Search

Among cereal crops, salinity tolerance is rare and complex. Multiple genes control numerous pathways, which constitute plant's response to salinity. Cell cultures act as model system and are useful to investigate the salinity response which can possibly mimic a plant's response to stress. In the present study two indica rice varieties, KS-282 and Super Basmati which exhibited contrasting sodium chloride (NaCl) stress response were used to establish cell cultures. The cell cultures showed a contrasting response to salt stress at 100 mM NaCl. High level of intracellular hydrogen peroxide (H2O2) and nitric oxide (NO) were observed in sensitive cell culture for prolonged period as compared to the tolerant cells in which an extracellular H2O2 burst along with controlled intracellular H2O2 and NO signal was seen. To evaluate the role of NO in inducing cell death under salt stress, cell death percentage (CDP) was measured after 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) pre-treatment. CDP was reduced significantly in both tolerant and sensitive cell cultures emphasizing NO's possible role in programmed cell death. Expression analysis of apoplastic NADPH oxidase, i.e. OsRbohA and recently characterised OSCA family members i.e. OsOSCA 1.2 and OsOSCA 3.1 was done. Intracellular H2O2/NO levels displayed an interplay between Ca2+ influx and ROS/RNS signal. Detoxifying enzyme (i.e. ascorbate peroxidase and catalase) activity was considerably higher in tolerant KS-282 while the activity of superoxide dismutase was significantly prominent in the sensitive cells triggering greater oxidative damage owing to the prolonged presence of intracellular H2O2. Salt stress and ROS responsive TFs i.e. OsSERF1 and OsDREB2A were expressed exclusively in the tolerant cells. Similarly, the expression of genes involved in maintaining high [K+]/[Na+] ratio was considerably higher and earlier in the tolerant variety. Overall, we suggest that a control over ROS production, and an increase in the expression of genes important for potassium homeostasis play a dynamic role in salinity tolerance in rice cell cultures.

Clear evidence has highlighted a role for hormones in the plant stress response, including salt stress. Interplay and cross-talk among different hormonal pathways are of vital importance in abiotic stress tolerance. A genome-wide transcriptional analysis was performed on leaves and roots of three-day salt treated and untreated plants of two Italian rice varieties, Baldo and Vialone Nano, which differ in salt sensitivity. Genes correlated with hormonal pathways were identified and analyzed. The contents of abscisic acid, indoleacetic acid, cytokinins, and gibberellins were measured in roots, stems, and leaves of seedlings exposed for one and three days to salt stress. From the transcriptomic analysis, a huge number of genes emerged as being involved in hormone regulation in response to salt stress. The expression profile of genes involved in biosynthesis, signaling, response, catabolism, and conjugation of phytohormones was analyzed and integrated with the measurements of hormones in roots, stems, and leaves of seedlings. Significant changes in the hormone levels, along with differences in morphological responses, emerged between the two varieties. These results support the faster regulation of hormones metabolism in the tolerant variety that allows a prompt growth reprogramming and the setting up of an acclimation program, leading to specific morpho-physiological responses and growth recovery.

An in vitro protocol has been developed for callus induction, somatic embryogenesis, and plant regeneration from stigma–style culture of grapevine. Four different grapevine cultivars (Vitis vinifera L.; cvs. ‘Bombino Nero,’ ‘Greco di Tufo,’ ‘Merlot,’ and ‘Sangiovese’) were tested. Explants were cultured on Nitsch and Nitsch medium (NN) supplemented with various combinations of 6-benzylaminopurine (BA; 4.5 and 9.0 mM) and b-naphthoxyacetic acid (NOA; 5.0 and 9.9 mM). Sucrose (88mM) was used as the carbon source. Somatic embryogenesis was induced within 3–7 mo. After culture initiation. Even though explants of different origin (unfertilized ovules and anthers) regenerated somatic embryos, the higher embryogenic potential was observed in stigma and style explants, with the exception of ‘Merlot,’ which regenerated somatic embryos only from unfertilized ovules. The percentages of stigma–style explants producing somatic embryos was 7% in ‘Bombino Nero’ (cultured on NN medium supplemented 9.0 mM BA and 9.9 mM NOA), 14% in ‘Greco di Tufo’ (4.5mM BA and 9.9 mM NOA), and 8% in ‘Sangiovese’ (9.0 mM BA and 9.9 mM NOA). The presence of growth regulators (BA and NOA) in the medium was essential for induction of somatic embryogenesis. Plants were regenerated on hormone-free NN medium containing 88mM sucrose.

Leaf senescence is the last stage of development of an organ and is aimed to its ordered disassembly and nutrient reallocation. Whereas chlorophyll gradually degrades during senescence in leaves, mitochondria need to maintain active to sustain the energy demands of senescing cells. Here we analysed the motility and morphology of mitochondria in different stages of senescence in leaves of grapevine (Vitis vinifera), by stably expressing a GFP (green fluorescent protein) reporter targeted to these organelles. Results show that mitochondria were less dynamic and markedly changed morphology during senescence, passing from the elongated, branched structures found in mature leaves to enlarged and sparse organelles in senescent leaves. Progression of senescence in leaves was not synchronous, since changes in mitochondria from stomata were delayed. Mitochondrial morphology was also analysed in grapevine cell cultures. Mitochondria from cells at the end of their growth curve resembled those from senescing leaves, suggesting that cell cultures might represent a useful model system for senescence. Additionally, senescence-associated mitochondrial changes were observed in plants treated with high concentrations of cytokinins. Overall, morphology and dynamics of mitochondria might represent a reliable senescence marker for plant cells.

Protein tyrosine phosphorylation plays a central role in a variety of signal transduction pathways regulating animal cell growth and differentiation, but its relevance and role in plants are controversial and still largely unknown. We report here that a large number of proteins from all plant subcellular fractions are recognized by recombinant, highly specific, anti-phosphotyrosine antibodies. Protein tyrosine phosphorylation patterns vary among different adult plant tissues or somatic embryo stages and somatic embryogenesis is blocked in vivo by a cell-permeable tyrosyl-phosphorylation inhibitor, demonstrating the involvement of protein tyrosine phosphorylation in control of specific steps in plant development.