Rapid accumulation of phosphatidylinositol 4,5-bisphosphate and inositol 1,4,5-trisphosphate correlates with calcium mobilization in salt-stressed arabidopsis.

The phosphoinositide phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] is a key signaling molecule in animal cells. It can be hydrolyzed to release 1,2-diacyglycerol and inositol 1,4,5-trisphosphate (IP(3)), which in animal cells lead to protein kinase C activation and cellular calcium mobilization, respectively. In addition to its critical roles in constitutive and regulated secretion of proteins, PtdIns(4,5)P(2) binds to proteins that modify cytoskeletal architecture and phospholipid constituents. Herein, we report that Arabidopsis plants grown in liquid media rapidly increase PtdIns(4,5)P(2) synthesis in response to treatment with sodium chloride, potassium chloride, and sorbitol. These results demonstrate that when challenged with salinity and osmotic stress, terrestrial plants respond differently than algae, yeasts, and animal cells that accumulate different species of phosphoinositides. We also show data demonstrating that whole-plant IP(3) levels increase significantly within 1 min of stress initiation, and that IP(3) levels continue to increase for more than 30 min during stress application. Furthermore, using the calcium indicators Fura-2 and Fluo-3 we show that root intracellular calcium concentrations increase in response to stress treatments. Taken together, these results suggest that in response to salt and osmotic stress, Arabidopsis uses a signaling pathway in which a small but significant portion of PtdIns(4,5)P(2) is hydrolyzed to IP(3). The accumulation of IP(3) occurs during a time frame similar to that observed for stress-induced calcium mobilization. These data also suggest that the majority of the PtdIns(4,5)P(2) synthesized in response to salt and osmotic stress may be utilized for cellular signaling events distinct from the canonical IP(3) signaling pathway.

Inheritance of UV-B tolerance in seven ecotypes of Arabidopsis thaliana L. Heynh. and their F1 hybrids.

We used a partial diallel mating design to examine morphologic response to supplementary ultraviolet-B (UV-B) radiation of seven ecotypes of Arabidopsis thaliana L. Heynh. from several geographic locations in Europe. We were particularly interested in the inheritance of UV-B tolerance by the F1 generation. Morphologic traits included plant height, rosette diameter, number of shoots (lateral branches from the rosette) and branches (lateral branches above the rosette), and reproductive and vegetative dry mass. To effect a large difference in UV treatments, plants under treatment received 11 kJ/m2/day of biologically effective UV-B radiation while control plants received no UV-B radiation. Genotype effects were observed for all traits (P < .0001), but a significant treatment effect and genotype x treatment interactions were detected only for plant height (P = .0001), rosette diameter (P = .0229), and vegetative (P = .0260) and reproductive dry mass (P = .0900). General combining ability was significant for plant height (P < .0001) and vegetative mass (P = .0563), whereas specific combining ability was significant for rosette diameter (P = .0220) and vegetative mass (P = .0506). These results suggest that both pure lines and hybrids of Arabidopsis can be developed for greater tolerance of UV-B radiation. Similar findings for crop species might lead to the development of UV tolerant varieties.

Susceptibility of pollen to UV-B radiation: an assay of 34 taxa.

Much of the ultraviolet-B radiation (UV-B) research on plants has concentrated on vegetative plant parts, and only a small fraction has dealt with the reproductive system. The present study analyzed pollen grains of 34 taxa germinated and grown under two levels of UV-B radiation (187 and 460 mW/m2) or no UV-B (control group). Visible radiation at 260 mmol/m/s was present in all treatments. Taxa included those with binucleate and trinucleate pollen types. We detected differences among species. A significant reduction in pollen germination occurred in only five species. Pollen tubes of >50% of the species showed significant reduction in length. Trinucleate pollen types were more likely to exhibit tube length reduction than the binucleate types. Proportionately more monocotyledonous species were sensitive to UV-B treatment than dicotyledonous species, and proportionately more wild species were sensitive than cultivated species and pollen collected from plants growing in the field were somewhat more sensitive than pollen collected from plants grown in the greenhouse. Species in which pollination occurred earlier in the season were more likely to be susceptible to UV-B radiation than those for which anthesis took place later in the season, suggesting a possible adaptation to UV-B radiation.

Genome constitution of the Australian hexaploid grass Elymus scabrus (Poaceae: Triticeae).

Eight intergeneric hybrid plants were obtained between Elymus scabrus (2n = 6x = 42, SSYY??) and Australopyrum pectinatum ssp. retrofractum (2n = 2x = 14, WW). The hybrids were vegetatively vigorous but reproductively sterile. Examination of pollen mother cells at metaphase I revealed an average of 16.63 I, 5.29 II, 0.19 III, and 0.05 IV per cell for the eight hybrids. The average chiasma frequency of 6.77 per cell in the above hybrids strongly supports the presence of a W genome from A. pectinatum ssp. retrofractum in E. scabrus. Meiotic pairing data of some other interspecific hybrids suggest the existence of the SY genomes in E. scabrus. Therefore, the genome constitution of E. scabrus should be written as SSYYWW. Two other hybrid plants resulted from Elymus yezoensis (2n = 4x = 28, SSYY) crosses with A. pectinatum ssp. pectinatum (2n = 2x = 14, WW). Both were weak and sterile. An average of 0.45 bivalents per cell were observed at metaphase I. This clearly indicates a lack of pairing between W genome of Australopyrum and S or Y genomes of E. yezoensis. In addition, six hybrid plants of E. scabrus with Psathyrostachys juncea (2n = 2x = 14, NN) and one with Thinopyrum bessarabicum (2n = 2x = 14, JJ) were also obtained. The average bivalents per cell formed in both combinations were 2.84 and 0.70, respectively. The results of the latter two combinations showed that there is no N or J genome in E. scabrus.

Genome analysis of intergeneric hybrids of apomictic and sexual Australian Elymus species with wheat, barley and rye: implication for the transfer of apomixis to cereals.

Four hybrids were obtained between three Australian Elymus taxa and three cereal grains: wheat, rye, and barley. Mean meiotic metaphase-I configurations were 41.14 I, 0.42 rod II, 0.003 ring II, and 0.01 III for E. scabrus var 'plurinervis' x Triticum aestivum (1 hybrid plant), 22.27 I, 2.63 rod II, 0.06 ring II, and 0.12 III for E. scabrus var 'scabrus' x Secale cereale (4 hybrid plants), and 26.65 I, 0.66 rod II, 0.00 ring II, and 0.01 III for E. scabrus var 'plurinervis' x Hordeum vulgare (13 hybrid plants). The I genome of barley also paired very little in a BIII hybrid of apomictic E. rectisetus x H. vulgare (2 hybrid plants). Megasporogenesis in this BIII hybrid was at least facultatively apomeiotic, with the same sort of nuclear elongation, apomeiotic division, and dyad formation seen previously in E. rectisetus itself. All four hybrid combinations were sterile. While spike morphology in the E. scabrus x T. aestivum and E. scabrus x H. vulgare hybrids were intermediate to their parents, E. scabrus x S. cereale and E. rectisetus x H. vulgare looked like their maternal parents.