No abstract

Development of salt tolerant rice varieties has become an urgent priority because of the increase of salinity in rice lands. The objectives of the present experiment were to determine: (a) the appropriate level of salt stress to be imposed for screening rice varieties grown in hydroponics for salt tolerance at Phase I (osmotic stress) and at Phase II (salt ion toxicity) of salt stress development; (b) the point of transition from Phase I to II and (c) the degree of salt tolerance in the Sri Lankan improved rice variety At354 in comparison to the known salt-tolerant rice variety, Pokkali. Seedlings of the two varieties were grown in a plant house in nutrient solutions in a range of salt concentrations, i.e. 1 (Control), 20, 40, 60, 80, 100, 120 and 150 mM NaCl. Area of the youngest fully-expanded leaf at salt stress commencement and at 2-7 day intervals was measured non-destructively. The total plant biomass was measured after 30 days of salt stress. Based on the time courses of relative area of the youngest fully-expanded leaf RL A (i.e. area of the leaf under salt stress as a proportion of that in the control), 100 mM Na + was determined as the optimum salinity level for varietal screening. At 100 mM Na + , the two phases could be identified clearly, with Phase I (from 0 to 10 days after reaching 100 mM Na + ) showing a significantly lower rate of reduction of RL A than Phase II (starting after 10 days). The Sri Lankan improved rice variety At354 showed lower rates of reduction of relative plant biomass and RL A and a slower rate of Na + accumulation in the shoot in comparison to Pokkali with increasing salt stress, demonstrating its greater salt tolerance than that of Pokkali.

It is predicted that the concentration of carbon dioxide in the ocean will continue to increase. This phenomenon certainly has an impact on the sustainability of the marine ecosystem, including the seagrass ecosystem. This study aims to determine the effect of carbon dioxide on the morphometrics and growth of E. acoroides seedling. This study was an experimental study where the seeds from the fruit were grown in a controlled environment for two months. There are two treatments, first treatment with the addition of carbon dioxide and second treatment without the addition of carbon dioxide. The results of this study indicate that there is significant result from the two treatments given. Seagrass seeds that grow on treatment with carbon dioxide gas generally have shorter morphological characteristics as well as their growth.

Rice is highly sensitive to salt stress, an expanding abiotic stress factor that limits rice yield improvement. Development of salt tolerant rice varieties based on molecular breeding methods requires identification of genes responsible for various mechanisms and responses that contribute to salt tolerance. The objective of the present work was to identify genes, which are differentially-expressed in response to salt stress in the salt-tolerant Sri Lankan rice variety, At354. Two cDNA libraries were constructed from mRNA of shoot samples of salt-stressed (100 mM NaCl) At354 at Phase I and Phase II (24 hours and 10 days, respectively after increasing salt stress up to 100 mM) of salt stress development. A total of 3192 and 960 cDNA clones respectively were screened from Phase I and II libraries. Differential hybridization of the cDNA clones with probes prepared from salt-stressed and unstressed At354 shoot samples enabled identification of up and down-regulated genes in response to salt stress in Phase I and Phase II. The identified, differentially-expressed cDNA clones were reconfirmed by another round of differential hybridization and through Northern hybridization by the RNA dot blot method. Relative reverse transcription polymerase chain reaction (RT-PCR) was performed to compare the expression levels of selected differentially-expressed genes. Sequencing and subsequent homology search in databases identified 14 up-regulated genes and 17 down-regulated genes during Phase I in At354. Similarly, 11 up-regulated genes and 2 down-regulated genes were identified during Phase II. Possible functions of the identified, differentially-expressed genes in conferring salt tolerance in At354 is discussed extensively. These genes may enable exploration of newer avenues for engineering salt tolerance in rice.