Scientific report: "The photosynthesis and root characteristics associated with drought tolerance in rice" potx

SUMMARY The pot experiment was conducted to estimate physiological and root characters related to drought tolerance of different cultivated rice cultivars including low land Indica subs

J Sci Dev 2009, 7 (Eng.Iss.1): 1 - 8 HA NOI UNIVERSITY OF AGRICULTURE

Photosynthetic and root characters related to drought

tolerance

in plant

Các đặc tính quang hợp và rễ liên quan đến chịu hạn ở cây lúa

Pham Van Cuong

Department of Food Crop Science, Faculty of Agronomy, Hanoi University of Agriculture

TÓM TẮT

Thí nghiệm trong chậu được tiến hành nhằm đánh giá các đặc tính sinh lý và đặc tính rễ liên quan đến tính chịu hạn của các giống lúa bao gồm lúa nước loài phụ indica, lúa nước loài phụ Japonica, lúa lai từ dòng bất dục đực nhân mẫn cảm nhiệt độ và loài lúa dại để so sánh với giống lúa Indica chịu hạn

Ở giai đoạn đẻ nhánh hữu hiệu, các chậu thí nghiệm được rút cạn nước rồi để khô trong vòng 4 ngày, sau đó được tưới nước trở lại Ở giai đoạn trước rút nước, hạn và sau phục hồi (sau tưới nước 4 ngày), chọn ngẫu nhiên 4 chậu của mỗi giống để đo các chỉ tiêu về quang hợp như cường độ quang hợp, độ dẫn khí khổng, cường độ thoái hơi nước và chỉ số khối lượng riêng của lá (một chỉ tiêu đánh giá độ dày lá) Những cây đo quang hợp được chọn để đo độ dẫn nước và các đặc tính về rễ như chiều dài rễ tối

đa, số lượng rễ và khối lượng rễ khô Khi xử lý hạn hầu hết các đặc tính quang hợp như cường độ trao đổi CO 2 , độ dẫn khí khổng và cường độ thoát hơi nước đều giảm mạnh ở lúa lai F1 và lúa dại tương tự như ở giống lúa chịu hạn (CH5), trong khi đó những chỉ tiêu này giảm ít hơn ở các giống lúa khác Ngược lại những chỉ tiêu này lại phục hồi tốt hơn ở lúa lai F1 lúa dại và giống lúa chịu hạn so với ở các giống khác Cường độ quang hợp tương quan thuận với độ dẫn khí khổng và cường độ thoát hơi nước

ở tất cả các giống lúa ở giai đoạn hạn và phục hồi, tuy nhiên tương quan này không ở mức ý nghĩa tại giai đoạn trước rút hạn Cường độ quang hợp và chỉ số diệp lục (SPAD) có tương quan thuận ở giai đoạn trước rút hạn và sau phục hồi, tuy nhiên tương quan này lại âm ở giai đoạn hạn Cường độ quang hợp có tương quan thuận với số lượng rế/cây ở giai đoạn phục hồi

Từ khoá: Cây lúa, chịu hạn, kiểu gien, quang hợp, rễ

SUMMARY The pot experiment was conducted to estimate physiological and root characters related to

drought tolerance of different cultivated rice cultivars including low land Indica subspecies, low land Japonica subspecies and F1 hybrid from thermo-sensitive genic male sterile line and wild rice specie (Oryza Rufipogon) in compared with drought tolerance cultivar (Indica low land rice) At the active

tillering stage, the plants were moved out all waters the kept dried during for four days, after that the pots were recovering Four plant of each cultivars was randomly selected for measuring

photosynthetic characters viz., photosynthetic rate, stomatal conductance, transpiration rate and

specific leaf area (SLA a revert indicator of leaf thickness) The plant measured photosynthetic characters were sampled for measuring water conductance and root characters such as root length, number of root per plant and root dry weight As drought treatment, most photosynthetic character such as CO 2 exchange rate, stomatal conductance and transpiration rate decreased in F1 hybrid and wild rice as much as in drought tolerance cultivar (CH5), whereas they were much higher in the other cultivars In contrary, these characters recovered in all F1 hybrid, wild rice and check cultivar were quite higher than those in the others at recovering stage Photosynthetic rate were significantly and positively correlated with stomatal conductance and transpiration rate in all rice cultivars at both drought and recovering stages, whereas the correlation was not significant at before drought stage A correlation between CER and SPAD was observed to be positive at before drought and recovering stages, however it was negative at drought stage CER was positively correlated with the number of root per plant at recovering stage

Key words: Drought tolerance, photosynthesis, rice plant, root

1 INTRODUCTION

Water is essential to plant growth because it

provides the medium within which most cellular

functions take place Nowadays, the restricted

availability of water resource has focused attention

On paddy and upland fields where the irrigation

water depends mainly on rainfall, rice plants are

often exposed to drought (O'Toole, 1982) On the

other hand, about 70% of the rice cultivation area in

Southeast and South Asia, which is about half of

the total world production, depends on irrigation

from rainfall From the worldwide viewpoint, the

fact indicates that studies on drought resistance are

very important at present According to

mechanisms of drought resistance, the responses to

drought in plants relate to photosynthetic rate,

stomatal conductance, transpiration rate, leaf

rolling, enhanced root growth, specific leaf area

and so on Accumulated evidence suggests that

both chemical and hydraulic signal are operative

and integrated in the regulation of leaf growth and

stomatal conductance when plants grown under

drought stress (Davies et al., 1994; Comstock,

2002) The hydraulic signals involve changes in

pressure potential in the xylem and changes in

water content of the guard cells and other epidermal

cells The chemical signals relate to abscisic acid

(ABA), which is synthesized in roots under water

stress and transported to leaves and/or together with

ABA synthesized in the leaves themselves, induce

stomatal closure Also, root development is

fundamentally involved in the response to many

plant stresses, such as drought (Adam et al., 2002)

The possession of a deep and thick root system

which allows access to water deep in the soil

profile is considered crucially important in

determining drought resistance in upland rice and

substantial genetic variation exists for this (Fukai

and Cooper, 1995; O'Toole, 1982; Yoshida and

Hasegawa, 1982) The drought resistance of

cultivated plants, including rice plants, refers not

only to their specific ability, such as survival

capacity or subsequent recovering ability, but also

to their integrated abilities in the production

processes through their growing period (Fukai and

Cooper, 1995; Mambani and Lal, 1983) In this

study, we estimated the drought tolerance in F1

hybrid, wild rice, upland rice and low land rice

cultivars in compared with drought tolerance rice at

the active tillering stage by measuring the photosynthetic rate, stomatal conductance, water conductance and root characters

2 MATERIALS AND METHODS

2.1 Plant Materials

The experiments were carried out with 8 different rice cultivars: CH5 (Drought resistance used as check cultivar), Khau Suu (local upland rice cultivar), 103S (low land, TGMS line -indica),

R20 (low land, restorer line- indica), Oryza Rufipogon (wild rice species), Vietlai 20 (F1 hybrid rice - 103S/R20), Lily 328 (low land rice, susceptible for drought, japonica): and Toitsu (low land rice, susceptible for drought, japonica) The experiments were set in green house in Faculty of Agronomy, Hanoi University for Agriculture, Vietnam during spring cropping season in 2006

2.2 Planting

Seed of rice cultivars were incubated and sown in the seedling bed (60 x 35 x 8 cm) Seedling

at the 3 - 4- leaf stage was transplanted singly into Wager pot (0.02 m2), one seedling per one pot (Gomez and Gomez, 1984)

2.3 Fertilization

Total fertilizer was applied with N, P2O5 and

K2O was at the rate of 0.48, 0.36 and 0.36 (g per pot), respectively Basal dressing for one pot with N,

P2O5 and K2O was at the rate of 0.16, 0.18 and 0.12

g, respectively Top dressing at 7 DAT and 14 DAT with N, P2O5 and K2O at the rate of 0.08, 0.18 and 0.08 g, respectively Final dressing at the panicle initiation stage (20-18 days before heading) was applied with N and K2O at the same rate of 0.06 g

2.4 Drought treatment

At the active tillering stage (30 days after transplanting), all the water inside in the pots were moved out then the pots were kept dried during 4 days, after that re-watering (O'Toole, 1982; Fukai and Cooper, 1995)

2.5 Measurement

Photosynthetic parameters: At three stages as

before draining, during drought treatment and 4 days after recovering, 4 plants of each rice cultivars were randomly selected for measuring photosynthetic

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characters Two top-fully expanded leaf of each

plant was selected for measuring CO2 exchange rate

(CER), transpiration rate (Tr) and stomatal

conductance (gs) using LICOR 6400, at temperature

of 30oC, light intensity of 1500 mol/m2/s and CO2

concentration of 370 ppm

The plants measured photosynthesis were

selected for measuring SPAD value (an indicator of

chlorophyll content) using SPAD, Motorola, 502,

Japan, Specific leaf area (SLA), water conductance

and root characters: The leaf measureed CER was

sampled for measuring leaf area using ANA-GA-5,

Japan, then dried at 80oC for 48h for calculating SLA

SLA = Leaf area/ Leaf dry weight

Water conductance: The plants were cut at 5

cm high from the base of plant and use dry cotton

to cover the stem After two hours the cotton was

weighted for calculating water conductance

Root characters: The plants were selected

maximum root length and counted the number of

active root per plant The roots of each plant were

dried at 80oC for 48 hours for root dried weight

measurement

Statistical analysis: Data was analyzed by

SAS program Ver.8.2, (1990) after Shinjo

(1994)[f1] Means were tested by least significant

difference at P0.05 level At each stage, correlation

among photosynthesis and root characters were

calculated of 4 plants considered as 4 replications

3 RESULTS AND DISCUSSION

CO 2 Exchange Rate: Table 1 showed that the

CO2 exchange rate (CER) of all 8 cultivars

decreased under drought condition (measured 4

days after draining) and increased in recovering stage (4 days after watering) The CER decreased

in wild rice (Oryza Rufipogon; from 31.23 molm -2

s-1 to 18.46 molm-2s-1) and F1 hybrid (Vietlai 20;

from 30.47 molm-2s-1 to 20.18 molm-2s-1) as much as in check cultivar (CH5; from 32.36

molm-2s-1 to 15.65 molm-2s-1), but it was higher than that in the others cultivars After recovering, the CER value in both CH5 (31.32 molm-2s-1) and F1 hybrid (28.74 molm-2s-1) were almost the same

as it before draining However at recovering stage,

the CER of Oryza Rufipogon was lower than that of

other cultivars, and lower than that at before draining stage

Stomatal Conductance (Gs): The stomatal

conductance of all rice cultivars reduced after draining and increased after recovering (Table 2)

The Gs of CH5, Oryza Rufipogon and Vietlai 20

dropped significantly during drought treatment

(especially with CH5, Oryza Rufipogon) and

recovered to the same level as of the well-watered treatment (with CH5 and Vietlai 20) This may be the changes in pressure potential in the xylem and changes in water content of the guard cells and other epidermal cells (Davies et al.,1994; Comstock, 2002) CER was not correlated with and stomatal conductance in all rice plant at before draining stage (r = 0.28), whereas it was significant

at drought at (r = 0.90) and recovering stage (r = 0.59) This might be due to abscisic acid (ABA), which is synthesized in roots under water stress and transported to leaves and induce stomatal closure (Davies et al ,1994)

Table 1 CO 2 exchange rate of rice cultivar at the active tillering stage (mol m -2 s -1 )

Cultivars Before draining 4 days after draining 4 days after recovering

Lily 328 32.75 26.85 30.64

Table 2 Stomatal conductance of rice cultivar at the active tillering stage (mol m -2 s -1 )

Cultivars Before draining 4 days after draining 4 days after recovering

Fig 1 Correlation between CO 2 exchange rate (CER) and stomatal conductance (gs)

in rice cultivars before draining (A), 4 days after draining (B) and 4 days after recovering stages (C)

B

y = 28.83x + 17.21

r = 0.90***

15 17 19 21 23 25 27 29

0.0 0.2 0.4 0.6 0.8 1.0

-2

s-C

y = 8.60x + 23.02

r = 0.59*

23 25 27 29 31 33

0.0 0.2 0.4 0.6 0.8 1.0

Gs(molm -2 s -1 )

A

y = 2.7202x + 29.754

r = 0.26

27 29 31 33 35

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

O.Rufipo go n CH5 Vietlai20 R20 Khausuu 103s Lily

T o itsu

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5

Transpiration rate: Similar to the changes of

photosynthetic rate and stomatal conductance,

transpiration rate of all rice cultivars decreased

after draining water and recovered almost similar to

the same of that after recovering (Table 3) As

drought treatment, transpiration rate reduced

significantly and strongly in CH5, following in

Vietlai 20 and Oryza Rufipogon The reduction was

less in the other cultivars than that in check variety

The reduced in transpiration rate cause to reduce

the effect of water deficit, the early drought

adaptation of plants Thus, both the F1 hybrid and

wild rice could be good for drought tolerance At

recovering time, the transpiration rate increased to

the same of that before with CH5, little bit higher

than before with Vietlai 20, Toisu , Khau Suu and Lily 328 A significant and positive correlation was observed between CO2 exchange rate and transpiration rate during drought condition (r = 0.89) and recovering time (r = 0.78), whereas it was not significant at the time before draining (r = 0.31) (Fig.2) At the drought time, which cultivars had transpiration rate reduced much, that cultivars would had low CER (CH5, F1 hybrid and wild rice) At the recovering time, the transpiration rate

of CH5 and F1 hybrid were similar before and the CER could recover well The lower transpiration rate in F1 hybrid and wild rice which is similar to check cultivars was caused by better stomatal system

Table 3 Transpiration rate of rice cultivar at the active tillering stage (mmol m -2 s -1 )

Cultivars Before draining 4 days after draining 4 days after Recovering

103 S

103 S

A

y = 0.35x + 28.26

r = 0.31

27

29

31

33

35

0 2 4 6 8 10 12 14

B

y = 1.70x + 16.97

r = 0.89**

15

20

25

30

0 2 4 6 8 10 12 14

-2 s

-1 )

C

y = 0.99x + 19.54

r = 0.78**

23

25

27

29

31

33

Fig 2 Correlation between CO 2 exchange rate (CER) and transpiration rate (Tr) in rice cultivars before draining (A), 4 days after draining (B) and

4 days after recovering stages (C)

Note: Symbols were the same as

shown in Fig.1

SPAD value: There were non-significant

differences in SPAD values in all rice cultivars

during three stages of experiment (Table 4) At

before draining and drought stage, the SPAD of

each cultivars were almost the same each other At

recovering stage, the SPAD decreased in Khau Suu,

Oryza Rufipogon, 103S, Vietlai 20 and CH5

Among of them, the decrease was much in Khau

Suu, following in 103S, Vietlai 20, Oryza

Rufipogon and CH5 Rice plants grown under water

deficit, the SPAD reduced with cultivars which

were considered to be drought resistance

The correlation between CER and SPAD was shown in Fig.3 CER was positively correlated with SPAD value at both before draining stage (r = 0.41) and recovering stage (r = 0.57), but the correlation was not significant at drought stage (r = -0.34)

Table 4 SPAD value of rice cultivars at the active tillering stage

Cultivars Before draining 4 days after draining 4 days after recovering

103 S

A

y = 0.44x + 14.38

r = 0.41*

27 29 31 33 35

30 32 34 36 38 40 42

B

y = -0.90x + 57.48

r = -0.34

15 17 19 21 23 25 27 29

-2 s

C

y = 0.39x + 14.34

r = 0.57*

20 22 24 26 28 30 32

30 32 34 36 38 40 42

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Fig 3 Correlation between CO 2 exchange rate (CER) and SPAD in rice cultivars before draining (A),

4 days after draining (B) and 4 days after recovering stages (C)

Note: Symbols were the same as shown in Fig.1

Specific leaf area (SLA): Vietlai 20 has the

highest value of SLA, following are 103S, R20,

Toisu, Lily 328, Khau Suu, CH5 and Oryza

Rufipogon has the lowest value of SLA (Table

5) Water evaporation through leaf is a driving

force of water flow from root to shoot When

water evaporation is low, root pressure plays an

important role to maintain the water flow from

root to shoot The specific leaf area of plants is

one of the genotype that related to genetic Many

observations pointed that cultivars that have thin

leaves (the value of SLA is high) that cultivars

are considered to be drought resistance Because

of thin blade, leaf will be easy to roll up to

reduce CO2 exchange rate, stomatal conductance

and transpiration rate CH5 and Oryza Rifipogon

had smallest value of SLA

Root characters: The cultivar that had the

longest maximum root length is CH5, following are

KhauSuu, Oryza Rufipogon, Toitsu, Vietlai 20, Lily

328, R20 and 103S It means CH5 and Oryza

Rufipogon had deeper roots (Table 5), which

increasing the ability to extract soil water from depth

(Mambani and Lal, 1983a,b,c; Yoshida and

Hasegawa, 1982) Despite the longest root length,

the number of root per plant was much higher in F1

hybrid (292) than that in CH5 (211) and Oryza Rufipogon (232), indicating that the F1 hybrid had

thick root system, which also allows access to water deep in the soil profile is considered crucially important in determining drought resistance in upland rice and substantial genetic variation exists

for this (Ekanayake et al., 1985b; Fukai and Cooper,

1995; O'Toole,1982; Yoshida and Hasegawa, 1982)

A significant and positive correlation was observed between CER and the number of root per plant in all rice cultivars at recovering stage, indicating that the greatest thick root system in F1 hybrid not only contributed to resistance during drought condition but also at recovering stage

Water conductance: Water conductance

from root to stem was shown in Table 5 In detail, the water conductance of Vietlai 20, CH5 and Toitsu was 0.55, 0.49 and 0.46, respectively, and it was higher than that in the other cultivars The result indicates that the cultivars had high value of water conductance, that also had high value of photosynthesis, stomatal conductance and transpiration rate at recovering stage and it contributed to drought resistance

Table 5 Specific leaf area (SLA), root characters and water conductance

in rice cultivars at recovering stage

Cultivars SLA

(cm2 g-1)

Maximum root length (cm)

Number of root plant-1

Root dry weight (g plant-1)

Water conductance (mg plant-1 s-1)

Oryza Rufipogon 197.29 27.70 232.00 4.17 0.29

Fig 4 Correlation between CO 2 exchange rate (CER) and number of root per plant in

rice cultivars at recovering stage

Note: Symbols were the same as shown in Fig.1

4 CONCLUSION

Among rice cultivars, F1 hybrid (Vietlai 20) and

wild rice (Oryza Rufipogon) was the best for

photosynthetic characters which similar to check

cultivar for drought tolerance

During drought condition, low photosynthetic rate

and transpiration rate caused by low stomatal

conductance contributed to drought tolerance in

rice plant

The larger number of root per plant was the reason

for better recovering of rice plant after drought

treatment

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