The Structure of the Mesophyll of Flag Leaves in Three Triticum Species

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Abstract
Flag leaves of Triticum urartu, T. monococcum and T. aestivum cv. Professeur Marchal were examined by light and electron microscopy and by separating cells to determine whether differences in leaf anatomy could be related to known differences in their light-saturated rates of photosynthesis. Mesophyll cells from the three species were lobed and orientated with their long axis parallel to the veins. The longest, most-lobed cells flanked the sclerenchyma associated with the veins. Mean cell dimensions were greatest in Professeur Marchal, but there was no significant difference in the ratio of the mesophyll cell surface area to cell volume amongst the three species. Flag leaves of T. urartu showed the highest rates of photosynthesis and were also the thickest, with closely-spaced veins from which many of the mesophyll cells radiated. These flag leaves also had significantly more (21.9 per cent) air-filled space, and the highest ratio (15.2) of mesophyll cell surface exposed to this air-filled space per unit leaf area. Ways in which these anatomical characteristics may contribute to the higher rate of photosynthesis are discussed.