Home
Add
Get on Google Play
Home
> Edit
Add/Update Thesis
Title*
Author's Name*
Supervisor's Name
Abstract
Salinity is one of the most important abiotic stresses that affect crop production globally as well as in Pakistan. Rice is regarded as an important cereal crop prone to salinity which drastically reduces its yield. This study was conducted to underpin the transcriptional changes in regulating genes engaged at different nodes of salt stressinduced signaling pathways in rice. Five indica rice cultivars of Pakistan viz. KSK-133, KS-282, Super Basmati, Shaheen Basmati and DilRosh were hydroponically given salt stress using 75, 100 and 150 mM NaCl as final concentrations. The optimal salt stress dose was identified as 100 mM at which Super Basmati was found sensitive to salt treatment while KS-282 was marked as salt tolerant amongst the five cultivars tested. The amounts of Na+ and K+ ions were compared for the two contrasting cultivars. High Na+ amounts were measured in the roots and shoots of the salt-sensitive Super Basmati plants three days post treatment as compared to salt tolerant KS-282 plants. The root architectural analysis showed a significant decrease in the root growth and lateral root density in Super Basmati 7 days post treatment along with reduced root surface area when compared to KS-282. We further investigated the change in the transcript concentration of stress-related genes (OsOSCA1.1, OsRbohA, OsDREB2A) and genes specifically known for Na+ homeostasis (OsNHX1, OsSOS1and OsHKT1.5) by qPCR. Interestingly, the relative transcript concentration of OsOSCA1.1, OsRbohA, OsDREB2A was significantly lower at 30 minutes post salt stress in Super Basmati while in KS-282, the expression level for these genes remained many folds high. Considering transcript accumulation for OsNHX1, OsSOS1 and OsHKT1.5, no significant difference was noticed in Super Basmati at 1 and 6 hours post treatment while in the relatively salt tolerant KS-282 plants, a remarkable increase in the transcript accumulation was observed 6 hours post treatment suggesting an important role of these genes. Similarly, a strong relationship between the expression of OsTPKa and OsHAK5 and plant K+ levels was noticed in KS-282, while OsKAT1 showed no change in the expression. The salt stress response in both Super Basmati and KS-282 was further investigated through cell cultures after working out the optimal media and hormone combination for callus induction and whole-plant regeneration. In the stabilized cell xii cultures independently grown on 100 mM NaCl, significantly high intracellular hydrogen peroxide (H2O2) and nitric oxide (NO) were found in Super Basmati cultures compared to KS-282. These data suggest a better ROS scavenging in KS-282 to cope with oxidative stress and cell damage caused by redox imbalance as a consequence of salt stress. To evaluate the role of NO in inducing cell death after salt stress, cell death percentage (CDP) was measured after NO scavenging through 2-4-carboxyphenyl4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). CDP was reduced significantly in cell cultures of both salt tolerant and sensitive cultivars emphasizing role of NO in programmed cell death. The transcript of OsRbohA, which encodes a plasma membrane NADPH oxidase, and genes of OSCA family members (OsOSCA1.1, OsOSCA1.2 and OsOSCA3.1) was quantified and found to be highly upregulated in the cell cultures of KS-282. The activity of ascorbate peroxidase and catalase was higher in KS-282 cells while the activity of superoxide dismutase was significantly higher in the Super Basmati cell cultures. Salt stress and ROS-responsive genes encoding transcription factors, OsSERF1 and OsDREB2A, were found to be upregulated relatively early in the KS-282 cells cultures, while not in Super Basmati. Similarly, the transcript of genes involved in maintaining a high [K+]/[Na+] ratio raised considerably higher and earlier in the cell cultures of the tolerant cultivar. These data suggest that the prompt upregulation of stress responsive genes and associated transcription factors transduces the stress signal by maintaining K+ and Na+ ion homeostasis and thus playing a dynamic role in salinity tolerance in rice plants and corresponding cell cultures. We also reported differential expression of OSCA genes in response to salt stress in rice. Based on our data we postulate a new potential model presenting crosstalk between important second messengers i.e. ROS, RNS and Ca2+ which may elucidate the mechanisms underlying salt stress signal transduction in rice.
Subject/Specialization
Language
Program
Faculty/Department's Name
Institute Name
Univeristy Type
Public
Private
Campus (if any)
Institute Affiliation Inforamtion (if any)
City where institute is located
Province
Country
Degree Starting Year
Degree Completion Year
Year of Viva Voce Exam
Thesis Completion Year
Thesis Status
Completed
Incomplete
Number of Pages
Urdu Keywords
English Keywords
Link
Select Category
Religious Studies
Social Sciences & Humanities
Science
Technology
Any other inforamtion you want to share such as Table of Contents, Conclusion.
Your email address*