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The influence of exogenous ethylene on growth and photosynthesis of mustard (Brassica juncea) following defoliation
Scientia Horticulturae 105 (2005) 499–505 www.elsevier.com/locate/scihorti
The influence of exogenous ethylene on growth and photosynthesis of mustard (Brassica juncea) following defoliation N.A. Khan * Department of Botany, Aligarh Muslim University, Aligarh 202 002, India Received 22 May 2004; received in revised form 1 February 2005; accepted 2 February 2005
Abstract Mustard (Brassica juncea L.) plant is characterized by a large number of broad leaves in the lower layers. These leaves remain below light compensation photosynthetic point and abscise at maturity. An experiment was conducted to find out the effect of early removal of such leaves on the growth of the plant, on assimilate balance and any association of growth with changes in ethylene level. Intact plants and plants with 50% of total leaves from lower-half axis of the plant removed after 40 d after sowing were compared. Removal of 50% lower leaves increased the emergence of new leaves, leaf area, plant dry mass, carbonic anhydrase (CA) activity and photosynthetic rate (PN). Ethephon at 200 ml l 1 increased the overall growth of the plants in no-defoliation treatment, which was equivalent to the defoliation plants treated with water spray. Ethephon spray on defoliated plants proved inhibitory. The ethylene level in 200 ml l 1 ethephon treatment on no-defoliated plants was equal to water spray on defoliated plants. The results suggest that there exists a correlation between defoliation, ethylene and growth of plants. # 2005 Elsevier B.V. All rights reserved. Keywords: Carbonic anhydrase; Ethylene; Leaf area; Mustard
* Tel.: +91 571 2702016; fax: +91 571 702 016. E-mail address: [email protected] 0304-4238/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2005.02.004
500
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
1. Introduction Mustard (Brassica juncea L.) is a dominant oilseed crop planted in tropical countries for human consumption as a condiment and spices, as fodder and for seed. The plant bears a large number of broad, oblong-shaped leaves in lower layers (Weiss, 1983). Such leaves contribute to the development of supra-optimal leaf area indices accompanied by self-shading and shading by other leaves within the plant axis (Anten et al., 1995). They are poorly illuminated, and therefore are less efficient in photosynthate production. Later, at maturity, these leaves are shed. It has been reported that defoliation brings about changes in growth, photosynthesis and carbon reserve remobilization (Ericsson et al., 1980; Mc Naughton, 1983; Foggo, 1996; Bruening and Egli, 1999; Collin et al., 2000; Khan et al., 2002). Earlier research has shown that removal of these senescing leaves modulates assimilate balance and growth in mustard (Khan, 2002; Khan and Ahsan, 2000; Khan et al., 2002). It is postulated that morphological and physiological adaptive signals are provided by alteration in plant hormones. Ethylene is such a plant hormone which is thought of coordinating events such as leaf emergence, expansion and biomass accumulation (Kieber et al., 1993; Rodrigues-Pousada et al., 1993; Lee and Reid, 1997; Hussain et al., 1999; Khan et al., 2000, 2002), senescence and abscission during normal development and other conditions (Abeles et al., 1992). To test the hypothesis that ethylene has a role in the growth and photosynthesis, the effect of ethephon, an ethylene releasing compound, application on intact and defoliated plants was observed after defoliation.
2. Material and methods 2.1. Plant material and cultural procedure Plants of mustard (Brassica juncea L. Czern & Coss.) cv. Varuna were raised from seeds in 23 cm plastic pots filled with acid-washed sand purified according to Hewitt (1966). The experiment was carried out under natural day/night conditions (PAR > 900 mmol m 2 s 1, temperature 22 3 8C, RH 62–70%) at the Botany Department, Aligarh Muslim University, Aligarh, India. The plants were grown with full-strength Hoagland’s nutrient solution (Hewitt, 1966). They were fed with 250 ml of nutrient solutions every alternate day and 200 ml of de-ionized water daily. One plant per pot and six pots per treatment were maintained. The details of nutrient solutions and other cultivation procedures were those which were described earlier (Khan et al., 2002). 2.2. Defoliation treatment The defoliation was done at 40 d after sowing. At defoliation, leaf number was counted which happened to be 14. A total of 50% of the leaves on the lower axis were removed as reported earlier (Khan et al., 2002). In control plants, all leaves were left intact. The control and defoliated group of plants were sprayed with 0, 100 or 200 ml l 1 ethephon (an ethylene-releasing compound) to run off. Ethephon on hydrolysis results in ethylene and
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
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phosphoric acid. Therefore, to account for the effects of ethylene alone, sufficient amount of phosphate was applied with the other ethephon concentrations and control so that equivalent amount of phosphate is present in all the treatments. Teepol (0.5%) was used as the wetting agent. Experiment was conducted in a completely randomized block design. Each treatment was replicated five times. At the time of defoliation (40 d after sowing) and 20 d after defoliation (60 d after sowing), three pots per treatment were used to record data on growth (leaf number, leaf area and plant dry mass), activity of carbonic anhydrase (CA), photosynthetic rate (PN) and ethylene evolution. 2.3. Determination of growth characteristics Leaf number was counted including the emergence of new leaves on upper axis following defoliation. Leaf area was measured with a leaf area meter (LA 211, Systronics, New Delhi, India). Aboveground-plant dry mass was determined after drying at 80 8C to a constant weight. 2.4. Assay of CA activity For measurement of CA activity, leaves from apex to base on the plant axis were collected, and homogenized as a composite sample in 5 mM Tris–HCl (pH 8.5), containing 1 mM MgCl2, 1 mM EDTA, and 1% polyvinylpyrrolidone. Homogenate was passed through Whatman 42 filter paper and centrifuged first at 1000 g for 10 min and then at 5000 g for 30 min. The CA activity was determined by an electrometric method (Rickli et al., 1964) in the supernatant. 2.5. Photosynthetic measurement PN was monitored on leaves at equal number of nodes in control and defoliation treatment. In the control and the treatment, the leaf present at node eight was selected for measuring photosynthesis using the infrared gas analyzer (Li-COR 6200 Nebraska, NE). The measurements were made before defoliation and at 20 d after defoliation during full sunlight between 1100 and 1200 h. 2.6. Determination of ethylene Ethylene evolution in control and defoliated plants was measured by trimming leaf material to small pieces and placed in 30 ml tubes containing moist paper to minimize evaporation from the tissue and were stoppered with secure rubber caps and kept in light for 2 h under the same conditions which were used for plant growth. A 1 ml gas sample was withdrawn with a hypodermic syringe and assayed on a gas chromatograph (Nucon 5700, New Delhi, India) equipped with 1.8 m Porapack N (80–100 mesh) column, a flame ionization detector and integrator. Nitrogen was used as a carrier gas. The flow rates of nitrogen, hydrogen and oxygen were 0.5, 0.5 and 5.0 ml s 1, respectively. The detector was at 150 8C. Ethylene identification was based on the retention time and quantified comparing with the peaks from standard ethylene concentrations.
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N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
2.7. Statistics Analysis of variance was performed on the data collected and the F-value was determined. Least significant difference (LSD) at P < 0.05 was calculated for the significant data to identify difference in the mean of the treatments.
3. Results Growth characteristics, when compared between water spray on defoliation and nodefoliation treatment, were found to increase significantly with defoliation (Table 1). Similar observation was noted for CA and PN. Ethephon spray increased the growth and PN in no-defoliation plant and the maximal effect was noted with 200 ml l 1 ethephon. In defoliation plant maximal effect was noted with water spray, and the concentration of 100 and 200 ml l 1 ethephon proved inhibitory. The effect of 200 ml l 1 ethephon on nodefoliation plant was equivalent to water spray on defoliation plant. This effect was seen for growth, CA and PN. Ethylene evolution was the greatest with 200 ml l 1 ethephon and defoliation treatment, which was equal to 100 ml l 1 ethephon and defoliation treatment. Ethylene level in no-defoliation plant treated with 200 ml l 1 ethephon was equal to that in defoliation plant treated with water spray (Table 2).
4. Discussion Defoliation of 50% of the shaded leaves in lower layers resulted in the maximum emergence of new leaves and maximal leaf area. The removal of unproductive leaves helped in diverting plant resources in the formation of new leaves. These leaves contributed to the increased activity of CA of composite leaf sample. The increased CA accelerated the Table 1 Leaf number, leaf area and plant dry mass of mustard (Brassica juncea cv. Varuna) at 60 d after sowing following 50% defoliation of lower leaves and ethephon treatment at 40 d after sowing Treatments
Leaf number
Leaf area (cm2 per plant)
Plant dry mass (g per plant)
No defoliation Ethephon spray (ml l 1) 0 100 200
17d 22c 29a
160c 184b 242a
6.2d 8.6bc 12.4a
30a 25b 21c 14
240a 194b 172c 132
12.6a 9.4b 7.6c 3.6
50% defoliation Ethephon spray (ml l 1) 0 100 200 No defoliation Control (at 40 d)
Data followed by the same letters within a column are significantly not different.
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
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Table 2 Carbonic anhydrase (CA) activity, photosynthetic rate (PN) and ethylene evolution of mustard (Brassica juncea cv. Varuna) at 60 d after sowing following 50% defoliation of lower leaves and ethephon treatment at 40 d after sowing Treatments No defoliation Ethephon spray (ml l 1) 0 100 200 50% defoliation Ethephon spray (ml l 1) 0 100 200 No defoliation Control (at 40 d)
CA (nmol g
1
f.m. h 1)
PN (mmol CO2 m
2
s 1)
Ethylene (mmol g
3.4d 5.2bc 7.6a
16.4d 19.4bc 23.6a
142.6d 172.4c 199.6b
7.8a 6.0b 4.8c 2.1
23.2a 20.4b 18.2c 13.4
200.4b 218.8a 236.6a 94.2
1
f.m. h 1)
Data followed by the same letters within a column are significantly not different.
reactions of HCO3 dehydration, increased the CO2 concentration in the place of carboxylation and thus contributed to the effective work of ribulose bisphosphate carboxylase (RuBPC) in the cell (Sultemeyer et al., 1993; Khan et al., 2004). A positive relationship of CA with PN has been shown (Khan, 1994; XinBin et al., 2001). It has been shown earlier that activities of CA and RuBPC increased after removal of shaded leaves (Khan, 2002), and with the removal of lower leaves the light intensity was utilized maximally, resulting in higher PN (Khan et al., 2002). This resulted in an increase in plant dry mass (Table 1). Compensatory growth following defoliation has long been known in plants (Mc Naughton, 1983; Hamilton et al., 1998; Collin et al., 2000; Khan, 2003). Chhabra and Krishnamoorthy (1995) and Singh and Singh (1996) have also reported that surplus leaves in mustard do not contribute to biomass accumulation but prevent translocation of assimilates to the reproductive sink. The commonly observed effects are increased leaf number and biomass accumulation, but an attempt has not been made to find an involvement of ethylene in the control of growth and photosynthesis. The growth and photosynthesis changes were found to be correlative with the changes in ethylene level. Ethephon at 200 ml l 1 increased the ethylene in no-defoliation plants that increased the characteristics maximally. However, in defoliated plants, such ethylene concentration was achieved in water spray. Ethephon applied on defoliation plant resulted in supra-optimal ethylene concentration that reduced the characteristics. Conclusively, it may be said that early loss of shaded leaves in lower layer is advantageous, before their cost of maintenance in terms of water and nutrients exceeds their contribution of fixed carbon. Further, growth and photosynthesis are linked to changes in ethylene. Any strategy that could modulate ethylene may help in early removal of shaded leaves and increase growth, photosynthesis and plant dry mass accumulation.
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N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
Acknowledgements Financial support for the work by the Department of Science & Technology, Government of India, New Delhi is gratefully acknowledged. References Abeles, F.B., Morgan, P.W., Saltveit, M.E., 1992. Ethylene in Plant Biology. Academic Press, London, p. 215. Anten, N.P.R., Schieving, F., Medina, E., Werger, M.J.A., Schuffelen, P., 1995. Optimal leaf area indices in C3 and C4 mono- and dicotyledonous species at low and high nitrogen availability. Physiol. Plant 95, 541–550. Bruening, W.P., Egli, D.B., 1999. Relationship between photosynthesis and seed number of phloem isolated nodes in soybean. Crop Sci. 39, 1769–1775. Chhabra, M.L., Krishnamoorthy, H.N., 1995. Investigation on the effect of partial defoliation on 14C-transport in Indian mustard. Cruciferae Newsletter 17, 62–63. Collin, P.D., Epron, D., Alaoui-Sosse, B., Badot, P.M., 2000. Growth responses of common ash seedlings ( Fraxinus excelsior L.) to total and partial defoliation. Ann. Bot. 85, 317–323. Ericsson, A.S., Larson, S., Tenow, W., 1980. Effects of early and late season defoliation on growth and carbohydrate dynamics in scot pine. Appl. Ecol. 17, 747–769. Foggo, A., 1996. Long- and short-term changes in plant growth following simulated herbivory: adaptive responses to damage? Ecol. Entomol. 21, 198–202. Hamilton, E.W., Giovannini, M.S., Moses, S.A., Coleman, J.S., Mc Naughton, S.J., 1998. Biomass and mineral element responses of a Serengeti shoot species to nitrogen supply and defoliation: compensation requires a critical N. Oecologia 116, 407–418. Hewitt, E.J., 1966. Sand and Water Culture Methods used in the Study of Plant Nutrition. Commonwealth Agricultural Bureaux, England, p. 56. Hussain, A., Black, C.R., Taylor, I.B., Roberts, J.A., 1999. Soil composition: a role of ethylene in regulating leaf expansion and shoot growth in tomato. Plant Physiol. 121, 1227–1237. Khan, N.A., 1994. Variation in carbonic anhydrase activity and its relationship with photosynthesis and dry mass of mustard. Photosynthetica 30, 317–320. Khan, N.A., 2002. Activities of carbonic anhydrase and ribulose-1,5-biphosphate carboxylase, and dry mass accumulation in Brassica juncea following defoliation. Photosynthetica 40, 633–634. Khan, N.A., 2003. Changes in photosynthetic biomass accumulation, auxin and ethylene level following defoliation in Brassica juncea. J. Food Agric. Environ. 1, 125–128. Khan, N.A., Ahsan, N., 2000. Evaluation of yield potential of defoliated mustard cultivars. Tests Agrochem. Cultivars 21, 33–34. Khan, N.A., Javid, S., Samiullah, 2004. Physiological role of carbonic anhydrase in CO2 fixation and carbon partitioning. Physiol. Mol. Biol. Plants 10, 153–166. Khan, N.A., Khan, M., Ansari, H.R., Samiullah, 2002. Auxin and defoliation effects on photosynthesis and ethylene evolution in mustard. Scientia Hort. 96, 43–51. Khan, N.A., Lone, N.A., Samiullah, 2000. Response of mustard (Brassica juncea L.) to applied nitrogen with or without ethrel sprays under non-irrigated conditions. J. Agron. Crop Sci. 184, 63–66. Kieber, J.J., Rothenberg, M., Roman, G., Fieldmann, K.A., Ecker, J.R., 1993. CTRI: a negative regulator of the ethylene response pathway in Arabidopsis: encodes a number of the Raf family of protein kinases. Cell 72, 427–441. Lee, S.H., Reid, D.M., 1997. The role of endogenous ethylene in the expansion of Helianthus annus leaves. Can. J. Bot. 75, 501–508. Mc Naughton, S.J., 1983. Compensatory plant growth as a response to herbivory. Oikos 40, 329–336. Rickli, E.E., Ghazanfar, S.A.S., Gibbons, B.H., Edsall, J.T., 1964. Carbonic anhydrase from human erythrocytes: preparation and properties of two enzymes. J. Biol. Chem. 239, 1065–1078. Rodrigues-Pousada, R.A., De Rycke, R., Dedonder, A., Van CArnegham, W., Engler, G., Van Montagu, M., Van der Straeten, D., 1993. The Arabidopsis 1-aminocyclopropane-1-carboxylate synthase gene 1 expressed during early development. Plant Cell 5, 897–911.
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Singh, S.P., Singh, G.S., 1996. Effect of defoliation on growth, yield and yield attributing characters in mustard (Brassica juncea L Czern & Coss.). Indian J. Plant Physiol. 1, 123–124. Sultemeyer, D., Schmidt, C., Fock, H.P., 1993. Carbonic anhydrase in higher plants and aquatic microorganisms. Physiol. Plant. 88, 179–190. Weiss, E.A., 1983. Oilseed Crops. Longman Inc, New York, p. 161. XinBin, D., RongXian, Z., Wei, L., Xiaming, X., Schuqing, C., 2001. Effects of carbonic anhydrase in wheat leaf on photosynthetic function under low CO2 concentration. Sci. Agric. Sinica 34, 97–100.
The influence of exogenous ethylene on growth and photosynthesis of mustard (Brassica juncea) following defoliation N.A. Khan * Department of Botany, Aligarh Muslim University, Aligarh 202 002, India Received 22 May 2004; received in revised form 1 February 2005; accepted 2 February 2005
Abstract Mustard (Brassica juncea L.) plant is characterized by a large number of broad leaves in the lower layers. These leaves remain below light compensation photosynthetic point and abscise at maturity. An experiment was conducted to find out the effect of early removal of such leaves on the growth of the plant, on assimilate balance and any association of growth with changes in ethylene level. Intact plants and plants with 50% of total leaves from lower-half axis of the plant removed after 40 d after sowing were compared. Removal of 50% lower leaves increased the emergence of new leaves, leaf area, plant dry mass, carbonic anhydrase (CA) activity and photosynthetic rate (PN). Ethephon at 200 ml l 1 increased the overall growth of the plants in no-defoliation treatment, which was equivalent to the defoliation plants treated with water spray. Ethephon spray on defoliated plants proved inhibitory. The ethylene level in 200 ml l 1 ethephon treatment on no-defoliated plants was equal to water spray on defoliated plants. The results suggest that there exists a correlation between defoliation, ethylene and growth of plants. # 2005 Elsevier B.V. All rights reserved. Keywords: Carbonic anhydrase; Ethylene; Leaf area; Mustard
* Tel.: +91 571 2702016; fax: +91 571 702 016. E-mail address: [email protected] 0304-4238/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2005.02.004
500
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
1. Introduction Mustard (Brassica juncea L.) is a dominant oilseed crop planted in tropical countries for human consumption as a condiment and spices, as fodder and for seed. The plant bears a large number of broad, oblong-shaped leaves in lower layers (Weiss, 1983). Such leaves contribute to the development of supra-optimal leaf area indices accompanied by self-shading and shading by other leaves within the plant axis (Anten et al., 1995). They are poorly illuminated, and therefore are less efficient in photosynthate production. Later, at maturity, these leaves are shed. It has been reported that defoliation brings about changes in growth, photosynthesis and carbon reserve remobilization (Ericsson et al., 1980; Mc Naughton, 1983; Foggo, 1996; Bruening and Egli, 1999; Collin et al., 2000; Khan et al., 2002). Earlier research has shown that removal of these senescing leaves modulates assimilate balance and growth in mustard (Khan, 2002; Khan and Ahsan, 2000; Khan et al., 2002). It is postulated that morphological and physiological adaptive signals are provided by alteration in plant hormones. Ethylene is such a plant hormone which is thought of coordinating events such as leaf emergence, expansion and biomass accumulation (Kieber et al., 1993; Rodrigues-Pousada et al., 1993; Lee and Reid, 1997; Hussain et al., 1999; Khan et al., 2000, 2002), senescence and abscission during normal development and other conditions (Abeles et al., 1992). To test the hypothesis that ethylene has a role in the growth and photosynthesis, the effect of ethephon, an ethylene releasing compound, application on intact and defoliated plants was observed after defoliation.
2. Material and methods 2.1. Plant material and cultural procedure Plants of mustard (Brassica juncea L. Czern & Coss.) cv. Varuna were raised from seeds in 23 cm plastic pots filled with acid-washed sand purified according to Hewitt (1966). The experiment was carried out under natural day/night conditions (PAR > 900 mmol m 2 s 1, temperature 22 3 8C, RH 62–70%) at the Botany Department, Aligarh Muslim University, Aligarh, India. The plants were grown with full-strength Hoagland’s nutrient solution (Hewitt, 1966). They were fed with 250 ml of nutrient solutions every alternate day and 200 ml of de-ionized water daily. One plant per pot and six pots per treatment were maintained. The details of nutrient solutions and other cultivation procedures were those which were described earlier (Khan et al., 2002). 2.2. Defoliation treatment The defoliation was done at 40 d after sowing. At defoliation, leaf number was counted which happened to be 14. A total of 50% of the leaves on the lower axis were removed as reported earlier (Khan et al., 2002). In control plants, all leaves were left intact. The control and defoliated group of plants were sprayed with 0, 100 or 200 ml l 1 ethephon (an ethylene-releasing compound) to run off. Ethephon on hydrolysis results in ethylene and
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
501
phosphoric acid. Therefore, to account for the effects of ethylene alone, sufficient amount of phosphate was applied with the other ethephon concentrations and control so that equivalent amount of phosphate is present in all the treatments. Teepol (0.5%) was used as the wetting agent. Experiment was conducted in a completely randomized block design. Each treatment was replicated five times. At the time of defoliation (40 d after sowing) and 20 d after defoliation (60 d after sowing), three pots per treatment were used to record data on growth (leaf number, leaf area and plant dry mass), activity of carbonic anhydrase (CA), photosynthetic rate (PN) and ethylene evolution. 2.3. Determination of growth characteristics Leaf number was counted including the emergence of new leaves on upper axis following defoliation. Leaf area was measured with a leaf area meter (LA 211, Systronics, New Delhi, India). Aboveground-plant dry mass was determined after drying at 80 8C to a constant weight. 2.4. Assay of CA activity For measurement of CA activity, leaves from apex to base on the plant axis were collected, and homogenized as a composite sample in 5 mM Tris–HCl (pH 8.5), containing 1 mM MgCl2, 1 mM EDTA, and 1% polyvinylpyrrolidone. Homogenate was passed through Whatman 42 filter paper and centrifuged first at 1000 g for 10 min and then at 5000 g for 30 min. The CA activity was determined by an electrometric method (Rickli et al., 1964) in the supernatant. 2.5. Photosynthetic measurement PN was monitored on leaves at equal number of nodes in control and defoliation treatment. In the control and the treatment, the leaf present at node eight was selected for measuring photosynthesis using the infrared gas analyzer (Li-COR 6200 Nebraska, NE). The measurements were made before defoliation and at 20 d after defoliation during full sunlight between 1100 and 1200 h. 2.6. Determination of ethylene Ethylene evolution in control and defoliated plants was measured by trimming leaf material to small pieces and placed in 30 ml tubes containing moist paper to minimize evaporation from the tissue and were stoppered with secure rubber caps and kept in light for 2 h under the same conditions which were used for plant growth. A 1 ml gas sample was withdrawn with a hypodermic syringe and assayed on a gas chromatograph (Nucon 5700, New Delhi, India) equipped with 1.8 m Porapack N (80–100 mesh) column, a flame ionization detector and integrator. Nitrogen was used as a carrier gas. The flow rates of nitrogen, hydrogen and oxygen were 0.5, 0.5 and 5.0 ml s 1, respectively. The detector was at 150 8C. Ethylene identification was based on the retention time and quantified comparing with the peaks from standard ethylene concentrations.
502
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
2.7. Statistics Analysis of variance was performed on the data collected and the F-value was determined. Least significant difference (LSD) at P < 0.05 was calculated for the significant data to identify difference in the mean of the treatments.
3. Results Growth characteristics, when compared between water spray on defoliation and nodefoliation treatment, were found to increase significantly with defoliation (Table 1). Similar observation was noted for CA and PN. Ethephon spray increased the growth and PN in no-defoliation plant and the maximal effect was noted with 200 ml l 1 ethephon. In defoliation plant maximal effect was noted with water spray, and the concentration of 100 and 200 ml l 1 ethephon proved inhibitory. The effect of 200 ml l 1 ethephon on nodefoliation plant was equivalent to water spray on defoliation plant. This effect was seen for growth, CA and PN. Ethylene evolution was the greatest with 200 ml l 1 ethephon and defoliation treatment, which was equal to 100 ml l 1 ethephon and defoliation treatment. Ethylene level in no-defoliation plant treated with 200 ml l 1 ethephon was equal to that in defoliation plant treated with water spray (Table 2).
4. Discussion Defoliation of 50% of the shaded leaves in lower layers resulted in the maximum emergence of new leaves and maximal leaf area. The removal of unproductive leaves helped in diverting plant resources in the formation of new leaves. These leaves contributed to the increased activity of CA of composite leaf sample. The increased CA accelerated the Table 1 Leaf number, leaf area and plant dry mass of mustard (Brassica juncea cv. Varuna) at 60 d after sowing following 50% defoliation of lower leaves and ethephon treatment at 40 d after sowing Treatments
Leaf number
Leaf area (cm2 per plant)
Plant dry mass (g per plant)
No defoliation Ethephon spray (ml l 1) 0 100 200
17d 22c 29a
160c 184b 242a
6.2d 8.6bc 12.4a
30a 25b 21c 14
240a 194b 172c 132
12.6a 9.4b 7.6c 3.6
50% defoliation Ethephon spray (ml l 1) 0 100 200 No defoliation Control (at 40 d)
Data followed by the same letters within a column are significantly not different.
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
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Table 2 Carbonic anhydrase (CA) activity, photosynthetic rate (PN) and ethylene evolution of mustard (Brassica juncea cv. Varuna) at 60 d after sowing following 50% defoliation of lower leaves and ethephon treatment at 40 d after sowing Treatments No defoliation Ethephon spray (ml l 1) 0 100 200 50% defoliation Ethephon spray (ml l 1) 0 100 200 No defoliation Control (at 40 d)
CA (nmol g
1
f.m. h 1)
PN (mmol CO2 m
2
s 1)
Ethylene (mmol g
3.4d 5.2bc 7.6a
16.4d 19.4bc 23.6a
142.6d 172.4c 199.6b
7.8a 6.0b 4.8c 2.1
23.2a 20.4b 18.2c 13.4
200.4b 218.8a 236.6a 94.2
1
f.m. h 1)
Data followed by the same letters within a column are significantly not different.
reactions of HCO3 dehydration, increased the CO2 concentration in the place of carboxylation and thus contributed to the effective work of ribulose bisphosphate carboxylase (RuBPC) in the cell (Sultemeyer et al., 1993; Khan et al., 2004). A positive relationship of CA with PN has been shown (Khan, 1994; XinBin et al., 2001). It has been shown earlier that activities of CA and RuBPC increased after removal of shaded leaves (Khan, 2002), and with the removal of lower leaves the light intensity was utilized maximally, resulting in higher PN (Khan et al., 2002). This resulted in an increase in plant dry mass (Table 1). Compensatory growth following defoliation has long been known in plants (Mc Naughton, 1983; Hamilton et al., 1998; Collin et al., 2000; Khan, 2003). Chhabra and Krishnamoorthy (1995) and Singh and Singh (1996) have also reported that surplus leaves in mustard do not contribute to biomass accumulation but prevent translocation of assimilates to the reproductive sink. The commonly observed effects are increased leaf number and biomass accumulation, but an attempt has not been made to find an involvement of ethylene in the control of growth and photosynthesis. The growth and photosynthesis changes were found to be correlative with the changes in ethylene level. Ethephon at 200 ml l 1 increased the ethylene in no-defoliation plants that increased the characteristics maximally. However, in defoliated plants, such ethylene concentration was achieved in water spray. Ethephon applied on defoliation plant resulted in supra-optimal ethylene concentration that reduced the characteristics. Conclusively, it may be said that early loss of shaded leaves in lower layer is advantageous, before their cost of maintenance in terms of water and nutrients exceeds their contribution of fixed carbon. Further, growth and photosynthesis are linked to changes in ethylene. Any strategy that could modulate ethylene may help in early removal of shaded leaves and increase growth, photosynthesis and plant dry mass accumulation.
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Acknowledgements Financial support for the work by the Department of Science & Technology, Government of India, New Delhi is gratefully acknowledged. References Abeles, F.B., Morgan, P.W., Saltveit, M.E., 1992. Ethylene in Plant Biology. Academic Press, London, p. 215. Anten, N.P.R., Schieving, F., Medina, E., Werger, M.J.A., Schuffelen, P., 1995. Optimal leaf area indices in C3 and C4 mono- and dicotyledonous species at low and high nitrogen availability. Physiol. Plant 95, 541–550. Bruening, W.P., Egli, D.B., 1999. Relationship between photosynthesis and seed number of phloem isolated nodes in soybean. Crop Sci. 39, 1769–1775. Chhabra, M.L., Krishnamoorthy, H.N., 1995. Investigation on the effect of partial defoliation on 14C-transport in Indian mustard. Cruciferae Newsletter 17, 62–63. Collin, P.D., Epron, D., Alaoui-Sosse, B., Badot, P.M., 2000. Growth responses of common ash seedlings ( Fraxinus excelsior L.) to total and partial defoliation. Ann. Bot. 85, 317–323. Ericsson, A.S., Larson, S., Tenow, W., 1980. Effects of early and late season defoliation on growth and carbohydrate dynamics in scot pine. Appl. Ecol. 17, 747–769. Foggo, A., 1996. Long- and short-term changes in plant growth following simulated herbivory: adaptive responses to damage? Ecol. Entomol. 21, 198–202. Hamilton, E.W., Giovannini, M.S., Moses, S.A., Coleman, J.S., Mc Naughton, S.J., 1998. Biomass and mineral element responses of a Serengeti shoot species to nitrogen supply and defoliation: compensation requires a critical N. Oecologia 116, 407–418. Hewitt, E.J., 1966. Sand and Water Culture Methods used in the Study of Plant Nutrition. Commonwealth Agricultural Bureaux, England, p. 56. Hussain, A., Black, C.R., Taylor, I.B., Roberts, J.A., 1999. Soil composition: a role of ethylene in regulating leaf expansion and shoot growth in tomato. Plant Physiol. 121, 1227–1237. Khan, N.A., 1994. Variation in carbonic anhydrase activity and its relationship with photosynthesis and dry mass of mustard. Photosynthetica 30, 317–320. Khan, N.A., 2002. Activities of carbonic anhydrase and ribulose-1,5-biphosphate carboxylase, and dry mass accumulation in Brassica juncea following defoliation. Photosynthetica 40, 633–634. Khan, N.A., 2003. Changes in photosynthetic biomass accumulation, auxin and ethylene level following defoliation in Brassica juncea. J. Food Agric. Environ. 1, 125–128. Khan, N.A., Ahsan, N., 2000. Evaluation of yield potential of defoliated mustard cultivars. Tests Agrochem. Cultivars 21, 33–34. Khan, N.A., Javid, S., Samiullah, 2004. Physiological role of carbonic anhydrase in CO2 fixation and carbon partitioning. Physiol. Mol. Biol. Plants 10, 153–166. Khan, N.A., Khan, M., Ansari, H.R., Samiullah, 2002. Auxin and defoliation effects on photosynthesis and ethylene evolution in mustard. Scientia Hort. 96, 43–51. Khan, N.A., Lone, N.A., Samiullah, 2000. Response of mustard (Brassica juncea L.) to applied nitrogen with or without ethrel sprays under non-irrigated conditions. J. Agron. Crop Sci. 184, 63–66. Kieber, J.J., Rothenberg, M., Roman, G., Fieldmann, K.A., Ecker, J.R., 1993. CTRI: a negative regulator of the ethylene response pathway in Arabidopsis: encodes a number of the Raf family of protein kinases. Cell 72, 427–441. Lee, S.H., Reid, D.M., 1997. The role of endogenous ethylene in the expansion of Helianthus annus leaves. Can. J. Bot. 75, 501–508. Mc Naughton, S.J., 1983. Compensatory plant growth as a response to herbivory. Oikos 40, 329–336. Rickli, E.E., Ghazanfar, S.A.S., Gibbons, B.H., Edsall, J.T., 1964. Carbonic anhydrase from human erythrocytes: preparation and properties of two enzymes. J. Biol. Chem. 239, 1065–1078. Rodrigues-Pousada, R.A., De Rycke, R., Dedonder, A., Van CArnegham, W., Engler, G., Van Montagu, M., Van der Straeten, D., 1993. The Arabidopsis 1-aminocyclopropane-1-carboxylate synthase gene 1 expressed during early development. Plant Cell 5, 897–911.
N.A. Khan / Scientia Horticulturae 105 (2005) 499–505
505
Singh, S.P., Singh, G.S., 1996. Effect of defoliation on growth, yield and yield attributing characters in mustard (Brassica juncea L Czern & Coss.). Indian J. Plant Physiol. 1, 123–124. Sultemeyer, D., Schmidt, C., Fock, H.P., 1993. Carbonic anhydrase in higher plants and aquatic microorganisms. Physiol. Plant. 88, 179–190. Weiss, E.A., 1983. Oilseed Crops. Longman Inc, New York, p. 161. XinBin, D., RongXian, Z., Wei, L., Xiaming, X., Schuqing, C., 2001. Effects of carbonic anhydrase in wheat leaf on photosynthetic function under low CO2 concentration. Sci. Agric. Sinica 34, 97–100.