Zea mays L. is less tolerant to drought than Sorghum bicolor L. In the present study, we
investigated the response of both plants to drought stress applied under field conditions by
withholding water for 10 d. The plant growth in terms of shoot fresh and dry weights was more
severely reduced in maize than in sorghum as a result of drought stress, consistently with reduction
of leaf relative water content (RWC). Gas exchange was also more greatly inhibited by drought in
maize than in sorghum. As a result, the water use efficiency (WUE) of maize was fluctuated
according to the time point during the day and in response to drought stress. In contrast, sorghum
was able to maintain largely constant WUE during the day in the well-watered plants as well as
under drought stress. This may indicate that sorghum was more efficiently controlled its water
status in particular water uptake than did maize. Studying the expression of four aquaporin genes
(PIP1;5, PIP1;6, PIP2;3 and TIP1;2) revealed that most of the genes responded weakly to drought
stress except PIP2;3 which was highly responsive to drought in sorghum but not in maize roots,
where it may have supported greater water uptake in sorghum, and thereby maintained higher leaf
RWC in sorghum than in maize and hence could account at least in part for the drought tolerance
of sorghum as compared to maize. The outcome of this study is that PIP2;3 may have role in
drought tolerance and maintenance of the WUE of sorghum plants compared to those of maize.