Figure 4.—

Histological analyses of S. latifolia wild type and Y chromosome deletion mutants. An outline of anther development is given on the left. The middle column shows sections of wild-type anthers, and the right-hand column displays sections of anther developmental mutants. Detailed descriptions of the wild-type anther development and Y-chromosome deletion mutant histology are given in supplemental Figures S1 and S2 at http://www.genetics.org/supplemental/. The anther rudiment in female plants stops developing before the formation of the parietal layers (A). The anthers of the Y chromosome deletion mutant asexua 1 (asx1) strongly resemble female anther rudiments (B). The inner subwhorl anthers of the anther development mutant ad1 also do not develop beyond this stage, probably because of the accumulation of deposits around the connective (C). Wild-type male anthers develop the primary parietal layer and the sporogenous tissue (D). In the anther development mutant ad6, the primary parietal layer is altered, but the sporogenous tissue is able to form microspore mother cells (E). In the ad3 mutant, abaxial locule development is arrested prematurely (F). Unlike the wild-type anthers, where no difference in the staining ability of the secondary parietal layers is observed (G), the inner secondary parietal layer of the ad7 mutant differentiates into a densely-stained tapetum-like layer (H). In the wild-type anthers, the tapetum becomes densely stained after the formation of all anther layers, and this process is connected with its differentiation (I). However, the tapetum is not stained in the pollen fertility mutant pf1 (J). During meiosis and tetrad formation, the tapetum starts to degenerate and its cells are released from each other but remain attached to the other anther layers (K). In the pf2 mutant, the tapetum is released from the anther layers and forms an agglutinate inside the anther (L). The wild-type microspores, when released from the tetrads, are round shaped (M), but in mutant pf3, the microspores are irregular in shape (N). Mutant pf4 forms round microspores, and the endothecial and tapetal cells do not degenerate, as deduced from the fact that the endothecium is present and the tapetal cells remain attached to each other (O). When compared to the wild type (P), both the anther locules and the pollen grains of the outer subwhorl of the mutant ad1 are abnormally small (Q). dep, Deposits; epid, epidermis; 1° par, primary parietal layer; spor, sporogenous cells; mmc, microspore mother cells; ab, abaxial locule; ad, adaxial locule; 2° par, secondary parietal layer; tap, tapetum; mi, microspores; pg; pollen grains. Bars, 10 μm (A–C, E, H, J, O), 25 μm (D, G, I, K–N, P, Q), and 50 μm (F).