The effects of a severe water deficit on total root (L(t)) and axial (L(x)) hydraulic conductances and on the development of the hypodermis, endodermis, and xylem were studied in sorghum (Sorghum bicolor L.). Water deficit was imposed in the upper rooting zone while the lower zones were kept moist. L(t) and L(x) were based on water flow rates obtained by applying suction to proximal xylem ends of excised roots. The development of the hypodermis, endodermis, and other tissues were examined by staining with fluorescent berberine hemisulfate and phloroglucinol-HCl. The L(t) value (x 10(-8) meters per second per megapascal) for unstressed control roots was 22.0 and only 5.9 for stressed roots. The low L(t) in stressed roots was attributed, in part, to accelerated deposition of lignin and suberin in the hypodermis and endodermis. Calcofluor, an apoplastic tracer that binds to cellulose, was blocked in stressed roots at the lignified and suberized outer tangential walls of the hypodermis but readily penetrated the cortical walls of similar root regions in controls where the casparian band was not developed. L(x) per unit root length was about 100 times lower in stressed roots than in controls because of the persistence of late metaxylem cross-walls and the smaller diameter and lower number of conductive protoxylem and early metaxylem vessels.

Numerous studies have associated increased stomatal resistance with response to water deficit in cereals. However, consideration of change in leaf form seems to have been neglected. The response of adaxial and abaxial stomatal resistance and leaf rolling in rice to decreasing leaf water potential was investigated. Two rice cultivars were subjected to control and water stress treatments in a deep (1-meter) aerobic soil. Concurrent measurements of leaf water potential, stomatal resistance, and degree of leaf rolling were made through a 29-day period after cessation of irrigation. Kinandang Patong, an upland adapted cultivar, maintained higher dawn and midday leaf water potential than IR28, a hybrid selected in irrigated conditions. This was not explained by differences in leaf diffusive resistance or leaf rolling, and is assumed to result from a difference in root system extent.Stomatal resistance increased more on the abaxial than the adaxial leaf surface in both cultivars. This was associated with a change in leaf form or rolling inward of the upper leaf surface. Both responses, increased stomatal resistance and leaf rolling, were initiated in a similar leaf water potential range (-8 to -12 bars). Leaves of IR28 became fully rolled at leaf water potential of about -22 bars; however, total leaf diffusive resistance was only about 4 to 5 seconds per centimeter (conductance 0.25 to 0.2 centimeter per second) at that stage. Leaf diffusive resistance and degree of leaf rolling were linearly related to leaf water potential. Thus, leaf rolling in rice may be used as an estimate of the other two less obvious effects of water deficit.Increased stomatal resistance as a plant response to water stress, has recently been reviewed (1,3,22 Control plants were grown in large drums (75-cm diameter and 100 cm deep) which had adequate drainage at the base and were kept well watered through the experiment. Four control drums were used for each variety. Two replications were sampled from the control plants at each sampling.Stress treatment plants were grown in a large well drained concrete tank (6.8 x 3.5 x 1.35 m) which simulated a deep (100-cm) aerobic upland clay-loam soil with 35 cm of subsoil gravel to enhance drainage. Each cultivar was planted to an area of 11.9 2 m2, which was subdivided into four sampling plots. In both treatments, rice was directly sown in dry soils in rows 25 cm apart at a rate of 100 kg/ha (10 g/m2).

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Sensitivity of rice (Oryza sativaL.) to flowering stage water stress is well recognized. However, as with other cereals, there is lack of field research which quantifies plant and soil water status at the flowering stage in relation to water stress‐mediated reductions in crop yield. A rice cultivar was subjected to six levels of irrigation using a line‐source sprinkler system in the field on a silty clay loam, Typic Hapludoll soil during the dry season in which a stable rainless period is the climatic norm. Irrigation level 6 (wettest) was irrigated at the rate of 1.10 of pan evaporation while level 1 (driest) relied solely on pre‐line source water storage. Evapotranspiration during the 15‐day treatment period at flowering was linearly related to grain yield. The dominant yield component influencing grain yield was spikelet sterility. At irrigation level 6 in which soil moisture was reduced to 95% of the total crop extractable water, midday leaf water potential was −0.9 MPa, and spikelet sterility was 20%. At level 1, soil moisture was 28.6% of the total crop extractable water, midday leaf water potential −2.5 MPa, and spikelet sterility 73%. The exsertion of the rice panicle was found to be sensitive to changes in leaf water potential. Up to 30% of water stress‐mediated spikelet sterility was associated with poor panicle exsertion. The degree of panicle exsertion during flowering stage water stress may be a useful visual criterion in the selection of breeding lines with high degree of reproductive stage drought resistance.