MSc

A study entitled ‘Physiological and molecular analyses of growth responses in black pepper (Piper nigrum L.) under elevated carbon dioxide environments’ was carried out with the objective to study the physiological, molecular and biochemical basis of growth responses in black pepper (Piper nigrum L.) under elevated CO2 conditions. In this study, 8 month old rooted cuttings and bush pepper plants of 3 varieties viz. Panniyur 1, Panniyur 5 and Karimunda were used. Technologies used for CO2 enrichment were Open Top Chamber (OTC) and Trench Systems. CO2 was released from CO2 cylinders to one of the two OTCs bringing the CO2 level to 500ppm (OTC Ec) and the second OTC worked as a control at ambient CO2 for chamber effect (OTC Ac). In trench system, CO2 concentration was enhanced to a level of 480 ppm. The plants were maintained under high CO2 level for a period of two months in both the systems. The experiment was laid out in CRD with 4 treatments and 3 replications. Observations on growth parameters and molecular studies were conducted at the end of exposure period and physiological and biochemical parameters were taken at monthly intervals. Elevated CO2 was found to have a promotional effect on all the growth parameters compared to absolute control. An increase of 18% was noticed in plant height, 84% in leaf production, 174.4% in leaf area, 147.8% in net assimilation rate, 51.1% in relative growth rate, 87.5% in root weight, 25.3% in shoot weight, 42.1% in root-shoot ratio and 62.27% in dry matter production. Specific leaf areawas found to have a 13.3% reduction under elevated CO2. Under elevated CO2, the variety Panniyur 1 bush recorded highest net assimilation rate (0.066 mg cm-2 day -1), relative growth rate (0.0078 mg g-1 day-1), shoot weight (13.03 g) and dry matter production (10.07 g). Highest root production, root shoot ratio and lowest transpiration rate were noticed in Karimunda variety. CO2 enrichment significantly lowered the stomatal frequency (1311 No. cm-2), stomatal conductivity (28.70 mmoles m s-1) and transpiration rate (0.72 mmoles m-2 s-1) in all the varieties except for Panniyur 5 bush pepper resulting in
better relative water content. Photosynthetic pigments in all varieties (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids) were increased under elevated CO2. Elevated CO2 had significant positive influence on biochemical parameters like total soluble protein (6.40 mg g-1), starch (29.92 mg g-1), reducing sugars (15.06 mg g-1), phenol content (0.70 mg g-1), free amino acids (2.59 mg g-1) and wax concentration (2.65mg cm-2). Though there was a reduction in membrane integrity during the initial phase, it got stabilized at later stages. Isotope discrimination values were enhanced under elevated CO2 in all the varieties except Panniyur 5. CO2 enrichment was found to have significant influence on peroxidase (2.41 activity g-1 min-1) and superoxide dismutase (0.91 activity g-1 min-1) activities but in the case of catalase and ascorbic acid no significant variation was observed. Protein profile revealed that elevated CO2 induced the production of a few new proteins but suppressed certain others. The expression levels of both the large and small subunits of rubisco were slightly brought down by CO2 enrichment. The plants kept in trench system also responded in a similar manner but to a lesser extent.
The present study revealed that elevated CO2 environment had a positive influence on growth and development of pepper. Panniyur 1 was the best performing bush pepper. Pepper plants of the variety Karimunda had the best root characters, high mesophyll efficiency and low transpiration rate under elevated CO2 environments which makes it suitable for water limited situations with higher water use efficiency.