Fig. 2.
(A to F) Internal composition after 48-hour N2 and O2 application via hoses. (A) Both gases increased total cell counts, and (B) most cells were somatic. (C) N2 gas resulted in about a threefold increase in presumptive and differentiated archesporial cells, as compared to O2 gas and no treatment. (D) The ratio of central archesporial cells to total L2-d cells was lower in O2-treated anthers than in untreated anthers, whereas N2-treated anthers had much higher ratios that dropped later during somatic bilayer formation. (E) Bilayer formation was measured as a proportion of L2-d somatic ring cells on the lobe arch that had divided periclinally. (F) Transverse reconstructions of single lobes in gas treatments. White arrowheads, periclinal divisions; purple dots, archesporial cells. Scale bar, 20 μm. (G and H) Cellular composition after 48-hour gas application via needle. All needle treatments resulted in excess pro liferation and excess archesporial cells; thus, compressed air was used as a control. (G) Central presumptive + differentiated archesporial counts were significantly higher in N2 and slightly lower in O2 as compared to compressed air. (H) The ratio of central archesporial cells to total L2-d cells is high in N2 early, dropping later from precocious somatic development. (I and J) In the chemical injections, needle puncture alone caused proliferation and excess archesporial cells versus untreated anthers, and served as a control. (I) KI promoted and H2O2 inhibited central archesporial cell counts at all stages versus control. (J) This led to increased ratios in KI and depressed ratios in H2O2, with precocious bilayer formation lowering the ratio in KI in the final size class. Error bars are ± SD (n > 10 plants). Asterisks represent significance compared to control by Student's t test (P < 0.01). See figs. S10 to S13 for additional data.