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Low Ribonuclease I Activity Prior to Cold Acclimation in Freeze Selected Winter Barley¹

Etiolated 4-day-old shoot tissue of freeze-resistant winter barley (Hordeum vulgare L.) contains low ribonuclease I (EC 3.1.27.5) activity compared to susceptible cultivars, an indigenous distinction found in nonacclimated tissue. The objective of this report was to determine if a shift in plant population caused by freeze selection resulted in changes in ribonuclease activity of leaf tissue. The RNA-degrading activity in tissue extracts was determined spectrophotometrically and by assays using disc polyacrylamide gel electrophoresis (PAGE) of tissue extracts. Increased freeze survival in hybrid lines and reduction of RNA-degrading activity were demonstrated by subjecting F₅ plants to freeze selection. Extracts from tissue of the freeze-susceptible (‘Tennessee Winter’) cultivar contained higher total activity than was present in extracts from the freeze-resistant (‘Dicktoo’) cultivar for range of tissue ages. The prominent distinction between the cultivars in 20-day leaf tissue was a slowly migrating ribonuclease band found at the midpoint of gels containing extracts of the susceptible cultivar, which was essentially absent in the resistant cultivar. A consequence of selection for freeze resistance in winter barley was a reduction in variation of enzyme activity among plants within a cultivar and a lowering of activity. These data were consistent with results showing a selective shift from high to lower activity in composite extracts of shoot tissue grown from seed of unselected and freeze selected plants, respectively.

Key Words: Hordeum vulgare L. • Hybrid population • Development stage • Ribonuclease methods • Winter-hardiness • Population characterization

² Professor, Plant Science and Chemistry Dep., South Dakota State Univ., Brookings, SD 57007, and assistant professor, Dep. of Plant and Soil Science, Montana State Univ., Bozeman, MT 59717, respectively. Assistantship support provided to T.K.B. by the Chemistry Dep., South Dakota State Univ.

Received for publication October 21, 1985.