Paramita Nandy

Salinity-imposed changes of some isozymes and total leaf protein expression in five mangroves from two different habitats

Abstract A comparative account of the polymorphic expression of two antioxidative enzymes (Peroxidase and Superoxide dismutase), two hydrolyzing enzymes (Esterase and Acid phosphatase) and total proteins was estimated both qualitatively and quantitatively from the leaves of five mangroves (Bruguiera gymnorrhiza, Excoecaria agallocha, Heritiera fomes, Phoenix paludosa and Xylocarpus granatum) from two different habitats (in situ habitat of Sundarbans and their replicas from ex situ habitat in fresh water condition) and discussed. The higher amount of total protein occurred in fresh water plants compared to their Sundarbans counterparts. The increment of total protein ranged among 156% to 5.7%. Gel electrophoresis experiments revealed that in most of the cases there were extra numbers of protein bands expressed with relatively low molecular weight in saline habitat. In all salinity imposed plants, there were sharp increases in band intensity and the number of isoforms of investigated enzyme. Peroxidase increment in saline plants ranged from 257–139%. Similarly, SOD was estimated at 247–147% in saline habitats. Increments of Esterase and Acid phosphatase varied from 287–154% and 293–139%, respectively.

Photosynthesis and water-use efficiency of some mangroves from Sundarbans, India

We studied seasonal fluctuations in the rates of photosynthesis, transpiration, PAR, and stomatal conductance for 16 species of true mangroves from the Sundarbans region of West Bengal. Soil salinity and pH were also measured. Leaf temperatures were almost always higher than the ambient temperature. We observed considerable seasonal (summer vs winter) as well as interspecific variations in photosynthesis, with the highest rates occurring inHeritiera fomes (13.21 pmol m-2s-1) andAvicennia marina (11.8 mol m-2s-1), and the lowest inNypa fruticans (1.56 mol m-2s-1) andCeriops decandra (2.32 pmol m-2s-1), in many species, an abrupt rise in leaf temperature retarded the photosyn-thetic process. In winter, the rate of transpiration and stomatal conductance reached their maxima inA. marina (4.83 mmol ra-2s-1 and 124.23 m mol m-2s-1, respectively) and their mimima inExcoecaria agallocha (1.85 mmol m-2s-1 and 49.19 mmol m-2s-1, respectively). In contrast, the maximum summer readings were recorded in E.agallocha (6.07 mmol m-2s-1 and 192.74 mmol m-2s-1 respectively).

Differential expression of physiological and biochemical characters of some Indian mangroves towards salt tolerance

Mangroves are physiologically interesting as potential models for stress tolerance and as sources of alternative ideas about physiological strategies relevant at the ecosystem level. Variation in habitat has great impact on the physiological behavior and biochemical expression level of a particular plant species. Five species of mangroves, growing in saline and fresh water conditions were assessed for their ecological fitness in two different habitats. Assessments were based on some physiological and biochemical parameters measured from the fully exposed mature leaves under saline (15–27 PPT) and non-saline (1.2–2 PPT) conditions. Among the five species considered for investigation Bruguiera gymnorrhiza, Excoecaria agallocha and Phoenix paludosa grow luxuriously in the Sundarbans forest, while the rest two (Heritiera fomes, Xylocarpus granatum) are scanty. A comparative account of photosynthetic efficiency, chlorophyll content, mesophyll and stomatal conductance, specific leaf area, photosynthetic nitrogen use efficiency, total foliar free amino acids and differential expression of some antioxidant isoenzymes in leaf were estimated between the saline and non-saline plants. Elevated assimilation rate coupled with increased chlorophyll content, increased conductance and higher specific leaf area in non-saline condition indicates ability of these mangroves to grow even under minimal substrate salinity. The optimum PAR acquisition for photosynthesis in B. gymnorrhiza, E. agallocha and P. paludosa was higher under salt stress, while the maximum assimilation rate was lower in control plants. The opposite trend occurred in H. fomes and X. granatum, where the peak photosynthesis was lower under non-saline conditions even at a higher irradiance than in the saline forest. The isoform patterns of peroxidase, acid phosphatase and esterase indicated considerable difference in regulation of these enzymes due to salt stress and /or reverse adaptation.

Photosynthesis and Water-Use Characteristics in Indian Mangroves

Photosynthesis and water efflux were measured in different PAR and stomatal conductance in members of Avicenniaceae and Rhizophoraceae. Trend of leaf temperature with irradiance and its effect on photosynthesis were also estimated. In most of the studied species, photosynthesis and stomatal conductance followed similar trends with increase in irradiance. The rate of net photosynthesis and stomatal conductance were higher in members of Avicenniaceae than in Rhizophoraceae. In Avicenniaceae, the optimum PAR for maximum photosynthesis ranged between 1340–1685 (μmol m-2s-1, which was also higher than that of Rhizophoraceae (840-1557 μmol m-2s-1). Almost in all the studied taxa, transpiration and stomatal conductance followed similar trends and reached the maximal peaks at the same PAR value. The range of breakeven leaf temperature was almost the same in both the families (34-36°C in Avicenniaceae and 33.5-36.3°C in Rhizophoraceae), beyond which assimilation rate declined.

Salt Stress: A Biochemical and Physiological Adaptation of Some Indian Halophytes of Sundarbans

Experiment was conducted with five typical mangroves (Bruguiera gymnorrhiza, Excoecaria agallocha, Heritiera fomes, Phoenix paludosa, and Xylocarpus granatum) both from Sundarbans (in-situ) and grown in mesophytic condition (ex-situ, in the Indian Statistical Institute’s premises) since 15–17 years. A comparative account on PAR utilization for maximum photosynthesis, stomatal conductance, total leaf proteins, and polymorphic expression of two antioxidative enzymes (peroxidase and superoxide dismutase) and two hydrolyzing enzymes (esterase and acid phosphatase) were estimated both qualitatively and quantitatively. The present work revealed that the net photosynthesis was higher in mangroves from mesophytic habitats than those of the native plants, but the PAR acquisitions for maximum photosynthesis were greater in most of the Sundarbans species, except H. fomes and X. granatum. At the same time, the stomatal conductance was remarkably depleted under salinity stressed habitats than those of the nonsaline counterparts and ranged between nearly 25 and 52%. Total leaf protein content form the above said taxa revealed that the increment of total protein occurred in mesophytic habitat and it was ranged between 156% (in P. paludosa) and 5.7% (in X. granatum). PAGE analysis revealed that in most of the cases there were extra numbers of protein bands expressed with relatively low molecular weight in saline habitat plants. In all salinity imposed plants, there were sharp increase in band intensity and number of isoforms of each enzyme. Peroxidase increment in saline plants was ranged between 257% (in Bruguiera) and 139% (in Excoecaria). Similarly, superoxide dismutase (SOD) was estimated as 247% (in Heritiera) to 147% (in Excoecaria) in saline habitats. Increments of esterase and acid phosphatase were varied from 287% (in Phoenix) to 154% (in Excoecaria) and 293% (in Bruguiera) to 139% (in Excoecaria), respectively. Salinity imposed increment of antioxidant enzymes proved their efficient scavenging ability to evolved reactive oxygen species (ROS), but these increments were relatively lower in Heritiera and Xylocarpus even though the net photosynthesis was higher. This might be related to their less adaptability in elevated salinity stress than those of the other three species investigated from the same regime. Among the plants grown in in situ condition, some taxa have the better ability of enzyme production, which might be correlated with the efficient stress management practice. A statistical relationship was observed between the total protein content and the investigated enzyme concentration, dependent on the habitat and discussed accordingly.

Genetic variation in relation to adaptability of three mangrove species from the Indian Sundarbans assessed with RAPD and ISSR markers

Rich genetic polymorphism is important for plants to adapt to changes because it enables the plant to make anatomical, physiological and biochemical changes in response to abiotic stress. Geomorphologic characteristics, demographic interference and a cumulative decrease in freshwater influx in the Indian Sundarbans region have proved detrimental to some economically important plants. In this study, genetic polymorphism of three mangrove species, Xylocarpus granatum, Excoecaria agallocha, and Phoenix paludosa, was assessed using RAPD and ISSR molecular markers. X. granatum, already in distress in the Sundarbans, had the least genetic polymorphism, 14.56% in the RAPD analysis and 12.92% in the ISSR. Relatively higher genetic polymorphism was recorded for the profusely growing E. agallocha and P. paludosa: 24.66 and 26.4% in RAPD; 24.87 and 20.32% in ISSR analysis respectively. A UPGMA dendrogram constructed using the similarity matrix from RAPD, ISSR and combined data showed that for X. granatum, the least and highest salinity zones clustered together, whereas for E. agallocha and P. paludosa, higher and lower salinity areas clustered in different clades. Nei’s genetic diversity, calculated from RAPD and ISSR data, was also in accordance with 0.0637 and 0.0583 for X. granatum, respectively, much lower than 0.0794 and 0.0818 for E. agallocha and 0.0799 and 0.0688 for P. paludosa. This opposing degree of polymorphism might be attributed to the profusely growing E. agallocha and P. paludosa and precarious status of X. granatum throughout the Indian Sundarbans.