicator of actual freezing tolerance and should not be used as a selectable marker for the identification of a freezing-tolerant genotype.     

The role of ABA in freezing tolerance and cold acclimation in barley

The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley ( Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT₅₀, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT₅₀ and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT₅₀ of leaves of cold‐acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT₅₀ decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.     

植物抗寒及其基因表达研究进展

植物经过逐渐降低的温度从而提高抗寒能力 ,这个过程被人们称为低温驯化。植物低温驯化过程是一个复杂的生理、生化和能量代谢变化过程 ,这些变化主要包括膜系统的稳定性、可溶性蛋白的积累和小分子渗透物质 ,比如脯氨酸、糖等 ,这些变化中的一些是植物抗寒必需的 ,而另外一些变化不是必需的。主要对冷害和低温生理生化变化、低温诱导表达基因的功能和作用、低温驯化的调节机制及其信号转导方面进行了综述。通过差别筛选 c DNA文库的方法已经鉴定了许多低温诱导表达、进而提高植物抗寒能力的基因 ,其中有脱水素、COR基因和 CBF1转录因子等。低温信号的感受、转导和调节表达是低温驯化的关键环节 ,低温信号的转导过程与干旱胁迫之间具有一定的交叉 ,这为利用 ABA等来提高植物抗寒能力成为可能 ,相信不久的将来人们可以通过提高植物抗寒能力从而增加经济产量成为现实。     

The synthesis of cold shock proteins and cold acclimation proteins in the psychrophilic bacteriumAquaspirillum arcticum

The synthesis of cold shock proteins (csps) in response to cold shock, and of cold acclimation proteins (caps) in response to continuous growth at low temperature, in the psychrophileAquaspirillum arcticum was investigated. With two-dimensional gel electrophoresis and computing scanning laser densitometry, cold shock treatments (10° to 0°C, 5° to 0°C, and 10° to 5°C) induced a total of 14 csps, 6 of which were induced by all three cold shocks. The production of caps in response to continuous growth at 0°C was also found. Five of the 8 caps produced were also csps which suggests that these proteins may share a common involvement in cold adaptation.     

Variation of total soluble seminal root proteins of tetraploid wild and cultivated wheat induced at cold acclimation and freezing

The relationship between total soluble seminal root proteins induced at cold acclimation and freezing tolerance in tetraploid wild wheat Aegilops L. (Ae. biuncialis, Ae. cylindrica) and cultivated wheat Triticum turgitum L. (Firat-93, Harran-95) was investigated. Cold acclimation was performed at 0 °C for 7 days. Freezing tolerance was determined with survived roots after freezing treatments at −5 and/or −7 °C for 3, 6, 12 and 24 h. At −5°C, all tetraploid genotypes showed over 60% tolerance for 3 h. This effect was also present in wild wheat for 6 h, but was decreased in cultivated wheat to 30–35% tolerance for 6 h. Only Ae. biuncialis was able to show 52% tolerance just for 3 h freezing period at −7 °C. However, all the genotypes were not survived at −7 °C, for 6, 12 and 24 h. Cold acclimation induced greater amounts of new soluble seminal root proteins in tolerant Ae. biuncialis (29–104 kDa, pI 5.4–7.4) than in sensitive Harran-95 (29–66 kDa, pI 6.1–8.3). Synthesis and accumulation of these proteins may be related to degree of freezing tolerance of these genotypes.     

Biochemical and physiological mechanisms related to cold acclimation and enhanced freezing tolerance in poplar plantlets

Temperature is one of the abiotic factors limiting growth and productivity of plants. In the present work, the effect of low non-freezing temperature, as inducer of 'cold acclimation', was studied in poplar. Actively growing plantlets of Populus tremula  ×  Populus tremuloides cv. Muhs 1 were used, and cold treatment consisted in whole plants exposure to 4°C in controlled conditions. Leaves of cold-treated poplars were shown to be acclimated, as an increase of their freezing tolerance was measured using electrolyte leakage. Chlorophyll fluorescence measurements revealed a decrease in photosystem II efficiency while the pigment contents of leaves did not vary. In contrast, after 1 week of cold exposure, an accumulation of pigments was noted in the stems near the apex of the stressed plants as confirmed by chromatographic analyses. Simultaneously, a rapid accumulation of osmoprotectants, i.e. carbohydrates (measured by spectrometry), and of stress indicators (e.g. putrescine) occurred; changes in protein patterns also arose. Indeed, Western blot studies revealed that the expression of three families of stress-related proteins, i.e. dehydrins, stress protein 1 and heat-shock protein 70, was activated or induced by low temperatures. This study complements a previous work on proteomic and individual carbohydrates and provides insight in the ability of poplar plantlets to cold acclimate and to cope with low temperatures by diverse mechanisms (growth cessation, carbohydrate, pigment, polyamine and protein accumulations) related to stress response or involved in acclimation process.     

Olive (Olea europaea L.) freezing tolerance related to antioxidant enzymes activity during cold acclimation and non acclimation

The changes in the antioxidant enzymes activity, total protein and proline content and their correlations with freezing tolerance (FT) (expressed as LT₅₀) were investigated at 11 different olive cultivars at cold-acclimation (CA, in February) and non-acclimation (NA, in August) stages. Leaf samples were collected from each cultivar and were divided into two groups. The first group was immediately frozen in liquid nitrogen for further biochemical analysis. The second ones was subjected to different freezing temperatures (?5, ?10, ?15 and ?20 °C) for 10 h, in order to determine their FT. The unfrozen control samples were kept at 4 °C. The results showed that Fishomi, Mission and Shengeh were the most freezing tolerant among other cultivars. In contrast, Zard, Manzanilla and Amigdalolia were the most sensitive ones. The cold acclimation enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), polyphenol oxidase (PPO) and total protein content. However, proline content and phenylalanine ammonia-lyase (PAL) activity did not change or even decreased slightly at CA stage, compare to those samples at NA stage. It was found that LT₅₀ to be closely correlated to POD, CAT, and PPO activity at CA and NA stages. Overall, higher leaf POD, CAT, and PPO activity could be used as important selection criteria in screening tolerant olive cultivars for cold zone climatic.     

寒冷适应差异表达基因的研究

为寻找寒冷适应机体表达上调的相关基因,以Balb／C小鼠建立寒冷适应模型,分别提取肌肉和肝脏RNA,运用代表性差异分析(RDA)方法,寻找寒冷适应表达上调的相关基因片段,进行序列分析和同源性比较。结果显示,在肌肉和肝脏中有部分表达上调的基因片段,经狭线杂交验证,其中3条基因表达存在显著差异。这些新发现的机体寒冷适应相关基因为进一步理解寒冷适应的分子机制提供了帮助。     

Accumulation of glycinebetaine during cold acclimation and freezing tolerance in leaves of winter and spring barley plants

A study was performed to examine whether or not betaine (glycinebetaine), a compatible solute, is accumulated in response to cold stress and is involved in mechanisms that protect plants from freezing injury. For this purpose, we used near-isogenic lines of barley, with each line differing only in a single gene for the spring type of growth habit; the various lines were produced by back-crosses to a recurrent cultivar of the winter type. The winter type of growth habit requires a low temperature for triggering of flower development (vernalization), whereas the spring type does not. Betaine was accumulated to five times the basal level over the course of 3 weeks at low temperature (5 °C) in the winter-type cultivar and in a spring-sh line having the sh gene for the spring-type growth habit, but the level was only doubled in the spring-Sh3 line, which carried the Sh₃ gene for the spring-type growth habit. Among near-isogenic lines of the same cultivar, the levels of betaine accumulated in leaves at low temperature were well correlated with the percentages (on a dry weight basis) of green leaves that survived freezing injury (-5 °C). This observation indicates the possibility, separate from the recognized role of betaine in the response to salinity and/or drought, that betaine accumulates in response to cold stress and that the accumulation of betaine during cold acclimation is associated to some extent with freezing tolerance in leaves of barley plants.     

Changes in carbohydrates and freezing tolerance during cold acclimation of red raspberry cultivars grown in vitro and in vivo

Changes in LT50 and carbohydrate levels in response to cold acclimation were monitored in vitro and in vivo in red raspberry ( Rubus idaeus L.) cultivars with different levels of cold hardiness. Entire micropropagated plantlets or shoot tips from 3 cultivars were harvested before, during and after cold acclimation. Cane samples from container-grown plants of 4 cultivars were harvested before and during cold acclimation and deacclimation. Samples were evaluated for cold hardiness (LT50) by controlled freezing, then analyzed for carbohydrates, including starch, sucrose, glucose, fructose and raffinose. Hardiness of cold-acclimated 'Muskoka' and 'Festival' was superior to that of 'Titan' or 'Willamette'. In vitro plantlets had higher levels of soluble carbohydrates on a dry weight basis and higher ratios of sucrose:(glucose+fructose) than the container-grown plants. Total soluble carbohydrates, primarily sucrose, accumulated during cold acclimation in both plantlets (33–56% relative increase) and plants (143–191% relative increase). Sucrose increased 124–165% in plantlets and 253–582% in container-grown plants during acclimation and declined rapidly to the level of control plants during deacclimation. Glucose and fructose also accumulated, but to a lesser extent than sucrose. Raffinose concentrations were very low, but increased significantly during cold acclimation. In vitro, genotype hardiness was related to the high concentrations of total soluble carbohydrates, sucrose and raffinose. In vivo, hardier genotypes had lower concentrations of starch than the less hardy genotypes. These results demonstrated the importance of soluble carbohydrates, especially sucrose, in cold hardening of red raspberry and that the in vitro conditions or controlled acclimation conditions do not necessarily reflect the phenomena observed in vivo.