Water Stress and Apical Morphogenesis in Barley

The formation of new primordia on the apical meristem of barley (Hordeum vulgare L.) was inhibited at levels of soil water potential (-1 bar and less) which had little or no effect on growth of the plant. Both leaf growth and morphogenesis of lateral spikelets on the developing ear proceeded at reduced rates at water-potential levels which completely suppressed primordium formation. This sensitivity of the apex to stress was unaffected by floral initiation and was apparently not due to changes in water potential in the apical tissues. Primordium formation was inhibited even though apical water potential was unchanged. Water stress suppressed the response of the apical meristem to an increase in the photoperiod to which the plant was exposed. In some circumstances, however, the photoperiodic response was displayed after the stress was relieved. During an episode of moderate water stress it was possible to observe an increase in the rate of primordium formation in response to an increase in light intensity.