MSc

The study entitled “Carbon dioxide enrichment induced drought tolerance responses in tomato (Solanum lycopersicum L.) and amaranthus (Amaranthus tricolor L.)” was undertaken with the objective to study the physiological basis of varietal responses of tomato and amaranthus to water stress conditions and to study their modifications under elevated CO2 environment. The experiments were conducted from August, 2015 to September, 2015 on tomato and from February, 2016 to March, 2016 on amaranthus. Two pot culture experiments were conducted with three varieties of tomato i.e, Manulakshmi, Vellayani Vijay, Anagha and three varieties of amaranthus i.e, Arun, CO -1 and Renusree. The technology used for CO2 enrichment was Open Top Chamber (OTC) system established under Department of Plant Physiology, college of Agriculture, Vellayani.
Carbon dioxide was released from CO2 cylinders to one of the two OTC s bringing the CO2 level to 600 ppm and the second OTC worked as control at ambient CO2 for chamber effect. The experiments were laid out in CRD with 18 treatments and three replications. One month old potted plants of tomato and amaranthus were shifted to the CO2 treatment conditions. Plants were maintained under well irrigated conditions for one week. Water stress conditions were imposed by withdrawing irrigation for two days after shifting and stress observations were taken. Thereafter plants were re-watered and on the 5th day of re-watering, recovery observations were taken.
In tomato, higher values were recorded for total dry matter production (5.74 g), shoot weight (4.42 g), root weight (1.32 g), root shoot ratio (0.40), relative water content (RWC) (80.69 %), membrane integrity (4.76% loss), superoxide dismutase (SOD) (0.66 activity g-1 min-1), phenol (2.86 mg/g), total chlorophyll content (1.00 mg/g), reducing sugar (15.13 mg/g), starch (4.63 mg/g), and photosynthetic rate (18.69 µmol CO2/m2/s) under elevated CO2 compared to control after stress. Parameters like stomatal frequency, transpiration rate and protein content recorded lower values (555.85 number/cm2 , 8.13 mmol water/m2/s, 14.41 mg/g respectively) under CO2 enriched treatments. Lower stable isotopic discrimination was observed under elevated CO2 compared to open control. Elevated CO2 was found to have a positive impact on recovery responses also. Mealy bugs, scales and serpentine leaf miner infestations were found to be more in open control compared to elevated CO2 treatment. Protein profiling revealed that elevated CO2 induced the production of formation of a few new proteins of molecular weight nearly 42 K Da to 50 K Da were observed under water stress for tomato varieties Anagha, Vellayani Vijay and Manulakshmi which can be stress proteins imparting tolerance and no changes were observed in expression levels of RuBISCO small or large sub units expression Among the three varieties of tomato, Vellayani Vijay was found to be the best responding variety to elevated CO2.
In the case of amaranthus, significantly higher values were recorded for root weight (0.92 g), shoot weight (6.88 g), total dry matter production (5.74 g), SOD (1.65 activity g-1 min-1 ) and reducing sugars (15.13 mg/g). Parameters like leaf number, free amino acid, chlorophyll, ascorbic acid and membrane integrity showed an increasing trend though not significant. Stomatal frequency and transpiration rate were lower under elevated CO2. Even in the case of amaranthus, elevated CO2 was found to have positive impact on recovery responses. Leaf webber and mite incidences were more in elevated CO2 treatment compared to control. Among the three varieties of amaranthus, CO-1 maintained highest root weight, shoot weight and dry matter production compared to Arun and Renusree. Protein profile and RuBISCO sub unit expressions were not modified by the experimental treatments.
In the present study, CO2 enrichment was revealed to have a role in improving the stress tolerance and recovery responses in the case of tomato and amaranthus. Considering all the physiological and biochemical studies carried out in the case of tomato and amaranthus, the better stress tolerance under elevated CO2 was found to be achieved mainly through better photosynthetic rate and activation of defense mechanisms, especially activation of antioxidants. The study also demonstrated the varietal variation existing in CO2 enrichment induced drought tolerance responses in tomato and amaranthus which will help in the selection of suitable varieties for a changing climatic scenario.