Abstract:
Acclimatization of in vitro apples and plums was examined in
four studies: l) Leaf anatomy and water stress of aseptically cultured
'Pixy' plum grown under different environments, 2) Acclimatization
of aseptically cultured 'Mac 9' apples to low relative humidity,
3) Stomatal functioning of aseptically cultured 'Mac 9' apple
leaves in darkness, mannitol, ABA, and CO₂, and W) Stomatal anatomy
and the duration of acclimatization of in vitro 'Mac 9' apples.
Leaf anatomy was examined using light microscopy. Acclimatization
was observed by opening culture jar lids and measuring relative
water content, percent of closed stomata in drying studies, darkness
studies, and percent survival after a transplant study. Stomatal
responses to darkness, mannitol, ABA, and CO₂ were evaluated by the
percent of closed stomata. Stomatal anatomy was examined in light
and scanning electron microscopy. Leaf anatomy of in vitro plants
was significantly different from that of greenhouse plants. In
vitro leaves had a single layer of ovoid shaped, small, openly spaced
palisade cells. Greenhouse leaves had one to two layers of oblong,
significantly longer, closely packed palisade cells. The % mesophyll
air space was significantly greater in in vitro than greenhouse
leaves. In vitro plants had less epicuticular wax than did greenhouse
leaves. The stomatal anatomy, however, of in vitro and greenhouse
leaves was similar. No structural differences, which could prevent
closure of in vitro stomata, were observed. Less than 10 % of in
vitro stomata closed after drying, darkness, mannitol, ABA, or CO₂
treatment; from 40 to 98 % of treated greenhouse stomata closed.
Lack of in vitro leaf stomatal closure caused significant water, loss
when plants were transferred to low RH. In vitro leaves lost 50 %
water, a critical injury level, in 30 min; greenhouse leaves required
90 min. Humidity acclimatization involved development of a stomatal
closure mechanism. In vitro plants were acclimatized to low RH within
1 week in jars with lids removed. Open jars of in vitro plants
acclimatized after 4 to 5 days exposure to 45 % EH or after 2 days
exposure to 65 % RH.
