Production of localized tissue necrosis by the Les1 allele occurs not only in the leaves and leaf sheaths of Les1/Les1 plants but apparently also in the roots. Sibling comparisons were made between 27 Les1/Les1, 12 +/Les1 and 38 +/+ 10- to 12-day-old seedlings from several different F2 families. Les1/Les1 seedlings exhibited small areas of tan discoloration and cellular collapse along the primary roots and in the central portions, or at the points of attachment, of some of the adventitious branch roots of the primary and lateral roots. The roots of all +/+ and most +/Les1 plants were unblemished.

The lesions on the primary roots were 2-5 mm long and about 1 mm wide. Lesions on the branch roots covered the circumference of the root and were 2-4 mm long. When lesions were present at the base of the branch roots they occasionally extended into a patch on the primary or lateral root.

The extent of lesion expression was variable. Some Les1/Les1 root systems had a decidedly brown appearance, while on others only a few lesions could be found. Whether this variation is genetic, physiological, or environmental is not known. Lesion expression on +/Les1 roots, when it was found, was always low. The severity of root-lesion expression did not appear to be correlated with the severity of leaf-lesion expression. This lack of correlation between expression in leaves and roots suggests that root lesions are not simply a physiological result of leaf-lesion formation. It also indicates that Les1 expression may be controlled by different environmental or physiological factors in different tissues.

The plants were grown in 8" x 1.5" (top dia.) conical plastic containers (Super-cell Cone-Tainers) filled with Pro-mix soil mixture. Following germination at 30 C, the seedlings were placed in growth chambers set for 14h 25 C days and 10h 20 C nights with an irradiance of 350 uE/m² /sec. Les1 genotypes were scored on the basis of wt1 expression (wt1 is a closely linked marker) or on the basis of relative severity of leaf-lesion expression. The roots were exposed intact by removing the soil plugs from the containers and separating the roots from the soil in a basin of water.

Craig Echt
 
 

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