Olive (Olea europaea L.) is one of the most important oil crops in the Mediterranean basin. Biotechnological improvement of this species is hampered by the recalcitrant nature of olive tissue to regenerate in vitro. In previous investigations, our group has developed a reliable Agrobacterium-mediated transformation protocol using olive somatic embryos as explants (Torreblanca et al., 2010). Embryogenic cultures derived from radicles of matured zygotic embryos are infected with Agrobacterium tumefaciens, AGL1 strain, containing a binary plasmid with the gene of interest and the nptII selection gene. After a meticulous selection procedure, carried out using solid and liquid media supplemented with paromomycin, the putative transformed lines are established. A preliminary confirmation of their transgenic nature is carried out through PCR amplification. Afterwards, plants can be obtained through an efficient regeneration protocol, whose main characteristics are the use of a low-ionic-strength mineral formulation, a phase in liquid medium for synchronization of cultures and the use of semi-permeable cellulose acetate membranes for embryo maturation (Cerezo et al., 2011). Final confirmation of transgene insertion is carried out through Southern or Northern analysis using leaf samples of regenerated plants.

Estimation of stomatal aperture using low viscosity silicone-base impression material has the advantage of working with the whole leaf. The developmental stage and the environment strongly affect the stomatal aperture. Therefore, it is mandatory to have accurate estimations of the stomatal aperture of intact leaves under different situations. With this technique, it is possible to get the real picture at any moment. The outputs of the data include studies on cell area and morphology, epidermis cell and stomata lineages, among others. This protocol is useful for the accurate estimation of stomatal aperture in many samples of intact leaves in Arabidopsis thaliana.

Since the discovery of the CRISPR (clustered regularly interspaced short palindromic repeats)-associated protein (Cas) as an efficient tool for genome editing in plants (Li et al., 2013; Shan et al., 2013; Nekrasov et al., 2013), a large variety of applications, such as gene knock-out, knock-in or transcriptional regulation, has been published. So far, the generation of multiple mutants in plants involved tedious crossing or mutagenesis followed by time-consuming screening of huge populations and the use of the Cas9-system appeared a promising method to overcome these issues. We designed a binary vector that combines both the coding sequence of the codon optimized Streptococcus pyogenes Cas9 nuclease under the control of the Arabidopsis thaliana UBIQUITIN10 (UBQ10)-promoter and guide RNA (gRNA) expression cassettes driven by the A. thaliana U6-promoter for efficient multiplex editing in Arabidopsis (Yan et al., 2016). Here, we describe a step-by-step protocol to cost-efficiently generate the binary vector containing multiple gRNAs and the Cas9 nuclease based on classic cloning procedure.

Measurement of auxin transport capacity provides quantitative data on the physiological machinery involved in auxin transport within plants. This technique is easy to perform and gives quick results. Radiolabelled auxin (indole-3-acetic-acid) is fed into the roots of Medicago truncatula via an agar block. The resulting radioactivity from radiolabelled auxin uptake in the roots is measured with a liquid scintillation counter. Here, we describe the measurement of auxin transport capacity around the nodulation susceptible zone in young seedling roots of M. truncatula in response to rhizobia inoculation. Similar assays could be adapted in other plant species and to answer other biological questions.

Low-molecular-weight (LMW) thiols are a class of highly reactive compounds due to their thiol moiety. They play important roles in the maintenance of cellular redox homeostasis, detoxification, and development. Monobromobimane (mBBr) is weakly fluorescent but selectively reacts with thiols to yield highly fluorescent thioethers (mBSR) products, which is especially useful for the quantification of LMW thiols. The stable mBSR products can be separated by high-performance liquid chromatography (HPLC) equipped with a fluorescent detector. The main cellular LMW thiols are L-cysteine, gamma-glutamylcysteine, and glutathione (GSH). The following protocol describes the extraction and quantification of L-cysteine, gamma-glutamylcysteine, and glutathione from Arabidopsis tissues as reported (Xiang and Oliver, 1998; Zhao et al., 2014; Wang et al., 2015) with minor revision. Modifications may be required if the HPLC system or the C18 column is different.

The leaf is the major functional part of the shoot performing the bulk of photosynthetic activity. Its development is relatively plastic allowing the plant to adapt to environmental changes by modifying leaf size and anatomy. Moreover, a leaf is made up of various distinct cell layers, each having specialized functions. To understand functional adaptation and the development of the leaf it is essential to obtain cross sections throughout leaf development and at maturity (Kalve et al., 2014). Here, we describe a protocol for transverse sectioning of Arabidopsis thaliana leaves using resin embedding. This protocol provides a reliable platform to yield high quality images of cross sections allowing study of development of various tissue layers across the transversal axis of the leaf. As this method is an adaptation of the protocol developed for the Arabidopsis root tip by Beeckman and Viane (1999) and De Smet et al. (2004), it can easily be modified to accommodate other organs and species.