Translocation of 14C‐labelled photoassimilates to roots in barley: effects of mildew on partitioning in roots and the mitotic index

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Abstract
First leaves of barley seedlings grown in solution culture were inoculated with powdery mildew when the second leaf was fully emerged. 14C‐labelled carbon dioxide was fed to either first or second leaves of infected and non‐infected plants. Translocation of labelled photoassimilates into roots, and partitioning into soluble, storage and structural fractions were studied in tip, mid and basal regions of primary roots 24 h after feeding. Mildew reduced the total activity in the plant, but had little effect on assimilate distribution since the percentage activity translocated to roots was only transiently reduced, approximately 7 days after infection. Reduced import led to a reduction in the specific activity of different fractions within roots, reductions being greatest in root tips. These changes were similar whichever leaf was fed. Changes in specific activity became progressively more pronounced in the 10 days following infection, and were paralleled by a reduction in the mitotic index of root tips. It is concluded that meristematic activity, and thus the growth, of primary roots of barley is particularly sensitive to reductions in photoassimilation caused by powdery mildew infection.