Despite these punctual successes, aquaporin manipulation will
not be sufficient for developing optimal stress-resistant genotypes.
Whereas beneficial effects may be observed in certain conditions, it
will be difficult to optimize plant growth in a wide range of climatic
scenarios. In addition, targeting other genes and functions that may be
needed to avoid or repair the damage caused by the stresses has been
proposed [132,147]. The most relevant genes are those involved in
antioxidant metabolism, or encoding heat-shock proteins and stressresponsive
transcription factors.
8. Conclusions
During the last twenty years, tremendous progresses have been
achieved in understanding the structure and function of plant aquaporins.
The realization that plant aquaporins transport water but also
many other physiological substrates has contributed to the great
expansion of this research field. As a result, specific aquaporin isoforms
were identified for their contribution to physiological and developmental
processes as diverse as seed germination, regulation of leaf and
root hydraulics, lateral root emergence but also carbon fixation or
nutrient absorption. Yet, we are still far from a fully integrated view.
Aquaporins show a particularly high molecular diversity in plants and
the function of many isoforms, even in the most studied model species
(Arabidopsis, rice), is as yet undetermined. In addition, each aquaporin
often contributes, in concert with other isoforms, to several physiological
functions. Thus, thorough cell-specific expression analyses of the
whole plant aquaporin family, in plants under optimal or stress conditions,
are still needed. Reverse genetic analyses of aquaporins in plants
require sharp phenotyping procedures and careful examination of
possible genetic redundancies. However, they provide a necessary
functional dimension to these integrative studies.