Photosynthetic Responses of A New Grapevine Variety‘Xinyu'in Turpan

JI Wei ，SUN Feng，LUO Qiang-wei ，ZHANG Zong-qin＊

（1.Key Laboratory of Biology and Genetic Improvement of Horticultural Crops（Northwest Region），Ministry of Agriculture，P.R.China，State Key Laboratory of Crop Stress Biology in Arid Areas，Northwest A&F University，Yangling，Shaanxi 712100 China；2.Institute of Grape and Melon of Xinjiang Uygur Autonomous Region，Shanshan，Xinjiang838200，China）

Grapes are the most popular and widely grown fruit in the world and grow successfully in almost every climate.Breeding objectives vary by region and market necessity，but many programs seek to combine high quality fruit with environmental adaptation and improved disease resistance.Breeding resistant rootstock has long been considered to be an effective approach to controlling Xiphinema index［1-2］.

Grapevine is cultivated nearly 2 300years old in Turpan District in Xinjiang，China［3］.Turpan is one of the major high-quality grape production bases in the world for years because of its hot，dry，and windy climate［4］.These growing conditions are significantly different from those in much of Europe.It is essential to provide supplementary water by irrigation for grapevines to both survive and to make satisfactory growth over the hot summer months.The size of viticulture here is over 27 000 hm2for years.80%of grapevine cultured in the area is ‘Thompson Seedless'（Vitis vinifera）for raisin and table grape production.Growers want high yielding grapes with good shelf life and suitability for Xinjiang＇s diverse growing regions.Therefore，new varieties of the great necessity need to be introduced or bred in Xinjiang.Some new varieties had been bred in the similar dry region［5］and been bred or studied via traditional and transgenic methodology［6］.‘Xinyu'is a new variety we bred in 2005，but it has not been studied extensively.

Fruit breeding requires testing of many characteristics to increase the probability of electing superior genotypes.These characters include physiology and molecular background as well as basically commercial important traits of grapes，such as berry ripening time，berry weight，soluble solids concentration，titratable acidity，and berry flesh texture［7-14］.However，many characteristics that are used to describe responses physiologically of the variety“Xinyu”are not known.

The objectives of this study were to evaluate the productivity，and to illustrate its physiological adaptation mechanism by determining the responsibility to climate factors of the new variety‘Xinyu'on photosynthesis in local vineyard，and to estimate the feasibility of the methodology of grapevine breeding via hybridization based on the photosynthetic responses in the arid desert region.

1 Materials and methods

1.1 Plant material and experimental site

‘Xinyu'was bred and selected at the experimental vineyard in Institute of Grape and Melon of Xinjiang Uygur Autonomous Region（Turpan，Xinjiang，China，90°17′30″E，42°54′32″N，altitude 435 m）.The site is in a typical continental temperate climate zone.It is rich in sunlight resource with a mean annual sunshine duration over 3 056h，mean annual temperature of 14.4℃，annual accumulated temperature（＞0℃）of 5 956℃ and （≥10℃）of 5 372.5℃，frost-free days of 224days.The highest temperature could reach 48.3℃ historically.The average duration of the temperature over 40℃is around 40days，Temperature difference between day and night could reach 20℃.However，the regions is limited in water resources with a mean annual precipitation of 16.6mm，and mean annual evaporation from a free water surface is 2 844.9 mm，and relative air humidity is as low as 30%.

The 5-year-old grapevines were planted with row spacing of 5mand plant spacing of 1m.The trellis for grapevine is shed at 1.5min height.

1.2 Gas exchanges

The net photosynthesis rate（Pn），the stomatal conductance（Gs），the transpiration rate（Tr），photosynthetic available radiation （PARi），and vapor deficit at the leaf surface（Vpdl）were measured simultaneously in fully developed leaves using aportable infrared gas analyser（Li-Cor 6400Photosynthetic Meter，Lincoln，NE，USA）.The infrared gas analysis system was equipped with a clamp-on leaf cuvette that exposed 6cm2of leaf area.Measurements were replicated at seven leaves for each time from morning till evening.

1.3 Environmental condition determination

Air temperature and humidity were determined by using three automatic hygrothermographs（ZDR-20，Zhejiang University of Electrical Equipment Factory，China）and two automatic thermographs（ZDR-21，Zhejiang University of E-lectrical Equipment Factory，China）placed on the grape leaf canopy.Three data of humidity and seven data of temperature were recorded automatically in every 30s.Sunlight intensity was determined by using a Dual Radiation Meter（Apogee Instruments Inc.，China）.

1.4 Chlorophyll measurements

Chlorophyll readings were taken with a handheld dual-wavelength meter （SPAD 502，Chlorophyll meter，Minolta Camera Co.，Ltd.，Japan）.For each time，the 11fully expanded leaves per plot were used.

1.5 Data analysis

Graphics and curve fitting were performed using Microsoft Excel 2003software （Microsoft Corporation）.All data analyzed using software DPS 3.01（Data Processing System，Refine Information Tech.Co.，LtD.，China）.Data regarding the interactions were reported when the interactions were statistically significant at Duncan＇s multiple range test at p＜0.05or p＜0.01.

2 Results and analysis

2.1 Diurnal variation of Pn，sunlight intensity，air temperature，relative humidity and PARi

In Turpan，Xinjiang，the time of sunrise in August was about 7.30a.m.（Beijing Time）.Air temperature and sunlight intensity kept at high levels from 10a.m.to 6p.m.，however the rela-tive humidity dropped to a relative lower value.Air temperature and sunlight intensity reached the intraday highest value during 1p.m.to 4p.m.，while Pn was at a relative high value.PARi reached peak at 1 454μmol·m-2·s-1，reached valley at 111μmol·m-2·s-1.The average PARi was at 938.889 6μmol·m-2·s-1which was 340.956 5μmol·m-2·s-1lower than intraday average canopy sunlight intensity.A steady increase in Pn was measured before 11a.m.and there was‘midday depression'during 11a.m.to 2 p.m.and the valley value was at 2.77μmol·m-2·s-1at noon，which respectively accounted for 49%and 38%of the peak value of Pn before midday depression and after midday depression （Fig.1）.It was obvious that the climate in Turpan provided an extremely hot and relatively dry condition for growing of grapevine.It is characterized by long-time simultaneous high sunlight intensity，high temperature and relatively low humidity here.‘Xinyu'，as a new fruitful variety，could adapt to this local environmental conditions well.

2.2 Relationship between Pnand the environmental factors

The changes of Pn of the leaves has no obvious regularity，but the trend line showed that the overall Pn was increasing as the rising of air temperature and sunlight intensity and decreasing as the rising of relative humidity（Fig.2A-C）.Even though the high-temperature up to 39℃ was not the major restriction factor on Pn （Fig.2A）.And the Pn reached peak at 2.78μmol·m-2·s-1when the relative humidity was 25.27%.The relative humidity neither was too high nor too low is conducive to photosynthesis（Fig.2B）.The sun-light intensity over 1 000μmol·m-2·s-1was from 9a.m.to 7p.m.，peaking at 1 920μmol·m-2·s-1at 3p.m.Solar radiation in this area is quite well（Fig.2C）.

Fig.1 Diurnal variation of the net photosynthesis rate（Pn），sunlight intensity，air temperature（T），relative humidity（RH）and photosynthetic available radiation（PARi）（Turpan，Aug.12th，2008）圖1 凈光合速率（Pn），日照強度，大氣溫度（T），相對濕度（RH）和光合有效輻射（PARi）的日變化（吐魯番，2008年8月12號）

Fig.2 A：relationship between the net photosynthesis rate（Pn）of the leaves and air temperature（Tair），B：relationship between Pnand Relative Humidity（RH）of canopy leaves，C：relationship between Pnand sunlight intensity of canopy leaves，D：relationship between Pnand chlorophyll content（Chl con.），E：relationship between Pnand stomatal conductance（Gs），F(xiàn)：relationship between Pnand transpiration rate（Tr）圖2 A：葉片凈光合速率（Pn）和大氣溫度（Tair）之間的關系，B：凈光合速率（Pn）和葉幕層相對濕度（RH）之間的關系，C：凈光合速率（Pn）和葉幕層光照強度之間的關系，D：凈光合速率（Pn）和葉綠素含量（Chl con.）之間的關系，E：凈光合速率（Pn）和氣孔導度（Gs）之間的關系，F(xiàn)：凈光合速率（Pn）和蒸騰速率（Tr）之間的關系

2.3 Diurnal variation of Pn，chlorophyll content，Tr and Vpdl

Statistical analysis showed that chlorophyll contents were significant difference in the different time periods（Fcal=2.462 988＞Fcrit=1.911 141，p-value（0.05）=0.010 3）.It showed that chlorophyll content affected by environmental conditions，but the changes of Pn was no correlation with leaf chlorophyll content（Fig.2D）.

Gs had significant difference in the different time periods （Fcal=14.710 4?Fcrit=2.343 1）based on statistical analysis.The peak value was at 0.174 429μmol·m-2·s-1at 5p.m.and the valley value was at 0.059 2μmol·m-2·s-1at 8p.m.The changes of Pnof the leaves had no apparent regularity，but the trend line showed that the overall Pn was increasing as the rising of Gs，that was to say，Pn was increasing with the increasing degree of stomatal opening（Fig.2E）.Tr was significant difference in the different time periods（Fcal=37.041 0?Fcrit=2.343 1）.Tr reached peak at 9.171 4μmol·m-2·s-1at 5p.m.，valley at 1.874 3at 8p.m.and average at 5.499 8 （Fig.2F）.

2.4 Relationship between diurnal variation of Pn and other indexes of photosynthesis

The chlorophyll content was increasing before 1p.m.，and reached the lowest value at 2p.m.Pn Significantly dropped when the chlorophyll content reached the highest value.It showed that chlorophyll content was not the determinant of Pn（Fig.3）.

Fig.3 Diurnal variation of the net photosynthesis rate（Pn），chlorophyll content（Chl con.），transpiration rate（Tr）and vapor deficit at the leaf surface（Vpdl）圖3 凈光合速率（Pn），葉綠素含量 （Chl con.），葉面蒸騰速率（Tr）和葉面飽和蒸汽壓虧缺（Vpdl）的日變化

2.5 Correlation analysis of Pnand other indexes of photosynthesis

The correlation analysis showed that there were significant positive correlations between Pn and PARi，sunlight intensity，Tair，Vpdl，Tr and Gs respectively.And the order of correlation was PARi＞sunlight intensity＞Tair＞Vpdl＞Tr＞Gs.But Pn has no correlation with chlorophyll content and RH.The chlorophyll content has significant correlations with sunlight intensity，Tr and Vpdl has significant correlations with Tair（Table 1）.

Table 1 Correlation analysis of net photosynthesis rate（Pn）and other indexes of photosynthesis＊表1 凈光合速率（Pn）和光合作用其他指標的相關性分析＊

3 Conclusion and discussion

3.1 The influences of environmental factors

The grape and wine consumption concerns at least 40countries in the world.The climate of the different grape-growing regions worldwide ac-counts for a large part of the diversity of varieties cultivated，and viticulture products［15］.Generally，in a given area，the soil type and viticultural practices do not change significantly from year to year and，therefore，climate is the most dominant factor in determining grape quality［16］.Exposure to sub-lethal high temperature can increase the thermotolerance of plants.Potential mechanisms of response include synthesis of heat-shock proteins and isoprene and antioxidant production to protect the photosynthetic apparatus and cellular metabolism［17］.The highest temperature in Turpan is about 40℃.Not only the temperature，but the low air humidity （15-25mm rainfall yearly）and strong radiation （solar radiation beyond 10℃ is 3 250-3 770mJ·m-2），make the region a rough but excellent place for organic viticulture.So the appropriate variety must be bred for viticulture that adapting the climate.‘Xinyu'is a new variety we released 2005［18］.For the reasons mentioned supra，it is not surprising to note that the number of papers in literature which have dealt with the variety‘Xinyu'is quite small.This is the purpose of the study we performed.The physiology of photosynthetic properties of the variety was studied and reported here.Further studies are essential to determine other physiological and molecular basis of the variety in different regions.

The available evidence indicates that exposure of plants to environmental stresses can cause damage to compensated leaf photosynthesis；reducing CO2assimilation rates［19］.Increased temperatures curtail photosynthesis and increase CO2transfer conductance between intercellular spaces and carboxylation sites［20］.Stomatal conductance and net photosynthesis are inhibited by moderate heat stress in many plant species due to decreases in the activation state of rubisco［13，21］.In maize the Pn was inhibited at leaf temperatures above 38℃ and inhibition was much more severe when temperature was increased abruptly rather than gradually.However，high temperatures inhibition was independent of stomatal response to high temperature［13］.We got the similar results that Pn was not inhibited at temperature even above 39℃，but weak midday depression when temperature increased abruptly during 11a.m.to 2p.m.Despite negative effects of high temperature was observed，the optimum temperature for leaf photosynthesis is likely to increase with elevated levels of atmospheric CO2.Several studies have concluded that CO2-induced increases in crop yields are much more plausible［20］.Our results indicated that there were significant positive correlations between Pn and PARi，sunlight intensity，Tair，Vpdl，Tr and Gs respectively.Pn was at a relative high value even the air temperature and sunlight intensity reached the intraday highest value during 1p.m.to 4p.m.，and the trend line showed that the overall Pn was increasing as the rising of air temperature，sunlight intensity，stomatal conductance and the transpiration rate.We could induced that‘Xinyu'could adapt to the environment in Turpan.

Heat shock reduces the amount of photosynthetic pigments［20］.We found that chlorophyll content had significant difference in the different time periods and chlorophyll content was affected by environmental conditions.However，the changes of Pnhad no correlation with leaf chlorophyll content in this study.More researches may be needed to explain this mechanism.

3.2 The economic characters of fructification

A successful new fruit variety must be superior for yield and quality characteristics.Yield depends on the quantity of product whereas quality often decides the market price.Fruit quality is of paramount importance in marketing table grapes，no matter how superior is its yield performance［22］.It would be unwise to select a vine based only on a few characteristics because they may have unfavorable impacts on other characteristics.

Progenies characteristics could be predicted by its parents and evaluated objectively by the responsibility to the environment factors.‘Xinyu'is a variety with acceptable quality and productivity of its parents and with the good performances to the specific climate.The bunch of‘Xinyu'is conical and compact，and the weight of a single bunch is over 800g.The berry is oblong and the pericarp is fuchsia.The average berry weight of ‘Xinyu'，E42-6and‘Rizamat'is 11.6g，8.6g and 9.1g，respectively.It is obvious that‘Xinyu'，as a new cultivar，has better economic characters than its parents.The multiple spot regional trials showed that the cultivar were excellent of its strong vigorous growth，high yield and good quality［18］.The results of the economic characters of fructification and the photosynthetic responses demonstrated that it is feasible of the methodology of grapevine breeding via hybridization in the arid desert region of northwest China.The results of this study could be used to instruct the variety extension，suitable cultivating technology development of the variety，and to be a reference for new variety breeding work especially in the similar climate region.

Therefore，we could conclude that the climate in Turpan District in Xinjiang，China，provides an extremely hot and relatively dry condition for growing of grapevine.It is characterized by long-time simultaneous high sunlight intensity，high temperature and relatively low humidity here.Xinyu，a new variety，can adapt to these special local environmental conditions and has a better economic character than its parents，and with great potential for extending to the region of climate similarity.

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