Assessing the genetic relatedness of higher ozone sensitivity of modern wheat to its wild and cultivated progenitors/relatives

Modern wheat (Triticum aestivum L.) is one of the most ozone(O₃)-sensitive crops. However, little is known about its geneticbackground of O₃ sensitivity, which is fundamental for breedingO₃-resistant cultivars. Wild and cultivated species of winterwheat including donors of the A, B and D genomes of T. aestivumwere exposed to 100 ppb O₃ or charcoal-filtered air in opentop chambers for 21 d. Responses to O₃ were assessed by visibleO₃ injury, gas exchange, chlorophyll fluorescence, relativegrowth rate, and biomass accumulation. Ozone significantly decreasedlight-saturated net photosynthetic rate (–37%) and instantaneoustranspiration efficiency (–42%), but increased stomatalconductance (+11%) and intercellular CO₂ concentration (+11%).Elevated O₃ depressed ground fluorescence (–8%), maximumfluorescence (–26%), variable fluorescence (–31%),and maximum photochemical efficiency (–7%). Ozone alsodecreased relative growth rate and the allometric coefficient,which finally reduced total biomass accumulation (–54%),but to a greater extent in roots (–77%) than in the shoot(–44%). Winter wheat exhibited significant interspeciesvariation in the impacts of elevated O₃ on photosynthesis andgrowth. Primitive cultivated wheat demonstrated the highestrelative O₃ tolerance followed by modern wheat and wild wheatshowed the lowest. Among the genome donors of modern wheat,Aegilops tauschii (DD) behaved as the most O₃-sensitive followedby T. monococcum (AA) and Triticum turgidum ssp. durum (AABB)appeared to be the most O₃-tolerant. It was concluded that thehigher O₃ sensitivity of modern wheat was attributed to theincreased O₃ sensitivity of Aegilops tauschii (DD), but notto Triticum turgidum ssp. durum (AABB) during speciation. Key words: Biomass, Chl a fluorescence, genome, ozone sensitivity, relative growth rate, stomatal conductance, winter wheat Received 20 September 2007; Revised 30 November 2007 Accepted 16 January 2008     

Presence of an alpha-amylase isozyme with high temperature optima in the wheat variety tolerant to high temperature at juvenile plant stage

In the present study α-amylase was partially purified from detached grains of five day old seedlings of two wheat (Triticum aestivum L.) varieties, showing differential responses to high temperature stress at seedling stage. A three step purification via ammonium sulphate precipitation, DEAE-cellulose column chromatography and gel filtration on Sephadex G-150 was employed. A single α-amylase was detected in the high temperature sensitive PBW-175 variety, while two isozymes namely, α-amylase-1 and α-amylase-2 were obtained in the relatively tolerant WL-711 variety. The pH optima of the three α-amylases were in 5.0–5.5 range and comparable to the cereal amylases. The temperature optima of PBW-175 α-amylase and α-amylase-1 of WL-711, which appeared to be the major isozyme of the variety, were same at 45 °C and also comparable to cereal amylases. On the other hand the optimum temperature for α-amylase-2 was high at 70 °C, which is unusual and not reported earlier for cereal amylases. The Km of PBW-175 α-amylase was lower than the Km values of WL-711 isozymes, this was well co-related with an overall high α-amylase activity detected in the detached grains of five day old seedlings of PBW-175 compared to WL-711. However WL-711 variety showed a better inherent seedling growth, vigour and EUE than PBW-175, may be because it had two α-amylase isozymes which could compensate for the higher enzyme activity detected in PBW-175. Moreover, the presence of α-amylase-2 in the grain of WL-711 having temperature optima of 70 °C, possibly rendered its seedlings tolerant to HS of 50 °C, while the seedlings of PBW-175 succumbed to this temperature shock.