Maintenance of the water use efficiency in the drought-stressed Sorghum bicolor L. as compared to Zea mays L. in relation to differential expression of aquaporin genes

Abstract

Zea mays L. is less tolerant to drought than Sorghum bicolor L. In the present study, weinvestigated the response of both plants to drought stress applied under field conditions bywithholding water for 10 d. The plant growth in terms of shoot fresh and dry weights was moreseverely reduced in maize than in sorghum as a result of drought stress, consistently with reductionof leaf relative water content (RWC). Gas exchange was also more greatly inhibited by drought inmaize than in sorghum. As a result, the water use efficiency (WUE) of maize was fluctuatedaccording to the time point during the day and in response to drought stress. In contrast, sorghumwas able to maintain largely constant WUE during the day in the well-watered plants as well asunder drought stress. This may indicate that sorghum was more efficiently controlled its waterstatus 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 droughtstress 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 leafRWC in sorghum than in maize and hence could account at least in part for the drought toleranceof sorghum as compared to maize. The outcome of this study is that PIP2;3 may have role indrought tolerance and maintenance of the WUE of sorghum plants compared to those of maize.