Auxin regulates SNARE-dependent vacuolar morphology restricting cell size

The control of cellular growth is central to multicellular patterning. In plants, the encapsulating cell wall literally binds neighbouring cells to each other and limits cellular sliding/migration. In contrast to its developmental importance, growth regulation is poorly understood in plants. Here, we reveal that the phytohormone auxin impacts on the shape of the biggest plant organelle, the vacuole. TIR1/AFBs-dependent auxin signalling posttranslationally controls the protein abundance of vacuolar SNARE components. Genetic and pharmacological interference with the auxin effect on vacuolar SNAREs interrelates with auxin-resistant vacuolar morphogenesis and cell size regulation. Vacuolar SNARE VTI11 is strictly required for auxin-reliant vacuolar morphogenesis and loss of function renders cells largely insensitive to auxin-dependent growth inhibition. Our data suggests that the adaptation of SNARE-dependent vacuolar morphogenesis allows auxin to limit cellular expansion, contributing to root organ growth rates.

Cytokinin and Auxin Effect on the Terpenoid Profile of the Essential Oil and Morphological Characteristics of Shoot Cultures of Artemisia alba

The influence of plant growth regulators (PGR) on the essential oil composition and in vitro development of A. alba shoot cultures was studied. Two types of oils were determined, based on their terpenoid content. Close relations between the morphogenetic effects of PGR and the essential oil profile of the species were observed. Predominance of root over shoot development was connected with a drop in the amounts of sesquiterpenoids and the direction of biosynthesis towards oxygenated monoterpenoids in the PGR-free control medium, as well in those with 1.0 mg L−1 indole-3-butyric acid (IBA) supplementation. On the contrary, lack of root formation and stimulated callusogenesis caused by the addition of 0.2 mg L−1 6-benzyladenine (BA), irrespectively of the presence of IBA (either 0.5 mg L−1 or 1.0 mg L−1), resulted in the strong prevalence of sesquiterpenoids in the oils. These results are indicative that the morphological development of A. alba shoot cultures affects the terpenoid biosynthetic pathway bringing out the hypothesis for a possible root to shoot signaling.

Effect of Root-promoting Products in the Propagation of Organic Olive (Olea europaea L. cv. Cornicabra) Nursery Plants

Olive cuttings root well using synthetic auxin indole-3-butyric acid (IBA). However, European and North American regulations do not allow the use of synthetic products to obtain organic vegetative propagation materials. In this work, we evaluated different products that could replace IBA in the propagation of olive cv. Cornicabra leafy-stem cuttings. In 2003, six products with a known auxin effect were assessed: IBA, algae extract, brewer's yeast, a bed of sunflower seed, seaweed dry extract (Sm-6 Organico™), and an extract of macerated seeds (Terrabal Organico™). The basal end of cuttings was treated with one of these products and placed on a mist bed with basal temperature control. After 2 months, rooting percentage, number of roots per cutting, number of cuttings with callus formation, and number of cuttings with basal thickening were determined. No significant differences were found in rooting percentage or number of roots per cutting between IBA and Terrabal Organico™ and Sm-6 Organico™. These last products had significantly higher percentage of rooted cuttings without callus formation than IBA. In 2004, a new trial was conducted in which seven treatments were evaluated: IBA applied for 7 s; Terrabal Organico™ applied for 1, 4, and 8 h; and Sm-6 Organico™ applied for 1, 4, and 8 h. No significant differences in rooting percentage or number of roots per cutting were observed between IBA and Terrabal Organico™ applied for 1 h, whereas all the Sm-6 Organico™ treatments had significantly lower rooting percentages than IBA. Both rooting percentage and the percentage of rooted cuttings without callus development decreased significantly as treatment duration with Terrabal Organico™ increased. Therefore, Terrabal Organico™ could produce a toxic effect on cuttings when treatment duration is increased. Thus, Terrabal Organico™ could be a valid alternative to IBA in the propagation of organic olive plants of cv. Cornicabra when applied to the basal end of cuttings for 1 h.