1. Department of Crop Physiology, TNAU, Coimbatore, 641 003, India
2. National Research Centre for Banana (ICAR), Thiruchirapalli, India
3. Department of Farm Management, TNAU, Coimbatore, 641003, India
Author
Correspondence author
International Journal of Horticulture, 2013, Vol. 3, No. 17 doi: 10.5376/ijh.2013.03.0017
Received: 22 Apr., 2013 Accepted: 25 Apr., 2013 Published: 28 Apr., 2013
Twelve cultivars of banana plants were grown in field conditions and were studied under two irrigation regimes under ratoon season in order to evaluate the relative water content, soluble protein content, total chlorophyll content and yield changes induced by water deficit. Irrigation was applied when soil water potential reached at 80 per cent ASM for the wet treatments and 50 per cent ASM for the stressed treatment plots. The ASM were calculated based on the soil moisture release curve. The soil moisture content was measured by using pressure plate membrane apparatus. The cultivars and hybrids of Karpuravalli, Karpuravalli×Pisang Jajee, Saba, and Sannachenkathali, the RWC was reduced in water-stressed leaves with 8 per cent over control, which could have accounted for the decreased soluble protein, total chlorophyll content and yield in the per cent reduction of 9 and 8 than the other cultivars and hybrids. The highest reduction of 24 per cent in RWC leads to 19 and 18 per cent reduction in soluble protein and chlorophyll content due to water deficit were registered by the cultivars and hybrid of Matti, Pisang Jajee×Matti, Matti×Anaikomban and Anaikomban×Pisang Jajee leads to reduce the yield.
In the forthcoming days drought is a major factor to limit plant productivity in many regions of the world. Most of the research studies have shown that, the plant growth rates were directly proportional to the availability of water in the soil (Kamel and Loser, 1995). In drought, water deï¬cit causes biochemical and physiological processes was changed ranging from photosynthesis to protein synthesis and also solute accumulation (Hu and Schmidhalter, 1998). The limited water resources in the area and the cost of pumping irrigation water are the most important factors that force many farmers to reduce irrigation in many arid and semi-arid regions. Banana is an important tropical fruits. In production viz., Tamil Nadu rank first in banana. Among the all fruit crops banana is the fourth largest fruit crop in the world. It is one of the most important fruit crops that can tolerate short periods of water deficit (Turner, 1998). This deficiency results in a water shortage for some activity, group, or environmental sector. Banana plant productivity is greatly affected by environmental stresses such as drought, water and cold. Plants respond and adopt to these stresses to survive under stress condition at the molecular and cellular levels as well as at the physiological and biochemical levels. Physiological responses to soil water deficit are the feature that is most likely to determine the response of the crop to irrigation. The banana plants are sensitivity to soil moisture stress is reflected in changes in reduced growth through reduced relative water content, soluble protein content and leaf size leads to reduction in photosynthetic pigments (Kallarackal et al., 1990) with increased leaf senescence (Turner, 1998). The banana plants are able to maintain their internal water status during drought by reducing radiation load and closing stomata (Thomas and Turner, 1998).The RWC was estimated in order to find out the plant water status of banana cultivars under water stress situations. Leaf RWC had a significant influence on photosynthesis, by reducing the net photosynthesis by more than 50 per cent when RWC was less than80 per cent. As observed by Slatyer (1955), a reduction by 5% in RWC led to reduction in photosynthesis by 40% to 50 %.The soluble protein content of the leaf, being a measure of RuBP carboxylase activity was considered as an index for photosynthetic efficiency. There were reports that RuBP-case enzyme forms nearly 80 per cent of the soluble proteins in leaves of many plants (Joseph et al., 1981). Diethelm and Shibles (1989) opined that the RUBISCO content per unit leaf area was positively correlated with that of souble protein content of the leaf. Soluble protein content was estimated in order to find out the photosynthetic capacity of banana cultivars under water deficit situations. With this above background, the experiment aimed at evaluating the effects of the progressive water deficit, as well as to investigating the physiological and biochemical behavior in twelve banana cultivars and hybrids submitted to water restriction during the different growth stages.
1 Result
1.1 Relative Water Content
The time trend of RWC revealed a gradual increase upto 7Th MAP with a slight decline towards harvest. Analyzing the two main plot treatments, M1 recorded a higher value of 75.5 per cent and M2 with a value of 66.0 per cent with a 13 per cent reduction over M1 at 7th MAP (Table 1). Sub-plottreatment was also significantly differed among themselves. S1 recorded the highest RWC of 81.1 per cent. This was followed by S2 (80.4%) and S3 (77.5%). The lowest RWC of 61.1 per cent was recorded by S12 followed by S11 (61.3%).The interaction effect of M at S and S at M also varied significantly. M1 subplotinteractions registered comparatively higher values than M2 subplot interactions. However, a considerable reduction could also be noticed in RWC due to interaction with M2 and subplot treatments. M2S1, M2S2, M2S3 and M2S4 recorded 5 to 6 per cent reduction, and M2S5, M2S6, M2S7 and M2S8 showed about 12 to 14 per cent reduction, whereas, M2S9, M2S10, M2S11 and M2S12 exhibited in the range of 20 to 21 per cent over M1 and subplot treatments. In this research study, the RWC was positively correlated with yield (Figure1).
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Table 1 Effect of water stress on Relative Water Content (RWC: %) at different growth stages of banana cultivars in ratoon crop
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Figure 1 Correlation of RWC and yield in banana cultivars and hybrids
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1.2 Soluble protein
The data on soluble protein content indicated a slight increasefrom 3rd to 7th MAP with a decline towards harvest (Table 2). The main plots M1 and M2 differed significantly at all the stages of growth. Among the main plots, M1 recorded highest protein content of 10.1 mg/g at 7th MAP whereas, M2 recorded 8.7 mg/g therefore a14 per cent reduction was observed in M2 over M1. All the subplot treatments significantly differed, among them, S1 registered the highest protein content of 11.6 mg g-1 and the lowest protein content was recorded in S12 (8.0 mg/g).Interaction effects of M at S and S at M also exhibited significant variations at all the stages of growth. All the M1 subplot interactions registered comparatively higher values. The highest value of 12.2 mg/gwas recorded by M1S1 followed by M1S2 (11.1 mg/g) M1S4 (10.4 mg/g) and M1S3 (10.3 mg/g). A remarkable reduction in protein content could also be observed as the result of the interaction of M2 and subplots. M2S1, M2S2, M2S3 and M2S4 showed a reduction of about 9 to 12 per cent, and M2S5 M2S6, M2S7 to M2S8 recorded about 13 to 14 per cent, whereas M2S9, M2S10, M2S11 and M2S12 showed about 16 to 18 per cent reduction over the M1 and sub plot treatments.
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Table 2 Effect of water stress on foliage soluble protein (mg/g) at different growth stages of banana cultivars in ratoon crop
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1.3 Total chlorophyll content
Theresult oftotal chlorophyll content showed a similar pattern of chlorophyll ‘a’, chlorophyll ‘b’ (Table 3). The two main plot treatments differed significantly atall growth stages. Between the main plot M1 recorded higher total chlorophyll content of 1.10 mg/g than M2 (0.98mg/g) 7th MAP. M2 registered 11 per cent reduction in total chlorophyll content over M1. All the sub-plot treatments differed significantly, among them, S1 showed rank first 1.38 mg/g followed by S2 (1.28 mg/g), S3 (1.16 mg/g) and S4 (1.12 mg/g). The lowest content was recorded by S12 (0.79 mg/g) at 7th MAP.The interaction effects of M at S and S at M were significantly differed at all growth stages. Here, M1S1 registered the highest total chlorophyll content of 1.42 mg/g followed by M1S2 (1.31 mg/g). However, the interaction between M2 subplot treatments resulted a considerable reduction over the M1 and subplots. M2S1, M2S2, M2S3, and M2S4 resulted in a lower range of 5 to 8 per cent reduction. However, all the other treatments showed a greater reduction per cent of 12 to 15 over the interaction between M1 and sub plot treatments.
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Table 3 Effect of water stress on total chlorophyll (mg/g) at different growth stages of banana cultivars in ratoon crop
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2 Discussion
2.1 RWC under water deficit stress
Relative water czative water content had a significant influence on photosynthesis, by reducing the netphotosynthesis by more than 50 per cent when relative water content was less than 80 per cent. As observed by Slatyer (1955), a reduction by 5% in RWC led to reduction in photosynthesis by 40 to 50%. Among thetwelve cultivars, Karpuravalli, Karpuravalli×Pisang jajee, Saba and Sannachenkathali were able to maintain higher relative water content under water deficit condition with 6 per cent reduction over control. These findings were in agreement with the results of David (2002), in which a positive correlation between relative water content and gas exchange activities was observed and therefore, the reduction of relative water content was found to cause a strong reduction in photosynthesis, transpiration and stomatal conductance. Besset et al(2001) reported that drought resistant varieties showed consistently higher leaf water potential in their tissues than susceptible types under soil moisture deficit. In the present studies, cultivars like Matti, Matti×Anaikomban, Matti×cultivar rose and Pisang jajee×Matti, recorded lower RWC with higher reduction in the range of 22 to 24 per cent than control. Similarly in banana plants, a major decrease of soil moisture hardly reduced the leaf relative water content. The early reduction of stomatal conductance and the minor diminution of leaf relative water content could indicate that the banana plants showed a drought avoidance mechanism to maintain a favorable plant water status involving stomatal closure in response to water stress.
2.2 Soluble protein under water deficit stress
Protein synthesis represents a major sink for energy (Penning de Vries, 1975). Smith and Stitt (2007) stated that strengthened the idea that a tight link between carbon metabolism and protein synthesis is necessary to prevent acute carbon starvation, especially in growing tissues where most of the protein synthesis contributes to building new biomass (Piques et al., 2009). Soluble protein is the most abundant protein in green tissue, containing the enzyme RUBISCO, involved in CO2 assimilation. As RuBisCO forms nearly 50% of the soluble protein in many plants, the enhancement in soluble protein content might have a direct impact on photosynthetic capacity of the crop plants (Joseph et al., 1981). RuBisCO activity is maintained even when leaf relative water content drops to 50% while stomata are already 75% closed (Smith and Stitt, 2007). A reduction in Rubisco activity during water deficit has also been reported by Castrillo et al(2001); Vu and Allen (2009). Plants leaf photosynthetic rate depends on photosynthetic components contents, such as RuBisCO, cytochromef, H+-ATPase and reaction centers, but also on structural parameters, such as leaf thickness and area per leaf mass. The significant correlations of leaf water potential, leaf relative water content, and leaf osmotic potential with protein content and Rubisco at day 8 of rehydration, after severe stress, revealed a close relationship of these parameters on recovery (Mediavilla et al., 2001). Water deficit depressed the protein synthesis and accelerated their degradation and disturbed the soluble amino acid protein ratio in plants. The results of the present study revealed the effect of water deficit on soluble protein content. Tolerant and moderately tolerant cultivars behaved lesser reduction in soluble protein content with 9 and 14 per cent in response to irrigated level of 50% available soil moisture over control. The susceptible cultivars showed a higher reduction in soluble protein content of 18 per cent due to water deficit over control. According to Martignone et al(1987), soluble protein content was the first nitrogenous compound affected under stress conditions, which at severity got denatured and lost its activity and also decreased the photosynthetic efficiency. Tezara et al(1999) stated that water stress decreased CO2 uptake more than O2 evolution and also reduced the amounts of ATP, RUBP and RuBisCO activity (Castrillo and Calgno 1989). This decline is associated with a decrease in osmotic potential (Kaiser and Heber, 1986) and protein content (Castrillo and Trujillo 1994). Protein content and RuBisCO activity decreased when water potential decreased to -1.70 MPa in bean and maize leaf.
2.3 Total chlorophyll under water deficit stress
Chlorophyll is one of the major chloroplast components for photosynthesis, and relative chlorophyll content has a positive relationship with photosynthetic rate. Photosynthetic pigments are composed of chlorophylls a, b and total, and the main functions are reception and storage of light energy by inductive resonance through antenna complexes, and consequent electron transport carried out by the photosystem II (Taiz and Zeiger 2002). Both chlorophyll a and b are prone to soil dehydration (Farooq et al., 2009). Decreased or unchanged chlorophyll level during drought stress has been reported in many species, depending on the duration and severity of drought. According to Kaiser and Heber (1986) who found that water deficit induced reduction in chlorophyll content has been ascribed to loss of chloroplast membranes, excessive swelling and distortion of the lamellae vesiculation and the appearance of lipid droplets leads to minimize the photosynthetic pigment concentration, which can directly limit photosynthetic potential and hence primary production. As observed in the present study, the water deficit caused considerable reduction in chlorophyll content during shooting stage (7th MAP) of about 16 to 18 per cent in Matti, Matti×Anaikomban, Matti×cultivar rose and Pisang jajee x Matti over control. The mechanism of reduction in chlorophyll content due to the consequence of reactive oxygen species leading to chlorophyll peroxidation and thereby its breakdown (Jabari et al., 2006). Jagtap et al(1998) noticed a reduction in chlorophyll content in drought stressed cotton. Robertson et al (1985) found that the total chlorophyll content decreased to a significant level at higher water deficits in sunflower plants. The reduction in chlorophyll content due to water deficit is loss of chlorophyll by the action of increased chlorophyllase enzyme activity and inactivation of photosynthesis in many crops (Mudrik et al., 2003). The photosynthesis performance and maintenance of chlorophyll concentrations under stress conditions can be considered among other physiological indices of drought tolerance. The present study revealed that tolerant and moderately tolerant cultivars showed lesser reduction in total chlorophyll content with5 and 10 per cent in response to irrigated level of 50% available soil moisture over control. Similar effect was observed by Jagtap et al(1998), with a 20% to 30% chlorophyll loss due to water deficit in sorghum. Jabari et al (2006) also observed a remarkable reduction in total chlorophyll concentration under drought stress condition. Yellowing of leaves (leaf chlorosis) and senescence normally occur before leaves abscise in plants under water deficit, which is associated with chlorophyll degradation and translocation of nutrients to newer leaves in crop plants (Boyer, 1976). The total chlorophyll and carotenoid pigments in the leaf tissues of extreme water deficit were degraded by 60 and 72% respectively in sugarcane. Reduction in water use efficiency in this crop under water deficit level had a direct impact on photosynthetic pigment degradation, leading to reduce water oxidation in photosystem II (Shao et al., 2008). Total chlorophyll content decreased when plants are subjected to severe drought (50% of field capacity), these could be a result of a reaction centre or a photosystem II modification (Blum et al., 1989).
3 Conclusion
Plants respond to drought stress through alteration in physiological and biochemical processes. Our results showed that the RWC, soluble protein and total chlorophyll content were decreased under the water deficit condition. The banana cultivars and hybrids of Karpuravalli, Karpuravalli×Pisang jajee, Saba and Sannachenkathali with slight decreasing trend of RWC, soluble protein and total chlorophyll throughout the growth period of the crop and these four cultivars and hybrids was considered as tolerant to water deficit stress. The findings of this research also showed that the RWC, soluble protein and total chlorophyll can be used as a drought tolerance index to selection tolerant genotypes under water deficit conditions in banana cultivars and hybrids.
4 Materials and Methods
The experimental design was a split plot design with three replications. The main plots are, M1 (control) with the soil pressure maintained from -0.69 to -6.00 bar, M2 (water deficit) with the Soil pressure maintained from -0.69 to -14.00 bar. Soil pressure of -14.00 bar was reached at 30 days and measured by using soil moisture release curve and measured the soil moisture by using the pressure plate membrane apparatus. The sub plots considered as twelve banana cultivars and hybrids (S1: Karpuravalli (ABB), S2: Karpuravalli×Pisang Jajee, S3: Saba (ABB), S4: Sanna Chenkathali (AA), S5: Poovan (AAB), S6: Ney poovan (AB), S7: Anaikomban (AA),S8: Matti× Cultivar Rose,S9: Matti (AA),S10: Pisang Jajee×Matti,S11: Matti×
Anaikomban and S12: Anaikomban×Pisang Jajee.) were randomly distributed within the sub-plots in each of the drought stress treatments (main plots). The RWC, soluble protein and total chlorophyll content were estimated during 3rd, 5th, 7th, 9th month after planting and at harvest stages of the crop and estimating procedure was given below.
4.1 Relative Water Content (RWC)
The Relative Water Content (RWC) of the leaf sample was estimated at all the stages of the crop by the method of Weatherly (1950) and expressed in percentage.
4.2 Soluble protein content
The content of soluble protein was estimated from the leaf samples following the method of Bradford (1974) and expressed as mg g-1 fresh weight.
Procedure: The leaf sample of0.5g was macerated with 10 mL of phosphate buffer (0.1M, pH 7.0) using a pestle and mortar. The extract was centrifuged at 10000 rpm @ 4ºC for 20 minutes. 0.1 mL of supernatant was taken and 5 ml of dye mixture was added. The solution was mixed well and kept aside for 15 minutes. The colour intensity was recorded at 595 nm optical density.
Dye mixture preparation: 100 mg of Coomassie brilliant blue (G 250) was dissolved in 50 mL of 95% ethanol and 100 mL of ortho phosphoric acid was added and made upto 200 mL by using distilled water. 1 Ml of dye solution was taken and 4 ml of distilled water was added and it was used for sample analysis.
4.3 Total chlorophyll content
The total Chlorophyll content were estimated in physiologically active leaves as per the procedure of Hixcox and Israelstam (1979) and expressed as mg g-1 fresh weight.
Acknowledgment
The research have been supported and facilitated by National Research Centre for Banana (ICAR), Trichy. Tamil Nadu. India. I extend my sincere thanks to Dr. M. M. Mustaffa (Director) NRC for banana, Dr. D. Durga Devi (Professor) TNAU and Dr. I. Ravi (Sr. Scientist) NRC for banana for given proper guidance during research.
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