Tijen Demiral

The regulation of antioxidant enzymes in two Plantago species differing in salinity tolerance under combination of waterlogging and salinity

Natural waterlogging affects vegetation dynamics in many areas of the world. Goose-tongue (Plantago spp.) plants include diverse group of species differing in salt tolerance, some of which are adapted to live in saline wetlands, which makes the genus Plantago a good model for comparative studies on the responses to waterlogging and salinity stresses. The aim of this study was to determine how waterlogging in combination with 200mM NaCl affect the tolerance mechanism of Plantago maritima L. (salt-tolerant) and Plantago media L. (salt-sensitive). Combination of salinity and waterlogging treatments (WLS) decreased shoot and root dry weights (DW) and leaf relative water content (RWC) of both P. maritima and P. media and these decreases were more dramatic in the latter. Lipid peroxidation level as measured by thiobarbutiric acid reactive substances (TBARS) content was increased in P. maritima by the combined salinity and waterlogging treatment, whereas in P. media it was increased by all stress treatments applied. Peroxidases (POX), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activities of P. maritima were increased whereas only POX and CAT activities of P. media were increased by salinity treatment alone. WLS treatment increased POX, APX and GR activities but did not affect CAT activities of both Plantago species. NADPH oxidase (NOX) activity did not seem to have any effect to control the level of lipid peroxidation. This study is the first to demonstrate that increased antioxidant activity protected against lipid peroxidation resulting from waterlogging and salinity stresses. In conclusion, we suggest that a salt-tolerant species would also have a higher tolerance of the combination of waterlogging and salinity stress than a salt-sensitive one.

Chapter 8 – Signalling Strategies During Drought and Salinity, Recent News

Agricultural production has been adversely affected worldwide by environmental restraints, especially by drought and salinity because of their high scale of impact and wide distribution. Conventional breeding programmes seeking improvement of stress tolerance are a long-term endeavour as the trait is multigenic, and genetic variability among crop plants is scarce. Many effective protection systems exist in plants that allow them to perceive, respond to and appropriately adapt to a range of stress signals, and a variety of genes and gene products have been identified that involve responses to drought and high-salinity stress. In the past decade, a genetic model plant, Arabidopsis thaliana, has been widely used for unravelling the molecular basis of stress tolerance. The availability of knockout mutants and its suitability to allow genetic transformation proved the vital importance of Arabidopsis for assessing functions for individual stress-associated genes. In this review, the responses of plants to salt and water stress are described, the regulatory circuits, which allow plants to cope with stress, are presented and how the present knowledge can be applied to obtain tolerant plants is discussed.

In Silico Functional Analyses of SWEETs Reveal Cues for Their Role in AMF Symbiosis

SWEETs are novel class of sugar effluxers, which have unique functional role in plant biology. Besides nectar production, freezing tolerance, and transport of hexoses across tonoplast and growth-supporting role of pathogens, these SWEETs could have potential role in establishing powerful symbiotic relationship at the root interface and also in feeding to arbuscular mycorrhizal fungi (AMF) symbionts. The microarray or transcriptome expression of SWEET genes from colonized roots revealed that out of 28 Medicago SWEETs, three genes (MtSWEET1b, MtSWEET3c, and MtSWEET12) were induced specifically due to AMF symbiosis. The root type specific expression of these three genes was also enhanced by AMF colonization in rice. The degree of expression of OsSWEET1b, OsSWEET3b, and OsSWEET12 was increased in colonized large lateral roots (LLRM) and crown roots (CRM), while OsSWEET3b and OsSWEET12 were induced in fine lateral roots (FLRM) and CRM, respectively. Promoter regions of these SWEETs represent critical motif elements (MYCS, PB1S, and PHR1) which play critical role in establishment of AMF symbiosis and phosphate starvation-induced responses, respectively. Taken together, these SWEETs have potential to be explored via functional genomics tools to understand feeding mechanisms to symbionts.