Formation, Elongation, and Longevity of Barley Root Hairs1

Abstract The root hairs of 1‐month‐old intact barley ( Hordeum vulgare L.) seedlings, grown in a growth chamber, were observed at three different constant root temperatures. Formation and elongation of root hairs were recorded hourly over 24‐hour periods. Death of root hairs was indicated by the use of neutral red; from these data longevity was determined. The number of root hairs formed was greater at 18 and 26C than at 15C. Formation was periodic, with three maxima and two minima rates. The changes in formation rates did not coincide precisely at each temperature. Elongation was greater at 26C than at 15C. The elongation rate was constant for each of the three temperatures over a 24‐hour period. Longevity of root hairs was 40, 45, and 55 hours at 26, 18, and 15C, respectively. A maximum number of deaths occurred 13 to 15 hours after the initiation of the light period. Phasic formation and death of root hairs may affect diurnal water absorption due to changes in the living and dead root hair areas. Elongation rate may also affect diurnal water uptake, in that elongation rate is affected by soil conditions.