Aliphatic alcohols naturally exist in many organisms as important cellular components; however, their roles in extracellular polymer biosynthesis are poorly defined. We report here the isolation and characterization of a rice (Oryza sativa) male-sterile mutant, defective pollen wall (dpw), which displays defective anther development and degenerated pollen grains with an irregular exine. Chemical analysis revealed that dpw anthers had a dramatic reduction in cutin monomers and an altered composition of cuticular wax, as well as soluble fatty acids and alcohols. Using map-based cloning, we identified the DPW gene, which is expressed in both tapetal cells and microspores during anther development. Biochemical analysis of the recombinant DPW enzyme shows that it is a novel fatty acid reductase that produces 1-hexadecanol and exhibits >270-fold higher specificity for palmiltoyl-acyl carrier protein than for C16:0 CoA substrates. DPW was predominantly targeted to plastids mediated by its N-terminal transit peptide. Moreover, we demonstrate that the monocot DPW from rice complements the dicot Arabidopsis thaliana male sterile2 (ms2) mutant and is the probable ortholog of MS2. These data suggest that DPWs participate in a conserved step in primary fatty alcohol synthesis for anther cuticle and pollen sporopollenin biosynthesis in monocots and dicots.

• Background The plant cuticle is an extracellular lipophilic biopolymer covering leaf and fruit surfaces. Its main function is the protection of land-living plants from uncontrolled water loss. In the past, the permeability of the cuticle to water and to non-ionic lipophilic molecules (pesticides, herbicides and other xenobiotics) was studied intensively, whereas cuticular penetration of polar ionic compounds was rarely investigated. • Recent Progress Recent work measuring cuticular penetration of inorganic and organic ions is presented; the effects of molecular size of ions, temperature, wax extraction, humidity and plasticizers strongly support the conclusion that ions penetrate cuticles via water-filled pores. The cuticle covering stomata and trichomes forms the preferential site of ion penetration. This indicates that cuticles possess a pronounced lateral heterogeneity: the largest fraction of the cuticle surface is covered by the lipophilic domains of cutin and wax, but to a certain extent polar domains are also present in the cuticle, which form preferential sites of penetration for polar compounds. • The Future The chemical nature of these polar domains awaits detailed characterization, which will be of major importance in agriculture and green biotechnology, since polar paths of diffusion represent the most important transport routes for foliar-applied nutrients. Furthermore, many compounds acting as inducers of gene expression in transgenic plants are ionic and need to penetrate the cuticle via polar paths in order to be active.

Analysis of fruit surface suberization leads to the identification and characterization of AtMYB107 and AtMYB9 as positive regulators of suberin deposition in A

Apoplastic transport barriers in the roots of rice (Oryza sativa L. cv. IR64) and corn (Zea mays L. cv. Helix) were isolated enzymatically. Following chemical degradation (monomerization, derivatization), the amounts of aliphatic and aromatic suberin monomers were analysed quantitatively by gas chromatography and mass spectrometry. In corn, suberin was determined for isolated endodermal (ECW) and rhizo-hypodermal (RHCW) cell walls. In rice, the strong lignification of the central cylinder (CC), did not allow the isolation of endodermal cell walls. Similarly, exodermal walls could not be separated from the rhizodermal and sclerenchyma cell layers. Suberin analyses of ECW and RHCW of rice, thus, refer to either the entire CC or to the entire outer part of the root (OPR), the latter lacking the inner cortical cell layer. In both species, aromatic suberin was mainly composed of coumaric and ferulic acids. Aliphatic suberin monomers released from rice and corn belonged to five substance classes: primary fatty acids, primary alcohols, diacids, ω-hydroxy fatty acids, and 2-hydroxy fatty acids, with ω-hydroxy fatty acids being the most prominent substance class. Qualitative composition of aliphatic suberin of rice was different from that of corn; (i) it was much less diverse, and (ii) besides monomers with chain lengths of C₁₆, a second maximum of C₂₈ was evident. In corn, C₂₄ monomers represented the most prominent class of chain lengths. When suberin quantities were related to surface areas of the respective tissues of interest (hypodermis and/or exodermis and endodermis), exodermal cell walls of rice contained, on average, six-times more aliphatic suberin than those of corn. In endodermal cell walls, amounts were 34 times greater in rice than in corn. Significantly higher amounts of suberin detected in the apoplastic barriers of rice corresponded with a substantially lower root hydraulic conductivity (Lp_r) compared with corn, when water flow was driven by hydrostatic pressure gradients across the apoplast. As the OPR of rice is highly porous and permeable to water, it is argued that this holds true only for the endodermis. The results imply that some caution is required when discussing the role of suberin in terms of an efficient transport barrier for water. The simple view that only the quantity of suberin present is important, may not hold. A more detailed consideration of both the chemical nature of suberins and of the microstructure of deposits is required, i.e. how suberins impregnate wall pores.