Development ofβ-amylase activity and polymorphism in wheat seedling shoot tissues8

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Abstract
Increasing β-amylase activity in wheat (Triticum aestlvum, var. Star) seedling shoot tissues was consistently accompanied by the development of a characteristic polymorphism of the enzyme, as shown by electrophoresis employing amylopectin-containing polyacrylamide gels. Very young shoot tissue contained one principal form of the enzyme (β1), whereas two other major forms (β2, β3) appeared complementary to this upon further growth. In vitro incubation experiments indicated that the polymorphism arose via a probably proteolytic conversion of β1 into β2 and β3. The conversion involved neither an activation of β-amylase nor a significant modification of β-amylase component pl values. The electrophoretic β-amylase patterns of subcellular leaf compartments suggested that β1 is synthesized in the cytoplasm of leaf mesophyfi cells and that the other forms arise upon transfer of this ‘primary’ form into the vacuole. The development of shoot β-amylase activity did not require light, but appeared to be under the negative control of the chloroplast and was stimulated by mineral nutrients. No clear relationship between β-amylase activity and starch metabolism was evident, since the leaf activity was largely absent from mesophyll protoplasts, could not be unequivocally demonstrated in the mesophyll chioroplasts, and developed regardless of whether the tissues contained significant amounts of starch or not.

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