Biochemical parameters: metabolites
Changes in certain metabolites were quantitatively determined in the lentil seedlings of different genotypes in response to simulated moisture stress, which lead to the identification of genotypes that are susceptible and tolerant to drought stress. Salient features of such changes in certain metabolites are described below.
Protein content
The data were analyzed for protein content of lentil Table 1. All the results were found to be significant (P<0.05) at genotypic level. Significant results observed between the genotypes under stress conditions. PL-4 showed significantly higher protein content to the other lentil genotypes. The content of protein was highest (11.75 mg/g f. wt.) in PL-4 seedlings followed by L-4147 (9.68 mg/g f. wt.), L-4594 (9.53 mg/g f. wt.) and L-4596 (9.04 mg/g f. wt.). Amongst macrosperma genotypes it was highest (11.91 mg/g f. wt.) in L-4076 followed by K-75 (10.16 mg/g f. wt.), DPL-15 (7.58 mg/g f. wt.) and DPL-62 (7.41 mg/g f. wt.). A general decrease in protein content was recorded in all the genotypes by water stress, the reduction was less in drought tolerant and it was more in drought susceptible. Drought stress negatively affects the accumulation of various seed components such as proteins
(Asthir et al., 2012; Farooq et al., 2017a,b) by inhibiting the enzymatic processes of synthesis of proteins
(Triboï et al., 2003).
Total carbohydrate content
In general, the level of carbohydrate increased in seedlings subjected to drought stress. Data in Table 1 shows the results and were found to be significant between genotypes and significant variations are also observed between stressed and non-stressed seedlings of genotypes. Drought stress led to significant (
P<0.05) increase in carbohydrate content in PL-4 and DPL-15 and increment was significantly more in DPL-15. In response to water stress PL-4 had highest level (21.86 mg/g f. wt.) of carbohydrate followed by L-4594 (18.00 mg/g f. wt.), L-4596 (13.46 mg/g f. wt.) and L-4147 (9.20 mg/g f. wt.). Under water stress seedlings of DPL-15 accumulated highest content (23.2 mg/g f. wt.) of carbohydrate followed by DPL-62 (19.2 mg/g f. wt.), L-4076 (12.4 mg/g f. wt.) and K-75 (6.53 mg/g f. wt.). Amongst all genotypes DPL-15 showed significantly highest carbohydrate content.
Vigna radiata nodules showed a significant increase in sugar content under drought conditions
(Hooda et al., 1999). Alfalfa plants also showed an increment in total soluble sugars in leaves and nodules under drought stress conditions
(Irigoyen et al., 1992). Soyabean genotypes shown a considerable variation in the sucrose level under drought conditions for example, myo-inositol and sucrose levels in the leaves decreased drastically in the sensitive soyabean genotype, but no significant changes were observed in the tolerant genotype
(Silvente et al., 2012).
Proline content
The free proline accumulation showed a common trend of increase in the seedlings under drought stress as depicted in Table 1. A Significant (
P<0.05) increment in free proline content was observed in seeds of all genotypes under drought stress. DPL-15 showed significantly highest proline content under drought conditions. The proline content in microsperma subspecies was highest in L-4594 (0.49 mg/g f. wt.) followed by PL-4 (0.327 mg/g f. wt.), L-4596 (0.160 mg/g f. wt.) and L-4147 (0.128 mg/g f. wt.). Among macrosperma group the proline accumulation was highest (0.768 mg/g f. wt.) in DPL-15 followed by DPL-62 (0.373 mg/g f. wt.), K-75 (0.288 mg/g f. wt.) and L-4076 (0.233 mg/g f. wt.).
Vigna radiata nodules showed a significant increase in proline content under drought conditions
(Hooda et al., 1999). Increase in proline content was reported in alfalfa leaves and nodules under drought stress
(Irigoyen et al., 1992). Proline accumulation has been reported under drought stress in different plant species
(Ashraf, 2004; Kumar et al., 2017; Awana et al., 2019). PEG induced drought stress in tomato showed 10-fold increase in proline content (
Zgalli et al., 2005).
Biochemical parameters: Enzymes
Acid phosphatase
Activity of acid phosphatase was enhanced in response to drought stress in PL-4 (5.52 mM P-nitrophenol) followed by L-4147 (4.53 mM P-nitrophenol), L-4594 (4.45 mM P-nitrophenol) and lowest (3.56 mM P-nitrophenol) in L-4596 genotype of microsperma lentil. The comparative data analysis is shown in Table 2. Contrary to microsperma group the activity of acid phosphatase in macrosperma group was lowered under drought stress and the reduction was highest in L-4076 where acid phosphatase activity was lowest (2.76 mM P-nitrophenol) as compared to control seedlings (3.28 mM P-nitrophenol). Acid phosphatase activity was increased by salt and drought stress in both cultivars of
Medicago sativa explants under
in vitro culture and the difference in activities between two genotypes of
Medicago sativa indicated that the acid phosphatase activity is highly genotype dependent (
Ehsanpour and Amini, 2003). Increased acid phosphatase activity has also been reported in different crop plants under different stresses
(Kumar et al., 2021; Sheteiwy et al., 2021).
Invertase
Simulated water stress also significantly increased invertase activity in seedlings under ambient laboratory conditions shown in Table 2. PEG-6000 treated seedlings of L-4594 recorded the highest (2.50 mg/g f. wt.) invertase activity under water stress followed by PL-4 (2.31 mg/g f. wt.), L-4147 (1.49 mg/g f. wt.) and L-4596 (1.09 mg/g f. wt.). Amongst macrosperma genotypes DPL-62 showed highest (3.93 mg/g f. wt.) invertase activity in the seedlings followed by DPL-15 (3.69 mg/g f. wt.), K-75 (1.58 mg/g f. wt.) and L-4076 (1.35 mg/g f. wt.). The invertase activity was observed to be increased under various biotic and abiotic stress
(Roitsch et al., 2003) in maize.
Nitrate reductase (NR)
There was a general reduction in the activity of nitrate reductase under simulated water stress in seedlings of lentil genotype seedlings, accordingly shown in Table 2. PEG-6000 treated seedlings of L-4594 showed the minimum reduction (2.79%) it is followed by PL-4 (2.36%), L-4147 (44.64%) and L-4596 (49.19%). Amongst macrosperma genotypes DPL-62 showed minimum reduction (3.94%) in nitrate reductase activity under simulated water stress followed by DPL-15 (10.14%), K-75 (43.73%) and L-4076 (44.58%). Our results are in accordance with previous results of water-stress-induced losses in nitrate reductase activity in other species
(Wellburn et al., 1996). In tomato also drought observed to decrease the Nitrate Reductase activity
(Brewitz et al., 1996). Similar results were observed in leaves of maize
(Foyer et al., 1998).