The Sources of Carbon for Developing Leaves of Barley

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Abstract
The contribution of carbon from various sources to leaves 2, 3 and 4 of Proctor barley as they expanded, was determined using data from photosynthetic measurements and 14CO2 feeding. By the time that it was half expanded, the growing leaf provided about half its carbon requirement from current photosynthesis, and this proportion increased further during the later phases of expansion. In all, about half of the carbon in a fully expanded leaf was derived from local photosynthesis. The pattern of supply from older leaves changed with time, depending on their age and photosynthetic activity. Shading the third or expanding fourth leaf led to enhanced photosynthetic activity in the unshaded leaf, but this was not sufficient to compensate fully for the reduction due to shade treatment, and carbon supply for the growing leaf was reduced.