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Effect of Waterlogging and Gibberellic Acid on Leaf Gas Exchange in Peanut (Arachis hypogaea L.)
JPlantPhysiol. Vol. 139.pp. 503-505(1992)
Effect of Waterlogging and Gibberellic Acid on Leaf Gas Exchange in Peanut (Arachis hypogaea L.) N. R.
BISHNOI
and H. N.
KRISHNAMOORTHY
Department of Botany, Haryana Agricultural University, HISAR-125004, India Received August 2, 1991 . Accepted September 26, 1991
Summary Plants of peanut (Arachis hypogaea L.) were waterlogged for 7 and 14 days and were sprayed with 10 and 100mgL -1 of gibberellic acid (GA3)' Waterlogging decreased the leaf area, chlorophyll content and rate of photosynthesis but slightly decreased the leaf water potential (1/1 leaf). However, the stomatal diffusive resistance (SDR) increased at all the stages. Application of GA3 increased the leaf area and rate of photosynthesis, decreased SDR but did not affect 1/1 leaf and chlorophyll content. GA3 also partially relieved the effects of waterlogging on leaf area, SDR and photosynthesis.
Key words: Water potential, photosynthesis, gibberellic acid, waterlogging, stomatal diffusive resistance, A rachis hypogaea L. Abbreviations: GA3 = Gibberellic acid; WL = Waterlogging; 1/Ileaf Megapascal; SDR = Stomatal diffusive resistance. Introduction Peanut, a sub-tropical grain legume exhibits high net photosynthetic rate and light saturation level (Pallas and Samish, 1974) which are more typical of C 4 plants. Waterlogging inhibits the rate of photosynthesis in many species (Regehr et al., 1975; Wample and Thornton, 1984). This is attributed to a decrease in leaf water potential and increase in stomatal resistance (Kramer, 1969), stomatal closure due to ABA accumulation and cytokinin depletion (Bradford, 1983 a), reduction in photosynthetic enzymes, more particularly RuBP carboxylase (Bradford, 1983 b), decrease in chlorophyll content Gackson, 1979} and inhibition of photosynthetic transport resulting from reduced sink demand (Wample and Thornton, 1984). Waterlogging decreases the gibberellin content of the plant (Reid and Crozier, 1971). Application of GA3 is reported to increase the rate of photosynthesis probably mediated by an increase,in the rate of cyclic and non cyclic photophosphorylation (Yakushina and Pushkina, 1975), enhanced RuBP carboxylase activity and chlorophyll content (Treharne and Stoddart, 1968; Braint, 1974) and reduced SDR of leaves (Livne and Vaadia, 1965). © 1992 by Gustav Fischer Verlag, Stuttgart
=
leaf water potential; MPa
The present study was conducted to investigate the effect of waterlogging and GA3 on stomatal diffusive resistance and photosynthesis of peanut.
Materials and Methods Plants of peanut (Arachis hypogaea L.) Var MH-2 raised under net house conditions were subjected to 7 and 14 days of waterlogging as described elsewhere (Bishnoi and Krishnamoorthy, 1990). Soon after the relieval of stress, these were sprayed with 10 and 100 mg l - 1 of GA3 and water sprayed plants served as control. The plants received the treatments when 16-day old and were sampled 14, 24 and 64 days later corresponding to late vegetative, flowering and pod-filling stages respectively. The rate of photosynthesis of the intact shoot was measured by monitoring changes in CO 2 concentration using Infra-red gas analyser (lRGA), ACD type, 225/2K, England) between 10.00 and l1.ooAM as described earlier (luthra et al., 1983), when the PAR density was 1117.3 ± 487.0 j.lmol m - 2 S - 1. Simultaneously, stomatal diffusive resistance (SDR) of both the surfaces of the fourth fully expanded leaf from the top was measured with diffusive resistance meter (li 60, wescor Inc. USA). This leaf was then detached and its water potential ("'leaf) was measured with pressure chamber
504
N. R.
BISHNOI
and H. N.
KRiSHNAMOORTHY
(Model-3OO5, Soil moisture Equipment Corporation, USA). The total leaf area was determined with a Li-COR area meter (Model LI3000) and the chlorophyll content was estimated by the method of Arnon (1949).
Results and Discussion Waterlogging significantly reduced the leaf area, the effect increasing with the duration of stress. Application of GA3 increased the leaf area and relieved the inhibitory effects of flooding, the effect increasing with the concentration of GA3. The duration of WL and concentration of GA3 had a reciprocal relationship (Table 1). The stomatal diffusive resistance of both adaxial and abaxial surfaces of the leaf increased markedly by waterlogging. The effect tended to fade out with the passage of time (Table 2). GA3 significantly decreased the SDR of both sides of the leaf at all the stages of sampling and partially relieved the effects of waterlogging. In contrast, leaf water potential became more negative by waterlogging at all the stages of sampling. However, the decrease was less with 14 days of waterlogging as compared with 7 days (Table 3). With the passage of time, the effect of stress became faded out. Application of GA3 did not affect the leaf water potential. The total chlorophyll content of the leaf decreased both with waterlogging and the age of the plant, but it was not affected by GA3 (Table 4). The rate of photosynthesis also decreased both with the age of the plant and with flooding (Table 5). However, the effect of water stress gradually decreased with time. On the other hand, application of GA3 significantly increased the rate of photosynthesis at all the stages of sampling and relieved partially the deleterious effects of waterlogging. Table 1: Effect of 7 and 14 days of waterlogging and application of GA3 on leaf area (scm2) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and pod-filling stage. Vegetative Flowering Pod-filling 14 7 7 0 14 0 0 7 14 114 92 76 232 162 120 462 321 210 128 97 81 259 191 146 575 491 291 134 108 87 284 201 169 152 455 289 at 5% 9.3 9.2 12.5
GA3 (mgL -I) 0 10 100 C.D.
Table 2: Effect of 7 and 14 days of waterlogging and application of GA3 on stomatal diffusive resistance (s cm -I) of adaxial and abaxial surface (figures in parenthesis) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and pod-filling stages. Vegetative Flowering Pod·filling GA 3 (mgL -I) 0 7 14 0 7 14 0 7 14 0
2.02 4.89 5.12 5.90 6.85 7.76 7.38 7.54 8.16 (1.57) (2.48) (3.84) (2.48) (2.95) (3.36) (2.46) (3.84) (4.18)
10
1.77 3.49 4.48 6.12 6.26 6.69 7.25 8.02 5.25 (1.18) (1.77) (2.36) (1.18) (2.36) (2.41) (1.61) (2.41) (3.84)
100
1.56 3.12 3.92 4.16 5.97 5.97 5.90 7.12 7.82 (1.12) (2.36) (2.20) (1.13) (2.35) (2.12) (1.69) (2.11) (3.49)
C.D.
at 5%
0.23 (0.34)
0.56 (0.32)
0.42 (0.37)
Table 3: Effect of 7 and 14 days of waterlogging and application of GA3 on leaf water potential (-MPa) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and pod-filling stages. GA3 (mgL-I)
0
Vegetative 7 14
0
Flowering 7 14
0
Pod-filling 7 14
o 0.55 0.70 0.62 0.64 0.73 0.68 0.84 0.87 0.88 10 0.58 0.82 0.70 0.72 0.81 0.76 0.89 0.92 0.91 100 0.54 0.75 0.74 0.68 0.75 0.72 0.83 0.88 0.85 C.D. at 5% 0.3 NS NS Table 4: Effect of 7 and 14 days of waterlogging and application of GA3 on chlorophyll content (gkg- I FW) of peanut (Arachis hypo· gaea L.) determined at vegetative, flowering and pod-filling stages. Vegetative Flowering Pod-filling 0 7 14 0 7 14 0 7 14 9.68 6.87 5.23 7.25 5.61 4.72 6.19 5.21 4.02 9.81 7.01 5.86 7.21 5.63 4.71 6.09 5.08 4.12 9.60 6.89 5.17 7.08 5.31 4.53 5.85 4.72 3.72 at 5% 0.09 0.12 0.16
GA3 (mgL -I) 0 10 100 C.D.
Table 5: Effect of 7 and 14 days of waterlogging and application of GA3 on the rate of photosynthesis (mg C0 2 dm- 2 h- l ) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and podfilling stages. Vegetative
Flowering Pod-filling 14 o 7 14 o 7 14 o 21.2 18.2 17.2 16.5 14.3 14.0 10.0 8.5 8.7 21.4 21.1 20.5 18.6 19.5 16.1 10.8 9.1 9.9 10 21.5 20.0 17.9 17.2 17.0 15.2 10.2 8.7 9.2 100 C.D.at5% 1.1 0.6 0.8
o
7
Waterlogging decreased the rate of photosynthesis in peanut confirming the earlier results in other plants (Regehr et al., 1975; Bradford, 1983 b). Such a reduction may be because of greater resistance to CO 2 diffusion as a consequence of stomatal closure as evidenced by increased stomatal diffusive resistance (Table 2). Stomatal closure in response to flooding is generally attributed to increased root resistance to water flow owing to anaerobiosis (Kramer, 1969). This would reduce replenishment of transpired water leading to decreased leaf water potential and stomatal closure (Elfying et al., 1972). This was in fact so in peanut as increased stomatal resistance in response to flooding was associated with decrease in leaf water potential (Table 3), stomata on the adaxial side being more sensitive than on the abaxial side. Similar differential sensitivity of stomata on the two sides of the leaf to water stress has been reported earlier (Kanemasu and Tanner, 1969). However, stomatal closure due to flooding need not always affect leaf water potential (Sojka and Stolzy, 1980; Bradford and Hsiao, 1982). In addition, decreased photosynthesis under flooded conditions may also be due to reduction in leaf area and chlorophyll content (Tables 1,4), decreased regeneration of the key enzyme of carbon fixation namely RuBP carboxylase (Bradford, 1983 b) and feedback inhibition as a consequence of poor sink availability (Wample and Thornton, 1984).
Waterlogging and GA3 effects on leaf gas exchange
The synthesis and transport of GA from the submerged root system also becomes inhibited under flooded conditions (Reid and Crozier, 1971). Such a deranged GA metabolism may also contribute to decreased photosynthetic rate. This is supported by the fact that application of GA3 partially relieved the effects of flooding on SDR and photosynthesis (Tables 2, 5). However, the possibility of GA3 acting on other partial processes of photosynthesis cannot be ruled out.
References AmON, D. 1.: Copper enzymes in isolated chloroplast. Polyphenol· oxidase in Beta vulgaris. Plant Physio!. 24, 1-15 (1949). BISHNOI, N. R. and H. N. KIuSHNAMOORTHY: Effect of waterlogging and gibberellic acid on nodulation and nitrogen fixation on peanut. Plant Physio!. Biochem. 28, 663-666 (1990). BRADFORD, K. J.: Involvement of plant growth substance in the alteration of leaf gas exchange of flooded tomato plants. Plant Physio!. 73, 480-483 (1983 a). - Effect of soil flooding on leaf gas exchange of tomato plants. Plant Physio!. 73,475-479 (1983 b). BRADFORD, K. J. and T. C. HSIAO: Stomatal behaviour and water reo lations of waterlogged tomato plants. Plant Physio!. 70,
1508-1513 (1982). BIWNT, R. E.: An analysis of the effects of GA on tomato leaf growth. J. Exp. Bot. 25, 764-769 (1974). BUIUlow, W. J. and D. J. CAIUl: Effects of flooding the root system of sunflower plants on the cytokinin content of the xylem sap. Plant Physio!. 22, 1105 -1112 (1969). ELFYtNG, D. C., M. R. KAUFMANN, and A. E. HAll: Interpreting leaf water potential measurements with a model of the soil-
505
plant- atmosphere continuum. Physio!. Plant. 27, 161-168 (1972). JACKSON, M. B.: Rapid injury to peas by soil waterlogging. J. Sci. Food Agric. 30, 143-152 (1979). KANEMASu, E. T. and C. B. TANNEJI.: Stomatal diffusive resistance of snap beans 1. influence of leaf water potential. Plant Physio!. 44, 1547 -1552 (1969). KRAMER, P. J.: Plant and soil water relationships. A Modern Syn· thesis. McGraw-Hill, New York (1969). LIVNE, A. and Y. VAADIA: Stimulation of transpiration rate in barley leaves by kinetin and gibberellic acid. Physio!. Plant. 18, 658-663 (1965). LUTHRA, Y. P., I. S. SHEORAN, and R. SINGH: Ontogenetic interaction between photosynthesis and symbiotic nitrogen fixation in pigeonpea (Cajanus cajan). Ann. App. Bio!. 103, 549-556 (1983). PALLAS, J. E., Jr. and Y. B. SAMISH: Photosynthetic response of peanut. Crop Sci. 14,478-481 (1974). REGEHR, D. L., F. A. BAzzAz, and W. R . BOGGESS: Photosynthesis, transpiration and leaf conductance of Populus deltoides in relation to flooding and drought. Photosynthetica. 9, 52-61 (1975). REm, D. M. and A. CROZIER: Effect of waterlogging on gibberellin content and growth of tomato plants. J. Exp. Bot. 22, 39-48 (1971). SoJKA, R. E. and L. H. STOLZY: Soil oxygen effects on stomatal response. Soil Sci. 130,350-358 (1980). TREHARNE, K. J. and J. L. STODDART: Effects of gibberellin on photosynthesis in red clover (Trifolium pratense L.). Nature 220, 457 -458 (1968). W AMPLE, R. L. and R. K. THORNTON: Differences in the response of sunflower (Helianthus annuus) subjected to flooding and drought stress. Physio!. Plant. 61, 611-616 (1984). Y AKUSHINA, N. 1. and G. P. PUSHKINA: Changes in the rate of photophosphorylation in corn seedlings under the influence of gibberellin and kinetin. Soviet Plant Physio!. 22, 994-998 (1975).
Effect of Waterlogging and Gibberellic Acid on Leaf Gas Exchange in Peanut (Arachis hypogaea L.) N. R.
BISHNOI
and H. N.
KRISHNAMOORTHY
Department of Botany, Haryana Agricultural University, HISAR-125004, India Received August 2, 1991 . Accepted September 26, 1991
Summary Plants of peanut (Arachis hypogaea L.) were waterlogged for 7 and 14 days and were sprayed with 10 and 100mgL -1 of gibberellic acid (GA3)' Waterlogging decreased the leaf area, chlorophyll content and rate of photosynthesis but slightly decreased the leaf water potential (1/1 leaf). However, the stomatal diffusive resistance (SDR) increased at all the stages. Application of GA3 increased the leaf area and rate of photosynthesis, decreased SDR but did not affect 1/1 leaf and chlorophyll content. GA3 also partially relieved the effects of waterlogging on leaf area, SDR and photosynthesis.
Key words: Water potential, photosynthesis, gibberellic acid, waterlogging, stomatal diffusive resistance, A rachis hypogaea L. Abbreviations: GA3 = Gibberellic acid; WL = Waterlogging; 1/Ileaf Megapascal; SDR = Stomatal diffusive resistance. Introduction Peanut, a sub-tropical grain legume exhibits high net photosynthetic rate and light saturation level (Pallas and Samish, 1974) which are more typical of C 4 plants. Waterlogging inhibits the rate of photosynthesis in many species (Regehr et al., 1975; Wample and Thornton, 1984). This is attributed to a decrease in leaf water potential and increase in stomatal resistance (Kramer, 1969), stomatal closure due to ABA accumulation and cytokinin depletion (Bradford, 1983 a), reduction in photosynthetic enzymes, more particularly RuBP carboxylase (Bradford, 1983 b), decrease in chlorophyll content Gackson, 1979} and inhibition of photosynthetic transport resulting from reduced sink demand (Wample and Thornton, 1984). Waterlogging decreases the gibberellin content of the plant (Reid and Crozier, 1971). Application of GA3 is reported to increase the rate of photosynthesis probably mediated by an increase,in the rate of cyclic and non cyclic photophosphorylation (Yakushina and Pushkina, 1975), enhanced RuBP carboxylase activity and chlorophyll content (Treharne and Stoddart, 1968; Braint, 1974) and reduced SDR of leaves (Livne and Vaadia, 1965). © 1992 by Gustav Fischer Verlag, Stuttgart
=
leaf water potential; MPa
The present study was conducted to investigate the effect of waterlogging and GA3 on stomatal diffusive resistance and photosynthesis of peanut.
Materials and Methods Plants of peanut (Arachis hypogaea L.) Var MH-2 raised under net house conditions were subjected to 7 and 14 days of waterlogging as described elsewhere (Bishnoi and Krishnamoorthy, 1990). Soon after the relieval of stress, these were sprayed with 10 and 100 mg l - 1 of GA3 and water sprayed plants served as control. The plants received the treatments when 16-day old and were sampled 14, 24 and 64 days later corresponding to late vegetative, flowering and pod-filling stages respectively. The rate of photosynthesis of the intact shoot was measured by monitoring changes in CO 2 concentration using Infra-red gas analyser (lRGA), ACD type, 225/2K, England) between 10.00 and l1.ooAM as described earlier (luthra et al., 1983), when the PAR density was 1117.3 ± 487.0 j.lmol m - 2 S - 1. Simultaneously, stomatal diffusive resistance (SDR) of both the surfaces of the fourth fully expanded leaf from the top was measured with diffusive resistance meter (li 60, wescor Inc. USA). This leaf was then detached and its water potential ("'leaf) was measured with pressure chamber
504
N. R.
BISHNOI
and H. N.
KRiSHNAMOORTHY
(Model-3OO5, Soil moisture Equipment Corporation, USA). The total leaf area was determined with a Li-COR area meter (Model LI3000) and the chlorophyll content was estimated by the method of Arnon (1949).
Results and Discussion Waterlogging significantly reduced the leaf area, the effect increasing with the duration of stress. Application of GA3 increased the leaf area and relieved the inhibitory effects of flooding, the effect increasing with the concentration of GA3. The duration of WL and concentration of GA3 had a reciprocal relationship (Table 1). The stomatal diffusive resistance of both adaxial and abaxial surfaces of the leaf increased markedly by waterlogging. The effect tended to fade out with the passage of time (Table 2). GA3 significantly decreased the SDR of both sides of the leaf at all the stages of sampling and partially relieved the effects of waterlogging. In contrast, leaf water potential became more negative by waterlogging at all the stages of sampling. However, the decrease was less with 14 days of waterlogging as compared with 7 days (Table 3). With the passage of time, the effect of stress became faded out. Application of GA3 did not affect the leaf water potential. The total chlorophyll content of the leaf decreased both with waterlogging and the age of the plant, but it was not affected by GA3 (Table 4). The rate of photosynthesis also decreased both with the age of the plant and with flooding (Table 5). However, the effect of water stress gradually decreased with time. On the other hand, application of GA3 significantly increased the rate of photosynthesis at all the stages of sampling and relieved partially the deleterious effects of waterlogging. Table 1: Effect of 7 and 14 days of waterlogging and application of GA3 on leaf area (scm2) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and pod-filling stage. Vegetative Flowering Pod-filling 14 7 7 0 14 0 0 7 14 114 92 76 232 162 120 462 321 210 128 97 81 259 191 146 575 491 291 134 108 87 284 201 169 152 455 289 at 5% 9.3 9.2 12.5
GA3 (mgL -I) 0 10 100 C.D.
Table 2: Effect of 7 and 14 days of waterlogging and application of GA3 on stomatal diffusive resistance (s cm -I) of adaxial and abaxial surface (figures in parenthesis) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and pod-filling stages. Vegetative Flowering Pod·filling GA 3 (mgL -I) 0 7 14 0 7 14 0 7 14 0
2.02 4.89 5.12 5.90 6.85 7.76 7.38 7.54 8.16 (1.57) (2.48) (3.84) (2.48) (2.95) (3.36) (2.46) (3.84) (4.18)
10
1.77 3.49 4.48 6.12 6.26 6.69 7.25 8.02 5.25 (1.18) (1.77) (2.36) (1.18) (2.36) (2.41) (1.61) (2.41) (3.84)
100
1.56 3.12 3.92 4.16 5.97 5.97 5.90 7.12 7.82 (1.12) (2.36) (2.20) (1.13) (2.35) (2.12) (1.69) (2.11) (3.49)
C.D.
at 5%
0.23 (0.34)
0.56 (0.32)
0.42 (0.37)
Table 3: Effect of 7 and 14 days of waterlogging and application of GA3 on leaf water potential (-MPa) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and pod-filling stages. GA3 (mgL-I)
0
Vegetative 7 14
0
Flowering 7 14
0
Pod-filling 7 14
o 0.55 0.70 0.62 0.64 0.73 0.68 0.84 0.87 0.88 10 0.58 0.82 0.70 0.72 0.81 0.76 0.89 0.92 0.91 100 0.54 0.75 0.74 0.68 0.75 0.72 0.83 0.88 0.85 C.D. at 5% 0.3 NS NS Table 4: Effect of 7 and 14 days of waterlogging and application of GA3 on chlorophyll content (gkg- I FW) of peanut (Arachis hypo· gaea L.) determined at vegetative, flowering and pod-filling stages. Vegetative Flowering Pod-filling 0 7 14 0 7 14 0 7 14 9.68 6.87 5.23 7.25 5.61 4.72 6.19 5.21 4.02 9.81 7.01 5.86 7.21 5.63 4.71 6.09 5.08 4.12 9.60 6.89 5.17 7.08 5.31 4.53 5.85 4.72 3.72 at 5% 0.09 0.12 0.16
GA3 (mgL -I) 0 10 100 C.D.
Table 5: Effect of 7 and 14 days of waterlogging and application of GA3 on the rate of photosynthesis (mg C0 2 dm- 2 h- l ) of peanut (Arachis hypogaea L.) determined at vegetative, flowering and podfilling stages. Vegetative
Flowering Pod-filling 14 o 7 14 o 7 14 o 21.2 18.2 17.2 16.5 14.3 14.0 10.0 8.5 8.7 21.4 21.1 20.5 18.6 19.5 16.1 10.8 9.1 9.9 10 21.5 20.0 17.9 17.2 17.0 15.2 10.2 8.7 9.2 100 C.D.at5% 1.1 0.6 0.8
o
7
Waterlogging decreased the rate of photosynthesis in peanut confirming the earlier results in other plants (Regehr et al., 1975; Bradford, 1983 b). Such a reduction may be because of greater resistance to CO 2 diffusion as a consequence of stomatal closure as evidenced by increased stomatal diffusive resistance (Table 2). Stomatal closure in response to flooding is generally attributed to increased root resistance to water flow owing to anaerobiosis (Kramer, 1969). This would reduce replenishment of transpired water leading to decreased leaf water potential and stomatal closure (Elfying et al., 1972). This was in fact so in peanut as increased stomatal resistance in response to flooding was associated with decrease in leaf water potential (Table 3), stomata on the adaxial side being more sensitive than on the abaxial side. Similar differential sensitivity of stomata on the two sides of the leaf to water stress has been reported earlier (Kanemasu and Tanner, 1969). However, stomatal closure due to flooding need not always affect leaf water potential (Sojka and Stolzy, 1980; Bradford and Hsiao, 1982). In addition, decreased photosynthesis under flooded conditions may also be due to reduction in leaf area and chlorophyll content (Tables 1,4), decreased regeneration of the key enzyme of carbon fixation namely RuBP carboxylase (Bradford, 1983 b) and feedback inhibition as a consequence of poor sink availability (Wample and Thornton, 1984).
Waterlogging and GA3 effects on leaf gas exchange
The synthesis and transport of GA from the submerged root system also becomes inhibited under flooded conditions (Reid and Crozier, 1971). Such a deranged GA metabolism may also contribute to decreased photosynthetic rate. This is supported by the fact that application of GA3 partially relieved the effects of flooding on SDR and photosynthesis (Tables 2, 5). However, the possibility of GA3 acting on other partial processes of photosynthesis cannot be ruled out.
References AmON, D. 1.: Copper enzymes in isolated chloroplast. Polyphenol· oxidase in Beta vulgaris. Plant Physio!. 24, 1-15 (1949). BISHNOI, N. R. and H. N. KIuSHNAMOORTHY: Effect of waterlogging and gibberellic acid on nodulation and nitrogen fixation on peanut. Plant Physio!. Biochem. 28, 663-666 (1990). BRADFORD, K. J.: Involvement of plant growth substance in the alteration of leaf gas exchange of flooded tomato plants. Plant Physio!. 73, 480-483 (1983 a). - Effect of soil flooding on leaf gas exchange of tomato plants. Plant Physio!. 73,475-479 (1983 b). BRADFORD, K. J. and T. C. HSIAO: Stomatal behaviour and water reo lations of waterlogged tomato plants. Plant Physio!. 70,
1508-1513 (1982). BIWNT, R. E.: An analysis of the effects of GA on tomato leaf growth. J. Exp. Bot. 25, 764-769 (1974). BUIUlow, W. J. and D. J. CAIUl: Effects of flooding the root system of sunflower plants on the cytokinin content of the xylem sap. Plant Physio!. 22, 1105 -1112 (1969). ELFYtNG, D. C., M. R. KAUFMANN, and A. E. HAll: Interpreting leaf water potential measurements with a model of the soil-
505
plant- atmosphere continuum. Physio!. Plant. 27, 161-168 (1972). JACKSON, M. B.: Rapid injury to peas by soil waterlogging. J. Sci. Food Agric. 30, 143-152 (1979). KANEMASu, E. T. and C. B. TANNEJI.: Stomatal diffusive resistance of snap beans 1. influence of leaf water potential. Plant Physio!. 44, 1547 -1552 (1969). KRAMER, P. J.: Plant and soil water relationships. A Modern Syn· thesis. McGraw-Hill, New York (1969). LIVNE, A. and Y. VAADIA: Stimulation of transpiration rate in barley leaves by kinetin and gibberellic acid. Physio!. Plant. 18, 658-663 (1965). LUTHRA, Y. P., I. S. SHEORAN, and R. SINGH: Ontogenetic interaction between photosynthesis and symbiotic nitrogen fixation in pigeonpea (Cajanus cajan). Ann. App. Bio!. 103, 549-556 (1983). PALLAS, J. E., Jr. and Y. B. SAMISH: Photosynthetic response of peanut. Crop Sci. 14,478-481 (1974). REGEHR, D. L., F. A. BAzzAz, and W. R . BOGGESS: Photosynthesis, transpiration and leaf conductance of Populus deltoides in relation to flooding and drought. Photosynthetica. 9, 52-61 (1975). REm, D. M. and A. CROZIER: Effect of waterlogging on gibberellin content and growth of tomato plants. J. Exp. Bot. 22, 39-48 (1971). SoJKA, R. E. and L. H. STOLZY: Soil oxygen effects on stomatal response. Soil Sci. 130,350-358 (1980). TREHARNE, K. J. and J. L. STODDART: Effects of gibberellin on photosynthesis in red clover (Trifolium pratense L.). Nature 220, 457 -458 (1968). W AMPLE, R. L. and R. K. THORNTON: Differences in the response of sunflower (Helianthus annuus) subjected to flooding and drought stress. Physio!. Plant. 61, 611-616 (1984). Y AKUSHINA, N. 1. and G. P. PUSHKINA: Changes in the rate of photophosphorylation in corn seedlings under the influence of gibberellin and kinetin. Soviet Plant Physio!. 22, 994-998 (1975).