AUTHOR=Chakraborty Koushik , Mondal Subhankar , Ray Soham , Samal Pankajini , Pradhan Bhubaneswar , Chattopadhyay Krishnendu , Kar Meera Kumari , Swain Padmini , Sarkar Ramani K. 

TITLE=Tissue Tolerance Coupled With Ionic Discrimination Can Potentially Minimize the Energy Cost of Salinity Tolerance in Rice

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 11 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00265

DOI=10.3389/fpls.2020.00265

ISSN=1664-462X

ABSTRACT=Salinity is one of the major constraints in rice production. Development of salt-tolerant rice cultivars is primarily focussed on salt-exclusion strategies which incur energy cost, as well. The present study aimed to evaluate a balancing strategy of ionic discrimination vis-à-vis tissue tolerance, which can potentially minimize the energy cost of salt-tolerance in rice. Four rice genotypes viz. FL478, IR29, Kamini and AC847 were grown hydroponically and subjected to salt stress equivalent to 12 dS m-1 at early vegetative stage. Physiological observations (leaf chlorophyll content, chlorophyll fluorescence traits, tissue Na+ and K+ content) and visual scoring suggested a superior salt-exclusion as well as Na+-partitioning strategy operating in FL478. Very low tissue Na+/K+ ratio in the leaves of FL478 after seven days of stress, suggested selective ion transport mechanism operating in this genotype. Interestingly, Kamini, a similar salt-tolerant genotype, had relatively higher leaf Na+/K+ ratio under same duration of stress. Salt induced expression of different Na+- and K+-transporters and H+-pumps showed significant upregulation of OsSOS1, OsHKT1;5, OsNHX1 and OsHAK5 in both leaf and root tissues of FL478, followed by Kamini. Similarly, expression of both plasma-membrane and tonoplast ATPases (OsAHA1, OsAHA7, OsV-ATPase) showed sharp induction under stress. But, genotype like IR29 and AC847 showed greater salt-susceptibility and nearly died within seven days of stress imposition due to excess transport of Na+ to the leaves. When ‘leaf clip’ assay was performed by taking excised leaf from control plants and immersed them in saline solution (12 dS m-1), we found IR29, the most susceptible genotype having highest chlorophyll retention ability, when the mesophyll tissues of all genotypes contained similar amount of Na+. FL478, having higher ionic discrimination ability showed least tissue tolerance ability as evident from LC50 score of 336 mmol g-1 as compared to 459 and 424 mmol g-1 for IR29 and Kamini, respectively. Overall, study indicated that the two components of salt tolerance mechanism, i.e. ion selectivity and tissue tolerance are distinct and genotype like Kamini effectively balance both of them to achieve similar level of salt-tolerance of FL478. This might give a new insight towards minimizing the energy cost of salt-tolerance.