Loblolly pine (Pinus taeda) female gametophyte and embryo pH changes during seed development

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Stage-specific measurements of female gametophyte (FG) and embryo pH (hydrogen ion concentration) were made through the sequence of loblolly pine (Pinus taeda L.) seed development. The FG tissue from two open-pollinated trees showed similar pH profiles starting at 5.5 shortly after fertilization, increasing to about 6.1 at stage 7, levelling off at 6.3–6.5 towards the end of development and dropping to 6.0 just before cone opening. Measurements of the chalazal end were 0.05–0.2 pH units less than the micropylar end through early-to-mid-development. In contrast, embryo pH maintained a nearly constant value near 7.0 through development. Profiles of pH through seed development were similar whether portrayed by date or stage of embryo present in the seed. The pH profiles assisted in the development of improved embryogenic tissue initiation techniques. When post-autoclaving maturation medium pH was raised from about 5.3 in control medium to 5.7 or 5.5–5.7 with 2(n-morpholino)ethanesulphonic acid, cotyledonary embryo yields increased.

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