Black spruce somatic embryo germination and desiccation tolerance. I. Effects of abscisic acid, cold, and heat treatments on the germinability of mature black spruce somatic embryos

Abstract

The effect of cold, abscisic acid (ABA), and heat treatments on the germination of mature black spruce somatic embryos (SEs) was examined. Specifically, the quality of mature black spruce SEs germinants (as assessed by the presence of hypocotyl vitrification), germination time (synchrony of root and shoot growth), and desiccation tolerance was evaluated following the treatments. Germination of black spruce SEs without any treatments was high (i.e., 89%), but 43% of germinants exhibited a vitrified hypocotyl and root growth lagged behind shoot growth. Mature SEs were exposed to cold (2 °C for 2 days), ABA (20 μM ABA for 7 days), and heat (40 °C for 10 min, 30 °C for 1 h, 25 °C for 12 h) treatments and then either germinated or exposed to fast or slow desiccation. The ABA, cold and heat treatments resulted in a slightly earlier, more uniform germination, due to increased root growth, but did not increase the quality of germinants. Sixty four percent of mature SEs were tolerant to slow desiccation, but only 18% were tolerant to fast desiccation to approximately a 20% water content (on a fresh mass basis). Tolerance to slow and fast desiccation significantly increased and the percentage of germinants with vitrified hypocotyls decreased significantly when the SEs were first exposed to the ABA and cold treatments compared with the mature SEs. None of the treatments resulted in an increase in the number of germinants compared with that of the mature SEs. These results show that the ABA and cold treatments are beneficial for increasing SE tolerance to slow and fast desiccation, decreasing germination time, and increasing the quality of germinants. The ABA treatment was superior with respect to desiccation tolerance and to the quality of germinants.