Some aspects of carbon relations in the barley – Helminthosporium teres complex. II. The effects of infection upon net accumulation of carbon in the tissues

First leaves of seedlings of the barley varieties Parkland (susceptible) and C.I. 5791 (resistant) were inoculated with Helminthosporium teres and the net accumulation of carbon (NA) in such leaves and in the uninoculated second leaves of these plants was examined in long-term experiments. In infected leaves of Parkland, NA in the light period of the diurnal cycle was maintained near the levels of controls even when photosynthetic capacity had decreased by ca. 50%, though NA in the dark period had increased 300–400%. However, neither this carbon nor that entering metabolism via β-carboxylation in the light was sufficient to compensate for the loss of photosynthetic capacity over 24 h. Translocation experiments showed that while infection did not increase the movement of carbon from the uninoculated second to infected first leaves, export of carbon by the first leaves (normally high) was greatly reduced, and this retained photosynthate appeared largely responsible for the maintenance of NA in the infected leaves. NA in the uninoculated second leaves of infected plants was reduced only while these leaves were heavily dependent on the first leaves for photosynthate. In infected leaves of C.I. 5791, though photosynthetic capacity dropped and β-carboxylation increased while the pathogen was developing, there was little effect on NA over 24 h. The implications of the effects of infection on NA are discussed.