Photosynthetic characteristics of modern and primitive wheat species in relation to ontogeny and adaptation to light

Abstract

Some characteristics of photosynthesis in seven species of Triticum and two of Aegilops were examined. Differences between species in the rate of net photosynthesisper unit area were more pronounced in later formed leaves than in earlier ones, flagleaves showing the greatest range of photosynthesis rates. The range in flag leaf netphotosynthetic rates was greatest for plants grown under high light intensity. Netphotosynthetic rates of flag leaves of diploid species of Triticum, measured under highlight intensity, increased progressively with increase in light intensity during growth, whereas the rates for the Aegilops species and the tetrapbid and hexaploid lines ofTriticum reached their maxima at intermediate light intensity during growth.Under one set of environmental conditions during growth, a diffusion resistancestudy of flag leaf photosynthesis revealed that both the gas phase resistance and“residual” (“mesophyll” or “intracellular”) resistance contribute to the observeddifferences in photosynthetic rate. When the average values of resiJual resistancefor each genotype were plotted against the corresponding gas phase resistance apositive correlation, to which all but three of the lines adhered, was found, an increaseof 0.5 s cm−1in gas phase resistance being associated with an increase of I. 0 s cm-1in residual resistance.When adaptaticJn to cifferent light intensities occurred over a prolongedperiod, the stomatal density on the flag leaf of two diploid lines and of a hexapbid(T. spelta) line adapted upwards to high light but did not do so for T. aestivum.However, the adaptation was small and of minor significance to the overall photosyntheticadaptation. Variation in stomatal density was not a major determinantof variation in stomatal resistance.Specific leaf weight bore no consistent relation with either photosyntheticrate or residual resistance. © 1973 CSIRO.