Temperature Effects on Cytokinin Accumulation and Kernel Mass in a Dwarf Wheat

The objectives of this study were: (1) to quantify post-anthesiskernel cytokinin levels in ‘Tibet Dwarf’, a dwarfwheat (Triticum aestivumL.) that accumulates elevated quantitiesof leaf cytokinins; and (2) to measure the effects of temperatureon kernel cytokinin accumulation and mature kernel mass in thiswheat. Post-anthesis kernel cytokinin accumulation was measuredin control plants maintained at 25/12 °C (day/night) andtreated plants which received a 7 d exposure to 35/25 °Cbeginning at anthesis and grown to maturity at 25/15 °C.Zeatin (Z), dihydrozeatin (diHZ) and their respective ribosideswere the predominant cytokinins detected in control and treatedplants. Minimal quantities of isopentenyl adenine-type cytokininswere detected. Kernel cytokinin content peaked within 3 d afteranthesis in both groups and returned to baseline levels within1–2 d. Relative to controls, exposure to high temperaturereduced kernel cytokinin content approx. 80% within 1 d afteranthesis. Because kernel cytokinin in control Tibet Dwarf plantsexceeded that previously measured in other varieties by over100-fold, the reduced content of treated plants still exceededthat of untreated plants of other varieties. The increased cytokinincontent did not enhance thermotolerance. The temperature treatmentreduced mature kernel weights approx. 27%, similar to reductionsmeasured in other wheat varieties.Copyright 1999 Annals of BotanyCompany Triticum aestivum, endosperm development, heat stress, kernel mass, cytokinins.     

Postanthesis temperatures influence cytokinin accumulation and wheat kernel weight

High temperatures during reproductive development alter kernel development and reduce yield and quality in wheat ( Triticum aestivum L.). Understanding how temperature alters kernel formation will help the development of genetic approaches to enhance heat tolerance in this cereal. A relationship between kernel development and postanthesis cytokinin accumulation is well documented, but the effect of temperature on this relationship is not known. This study quantified the effects of a postanthesis temperature treatment (7 d at 35/25 °C day/night) on kernel development and cytokinin accumulation in a soft white winter wheat (c.v. Stephens). Kernels from control plants maintained at 25/15 °C accumulated zeatin, dihydrozeatin and their corresponding 9-ribosides from 1 to 4 d postanthesis. Postanthesis kernel cytokinin accumulation was reduced by 50–80% by the temperature treatment. Kernel cytokinin content in control plants declined to baseline by 5 d postanthesis and remained at that level. Kernels from treated plants had a secondary peak of cytokinin accumulation 6–8 d after anthesis. This treatment significantly reduced kernel weight. The magnitude of the effect on kernel number was smaller than on kernel weight, but was statistically significant. Reduced kernel weight was accompanied by reduced cytokinin accumulation. Exogenous cytokinins did not mitigate the temperature effects on kernel weight, but at the highest concentrations, did reduce the effect on kernel number.     

Cultivars of Hexaploid Wheat of Contrasting Stature and Chlorophyll Retention Differ in Cytokinin Content and Responsiveness

The work reported here compared cytokinin content and sensitivityin a selection of hexaploid wheat (Triticum aestivum L.) cultivarsusing the following measurements: leaf cytokinins at three timepoints during light-growth and at four 24 h intervals afterlight-grown plants were transferred to darkness; sensitivityof root growth to direct applications of isopentenyl adenosine([9R]iP); and, sensitivity of germination and subsequent rootand shoot growth to 18 h imbibition of seeds in benzyladenine(BA). Accumulation of zeatin riboside-type cultivars was greatestduring light-growth in Tibet Dwarf, a wheat with an extremedwarf phenotype, intermediate in Omar standard and dwarf cultivars,and lowest in the standard and dwarf versions of Itana. Cytokininlevels were otherwise not directly correlated to plant staturein these wheats. There were no cultivar-associated qualitativedifferences in the types of cytokinins detected in this study.During the 16 h light period, the content of zeatin riboside-typecytokinins increased up to tenfold and then declined to basallevels during dark growth. Chlorophyll retention during dark-growthwas correlated with leaf cytokinin content. Data collected ata restricted number of sampling points during dark-growth suggesteda cyclic accumulation of [9R]iP-type cytokinins and the apparentcycle in Tibet Dwarf was offset by 24 h. Tibet Dwarf showedthe greatest root growth inhibition after exposure of seedlingroots to [9R]iP or imbibition of seeds in BA. Neither of thesetreatments affected shoot growth in any of the cultivars. Wheat; Triticum aestivum ; cytokinin; zeatin riboside; benzyladenine; root inhibition