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ISSN : 1225-8504(Print)
ISSN : 2287-8165(Online)
Journal of the Korean Society of International Agriculture Vol.26 No.4 pp.561-567
DOI : https://doi.org/10.12719/KSIA.2014.26.4.561

Evaluation of Physiochemical Changes of Asian Pear Cultivars During Winter Season

Sherzod Rajametov, Sam-Seok Kang*, Yoon-Kyeong Kim*, Hyung-Jin Baek†
National Agrobiodiveristy Center, NAAS, RDA, Jeonju, 560-500, Korea
*Pear Research Station, NIHHS, RDA, Naju 520-821, Korea
Corresponding Author : (Phone) +82-63-238-9490 (hjbaek@korea.kr)
November 7, 2014 November 19, 2014 November 20, 2014

Abstract

This study was conducted to evaluate the physicochemical changes of Asian pear cultivars ‘Niitaka’ and ‘Chuwhangbae’ during the winter of 2012 and 2013. Cultivar ‘Chuwhangbae’ distinguished with high water deficit and water content in shoots as compared with cv. ‘Niitaka’. However, water content of ‘Chuwhangbae’ was higher in buds than ‘Niitaka’. Chemical content in shoots and buds were varied during the winter season. Mineral compositions were higher in buds than in shoots, also values insignificantly varied and showed stable compared to shoots in both cultivars. During cold period in shoots of both cultivars significantly increased of glucose and fructose. Therefore, response of plants and the transition into the new level under action of the minus celsius degrees should be held equally at the all levels of the metabolism depending on the phase of development. All processes are interrelated and the backlog of any of them is the reason that leads to violation of conjugation between them, the accumulation of the metabolic products that reduce the stability of the entire system.


Evaluation of Physiochemical Changes of Asian Pear Cultivars During Winter Season

Sherzod Rajametov, Sam-Seok Kang*, Yoon-Kyeong Kim*, Hyung-Jin Baek†
National Agrobiodiveristy Center, NAAS, RDA, Jeonju, 560-500, Korea
*Pear Research Station, NIHHS, RDA, Naju 520-821, Korea

초록


    Rural Development Administration
    PJ010153

    Most plant physiological events are closely related with environmental conditions. The adaptation is achieved through various mechanisms: genetic, biochemical, physiological, anatomical, etc. (Liu et al., 1999; Sparks et al., 2001; Alehina et al., 2005; Gusta et al., 2005; Sysoeva 2006). Particularly in winter, physiological and biochemical alterations in plants, such as changes in carbohydrates, lipid, protein composition, and water status in the plant have been correlated with cold acclimation, and upon occurrence of negative temperature, increase of sugars in plant tissues is largely a result of hydrolysis of starch and associated with cold hardness (Steponkus and Webb 1992; Sperry 1993; Sparks et al., 2001). During this period, especially important in plants is the accumulation of significant amounts of a special type of sugar. These substances hinder the appearance of ice crystals in the cells and the slowing growth during severe frosts (Ashworth, 1992; Childers et al., 1995; Sugiura., 2002; Liu et al., 2007; Satibalov and Bekkiev. 2008), although a clear role for any of these changes in development of freezing tolerance is yet to be demonstrated.

    Also, in winter it is well known that root vital activity is lower than during the growing period. Decrease of water potential in trees during winter is associated with ability to transport water from the soil through the plant for growth and survival. Water balance of plants depends on the shoot water potential, xylem hydraulic conductivity, freeze-thaw events, etc. (Salleo and Gullo, 1989; Sperry et al., 1994; Sparks et al., 2001).

    The physiological and biochemical responses of pear cultivars under low winter temperature can help to understand the ability of the plants to adapt to low temperature stress. Therefore, the present work aimed to investigate the physiological and biochemical of Asian pear cultivars during the winter period.

    MATERIALS AND METHODS

    Plant materials

    The experiment was done in Pear Research Station, NIHHS, RDA (Republic of Korea) during the winter 2012- 2013. Study of changing of physiochemical composition in shoots and flower buds was carried out in two cultivars of Pyrus pyrifolia: ‘Chuwhangbae’ and ‘Niitaka’. The annual shoots (shoots) and flower buds (buds) used directly from the field where for each investigation were used three replicas (shoot length were 0.80 - 1.0 m and diameter 0.7 - 1.0 mm). The trees age were 25 years old.

    Evaluation for water balance

    Water deficit (WD) as a percentage of its total content in state of complete saturation in annual shoot was determined (shoots were kept in water 48 hours) (Weatherley, 1950) and expressed as:

    WD% = (WA 100)/W

    where WD= water deficit; WA = water absorbed at saturation of the shoots, determined by the difference of mass of shoots before and after complete saturation; W= presence of water, the difference between the mass of shoots after complete saturation with water and dry mass of sample. Water contents (WC) was tested as a percentage of its total content in annual shoots and in flower buds and calculated by the formula:

    WC%= ( W 1  − W 2 ) 100/ W 1

    where WC%- water content, W1- initial mass of shoots, W2 - dry mass of shoots.

    Evaluation of chemical composition in shoots and flower buds

    Determination of the soluble starch and sugar contents in shoots and nutrition- N, P, K, Ca and Mg contents in shoots and buds were analyzed in intervals of 15 days. The sugar content (glucose, sucrose, fructose and sorbitol) measured by a HPLC (Differential Refractometer Waters 410 and Waters 717 plus Autosampler USA), and the starch by a BioTech Microplate Spectrophometer (USA). P, K, Ca and Mg contents in shoot and flower bud on a dry weight basis by a Polarized Zeeman Atomic Absorption Spectrophotometer Z-5300 (Hitachi) and P by a Spectrophotometer U- 3900 (Hitachi) at wavelengths specific for each element (K: 766.5 nm; Ca: 422.7 nm; Mg: 285.2 nm; P: 470.0 nm) and N measured by using ICP (Perkin Elmer 2100, Norwalk, CT, USA) (Hudina et al., 2007).

    The climatic condition of winter season 2012 - 2013

    In South Korea, although the autumn is usually relatively warm and long, there are years with early onsets of frosts. According to perennial data, the first frosts in the region begin in mid-November, which coincides with the conduct of our experiment where temperature went down to −0.6°C, which further decreased to a minimum −3.8°C in late November (Fig. 1). However, the average and maximal daily temperatures were significantly high in that period. From early December the average and minimal daily temperatures slowly decreased and reached a minimum by mid-January at −6.2 and −12.9°C, respectively. Thereafter the maximum temperature started to decrease and stayed around 8.0-11.0°C, and the duration of the warm weather was insignificantly long. It should be noted that the average and minimal daily temperatures were lower than on perennial data. Afterward, from late January to early March, the average and minimal daily temperatures increased and a rise in maximal temperature over 15.0°C was noted whereas the minimal temperature was about - 7.0 and −10°C. Compared to perennial data, the average daily temperature in this winter was relatively low.

    RESULTS

    Water potential of pear cultivars

    Investigation of the plant water potential, physiological and structural changes is imperative for evaluation features of cultivar. So, WD in shoots and WC in shoots and buds of ‘Chuwhangbae’ and ‘Niitaka’ were investigated in the winter inactive period and after came out from an organic rest period of pear trees. In late November WD in both cultivars was identical 0.8% respectively and hereinafter from January till February increased and reached maximum in ‘Chuwhangbae’- 5.4% and ‘Niitaka’- 4.1% (Fig. 2). Further it starts to decrease till mid-February and continued until the beginning of March, but by mid-March WD in both cultivars was increased again and showed 7.5 and 6.0% respectively.

    The WC were over 50% in both cultivar shoots before starting the cold period (Fig. 3) and from December began stable slowly decreasing and at the end of January showed a minimal level where values in both cultivars were almost the same- 43.6 and 43.7% respectively. By mid-February in both cultivars was observed an intense rise of WC. The WC in the buds was quite different from the WC in the shoots, where buds displayed an opposite tendency. According to our results, the WC in the buds was higher than in shoots, the highest level being concentrated in ‘Chuwhangbae’. In late November before starting the cold period the WC in ‘Chuwhangbae’ and Niitaka was 55.2 and 52.2% respectively and in contrast from December to mid-January WC showed a low level and then from early February was observed a rapidly rise.

    A chemical property of the pear cultivars during winter

    It is well known that the organic rest period is a physiological condition of plants, where they have a sharply reduced growth and metabolic rate, the plant is undergoing deep physiological and biochemical changes in plant cells. Therefore, investigation of changing chemical composition in each cultivar during winter period to assess the dignity of plant to stress responses and to negative temperatures is very important. Reciprocally changing of N, P, K, Ca and Mg in the buds and shoots were observed. The highest accumulation ability in the buds was investigated in ‘Chuwhangbae’ except for K. However, the same pattern was not revealed in shoots and data varied significantly depending on period.

    So, ‘Chuwhangbae’ showed high accumulation over 20% of N in buds compared to ‘Niitaka’ (Fig. 4) and they saved steady concentration during winter period. However, from December in shoots of ‘Chuwhangbae’ was observed depletion of N until March, whereas in ‘Niitaka’ it was not significantly fluctuated.

    As in nitrogen composition a P, Mg and Ca showed the similar tendency in buds with not significant increasing and the highest concentration observed in ‘Chuwhangbae’ in comparison with ‘Niitaka’ (Fig. 4 and 5). However, regardless of cultivars this tendency in shoots was significantly low with the essential depletion of P, Mg and Ca in shoots during winter.

    Concentration of K in ‘Chuwhangbae’ buds showed con- trary low rates compared to ‘Niitaka’, but it was not noticeably (Fig. 6). In shoots this trend was significantly fluctuated and not steady. This was particularly seen in the mid of winter where fixed significantly low minimal and average daily temperature.

    Before entrance to deep dormancy shoots of cultivar ‘Chuwhangbae’ was revealed the highest soluble starch content, and with beginning of winter cold period detected degradation it (Fig. 6), whereas ‘Niitaka’ showed relatively low level but saved stable rates during winter.

    Accumulation of the carbohydrates in shoots varied compared to starch values (Fig. 7). So, in late of November both cultivars accumulated the similar sugar content and then after starting of cold period were determined fluctuation and decreasing values. However, regardless of cold season during winter ‘Chuwhangbae’ could keep high level of sugar compared to ‘Niitaka’.

    The knowledge of accumulation cryo-protectants which carried out protective functions such as: sucrose, monosaccharide, soluble proteins, etc., has a great role in developing frost tolerance cultivars.

    According to results of study the change of carbohydrate compositions in shoots such as: sucrose, glucose, galactose, fructose and sorbitol showed that sorbitol had more high level in both cultivars compared to another element. It should be noted that sorbitol showed almost similar activity in both cultivars during winter.

    Following more active substances was sucrose which from late November to mid-December showed high content and then noted rapidly decreasing sucrose till early February, whereas in this case observed significantly activity of glucose, fructose and small amount of galactose. And, by mid-February was detected again high accumulation of sucrose and dramatic reducing of glucose, fructose and small amount of galactose.

    DISCUSSION

    During the winter in both pear cultivar shoots was observed the highest dehydration but in buds where WC was higher it have been detected reverse pattern and it can be related with content of bound water (cell sap determines osmotic properties and cell turgor and consequently, the elasticity of tissues and organs of plants, the water serves as a receptacle, and various substances involved in the metabolism of the cells and place deposits end products of the metabolism), the rate of growth, where the flow of the water is connected in this case with the energy consumption and with vital activity of cells in flower organelle. The water can be absorbed into the cell of bud also by the forces of swelling- matrix potential and proteins and other substances contained in the cell which attract dipoles of water having positively and negatively charged groups. Also, water gets into swellable structure by diffusion; the movement of water is going on the concentration gradient (Medvedev, 2004; Alehina et al., 2005). Before decline of daily temperature to minimum in the beginning of December, both cultivars had a high vital activity, but after decreasing average daily and minimal temperature the activity of plant reduced and WD increased and correspondingly WC in shoots were reduced. Increasing WD in shoots of ‘Chuwhangbae’ might be related with high starch and soluble sugar which plays mechanism of improving tolerance to stress factor (Bonhert and Jensen, 1996; Jung et al., 2014). Thereafter, rising WD in shoots and declining WC in shoots and buds is associated with plant organs development and outside average daily and minimal temperature. Rise of average daily and maximal temperature in early February has led to increase vital activity of plant more intensively, but the cultivars showed a different ability to the transition on the new level of metabolism activity.

    Many plant species adapt to cellular dehydration stress by osmotic adjustment (Levitt, 1980b; Alehina et al., 2005) and level of ABA (Zhu, 2002; Shinozaki et al., 2003; Lata and Prasad, 2011; Shin, et al., 2012). This adjustment is achieved by accumulation of compatible osmolytes and results in the retention of turgor and the capacity for cell elongation at low water potential. Various level of osmotic adjustment have been reported in different plants during cold acclimation (Levitt, 1980a; Yelenosky and Guy, 1989), but more importantly, cold acclimationinduced osmolytes such as sugars and amino acids might help the plant survive freeze-induced cellular dehydration stress by acting as non-colligative cryo- or osmoprotectants (Yelenosky and Guy, 1989; Alehina et al., 2005; Jung et al., 2014).

    Before turning attention to the accumulation of soluble sugars and starch in plant organs, it is necessary to discuss the content of mineral compounds. As well-known that N plays a big role to involve the action of a sequence of specific enzymes, biosynthesis of proteins, amino acids, etc., P is the essential biogenic element involved in the synthesis of ATP (Rich, 2003) and a part of proteins and other important organic compounds (Scheeff and Bourne, 2005). K has also been implicated to have a role in the proper thickening of cell walls (Datnoff et al., 2007), maintenance of acid-base balance and water balance, protein synthesis, activation of some enzymes (Leigh and Jones, 1984). Ca especially Ca2+ ions are an essential component of plant cell walls and are needed to stabilize the permeability cell membranes. They are also used as cations to balance organic anions in the plant vacuole and increase the viscosity of the cytoplasm (White and Martin, 2003). Mg plays a role in the stability of all polyphosphate compounds in the cells, including those associated with DNA- and RNA synthesis. Additionally, Mg ions are very important for enzyme catalytic action and for ATP, the main source of energy in cells, which must be bound to a magnesium ion in order to be biologically active (Lusk et al., 1968; Marschner, 1995). In our results, the reduction of the N, P, K, Ca and Mg content in shoots are associated with requirements of the buds, which absorb water and nutrients from the shoots to save energy during cell division under cold accumulation during the winter.

    It might be assumed that the ABA accumulation that has been observed during cold accumulation (Thomashow, 1999; Shinozaki and Yamaguchi-Shinozaki, 2000; Zhu, 2002; Shinozaki et al., 2003; Lata and Prasad, 2011) may be characterized by the higher ability to accumulate carbohydrate, the appearance of dehydration in shoots, the increase of N, P, Ca,Mg and WC in the buds of ‘Chuwhangbae’, which induces gene expression to confer stress tolerance. Whereas, in previous our research report was presented results of study on cold resistance of cultivar ‘Chuwhangbae’ which showed low injury compared to ‘Niitaka’ (Rajametov and Kang, 2014). Also, the reverse genetic approach, as well as classical forward genetics, will become more important for understanding not only the functions of stress-inducible genes but also the complex signaling processes of the dehydration- and coldstress responses (Lang et al., 1994; Alehina et al., 2005; Shinozaki and Yamaguchi-Shinozaki, 2000).

    According to results cultivar ‘Chuwhangbae’ has almost high ability to accumulate of the physiochemical composition. An interesting situation was determined in changing of carbohydrates in winter. Both cultivars, until mid- December showed high accumulation of sorbitol and sucrose content. Subsequently, they dramatically reduced and glucose, fructose, and a little amount of galactose significantly increased during cold acclimation as evidenced in work (Lee et al., 2011). And the plant to started to respond to stress of condition (low temperature) and began to hydrolyze of glucose, fructose and galactose in order to protect from frosts. By early February, there were revealed of redistribution carbohydrate in the opposite direction that means increasing of sorbitol and sucrose, and thereafter glucose, fructose and a little amount of galactose again reduced. Additionally, early March a different rate of accumulation carbohydrate observed – a rise in glucose, fructose, and again a reduction of sorbitol and sucrose. It might be associated with transition process of metabolism on the new energy level where growing activity in plant organs becomes higher.

    Lee et al. (2011) reported that soluble sugars, especially fructose and glucose, are strongly associated with cold har diness in blueberries starch started to degrade to maltose and decreased from mid-November, whereas in our experience during the winter the starch content was steady.

    Magnification of glucose during the winter period can be broken down and converted into lipids (Clark and Sokoloff, 1999), which is the basic and most universal source of energy for metabolic processes in cells. The same tendency was also observed in fructose, which has a greater effect on freezing point depression, which may protect the integrity of cell walls of plant by reducing ice crystal formation (Hanover and White, 1993). According to Rich (2003) the overall process of oxidizing glucose to carbon dioxide is known as cellular respiration and can produce about 30 molecules of ATP (which plays an extremely important role in the exchange energy and substances in organisms) from a single molecule of glucose. Prolonged cool weather contributes to the depletion of substances, especially carbohydrates, which reacts strongly to the resistance of plants to negative temperatures.

    Teo et al. (2006) remarked that sorbitol can be obtained by reduction of glucose. However, it should be noted that in our case the same pattern was observed not only under reduction of glucose and by the fructose, but also with positive correlation between sorbitol and sucrose. And it may play a great role in metabolic processes. It possibly serves as a key ingredient in the chemical synthesis of organic compounds such as hydroxyl functional group (as alcohol).

    According to Kim at al. (2011) peach trees which had higher shoot starch content, were not damaged by freezing injury and starch accumulation tendency reduction during winter. In contrast, in our study year essential reducing of starch during winter was not determined, and it can be associated with daily average temperature in the winter, where fluctuation was not significantly different and relatively low in comparison with perennial data. Apparently this is related to the response of plants to thaws, where sugar rises to hold the energy balance.

    In conclusion, according to our data and literature, winter resistant cultivars should be distinguished with the highest ability to accumulate and efficiency uses the chemical components, which contribute to decrease injury level under low temperatures. Therefore, when developing new cultivars, breeders need to pay attention to parental forms in which is concentrated ability to immediately respond to external low temperature. The transition to the new level under action of the minus temperatures should be held equally at all levels of the metabolism, depending on the phase of floral organ development. All processes are interrelated and the malfunction of any of them will leads to conditions, which compromise the function and stability of the whole energy system.

    적 요

    이 연구는 2012년과 2013년 동절기에 아시아 배 품종인 신 고와 추황배를 공시하여 생리화학적인 상태의 변화를 평가하 기 위해 실시하였다.

    추황배는 줄기에서 높은 수분부족과 수분함량을 보여 신고 와 구별되었다. 겨울동안 줄기와 눈에서 화학성분이 다양하게 변화하였으며, 미네랄 성분은 줄기보다 눈에서 높게 나타났다.

    두 품종 모두 겨울동안 줄기에서 포도당, 과당, 갈락토오스가 증가하였기 때문에 기관 발달과정에서의 식물의 생장반응과 온 도의 변화에 따른 신진대사의 수준이 일정하게 유지되었다.

    신진대사의 모든 과정은 상호 연관되며 그들 사이에 접합이 방해하는 이유는 시스템 전체의 안정성을 저하시키는 대사산 물을 축적하기 때문으로 판단된다.

    Figure

    KSIA-26-561_F1.gif

    Temperature conditions in winter period, Naju 2012-2013.

    KSIA-26-561_F2.gif

    Water deficit in annual shoots during winter. Data represented by Mean ± SD (n = 3).

    KSIA-26-561_F3.gif

    Water content in flower buds and in annual shoots during winter. Data represented by Mean ± SD (n= 3).

    KSIA-26-561_F4.gif

    Nitrogen and Phosphorus content in shoots and in flower buds during winter. Data represented by Mean ± SD (n= 3).

    KSIA-26-561_F5.gif

    Magnesium and Calcium content in shoots and in flower buds during winter. Data represented by Mean ± SD (n= 3).

    KSIA-26-561_F6.gif

    Potassium content in shoots and buds and soluble starch and sugar in shoots during winter. Data represented by Mean ± SD (n= 3).

    KSIA-26-561_F7.gif

    Carbohydrates content in shoots of ‘Chuwhangbae’ and ‘Niitaka’ during the winter. Data represented by Mean ± SD (n= 3).

    Table

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