The surface of a pollen grain consists of an outermost coat and an underlying wall. In maize (Zea mays L.), the pollen coat contains two major proteins derived from the adjacent tapetum cells in the anthers. One of the proteins is a 35-kDa endoxylanase (Wu, S. S. H., Suen, D. F., Chang, H. C., and Huang, A. H. C. (2002) J. Biol. Chem. 277, 49055-49064). The other protein of 70 kDa was purified to homogeneity and shown to be a ␤-glucanase. Its gene sequence and the developmental pattern of its mRNA differ from those of the known ␤-glucanases that hydrolyze the callose wall of the microspore tetrad. Mature pollen placed in a liquid medium released about nine major proteins. These proteins were partially sequenced and identified via GenBank TM data bases, and some had not been previously reported to be in pollen. They appear to have wall-loosening, structural, and enzymatic functions. A novel pollen wall-bound protein of 17 kDa has a unique pattern of cysteine distribution in its sequence (six tandem repeats of CX 3 CX 10 -15 ) that could chelate cations and form signal-receiving finger motifs. These pollen-released proteins were synthesized in the pollen interior, and their mRNA increased during pollen maturation and germination. They were localized mainly in the pollen tube wall. The pollen shell was isolated and found to contain no detectable proteins. We suggest that the pollen-coat ␤-glucanase and xylanase hydrolyze the stigma wall for pollen tube entry and that the pollen secrete proteins to loosen or become new wall constituents of the tube and to break the wall of the transmitting track for tube advance.In plants, sexual reproduction is initiated when the pollen grain (male component) lands on the stigma of the style (female component) in the flowers (for reviews, see Refs.

Pollen coat contains ingredients that interact with the stigma surface during sexual reproduction. In maize (Zea mays L.) pollen coat, the predominant protein is a 35-kDa endoxylanase, whose mRNA is located in the tapetum cells enclosing the maturing pollen in the anthers. This 2.0-kb mRNA was found to have an open reading frame of 1,635 nucleotides encoding a 60-kDa pre-xylanase. In developing anthers, the pre-xylanase protein appeared prior to the 35-kDa xylanase protein and enzyme activity and then peaked and declined, whereas the 35-kDa xylanase protein and activity continued to increase until anther maturation. An acid protease in the anther extract converted the inactive prexylanase to the active 35-kDa xylanase in vitro. The protease activity was inhibited by inhibitors of serine proteases but unaffected by inhibitors of cysteine, aspartic, or metallic proteases. Sequence analysis revealed that the 60-kDa pre-xylanase was converted to the 35-kDa xylanase with the removal of 198 and 48 residues from the N and C termini, respectively. During in vitro and in vivo conversions, no intermediates of 60 -35 kDa were observed, and the 35-kDa xylanase was highly stable. The pre-xylanase was localized in the tapetum-containing anther wall, whereas the 35-kDa xylanase was found in the pollen coat. The significance of having a large non-active pre-xylanase and the mode of transfer of the xylanase to the pollen coat are discussed. A gene encoding the barley (Hordeum vulgare L.) tapetum xylanase was cloned; this gene and the gene encoding the seed aleurone-layer xylanase had strict tissuespecific expressions.A major step in sexual reproduction in plants is the interaction between the male gamete-containing pollen and the pollen-receiving stigma in flowers (1-4). This interaction manifests at the contact between the pollen coat and the surface structures of the stigma. The coat of pollen contains special constituents that are essential to the initial sexual contact and thus the success of fertilization. Its chemical compositions vary, depending on the species. In insect or self-pollinating species, of which Brassica and Arabidopsis are the best studied (5-10), the pollen coat is thick and contains steryl esters and very non-polar lipids as the major lipids and oleosins as the predominant proteins. The lipids are for water-proofing, whereas the amphipathic oleosins may act as a "wick" for water uptake to initiate germination. These major coat lipids and proteins are synthesized and accumulated initially in the tapetum cells, which enclose the pollen locule in the anthers.

Self‐assembled and aligned in a block! Self‐assembled CdSe nanorods within the poly(4‐vinylpyridine) nanodomains of a poly(styrene‐b‐4‐vinylpyridine) diblock copolymer thin film can be aligned under the influence of the polarization forces created by an applied electric field. The electron mobilities of the CdSe/poly(4‐vinylpyridine) nanodomains in the out‐of‐plane cases were about eight times larger than those in the in‐plane cases.