A viviparous mutant of maize exhibiting permanent water stress symptoms |
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Authors: | Anna Giulini Nicoletta La Rocca Diego Durantini Antonino Malgioglio Francesca Dalla Vecchia Priscilla Manzotti Gabriella Consonni Nicoletta Rascio Giuseppe Gavazzi |
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Institution: | 1.Dipartimento di Produzione Vegetale,Università degli Studi di Milano,Milan,Italy;2.Dipartimento di Biologia,Università degli Studi di Padova,Padova,Italy |
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Abstract: | In maize vivipary, the precocious germination of the seed while it is still attached to the ear is a reliable phenotype for
the identification of mutants impaired in the biosynthesis or response to abscisic acid (ABA). Here we present the characterization
of a new allele of vp10, a gene encoding for a cofactor (MoCo) required for the last step of ABA biosynthesis. The lesion in this gene leads to a
reduction in the endogenous ABA level. Embryonic messenger RNAs of the ABA inducible genes glb1, lea3, and rab17 are barely detectable, although their level increases when stimulated by exogenous ABA administration. These findings confirm
that the mutant can be ascribed to a defect in ABA biosynthesis. In the absence of water stress, mutant plants grow like wild-type
siblings; however when mutant tissues are exposed to air they differ from non-mutant ones by showing a higher rate of water
loss, of transpiration and of stomatal conductance. These events are restored to almost normal values by adding exogenous
ABA. All these defects are ascribable to an impairment in the regulation of stomatal opening since, in contrast to wild-type,
some of the mutant stomata exhibit partially or totally open rims. The defect in ABA biosynthesis is also associated with
loss of regulation of the expression of rab17 and rab28, two genes expressed in vegetative tissues under abiotic stress. These genes are constitutively expressed in the mutant plant
tissues independently of the water regime applied. Thus this mutant may provide a tool for the study of molecular mechanisms
underlying drought-stress responses in crop plants. |
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